Download Cells Notes

Today’s Plan: 1/18/11
 Bellwork: Go over Test (20 mins)
 Cell Microscopy Lab(40 mins)
 Cells Notes (25 mins)
Today’s Plan: 1/19/11
 Bellwork: Finish Microscopy (20 mins)
 Begin AP Lab 1 (40 mins)
 Cells Notes (the rest of class)
Cells Notes
 Inside the “black box”
 Until the advent of the electron microscope, only the
nucleus and membrane were known
 Chemical analysis and cell fractionation gave us some
clue as to the chemical make up of cells, but that’s
only part of the picture
 The human eye is unable to detect things smaller than
.1mm
 Eukaryotic cells range from 10-100 micrometers
 Prokaryotic cells run from 1-10 micrometers, but the
smallest are almost 100 nm
 Most cellular organelles are about the size of bacteria,
however, a few, like the ribosome, are smaller still
2 Main Cell Types
 Prokaryotes
 No nucleus or membrane-bound organelles
 Has a region called the nucleoid for its genetic
material
 Only Archaebacteria and Eubacteria are
prokaryotic
 Eukaryotes
 Have a nucleus and an array of membranebound organelles
 Because of the membrane system, cell parts are
compartmentalized and division of labor is more
efficient
Figure 7-1
Ribosomes
Plasmids
Cytoplasm
Flagellum
Chromosome
Plasma
membrane
Cell wall
Figure 7-6a
Generalized animal cell
Nuclear envelope
Nucleus
Nucleolus
Chromosomes
Centrioles
Rough endoplasmic
reticulum
Ribosomes
Peroxisome
Structures that
occur in animal cells
but not plant cells
Smooth endoplasmic
reticulum
Golgi apparatus
Lysosome
Mitochondrion
Cytoskeletal element
Plasma membrane
Figure 7-6b
Generalized plant cell
Nuclear envelope
Nucleolus
Nucleus
Chromosomes
Structures that
occur in plant cells
but not animal cells
Cell wall
Chloroplast
Rough endoplasmic
reticulum
Ribosomes
Smooth endoplasmic
reticulum
Golgi apparatus
Vacuole (lysosome)
Peroxisome
Mitochondrion
Plasma membrane
Cytoskeletal element
On average, prokaryotes are about 10
times smaller than eukaryotic cells in
diameter and about 1000 times smaller
than eukaryotic cells in volume.
Today’s Plan: 1/15/10
 Bellwork: Set up Dialysis Tubes (25
mins)
 Continue with Cells notes/Finish
Microscopy lab (40 mins)
 Finish Dialysis Tubes (20 mins)
Nucleus
 Contains the genes responsible for cell function
(chromatin-uncoiled, tangled, DNA mass)
 Contains Nucleolus which makes the ribosomes
 Nuclear pores in the nuclear envelope allow RNA and
ribosomes to pass to the cytoplasm for making
proteins
 Free ribosomes usually make proteins to be used
within the cytoplasm
 Bound ribosomes usually make proteins that need
packaging
 Nuclear envelope is lined with the nuclear lamina-a
network of proteins that help the nucleus maintain its
shape
Figure 7-7
Nucleus
Loosely
packed sections
of chromosomes
Densely
packed sections
of chromosomes
Nucleolus
Nuclear envelope
Figure 7-23
Outer surface
of nuclear
envelope
Nuclear pores
The Endomembrane System
 Endoplasmic Reticulum (ER)
 Vast network of membrane and sacs called
cisternae
 Consists of approximately ½ of the
totalmembrane of the cell
 Smooth=no bound ribosomes, synthesizes
lipids, metabolizes glucose and detoxifies
drugs/poisons
 Rough=bound ribosomes, which thread the
emerging proteins that they make through the
cisternal space into the ER
 Transitional=“budding” area where secretory
proteins are sent in transport vesicles to the
Golgi apparatus
Figure 7-9
Rough endoplasmic
reticulum
Lumen of
rough ER
Ribosomes
on outside
of rough ER
Free
ribosomes
in cytoplasm
Golgi Apparatus
 Part of the endomembrane system
that consists of flattened
membranous sacs
 Wharehouses, sorts, modifies,
packages, and ships the products of
the ER
 “Polarity” exists because of the 1-way
movement through the cisternae as
ER products pass from the cis pole to
the trans pole of the sac
Figure 7-10
The cis face of the Golgi apparatus
is oriented towards the rough ER
The trans face of the Golgi apparatus
is oriented towards the plasma
membrane
Golgi apparatus
Vesicle
cis face
Lumen of Golgi
apparatus
Cisternae
Vesicles
trans face
Figure 7-26
THE SECRETORY PATHWAY: A MODEL
RNA
Rough ER
1. Protein enters
ER while being
synthesized by
ribosome.
2. Protein exits ER,
travels to cis face
of Golgi apparatus.
cis face of
Golgi apparatus
Golgi apparatus
3. Protein enters
Golgi apparatus and
is processed as the
cisternum moves
toward the trans face.
4. Protein exits Golgi
trans face of
Golgi apparatus
apparatus at trans
face and moves to
plasma membrane.
Plasma membrane
5. Protein is
secreted from cell.
Today’s Plan: 1/19/10
 Bellwork: Set up potatoes (20 mins)
 Do Lab Part E and finish Microscopy
(40 mins)
 Plasma Membrane notes (25 mins)
Lysosomes and Vacuoles
 Lysosomes are sacs for storage of hydrolytic enzymes
 These enzymes work best in an acidic environment,
so H+ are pumped into the lysosome
 Can digest external elements that are brought into
the cell or can digest old, worn-out cell components
 Pompe’s disease-occurs when a person’s lysosomes
lack an enzyme for metabolizing glycogen, which
builds up
 Tay-Sachs disease-occurs when lysosomes lack a
lipid-digesting enzyme and causes brain impairment
 Vacuoles are membrane sacs for general storage
 Food vacuoles
 Contractile vacuoles (pump water out of the cell)
 Central vacuole (in plants) is surrounded by
membrane called the tonoplast-part of the plants
endomembrane system
Figure 7-13
Lysosomes
Material being
digested within
lysosomes
Figure 7-16
Vacuole
Vacuole
Other membrane-bound organelles

Mitochondria




Chloroplasts (and other plastids)




Generates ATP during the last 2 stages of aerobic cellular
respiration
Consists of 2 membranes. The inner membrane is folded into
cristae, and inside is called the matrix
2 membranes form the intermembrane space
Contains membranous discs called thylakoids that are stacked
into grana-chlorophyll is embedded on the thylakoid
membranes
Contains fluid called stroma that surrounds the thylakoids
Other plastids store pigments or starch (amyloplasts)
Peroxisome


Single membrane-bound organelle that contain enzymes which
transfer hydrogen to oxygen, making Hydrogen peroxide
Also contains enzymes that convert the peroxide to water
since the peroxide is toxic to the cell
Figure 7-17
Mitochondrion
Outer
and inner
membranes
Matrix
Cristae
Figure 7-18
Chloroplast
Stroma
Thylakoids
Granum
Outer and inner
membranes
Figure 7-12
Peroxisomes
Peroxisome
membrane
Peroxisome
lumen
Cytoskeleton
 Supports and gives structure to the cell
 Also involved in movement (cilia and flagella)
 Can act as a “monorail” for the organelles to move
around the cell
 Consists of proteins
 Microtubules (thickest)-hollow, walls made of tubulin
molecules, grow from centrosome (near nucleus) to
also form the centrioles for cell division
 Microfilaments (thinnest)-twisted actin molecules, in
muscle cells are paired with myosin filaments for
contraction
 Intermediate filaments-fibrous proteins supercoiled,
make up nuclear lamella, and support long
extensions of the cell
Figure 7-30-Table 7-3
Figure 7-31
Actin filaments in mammalian cell
Intermediate filaments in mammalian cell
Microtubules in mammalian cell
Cell Surfaces

Cell Wall-Plant Cells only





Made of cellulose
Primary cell wall-thin, flexible, secreted in young plant cells
(outermost cell surface)
Middle Lamella-sticky layer between primary cell walls of
adjacent plant cells (contains pectin)
Secondary Cell wall-laid down by older plant cells between the
p.m. and primary cell wall. This is much thicker, and usually
consists of several layers
Extracellular Matrix-Animal Cells only


Network of glycoproteins (like collagen) and proteoglycans
(another type of glycoprotein that’s thinner and contain more
carbohydrate than the typical glycoprotein) which connect to
fibronectins and integrins that connect directly to the
cytoskeleton.
This allows changes on the outside of the cell to be transmitted
to the inside of the cell and vice-versa, which allows for
regulation of the cell’s behavior
Figure 7-19
Cell wall
Plasma
membrane
of cell 1
Plasma
membrane
of cell 2
Cytoplasm Cell wall Cell wall
of cell 1 of cell 2
of cell 1
Cytoplasm
of cell 2
Figure 8-5
Gel-forming
polysaccharides
Collagen
ECM
Fibronectin
Integrin
Plasma
membrane
Cytoskeleton
Actin filament
Figure 8-4
Collagen molecules are made of three chains that wind
around each other.
3 chains
Collagen molecule
Collagen fibrils in the extracellular matrix
Cell in connective tissue
Collagen fibrils
running lengthwise
Collagen fibrils
in cross section
Each collagen fibril is
composed of many
collagen molecules
Today’s Plan:1/20/10
 Bellwork: Finish Lab 1 (20 mins)
 Begin Lab 3 (30 mins)
 Continue Notes (30 mins)
Cell Junctions
 In plants, the cell walls have plasmodesmata to allow
for cytoplasmic exchange between cells.
 Animal cells have 3 main junctions
 Tight junction-membranes are fused, forms a seal
(useful in intestines)
 Desmosomes-intermediate fillaments transect
neighboring membranes, acting like bolts to hold
cells together
 Gap Junction-Proteinaceous pores between
membranes allowing for cytoplasmic exchange
 Why different junctions?
 There are situations where strength is integral,
however there are other situations where cells must
chemically communicate, requiring flow between
membranes
Figure 8-14
Plasmodesmata create gaps that connect plant cells.
Cell walls
Tubule of
endoplasmic
reticulum
passing through
plasmodesmata
Smooth
endoplasmic
reticulum
Cell wall Cell wall
of cell 1 of cell 2
Membrane
of cell 1
Membrane
of cell 2
Gap junctions create gaps that connect animal cells.
Gap
junctions
Membrane proteins
from adjacent cells
line up to form
a channel
Figure 8-10
Electron micrograph of a tight junction
Three-dimensional view of a tight junction
A tight junction forms a
watertight seal between
epithelial cells
Plasma membranes
of adjacent cells
Tight junction
Membrane proteins that
form a tight junction
Figure 8-11
Micrograph of desmosome
3-D view of desmosome
Plasma membranes
of adjacent cells
Desmosome
Anchoring
proteins
inside cell
Membrane
proteins that
link cells
Intermediate
filaments
Plasma Membrane Structure
 Recall that phospholipids are the basic
membrane molecules
 They contain a phosphate (hydrophilic) and 2
fatty acid tails (hydrophobic)-amphipathic
 They form bilayers so that the lipid tails are
always isolated from water.
 Chemical analysis reveals that proteins are
present as well. It was originally believed
that the proteins coated the inner and outer
surfaces of the P.M.
 However our current understanding is that
proteins of the plasma membrane also have
hydrophobic and hydrophilic regions, and
therefore transect the P.M
Figure 6-4b
Phospholipid
Polar head
(hydrophilic)
Nonpolar tail
(hydrophobic)
Figure 6-5
Lipid micelles
Lipid bilayers
Water
No water
Hydrophilic heads interact with water
Hydrophobic tails interact with each other
Hydrophilic heads interact with water
The Fluid Mosaic Model of the P.M.
 Phospholipids within the P.M. aren’t static,
they shift laterally past one another
because the interactions of these molecules
are weaker than covalent bonds-Fluid
 Proteins appear to be directed by the
cytoskeleton below the PM
 Besides phospholipids and proteins,
cholesterol is embedded in the membraneMosaic
 This lends stability to the membrane by reducing
the fluid nature of the membrane at high temps
and keeps the phospholipids from compacting at
low temperatures and solidifying-this would
reduce its permeability
Figure 6-10
Lipid bilayer with
no unsaturated
fatty acids
Lower permeability
Lipid bilayer with
many unsaturated
fatty acids
Higher permeability
Figure 6-13
Phospholipids are
in constant lateral
motion, but rarely
flip to the other
side of the bilayer
Membrane Proteins
 Integral proteins (embedded)
 Transect the membrane (either entirely
or partially)
 Peripheral proteins
 Bound loosely to the surface of the PM
(or embedded proteins)
 On inner surface, can be bound to
cytoskeleton
 On outer surface, can be bound to the ECM
Figure 6-20
Outside cell
Peripheral
membrane
protein
Integral
membrane
protein
Inside cell
Peripheral
membrane
protein
Today’s Plan: 1/21/10
 Finish Membrane Notes (20 mins)
 Finish Part I of Lab 3(30 mins)
 Finish notes on cell cycle(30 mins)
Membrane Functions
 Transport-to maintain homeostasis
 Enzymatic activity-enzymes embedded in membranes
that do metabolic processes (ATP synthase)
 Signal transduction-a binding site on a receptor
protein may chemically change when bound,
transmitting the signal to the inside of the cell
 Intercellular joining-proteins link together cells
(desmosomes)
 Recognition-glycoproteins on cell surfaces may bind to
sites on adjacent membrane proteins so that the cells
may recognize one another
 Attachment to the cytoskeleton and ECM-can allow for
coordination between the two
Transport across membranes
 Hydrophobic core Barrier for most polar substances (except very
small ones like water and ethanol)
 Does not inhibit hydrophobic molecules like
oxygen gas, carbon dioxide, and hydrocarbons
 Whatever can’t get in through the
membrane, must somehow use a protein to
get in (either by pump or channel with a
hydrophilic tube in the center)
Concentration and transport Rules
 Concentration gradient=
 Diffusion rule= particles move from ____ to
____ concentration until they reach
__________ ______________ (movement
with a concentration gradient)
 Osmosis=
 Passive=
 Active=
 Water always moves to the _______
_______ because _______________.
Figure 6-15
OSMOSIS
1. Start with more solute
2. Water undergoes a net
on one side of the lipid
bilayer than the other,
using molecules that
cannot cross the
selectively permeable
membrane.
movement from the region
of low concentration of
solute to the region of
high concentration.
Concentration descriptors




Hypertonic solutions=
Hypotonic solutions=
Isotonic solutions=
Remember, Hypotonic and hypertonic
work in pairs! If the cell’s
environment is hypotonic to the cell,
than the cell is hypertonic to the
environment (and vice-versa)
Figure 6-16
Hypertonic solution
Hypotonic solution
Net flow of water out of cell;
cell shrinks
Net flow of water into cell;
cell swells or even bursts
Isotonic solution
No change
Osmoregulation
 Cells have to constantly regulate
water uptake and loss or there are
consequences (particularly animal
cells)
 Lysis occurs if too much water flows in
(some cells have contractile vacuoles to
cope with this)
 Shrivelling and dehydration occur if too
much water is lost from the cell
(plasmolysis in plant cells occurs when
this happens and the PM pulls away from
the cell wall)
Protein-Facilitated Diffusion
 Some proteins can change shape
(enzyme-style) when molecules that
need transport bind to specific sites
 This is done with a concentration
gradient and therefore requires no
energy
Figure 6-25b
Potassium channels allow only potassium ions to pass
Potassium ions can enter the
through.
channel, but cannot pass into the cell
Outside cell
Inside cell
Closed
When a change in electrical charge occurs
outside the membrane, the protein changes
shape and allows the ions to pass through
Open
Active Transport
 Goes against a concentration gradient
 Therefore requires energy
 Ex: Sodium/Potassium Pump
Figure 6-28-1
HOW THE SODIUM-POTASSIUM PUMP (Na+/K+- ATPase) WORKS
Outside
cell
Inside
cell
Phosphate
group
1. Three binding sites within
2. Three sodium ions from
the protein have a high
affinity for sodium ions.
the inside of the cell bind to
these sites.
3. A phosphate group from
ATP binds to the protein.
In response, the protein
changes shape.
4. The sodium ions leave
the protein and diffuse to
the exterior of the cell.
Figure 6-28-2
HOW THE SODIUM-POTASSIUM PUMP (Na+/K+- ATPase) WORKS
5. In this conformation, the
6. Two potassium ions bind
7. The phosphate group drops
8. The potassium ions leave
protein has binding sites with
a high affinity for potassium
ions.
to the pump.
off the protein. In response,
the protein changes back to
its original shape.
the protein and diffuse to the
interior of the cell. These 8
steps repeat.
Figure 6-29
Diffusion
Facilitated diffusion
Active transport
Outside
cell
Inside
cell
Passive movement of small,
uncharged molecules along
an electrochemical gradient,
through a membrane
Passive movement of …
Active movement of …
Cell Communication
 Is believed to have evolved in prokaryotes and singlecelled eukaryotes
 In single-celled organisms, the primary purpose of
signaling is to induce conjugation
 This has become a useful process for multicellular
organisms, which have evolved the ability to do longdistance signaling
 Local regulators-travel short distances from the cell
 Synaptic signaling-between nerve cells
 Hormonal signaling
 Cell junction signaling and cell recognition (as
discussed before)
The 3 Stages of Cell Signaling
 Reception
 Signal is detected when it binds to a receptor
protein on the cell’s surface
 Transduction
 The surface binding causes a change in the
integral protein which initiates transduction
inside the cell (can be 1-step, but more often
involves multiple steps in a biochemical
pathway)
 Response
 The signal triggers a cell’s response
 Ex:Lactose present in the body needs lactase to
break it down
Figure 8-17
OVERVIEW OF SIGNAL TRANSDUCTION PATHWAY
Intercellular
signal
Outside of cell
Receptor
protein
in membrane
1. Signal is received.
Inside of cell
2. Signal is transduced.
Intracellular
signal
3. Signal is amplified.
Cell activity changes
For example, specific genes or
proteins are activated or deactivated.
4. Cell responds.
Receptors
 Just as with enzymes, the signaling
molecule and receptor shape must be
complimentary
 Ligand=molecule that specifically binds to
another molecule
 This ligand binding generally causes a
change in the shape of the protein
receptor, enabling it to react with other
cellular molecules
 Some receptors are found within the cell,
so the signal molecule has to pass through
the membrane to dock with the receptor
(ex: testosterone)
Figure 8-18
HOW DO G PROTEINS WORK?
Enzyme
Signal
Receptor
Enzyme
GTP
GDP
Substrate
Second messenger
GTP
G protein in “off”
conformation
G protein in “on”
conformation
Triggers response
1. G protein binds GDP. Signal
2. Signal-receptor complex changes
3. In response to binding of activated
arrives and binds to receptor.
conformation. G protein binds GTP
and splits into two parts.
G protein, enzyme catalyzes a
reaction that produces a second
messenger.
Figure 8-16
STEROID HORMONES BIND TO SIGNAL RECEPTORS
INSIDE THE CELL.
Steroid
hormone
Plasma
membrane
Receptor
in cytosol
1. Steroid hormone
diffuses across plasma
membrane into cell.
2. Hormone binds to
receptor, inducing
conformational change.
Nucleus
3. Hormone-receptor
complex binds to DNA,
inducing change in
gene activity.
Target gene DNA
Signal Transduction Pathways
 Protein Phosphorylation and Dephosphorylation
 Protein kinase transfers phosphate groups from ATP
to a protein (usually another proteing kinase), wich
activates the protein, causing the next step in the
pathway until the correct protein is activated
 This is turned off by special enzymes which later
remove the phosphates from the protein, called
protein phosphatases
 Second Messengers
 Small molecules or ions that are not proteins and can
be triggered inside the cell once reception occurs
 Ex: cAMP (in the liver cells for the breakup of
glycogen), Ca 2+ (muscle cell contrations, secretion,
cell division)
Figure 8-19
HOW DO ENZYME-LINKED RECEPTORS WORK?
GTP
P
ATP
ADP
Inactive
protein 1
Inactive
protein 2
Signal
GDP
GDP
Ras protein
P Active
protein 1
P
ATP
ADP
P Active
protein 2
ATP
ADP
Inactive
protein 3
Triggers response
Ras
protein
Receptor
tyrosine
kinase (RTK)
P
GTP
ATP
ADP
Bridging
proteins
1. Signal arrives and binds to
2. Signal-receptor complex
3. Proteins form a bridge to Ras.
4. Ras catalyzes the
receptor.
changes conformation and is
phosphorylated.
Ras exchanges its GDP for a GTP.
phosphorylation of an
intracellular protein, activating it.
5. Phosphorylation cascade
results, each protein
phosphorylating another until
a response is triggered in the
cell.
Cellular Responses
 Responses are triggered either in the
nucleus (triggering transcription) or
cytoplasm (regulating the proteins’
activities)
 Fine-tuning the response
 Amplification-cascades where each step
produces a greater concentration of activated
products
 Specificity of proteins-ex: epi has one effect on
the heart and another on the liver because each
cell type has different proteins that respond to
epi
Today’s Plan: 8/13/09
 Finish AP Lab 3 (1st ½ of class)
 Finish notes (Last ½ of class)
The Cell Cycle

Interphase




Mitosis (M Phase)





G1 Phase-cell growth (2n l-shaped)
S Phase-copying chromosomes in prep. For Mitosis (2n xshaped)
G2 Phase-More cell growth and prep for mitosis
Prophase-mitotic spindles form (centrioles in animal cells only)
and attach to spindle at kinetochore (centromere and
corresponding DNA Segment)
Metaphase-chromosomes migrate to middle of cell (metaphase
plate)
Anaphase-kinetochore microtubules shorten, pulling
chromosomes
Telophase-accompanies cytokinesis (2 daughter nuclei, each is
2n l-shaped)
Cytokinesis-clevage furrow forms as actin and myosin
contract in a ring around the elongated cell in animal cells.
In plants, a cell plate forms between the daughter cells,
dividing them (results in 2 cells
Figure 11-3
Unreplicated chromosome
The unreplicated chromosome consists of
a single, long strand of DNA wrapped
around proteins (proteins not shown).
Gene 1
Gene 2
The DNA replicates,
resulting in two copies of
the same chromosome..
Replicated
chromosome
Gene 1
Gene 2
Copies of same
chromosome
Gene 1
Gene 2
The DNA condenses
around its associated
proteins, resulting in a
compact chromosome
that is 10,000 times shorter
than its original length.
Condensed
replicated
chromosome
Copies of same
chromosome,
condensed
Centromere
Figure 11-5
Mitosis
M
DIVISION
G2
G1
S
INTERPHASE
Figure 11-7a-1
PRIOR TO MITOSIS
Chromosomes replicate.
Centrosomes
Chromosomes
Centrioles
1. Interphase: After chromosome
replication, each chromosome is
composed of two sister chromatids.
Centrosomes have replicated.
Figure 11-7a-2
MITOSIS
Sister chromatids separate; one chromosome copy goes to each daughter nucleus.
Early mitotic spindle
Kinetochore
Spindle
fibers
2. Prophase: Chromosomes 3. Prometaphase: Nuclear
condense, and mitotic spindle
begins to form.
envelope breaks down.
Spindle fibers contact
chromosomes at kinetochore.
4. Metaphase:
Chromosomes complete
migration to middle of cell.
Figure 11-7b
CYTOKINESIS
Cytoplasm
is divided.
5. Anaphase: Sister chromatids
6. Telophase: The nuclear
separate. Chromosomes are
envelope re-forms, and the
pulled to opposite poles of the cell. spindle apparatus disintegrates.
7. Cell division begins: Actin- 8. Cell division is
myosin ring causes the plasma
complete: Two
membrane to begin pinching in.
daughter cells form.
Figure 11-7b-1
5. Anaphase: Sister chromatids
6. Telophase: The nuclear
separate. Chromosomes are
envelope re-forms, and the
pulled to opposite poles of the cell. spindle apparatus disintegrates.
Binary Fission
 Bacterial Cell Division
 In stead of centrioles, chromosome is
attached to and remains attached to the
plasma membrane
 The bacterial cell elongates, separating
the chromosome and its copy
 When the growth and separation are
complete, cytokinesis occurs
Figure 11-8
STEPS IN BACTERIAL CELL DIVISION
1. Chromosome
2. Chromosome
3. Chromosomes 4. FtsZ ring
5. Fission
is located midcell.
replicates.
pull apart; ring
of FtsZ protein
forms.
complete.
constricts.
Membrane
and cell wall
infold.
Controlling the cell cycle
 Cell cycle Control System
 Molecule cycling system for regulation
 Checkpoints-points in the cycle where the cell is
halted until the go ahead chemical signal is
given (ex: G1 in animal cells is most critical)
 Cell Cycle clock-Cyclin-dependent kinases
(Cdks) are protein kinases that need cyclin to
be active (regulating the levels of cyclin and
Cdks regulates the cell cycle)
 Ex: MPF (maturation promoting factor)-cyclins
accumulate during the G2, making Cdks activate
which initiate Mitosis. This is turned off during the
M phase when proteolytic enzymes break down the
cyclin, allowing the cell to proceed through
anaphase
Figure 11-14
MPF component concentration
Cyclin concentration regulates MPF concentration.
G1
S
G2
M phase G1
MPF activated by
dephosphorylation
of MPF Cdk P
S
G2
M phase G1 S
MPF activated by
dephosphorylation
of MPF Cdk P
MPF Cdk
Time
Activated MPF has an array of effects.
Phosphorylate chromosomal
proteins; initiate M phase
Activated MPF
P
Cyclin
Cdk
Phosphorylate nuclear
lamins; initiate nuclear
envelope breakdown
Phosphorylate microtubuleassociated proteins. Activate
mitotic spindle?
Cyclin + Cdk with P
dephosphorylated,
cyclin-dependent
kinase subunit
Phosphorylate an enzyme
that degrades cyclin; cyclin
concentrations decline
Internal and External Regulating
Cues
 Internal Cues
 Ex: M-phase checkpoint which occurs at
Metaphase and ensures that all chromosomes
are attached to spindles
 Kinetochores that aren’t attached to spindles
send signals halting anaphase until they’re
attached
 External Cues
 Growth factors released from other body cells
 Density-dependent inhibition-in Biology, we
called this contact inhibition (when cells are lost,
the Growth factor level increases so cells grow
and divide)
Figure 11-18
THE G1 CHECKPOINT IS SUBJECT TO SOCIAL CONTROL
1. Growth factors
2. Growth factors
3. Cyclin binds to
4. Cdk is activated
arrive from other
cells.
cause increase in
cyclin and E2F
concentration.
Cdk; Cdk is
phosphorylated.
Rb inactivates E2F
by binding to it.
by dephosphorylation.
It catalyzes
phosphorylation of Rb.
5. Rb releases E2F.
6. E2F enters
nucleus and
triggers production
of S-phase proteins.
Cancer
 Cells that are cancerous don’t respond to the cell’s
normal controls of the cell cycle
 Some cancerous cells divide continuously and spread
easily, while others stop completely at one of the
various checkpoints
 Cancers can transform adjacent cells to form tumors
 Benign=cells remain unchanged within the tumor
 Malignant=tumor becomes invasive and impairs the
organ’s function
 If cells break away from the tumor and spread
through the blood stream, we say they metastasize
Figure 11-17
Benign tumor
Normal cells
Benign tumor cells
may continue to
divide, but are not
invasive (they do not
spread from tumor)
Malignant tumor
Malignant tumor cells
divide and spread to
adjacent tissues and to
distant tissues through
lymphatic vessels and
blood vessels
Lymph vessel
Blood vessel
New tumor that has
formed in distant
tissue by metastasis
Meiosis
 Forms the precursors of gametes
(Cell goes from 2nn (x-shaped, 2
cells)n (l-shaped, 4 cells)
 Occurs in 2 divisions: Meiosis I
(homologs line up during prophase I
and crossing over occurs) and Meiosis
II (looks the most like mitosis)
Figure 12-4l
PRIOR TO MEIOSIS
MEIOSIS I
Chromosomes replicate,
forming sister chromatids.
Homologous chromosomes separate.
Tetrad (4 chromatids from
homologous chromosomes)
Nuclear Chromatin
envelope
Non-sister
chromatids
Spindle apparatus
Chiasma
1. Interphase:
2. Early Prophase I:
3. Late Prophase I:
4. Metaphase I:
5. Anaphase I:
Chromosomes replicate
in parent cell, in
uncondensed state.
Chromosomes condense,
nuclear envelope breaks up,
spindle apparatus forms.
Synapsis of homologous
chromosomes.
Crossing over of
non-sister chromatids
(often multiple crossovers between the
same chromatids).
Tetrads migrate to
metaphase plate.
Homologs separate
and begin moving to
opposite sides of cell.
6. Telophase I and
Cytokinesis:
Chromosomes move to
opposite sides of cell,
then cell divides.
Figure 12-4r
MEIOSIS II
Sister chromatids separate.
7. Prophase II:
8. Metaphase II:
9. Anaphase II:
Spindle apparatus
forms.
Chromosomes line
up at middle of cell
(metaphase plate).
Sister chromatids
separate, begin
moving to opposite
sides of cell.
10. Telophase II and
Cytokinesis:
Chromosomes move to
opposite sides of cell,
then cell divides.
Genetic Variation
 Crossing over
 Synapsis of homologs during prophase I causes
tetrads with chiasmata (crossing-over of
chromatids from neighboring chromosomes),
which mixes up sections of the chromosome
between homologs
 Used to make linkage-maps
 Independent assortment
 Inheritance of one chromosome doesn’t affect
the inheritance of another (non-linkage)
 Random fertilization
 You never know which resultant sperm will
fertilize which resultant egg
Figure 12-7-2
A CLOSER LOOK AT THREE KEY EVENTS IN MEIOSIS
Centromere
Non-sister
chromatids
3. Crossing over, during prophase I.
Complex of proteins forms where
crossing over will occur. Chromosome
segments are swapped between
non-sister chromatids.
Protein complex
Crossing over usually occurs at least
once in each non-sister chromatid,
but is only shown on 1 pair here