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King Saud University
College of Science
Department of Biochemistry
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
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Cellular Biochemistry
BCH 102
Professor A. S. Alhomida
Cellular Biochemistry:
Cell Structure & Function
THE CELL
How We Study Cells
1. Microscopes provide windows to the
world of the cell
2. Cell biologists can isolate organelles to
study their function
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopes provide windows to
the world of the cell


The discovery and early study of cells
progressed with the invention and
improvement of microscopes in the 17th
century.
In a light microscope (LMs) visible light
passes through the specimen and then
through glass lenses.

The lenses refract light such that the image is
magnified into the eye or a video screen.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings



Microscopes vary in magnification and
resolving power.
Magnification is the ratio of an object’s
image to its real size.
Resolving power is a measure of image
clarity.


It is the minimum distance two points can be
separated and still viewed as two separate
points.
Resolution is limited by the shortest
wavelength of the source, in this case light.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The minimum resolution of a light
microscope is about 2 microns, the
size of a small bacterium
 Light microscopes can magnify
effectively to about 1,000 times the
size of the actual specimen.
 At higher magnifications, the image
blurs.

Fig. 7.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 7.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings


Techniques developed in the 20th
century have enhanced contrast and
enabled particular cell components to
be labeled so that they stand out.
While a light microscope can resolve
individual cells, it cannot resolve much of
the internal anatomy, especially the
organelles.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

To resolve smaller structures we use
an electron microscope (EM),
which focuses a beam of electrons
through the specimen or onto its
surface.


Because resolution is inversely related to
wavelength used, electron microscopes with
shorter wavelengths than visible light have
finer resolution.
Theoretically, the resolution of a modern EM
could reach 0.1 nanometer (nm), but the
practical limit is closer to about 2 nm.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Transmission electron microscopes
(TEM) are used mainly to study the
internal ultrastructure of cells.
A TEM aims an electron beam through a thin section
of the specimen.
 The image is focused
and magnified by
electromagnets.
 To enhance contrast,
the thin sections are
stained with atoms
of heavy metals.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Scanning electron microscopes (SEM)
are useful for studying surface structures.




The sample surface is covered with a thin film
of gold.
The beam excites electrons on the surface.
These secondary electrons are collected and
focused on a screen.
The SEM has great
depth of field,
resulting in an
image that seems
three-dimensional.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings


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
Electron microscopes reveal organelles, but
they can only be used on dead cells and
they may introduce some artifacts.
Light microscopes do not have as high a
resolution, but they can be used to study
live cells.
Microscopes are a major tool in cytology,
the study of cell structures.
Cytology coupled with biochemistry, the
study of molecules and chemical processes
in metabolism, developed modern cell
biology.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Isolating Organelles by Cell Fractionation

Cell fractionation


Takes cells apart and separates the major
organelles from one another
The centrifuge

Is used to fractionate cells into their component
parts
Isolation of organelles to study their
functions

The goal of cell fractionation is to
separate the major organelles of the
cells so that their individual functions
can be studied.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings



This process is driven by a ultracentrifuge, a
machine that can spin at up to 130,000
revolutions per minute and apply forces more
than 1 million times gravity (1,000,000 g).
Fractionation begins with homogenization, gently
disrupting the cell.
Then, the homogenate is spun in a centrifuge to
separate heavier pieces into the pellet while
lighter particles remain in the supernatant.

As the process is repeated at higher speeds and longer
durations, smaller and smaller organelles can be
collected in subsequent pellets.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings


Cell fractionation prepares quantities of
specific cell components.
This enables the functions of these
organelles to be isolated, especially by the
reactions or processes catalyzed by their
proteins.



For example, one cellular fraction is enriched in enzymes
that function in cellular respiration.
Electron microscopy reveals that this fraction is rich in
the organelles called mitochondria.
Cytology and biochemistry complement each
other in connecting cellular structure and
function.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The Cell
A
cell is the smallest unit of living
matter.
 Don’t confuse this with: atom,
element, proton, etc.
Cell Theory

Who? Matthias Schleiden, Theodor Schwann,

Rudolf Virchow
When? 1800s

What does it say?




All organisms are made of cells.
A cell is the structural & function unit of organs.
All cells come from pre-existing cells.
Cells are capable of self-reproduction.
Cell Size
Types of Cells

Unicellular organisms


Bacteria, Protists, etc.
Multicellular organisms


Plants
Animals

Muscles, skin, nerves, liver, digestive, bones, blood,
immune system, lungs, etc.
How do we know what happens in
each part of the cell?



Radioisotopes are used to "trace"
different chemical reactions through a cell.
Separate cellular structures with a blender
Centrifuge material and analyze each
layer.
Two basic cell types
Eukaryotes (Eu = true) (kary = nucleus)
Organisms whose cells contain a membrane-bound
nucleus and other organelles.
Prokaryotes (Pro = before) Organisms without a
membrane-bound nucleus (bacteria).
* These cells have genetic information,
but not in a nucleus.
* Evolutionists chose the prefix “pro” because
they believe these evolved before others.
A Typical Cell
1.
2.
3.
4.
Has structural components - cytoskeleton
(made up of protein filaments)
Has organelles that perform specific functions
in the cell (Mitochondria -produces energy)
Has certain active genes to give the cell a
specific function (heart cells, liver cells, brain
cells, etc)
Has the information to perpetuate the whole
organism as well as its specific function
(Nucleus - DNA)
Prokaryotic Cells
Organisms with prokaryotic cells are called
“prokaryotes”
Prokaryotes have no true nucleus or organelles.
Have a single strand of “looped” DNA
Most prokaryotes are single-celled microscopic
organisms.
Eukaryotic Cells
1. Organisms composed of eukaryotic cells are called
“eukaryotes”
2. Have a membrane bound nucleus which contains
the cell’s DNA
3. Some eukaryotes are one-celled organisms
4. All multicellular organisms are eukaryotes
5. Have organelles, each of which is surrounded by
(or bound in) a “plasma membrane”
Some Example Prokaryotes
Coccusshaped
bacterium
Bacillusshaped
bacterium
Spirillumshaped
bacterium
Prokaryotes vs. Eukaryotes (1)


Size

Prokaryotes ≤ 10 µm example: Bacteria & Archea

Eukaryotes ≥ 10 µm example: Protista, Fungi, Plants,
Complexity



Prokaryotes – simple
Eukaryotes – complex
Location of chromosomes



Animals
Prokaryotes – free in cytosol
Eukaryotes – within a membrane-bound nucleus
Flagellar mechanisms differ
Prokaryotes vs. Eukaryotes (2)





Very simple cells
Always single-celled
No nucleus
DNA arranged in one
single loop
Found only in
kingdom Monera
(bacteria)





Complex cells
Can be singlecelled or
multicellular
Have a nucleus
DNA arranged in
many separate
strands
Found in Animal,
Plant, Protists, and
Fungi kingdoms
Prokaryotic Cells
1.
2.
3.
4.
Have no membrane-bound organelles
Include true bacteria
On earth 3.8 million years
Found nearly everywhere
1. Naturally in soil, air,
2. Hot springs
nucleoid (DNA)
Prokaryotic Cells
ribosomes
food granule
prokaryotic
flagellum
plasma membrane
cytoplasm
cell wall
Viruses
1. Viruses contain DNA or RNA & a protein
coat
2. Some are enclosed by an envelope
3. Most viruses infect only specific types of
cells in one host
4. Host range is determined by specific host
attachment sites and cellular factors
Comparison of Cells and Viruses
Bacterium
(prokaryote)
Animal
(eukaryote)
Plant
(eukaryote)
Prokaryotic bacteria cells
surrounding a eukaryotic cell
(possibly a white blood cell?)
Comparison between prokaryotes &
eukaryotes (1)
Prokaryotes
Eukaryotes
Typical organisms
Bacteria, archaea
Protists, fungi, plants,
animals
Typical size
1 - 10 mm
10 – 100 mm
Type of nucleus
Nucleoid, no real
membrane
Real nucleus w/ double
membrane
DNA
Circular (usually)
Linear molecules
(chromosomes) with
histone proteins
RNA/protein
synthesis
Coupled in cytoplasm
RNA synthesis inside
the nucleus, protein
synthesis in cytosol
Comparison between prokaryotes &
eukaryotes (2)
Prokaryotes
Eukaryotes
Ribosomes
50S + 30S
60S + 40S
Cytoplasmic
structure
Very few structures
Highly structured by
endomembraes and a
cytoskeleton
Cell movement
Flagella
Flagella & cilia made of
tubulin
Mitochondria
None
One to several dozen
Chloroplasts
None
Algae & plants
Comparison between prokaryotes &
eukaryotes (3)
Prokaryotes
Eukaryotes
Organization
Usually single cells
Single cells, colonies,
higher multicultural
organisms w/
specialized cells
Cell division
Binary fission (simple
division)
Mitosis & meiosis
Eukaryotic Cell
Cell Structure & Function (1)
Bacteria
Cell Structure & Function (2)
Typical Plant
Cell Structure & Function (3)
Generic Animal Cell
Eukaryotic Cells Structure (1)
1. Have numerous internal
structures
2. Various types & forms
3. Plants, animals, fungi, protists
4. Multicellular organisms
Eukaryotic Cells Structure (2)
1. The cell consists of two main
compartments:
1. The nuclear
2. The cytoplasmic
2. The nucleus contains the genetic
information that regulates the structure and
function of all eukaryotic cells
3. The cytoplasm contains numerous cellular
organelles, which perform specific functions
Plant & Animal Cells (1)

Similarities
1. Both constructed from eukaryotic
cells
2. Both contain similar organelles
3. Both surrounded by cell membrane
Plant & Animal Cells (2)

Differences


Plants have
1. Cell wall – provides strength & rigidity
2. Have chloroplasts, photosynthetic site
3. Large vacuoles
Animals have
1. Other organelle not found in plants
(lysosomes formed from Golgi)
2. Centrioles, important in cell division
Cellular Organelles





Cytoplasm
Nucleus
 Chromosomes,
nuclear
envelope,
nuclear pores,
nucleolus
Ribosomes
Endoplasmic
reticulum (smooth
& rough)
Golgi Apparatus










Lysosomes
Vesicles
Peroxisomes
Vacuoles
Chloroplast
Mitochondria
Cytoskeleton
Centrioles
Cilia, Flagella
Plasma Membrane
Nucleus

The nucleus is separated from the
cytoplasm by the nuclear envelope
Nucleus Structure
Nucleus: DNA stored here.
Nuclear
The Control Center envelope:
membrane
surrounding the
nucleus
Nuclear pores:
open portals of
communication
between the
nucleus &
cytoplasm
Chromatin:
condensed DNA
Chromosome:
very tightly
packed DNA
Nucleolus:
dense region of
chromatin
DNA proteins
1. DNA is associated with two major types of
proteins:
2. The histone and nonhistone chromosomal proteins
3. The histones are primarily structure molecules
that pack DNA into chromatin fibers
4. The nonhistones include proteins that carry out
one of the most important cellular functions, the
regulation of gene activity
Chromosomes


1.
2.
3.
4.
5.
DNA molecule, with its associated histone and
nonhistone proteins, is a chromosome
There are five classes of histone proteins:
H1
H2A
H2B
H3
H4
Nucleosomes


H2A, H2B, H3, and H4 are called core histones
because they form a beadlike core structure
around which DNA wraps to form
nucleosomes.
H1 is called the linker
Human Chromosomes

The entire complement of 46
chromosomes in a human cell, has a total
length of about 1 meter
Nucleolus (Nucleoli)


The RNA of ribosomes is synthesized from
genes in the nucleolus
No membranes separate nucleoli from the
surrounding chromatin in the nucleus
Protein-encoding gene




Each DNA segment containing the information in a
protein constitutes a gene
The information in a Protein-encoding gene is copied
into a messenger RNA (mRNA) molecules that moves
to the cytoplasm through the pores of the nuclear
envelop
In the cytoplasm, mRNA molecules are used by
ribosomes as directions for the assembly of proteins
DNA -----------> mRNA -----------> Protein (enzymes)
RNA types
1. mRNA
2. rRNA
3. tRNA
Ribosomes: protein factories
Rough ER: make proteins (studded with
ribosomes)
Smooth ER: make lipids, modify proteins made
in RER
Mitochondria & Chloroplast:
Power Stations of the cell
Mitochondria (1)
1. The mitochondria major role is ATP
production in the eukaryotic cell
2. These are mobile and flexible organelles
3. Although in some cells they tend to stay
in a fixed position
4. Mitochondria are also self-reproducing,
they have their own circular DNA
Mitochondria (2)
1. Generate cellular energy
in the form of ATP
molecules
2. ATP is generated by the
systematic breakdown of
glucose = cell respiration
3. Also, surrounded by 2
membrane layers
4. Contain their own DNA!
5. A typical liver cell may
have 1,700 mitochondria
6. All your mitochondria
come from your mother
Inner Membrane and matrix (3)

Electron transport system
Oxidative phosphorylation (4)
H+
H+
3H+
H+
ATP
synthase
IV
III
I
H+
H+
3
ATP
H+
2e-
NADH
3H+
3 ADP +
3 Pi
Inner
Membrane
Electron
transport system
Mitochondria
Chloroplasts
Compartments
2
3
pH
7–8
5-8
Metabolic Sites
Matrix: TCA cycle, ATP
synthesis
ETC: 3H+ pumps
Stroma: Calvin cycle &
ATP synthesis
ETC: 1H+ pump
Substrates
Oxidizes glucose, other
metabolites to make ATP
Light Rxn: use energy
from light to synthesize
NADPH & ATP
Dark Rxn: use CO2 &
H2O & NADPH & ATP to
synthesize glucose
Wastes
CO2 & H2O
O2
Chloroplast
Mitochondria
Endoplasmic reticulum (1)
1. Rough endoplasmic reticulum
2. smooth endoplasmic reticulum

are connected and are continuous with the
nuclear envelope
Rough endoplasmic reticulum (2)
1. It is rough because imbedded in the membrane
are ribosomes
2. The site of the synthesis of secretory proteins
3. The rough ER is also the site for the synthesis of
membrane
4. Enzymes synthesize phospholipid that forms all
the membranes of the cell
5. Ribosomes in the rough ER synthesize protein
that then are converted to glycoprotein and
packaged in transport vesicles for secretion
Smooth endoplasmic reticulum (3)
1. The smooth ER is the site for the synthesis of
lipids, phospholipids, and steriods
2. Note that the production of steriod hormones is
tissue specific
3. For example, it is the smooth ER of the cells of
the ovaries and testes that synthesize the sex
hormones
4. The smooth ER of the liver has several
additional functions
Smooth endoplasmic reticulum (4)
5. Enzymes in the smooth ER regulate the release of
sugar into the bloodstream
6. Other enzymes break down toxic chemicals
7. As the liver is exposed to additional doses of a
drug the liver increases the amount of smooth ER
to handle it
8. It then takes more drug to get past the
detoxifiying ability of the liver
9. Finally the smooth ER functions to store calcium
ions
Golgi apparatus
1. The Golgi apparatus, like the ER, is a series of
folded membranes
2. It functions in processing enzymes and other
products of the ER to a finished product
3. It is the source of the production of lysosomes
4. Receives proteins & lipids in membrane-bound
vesicles from ER
5. Modifies those proteins & lipids
6. Sorts and ships the proteins & lipids away in
membrane-bound vesicles
vesicles
from ER
vesicles
leaving
Golgi
complex
Golgi
complex
Lysosomes
1. These are membrane bound vesicles that
harbor digestive enzymes
2. The membrane of a lysosome will fuse
with the membrane of vacuoles releases
these digestive enzymes to the interior
of the vacuole to digest the material
inside the vacuole
Vacuoles
1. These are membrane-bound sacs that
have many different functions
2. The central vacuole of a plant cell serves
as a large lysosome
3. It may also function in absorbing water
4. The central vacuoles of flower petal
cells may hold the pigments that give the
flower its color
Endomembrane system
This section reviews the endomembrane
system which encludes the nuclear envelope,
the rough and smooth ER, the Golgi
apparatus, lysosomes and vacuoles
Ribosomes
1. Ribosomes assemble amino acid
monomers into polypeptide chains
2. Associated with the ER
3. Composed of RNA and proteins
rough endoplasmic reticulum
ribosomes
0.5 micrometers
smooth endoplasmic reticulum
0.5 micrometers
vesicles
Ribosome Assembly/Structure



If individual proteins and rRNAs are
mixed, functional ribosomes will assemble
Structures of large and small subunits
have been determined in 2000/2001
Growing peptide chain is thought to
thread through the tunnel during protein
synthesis
Eukaryotic ribosomes


Mitochondrial and chloroplast ribosomes are
quite similar to prokaryotic ribosomes, reflecting
their supposed prokaryotic origin
Cytoplasmic ribosomes are larger and more
complex, but many of the structural and
functional properties are similar
Mechanics of protein synthesis
1. All protein synthesis involves three phases:
initiation, elongation, termination
2. Initiation involves binding of mRNA and
initiator aminoacyl-tRNA to a small subunit,
followed by binding of a large subunit
3. Elongation: synthesis of all peptide bonds with tRNAs bound to acceptor (A) and
peptidyl (P) sites
4. Termination occurs when "stop codon"
reached
Cell Motility
The movement of whole cells is made
possible through the membrane
pliability and the rearrangement of the
cytoskeleton and internal components
Cytoskeleton provides strength,
flexibility and motility
Cytoskeleton
Eukaryotic cells has a meshwork of tiny fibers that support the
structure. This network is the cytoskeleton. Three types of
fibers exist.
1. Microfilaments are solid helical rods composed of the
protein actin. There is a twist double chain of actin molecules
that make up microfilaments. These are found in cells that must
contract such as muscle cells.
2. Intermediate filaments are variable but in general are
ropelike structures made of twisted filaments of fibrous proteins.
These function in bearing tension and anchoring organelles.
3. Microtubles are straight, hollow tubes composed of proteins
called tubulins. These anchor organelles and provide tract
along which organelles may move. They also make up flagella
and cilia.
1. Microfilaments(6 nm)
Functions
1. Anchor cytockeleton to integral proteins
2. Determine the consistency of the cytoplasm,
3. Interacts with myosin to produce movement
2. Intermediate filaments (7-11 nm) (Protein
composition varies between cell types)
Functions
1. Strengthen cell and help maintain shape
2. Stabilize the position of organelles
3. Stabilize the position of the cell with respect to
surrounding cells thru specialized membrane
attachments
3. Microtubules (up to 25 nm)
all cells contain microtubules, made up of
protein tubulin. Largest cytoskeletal component
Functions
1. Primary cytoskeletal component
2. Disassembly of microtubules provides a mechanism
for changing the shape of the cell and assisting in
movement
3. Used to transport other proteins around the cell in
association with motor proteins kinesin and dynein
4. Forms spindle apparatus during cell division
5. Form structural cell components such as cilia and
centrioles
The Cytoskeleton
Figure 3.5
Cilia and flagella
These are found on cells, such as
protists, that are motile. Cilia are short
and numerous. Longer less numerous
appendages are flagella. These are
composed of a core of microtubules
wrapped in an extension of the plasma
membrane. It is sufficient to know that
Energy is required to move the cilia or
flagella in a whiplike motion to propel the
cell.
Cell surfaces
Cells are held tightly together is higher organisms. There
is also a considerable amount of cell communication for
lack of a better term. Cell junctions are structures that
hold cells together. There are three types. Tight
junctions bind cells together forming a leakproof sheet.
Anchoring junctions attach adjacent cells or cells to an
extracellular matrix (the substance in which tissues cells
are embedded. These are leaky compared to tight
junctions. Communicating junctions are channels
between similar cells. Plasmodesmata are passages
between adjacent plant cells that allow material to go
from one cell to the next. Communication junctions fulfill
the same role between animal cells.
Cytoskeleton: provides structure and Support for
the cell. Also provides a Scaffolding for vesicle
transportation
Rapid Review (1)
Organelle
Prokaryotes Eukaryotes
Functions
Animal
cells
Plant
cells
+
_
+
Protects & shapes the
cell
+
Plasma
membrane
+
+
Selective barrier
consisting of bilayers
of phospholipids,
proteins, & CHO
+
+
+
Protein synthesis,
formed in nucleolus
Cell wall
Ribosome
Rapid Review (2)
Organelle
Prokaryotes Eukaryotes
Animal
cells
Plant
cells
Functions
Sooth ER
_
+
+
Lipid synthesis,
detoxification, CHO
metabolism, no
ribosomes on
cytoplasmic surface
Rough ER
_
+
+
Synthesizes proteins
to secrete or send to
plasma membrane.
Contains ribosomes
on cytoplasmic
surface
Gogli
_
+
+
Modifies lipids,
proteins, etc & sends
them to other sites in
the cell
Rapid Review (3)
Organelle
Prokaryotes Eukaryotes
Functions
Animal
cells
Plant
cells
Mitochondria _
+
+
Powerhouse of
cell; host major
energy-producing
steps of
respiration
Lysosome
_
+
+
Contains enzymes
that digest organic
compounds;
serves as cell’s
stomach
Nucleus
_
+
+
Control center of
cell. Host for
transcription,
replication & DNA
Rapid Review (4)
Organelle
Prokaryotes Eukaryotes
Functions
Animal Plant
cells
cells
Peroxisome
_
+
+
Breakdown of FA,
detoxification of
alcohol
Chloroplast
_
_
+
Site of
photosynthesis
Vacuole
_
+ (small)
+
(large)
Storage vault of
cells
Rapid Review (5)
Organelle
Prokaryotes Eukaryotes
Functions
Animal Plant
cells
cells
Cytoskeleton _
+
+
Consists of
microtubules (cell
division, cilia,
flagella),
microfilaments
(muscles), &
intermediate
filaments
(reinforcing
position of
organelles
_
+
_
Part of microtubule
separation
apparatus that
assists cell division
Centrioles
Plasma Membrane




Boundary that separates the living cell from it’s nonliving surroundings.
Phospholipid bilayer
Amphipathic - having both:
hydrophilic heads
hydrophobic tails
~8 nm thick
Phospholipid
Plasma Membrane - cont.

Controls traffic into and out of the cell with
phospholipids and transport proteins.

Selectively permeable
Transport protein
The Permeability of the Plasma Membrane

The property of biological membranes
which allows some substances to cross more
easily than others.
The plasma membrane is differentially permeable.
Macromolecules cannot pass through because of
size, and tiny charged molecules do not pass
through the nonpolar interior of the membrane.
Small, uncharged molecules pass through the
membrane, following their concentration gradient.
How molecules cross the plasma membrane
Movement of materials across a membrane may be
passive or active.
Passive transport does not use chemical energy;
diffusion and facilitated transport are both passive.
Active transport requires chemical energy and usually
a carrier protein.
Exocytosis and endocytosis transport macromolecules
across plasma membranes using vesicle formation,
which requires energy.
Fluid Mosaic

1972 - Singer and Nicolson called the
membrane a “Fluid Mosaic Model”.

Mosaic:

Fluid: proteins and phospholipids can
move freely in the membrane.
different proteins embedded in
the phospholipids.
Fluid-mosaic model of membrane structure
Fluid Mosaic - cont.

Components of a phospholipid
bilayer.
1. phospholipids
2. proteins - enzymes, receptors,
transport.
3. glycolipids
4. glycoproteins
5. carbohydrates
6. cholesterol
Cells live in fluid environments, with water
inside and outside the cell.
Hydrophilic (water-loving) polar heads of the
phospholipid molecules lie on the outwardfacing surfaces of the plasma membrane.
Hydrophobic (water-fearing) nonpolar tails
extend to the interior of the plasma membrane.
Plasma membrane proteins may be peripheral
proteins or integral proteins.
Aside from phospholipid, cholesterol is another
lipid in animal plasma membranes; related
steroids are found in plants.
Cholesterol strengthens the plasma membrane.
When phospholipids have carbohydrate chains
attached, they are called glycolipids.
When proteins have carbohydrate chains
attached, they are called glycoproteins.
Carbohydrate chains occur only on the exterior
surface of the plasma membrane.
The outside and inside surfaces of the plasma
membrane are not identical.
In animal cells, the carbohydrate chains of cell
recognition proteins are collectively called the
glycocalyx.
The glycocalyx can function in cell-to-cell
recognition, adhesion between cells, and
reception of signal molecules.
The diversity of carbohydrate chains is
enormous, providing each individual with a
unique cellular “fingerprint”.
Osmosis

The movement of water across selectively
permeable membranes.

The water moves from a high concentration to low
concentration.
Osmosis
The diffusion of water across a differentially
permeable membrane due to concentration
differences is called osmosis.
Diffusion always occurs from higher to lower
concentration.
Water enters cells due to osmotic pressure
within cells.
Osmosis in cells
A solution contains a solute (solid) and a
solvent (liquid).
Cells are normally isotonic to their
surroundings, and the solute concentration is
the same inside and out of the cell.
“Iso” means the same as, and “tonocity”
refers to the strength of the solution.
Osmosis in plant and animal cells
Question:
What’s in a Solution?
Answer:

solute +
solvent

solution

NaCl
H2 0

saltwater
+
Hypertonic

A solution with a greater solute concentration
compared to another solution.
3% NaCl
97% H2O
Red Blood Cell
solution
5% NaCl
95% H2O
Hypertonic solutions cause cells to lose
water.
“Hyper” means more than; hypertonic
solutions contain more solute.
Animal cells undergo crenation (shrivel) in
hypertonic solutions.
Plant cells undergo plasmolysis, the
shrinking of the cytoplasm.
Hypotonic

A solution with a lower solute concentration
compared to another solution.
3% Na
97% H2O
Red Blood Cell
solution
1% Na
99% H2O
Hypotonic solutions cause cells to swell and possibly
burst.
“Hypo” means less than.
Animal cells undergo lysis in hypotonic solution.
Increased turgor pressure occurs in plant cells in
hypotonic solutions.
Plant cells do not burst because they have a cell wall.
Isotonic

A solution with an equal solute concentration
compared to another solution.
3% Na
97% H2O
Red Blood Cell
solution
3% Na
97% H2O
Movement of H2O

Water will “ALWAYS” diffuses down a
concentration gradient from a HYPOTONIC
solution to a HYPERTONIC solution.
“ALWAYS REMEMBER”
 HYPOTONIC 
HYPERTONIC
Animal Cells


Animal cells placed into a hypotonic solution
will HEMOLYSIS (EXPLODE).
Animal cells placed into a hypertonic solution
will CRENATE (SHRIVEL).
Hemolysis
Crenation
Red
Blood
Cells
Plant Cells


Firmness or tension (vacuole full) that is found
in plant cells (cell wall) that are in a hypotonic
environment is called TURGID.
This process is called TURGOR PRESSURE.
Water
Cell
Wall
Water
Central
Vacuole
Water
Plant Cells

When the plasma membrane pulls away from the
cell wall (vacuole empty) in a hypertonic
environment (loss of water) is called
PLASMOLYSIS.
Water
Water
plasma membrane
Cell
Wall
Water
Transport Proteins


Transports molecules or ions across biological
membranes
3 types of transport proteins:
1. uniport
2. symport
3. antiport
Uniport Transport Protein

Carries a single solute across the membrane.
extracellular
fluid
intracellular
fluid
Symport Transport Protein

Translocate 2 different solutes simultaneously in
same direction.
extracellular
fluid
intracellular
fluid
Antiport Transport Protein

Exchanges 2 solutes by transporting them in
opposite directions.
extracellular
fluid
intracellular
fluid
Diffusion

The net movement of a substance
(molecules) down a concentration gradient
from an area of high concentration to an area
of low concentration.

passive transport:
expended.

facilitated diffusion: type of passive
transport which uses transport proteins.
NO energy is
Diffusion
Diffusion is the passive movement of molecules
from a higher to a lower concentration until
equilibrium is reached.
Gases move through plasma membranes by
diffusion.
Transport by Carrier Proteins
Some biologically useful molecules pass
through the plasma membrane because of
channel proteins and carrier proteins that span
the membrane.
Carrier proteins are specific and combine with
only a certain type of molecule.
Facilitated transport and active transport
both require carrier proteins.
Facilitated transport
During facilitated transport, substances pass
through a carrier protein following their
concentration gradients.
Facilitated transport does not require energy.
The carrier protein for glucose has two
conformations and switches back and forth
between the two, carrying glucose across the
membrane.
Facilitated diffusion of glucose
Active Transport

The movement of molecules (small or large)
across the plasma membrane in which energy
(ATP) is required.

Examples:
1.
2.
3.
Sodium (Na) - Potassium (K) Pump
Exocytosis
Endocytosis
Sodium-Potassium Pump

The mechanism that uses energy (active transport)
released from splitting ATP to transport Sodium
(Na+) out of and Potassium (K+) into cells.
extracellular
fluid
intracellular
fluid
K+
K+
Na+
Na+
Active transport
Carrier proteins involved in active transport
are called pumps.
The sodium-potassium pump is active in all
animal cells, and moves sodium ions to the
outside of the cell and potassium ions to the
inside.
The sodium-potassium pump carrier protein
exists in two conformations; one that moves
sodium to the inside, and the other that moves
potassium out of the cell.
The sodium-potassium pump
Question:

How are large molecules transported
into and out of the plasma
membranes?
Answer:
Exocytosis
and Endocytosis
Exocytosis
 Cell
secretes macromolecules
(proteins and other biochemicals) out
of cell.
 Part
of the Endomembrane System:
the fusion of transport vesicles with
plasma membrane.
Exocytosis and Endocytosis
During exocytosis, vesicles fuse with the
plasma membrane for secretion.
Some cells are specialized to produce and
release specific molecules.
Examples include release of digestive
enzymes from cells of the pancreas, or
secretion of the hormone insulin in response
to rising blood glucose levels.
Exocytosis
Endocytosis

The energy requiring movement of particles
(foreign or natural) into the cell.

3 types of endocytosis:
A. Phagocytosis
B. Pinocytosis
C. Receptor-mediated endocytosis
Endocytosis
During endocytosis, cells take in substances by
invaginating a portion of the plasma membrane,
and forming a vesicle around the substance.
Endocytosis occurs as:
Phagocytosis – large particles
Pinocytosis – small particles
Receptor-mediated endocytosis – specific
particles
Receptor-mediated endocytosis
A. Phagocytosis

Cell eating: cells engulf particles with pseudopodia
and pinches off a food vacuole.

Two examples:
1. White Blood Cell
2. Amoeba
Food
Vacuole
Bacteria
White Blood Cell
Phagocytosis
B. Pinocytosis

Cell drinking: droplets of extracellular fluid are
absorbed into the cell by small vesicles.

Example:
1. Fungi
Hyphae
Food Particles
Pinocytosis
C. Receptor-Mediated Endocytosis

Importing specific macromolecules (hormones)
into the cell by the inward budding of vesicles
formed from coated pits (receptors).
Liver Cell
Hormones
Receptors
Types eucaryotic cells
1.
2.
3.
4.
5.
Stem Cells
Hemopoietic cells
Monocytes
Macrophages
Phagocytes
What are stem cells ?





Stem = Root = Source
Stem cells are the source of all cells
Some stem cells can become any cell type
Eventually differentiate to 200 cell types
Very complex, poorly understood process

Several stages of differentiation


Stem, blood, red blood, . . .
Reversible? Yes, no, maybe, perhaps, don’t know
Where are the Stem Cells ?


Two choices – Embryo & Adult
Embryo
1. Start with one single cell - the fertilized egg
2. Most flexible - can become any cell type
3. Two choices of embryo source



Fertilized in the usual way (Man & Woman)
Cloned (use your own cells)
Adult
1. Present in normal tissues, including brain
2. Have significant and poorly understood
limitations
Getting Embryonic Stem Cells


Need an embryo
Old fashioned way - With egg & sperm

In Vitro Fertilization





Most common
Excess embryos (usually dozens created)
Never implanted, so not aborted
Fetal (Abortion) – Used for some R&D
Therapeutic Cloning




More exciting – allows use of own cells
Needed to eliminate rejection
Not reproductive cloning
Move in Congress to ban therapeutic cloning
Getting Embryonic Stem Cells

Egg divides - first 2 cells, then 4, then 8 . .

Becomes “Blastocyst”




Hollow ball with key cells inside
Harvest at 3-5 days – 30 cells in inner mass
Embryo is destroyed in process, key ethical
issue
Two crucial embryonic cell characteristics


Not yet differentiated (pluripotent)
Can divide forever (key to culturing)
Adult Stem Cells
1. Extracted in VERY small amounts from normal
tissues
2. Key to avoiding rejection issues – your own cells
1.
2.
Traditional rejection
Graft vs. Host Disease – The Stems Attack!
3. Key to avoiding embryonic ethical issues
4. Always partially differentiated (for now)
1. BUT, research points to plasticity
1. Liver stem cells to brain, muscle, and liver
2. Bone marrow to muscle
5.
6.
7.
8.
Brain stem cells to blood and muscle
Not found in many key organs (Pancreas)
Difficult to grow in culture; can’t mass produce
Holy Grail-Is there a real master adult stem cell
Using Stem Cells
1. Reverse damage
1. Central Nervous System (CNS) damage
1.
2.
3.
4.
Parkinson’s Disease
Multiple Sclerosis
Heart Damage, Diabetes, Bone/Joint loss
Cancer - Bone marrow transplant avoidance
2. Fix genetic problems
1. Severe Combined Immune Deficiency (SCID)
2. Chronic Granulomatous Disease (CGD)
3. Make good cells as needed
4. Make whole organs as needed
1. Kidney, Liver, Pancreas, maybe a Thumb
Recent Research
1.
2.
Three ongoing key focal points
Understand basic processes, especially differentiation
1.
2.
3.
4.
5.
6.
7.
8.
3.
Differentiation triggers
Expand uses (usually embryonic & cloning)
Brain – Lots of progress, especially in dopamine, neurons
Blood – Lots of immune system work
Bones / Joints
Pancreas (Diabetes)
Liver – Cells come from marrow?
Weekly announcements – eyes, veins, heart muscle, skin
Improve Adult Cells - Transdifferentiating / Plasticity
1.
2.
3.
Found a receptor/protein that limits plasticity (GCNF)
Stanford found in Sept they cannot make other cells from adult
blood stem cells
How do adult cells work – fusion, division; Cancer risk?
Treatment Progress
1.
2.
Modest to date – Very early in clinical process
Parkinson’s injections
1.
2.
3.
Multiple Sclerosis
1.
4.
Treat by killing own rogue stem cells
Israel in June
1.
2.
5.
Mixed, but promising results
Last week - Got neural stem cells to make dopamine
22 month old infant with immune system failure (SCID)
Cured via repaired bone marry stem cells
Mouse research this year
1.
2.
3.
Extract and fix cell DNA
Clone cells to get embryonic stem cells
Inject new stem cells to fix immune system
Fixing an Immune System

Baby with damaged immune system
1.
2.
3.
4.
5.
6.

Remove bone marrow stem cells
Fix genetic problem in DNA
Culture cells to get useful volume
Inject new immune cells into baby
Normal immune system results !!
Works when you have stem cells
Mouse Immune Research - Cloned embryonic cells
1.
2.
3.
4.
5.
6.
7.
Remove ANY cell
Fix DNA problem
Clone cells to produce embryo/blastocyst
Harvest stem cells
Coax to differentiate into immune cells
Inject new cells
Crucial when body has no usable stem cells
Ethics – What’s Wrong ?





Most issues surround Embryonic Stem Cells
 Embryo cannot survive cell extraction
When does life begin? What is an Embryo?
 Does it matter if it’s cloned (no sperm)?
 Does it matter if not implanted (not aborted)?
Is it okay if IVF embryos discarded anyway?
Abortions also a source and worry
Will we harvest humans?
 Already having kids for marrow matching
 But, must abort for stem cells (cord blood?)
Future of Stem Cells



Immense promise, though much work remains
Therapies beginning to emerge – SCID, Parkinson’s
Embryonic cells from cloning


Adult stem cells will work eventually


Eliminate need for embryonic cells & ethical issues
Tremendous progress with applications




No actual embryo, reduced ethical issues
Repaired genetic defects, maybe in womb
New therapies for non-genetic diseases (Heart)
New organs
Repairing genetic defects will be common

Change brown hair to blonde ? Ethics, ethics, ethics . . .
Hemopoietic cells
1. The basis of hemopoiesis is a small
population of self-replicating stem
cells, which ultimately can generate all
types of blood cells.
2. The process of hematopoiesis is
controlled by a group of at least 11
growth factors.
3. Three of these glycoproteins initiate
the differentiation of macrophages
from uni- and bipotential progenitor
cells in the bone marrow.
Macrophages and monocytes


Their development takes in the bone marrow
and passes through the following steps:
stem cell






committed stem cell
monoblast
promonocyte
monocyte (bone marrow)
monocyte (peripheral blood)
macrophage (tissues)
Blood monocytes





The blood monocytes are
young cells that already
possess migratory,
chemotactic,
pinocytic
and phagocytic activities,
as well as receptors for IgG
Macrophages





Macrophages can be divided into
normal macrophages and inflammatory
macrophages.
Normal macrophages includes macrophages in
connective tissue .
Inflammatory macrophages are present in various
exudates.
Phagocytes and since they are derived exclusively
from monocytes they share similar properties.
Phagocytes


Phagocytes are cells
which ingest particles.
The process of eating
particles is called
"phagocytosis," a
process which is one of
the distinguishing
features of eukaryotic
cells,
The Cell Cycle
Cell division increases the number of somatic (body)
cells, and consists of:
Mitosis (division of nucleus)
Cytokinesis (division of cytoplasm)
Apoptosis (cell death) decreases the number of cells.
Both cell division and apoptosis occur during normal
development and growth.
The cell cycle is an orderly sequence of events
that occurs from the time when a cell is first
formed until it divides into two new cells.
Most of the cell cycle is spent in interphase.
Following interphase, the mitotic stage of cell
division occurs.
The stages of interphase
G1 stage – cell growth, cell doubles its
organelles,
accumulates materials for DNA
synthesis.
S stage – DNA synthesis occurs, and DNA
replication
results in duplicated
chromosomes.
G2 stage – cell synthesizes proteins needed for
cell division
The cell cycle
The Mitotic Stage
Following interphase is the M stage, including
mitosis and cytokinesis.
During mitosis, sister chromatids of each
chromosome separate, and become the nuclei of
the two daughter cells.
The cell cycle ends when cytokinesis, the
cleaving of the cytoplasm, is complete.
The cell cycle is controlled at three checkpoints:
1. During G1 prior to the S stage
2. During G2 prior to the M stage
3. During the M stage prior to the end of
mitosis
DNA damage can also stop the cell cycle at the
G1 checkpoint.
Apoptosis
Apoptosis is programmed cell death.
Apoptosis occurs because of two sets of
enzymes called capsases.
The first set, the “initiators” receive a signal to
activate the second set, the “executioners”.
The second set of capsases activate enzymes
that tear apart the cell and its DNA.
Maintaining the Chromosome Number
When a eukaryotic cell is not dividing, the DNA
and associated proteins is a tangled mass of thin
threads called chromatin.
At the time of cell division, the chromatin
condenses to form highly compacted structures
called chromosomes.
Each species has a characteristic number of
chromosomes.
Overview of Mitosis
The diploid number of chromosomes is found in the
somatic (non-sex) cells.
The diploid (2n) number of chromosomes contains
two chromosomes of each kind.
The haploid (n) number of chromosomes contains one
chromosome of each kind.
In the life cycle of many animals, only sperm and
eggs have the haploid number of chromosomes.
The nuclei of somatic cells undergo mitosis, a nuclear
division in which the number of chromosomes stays
constant.
Before nuclear division occurs, DNA replication
takes place, duplicating the chromosomes.
A duplicated chromosome is made of two sister
chromatids held together in a region called the
centromere.
Sister chromatids are genetically identical.
At the end of mitosis, each chromosome consists of a
single chromatid.
During mitosis, the centromeres divide and then the
sister chromatids separate, becoming daughter
chromosomes.
Following mitosis, a 2n parental cell gives rise
to two 2n daughter cells, or 2n → 2n.
Mitosis occurs when tissues grow or when
repair occurs.
Following fertilization, the zygote divides
mitotically, and mitosis continues throughout
the lifespan of the organism.
Chromosomes (n)





n refers to the number of pairs (or the number
of different types of chromosomes)
2n refers to the total number of chromosomes
In humans n = 23
In chimpanzees n = 24
In the king crab n = 104
More on Chromosomes




Humans reproduce sexually
Sexual reproduction means simply that the
offspring receive genetic material from BOTH
the mother and father
Not all organisms reproduce this way
For many organisms the offspring receive
genetic material from only 1 individual
Meiosis
1. Meiosis is the process where the genetic
material is reduced to half (i.e. only ONE
set of chromosomes per daughter cell)
2. Because Meiosis creates cells with only
half the “normal” number of
chromosomes, (gametes), when these
cells join (as in fertilization) the new
individual has the same number of
chromosomes as each parent.
Meiosis
3. So in fact not ALL human cells have the 23
pairs of chromosomes
4. Humans gametes have 1 copy of each
chromosome, not 23 pairs.
5. Gametes are human reproductive cells
1. Male gametes are sperm
2. Female gametes are eggs
Meiosis versus Mitosis

Mitosis is essential for cell growth
1. It is the process that distributes the genetic
evenly material between two daughter cells,
so that each daughter cell is genetically
identical to the parent cell.
2. It’s simply a way to make more of the same
cell
Mitosis
Phases of Mitosis
1.
2.
3.
4.
5.
Interphase
Prophase
Metaphase
Anaphase
Telophase

REPEAT
(This process produces two identical cells.
The process then repeats for each of the
new cells.)
Mitosis
1. Interphase


DNA replication
Centrosomes form
3. Metaphase


2. Prophase



Chromosomes condense
become visible as sister
chromatids (Condensation)
Centrosomes move away from
each other
Mitotic spindle forms

Centrosomes at opposite poles
Chromosomes line up at
metaphase plate (centromeres
line up)
Each chromatid is attached to
one of the poles via
microtubules
4. Anaphase

Each of the sister chromatids
moves toward the opposite
pole
Mitosis
5. Telophase
 Formation of cleavage furrow
 Cell divides  2 identical copies
 New nuclear envelope forms
 New Interphase begins
 And the process starts all over
Late Interphase
Early Prophase
Late Prophase
Metaphase
Anaphase
Telophase
Homologues versus chromatids

Homologous chromosomes



One from Mom and One from Dad
Have different versions of the same genes
Sister chromatids



Bound at center by centromere
Chromatids are identical
Product of DNA replication
Phases of Meiosis

Interphase


Meiosis I
Cell spends 90 % of it’s
life in this phase (like
mitosis)
Chromosome replication
takes place  sister
chromatids

Prophase I




Homologous
chromosomes come
together (synapsis)
Form tetrads
This is when Crossing
Over occurs (at
chiasmata, between
NON-SISTER
chromatids)
Centrosomes move
away from each other
Meiosis I

Metaphase I



Chromosomes aligned on
Metaphase plate (grouped
in homologous pairs)
Each chromosome is
attached to opposite pole
Anaphase I


Sister chromatids remain
attached at centromeres
Chromosomes move to
opp. poles

Telophase I




Chromosomes reach poles
Cell starts to cleave
Produces 2 haploid cells Each
cell is NOT identical (crossing
over)
Cytokinesis
Meiosis I
Chromosomes and Chromatids
During Meiosis I
Begin
Interphase
After
Interphase
After
Prophase
I
After
Metaphase
I
After
Anaphase
I
After
Telophase
I
# of
Chromosomes
4
4
4
4
4
2
# of
Chromatids
4
8
8
8
8
4
Meiosis II

Prophase II



Spindle forms
Chromosomes move
toward metaphase plate
Metaphase II

Chromosomes line up
along metaphase plate

Anaphase II


Sister chromatids move
toward opposite poles
Telophase II



Nuclei form at opposite
poles
Cytokinesis (division of
cell)
Produces 4 haploid cells
Chromosomes and Chromatids
During Meiosis II
After
Prophase
II
After
Metaphase
II
After
Anaphase
II
After
Telophase
II
# of
Chromosomes
2
2
4
2
# of
Chromatids
4
4
4
2
Meiosis II
Haploidy and Diploidy

A cell that has 1 copy of each chromosome is
haploid


Human gametes are haploid (n)
A cell that has 2 copies of each chromosome
are diploid

Human somatic cells (body cells) are diploid (2n)
The 4 Main differences between
Meiosis and Mitosis
1. In Meiosis (prophase I) homologous chromosomes
pair up and crossing over occurs (Neither of these
happens in Mitosis)
2. In Meiosis, homologous pairs align on opposite sides
of the metaphase plate
Meiosis (Metaphase I)
Mitosis (Metaphase)
3. In Meiosis (Anaphase I) sister chromatids do
not separate
Meiosis (Anaphse I)
Mitosis (Anaphase)
4. Meiosis I separates homologous pairs of
chromosomes NOT sister chromatids
Meiosis (Anaphase I)
Mitosis (Anaphase)
Cytokinesis
Cytokinesis, or cytoplasmic cleavage, accompanies
mitosis.
Cleavage of the cytoplasm begins in anaphase, but is
not completed until just before the next interphase.
Newly-formed cells receive a share of cytoplasmic
organelles duplicated during the previous interphase.
A cleavage furrow begins at the end of anaphase.
A band of actin and myosin filaments, called the
contractile ring, slowly forms a constriction between
the two daughter cells.
A narrow bridge between the two cells is apparent
during telophase, then the contractile ring completes
the division.
Cytokinesis
Cell Division in Prokaryotes
The process of asexual reproduction in
prokaryotes is called binary fission.
The two daughter cells are identical to the
original parent cell, each with a single
chromosome.
Following DNA replication, the two
resulting chromosomes separate as the
cell elongates.
Meiosis in humans
Humans have 23 pairs of homologous chromosomes,
or 46 chromosomes total.
Prior to meiosis I, DNA replication occurs.
During meiosis, there will be two nuclear divisions,
and the result will be four haploid nuclei.
No replication of DNA occurs between meiosis I and
meiosis II.
Meiosis I separates homologous pairs
of chromosomes
Daughter cells are haploid, but chromosomes are still in
duplicated condition.
Synapsis occurs during meiosis I
Meiosis II separates sister chromatids.
The completely haploid daughter cells mature into gametes.
Fertilization restores the diploid number of chromosomes
during sexual reproduction.
Meiosis in Detail
Meiosis involves the same four phases seen in
mitosis
prophase
metaphase
anaphase
telophase
The occur during both meiosis I and meiosis II.
The period of time between meiosis I and meiosis II
is called interkinesis.
No replication of DNA occurs during interkinesis
because the DNA is already duplicated.
Comparison of Meiosis with Mitosis
1.Before mitosis and meiosis, DNA replication
occurs only once during the interphase prior to
cell division.
2.Mitosis requires one division
3.Meiosis requires two divisions.
4.Two diploid daughter cells result from mitosis
5.Four haploid daughter cells result from
meiosis.
Comparison of Meiosis with Mitosis (cont)
6.Daughter cells from mitosis are genetically
identical to parental cells
7.Daughter cells from meiosis are not
genetically identical to parental cells.
8.Mitosis occurs in all somatic cells for growth
and repair.
9.Meiosis occurs only in the reproductive organs
for the production of gametes.
Comparison of Meiosis I to Mitosis





Meiosis I:
Prophase I - pairing of
homologous
chromosomes
Metaphase I –
homologous pairs line up
at metaphase plate
Anaphase I –
homologous
chromosomes separate
Telophase I – daughter
cells are haploid





Mitosis:
Prophase has no
such pairing
Metaphase –
chromosomes align at
metaphase plate
Anaphase – sister
chromatids separate
Telophase – diploid
cells
Comparison of Meiosis II to Mitosis
1.The events of meiosis II are like those of
mitosis except in meiosis II, the nuclei contain
the haploid number of chromosomes.
2.At the end of telophase II of meiosis II, there
are four haploid daughter cells that are not
genetically identical.
3.At the end of mitosis, there are two diploid
daughter cells that are identical.
The human life cycle requires both
mitosis and meiosis
In males, meiosis occurs as
spermatogenesis and produces sperm.
In females, meiosis occurs as oogenesis
and produces egg cells.
Mitosis is involved in the growth of a
child and repair of tissues during life.
Spermatogenesis in human males produces
four viable haploid sperm.
Diploid primary spermatocytes undergo
meiosis I to produce haploid secondary
spermatocytes.
Secondary spermatocytes divide by meiosis II
to produce haploid spermatids.
Spermatids mature into sperm with 23
chromosomes.
During oogenesis, a diploid primary oocyte undergoes
meiosis I to produce one haploid secondary oocyte and
one haploid polar body.
The secondary oocyte begins meiosis II but stops at
metaphase II and is released at this stage from the ovary.
Meiosis II will be completed only if sperm are present.
Following meiosis II, there is one haploid egg cell with 23
chromosomes and up to three polar bodies.
Polar bodies serve as a dumping ground for extra
chromosomes.
Oogenesis
In humans, both sperm cells and the egg
cell have 23 chromosomes each.
Following fertilization of the egg cell by a
single sperm, the zygote has 46
chromosomes, the diploid number found in
human somatic cells.
The 46 chromosomes represent 23 pairs of
homologous chromosomes.
Summary
Cell division increases the number of body cells;
Apoptosis decreases cell number.
Cells goes through a cell cycle.
Each species has a characteristic number of chromosomes.
Mitosis
1. produces daughter cells that are identical to the
parental cell.
2. has four phases designed to maintain the
chromosome number.
3. is used for growth and repair of tissues.
Summary continued
Meiosis
1. reduces the chromosome number.
2. includes two nuclear divisions.
3. results in non-identical haploid gametes.
The human life cycle includes both mitosis and
meiosis.
The process of meiosis and fertilization in humans and
other sexually reproducing organisms result in
offspring with new genetic combination.
A comparison of mitosis and meiosis
A comparison of mitosis and meiosis: summary
SEXUAL(MEIOSIS)
Figure 14.32. Comparison of meiosis
and mitosis. Both meiosis and mitosis
initiate after DNA replication, so each
chromosome consists of two sister
chromatids. In meiosis I, homologous
chromosomes pair and then segregate to
different cells. Sister chromatids then
separate during meiosis II, which
resembles a normal mitosis. Meiosis thus
gives rise to four haploid daughter cells.
Fuente: Cooper, 2000
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PENETRATION
UNCOATING
HOST
FUNCTIONS
Transcription
Translation
VIRAL
LIFE
CYCLE
REPLICATION
ASSEMBLY
(MATURATION)
RELEASE
MULTIPLICATION