CM10 | Cell Cycle Regulation and Growth Control

Comprehensive practice flashcards covering cell cycle regulation, stages of mitosis and interphase, checkpoints, cyclins, CDKs, and DNA damage response mechanisms.

Which is a primary reason cells divide?

Growth and tissue maintenance

Replacement of damaged cells during wound healing illustrates which purpose of division?

Tissue repair

Which cells are listed as terminally differentiated?

Neurons, myocytes, and osteocytes

Which cells are described as reversibly quiescent?

Hepatocytes and stem cells

Which cells are described as dividing frequently, about every 12–24 hours?

Epithelial and bone marrow cells

The Hayflick limit in the lecture is approximately how many divisions?

$$20\text{--}50$$

Which cells are described as dividing approximately every 20 minutes?

Embryonic cells

Which cells may divide indefinitely?

Cancerous or immortalized cultured cells

Which is an internal growth signal category?

Kinases and phosphatases

How do external growth factors influence the cell cycle?

Bind receptors and trigger signaling pathways

What does the cell cycle ultimately produce?

Two identical daughter cells

Which broad period is generally long and nondividing?

Interphase

Which sequence lists the interphase stages correctly?

G1 → S → G2

Which process predominates in G1?

Cell growth with RNA and protein synthesis

Which phase doubles DNA content?

S phase

What is emphasized as occurring during G2?

Protein synthesis for division and centrosome duplication

Which stage directly follows G1 in a cycling cell?

S phase

What does karyokinesis refer to?

Separation of chromosomes during nuclear division

What does cytokinesis refer to?

Division of cytoplasm

Mitosis in the lecture is associated with which cells?

Somatic cells

Which is the correct order of mitotic stages?

Prophase → metaphase → anaphase → telophase

What happens to sister chromatids in prophase?

They condense into visible chromosomes

Which structure assembles in prophase?

Mitotic spindle

What happens to the nuclear envelope in prophase, as presented in the lecture?

It disintegrates

Where do centrosomes begin moving in prophase?

Toward opposite poles

What defines metaphase?

Chromosomes align at the spindle equator

What is the metaphase plate?

The equatorial alignment of chromosomes

Where do spindle fibers attach to chromosomes?

Kinetochores

Where are kinetochores located?

On centromeres

What is a kinetochore primarily composed of?

A multiprotein structure

Which microtubule end is anchored to spindle poles according to the lecture?

Minus end

Which microtubule end attaches to kinetochores according to the lecture?

Plus end

Why is stable kinetochore attachment important?

Correct chromosome segregation

What occurs first in anaphase as described?

Centromeres split and sister chromatids separate

What moves chromatids toward opposite poles in anaphase?

Shortening of spindle fibers

Where do chromosomes cluster in telophase?

At opposite poles

Which structure reassembles in telophase?

Nuclear envelope

Which structure reappears during telophase?

Nucleolus

What contractile structure appears in telophase?

Contractile ring

What proteins generate the cleavage furrow in cytokinesis?

Actin and myosin

What is the midbody?

A thin intercellular bridge during cytokinesis

What is the final outcome of cytokinesis?

Separation into two daughter cells

What is the overall role of cell-cycle checkpoints?

Surveil events and control progression

Which components form a checkpoint pathway?

Sensor, signaling pathway, and effector

What can a checkpoint effector do?

Halt progression and activate repair

Which checkpoint is called the restriction point?

G1 checkpoint

Which checkpoint is described as most important and rate limiting?

G1 checkpoint

Which factor is evaluated at the G1 checkpoint?

Cell size

Which additional factors are evaluated at the G1 checkpoint?

Nutrients, molecular cues, and DNA integrity

A cell passing the G1 restriction point proceeds into which phase?

S phase

A cell that does not pass the G1 restriction point may enter which state?

G0

Which description best fits G0?

A nondividing, working state

Which G0 cells can reenter the cycle with appropriate signals?

Quiescent cells

Which cells are permanently withdrawn due to aging?

Senescent cells

Which G0 category consists of fully functioning cells withdrawn from the cycle?

Terminally differentiated cells

What does the G2/M checkpoint verify?

DNA replication completion and DNA damage

What does the spindle checkpoint evaluate?

Chromosome–microtubule attachment

What else does the M checkpoint assess?

Whether chromatids are ready to separate

According to the lecture slide, what is a STOP outcome at the G2/M or M checkpoint?

Apoptosis

Why are checkpoints described as binary switches?

They permit progression or block it

What cyclical change helps control cell-cycle progression?

Cyclin synthesis and degradation

What is the main enzymatic action of active CDKs?

Protein phosphorylation

What initially obscures the CDK active site?

T-loop

What is the first activating effect of cyclin binding to CDK?

Partial activation by relieving T-loop blockage

What yields full CDK activation in the lecture?

Activating phosphorylation

What does CKI stand for in the lecture context?

Cyclin-dependent kinase inhibitor

How do CKIs inhibit cyclin–CDK complexes?

Distort the active site and inhibit enzymatic activity

Which cyclin pairs with CDK4 and CDK6 in the cycle diagram?

Cyclin D

Which cyclin pairs with CDK2 at the G1/S transition in the diagram?

Cyclin E

Which cyclin pairs with CDK1 in mitosis in the diagram?

Cyclin B

Which cyclin is shown pairing with CDK2 during S phase?

Cyclin A

Which cyclin is shown pairing with CDK1 around G2/M?

Cyclin A

What does the Rb–E2F complex do in G0?

Blocks cell-cycle progression

What do mitogens stimulate in G1?

G1-CDKs that phosphorylate Rb

What is released when Rb is phosphorylated?

E2F

What does E2F promote?

Transcription of G1/S-phase CDKs

What is an outcome of G1/S-CDK activity?

Passage through G1 and initiation of DNA replication

According to the lecture, cells in G0 do not synthesize which regulators?

Cyclins or CDKs

Which sequence best represents mitogen-driven G1 progression?

Mitogen → G1-CDK → Rb phosphorylation → E2F release

What is the main effect of Rb phosphorylation in this pathway?

Release of a transcriptional activator

What does SPF stand for?

S-phase promoting factor

Which complex is identified as SPF?

S-phase cyclin–CDK complex

What does SPF phosphorylate to promote replication initiation?

Helicase

Where does SPF recruit helicase activators?

Origins of replication

Which enzymes are subsequently recruited to initiate DNA replication?

DNA polymerases

What does MPF stand for?

Mitosis promoting factor

When are mitotic cyclin–CDK complexes produced according to the lecture?

During G2

Which kinase inhibits MPF until DNA replication is completed?

Wee1

Which enzyme reverses Wee1 inhibition and activates MPF?

Cdc25 phosphatase

How does Cdc25 activate MPF?

Dephosphorylation

Which complex is activated by MPF to promote exit from mitosis?

APC/C

How does APC/C promote mitotic cyclin degradation?

Ubiquitination

Which proteins hold sister chromatids together during metaphase according to the lecture?

Cohesins including SMC1 and SMC3

What inhibits separase protease activity during metaphase in the lecture?

CDK phosphorylation

What occurs after successful M-checkpoint passage in the lecture mechanism?

APC/C promotes mitotic cyclin ubiquitination

What is the consequence of separase activation in the lecture?

Cohesin cleavage and sister chromatid release

Which kinase responds to single-strand DNA damage according to the lecture?

ATR

Which kinase responds to double-strand DNA damage according to the lecture?

ATM

What tumor suppressor is stabilized in the DNA damage response?

p53

What does p53-induced p21 contribute to?

Cell-cycle arrest that allows DNA repair