Cell Biology Final Material

What is the cell cycle

It is the ordered events of a cell to duplicate its material and divide into two

1. Cell growth/Duplication

2. Chromosome segregation

3. Cell division

Does every cell have the same duration of the cell cycle?

No, not every cell has the same duration of cell cycle

for examples gut cells divide very quickly and nerve cells very slowly

they have different generation times

What are the 4 phases of the cell cycle

• G1 - Gap 1 - cell gets ready to do the rest of the work - it grows and metabolises, preparing for S

• S phase - DNA is replicated - commital phase - if cell enters S it is commited to dividing (becuase if it produces twice the DNA and doesnt divide it is lethal)

• G2 - Gap 2 - gets the cell ready for M

• M - division phase - subcategories

  • Nuclear division

  • Cytoplasmic division

G1, S, G2 make up interphase

If cell cycle was on a clock

• 23 hours in interphase

• 1 hour in division phase

Is the cell cycle regulated

Yes, there is a control system that monitors the process of the cell cycle

it is one of the most tightly regulated processes

How does a cell pass the checkpoint

• at each phase every cell is assessed and it needs to pass a checkpoint to go to the next phase

Between G1 and S

It is assessed whether the environment is favorable and if it has everything to successfully move on

Between G2 and M

• Assess whether all DNA got replicated

• DNA polymerase check if things are done right

In M

• makes sure things go well like if all chromosomes attacked to proper spindle

What are checkpoints

chemical in nature

What are the control molecules

Activity is regulated by the complex of two molecules joining

1. Cyclin

2. Cyclin dependent Kinases (CDK) - it adds a phosphate to something to phosphorylate target protein

Names of the CDK’s

The ones that control Cell into M would be named (M- CDK activity or M- cyclin concentration) with S it would be S-…

etc…

M- CDK activity

When M-CDK activity high the cell is undergoing mitosis and this is when cyclin is high

you cant get activity of CDK without enough of the paired cyclin

Concentration first goes down (cyclin) then the activity (CDK - phosphorylation - changes shape and function) and then it moves out of the phase

What does it mean that the activity of individual CDKs varies during the cell cycle?

Each CDK is active only at specific stages of the cell cycle because it must bind to a specific cyclin. Cyclin levels rise and fall, so CDK–cyclin complexes form and activate at different times to control each phase (e.g. S-CDK and M-CDK active at different times).

How does CDK work

Transfers a phosphate from ATP to the target protein

What do cyclin molecules do

• they bind to the CDK’s as a step towards activation

Life cycle of CDK

1. Active CDK is when cyclin is binded

2. At the right time when it wants to be inactivated Anaphase-Promoting Complex/Cyclosome (APC/C) becomes active

3. APC/C adds a chain of ubiquitin molecules to the cyclin (ubiquitylation)

4. ubiquitylated cyclin is then recognized and degraded by the proteasome

5. Inactivated CD

What else is CDK’s function controlled by

• Addition and removal of phosphate is also necessary for activity

• They need to take out the inhibitory phosphate to function

What else can CDK be controlled by

• CDK can also be blocked by inhibitor proteins

• for example P27 is one

what does a phosphatase do

it removes a phosphate

Levels of CDK and cyclin through cycle

LOOK at notes for specific ones

Movement from G1 to S

• CDC6 (not a CDK but a licensing factor) sits at a replication origin called the ORC

• Helicase binds near cdc6

• once binds cdc6 is phosphorylated for helicases to move

• the phosphorylation is done by S-cdl

• cant get movement out of helicase until it is phosphorylated by S-CDK

P53

• It is a tumor suppressor gene

• A regulatory protein whose activity is increased due to DNA damage (especially UV light)

• 50% of non inherited cancer is due to mutations in P53 - dont get P21

• Normal activity: turn on when DNAA damage, turn on P21 which inactivates CDK (this is correct since damage leads to no S- dont want to bring damaged DNA in S)

1. DNA damage

2. Increase P53

3. Increase P21

4. P21 binds CDK complex and arrests in G1

GO

Cells can withdraw from the cell cycle to GO

this can happen in cells with realling long cell cycle tumes

if a cell withdraws they are called terminally differentiated

What is organ and body size regulated by

It is regulated by the interplay of 3 processes

1. Cell growth

2. Cell proliferation (division)

3. Cell death

Apoptosis

• Programmed cell death for the purpose of

1. Developing structures

   1. forming digits - fingers/toes

   2. ear lobe - free (they had an apoptotic event occur)

   3. Very important for body plants

   4. In embryos very common

2. Regulation of cell numbers

   1. no increase or decrease in the size of an internal organ

• it is cleaned cell death - beneficial not problematic

difference between apoptosis and necrotic events

• Necrotic event - expulsion of cellular material - an explosion

• Apoptosis - everything implodes

  • building skyscraper imploding

  • very regulated

How does apoptosis work

• It is a highly regulated program it uses the caspase family of proteases cleaves the laminar proteins, causes breakdown of nuclear membrane

1. cytoskeleton collapse

2. nuclear envelope dissassembles

3. DNA fragments

4. Cell surgace altered (cell wont look normal so macrophages engulg)

5. Macrophages engulf

What are the external signals

1. Survival factors

2. Mitogens

3. Growth factors

4. Negative control factors

1-3 are stimulating

4 is inhibitory

Survival factors

• promote cell survival

• there to make sure cell stays viable

• for example nerve cell. some stay (good connection to target cell) and get survival factor and others apoptosis (bad connection)

• so the survival factor is a chemical signal molecule that blocks apoptosis so the cell survives

Mitogens

• stimulate cell proliferation (division)

• When activated it activates a CDK phosphorylate Rb (usually blocks DNA replication. its an inhibitor so when inactivated it turns on the DNA replication) which inactivates it allowing cell to start transcription

Growth factors

• stimulate cell growth

  • inhibit protein degradation

  • OR stimulate protein production

Both stimulate growth

Negative Control factors

• inhibit the survival factors

  • growth, cell division, cell death

structural and organizational changes a cell undergoes to prepare for division.

1. chromosome condensation (first sign moving into M phase)

2. nuclear envelope breakdown

3. ER and golgi reorginize cuz close to nuclear envelope

4. cell loosens attachment (surrounding neigboring cells)

5. cytoskeleton reorginzation

Division necessities

• DNA replication

• Cytoskeleton structures appearing

• Centrosomes Duplicated

• Dynamic intability

• Microtubule instability

DNA replicated

• each chromosome is replicated and copied parts remain together until segr

• cell division wont happen of replication doesnt

• Cohesin - make sure sisters stay close

• Condensins- part of looping domains in condensation

Whats a chromosome pair

• one from mom one from dad can be replicated or not

Are their homologous chromosomes in G1

Yes

Cytoskeleton structures appear

1. Mitotic spindle

2. contractile ring- myoson and actin filaments in animals

Centrosomes duplicated

• Centrosome: region of the cell where the centrioles are. there may or may not be centrioles there

• Plant cells have centrosomes not centrioles

• Centrioles run perpendicular to each other = 2 centrioles 

  • locate organizing site

  • in nucleation site

Interphase: 1 centrosome, 2 centrioles

After duplication (mitosis):2 centrosomes, 4 centrioles

Centrosome life cycle

1. Nucleation site for microtubules of spindle

2. Pair of centrioles in animal cells

3. Duplication - movement centrosome cycle

4. g1 1 pair S-G2 2 pairs (next to each other) M- centrosomes move to either side and place spindle (good placement poles)

NOT IN PLANT CELLS

Microtubules 

• long, hollow and stiff tubes of protein

  • straw

• Each microtibule has a polarity (plus end beta and minus end alpha)

  • Molecules of tubulin = dimer of an alpha and a beta tubulin

  • Tubulin dimers stack to form protofilaments  (alpha and beta)

  • Wall has 13 protofilaments alpha and beta on each ends determining polarity

• Assembly of a microtubule at centrosome begins with an initial ring of 13 tubulin molecules (Y tubulin rings) addition occurs faster to the plus end then the minus end

LOOK AT NOTES DRAWING

Dynamic instability

• the growth and dissasembly of individual microtubules at any single time allows for movements of chromosomes

Microtubule instability

GTP cap loss

• at the ends of it has a lot stabilized to growth

• if there is no cap causes the breakdown of microtubules and dimers are released

  • this is how u can get growing microtubules to shrink

• if growth faster than hydrolysis → tubule grows

Variety of microtubule associated proteins regulated microtubules

• growth/shrink/stable/unstable

What can mitosis be defined as

A continuous process that can be defined as moving through 6 phases

Reorganization of microtubule arrays

• Large number of microtubules

• shorter microtubules

• Depolymerization rate 20X faster than normal interphase stage

• Change occurs due to activites of MAPs(microtubule associated proteins)

Kinesisna and Dyneins

Kinesins are motor proteins that move toward the plus end of microtubules, helping separate spindle poles and move chromosomes toward the cell center.

Dyneins move toward the minus end of microtubules, pulling chromosomes toward spindle poles and positioning the spindle within the cell.

Prophase

1. centrosome separate and move to poles

2. microtubules extend from 1 centrosome to other and this interaction stabilizes the spindle

• interpolar microtubules - between 2 poles - stabilize spindle cuz connected to each other

3. chromosomes condense

Prometaphase

1. breakdown of nuclear membrane

2. spindle microtubule bind to the chromosome at kinetochores

3. Each chromatid bound by microtubule from opposite poles

   1. kinetechore proteins bound to centromere which microtubule binds to

   2. microtubule not directly bound to chromosome cuz then not able to shrink if it were directly attached

types of microtubules

Astral microtiules - attach to same pole side

Kinetichore - move chromosomes

interpolar- non kinetechore 

Metaphase

• chromosomes align at equatorial plate of spindle = metaphase plate

• chromosome are under tension

Anaphase

• release of cohesins

• sister chromatids begin to move to poles

• protein breaks down cohesins (a protease called separase) → happens really quickly

A. kinetechore microtubules shorten - remove tubulin subunits at the kinetechore

B. overlapping interpolar microtubules move past each other, pushing poles further apart so they slide past each other

Telophase

• prophase backwards

1. Nuclear membrane reforms including pores

2. Decondense so transcription begins again

How does nuclear membrane breakdown/reformation happen

• It breaks in a bunch of packets

  • phosphorylation

• Comes back together by dephosphorylation

Cytokineses process and timing

• begins in late anaphase and doesn’t end until late telophase

• Utilizes a contractile ring (animals) of actin and myosin that sever the 2 cells from each other

  • like a drawstring on a pair of pants - pinch action

• First evidence of cytokinesis is puckering and cleavage furrow

• In plants a fragmoplast forms in the middle of the cell which forms the start of the cell wall which grows out dividing the cells into two

How does division of organelles occur

1. either double the number and then divide 

   1. Binary fission - chloroplasts and mitochondria

2. Fragment and reassemble in new cells

   1. Golgi and ER

Somatic Cell

Fully differentiated body cell

all have pairs of chromosomes

Germ cell

Gametes, sex cells. Produced by meiosis

Homologous pairs

• maternal and paternal

• Same gene at same locus (position)

• Different allele can occur

Diploid

• pairs of homologous chromosomes

• somatic cells

Haploid

• One chromosome of each type

• Gametes

• Even if replicated still haploid cuz no pairs

Meiosis

• Production of haploid cells (gametes) from a diploid cell

• In preparation chromosomes duplicate

Meisosis 1

• Homologous pairs find each other (synapsis) and form a bivalent/tetrad in prophase 1

• cohesins keep sisters together

• synaptonemal complex keeps bivalent together

• Recombination/crossing over occurs and formation of chiasmata

  • double stranded breaks occur then new bindin within the homologous chromosome

  • + variability

• Sister crhomatids locked by cohesins and homologous tied by chiasma

• Split homologous pairs

• Rnadom assortment - way homologous chromosomes line up on metaphase plate to generate variability

• 2n-n

Meiosis 2

• Duplicated chromosomes separate (sisters)

What does each cell remain with after meisosis

it ends up with 1 chromosome from each homologous pair

Difference between meiosis and mitosis

• mitosis produces identical diploid daughter cells

• Meiosis produces non identical haploid cells

Cancer genes

oncogens

tumor supressor genes

Oncogenes

send constant divide signals

tumor supressor genes

prevent cancer by stopping cell division,

Whats a neoplasm

A neoplasm is an abnormal mass of cells that grows uncontrollably — basically another word for a tumor, which can be benign (non-cancerous) or malignant (cancerous).

Benign

• Essentially normal cells which stays at the site of origin

• A little mass

• dont have a real removal plan unless large enough to affect other organs

• a wart is techincall a benign tumor

Malignant

• Mass of cancerous cells that displaces normal tissue during its growth

• leak out into blood vessels so spread throughout body

• more dangerous

Metastatic

• came from another place

How does the inside of a tumor function

• inside the tumor is a microenvironment - may not participate in the normal function of that region of the body

• can have its down blood vessels cuz needs blood supply

Number of mutations

• most cancers require more than one mutation to occur

inactivation of P53

get rapid accumulation of other mutations

P53 is a tumor suppressor gene

Why do most cancers appear later in life

cuz it takes time for a cell to develop numerous mutations

Can cancer be inherited

• Yes and no

• If inherit one mutation and the cancer requires 4 you have a predisposition to that cancer - doesnt necessarily mean u will get it

• Some cancers can also develop during life from factors and arent passsed down ex. lung cancer from smoking

Nomal tissue organization

• cells organize into tissues and tissues into organs

• epithelia cells, smooth muscle cells, connective tissues in distinct layers

• Many tissues organize into epithelial (sheets) of cells

• To coordinate function, cells connect via junctions (Tight junction, Adherens junction, Desmosome, Gap junction, Hemidesmosome)

• They are polarized- each side diff function

• Tissues/organs are mixtures of cell types

Renewal rats of normal cells

• renewal rates of different cell types differ

  • most terminally differentiated cells cant divide, they go to. G0

  • These cells are replaced by precursor cells

  • Precursor cells come from step cells (undifferentiated cells)

Precursor cells

• Totipotent - can become any part of the body

• Pluripotent - already walked down a lineage - produce 1 type of organ

Characteristics of cancerous tissues

• Cant really see boundaries, unorganized, weird shape/nuclei size

• uncontrolled cell division

• loss of cell specialization

• cancerous cells change shape

• loss of contact inhibition

  • leads to plasma membrane changes (ruffling)

  • loss of contact with neighbors (malignant)

• Genetic instability (# of chromosomes in cells differ)

  • from dividing abnormally

• invade normal tissue

  • can move into the blood stream and colonize a new site (metastasis)

contact inhibition

• in normal cells

• when one cell grows next to another cell it will stop dividing- why it forms a single layer in the petri dish

Patterns of metastasis

Breast cancer → brain liver, bones, lungs

prostate → bones

Colon → liver

What abilities do cancercells evolve

1. break through tissues

2. Angiogenesis- creation of blood vessles

• tumor full of cells needs to maintain themselves by developing their own blood vessles in tumor to support cell division

General traits of cancer cells

1. reduced dependance on signals from other cells

2. survive stress and internal changes that would cause normal cells to undergo apoptosis

3. can proliferate indefinitely

4. Genetically unstable

5. abnormally invasive

6. abnormally avid for nutrients cuz always dividing- very metabolically active

7. can colonize inappropriate locations

8. can modify the cells behaviour in surrounding connective tissue

How many tissues in body

270 - for each is a type of cancer

Types of cancers

1. carcinomas

2. sarcomas

3. leukemia

4. lymphomas

Carcinomas

• originate in coverings of the body or glandular tissues (skin, lining of intestines, breast, liver) 

Sarcomas

Arise in connective tissue (bone/muscle)

Leukemia

Arise from the bone marrow or blood forming tissues

Lymphomas

arise in the immune system

Carcinogens

agents that contribute to the development of cancer

development of learning about carcinogens over time

• 1761 - john hill noticed increased nasal cancers in men with excessive tobacco snuff

• 1775 - percival pott- reported skin cancers in scrotum of adolescent ment who in youth worked as chimney sweeks

• 1915- chemically linked by Dr. yamagiwa - used coal tars to inducecancers in ears of rabbits

3 types of skin cancers

• basal cell carcinoma, squamous cell carcinoma, malignant melanoma

• in order from less bad to worst

UV radiation

causes breaks between A-T base pairs and forms TT dimers

Chemical carcinogens

Smoke, red dye 2, asbestos

can u recover from smoking and not get cancer

yes the cells can recover and your risk of cancer can go down

Finding out that viruses are carcinogens

chicken with sarcoma in breast tissue → removed from it an grinded it with sand → filtered it and colected filtrate → inject filtrate in young tissue → observe sarcoma in injected chicken

Smth smaller than bacteria cause cancer - this is a virus

how oncogenic viruses contribute to cancer development

1. Insertion of an oncogene → produces viral oncogene protein or produces a protein that can influence adjacent genes

2. Induce genetic instability → disrupt DNA repair mechanisms

3. Disrupt cell cycle

4. Infection causes chronic inflammation → changes the microenvironment

5. Causes immunosuppression