BIO 344 Final Exam (#5)

During what phase does mitosis occur?

M phase

What are the step of the cell cycle?

1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase
6. Cytokinesis

Interphase

cell prepares for division

Prophase

centrosomes move apart, spindle starts to develop, DNA packaged into chromatids

Metaphase

microtubules have located and attached to the kinetochores in pro-metaphase, the two centrosomes begin pulling the chromosomes towards opposite ends of the cell

Anaphase

cohesions that bind sister chromatids are cleaved resulting in two identical daughter chromosomes, these are pulled toward opposite ends of the cell

Telophase

nuclear envelopes form around daughter chromosomes

Cytokinesis

cell splits

G1 phase

resting phase - most cells (46 chromosomes)

S phase

DNA replication (92 chromosomes)

G2 phase

Resting, making sure all DNA was replicated

M phase

nuclear division

DNA separated to opposite ends cell division (cytokinesis)

What are cyclin dependent kinases?

proteins that regulate the cell cycle and phosphorylate other proteins

* Cdk

What are cyclins?

a family of regulatory proteins that control the progression of the cell cycle

* activate the Cdks, which control the cell cycle processes through phosphorylation

What are all the different kinds of cyclins involved in the cell cycle?

* G1 cyclin
* S cyclin
* G1/S cyclin

What process does the G1 cyclin control?

growth regulation

What process does the S cyclin control?

phosphorylate the inhibitory protein to allow G1 to shift to S phase

What does the G1/S cyclin control?

cyclin checkpoint where DNA integrity is assessed, and the cell cycle can pause in response to improperly or partially replicated DNA

What are Cdk inhibitory proteins?

inhibit Cdk and stop them from phosphorylating regulatory genes and others involved in the cell cycle

What does p27 do?

An inhibitory gene that is inactivated by Myc binding to the SCF subunit. P27 is very important to cancer and an overactive myc protein

What does p21 do?

is a cdk inhibitor protein, it becomes activated when p53 is phosphorylated and binds to the regulatory region of the p21 gene

How else can cdk be inactivated?

inhibitory phosphorylation

* phosphorylated twice

What is APC and what does it do?

Anaphase promoting complex

* it is activated by M cdk then activates seperase to cut cohesion proteins
* destruction of M cyclin via ubiquitin

How come a cell in G1 phase that has assembled the pre-replicative complex does not immediately go into the S phase?

An inhibitory protein is bound to the pre-replicative complex to prevent replication, S-Cdk is required to phosphorylate the inhibitory protein

Describe the roles of cyclins G1, G1/S and S in moving a cell from the G1-phase to the S-phase.

S-Cdk phosphorylate inhibitory proteins causing them to dissociate from replicative complex and DNA replication begins (S phase)

Describe the roles of the Myc protein, E2F, MAP kinase and Ras proteins in moving a cell from the G1-phase to the S-phase.

Myc- is a DNA binding protein that causes increased transcription of genes that encode enzymes that facilitate the cell cycle, turns on expression of many genes (SCF, G1 cyclin, E2F) that move cycle into S-phase \n E2F- transcription factor bound to the Rb protein, Increases transcription of S-phase related genes like G1/S cyclin and S cyclin \n MAP kinase- phosphorylates transcription factor, increases transcription of Myc \n Ras- is a signal activator, activates MAP kinase

What is an Rb protein?

* binds E2F and functions as a brake in the cell cycle
* When phosphorylated, it released E2F which is done by C1/Cdk

What is the pre-replicative complex?

a protein complex that forms at the origin of replication (G1)

What does p53 do?

is a tumor supressor protein

How is p53 activated?

by damaged DNA and excessive Myc production

Why can p53 lead to cancer?

stops the cell cycle, if it can’t then cancer forms

Give an example of a gene that p53 turns on.

the p21 gene, a cdk inhibitor protein

What are mitogens?

a signal molecule/growth factor

Why would an activated blood platelet secrete mitogens?

Mitogens stimulate mitosis (cell division) and an activated platelet will need to divide and fast to help blood clot during an injury

What is transcriptase factor?

a protein that controls the rate of transcription of genetic information from DNA to messenger RNA by binding to a specific DNA sequence

What is a growth factor?

a mitogen, causes cell division

What is cancer?

uncontrollable cell growth

* caused by DNA methylation changes, gene mutations (nucleotide sequence), and changes in histone code

What is metastasis?

When cancer break away from the main tumor and may move through the circulatory systems of the body to spread and infect other cells

Is a single mutation sufficient to give rise to cancer? Why?

NO

* because that single mutation will be taken care of by the body and will not be expressed enough to cause cancer
* Multiple mutations are needed to cause cancer.

How could over-activity of a protein or gene contribute to cancer? Give an example of a protein that could contribute to cancer if overactive.

APC, Ras, and Myc all promote cell division, so if any of these genes are over active, they will make cells keep dividing and cause cancer

How could elimination of a gene contribute to cancer? Give an example of a protein that could contribute to cancer if absent.

If P53 was eliminated, the cell cycle would not be able to be stopped, so if cells did start dividing excessively, there would eb no way to stop it

What is the difference between an oncogene and a tumor suppressor gene?

Oncogenes promote cell division while tumor suppressor genes stop cell division

How did virology contribute to the discovery of oncogenes and tumor suppressor genes?

They were able to determine the DNA sequences in viruses and found many genes that are in humans, such as the Myc and Ras proteins which both promote cell division

Describe how a person could be genetically predisposed for cancer.

* Retinoblastoma is a mutant Rb gene that is inherited
* People who are born will most likely develop tumors in both of their eyes and may even develop multiple during their lifetime
* Another possible route of retinoblastoma is to have excessive proliferation but both genes have to be replicated for it to happen so it is not as common as hereditary

What is apoptosis?

programmed cell death

Why is apoptosis important in development of an organism?

not all cells need to survive during development and if they do they can cause defects

* we do not need all cells

Why is apoptosis important in cancer?

If a cell is transformed, then it most likely has excessive Myc which will turn on P53 and force the cell into apoptosis

How could extensive DNA damage lead to apoptosis?

Extensive DNA damage can cause P53 to become activated which will stop the cell cycle

* If the cell cycle stops it may turn on apoptosis

Initiator caspases

will begin the cascade

Execution caspases

the ones that will destroy many of the proteins inside the cell

* are activated by active initiator caspases

What do executioner caspases do?

role in coordinating the destruction of cellular structures such as DNA fragmentation or degradation of cytoskeleton protein

What is an apoptosome?

is a fan like structure that is formed by the release of cytochrome C from the mitochondria

* acts as a scaffold for caspase 9 which is an initiator

What proteins mediate apoptosis?

caspases

How are the proteins that mediate apoptosis activated?

1. Extrinsic: killer lymphocyte induced apoptosis
2. Intrinsic: cytochrome C release from mitochondria

What is a survival factor? What enzymes do they eventually inhibit?

a signal that allows a cell to prevent apoptosis

* the enzymes they inhibit are ones that are programmed for apoptosis, so you do need survival factors to prevent apoptosis from occuring

How does an organism ensure that each nerve cell is attached to a target cell and that extra nerve cells eliminated?

* An organism will ensure it is attached when the target cell releases survival factors
* Apoptosis will be adjusted, and the number of cells attached to target cell will change
* This is because nerve cells compete for the limited amount of survival factors released

What could the red protein that is attached to the E2F protein in the image below?

the Rb protein

What is a role of cyclin proteins in the cell cycle?

they will help to activate the cyclin dependent kinases

In which phases of the cell cycle is DNA replicated?

S phase

what accurately describes the image of a Cdk complex below?

the Cdk complex has been inactivated because it has been phosphorylated twice

How is mitosis initiated?

a signaling molecule such as a mitogen starts mitosis

a receptor that binds a growth factor is activated

What happens if the DNA of a dividing cell is damaged?

the enzyme p53 is activated

The SCF protein degrades the Cdk inhibitor p27. If the SCF gene was transcribed in a cell what would likely happen soon after?

the Rb protein would be phosphorylated

The blue arrow is pointing at a cohesion protein. Describe the red DNA strands shown in the image below.

these two DNA strands have the same genes

the two DNA strands have identical sequences

What does the E2F protein do?

it is a DNA binding protein that initiates S phase gene transcription

How many chromosomes are there in a human cell that is in the G1 phase?

46

How can a cyclin-Cdk complex be inactivated?

an inhibitory protein such as p27 can bind the complex to inactivate it

What proteins can bind DNA and are transcription factors?

* the p53 protein
* the E2F protein
* the Myc protein

What could activate the enzyme p53?

DNA damage

What is the role of the Rb protein in cell division?

it is a brake that prevents the cell from entering the S phase

How many chromosomes are there in a human cell that is in the G2 phase?

92

How were many oncogenes identified?

they were discovered on genomes of retroviruses that caused cancer

What proteins are tumor suppressor proteins?

the p53 protein

What is the difference between a benign tumor and malignant tumor?

In a malignant tumor, but not in a benign tumor, cancer cells will have invaded other tissues

What does a kinase do?

it can add phosphate to proteins

Why did the nerve cells in this image undergo apoptosis?

they did not compete successfully for survival factors released by the blue cells

What is shown in the image below?

an apoptosome

What are the red circles being released by the mitochondria in the image below?

cytochrome C

The images show the development of a mouse paw. What proteins are activated in the fluorescent cells in between the digits of the paw shown in the image below?

executioner caspases

What is shown in this electron microscope image?

a chromosome being pulled along a mitotic spindle

What is the role of cyclin proteins in the cell cycle?

they will help to activate the cyclin dependent kinases

What will happen to the M cyclin shown in this image?

it will be degraded

What protein can be activated if a cell does not bind to survival factors?

a caspase

What is the signal represented by the red question mark that causes activation of the Arf protein?

excessive mitogenic stimulation

Describe the green fluorescent cells in this image?

they are stem cells that renew the epithelial cell layer in this image

they are cells that have telomerase activity so that they can divide many times

What proteins are encoded by oncogenes?

* the Myc protein
* the Ras protein

What would happen if the SCF gene were mutated in a cell line?

the G1-Cdk would be inhibited, and the cell would not divide

What is happening in the cell that contains the protein complex shown below?

the cell is in the G1 phase and not dividing

What enzyme catalyzes the reaction identified with the red arrow?

anaphase promoting complex

What enzyme catalyzes the reaction shown in this image?

the G1-Cdk complex

What does the protein Myc do?

it is a DNA binding protein that increases transcription of the cyclin D gene which codes for the G1 cyclin

IN which phase of the cell cycle are sister chromatids separated from each other?

the M phase

What happens to actin filaments when apoptosis is activated?

The actin filaments will be cut into pieces, thereby destroying the cytoskeleton

What does the E2F protein do?

It is a DNA binding protein that initiates S-phase gene transcription

What is a function of the Anaphase Promoting Complex?

labeling the M cyclin with ubiquitin

In which phase of the cell cycle does cytokinesis occur?

the M phase

What could cause the process illustrated in this image?

DNA damage

What is the red symbol binding a receptor in this image?

a survival factor

What happens if the DNA of a dividing cell is damaged?

the enzyme p53 is activated

What does the protein condesin do?

it packages chromosomes very tightly during the M phase of the cell cycle