Todo el topic 2. Diapositivas de Miss Clarita

1. Cell theory, Eukaryotic and
Prokaryotic cells, Membranes, Cell
division

2. CELLS

3. 1.- Cell theory
The invention of the microscope in
the 17th century quicly led to the
discovery of cells.
Robert Hooke was the first to use the
term cell in 1665, after examining
cork and other plant tissues under
the microscope.
Later on the CELL THEORY WAS
DEVELOPED.

4. CELL THEORY:
1.- Cells are the smallest unit of life and nothing
smaller can survive independently.
2.- All living things consist of cells, although the
smallest organism may consist of one cell only.
3.- All cells come from pre-existing cells, by
division and therefore new cells cannot be
constructed from non-living chemical
substances.

5. 2.- Plant and animal cells
Prokaryotic  No nucleus
Eukaryotic  True nucleus
- Animal cells: no chloroplast no cell wall
- Plant cells: Chloroplasts and cell wall
There are many similarities in the structure of plant
and animal cells.
A nucleus is usually present, with cytoplasm around
it.
The cytoplasm is enclosed by a plasma membrane.

6. Animal cell / Plant cell

7. Main differences between plant and
animal cells:
1) Plant cells have cellulose cell wall outside their
plasma membrane, which animal cells never
have.
2) Plant cells often have large permanent vacuole,
which contains a solution of mineral ions such as
potassium and other solutes. Animal cells only
have small vesicles.
3) Many plant cells in stems and leaves have
chloroplasts in their cytoplasm. Thye contain
chlorophyll and starch. Animal cells dont have
them. Instead of starch they have glycogen.

8. 3.- Unicellular organisms
Some organisms consist of one single cell.
Example: Amoebas.
These cells must carry out all the functions of life
on their own.

9. Functions of life:
1) Nutrition: obtaining food, to provide energy and
the materials needed for growth
2) Metabolism: chemical reactions inside the cell,
including cell respiration to release energy
3) Growth: an irreversible increase in size
4) Sensitivity: perceiving and responding to
changes in their environment
5) Homeostais: keeping conditions inside the
organism within tolerable limits
6) Reproduction: producing offspring either
sexually or asexually

10. 4.- Size of cells
CELL TYPE SIZE
Mycoplasma pneumoniae 200 nm
( a very small bacterium)
Minivirus 400nm
(a giant virus found in amoebae)
Megakaryocyte 160 micrometer
(a cell that makes blood platelets)
Thiomargarita namibiensis 0.7mm
( largest known bacteria)
Diameter of the nerve fiber of a squid 1mm
giant nerve cell
Diameter of the yolk cell of an ostrich egg 120mm

11. Magnification and scale bars
• Biologists often need to do calculations involving
the magnification and sizes of images and
specimens.
• The size of a specimen is how large something
actually is.
• The size of an image is how large the specimen
appears in a drawing or a photograph.
• Magnification is how much larger the image is
than the actual size.

12. Magnification= Size image/ actual size sp
Scale bars are sometimes used on drawings or
micrographs.
- A micrograph is a photograph of an image
under the microscope.
- The scale bar consists of a line, with the actual
size that the line represents.

13. Micrograph

14. Graphs in Biology
1) Independent variable  X- axis
2) Dependents  Y- axis

15. 5.- Multicellular organisms and cell
differentiation
• Some multicellular organisms live together in
colonies. In a colony cells act in a co-operating
way but they are not fused and do not form a
single organism.
• Organisms consisting of a single mass of cells
fused together are considered multicellular
organisms. They have specialized cells for
specific functions.

16. Algae colony

17. • The development of cells in different functions
is called DIFFERENTIATION. This involves each
cell type using some of the genes in its
nucleus, and not others.
• When a gene is being used in a cell, we say
that the gene is being EXPRESSED.
• In simple terms the gene is switched on and
the information in it is used to make a protein
or other gene product.

18. 6.- STEM CELLS
• Stem cells are defined as cells that have the
capacity of self-renew by cell division and to
differentiate.
• At an early stage the whole of a human embryo
consists of stem cells. Gradually the cells become
committed to differentiating in a particular way.
Once committed a cell may still be able to divide
about six more times.
• However all the cells produced will differentiate
in the same way and will no longer be stem cells.

19. • In the human body only a few tissues have
stem cells: bone marrow, skin and liver.
• There has been great interest in stem cells
because of their potential for tissue repair and
for treating a variety of degenerative
conditions. Example: Parkinson’s disease and
strokes are all caused by the loss of neurons or
other cells. Stem cells may one day be used to
replace these cells.

21. 6.1.- Therapeutic use of stem cells
• The greatest success so far in the therapeutic use
of stem cels involves bone marrow transplants.
• The cells needed are hematopoietic stem cells
(HS). They give place to white and red blood cells.
• These cells are used in a variety of treatments:
- Leukemia
- Lymphoma
- Myeloma

22. LYMPHOMA:
Is a cancer of the lymphatic system.
Some lymphomas can be treated following this
procedure:
1) Cells are removed from the bone marrow of the
patient
2) The patient goes through chemotherapy to kill
dividing cells.
3) HS cells are retransplanted back into the patient
and begin to produce new healthy cells.

23. Origin of blood cells

24. 7.- Extracellular components
• The plasma membrane of the cell is usually
considered to be the barrier between the
inside of the cell and the outside.
• The plasma mebrane is composed mainly by
phospholipids and glycoproteins.
• These are called EXTRACELLULAR
COMPONENTS. Anything inside the plasma
membrane is Intracellular.

25. The matrix glues the cells in animal
tissues (adhesion). Helps form the
cartilage, tendons, ligaments, etc.

26. 7.1.- The plant cell wall
• The plant cell wall can be regarded as well as
an extracellular component.
• The cell wall is composed by CELLULOSE
MICROFIBRILS.
• This wall mantains the shape of the cell and
supports the plasma membrane. It also
protects the cell againts dehydration and solar
radiation.

28. 8.- Life as an emergent property
• Emergent properties are those that arise
from the interaction of component parts 
The whole is greater than the sum of its parts.
• Ex: consciousness is a property that emerges
from the interaction of nerve cells in the brain.
• Multicellular organisms show many emergent
properties.
• LIFE ITSELF IS AN EMERGENT PROPERTY.

29. 9.- PROKARYOTIC CELLS
• Prokaryotes were the first organisms to evolve
on Earth and they still have the simplest
structure.
• Bacteria are prokaryotes.
• They are mostly small in size, unicellular and
are found almost everywhere: in soil, water, in
our skin, hot water, volcanic areas,
everywhere.

31. Prokaryotic cell’s structure
1) Cell wall: 3) Ribosomes:
- Always present - Small granular structures
- Composed of peptidoglycan - Smaller tha eukaryotic
- Protects the cell ribosomes
- Mantains its shape - Synthesizes proteins
- Prevents cell from bursting 4) Cytoplasm:
2) Plasma membrane: - Fluid filling the space inside
- Thin layer mainly composed of the plasma membrane
phospholipids - Water with many dissolved
- Partially permeable substances
- Controls entry and exit of - Contains enzymes and
substances ribosomes
- Pumps substances by active - Carries out chemical reactions
transport of metabolism

32. 5) Nucleoid: 6) Flagella:
- Structures protruding from the
- Region of cytoplasm cell wall
containing the genetic - Base is embedded in the cell wall
material (usually one - Using energy they can be rotated
molecule of DNA) to propel the cell from one area
to another
- DNA molecule is circular - Unlike aukaryotic flagella they are
and naked (no associated solid and inflexible
proteins) 7) Pili:
- Total amount of DNA is - Protein filaments protruding from
the cell wall
much smaller than in - Can be pulled in or pushed out by
eukaryotes a rachet mechanism
- The nucleoid is stained less - Used for cell to cell adhesion
densely than the rest of the - Used when bacteria stick
together to form aggregations of
cytoplasm because there cells
are fewer ribosomes in it - Used in DNA exchanging process:
and less protein. conjugation

33. 10.- Eukaryotic cells
Eukaryotic cell micrograph
Eukaryotic cells have a much
more complicated internal
structure than Prokaryotic
cells.
- They have a NUCLEUS and
organelles in the cytoplasm
with single of double
membranes.
- Each organelle has a
distinctive structure and
function.

34. Eukaryotic cell’s structure
1) Nucleus: 2) Rough Endoplasmic reticulum:
-The nuclear membrane is - Consists of flattened
membrane sacs called
double and has pores through cisternae. Attached to its walls
it. there are ribosomes.
-Uncoiled chromosomes are - Its function is to produce
spread through the nucleus proteins for secretion from the
cell.
and are called chromatin.
3) Golgi apparatus:
-The nucleus stores almost all - Its structure is similiar the RER.
the genetic material of the cell. - Here the proteins from the
- It is where DNA is replicated RER are processed and
and transcribed into mRNA exported out of the cell.

35. 4) Lysosomes: 6) Ribosomes:
- Spherical organelles with a These appear as dark granules
single membrane
in the cytoplasm and are
- They contain digestive
enzymes which can be used to surrounded by a
break down ingested food, or membrane.
damaged organelles. In some They synthesize proteins.
cases even the entire cell.
5) Mitochondria:
- Is a double membrane
organelle.
- They produce ATP by aerobic
cell respiration
- Fat is digested here if it is
being used as an energy
source in the cell.

36. 11.- MEMBRANES
- Phospholipids are essential components of
membranes:
1) In the plasma membrane
2) Internal cellular membranes (mitochondria,
lysosomes, etc).
- They have two regions with very different properties:
1) Two hydrocarbon tails which are not attracted to
water  hydrophobic
2) A phosphate head, that is negatively charged to which
water is attracted  hydrophilic

38. • When phospholipids are mixed with water
they become arranged in double layers, with
the heads facing outwards and the tails
inwards.
• This arrangement called phospholipid bilayer
is the basis of cellular membranes.
• Its a very stable structure.

39. Membrane structure
• Membrane’s are not composed entirely by
phospholipids, there are also proteins.
-Integral proteins: embedded in the bilayer
-Peripheral proteins: attached to the surface.

40. Membrane proteins
PROTEIN FUNCTION
Insuline receptor Hormone receptor
Enzymes Proteins with enzymatic activity. Ex: In the
small intestine
Cell adhesion proteins Cell adhesion to form tight junctions
between groups of cells in tissues
Transport proteins Channels for passive transport to allow
hydrophilic particles across by facilitated
difussion
Cell signaling proteins Cell.to-cell communication. Ex: receptors
for neurotransmitters at synapses.
Pumps Pumps for active transport which use ATP
to move particles across the membrane.

41. a) Diffusion
• Liquids and gases are fluids. Within
fluids, individual particles move independently
and the direction of their movement is random.
• These movements of particles results in a process
called DIFFUSION.
• More particles move randomly from an area with
a high concentration to an area of a low
concentration.
• There is a net movement from the higher to the
lower concentration, in order to reach BALANCE.

43. • For example oxygen and carbon dioxide move
into and out of cells by diffusion.
• It is an effective method of moving particles a
few micrometres but it is too slow over
greater distances.
 DIFFUSION: is the passive movement of
particles from a region of high concentration to
a region of lower concentration.

44. b) Simple difussion across membranes
• Simple diffusion across membranes involves
particles passing between the phospholipids
in the membrane.
• It can only happen if the phospholipids bilayer
is permeable to the particles.
• Small particles can pass through more easily
than other large particles or charged ones
(positive or negatively charged molecules
cannot easily go through).

45. • Simple diffussion also happens if the
concentration of the particle is higher on one
side of the membrane than the other.

46. c) Facilitated diffusion
• Ions and other particles, which cannot diffuse
between phospholipids, can pass into or out of
cells if there are channels for them, through the
plasma membrane.
• The diameter and chemical properties of the
channel ensure that only one type of particles
passes through.
• Because these channels help particles to pass
through the membrane, from a higher to a lower
concentration, this process is called 
FACILITATED DIFUSSION.

47. d) Osmosis
• Osmosis is the diffusion of water across the
plasma membrane.
• Osmosis only occurs when there are
substances dissolved in water  solutes.
• Regions with a higher solute concentration
have a lower water concentration, than
regions with a lower solute concentration.
• Water tends to move from regions of lower to
higher solute concentration.

49. ACTIVE TRANSPORT
• When substances move across the plasma
membrane against the cincentration gradient,
energy must be spent for the process to take
place  this type of transport is called ACTIVE
TRANSPORT.
• The energy supplied for this process comes
from ATP (cellular respiration).
• Transporter proteins, carry out active
transport.

52. ENDOCYTOSIS AND EXOCYTOSIS
• A vesicle is a small sac of membrane with fluid
inside.
• To form a vesicle, a small region of a
membrane is pulled from the rest of the
membrane and is pinched off.
• This vesicles are used to absorb fluid from the
outside  ENDOCYTOSIS
• Or also to secrete certain fluids towards the
outside  EXOCYTOSIS

54. 12.- CELL DIVISION
In prokaryotic:
Cells its called BINARY FISSION and it is used for
asexual reproduction.
-It involves single circular chromosome
replication.
-The two copies os the chromosome move to
opposite ends of the cell.
-Finally the cytoplasm is divided by a process
called cytokinesis.

55. Binary fission

56. In Eukaryotic cells:
-First step is the nucleus division MITOSIS
-DNA is replicated in order to obtain two
identical DNA molecules
-Once the DNA has been replicated, the
cytoplasm of the cell divides by cytokinesis and
two identical daughter cells are obtained.
Mitosis is a 4 phases process: Prophase,
Metaphase, Anaphase and Telophase

57. The cell cycle
• The cell cycle refers to the events between
one cell division and the next one, in
eukaryotic cells.
• It can be divided in 2 stages:
1).- Interphase: cellular growth + metabolic
reactions + DNA replication.
It has 3 stages: G1 phase, S phase and G2
phase.
2).- Cell division: MITOSIS

59. Mitosis
1) Prophase:
- The chromosomes become shorter.
- The nuclear membrane breaks down.
- Microtubules grow from the poles of the cell from a
structure MTOC (microtubules organizing center).
These microtubules conform the mitotic spindle.
2) Metaphase:
- Chromosomes are moved to the equator of the cell,
with a spindle microtubule attached to one of the sister
chromatids from one pole, and another s.microtubule
attached to the opposite sister chromatid from the other
pole.

61. 3) Anaphase:
- The pairs of sister chromatids separate and the
spindle microtubules pull the towards the poles
of the cell.
- Identical chromatides go to both poles of the cell
in order to obtain two indentical daughter cells.
4) Telophase:
Nuclear membranes reform around the
chromatids, now called chromosomes, and uncoil
 into chromatine.
- The cell divides and the two daughter cells enter
interphase again.