2. Unit Contents
Unit 1: The science of biology (1 hrs.)
1.1. The methods of science
1.2. Tools of the biologist
Unit 2: Biochemical molecules (6hrs.)
2.1. Inorganic molecules
2.2. Organic Molecules
Unit 3: Cell biology (7 hrs.)
3.1. Cell theory
3.2. Types of cell
3.3. Parts of the cell and its function
3.4. The cell and its environment
3.5. Cellular respiration
Unit 4: Microorganisms (7 hrs.)
4.1. Introduction to microorganisms
3 | P a g e
4.2. Beneficial microorganisms
4.3 Pathogenic microorganisms
3. Unit 5: Genetics (7 hrs.)
5.1. DNA and chromosome structure
5.2. DNA replication
5.3. Protein synthesis
5.4. Mitosis and meiosis
5.5. Mendelian inheritance
5.6. Mutations
Unit 6: Evolution (2hrs.)
6.1. Theories of origin of life
6.2. Theories of mechanisms of evolution
6.3. Speciation through natural selection
6.4. Modern theories of evolution
4. Unit 7: Biotechnology (4 hrs.)
7.1. Scope and definition
7.2. Agricultural biotechnology
7.3. Medical biotechnology
7.4. Industrial biotechnology
7.5. Environmental biotechnology
Unit 8: Human biology and health (10 hrs.)
8.1. Food and nutrition
8.2. Non communicable diseases
8.3. The digestive system
8.4 The respiratory system
8.5. The circulatory system
8.6. The nervous system
8.7. Sense organs
8.8. Endocrine glands
8.9. The reproductive system
5. Unit 9: Food making and growth in plants (4
hrs.)
9.1. Plant organs
9.2. Photosynthesis
9.3. Transport in plants
9.4. Response in plants
Unit 10: Ecology and conservation of natural
resources (5 hrs.)
10.1. Definitions
10.2. Cycling matter through ecosystems
10.3. Ecological succession
10.4. Biomes
10.5. Conservation and Biodiversity
10.6. Vegetation and wildlife
10.7. Global warming and air pollution
6.
7. • Biology is the science of life and living organisms.
Living organisms are either unicellular or
multicellular
Areas of biological study
Astrobiologists: are engage in all kinds of
research to try to find evidence of life on other
planets in our Solar System and in galaxies
elsewhere in the Universe.
Biomedical: help in the development of new
drugs and vaccines treatment.
8. Microbioloy: study how micro-organisms of all kinds
function. Some micro-organisms cause disease, and
understanding how they work makes a treatment more
likely.
Paleobiology: try to find out more about the way in which
life began on Earth and how it has evolved from simple
life forms into more complex ones.
Besides these biologists, there are others who are, perhaps,
more recognizable. These include:
Doctors, Dentists, Veterinary Surgeons, Nurses,
Physiotherapists, Botanists, Zoologists, Physiologists,
Biochemists, Agricultural Biologists, Ecologists,
Ethologists, Oncologists, Neurobiologists,
9. 1.1 What is science?
• The word science comes from the Latin word
scientia, which means ‘knowledge’. But science isn’t
just about having knowledge. Rather it is a unique
system of acquiring knowledge based on the
scientific method.
• It is sometimes called experimental science, but
unlike applied science, it depends very heavily on
experimentation to obtain the information. However,
it is often difficult to separate the two.
• Science is an ongoing effort to find new
information and principles which can increase
human knowledge and understanding.
10. 1.2 Scientific method
• Is the process by which biologists and all other scientists
approach their work scientifically. It depends on evidence.
Steps of the scientific method
11. Disproving the theory of spontaneous
generation (S.G.)
• S.G. suggests that nonliving objects can
give rise to living organisms.
Francesco Redi
oPreformed experiments that disproved theory of
SG for larger organisms but not for
microscopic
oUtilized jars containing meat. Some were
covered, some were not.
oMaggots appeared in uncovered jars.
oIntroduced experimental procedure for disproof
S.G.
oS. G. took another 200 years to disprove.
12.
13. Louis Pasteur (1861)
• is a French microbiologist
• proved that microorganisms were present in
the air and were not spontaneously
produced.
–Filtered air through cotton plug.
–Placed plug in infusion broth, broth
became cloudy - organisms present in the
air.
–Placed boiled infusion broths in “swan-
necked” flasks
–Flasks remained sterile unless tilted or
neck broken.
14.
15. 1.2.1 Cause and Effect
• Scientific experiments try to establish cause and
effect. This means that they try to prove that a
change in one factor brings about a change in
another factor.
• The factor that the scientist changes, or manipulates,
is called the independent variable (or IV for short).
• The factor that the scientist measures to see if it
changes when the IV is changed is called the
dependent variable (or DV for short).
• Q. Define the following phrases
– Control group
– Experimental group
– Confounding variables
– Fair test
16. 1.2.2 Accuracy, reliability and validity in
scientific experiments
• Accuracy refers to how precisely
you measure or count something.
• Validity is about whether or not
our experiment measures what it
says it is measuring.
• Reliability is measure of how
dependable and consistent the
results of an experiment are.
17. 1.3 Report writing on scientific experiments
•Any report must contain:
– A title states clearly what is being investigated
– A hypothesis often extended to a prediction for the
particular experiment.
– A procedure - clear description of the experimental
– A results obtained is often helpful to summarize
these (where appropriate) in graphs, charts and
tables
– A conclusions that have been drawn from the
results
– An evaluation of the procedure
– An acknowledgement of the use of any other
person’s work
– References
18. 1.4. The tools of a Biologist
• Biologists use different biological lab equipment both in a
laboratory and outside (in field)
• The following are some basic tools used in a laboratory.
– Microscopes- are used to see objects that are too small to be
seen with unaided eye
– Dissecting equipment- are used to dissect different animals
– Petri dishes- usually used to culture microbes – such as
bacteria
– Pipettes and syringes- are devices used for measuring or
transferring small volumes of liquid from one container to
another with great precision.
– Centrifuges- a device that is used to separate solids from
liquids where simple filtration is not adequate for the task.
– Measuring cylinders- is used to measure a precise volume
of a liquid
– Balances- is sed for measuring mass.
19. • The following are some basic tools used in a field to:
– taking measurements of the abundance of
organisms in the field
Quadrats are used to estimate abundance of
organisms in an area
Net to caught some insects.
– taking samples of the environment (for example,
soil, rocks, water)
A flow meter – this is used to measure the rate of
flow of water
– collecting specimens for identification and analysis
in the laboratory.
A pH kit – this is used to measure the pH of soil or
water
20. 1.5 The relevance and promise of biological science
• The science biology is related to food
production, health and disease, conservation,
control of the population and to genetic
engineering and biotechnology.
i. Biology and agriculture
• To alleviate food insecurity (how to produce
crop plants that):
adapted to the new conditions
are capable of producing their crop quickly
are disease resistant
are drought resistant and environmental
friendly
21. ii. Biology and medicine
• Biologists are also able to give advice on ways of reducing
the rate of population growth. E.g. contraceptive
iii. Biology and the environment
• Biologists are actively involved in monitoring the impact of
global warming on the environment, conserve environments.
iv. Biology and Biotechnology
• Producing genetically modifying plants to meet a specific
need
• production of monoclonal antibodies that can deliver a drug
to only those cells that need treatment (for example, cancer
cells)
• using stem cells to repair damaged organs and, ultimately,
to grow whole new organs from just a few of a person’s stem
cells…
22. 1.6. Biology and HIV/AIDS
• AIDS (acquired immune deficiency syndrome) is caused
by the human immuno deficiency virus (HIV).
• It infects cells in our immune systems called T-helper
cells that enable us to fight other diseases.
• AIDS is usually fatal.
• AIDS is largely a sexually transmitted disease (STD),
although there are four main ways in which HIV can be
transmitted:
i. homosexual or heterosexual intercourse with an
infected person
ii. transfusion of infected blood or blood products
iii. sharing infected needles
iv. from mother to child during pregnancy
23. How can biology help in the fight against AIDS?
i. Break the transmission pathway
ii. Produce drugs that kill the virus or at least
stop it from reproducing.
iii. Produce a vaccine against the virus.
How biologists combat the spread of the disease?
• There are things we can do to help control the
spread of AIDS:
i. Restricting the number of sexual partners.
ii. Men can elect to be circumcised.
iii. Not sharing infected needles.
24.
25. Biochemical Molecules
• Are molecules of life.
• They can be classified into two main types:
o Inorganic molecules
o Organic molecules
26. 2.1.Water
• The chemical formula for water – H2O.
• Covers three-quarters of the planet
• It is the only substance that exists in three
states(solid, liquid and gas).
• Some of the importance of water are:
–a place to live
–a transport medium
–a reactant in many chemical reaction
–a place for other reactions to take place
–water is a vital chemical constituent of living
cells. E.g. Most cells are about 70% water and
some are as high as 90%.
27. 2.1.1 Properties of water
•Water:
– is transparent; light can pass through the water
– has a high specific heat capacity; it takes quite a lot of
energy to heat water up. Water also loses heat quite
slowly.
– has a high latent heat of vaporization; it takes a lot
of energy to turn liquid water into water vapor (or
steam).
– has a high surface tension; the molecules at the
surface are held together more strongly.
– Ice is less dense than liquid water.
– Water has the ideal viscosity for a transport medium.
Viscosity is a measure of how fluid a liquid is – how
easily it flows. More viscous means less fluid.
28. 2.2 Organic molecules
• They always contain both carbon and
hydrogen
• Most biological organic molecules contain
oxygen in addition to carbon and hydrogen
and some also contain nitrogen.
• Chemical elements that are found most
frequently in living organisms are:
Hydrogen (H) 59% , Oxygen (O) 24%,
Carbon (C) 11%
29.
30. 2.2.1 Carbohydrates
• All carbohydrates contain the elements carbon, hydrogen and
oxygen. For example, glucose, C6H12O6, and maltose, C12H22O11.
• They are the most abundant organic molecules in nature.
• They are substances that yield aldehydes or ketones on hydrolysis.
Aldose: Glucose
Ketose: Fructose
• Based on the number of sugar units they contain, they are
categorized into:
i. Monosaccharaides
ii. Disaccharides
iii. Polysaccharides
Sugar molecules are bonded together through the glycosidic
linkage
31. • Carbohydrates have a range of functions:
– They are used to release energy.
– Storage carbohydrates include:
• starch in plants
• glycogen in animals
– Some carbohydrates are used to build structures; structural
carbohydrates include:
• cellulose, which is the main constituent of the primary
cell wall of plants
• chitin, which occurs in the cell walls of fungi and in the
• exoskeletons of insects
• peptidoglycan, which occurs in bacterial cell walls
– Help for communication between cells (cell-cell
recognition)
32. I. MONOSACCHARAIDES (SINGLE SUGAR)
• Are simplest carbohydrates (sugars)
• Based on functional group that they possess, monosaccharaides can be
classified:
i. Aldoses- with aldehyde functional group (CHO). E.g. Ribose,
Glyceraldehyde, Glucose, Galactose
ii. Ketoses- with ketone functional group (C=O). E.g., Ribulose,
Dihydroxyacetone, Fructose
NB. Nearly all the polysaccharides found in living things are polymers of aldose
monosaccharaides.
• Based on the number of carbon atoms are present in the molecule,
monosaccharaides can be classified:
i. Triose - has three carbon atoms – formula C3H6O3. E.g.,
Glyceraldehyde, Dihydroxyacetone,
ii. Pentose - has five carbon atoms – formula C5H10O5. E.g., Ribose,
Ribulose
iii. Hexose - has six carbon atoms – formula C6H12O6. E.g., Glucose,
Galactose, Fructose
33. II. DISACCHARIDE
• Two monosaccharaides chemically combine by
glycosidic bond to form disaccharide via dehydration.
i. Maltose = 𝛼 glucose + glucose
ii. Sucrose = 𝛼 glucose and fructose
iii. Lactose (milk sugar) =β glucose + 𝛽 galactose
• Are soluble in water, but they are too big to pass
through the cell membrane by diffusion.
• C12H22O11 +H2O hydrolysis reaction C6H1206 + C6H1206
• Hydrolysis reaction is the reverse of a
condensation reaction. A condensation reaction
takes place by releasing water. This process
requires energy.
34. 34
III. Polysaccharides: many sugar units
• Many simple sugars can be joined together
by glycosidic bond to formpolysaccharides
by dehydration. Examples:
Starch(bread, potatoes), - a mixture of
amylose and amylopectin.
Glycogen (beef muscle)-
Cellulose (lettuce, corn)- made from
β-glucose molecules, it is not a source of
energy for humans.
Chitin - exoskeleton of insects, cell
wall of true fungi
35. 2.3 Lipids
• Like carbohydrates, nearly all lipids contain only the elements
carbon, hydrogen and oxygen, but they contain much less oxygen
than carbohydrates.
• Lipids are a varied group of compounds that include:
i. Triglycerides = glycerol and three fatty acids joined by ester
bonds.
ii. Phospholipids = glycerol+ two fatty acids + a phosphate
group. There are two distinct regions to a phospholipid
molecule: a hydrophilic (water-loving) region, consisting of
the phosphate ‘head’ a hydrophobic (water-hating) region,
consisting of the hydrocarbon ‘tails’
iii. Waxes = fatty acids + long-chain alcohols
36. • Lipids have a range of functions:
oWaxes for coating birds’ feathers and the epidermis of
the leaves of plants (the waxy cuticle).
oPhospholipids are basic components of all cell
membranes.
oTriglycerides have several functions including:
Respiratory substrate- a molecule of triglyceride
yields over twice as many molecules of ATP (twice as
much energy) as a molecule of glucose
Thermal insulation- adipose tissue contain large
amounts of triglycerides, which give good thermal
insulation
Buoyancy- lipids are less dense than water.
Waterproofing- the oils secreted by some animals
onto their skin are triglycerides.
37. 2.3.1 Saturated vs. Unsaturated Fatty Acids
i. Unsaturated fatty acids:
• have at least one double bond between
carbon atoms in the tail chain.
• Fats are solid at room temperature.
• Oils are liquid at room temperature.
ii. Monounsaturated fatty acids:
• have one double bond in the carbon
chain. E.g., Butter, Olives, and Peanuts.
iii. Polyunsaturated fatty acids:
• contain two or more double bonds. E.g.,
Soybeans, Safflowers, and Corn.
38. 2.4. Proteins
• They contain the elements carbon,
hydrogen and oxygen (like carbohydrates
and lipids), but they also contain
nitrogen and most contain sulphur.
• Protein molecules are polymers of amino
acids which joined by peptide bonds.
• Proteins are extremely important
substances that are needed to form all
living cells.
39. 2.4.1 Function of proteins
• Proteins are important in the:
structure of plasma membranes: protein
form ion channels, transport proteins and
surface receptors for hormones,
neurotransmitters and other molecules
immune system: antigen and antibody
molecules are proteins
control of metabolism: all enzymes are
proteins
structure of chromosomes: DNA is wound
around molecules of the protein histone to
form a chromosome.
40. 2.4. 2 Types of Proteins
•Proteins are classified into two main
groups, according to their molecular
shapes:
i. Fibrous proteins that have a tertiary
structure that resembles a long string or
fiber. E.g., Collagen And Keratin
ii. Globular proteins that have a tertiary
structure that resembles a globule or
ball. E.g., Enzymes And Receptor
Proteins.
41. Amino acids:
• consists of a central carbon atom bonded to
amino group(–NH2), carboxyl group(–
COOH), Hydrogen and R group .
Amino group, carboxyl group, and
Hydrogen are common to all amino acids.
But the R group varies between amino acids
and determine their identities and much of
the chemical properties.
42. 2.4.3. Structure of proteins
•Proteins have 4 levels of organization
or structure
i. Primary structure:
• is the sequence of amino acids in the
peptide chain.
43. ii. Secondary structure:
• is determined by the folding
of the primary structure into
either an α-helix or a β-
pleated sheet; these structures
are held in shape by hydrogen
bonds
α-helix a coiled(spiral) secondary
structure of a polypeptide
β-pleated sheet a
folded(zigzag) secondary
structure of a polypeptide.
44. iii. Tertiary structure:
• is determined by the further folding of
the secondary structure into either a
fibrous or a globular shape; these
structures are held in place by further
hydrogen bonds, disulphide bridges and
ionic bonds.
• These new bonds include:
Hydrogen bonds- between the R-groups of
some amino acids
Disulphide bridges- between amino acids that
contain sulphur
Ionic bonds- between amino acids with
positively charged R-groups and those with
negatively charged R-groups
45. iv. Quaternary structure:
• It is the final three-dimensional
structure of the protein.
• Structures formed when two or
more polypeptide chains (folded
into a tertiary structure) become
associated in the final structure of
the protein. E.g. Haemoglobin,
Collagen
quaternary structure (4)
example: hemoglobin has
4 polypeptide chains
46. 2.5 Nucleic Acids
• Made up of elements of Carbon, Hydrogen and Oxygen,
Nitrogen, and Phosphorus
• are made up of smaller units called nucleotides.
3/1/2020 46
47. •Nucleic Acidsare two types:
i. DNA or Deoxyribonucleic Acid :
DNA is the nucleic acid found in
chromosomes. DNA is the genetic
material.
ii. RNA or Ribonucleic Acid:
RNA is a nucleic acid found both in
the nucleus and the cytoplasm.
•Q. Explain the difference between
DNA and RNA
48.
49.
50.
51. 3.1. Cell theory
• In 1839 Matthias Schleiden and Teodore Schwann
introduced an idea known as the cell theory and In
1858 Rudolf Virchow, completes the first
accepted version of the cell theory:
i. All organisms are made up of one or more
cells
ii. All cells come from pre-existing cells
iii. The cell is the unit of structure, and
physiology in living things.
iv. The cell retains a dual existence as a
distinct entity and a building block in the
construction of organisms.
52. Features of Living Organisms :
• Respiration – the process by which living organisms get
the energy from their food.
• Excretion – getting rid of the waste products produced by
the cells.
• Growth – living organisms get bigger. They increase in
both size and mass, using chemicals from their food to
build new material.
• Irritability – all living organisms are sensitive to changes
in their surroundings
• Movement – all living organisms need to move to get near
to things they need or away from problems. Animals move
using muscles, plants move more slowly using growth.
• Reproduction – producing offspring is vital to the long-
term survival of any type of living organism.
53. 3.2. Types of cell
i. Prokaryotic:
• The first type of cells to be formed when life first
evolved.
• A type of cell that does not have a nucleus.
• Are much smaller and simpler than eukaryotic cells.
ii. Eukaryotic cells:
• A type of cell that has a nucleus.
• Have many more different individual structures,
called organelles,
• Have many more membranes in the cell.
• Have membrane-bound organelles: endoplasmic
reticulum, nucleus, mitochondria, chloroplasts (if
present), lysosomes, Golgi apparatus.
55. 3.3. Parts of the Cell and Its Function
• A cell contain small units called organelles.
• Many of these organelles contain enzymes and
chemicals to carry out specialised jobs within the
cell.
Nucleus:
• Controls all the activities of the cell.
• Contains the instructions for making new cells or
new organisms in the form of long threads known as
chromosomes.
Cell wall:
• is made mainly of a carbohydrate called cellulose,
which strengthens the cell and gives it support. It is
found outside the cell membrane.
56. Cytoplasm:
• Is a liquid gel in which most of the chemical reactions
needed for life take place. About 70% of the cytoplasm
of a cell is actually water!
• contains all the other organelles of the cell where most of
the chemical reactions take place.
Endoplasmic reticulum:
• It links the nucleus with the cell membrane.
• Divided into:
i. Rough endoplasmic
• has ribosomes on its surface and is responsible for the
manufacture and transport of proteins.
ii. Smooth endoplasmic reticulum.
• has no ribosomes on its surface. It is concerned
with the synthesis of lipids.
57. Ribosomes:
• are found on the endoplasmic reticulum in your cells.
• are vital for protein synthesis, the process by which the body
makes all the enzymes that control the reactions of the cells.
Mitochondria:
• Are the powerhouse of the cell.
• Carry out most of the reactions of respiration.
Golgi Complex:
• It is made up of a series of flattened, stacked pouches called
cisternae.
• It processes the raw material into finished products.
• It is referred to as the manufacturing and the shipping center of
the cell.
• It is responsible for transporting, modifying, and packaging
proteins and lipids into vesicles for delivery to targeted
destinations.
58. Vacuole:
• is a space in the cytoplasm filled with cell sap, a
liquid containing sugars, mineral ions and other
chemicals dissolved in water.
Lysosomes:
• They are membrane-enclosed sacs containing powerful
hydrolytic enzymes capable of digesting and removing
unwanted cellular debris and foreign materials such as
bacteria that have been internalized within the cell.
Peroxisome:
• It is membrane-enclosed sacs containing oxidative
enzymes and catalase that detoxify various wastes
(decomposing deadly hydrogen peroxide into harmless
water and oxygen
59. Vesicles:
• They are membrane bound sacs that are used to store or
transport substances around the cell. Lysosomes are actually
Vesicles.
Cytoskeleton:
• It is a complex protein network that act as the “bone and
muscle” of the cell.
• This network has at least four distinct elements: Microtubules,
Microfilaments, Intermediate filaments and Micro-tubular
lattice
Cell membrane:
• forms a barrier like a very thin ‘skin’ around the outside of
the cell.
• controls the passage of substances. It is selectively
permeable. i.e., it lets some substances through but not
others.
61. • The components of the membrane are:
i. Phospholipid bilayer:
• is the basis for the membrane
ii. Integral proteins:
• Are intrinsic proteins and transmembrane
proteins that span the membrane.
• The main types of these transport proteins
are:
Channel proteins: these proteins have
a channel through them along which a
specific ion can pass
Carrier proteins: these proteins
transport larger molecules through the
62. iii. Peripheral proteins:
• Are extrinsic proteins that span only one layer (or
sometimes less) of the membrane.
• They have a range of functions; some are
enzymes, others anchor integral proteins to the
cytoskeleton
iv.Glycoproteins and glycolipids:
• often serve as signals to other cells.
• act as receptor sites for hormones and
drugs.
• allow identification of the cell by the immune
system.
65. 3.4. The cell and its environment
Diffusion:
• is movement of particles from an area of high
concentration to an area of low
concentration along a concentration gradient
Osmosis:
• is the process by which water moves across a
partially permeable membrane.
• is the movement of water from a system with a
high water potential to a system with a low
water potential across a partially permeable
membrane.
• Pure liquid water has a higher water potential
66. •When comparing the water potential of a
solution to that of a cell, we could
describe it as:
i. Isotonic: having the same water
potential as the cell
ii. Hypertonic: having a lower (more
negative) water potential than the cell
iii. Hypotonic: having a higher (less
negative) water potential than the cell.
67. • The plant cell in hypotonic environment will be
turgid when the cytoplasm of a plant cell is pushed
hard against the cell wall by the vacuole which is
filled with water
• The plant cell in hypertonic environment will be
flaccid when the vacuole shrinks and the cell
becomes plasmolyzed when the cytoplasm shrinks
away from the cell wall due to osmotic movement
of water.
68. Facilitated transport:
• material moves across the plasma
membrane with the assistance of
transmembrane proteins down a
concentration gradient (from high to low
concentration) without the expenditure
of cellular energy.
Active transport:
• Is the movement of substances against a
concentration gradient using energy
from respiration.
69. Endocytosis
• In this process, large particles are
engulfed by a cell.
• Can be phagocytosis (ingestion of
large particles or even whole
organisms outside the cell.) ,
pinocytosis (the ingestion of
smaller particles).
Exocytosis:
•In this process, substances are
moved from the inside to the outside
70. 3.5. Cellular Respiration
ATP:
• is Adenosine Tri-Phosphate
• is sometimes described as a phosphorylated
nucleotide.
• is essentially the adenine nucleotide that contains
pentose sugar, nitrogen base(adenine), and
phosphate group.
Figure 5.1 A nucleotide containing base Figure 5.2 structure of the ATP
71. • The processes that require energy from ATP:
synthesis of macromolecules-E.g., proteins
active transport across a plasma
membrane.
muscle contraction
conduction of nerve impulses
initial reactions of respiration.
• There are two main pathways by which
respiration can produce ATP by using ATP
synthase enzyme :
i. aerobic pathway (aerobic respiration) –
this requires the presence of oxygen,
and
ii. anaerobic pathway (anaerobic
72. Stages of aerobic respiration of glucose
• There are four stages:
i. Glycolysis
ii. Link Reaction
iii. Krebs Cycle
iv. Electron Transport and Chemiosmosis
Glycolysis:
• Anaerobic respiration
• Occurs in the cytosol (both in prokaryotes and
eukaryotes) under both aerobic and anaerobic
conditions
• It does not take place inside the mitochondria because:
• the glucose molecule cannot diffuse through the
mitochondrial membranes, and
• there are no carrier proteins to transport the glucose
molecule across the membranes.
73. • In ten steps, glycolysis produce a
net yield of:
i. 2 ATP,
ii. 2 NADH,
iii. 2 pyruvate(3C) molecules
74. • The following reactions take place in glycolysis:
i. two molecules of ATP are used to
‘phosphorylate’ each molecule of glucose.
This makes the glucose more reactive.
ii. In the phosphorylation process, glucose is
converted fructose 1,6-bisphosphate.
iii. The fructose 1,6-bisphosphate is split into
two molecules of the three-carbon sugar
glyceraldehyde-3 phosphate (GP)
iv. Each molecule of GP is then converted into
pyruvate, with the production of two
molecules of ATP (by substrate level
phosphorylation) and one molecule of
reduced NAD.
75.
76. Link reaction:
• In the reaction:
A molecule of pyruvate reacts
with a molecule of coenzyme
A (CoA) to form a molecule of
acetyl coenzyme
A (acetyl CoA).
Hydrogen is
lost
(dehydrogenation) and
reduced NAD is
formed.
A carbon atom
is lost(decarboxylation)
77. Krebs Cycle:
1) 1Acetyl coenzyme A (2C) reacts with the oxaloacetate (4C)
to form called citrate (6C).
2) Citrate then loses a carbon atom (decarboxylated) to form a
five-carbon compound and CO2 is produced.
3) The five-carbon compound is then further decarboxylated to
form a four-carbon compound and CO2 is again
produced; 1ATP is also produced by substrate level
phosphorylation.
4) The four-carbon compound undergoes several molecular
transformations to regenerate(oxaloacetate) and the cycle is
complete and can begin again with oxaloacetate reacting
with another molecule of acetyl CoA.
5) In several reactions in the cycle, reduced NAD is
produced and, in just one reaction, reduced FAD is
produced.
79. Electron Transport Chain and Chemiosmosis
• In these process oxidative phosphorylation will
occur.
• The link reaction and Krebs cycle take place in the
fluid matrix of the mitochondrion, the reactions of
the electron transport chain and chemiosmosis take
place on the inner mitochondrial membrane.
• On the cristae (is a fold in the inner membrane of a
mitochondrion.), the following events take place:
oThe hydrogen atoms carried by reduced NAD
and reduced FAD are released and split into
protons (hydrogen ions) and electrons.
oThe electrons pass along a series of electron
carriers that form the transport chain; they lose
80. oThree of the electron carriers that pump protons
from the matrix of the mitochondrion to the inter-
membrane space. These are:
i. Reduced NAD dehydrogenase (also a
proton pump)
ii. Ubiquinone (also a proton pump), and
iii. Cytochromes (the third proton pump).
oElectrons from reduced NAD make this happen at
all three pumps.
oAt the end of the electron transport chain,
the electrons combine with protons and with
oxygen to form molecules of water. Because
of this, oxygen is known as the terminal
electron acceptor.
81. The carrier molecules in the electron transport chain on the
inner membrane of a mitochondrion
82.
83. Anaerobic Pathway:
• No oxygen involvement.
• Electrons and protons react with oxygen to form
water, cannot take place
• The link reaction, Krebs cycle and electron transport
chain come to a halt.
• Different organisms produce different fermentation
end products:
Animal cells produce lactate (lactic acid) when
they ferment glucose.
Yeast cells produce ethanol (ethyl alcohol).
84.
85.
86. 4.1. Introduction to microorganisms
Micro-organisms:
• are tiny living organisms that are
usually too small to be seen with the
naked eye or can only be seen with
the aid of a microscope.
• There are five main groups of
micro-organisms :
–Protozoa, some fungi, some algae,
Viruses, bacteria
87. Bacteria:
– are single-celled organisms.
– have prokaryotic cells
– Its cell is made up of a cell membrane,
cytoplasm, ribosomes and cell wall
(peptidoglycan), genetic material (DNA), but
this is not contained in a nucleus.
– Some bacteria have flagella to help them move,
or protective slime capsules.
– Have different shapes and sizes:
• Cocci (singular, coccus) – spherical bacteria
• Bacilli (singular, bacillus) – rod-shaped
bacteria
• Spirochaetes – spiral or corkscrew-shaped
88.
89. • Whether or not they are colored by Gram’s stain, bacteria are
classified in to two:
– Gram-positive – these bacteria are stained purple by
Gram’s stain
– Gram-negative – these bacteria are stained pink by
Gram’s stain.
90. Viruses:
• are even smaller than
bacteria.
• usually have regular
geometric shapes
• are made up of a protein coat
surrounding genetic material
containing relatively few
genes.
• They do not carry out any of
the functions of normal living
organisms except
reproduction, and they can
only reproduce by taking over
another living cell.
• all naturally occurring viruses
91. • Based on the nature of their genetic material
and the way in which it is expressed, viruses
are grouped into:
i. DNA viruses – for example, Herpes simplex
(causes cold sores)
ii. RNA viruses – for example, H1N1 virus (causes
swine flu)
iii. Retroviruses – for example, HIV (causes AIDS)
• Based on the type of organism they infect,
viruses can also be classified in to:
i. animal-infecting viruses
ii. plant-infecting viruses
iii. bacteria-infecting viruses – these are called
bacteriophages
92. • There are three different life cycles in
viruses:
i. Lytic life cycle:
–infection causes the host cell to burst
and release new viruses.
ii. Lysogenic life cycle
–infection causes the virus to enter a latent
state where its DNA is reproduced with the
host DNA, but no new viruses are formed
iii. Chronic release life cycle
–infection causes viruses to be released
93. Protozoa:
• are unicellular organisms that lack a cell
wall.
• most of them are motile (able to move)
• include organisms such as Amoeba,
Plasmodium, and Paramecium.
Fungi:
• living organisms which obtain their food from
other dead or living organisms.
• decomposers, breaking down animal and
plant material and returning nutrients to the
environment. E.g. moulds and yeasts.
• do not have true roots, stems and leaves.
94. Yeast:
• Is a single-celled organisms.
• Has a nucleus, cytoplasm, a membrane. and a
cell wall.
• Reproduces by asexual budding – splitting to form
new yeast cells.
• The yeast-like organism that causes thrush in humans
(Candida).
Figure 4.3 Yeast cell structures
95. Moulds:
• are made up of minute, threadlike structures
called hyphae. Hyphae are tubes consisting of
a cell wall, cytoplasm and nuclei. Mycelium
is the collection of very fine strands that
makes up a fungus.
• reproduce asexually by producing fruiting
bodies
containing spores.
96. Alga (plural algae):
• is an organism that obtains its nutrition using
photosynthesis.
• Many are large (seaweeds), but some algae are
unicellular.
• The unicellular algae:
– are part of the plankton:
• are collections of small microscopic plant organisms that
float or drift in large numbers in fresh or salt water,
• are providing food for fish and other larger organisms.
– in the oceans produce far more oxygen during
photosynthesis than all the forests in the world
together.
– Some unicellular algae are motile – they can move.
E.g. Chlamydomonas.
97. Control of micro-organisms
• Sterilization is the killing of all micro-organisms in a
material or on the surface of an object, making it safe to
handle without fear of contamination.
• There are a number of different ways we can sterilize
things:
i. High temperatures or heat E.g. Autoclaving, Ultra high
temperature (UHT), Pasteurisation,
ii. Disinfectants: is a chemical substance or compound used
to inactivate or destroy microorganisms on inert surfaces.
• fast acting
• effective against all types of infectious agents
• able to easily penetrate material to be disinfected without
damaging or discoloring it.
iii. Antiseptics - is a chemical agent that slows or stops the
growth of microorganisms on external surfaces of the body
and helps to prevent infection.
98. Germ theory:
• Is the theory that disease can be
caused by micro-organisms.
–Organisms that cause disease are
called pathogens.
–A disease that is caused by a micro-
organism infecting the body is an
infectious disease.
–Infectious disease is just one type of
disease.
99.
100. •Disease can be caused by a number of other factors.
1) Human induced diseases are diseases that arise as a
result of a person’s lifestyle.
2) Degenerative diseases often result from the ageing
process during which the affected tissues deteriorate
over time due to simple ‘wear and tear’.
3) Genetic diseases are diseases that result from the
action of mutated genes.
4) Deficiency diseases are diseases that result from a
lack of a nutrient in our diet.
5) Social diseases are conditions that result from social
activities and may lead to socially unacceptable
behaviour.
6) Multifactorial describes a condition that is affected
by the interaction of many factors.
101. Reservoirs of infection:
1) Human beings – the reservoir for many diseases,
including the common cold, diphtheria and others
2) Other animals – for example: chickens, the
reservoir for
salmonella infections; mosquito, the reservoir for
malaria
3) Soil – the reservoir for tetanus and many other
pathogens
4) Water – the reservoir for Legionnaire’s disease,
amoeba, cholera, etc.
5) Food – the reservoir for many diseases including
typhoid
6) Contaminated objects – contact infections such as
HIV/AIDS and trachoma
7) Air – the reservoir for pneumonia, tuberculosis, etc.
102.
103. 4.2. Beneficial Microorganisms
i. Recycling minerals through ecosystems:
• Many bacteria are decomposers and recycle many
elements, including: Carbon, Nitrogen, Sulphur and
Phosphorus.
The nitrogen cycle:
• The element nitrogen is found in proteins, DNA, RNA, ATP
104. The sulphur cycle:
• Sulphur is found in fewer types of organic molecule than
nitrogen, but it is found in many proteins.
105. ii. Industrial importance
•Food and beverage fermentation
Bacteria and other micro-organisms have
been used to make: Bread. Alcohol, irgo or
yoghurt, vinegar, sewage treatment
•Production of vinegar
Vinegar is a dilute solution of ethanoic acid
in water. Vinegar is used in two main ways:
to favour foods, and to preserve foods
106. • Producing antibiotics
the first antibiotics all came from fungi.
Genetically modified bacteria are also used to
produce: insulin, human growth hormone,
antibiotics, enzymes for washing powders and
human vaccines, such as the vaccine against
hepatitis B.
• Sewage treatment
All types of sewage treatment rely on the action of a
range of microorganisms to oxidise the organic matter
present in sewage. there are two main methods:
i. the percolating filter method and
ii. the activated sludge method
Read How Do the Methods Work!
107.
108. Definitions of terms
• Gene a section of DNA that determines a specific
feature.
• Histone the core of a chromosome around which
the chromosome’s DNA is wrapped.
• Chromosome a long strand of DNA on which a
large number of genes is stored.
• Allele a version of a gene that determines a
particular trait.
• Locus (plural loci) the position of a particular gene
on a chromosome.
• Codominant or incomplete dominant alleles the
pattern
of inheritance where both alleles of a gene are
equally expressed and determine which trait occurs
in a heterozygous organism.
109. • Homozygous an organism is homozygous
for a particular gene if it has the same allele
for that gene on each of the chromosomes in
the homologous pair.
• Heterozygous an organism is heterozygous
for a particular gene if it has different alleles
for that gene on each of the chromosomes in
the relevant homologous pair.
• Genotype a genotype describes the pair of
alleles for a particular gene possessed by a
organism.
• Phenotype a phenotype describes the trait
or traits determined by a particular genotype.
110. 5.1. DNA and chromosome structure
• Inside the nucleus of every cell there are thread-like structures
called chromosomes.
• A chromosome is a structure in the nucleus of a cell
consisting of genes.
A gene is a unit of hereditary material located on the
chromosomes.
• Chromosomes are made from two chemicals:
DNA (deoxyribonucleic acid) and
Histones (a set of globular proteins)
• Chromosomes come in pairs known as homologous pairs.
• Homologous chromosomes a pair of chromosomes
having the same gene sequences, each derived from one
parent.
• Karyotype map of the chromosomes in the nucleus
of a single cell.
111. • Human have 23 pairs, tomatoes have 12 pairs
and elephants have 28 pairs of chromosomes.
22 pairs of chromosomes in human are
known as the autosomes. The remaining
(1Pair) is sex chromosomes because they
determine whether you are male(XY) or
female(XX).
• Chromosomes are made up of the genetic
material DNA in a DNA–protein complex.
humans have 46 chromosomes and
tomatoes have 24, while elephants have
56.
• DNA nucleic acid containing the genetic
instructions used in the development and
functioning of all known living organisms and
112. •The two DNA strands are linked by the
bases: adenine, thymine, guanine and
cytosine.
Adenine is a base that comprise DNA
which pairs with thymine.
Guanine is a base that comprise DNA
which pairs with cytosine.
•Nucleotide is a building block of DNA
or RNA which consists of a sugar, a
phosphate, and one of the four bases.
•Polynucleotide is long chains of
linked nucleotides.
113. •The basic unit of a DNA strand is
a nucleotide. There are four
types of nucleotides:
i. Adenine-containing nucleotide
ii. Guanine-containing nucleotide
iii.Cytosine-containing
nucleotide, and
iv.Thymine-containing nucleotide
(in DNA, or Uracil-containing
nucleotide in RNA)
114.
115. 5.2. DNA Replication
• DNA molecule replicates in such a way that:
each new DNA molecule formed contains one
strand from the original DNA
both new DNA molecules formed are identical to
each other and to the original molecule
• The process of DNA molecule replication involves
several enzymes and proteins, but the key stages are
as follows:
i. Molecules of the enzyme DNA helicase break
hydrogen bonds and ‘unwind’ part of the helix of the
DNA molecule, revealing two single-stranded
regions.
ii. Molecules of DNA polymerase follow the helicase
along each single-stranded region, which acts as a
116. iii. The DNA polymerase assembles free DNA
nucleotides into a new strand alongside each
of the template strands. e base sequence in
each of these new strands is complementary
to its template strand because of the base-
pairing rule, A-T, C-G.
iv. The processes of unwinding followed by
complementary strand synthesis progresses
along the whole length of the DNA molecule.
v. The result is two DNA molecules that are
identical to each other (and to the original
molecule); each contains one strand from the
original DNA molecule and one newly
synthesized strand that is complementary to
this.
117.
118. Cloning and Genetic Engineering
• A clone of an organism is a group of organisms that
are genetically identical to each other and to the
organism from which they were derived.
• Gene cloning means making multiple copies of a
gene. There are several ways in which this can be
done. The principal methods are divided into two main
categories:
i. In vivo cloning – the gene is introduced into a
cell and is copied as the cell divides.
ii. In vitro cloning – this does not take place in
living cells but the DNA is copied many times
over using the polymerase chain reaction
(PCR). It is a process mimics the natural
119. •Genetic engineering is a process in
which the genome of an organism is
altered, usually by having an extra gene
from a different organism added. The
organism is then a genetically modified
or a transgenic organism.
•Transgenic organism a genetically
modified organism that contains a gene
or genes transferred from another
organism belonging to a different
species.
120. • Genetic engineering has many potential benefits:
to treat infectious diseases by implanting genes that code
for antiviral proteins specific to each antigen.
to give increased growth rates and reduced susceptibility
to disease. This would reduce the use of fertilizers and
pesticides and the chemical pollution that results from
their use.
to absorb more CO2 and reduce the threat of global
warming.
to increase genetic diversity, and produce more variant
alleles which could also be crossed over and implanted
into other species.
Genetic engineering is a much quicker process than
traditional selective breeding.
121. 5.3. Protein synthesis
•mRNA (messenger RNA) is a nucleic
acid that transmits the genetic code from
DNA to ribosome.
•Transcription the process that converts
genetic information from a DNA code into
an mRNA code.
•tRNA (transfer RNA) transfers individual
amino acids during translation
•Translation the process in which the
mRNA code is converted into a sequence
of amino acids.
122. • Events occur during protein synthesis :
–The DNA code for the protein is rewritten in
a molecule of messenger RNA (mRNA);
this rewriting of the code is called
transcription.
–The mRNA travels from the nucleus through
pores in the nuclear envelope to the
ribosomes.
–Free amino acids are carried from the
cytoplasm to the ribosomes by molecules of
transfer RNA (tRNA).
–The ribosome reads the mRNA code and
assembles the amino acids carried by tRNA
123.
124. Genetic code:
• It is the sequence of bases in the nucleotides of the
DNA that makes up a gene that codes for the protein
and that each amino acid in the protein is coded for
by a triplet (sequence of three) of bases.
• A gene is a sequence of base triplets in the DNA
molecule that carries the code for a protein.
• With four different bases to work with (adenine,
thymine, cytosine and guanine), there are 64 possible
triplet codes, but only 20 amino acids are used to
make all the different proteins.
• In DNA there is coding strand or the sense strand
and non-coding or antisense strand.
125. • Different amino acids have different codes:
– Methionine and tryptophan have one triplet each
– Asparagine, Aspartic acid, Cysteine, Glutamic acid,
Glutamine, Histidine, Lysine, Phenyl -alanine and
Tyrosine have two triplets each
– Alanine, Glycine, Proline, Threonine, Valine have four
triplets each
– Arginine, Serine and Leucine have six triplets each.
– Isoleucine and Stop have three triplets each
• ‘Stop’ codes(TAA, TAG and TGA):
– do not code for amino acids at all
– signals the end of protein manufacturing inside the
cell, like a period at the end of a sentence. Because
there is this extra capacity in the genetic code, over
and above what is essential, it is said to be a
degenerate code.
126. • DNA code is a:
– Non-overlapping code. This means that each triplet is
distinct from all other triplets. The last base in one triplet
cannot also be the first base (or second base) in another
triplet.
– Universal code. This means that the triplet TAT is the DNA
code for the amino acid tyrosine in a human, a giant
redwood tree, a bacterium or in any other living organism
128. Transcription in eukaryotic cells
• During this process, the coded information in the DNA of
one gene is used to synthesize a molecule of mRNA that
will carry the code to the ribosomes.
• To form the single-stranded mRNA when transcription
takes place, only the antisense strand of DNA is
transcribed.
• mRNA is similar to DNA in that it is built from
nucleotides; however, it is different from DNA in a number
of ways:
–it is a much smaller molecule
–it is single stranded
–the base thymine is replaced by uracil
–the sugar in the nucleotides is ribose, not deoxyribose.
• The triplets of bases in mRNA that code for amino
acids are called codons.
129. • In eukaryotic cells, transcription takes place in the
following way:
– The enzyme DNA-dependent RNA polymerase (RNA
polymerase) binds with a section of DNA next to the
gene to be transcribed.
– Transcription factors activate the enzyme.
– The enzyme begins to ‘unwind’ a section of DNA. RNA
polymerase moves along the antisense strand, using it
as a
template for synthesizing the mRNA.
– The polymerase assembles free RNA nucleotides into
a chain in which the base sequence is complementary
to the base sequence on the antisense strand of the
DNA. This, therefore, carries the same triplet code as
the sense strand (except that uracil replaces thymine).
– The completed molecule leaves the DNA; the strands
of DNA rejoin and re-coil.
130.
131. • Translation
• Translation of the mRNA code
into a protein depends on the
interaction within a ribosome
between mRNA and tRNA.
• The tRNA is has an anticodon
loop and amino acid acceptor
end.
– The anticodon loop
makes bases
complementary to the
codes on the mRNA and
amino acid end has an
attachment site for the
amino acid that is
specified by the mRNA
132. • Within the
ribosome, there
are three sites that
can be occupied
by a tRNA
molecule, called
the A, P and E
sites.
133. • The following events take place during translation:
– The first two codons of the mRNA enter the ribosome.
– Transfer RNA molecules (with amino acids attached) that
have complementary anticodons bind to the first two codons
of the mRNA.
– A peptide bond forms between the amino acids carried by
these two tRNA molecules and the dipeptide is transferred to
the tRNA in the A site.
– The ribosome moves along the mRNA by one codon,
bringing the third codon into the ribosome; at the same time
the ‘free’ tRNA exits the ribosome and the tRNA with the
dipeptide moves into the P site.
– A tRNA with a complementary anticodon binds with the third
codon, bringing its amino acid into position next to the
second amino acid.
– A peptide bond forms between the second and third amino
acids.
– The ribosome moves along the mRNA by one codon,
bringing the fourth mRNA codon into the ribosome, and the
whole process is repeated until a ‘stop’ codon is in position
134.
135. Protein synthesis different in prokaryotic cells
• The process is essentially similar in both types of cells, with DNA
being transcribed to mRNA, which is then translated to a
polypeptide chain. However, there are some differences and
these are linked to the fact that:
– prokaryotic cells do not have a nucleus
– prokaryotic mRNA does not need post-transcriptional
processing
– Prokaryotes:
transcription and translation are coupled; mRNA can be
translated by ribosomes at one end of its molecule while it
is still being transcribed from DNA at the other end
– Eukaryotes:
transcription and translation are separated
transcription occurs in the nucleus
translation occurs in the cytoplasm
eukaryotic mRNAs are modified before leaving the
136.
137. Gene expression
• All genes aren’t active all the time. For examples: the genes that control
the color of your iris are present in all your cells, but all your other cells
aren’t this color – just the iris.
Genes switch on:
• very often, genes are switched on by
‘transcription factors’ that are present in the
cell. E.g. Protein
• Gene transcription factors operate in the
following way:
The transcription factors bind to a
promoter sequence of DNA near to the
gene to be activated.
RNA polymerase binds to the DNA/
transcription factor complex.
The RNA polymerase is ‘activated’ and
moves away from the
DNA/transcription factor complex along
the gene.
The RNA polymerase transcribes the
antisense strand of the
DNA as it moves along; the gene is now
being expressed.
138. Genes switched off
• Besides transcription factors that
promote the expression of genes, other
factors can act to repress gene action.
E.g. short interfering RNA(siRNA).
Short interfering RNA is a short
sequence of RNA which can be used to
silence gene expression. They don’t act
on the gene itself, but they ‘interfere
with’ or ‘silence’ the mRNA once it has
been transcribed from the DNA. This is
called posttranscriptional interference.
139. • Biologists think that the action of
siRNA is as follows:
– Double-stranded RNA
(dsRNA) is produced in the
nucleus from a range of
genes.
– It is then split into the very
short lengths that characterize
siRNA by an enzyme called
‘Dicer’.
– The antisense strand of the
siRNA then binds with a
complex of molecules called
RISC.
– The siRNA binds with mRNA
and allows RISC to degrade/
cleave the mRNA into small
140. 5.4. Mitosis and meiosis
Mitosis
• Body cells divide by mitosis to produce more identical cells for
growth, repair, replacement and, in some cases, asexual
reproduction.
• Mitosis is division of the somatic cells to make identical
daughter cells.
• Before a cell divides,
• It produces new copies of the homologous pairs of
chromosomes in the nucleus. Each chromosome forms two
identical chromatids.
• Then the chromatids divide into two identical packages,
and the rest of the cytoplasm divides as well to form two
genetically identical daughter cells.
• Once the new cells have formed, the chromatids are again
referred to as chromosomes.
• Mitosis is one continuous process.
141. • There are four stages in mitosis: interphase,
prophase, metaphase, anaphase and telophase.
•
.
142. The cell cycle
• The cells in your body divide on a regular basis to
bring about growth. They divide in a set sequence,
known as the cell cycle , which involves several
different stages.
A period of active cell
division:
o this is when mitosis takes
place and the number of
cells increases.
A long period of non-division:
o when the cells get bigger,
increase their mass, carry
out normal cell activities
and replicate their DNA
143. Meiosis
• The cells in the reproductive organs (germ cells)
divide to make sex cells. The cell division that takes
place in the reproductive organ cells and produces
gametes is known as meiosis.
• Meiosis is a special form of cell division where the
chromosome number is reduced by half.
• When a cell divides to form gametes, meiosis is
divided into two divisions.
• In the first meiotic division:
• The chromosomes are copied so there are four
sets of chromatids.
• The cell then divides to form two identical
daughter cells.
• The first meiotic division is very similar to
mitosis.
144. •In the second meiotic division:
oidentical daughter cells divide to
form four gametes, each with a
single set of chromosomes.
oThe second is again similar, but
there is no more replication of
chromosomes i.e., without the
chromatids doubling again.
There is no crossing over in prophase
The chromosomes line up side by side
in metaphase
Chromatids are separated in anaphase
145. Figure 2.8 Tis simple diagram sums up the main stages of meiosis – see
figure 2.9 for the details.
146. • Meiosis occurs as part of a process known as
gametogenesis, or gamete formation.
• In females this is called oogenesis (forms
the ova). In a baby girl, the first stage of
meiosis is completed before she is even
born. The second stage occurs as the eggs
ripen during the menstrual cycle and is
completed after fertilization of the egg.
• In males, meiosis doesn’t start until
puberty, when the testes start to produce
sperm. The production of sperm is called
spermatogenesis, and carries on
throughout a man’s life.
150. 5.5. Mendelian inheritance
• Inheritance is the science of how information is
passed from parents to their children.
• Mendel used seven clearly different, pure-breeding
traits (homozygotes) of the pea plant for his
experiments. They are shown here in both their
dominant and recessive forms.
• Dominant allele is an allele where the characteristic is
expressed in the phenotype even if only one copy of the
allele is present
• Recessive allele is an allele where the characteristic is
only expressed in the phenotype if two copies of the allele
are present.
151.
152. • Mendel observed,
for example, that the
round shape of peas
seemed to dominate
the wrinkled shape,
but that the
information for a
wrinkled shape
continued to be
carried and could
emerge again in
later generations – in
other words there
were unique units of
inheritance that were
not blended
together.
153. Figure 2.16 A cross between a pea plant homozygous for the round pea
allele, and a plant homozygous for the wrinkled pea allele, through the F1
154. • The first generation of any cross is called the F1 (first
filial generation) and they all have:
• the same heterozygous genotype and
• they also all have the same phenotype (the round
pea shape) because the round allele is dominant.
There is no sign of the wrinkled pea allele.
• If we then cross members of the F1 generation we call
the next generation the F2 (second filial generation).
The genotypes of F2 will be:
• one homozygous round pea,
• two heterozygous round peas and
• one homozygous wrinkled pea.
The recessive trait for the wrinkled pea has
become visible again, after being ‘hidden’ in the
F1 generation.
155. • Some genes have more than two alleles, and then the pattern
of inheritance is a little more complex. We call this situation
multiple allele inheritance. E.g., ABO blood groups
• There are three alleles involved in the inheritance of these
blood groups:
i. IA, which determines the production of the A antigen
ii. IB, which determines the production of the B antigen
iii. IO, which determines that neither antigen is produced
• Alleles IA and IB are codominant, but IO is recessive to both.
• The possible genotypes and phenotypes (blood groups) are
shown below.
Genotype Blood group
IAIA, IAIO A
IBIB, IBIO B
IAIB AB
IOIO O
156. How inheritance works?
• The chromosomes we inherit carry our genetic information in
the form of genes.
• Many of these genes have different forms, known as alleles.
• An allele is the particular form of information in an individual
chromosome.
There are genes that decide
whether:
your earlobes are attached
closely to the side of your
head or hang freely
your thumb is straight or
curved
you have dimples when
you smile
you have hair on the
second segment of your
Figure 2.14 These are all human characteristics that
are controlled by a single pair of genes, so they can
be very useful in helping us to understand how
sexual reproduction introduces variety and how
inheritance works.
157. Heredity and breeding
i. In selective breeding, only the animals or
plants with the characteristic you want are allowed
to breed. In time, every member of the breed shows
that characteristic.
ii. Cross–breed (Combination of traits)
between two different breeds. This gives you a
combination of traits from the two different breeds –
the best of both can be used to develop a new
breed.
• Breeding animals and plants is very important for
society:
• to enable us to make the best possible use of our
resources,
• to feed our population,
• to maintain our genetic diversity and
158. 5.6. Mutations
• A mutation is any spontaneous change in the genetic material of
an organism.
• There can be:
– whole chromosomes changes or
– parts of chromosomes changes, or
– only a single base changes. The changes involving only a
single base are called point mutations.
• There are several types of point mutation:
i. Substitution
ii. Addition
iii. Deletions
– These mutations occur quite randomly when DNA is replicating
and each involves a change to just one base, but the change to
the
gene can be dramatic and the result can be that:
• the protein the gene should code for is not made at all or
• a different protein is made.
161. Addition and deletion
• In a deletion mutation a base is ‘missed out’ during
replication, whilst in additions, an extra base is
added.
• Both these are more significant mutations than
substitutions.
162.
163. Causes of Point Mutations
• The rate of mutation can be increased by a
number of factors including:
– carcinogenic chemicals, for example, those in tobacco
smoke
– high-energy radiation, for example, ultraviolet
radiation, X-rays
Consequences of Gene Mutations
• Mutations that occur in a normal body cell (a
non-sex cell) will have one of four possible
consequences:
– It will be completely harmless.
– It will damage the cell.
– It will kill the cell.
– It will make the cell cancerous, which might kill the
person.
164. • Genes called proto-oncogenes and tumour
suppressor genes play important roles in
regulating cell division and preventing the
formation of a tumour.
– When proto-oncogenes mutate, they often
become active oncogenes, which stimulate the
cell to divide in an uncontrolled manner.
– Tumour suppressor genes recognize uncontrolled
cell division and act to suppress cell division. If
these genes mutate and become inactive, a
tumour will form as uncontrolled cell division
continues.
• A tumour is a mass of cells created when cell
replication gets out of control. Tumours cause
165. Mutations benefit an
organism
• Mutations are the raw material
of evolution.
• It is the only process that
creates new genes.
• It gives bacteria resistance to
a specific antibiotic, such as
166. Chromosome mutations
• These occur:
–when there is any change in the
arrangement or structure of the
chromosomes.
–occur most often during meiosis at
crossing over in prophase I.
–They are much bigger events than
point mutations and usually result
in the death of a cell, may abort a
167. Inversion:
• occurs when an area of DNA on a
chromosome reverses its orientation
on the chromosome.
• Just one inversion on chromosome
16 can cause leukemia.
• An inversion can cause the embryo
to miscarry, fail to grow, or be born
with substantial medical problems.
• Chromosome 16 is one of the 23
pairs of chromosomes in humans. It
spans about 90 million base pairs
and accounts for nearly 3% of DNA in
cells. Chromosome 21 is one of the
23 pairs of chromosomes in humans.
It is the smallest of the
chromosomes.
168. Deletion:
• occurs due to the deletion of a
large section of a chromosome.
• can result in a variety of genetic
disorders, such as
Prader-Willi syndrome. This
results from a malfunction of the
hypothalamus (a small endocrine
organ at the base of the brain),
which plays a crucial role in
many bodily functions, including
hunger and satiety, temperature
and pain regulation, fluid
balance, puberty, emotions and
169. Insertion:
• is type of mutation
describes an increase
in the number of genes
caused when an
unequal crossover
happens during
meiosis.
• The chromosome may
become abnormally
long or short and stop
functioning as a result.
170. • Duplications:
– When genes are duplicated it
results in them being displayed
twice on a single chromosome.
This is usually harmless as the
chromosome still has all its
genes. However, duplication of
the whole chromosome is more
serious. Having three copies of
chromosome 16, known as
trisomy 16, leads to babies being
born with a range of medical
issues, such as poor foetal
growth, muscular and skeletal
anomalies, congenital heart
defects and underdeveloped
lungs.
171. Chromosome non-disjunction
– When homologous chromosomes do not separate
successfully to opposite poles during meiosis, the
result is one of the gametes lacking a chromosome
and the other having an extra chromosome. If this
happens with chromosome 21, Down’s syndrome
results. Those with the condition will have 47
chromosomes in every cell (because they have
three copies of chromosome 21) as opposed to 46
like normal. Down’s syndrome is characterized by
mental retardation, heart defects and stunted
growth.
–
172. Translocations
• A piece of one
chromosome is
transferred to another
non-homologous
chromosome.
• This type of
chromosome mutation
is often responsible for
chronic myelogenous
leukemia.
