The document discusses cell structure and function, highlighting the importance of cells as the basic unit of life. It details the historical discoveries in cell biology, the components and functions of cells, including nutrition, respiration, and reproduction, as well as the various organelles within cells such as the nucleus, mitochondria, and ribosomes. The document also covers the principles of membrane transport, osmosis, and the differences between prokaryotic and eukaryotic cells.

1. CELL
STRUCTURE
AND
FUNCTION

2. Examine the tip of your finger, and you see the
ridges and valleys that make up your
fingerprints; a blade of grass, an insect. Using
powerful dissecting microscope you’ll see that
there is a common structure that makes up
every living things ---- the cell.
Cells come in many shapes and sizes. Although
typical cells range from 5 to 50 micrometers in
diameter. The tiniest bacteria are only 0.2
micrometers across. In contrast, the giant
amoeba, may reach 1000 micrometers in
diameter.

3. Early Discoveries Related to the Study of Cells
 In 1665, Robert Hooke examined a thin slice of cork. The piece of cork was
composed of many tiny compartments, named cells.
 In 1674, Anton Van Leeuwenhoek observed red blood cells, sperm cells,
bacteria, free living and parasitic protists
 In 1831, Robert Brown discovered the nucleus, discovered Brownian
Movement (1827) when he observed the movement of plant spores
floating in water.
 In 1835, Felix Dujardin found out that living cells contain an internal
substance (sarcode)
 Jan Evangelista Purkenji gave the name protoplasm
 In 1838, Mathias Schleiden stated that all plants are composed of cells
 In 1839, Theodor Schwann concluded that animals are composed of cells
 In 1858, Rudolf Virchow theorized that all living cells come from preexisting
living cells.

4. Components of the Cell Theory
a) All living things are composed of
one or more cells;
b) All living cells come from other living
cells by cell division;
c) Cells are the basic units of structure
and function in organisms.

5. Cell Functions:
1. Nutrition- the process by which cells obtain food molecules
to support their activities;
2. Digestion- the process by which food particles are broken
down with the help of enzymes;
3. Absorption- the process by which cells absorb from their
environment water and other materials
4. Biosynthesis- the process by which all cells organize
complex chemicals from simple substances
5. Excretion- the process by which cell by-products are
eliminated;
6. Egestion- the process by which insoluble, undigested
particles are eliminated by the cell;
7. Secretion- the process by which substances that are
synthesized by the cells are expelled in the elimination
process.

6. 8.Movement- a process that consists of the locomotion of cells
by means of special structures like cilia or flagella.
9. Irritability- the process by which cells respond or react to
external factors
.10. Respiration- the process of breaking down food molecules
into chemical energy that cells need to function;
11. Cellular reproduction- a process by which a cell copies its
DNA and increases in number by cell division. In reproduction,
cells give rise to new cells as a result, organisms grow.

9. Basic cell Structures are:
 Cell membrane -- a thin, flexible barrier around the cell.
 Cell wall – strong layer around the membrane.
 Nucleus – a large structure that contains the cell’s genetic
material and controls the cell’ activities.
 Cytoplasm –material inside the cell membrane; but not including
the nucleus. It contains many important structures.

10. CELL STRUCTURES.
A. Cell wall – its main function is to provide support and protection for the cell.
Composition varies in different cell types and from one species to
another.
 about 60% of it is cellulose; other components include
hemicelluloses; pectins; lignins and proteins.
Young cells and cells in actively growing areas have primary cell
walls (25% cellulose – relatively thin and flexible).
Certain kinds of cells stop growing at maturity and form secondary
cell wall (25% lignin, which adds hardness and resists decay).
Cell walls of cork cells contain suberin that inhibit water loss
through bark (cork oak)
Cells that adjoin one another are probably held together by pectins.
Pectic layer between cells are called the middle lamella.
Pits and perforations in the cell walls are called plasmodesmata where
water & dissolved substances diffuse from one cell to another.

11. B. Nucleus – controls most cell processes.
 contains the hereditary information of DNA, occurs bound to
proteins (histones) in a threadlike chromatin. when cells divide
chromatin condenses to form chromosomes.
 surrounded by 2 membranes called nuclear envelope; outer
membrane is continuous w/ the membrane of the ER.
 inner & outer membranes are separated by a space except
where they fuse to form pores in the envelope.
B. chromosomes are not usually visible in a living cell except
during divisions.
 nucleoli – contain nucleic acids and proteins but function as
intermediate in protein synthesis.

12. C. Protoplasm – it is the structurally complex, constantly changing
aggregation of materials, w/c fills cells and is classically known as the
“living substance”.
 it is opalescent or transparent , & variously viscid.
 grayish, but may contain red, green, yellow, blue or black pigments
 Consists of a watery solution of salts and organic compounds.
 In most cells, the bulk of the protoplasm is the cytoplasm – outside the
nucleus.
D. Cytoskeleton --- helps support the cell. It is a network of protein filaments
that helps the cell maintain its shape. Also involved in many forms of cell
movement.
 Made up of microtubules and microfilaments.
 Microtubules are hollow tubes of protein. They maintain cell shape and
can serve as tracks along which organelles are moved. About 25
nanometers.
 Microfilaments are long thin fibers that function in the movement and
support of the cell. About 7 nanometers

13.  Cytoplasm – non-nuclear protoplasm; bounded by plasma
membrane
Organelles:
1. Ribosomes -- are the sites of protein synthesis.
 Proteins are assembled on ribosomes , small particles made
of RNA and protein.
 About 0.025 micrometers in diameter.
 Ribosomes produce proteins following coded instructions that
come from the nucleus.
 Usually occur in clusters called polysomes
 Either attached to membranes or free.

14. 2. Endoplasmic Reticulum – is a system of flattened tubes and sacs
that is continuous between the plasma membrane and the outer
membrane of the nuclear envelope.
 Where components of the cell membrane are assembled &
some proteins are modified.
2 regions of ER:
a) Rough ER – region where many ribosomes attached to it;
involved in the synthesis of proteins.
b) Smooth ER – no ribosomes are attached; contains collections
of enzymes that perform specialized tasks such as the synthesis of
lipids.
 Both types of ER form vesicles that break away & fuse w/ other
membranes.

15. 3. Golgi bodies or dictyosomes – are usually two-sided w/ one side
facing ER & one side facing the plasma membrane.
 Transport vesicles from the ER fuse w/ the inner face of the
dictyosome & release their contents into its interior. Enzymes
in the Golgi apparatus attach carbohydrates and lipids to
proteins.
 Named after the Italian biologist Camillo Golgi who
discovered it.
 Exocytosis – when contents are secreted to the exterior of the
cell.
 Aid specialized cells in secreting substances like nectar, oils, &
resinous chemicals.
 In dividing cells, they help build new primary walls after nuclei
have divided. Vesicles containing cell wall precursors fuse in
this region to form a cell plate.

16. 4. Lysosomes are small organelles filled with enzymes.
Functions:
1. Break down lipids, carbohydrates, and proteins from food into particles
that can be used by the rest of the cell.
2. Help break down organelles that have outlived their usefulness.
3. Perform the vital function of removing debris that might otherwise
accumulate and clutter up the cell.
5. Vacuoles – constitute the bulk of most mature Plant cells.
 can swell, coalesce, about nine tenths of the volume of a ce
ll.
 Main water-storage centers of cells
 Contain mostly water with dissolved pigments, mineral salt
s, organic acids, proteins, crystals and various metabolic p
roducts.
 Their turgor keeps cells, tissues, and organs firm.
 The membrane of the central vacuole is known as tonoplast.

17. Endoplasmic
Reticulum
Golgi
Bodies

18. 6. Plastids – peculiar to plants that contain photosynthetic pigments.
Membrane-bound; usually flattened, ellipsoid bodies.
 Chromoplasts – with yellow & red pigments
 Leucoplasts – colorless plastid
 Amyloplasts – store starch
 Elioplasts – store oils
 Chloroplasts – green plastids; the fluid inside it is called stroma;
membranes occuring throughout the stroma are called thylakoids w/c
are aggregated into stacks called grana.
7. Mitochondria – function in the formation of energy-rich compounds,
especially ATP.
 Sausage-shaped, smaller than plastids, colorless, flexible & motile.
 Consist of smooth outer membranes & an inner membrane that is
folded into tubular or vesicle shaped cristae (mitochondrial crests)
 Involved in other metabolic activities, including synthesis of rubber
particles.

20. 8. Microbodies
 Peroxisomes – occur primarily in leaves, they metabolize hydrogen
peroxide (H2 O2); contain enzymes catalase and oxidase
-- peroxide- detoxifying organelle, use H2 O2 to oxidize other toxins such
as ethanol & nitrites.
 Glyoxysomes – common in germinating oil-bearing seeds & the
young seedlings that grow from them; contain enzymes that
catalyze the breakdown of fatty acids & acetyl CoA.
E. Flagella and Cilia – threadlike cytoplasmic extensions w/c are the
locomotor organelles of swimming spores or sex cells.
 These two structures are similar to one another except that cilia are
short, proportional about like eyelashes and flagella are longer.
 They occur in many lower plants and in sperm of a few seed- plants.

22. F. Membranes – elastic, double layers of protein and fatty materials. Form
special surfaces over almost all subcellular particles as well as over entire cells.

23. MEMBRANE AND MEMBRANE TRANSPORT
Important features:
 The long hydrocarbon ‘tails’ of the phospholipid is nonpolar &
hydrophobic (“water-fearing” – refers to chemicals that do not dissolve
in water).
The phosphate ‘head’ is polar & hydrophilic (“water-loving” – refers
to chemicals that can dissolve in water).
Fluid mosaic – description of Davson & Danielli to the structure of
the membrane. This model holds that proteins occur as a mosaic in a
fluid of bilayer of phospholipid.
 One side of a membrane structure is different from the other --- this
is due to the carbohydrates attached to proteins & lipids.
 glycoproteins – proteins with carbohydrates attached to them.
 glycolipids – lipids with carbohydrates attached to them.

25. 5. Cellular communication – proteins in the plasma membrane bind
molecules released from other cells. Once bound to an external
molecule, these proteins activate other proteins in the membrane that
cause metabolic changes in the cell.
 glycoproteins and glycolipids vary from species to species, from
one individual to another in the same species, and even from one
cell type to another in a single individual.
 cell identification tags - crucial to life - allow cells in an
embryo to sort themselves into tissues and organs.
 it also enables cells of the immune system to recognize and
reject foreign cells, such as infectious bacteria.
 Cholesterol in animal cell membranes, animal cells use it as starting
material for making some steroids, including the female and male sex
hormones.

26. Functions of membrane proteins include:
attaching the membrane to the cytoskleton and external fibers
providing identification tags
forming junction to adjacent cells
many membrane proteins are enzymes - catalytic teams for
molecular assembly lines
other proteins function as receptors for chemical messengers
from other cells - signal transduction.

27. MOVEMENT OF WATER & OTHER MOLECULES THROUGH
MEMBRANES
 Water is the most common molecules in cells
 Ions & other polar molecules (the solutes) are dissolved in water
(the solvent). The resulting mixture is a solution.
 The solutes include: protons (H+
), mineral ions (K+
& Mg2+
) and
organic compounds such as sugars & amino acids.
 Nonpolar molecules such as hydrocarbons & oxygen, small &
uncharged polar molecules such as water pass easily w/o
hindrance.
 Ions are almost entirely prevented.

28. MOVEMENT OF SOLUTES
All molecules display random thermal motion, or kinetic energy, a solute
molecule has a tendency to move around in a solution ---- results in the
diffusion of molecules outward from regions of high concentration to
regions of lower concentration.
 Diffusion – is the tendency for particles of any kind to spread out
spontaneously to regions where they are less concentrated.
 that is down a concentration gradient.
 The rate of diffusion depends on the ff:
a. Size of molecules – larger molecules move slower
b. Temperature of the solution – higher temperatures cause faster
movement.
 Anything that can fall, change, or flow from higher level to a lower one
has the potential to do work, w/c is called potential energy.
 When the solute is moving, it has energy of movement called Kinetic
energy.

29. Passive Transport is diffusion across a membrane
Diffusion requires no work; it results from the random
motion (KE) of atoms and molecules.
the diffusion of a substance across its membrane is
called passive transport.
molecules of solution tend to diffuse from the side of
the membrane where they are more concentrated to
the side where they are less concentrated until
equilibrium is reached - down its concetration
gradient.
 Passive transport is extremely important to all cells -
in the lungs, the oxygen enters red blood cells and
carbon dioxide passes out of them.
Water also crosses membranes by passive transport.
 Osmosis

30. Facilitated diffusion – substances that do not diffuse freely across membranes because
of their size and charge move through transport proteins from the hypertonic side of the
membrane to the hypotonic side of the membrane.
It is like osmosis that is driven by a concentration gradient.
Active transport – substances move into or out of cells and organelles requiring energy.
 in this situation - a transport protein actively pumps a specific solute across a
membrane against the solute's concentration gradient.
 Example below shows an AT system of 2 different solutes in opposite directions.

31. Transport of Large molecules:
Exocytosis – export bulky materials.
Endocytosis -- cells take in macromolecules or other particles by forming vesicles or
vacuoles from its plasma membrane.
3 kinds of endocytosis:
1. Phagocytosis – “cellular eating” ex. Amoeba taking in a food particle.
2. Pinocytosis – “cellular drinking” cell is in the process of taking droplets of fluid
from its surrounding.
3. Receptor- mediated endocytosis – highly specific. Plasma membrane has
indented to form a pit, and this pit is lined with proteins

32. WATER POTENTIAL
 like solutes, water also has potential energy to flow. Its potential energy is
called water potential.
 Water tends to move down a water-potential gradient, that is from a region of
high water potential to a region of low water potential.
OSMOSIS – is the diffusion of water through a selectively permeable
membrane.
 It is influenced by different water potentials on either side of a
membrane.
 Before osmosis begins, water on the side with hypotonic solution ( low
solute concentration) of the membrane has a higher water potential –
greater potential to move.
 Hypertonic solution – high solute concentration.
 Isotonic solution - equal solute concentration.

34. Osmotic pressure – is the potential of pure water to move into a solution
on the other side of a membrane.
Osmotic potential – is the potential of a solution to cause osmotic
pressure.
Ex. The potential for water movement into a cell is continuous due
to higher concentration of solution in the cytoplasm than outside the cell.
This potential causes pressure called osmotic pressure, & inside the cell, its
counterpart is osmotic potential.
For animal to survive if its cells are exposed to a hypertonic or hypotonic
environment - they are capable of water balance called osmoregulation.
Ex. Freshwater fish - its kidneys and gills do the water balance.
Plant cells have rigid cell walls - water balance is different.

35. How Cells behave in different solutions

36. TURGOR
Most plant cells are surrounded by a hypotonic environment that
results in cells absorbing much water as they can hold.
Turgor pressure – is the outward pressure of the plasma membrane
against the cell walls. It keeps the cell turgid.
Ways in w/c turgor pressure is vital to plants:
1. During growth – cell expansion is caused by turgor pressure.
2. It keeps herbaceous (non woody) plants upright, supports the
fleshy stalks & leaves of trees & shrubs; & keeps supermarket
vegetables crisp when they are sprayed w/ water.
3. Change in turgor also cause movements in plants, such as the
opening & closing of stomata & the curling of grass leaves.
Cells lose turgor when they are placed in a hypertonic solution.
 Plasmolysis – is osmotically induced shrinkage of the cytoplasm.
(causes wilting of leaves & stems)
Ex. Garden plants – when salts accumulate in the soil
from excessive use of hard water.

37. Comparison of Prokaryotic
and Eukaryotic Cells
Prokaryotes Eukaryotes
Size ~ 1 – 10 µm ~ 1 – 10 µm
Nucleus Absent Present
DNA Circular
Linear molecules with
histone proteins
Mitochondria None One to several dozens
Organization Unicellular
Single cells, colonies,
multicellular

38. Differences Between Plant and Animal Cells
Structure/Part Plant Cell Animal Cell
1. Cell wall Present, made of
cellulose, found just
outside the plasma
membrane
Absent, only plasma
membrane is present
2. Chloroplasts Present Absent
3. Vacuoles One large central
vacuole
Many small vacuoles
4. Centriole
5. Lysosomes
Absent
Absent
Present (paired
centrioles)
Presesnt

40. Unicellular Organisms
Cells are the basic living units of all organisms, but
sometimes a cell is the organism itself.
A single-celled organism is also called a unicellular
organism.
Unicellular organisms do everything that you would
expect a living thing to do – they grow, respond to the
environment, & reproduce.
Unicellular organisms include both prokaryotes and
eukaryotes.
Prokaryotes, especially bacteria are remarkably
adaptable -- live almost everywhere – in the soil, on
leaves, in the ocean, in the air, and even within human
body.

41. Many eukaryotes also spend their lives as single
cells. Some types of algae, which contain chloroplasts
and are found in oceans, lakes, and streams around
the world are single celled.
 Yeasts are unicellular fungi.
Some species of protists and algae are colonial.
Colonial organisms live in groups of individuals of the
same species that are attached to one another but
have few specialized structures

43. Multicellular Organisms
Organisms that are made up of many cells that work together
are called multicellular organisms.
The cells of multicellular organisms, such as human beings, do
not live on their own.
Cells in multicellular organisms are specialized to perform
particular functions within the organism. --- they have cell
specialization, or separate roles for each type of cell.
Example: pancreatic cells that are specialized to produce
protein enzymes that make it possible to digest food. To
perform this function, these cells contain enormous amounts of
the organelles involved in protein synthesis – rough
endoplasmic reticulum, Golgi apparatus, and clusters of
storage vacuoles loaded with protein.

45. Homeostasis in Unicellular and Multicellular
Organisms
 As an organism, you are an open thermodynamic
system; that is there is a constant flow of energy
and matter between you and the environment. It is
a flow that is dynamic equilibrium , often called a
steady state.
 A steady state occurs at all levels of organization-
from unicellular to colonial or to multicellular
organisms. It may also be from cell, to tissue, to
organ, to organ system, to organism.

46. Homeostasis- a regulating control, by which
a constant internal environment is
maintained despite external changes.
At the cellular level, a single cell has the
capacity for self regulation ( made possible
by the control of enzyme synthesis, product
formation, and uptake of matter from the
environment and release of energy)
Example: an amoeba

47. As an organism becomes more complex,
the more vital the process of
homeostasis becomes.
How do you adjust and maintain a steady
state in spite of temperature changes
outside?

48. Cell Specialization: The Levels of Organization
CELL
TISSUE
ORGAN
ORGAN SYSTEM
ORGANISM

51. Energy and the cell
Energy is the capacity to perform work
2 Types of energy:
1. Kinetic energy – energy that is actually doing work. Heat, the
energy associated with the movement of molecules in body of
matter. Light is another kind of kinetic energy.
2. Potential energy – stored energy. This is the capacity to do
work that matter possesses as result of its location or
arrangement. In a teaspoon of sugar, unlit firecracker, a rock
atop of a hill. In organisms– stored in the chemical bonds such
as sugar.

52. Two laws that govern energy conversions
Thermodynamics – is the study of energy transformations that occur in a
collection of matter.
1. First Law of Thermodynamics – also known as the law of energy
conservation.
 It states that energy cannot be created or destroyed but only converted to
other forms
 The amount of energy in the universe is constant.
• Second Law of Thermodynamics – states that energy conversions reduce
the order of the universe. The amount of disorder in a system is called
entropy.
 Heat which is random molecular motion, is one form of disorder. The
more heat that is generated when one form of energy is converted to
another, the more entropy of the system increases.
 Tells us that the entropy of the universe as a whole is increasing.

53. Chemical Reactions Either Store or Release Energy
Chemical reactions are of two kinds:
1. Endergonic reaction – requires a net input of energy. Reactant molecules
contain relatively little potential energy; energy is absorbed from the
surroundings as the reaction occurs, so that products store more energy
than the reactants.
 Energy is stored in the covalent bonds of the product molecules.
 Example is photosynthesis.
2. Exergonic reaction – is a chemical reaction that releases energy.
 Example when wood burns (contains cellulose which is a carbohydrate )–
the potential energy is released as heat and light. CO2 and water are the
products of the reaction.
 Example is cellular respiration– the energy releasing chemical breakdown of
glucose molecules and the storage of energy in a form that the cell can use
to perform work.

54. Every working cell in every organism carries out thousands of
endergonic and exergonic reactions, the sum total of which is
known as cellular metabolism.
ATP powers nearly all forms of cellular work.
When a cell uses chemical energy to perform work, it couples an
exergonic reaction with an endergonic one. It first obtains
chemical energy from an exergonic reaction and then uses the
energy to drive endergonic reaction ---- energy coupling.
ATP (Adenosine triphosphate) has three parts, connected by
covalent bonds: 1) adenine, a nitrogenous base; 2) ribose, a five
carbon sugar; and 3) a chain of three phosphate groups (P)

56. The covalent bonds connecting the second and the third
phosphate are unstable – can readily be broken by hydrolysis .
Three things happen when the third bond breaks:
1. A phosphate is removed.
2. ATP becomes ADP (adenosine diphosphate).
3. Energy is released.
Chemical reaction:
ATP + H 2O ADP + Pi + energy
The transfer of a phosphate group to a molecule is called
phosphorylation, and most cellular work depends on ATP
energizing other molecules by phosphorylating them.

57. Substrate – substance that an enzyme acts on --- a reactant in a chemical
reaction. Each enzyme recognizes only one specific substrate or substrates of
the reaction it catalyzes.
Active site -- small part of an enzyme molecule that actually binds to
substrate.
The cellular environment affects enzyme activity.
 Temperature – affects molecular motion, and an enzyme’s optimal
temperature produces the highest rate of contact between reactant and the
enzyme’s active site.
 higher temperatures denature the enzyme.
 Most human enzymes have temperature optima of 35—40 degrees Celsius.
Salt concentration – salt ions interfere with some of the chemical bonds that
maintain protein structure.
pH – extra hydrogen ions present at very low pH also. Optimal pH for most
enzymes is in the range of 6—8.

58. Enzymes speed up the cell’s chemical reactions by
lowering energy barriers
An energy barrier is an amount of energy, called the energy of
activation (EA), that reactants must absorb to start a chemical
reaction.
In the case of ATP breakdown, EA is the amount of energy needed
to break the bond between the 2nd
and 3rd
phosphates.
Since most reactions require energy to get started, ATP and most
other vital molecules in our cells do not break spontaneously.
Most of the essential reactions of metabolism must occur quickly
and precisely for a cell to survive. If a chemical reactants of
metabolism are slow, a cell may die because it cannot make vital
products fast enough.

59. An enzyme is a protein molecule that serves as a biological
catalyst, increasing the rate of a reaction without itself being
changed into a different molecule.
It does not add energy to a cellular reaction; it speeds up a
reaction by lowering the EA barrier.
They are critical to life because they speed spontaneous reactions
to a biologically useful rate.
Example: Carbonic anhydrase
Enzymes are very selective in the reaction they catalyze, and their
selectivity determines which chemical processes occur in a cell at
any particular time.

60. Many enzymes will not work unless they are accompanied by
nonprotein helpers called cofactors. They may be inorganic
substances such as atoms of zinc, iron, or copper.
Coenzyme – cofactor that is an organic molecule. Most of them
are from vitamins or are vitamins themselves. For example,
vitamin B6 is a coenzyme required by enzymes involved in
converting one amino acid to another.
Coenzymes:
1. NAD+
-- Nicotinamide Adenine Dinucleotide
 It is similar to ATP in that it is made of adenine, ribose &
phosphate groups.
 The active site is a nitrogen-containing ring called nicotinamide,
which is a derivative of nicotinic acidn(niacin, or Vitamin B3 ,
added to products such as cornflake to make them “Vitamin
fortified”)

61. NAD+
+ 2H+
+ 2e-
NADH + H+
2. NADP+
–Nicotinamide Adenine Dinucleotide Phosphate
 Has a structure similar to NAD with an added phosphate group.
 NADPH supplies the hydrogen that reduces CO 2 to
carbohydrate during photosynthesis
• FAD -- Flavin Adenine Dinucleotide
2. Forms of riboflavin (Vitamin B2 )
3. Carries two electrons ; however FAD accepts both protons to
become FADH2

62. 4. Cytochromes -- like chlorophyl & hemoglobin, cytochromes
are a group of metal containing molecules that participate in
metabolism by transferring electrons.
Regulating metabolism:
 Feedback inhibition – this means slowing a pathway when
its products are not needed.
Ex. Plants use a five-step pathway to make isoleucine from
threonine. When isoleucine accumulates, it inhibits the first
enzyme of the pathway, thereby decreasing production of
isoleucine until the current supply is used.

63. Enzyme inhibitors block enzyme action
1. Competitive inhibitors – many enzymes are inhibited by other molecules
compete for the enzyme’s active site. They mimic the substrate & can
overcome by increasing the substrate.
Ex. Sulfanilamide – a drug that competitively inhibit enzymes.
2. Noncompetitive inhibitors – other compounds inactivate enzymes by binding
to parts of the enzyme that are different from the active site.
Examples: insecticide malathion– inhibits a nervous system enzyme called
cholinesterase; this inhibition prevent nerve cells from transmitting signals &
kills the insect.
 Antibiotic Penicillin – inhibits an enzyme that bacteria use in making cell
walls; since humans lack this enzyme, we are not harmed by the drug.