genetics lecture 21: cell cycle and cancer

What is the main outcome of mitosis?
A) Production of genetically different daughter cells
B) Production of genetically identical daughter cells
C) Cell death
D) DNA replication only

Production of genetically identical daughter cells

Which process usually accompanies mitosis and involves the division of the cell itself?
A) Transcription
B) Cytokinesis
C) Meiosis
D) Apoptosis

Cytokinesis

The cell cycle is:
A) A random process with no specific order
B) A series of irreversible stages through which a cell grows and divides
C) A reversible process where cells can move backwards through phases
D) A process that only happens in multicellular organisms

A series of irreversible stages through which a cell grows and divides

How is progression through the cell cycle regulated?
A) By the environment alone
B) By special genes that control timing and order of stages
C) Random chance
D) None of the above

By special genes that control timing and order of stages

The cell cycle is ____________, meaning cells only move forward through stages and never backward.

irreversible

True or False: Many genes are turned on only at specific times during the cell cycle to produce proteins needed for progression

true

True or False: Studying mutations that affect the cell cycle has helped identify key regulatory genes.

true

What is the role of growth factors in the cell cycle?
A) To inhibit DNA replication
B) To signal the cell to grow and divide
C) To cause the cell to enter G0 phase
D) To break down damaged DNA

To signal the cell to grow and divide

How do growth factors initiate the cell’s progression from G1 to S phase?
A) By entering the nucleus and directly activating DNA synthesis
B) By binding to a receptor on the cell surface, causing a conformational change that triggers internal signaling
C) By breaking down the cell membrane
D) By inhibiting the receptor on the cell surface

By binding to a receptor on the cell surface, causing a conformational change that triggers internal signaling

Which of the following conditions must be met before a cell moves from G1 to S phase?
A) The cell must be small and have limited nutrients
B) The cell’s DNA must be damaged
C) The cell must be large enough, have sufficient nutrients, and have undamaged DNA
D) The cell must stop all protein synthesis

The cell must be large enough, have sufficient nutrients, and have undamaged DNA

Growth factors are special ____________ proteins that bind to receptors on the ___________ of the cell to stimulate cell division.

signaling, outside (or cell surface)

The receptor undergoes a ____________ change when growth factors bind, which activates signaling inside the cell.

conformational

True or False: Cells in G0 phase are actively dividing.

false

True or False: A cell will only start DNA replication if it is ready, meaning it has enough nutrients, size, and undamaged DNA.

true

Which of the following is an example of a second messenger involved in growth factor signaling?
A) Ras
B) cAMP
C) Kinase
D) Receptor tyrosine kinase

cAMP

What is the role of Ras in the growth factor signaling pathway?
A) Acts as a secondary messenger to directly bind DNA
B) Functions as an inactive kinase that deactivates signaling
C) Acts as a molecular switch that activates a kinase cascade when turned on
D) Represses gene transcription in response to growth factors

Acts as a molecular switch that activates a kinase cascade when turned on

Which statement best describes the kinase cascade in the Ras pathway?
A) Ras directly binds DNA and activates transcription factors
B) Kinases activate each other sequentially, amplifying the signal until genes promoting cell division are turned on
C) Kinases inhibit growth factor receptors to stop cell division
D) Kinase cascade involves second messengers like cAMP and Ca²⁺

Kinases activate each other sequentially, amplifying the signal until genes promoting cell division are turned on

What happens after a growth factor binds its receptor in the secondary messenger pathway?
A) Ras is activated and initiates a kinase cascade
B) Second messengers like cAMP and Ca²⁺ are activated and spread the signal inside the cell
C) The receptor moves into the nucleus to regulate gene expression
D) The cell immediately enters mitosis

Second messengers like cAMP and Ca²⁺ are activated and spread the signal inside the cell

In the secondary messenger pathway, molecules such as _______ and _______ quickly spread the growth factor signal inside the cell.

cAMP, Ca²⁺

Ras is a protein that acts as a molecular ________, which is turned on after growth factor binding and starts a kinase cascade.

switch

The kinase cascade results in activation of transcription factors that promote __________ and __________.

cell division; growth

True or False: The kinase cascade amplifies the growth factor signal by sequentially activating multiple kinases.

true

True or False: Ras is always active inside the cell, regardless of growth factor binding.

false

What is the consequence of a mutation that locks Ras in the "on" state?
A) Cell cycle arrest
B) Uncontrolled cell growth, potentially leading to cancer
C) Inactivation of cyclin-dependent kinases
D) Increased production of cyclins

Uncontrolled cell growth, potentially leading to cancer

Cyclin-dependent kinases (CDKs) require which of the following to become active?
A) Phosphorylation by Ras
B) Binding to cyclins
C) Binding to DNA
D) Activation by second messengers

Binding to cyclins

What is the primary function of active CDKs during the cell cycle?
A) To degrade cyclins
B) To phosphorylate target proteins that regulate cell cycle progression
C) To directly replicate DNA
D) To inhibit growth factor signaling

To phosphorylate target proteins that regulate cell cycle progression

hich event is NOT directly controlled by CDKs?
A) DNA replication
B) Entry into mitosis
C) Exit from mitosis
D) Protein synthesis in the cytoplasm

Protein synthesis in the cytoplasm

Cyclins regulate the cell cycle by binding to and activating enzymes called ________.

cyclin-dependent kinases (CDKs)

When activated, CDKs add phosphate groups to specific proteins, a process known as ____________.

phosphorylation

Different ________ appear and disappear during various phases of the cell cycle to ensure proper timing of CDK activation.

cyclins

True or False: CDKs are fully active enzymes even without cyclin binding.

false

True or False: Mutations causing Ras to be permanently active can contribute to cancer by promoting continuous cell division.

true

True or False: Cyclins remain at constant levels throughout the entire cell cycle.

false

o S phase?
A) Cyclin A - CDK2
B) Cyclin B - CDK1
C) Cyclin D - CDK4/6
D) Cyclin E - CDK5

Cyclin D - CDK4/6

What is the main role of cyclin-CDK complexes during the cell cycle?
A) To degrade DNA
B) To phosphorylate target proteins that regulate cell cycle progression
C) To bind growth factors
D) To produce energy for the cell

To phosphorylate target proteins that regulate cell cycle progression

Why are cyclins important for the cell cycle?
A) They directly replicate DNA
B) They bind to CDKs and activate them at specific times
C) They are permanently present to maintain constant CDK activity
D) They inhibit phosphorylation

They bind to CDKs and activate them at specific times

Which statement is true about cyclins during the cell cycle?
A) Cyclins are present in all phases at constant levels
B) Cyclins bind non-specifically to any CDK
C) Different cyclins appear at specific stages to regulate progression
D) Cyclins act as enzymes that phosphorylate proteins

Different cyclins appear at specific stages to regulate progression

True or False: Once cyclins bind to CDKs, they permanently activate the CDKs throughout the cell cycle.

false

True or False: The timing of cyclin production helps ensure that the cell cycle progresses in the correct order.

true

T/F: Cyclins are not always present. 

true

What role does the RB protein play in the G1 phase of the cell cycle?
A) Activates DNA replication
B) Acts as a brake to prevent premature entry into S phase
C) Phosphorylates cyclins
D) Binds to growth factors

Acts as a brake to prevent premature entry into S phase

How does RB prevent the cell from entering S phase too early?
A) By degrading cyclins
B) By binding to and inhibiting the E2F transcription factor
C) By phosphorylating DNA
D) By activating CDKs

By binding to and inhibiting the E2F transcription factor

What event causes RB to release E2F and allow progression into S phase?
A) Cyclin-CDK complexes phosphorylate RB
B) E2F binds to DNA
C) Growth factors bind to the receptor
D) DNA is replicated

Cyclin-CDK complexes phosphorylate RB

What is the function of E2F once it is released from RB?
A) To bind to RB again
B) To phosphorylate cyclins
C) To activate genes required for DNA synthesis
D) To inhibit CDKs

To activate genes required for DNA synthesis

What happens to E2F once the cell has entered S phase?
A) It becomes more active
B) It is phosphorylated and turned off
C) It binds RB again
D) It degrades RB

It is phosphorylated and turned off

When phosphorylated by Cyclin-CDK complexes, RB ___________ its hold on E2F.

releases

E2F is a ____________ factor that activates genes necessary for DNA replication.

transcription

True or False: RB phosphorylation leads to its activation, which stops the cell cycle from progressing.

false

T/F: Cyclins create an all-or-nothing response — once the right complex is active, the cell is fully committed to moving to the next phase.

true

What does the G1/S checkpoint primarily monitor?
A) Chromosome attachment
B) DNA damage, cell size, growth factors
C) Completion of DNA replication
D) Cytokinesis

DNA damage, cell size, growth factors

Which checkpoint ensures chromosomes are properly attached before mitosis completes?
A) G1/S
B) G2/M
C) Spindle checkpoint
D) DNA replication checkpoint

Spindle checkpoint

What can happen if checkpoint controls fail?
A) Cells stop dividing
B) Cells divide uncontrollably with DNA errors
C) Cells repair damage more quickly
D) Cells enter apoptosis prematurely

Cells divide uncontrollably with DNA errors

True or False: The G2/M checkpoint checks if DNA replication is complete before allowing mitosis to proceed.

true

True or False: If DNA damage is too severe, the cell can trigger apoptosis to prevent propagation of mutations.

true

What is the main function of p21 in the DNA damage response pathway?
A) Activates Ras signaling
B) Degrades p53
C) Inhibits cyclin-CDK complexes to pause the cell cycle
D) Promotes DNA replication

Inhibits cyclin-CDK complexes to pause the cell cycle

How does Mdm2 regulate p53 under normal (non-stressed) conditions?
A) Activates p53 by phosphorylation
B) Binds and exports p53 from the nucleus
C) Promotes p53-mediated apoptosis
D) Transcribes p21 directly

Binds and exports p53 from the nucleus

Which of the following conditions is most likely to result in persistent high levels of active p53?
A) Nutrient abundance
B) DNA damage
C) Cyclin degradation
D) Normal mitosis

DNA damage

Which modification is necessary for p53 to become transcriptionally active?
A) Degradation by Mdm2
B) Inhibition by p21
C) Acetylation and phosphorylation
D) Binding to cyclins

Acetylation and phosphorylation

Under normal conditions, the protein _____ keeps p53 levels low by promoting its degradation and exporting it from the nucleus.

Mdm2

When activated, p53 functions as a _____ factor that can either pause the cell cycle or trigger _____.

transcription; apoptosis

p53 stops the cell cycle primarily by activating the gene _____, which blocks the activity of cyclin-CDK complexes.

p21

T/F: Without functional p53, cells may continue dividing despite having DNA damage.

true

Which of the following is NOT a way Mdm2 suppresses p53 activity?
A. Promotes chemical modifications of p53
B. Exports p53 out of the nucleus
C. Tags p53 for degradation
D. Binds to p53 and inactivates it

Promotes chemical modifications of p53

What happens to p53 in a healthy, unstressed cell?
A. It accumulates and triggers cell cycle arrest
B. It is exported from the cell
C. It is maintained at low levels by Mdm2
D. It activates cyclin-CDK complexes

It is maintained at low levels by Mdm2

What immediate effect does phosphorylation of p53 have during the DNA damage response?
A. It enables p53 to degrade Mdm2
B. It promotes p53 export from the nucleus
C. It prevents Mdm2 from binding to p53
D. It initiates translation of p21

It prevents Mdm2 from binding to p53

DNA damage activates enzymes that __________ p53, preventing its interaction with __________.

phosphorylate; Mdm2

Once activated, p53 accumulates in the __________ where it initiates the transcription of genes involved in cell cycle arrest, DNA repair, or __________.

nucleus; apoptosis

What is the functional consequence of reduced DNA polymerase processivity during S phase in response to DNA damage?
A. Increased mutation rate
B. Faster replication
C. More time for DNA repair mechanisms to act
D. Enhanced cyclin-CDK activity

More time for DNA repair mechanisms to act

When p53 is activated, it acts as a __________, turning on various genes such as p21, Bax, and GADD45.

switchboard

The term __________ refers to how long DNA polymerase can synthesize DNA before dissociating from the template.

processivity

T/F: p53 slows replication during S phase by reducing DNA polymerase speed, giving the cell more time to repair damage.

true

Which of the following best describes the role of p53 in response to irreparable DNA damage?
A. It directly degrades damaged DNA
B. It activates survival pathways only
C. It initiates apoptosis by activating specific genes
D. It reprograms the cell into a stem-like state

It initiates apoptosis by activating specific genes

Apoptosis is a __________ and controlled form of cell death that prevents damaged cells from dividing and causing harm.

safe

One key decision p53 makes is whether a cell should attempt DNA __________ or undergo __________.

repair; apoptosis

What is the primary role of caspases in apoptosis?
A. Repair DNA damage
B. Promote inflammation
C. Break down cellular components in a controlled manner
D. Stimulate the immune system to attack the cell

Break down cellular components in a controlled manner

Why is apoptosis considered a "clean" form of cell death?
A. Because it prevents DNA degradation
B. Because it involves rapid necrosis
C. Because it avoids triggering inflammation in surrounding tissues
D. Because it causes cell lysis, dispersing contents safely

Because it avoids triggering inflammation in surrounding tissues

What cellular structures are directly dismantled by activated caspases during apoptosis?
A. Only the plasma membrane
B. Mitochondria and ribosomes
C. Nucleus and DNA
D. Microtubules only

Nucleus and DNA

Caspases are a family of __________ enzymes that initiate and carry out apoptosis.

protease

Caspase activation begins a __________ reaction that results in controlled cellular disassembly.

chain

T/F: Apoptosis ensures tissue homeostasis by safely eliminating damaged or unwanted cells.

true

What would most likely happen if the spindle checkpoint failed and a chromosome was not properly attached to spindle fibers?
A. The cell would permanently arrest in prophase
B. The cell would exit mitosis prematurely and return to G1
C. Sister chromatids could be unequally distributed, leading to aneuploidy
D. The cell would skip mitosis entirely

Sister chromatids could be unequally distributed, leading to aneuploidy

What is the role of the anaphase-promoting complex (APC/C) in mitosis?
A. To stabilize spindle fibers
B. To prevent kinetochores from forming
C. To initiate the separation of sister chromatids
D. To degrade microtubules

To initiate the separation of sister chromatids

Which structure ensures that spindle fibers are properly connected to chromosomes?
A. Centrosome
B. Kinetochore
C. Nucleolus
D. Centriole

The spindle checkpoint monitors the attachment of __________ to spindle fibers during mitosis.

The spindle checkpoint monitors the attachment of __________ to spindle fibers during mitosis.

The spindle checkpoint monitors the attachment of __________ to spindle fibers during mitosis.

If even one kinetochore is improperly attached, the checkpoint blocks activation of the __________, delaying the onset of anaphase.

anaphase-promoting complex (APC/C)

The purpose of the spindle checkpoint is to maintain __________ stability by ensuring proper chromosome segregation.

genetic

Which of the following best explains why cancer risk increases with age?
A. Older individuals have weaker immune systems
B. Cell division completely stops in older people
C. More mutations accumulate over time in somatic cells
D. All genes related to cancer are inherited, and age activates them

More mutations accumulate over time in somatic cells

What does it mean that tumors are “clonal”?
A. Tumors can clone other cells from different organs
B. Every tumor is made of different, unrelated cells
C. All tumor cells descend from a single mutated ancestor cell
D. Tumor cells avoid mutation by maintaining original gene sequences

All tumor cells descend from a single mutated ancestor cell

Which type of cancer is most common based on how mutations arise?
A. Familial
B. Viral
C. Somatic
D. Sporadic

Sporadic

Why did lung cancer rates not immediately increase when smoking became widespread in the early 20th century?
A. Tobacco was not as carcinogenic back then
B. Cancer takes time to develop as mutations accumulate over years
C. Early detection methods were unavailable
D. Only a few people actually smoked

Cancer takes time to develop as mutations accumulate over years

Mutagens such as radiation, chemicals, or tobacco smoke increase the rate of __________, which raises cancer risk.

mutations

Cancer cells typically arise due to the failure of cell cycle __________ that would normally prevent uncontrolled division.

checkpoints

Only about __________ percent of cancers are inherited (familial), while the rest arise from mutations acquired during a person’s lifetime.

1

T/F: Cancer is a single disease caused by one specific mutation in all cases.

false

T/F: Most cancers affect reproductive (germline) cells and are passed to the next generation.

false

T/F: The more mutations a cell’s descendants have, the higher the chance some will lead to cancer. 

true

What is the term for cancer cells producing their own growth signals to stimulate cell division?
A. Autophagy
B. Contact inhibition
C. Autocrine stimulation
D. Paracrine signaling

Autocrine stimulation

Which of the following cellular behaviors is lost in cancer cells but present in normal cells?
A. Unlimited division regardless of space
B. Secretion of growth factors to stimulate their own growth
C. Contact inhibition that prevents overgrowth
D. Ability to metastasize

Contact inhibition that prevents overgrowth

How do cancer cells typically avoid programmed cell death?
A. By activating the spindle checkpoint
B. By increasing cyclin levels
C. By disabling apoptosis-related pathways
D. By increasing DNA repair mechanisms

By disabling apoptosis-related pathways

In autocrine stimulation, cancer cells produce their own __________ __________ to continuously drive cell division.

growth factors