Exam 2: Cell Cycle

Cell division (proliferation)

What process produces new cells for growth or replacement of lost cells?

Two genetically identical daughter cells

What is the overall outcome when a somatic cell duplicates its contents and divides?

Interphase → M phase → cytokinesis

★ HIGH YIELD — What is the overall order of the cell cycle?

G1, S, and G2

Which three phases make up interphase?

Interphase

The extended period between cell divisions that includes growth and DNA replication.

M phase (mitotic phase)

What phase involves division of the cell's genetic information?

Prophase → prometaphase → metaphase → anaphase → telophase

★ HIGH YIELD — What is the correct order of the five stages of mitosis?

Cytokinesis

What process divides the cytoplasm to produce two separate daughter cells?

G1 phase

Which phase is primarily devoted to growth and preparation for DNA synthesis?

RNA/protein synthesis, organelle duplication, and cell growth

What major processes occur during G1?

G1/S checkpoint

What regulated decision point determines whether the cell proceeds toward DNA synthesis?

Restriction point

The point in G1 after which a cell is committed to DNA synthesis in S phase.

Growth-factor stimulation

What does a cell still depend on before passing the restriction point?

No further growth-factor stimulation is required.

What changes after a cell passes the restriction point?

G0 phase

A resting/quiescent state entered by cells in G1 that are not committed to DNA synthesis.

They may reenter the active cell cycle with proper stimulation.

What can happen to quiescent cells in G0?

S phase

★ HIGH YIELD — During which phase does nuclear DNA replication occur?

46 chromosomes are copied to form sister chromatids.

What happens to the human chromosome complement during S phase?

Helicase

Which ATP-dependent enzyme unwinds DNA during S phase?

Multiple replication forks

What allows the entire genome to be duplicated within the time span of S phase?

Approximately 6 hours

Approximately how long does S phase take according to this lecture?

Heterochromatin

According to the slide, into what tightly coiled state do chromosome strands condense after DNA synthesis?

G2 phase

Which phase is the gap between completion of S phase and the start of mitosis?

Preparation for nuclear division

What is the main purpose of G2?

Safety gap

What term does the professor use for G2 because it helps ensure DNA synthesis is complete?

G2/M checkpoint

★ HIGH YIELD — Which checkpoint verifies that DNA is completely replicated and undamaged before mitosis?

Nuclear integrity

What do intracellular regulatory molecules assess at the G2 checkpoint?

Approximately 4 hours

Approximately how long does G2 last according to the lecture?

Mitosis

Division of the nucleus/genetic information and separation of sister chromatids.

Approximately 1 hour

Approximately how long does mitosis take according to the lecture?

Mitosis divides the nucleus/genetic material; cytokinesis divides the cytoplasm.

★ HIGH YIELD — How do mitosis and cytokinesis differ?

Prophase

Which mitotic stage begins chromosome condensation while the nuclear envelope is still intact?

Chromatin condenses into defined chromatids.

What happens to duplicated chromatin during prophase?

Centromere

What region connects the two sister chromatids during prophase?

Kinetochores

What structures form on each chromatid for later spindle attachment?

The nucleolus disassembles.

What happens to the nucleolus during prophase?

Nuclear envelope remains intact.

★ HIGH YIELD — What is the state of the nuclear envelope during prophase?

Prometaphase

Which mitotic stage is characterized by nuclear-envelope breakdown and spindle attachment?

The nuclear envelope disassembles.

★ HIGH YIELD — What major nuclear event distinguishes prometaphase from prophase?

Spindle microtubules bind kinetochores.

What key chromosome-spindle interaction occurs during prometaphase?

Prophase = envelope intact; prometaphase = envelope disassembles and microtubules attach.

★ HIGH YIELD — Distinguish prophase from prometaphase.

Metaphase

★ HIGH YIELD — During which stage do chromatids align at the equator of the spindle?

Metaphase plate

What is the plane formed by chromosomes aligned halfway between the two spindle poles?

Anaphase

Which stage begins when sister chromatids separate and move toward opposite poles?

Centromeres split and paired kinetochores separate.

★ HIGH YIELD — What happens to centromeres and kinetochores during anaphase?

Sister chromatids migrate to opposite spindle poles.

What defining chromosome movement occurs during anaphase?

Polar microtubules elongate and push the mitotic poles apart.

How do the spindle poles move during anaphase?

Telophase

Which mitotic stage reforms nuclei around the separated chromosomes?

Kinetochore microtubules and the mitotic spindle disassemble.

What happens to spindle structures during telophase?

Nuclear envelopes reform.

★ HIGH YIELD — What happens to the nuclear envelope during telophase?

Chromatids decondense and nucleoli reform.

What happens to chromosomes and nucleoli during telophase?

Prometaphase = envelope disappears; telophase = envelope reforms.

★ HIGH YIELD — Contrast nuclear-envelope behavior in prometaphase and telophase.

Metaphase = chromosomes align; anaphase = sister chromatids separate.

★ HIGH YIELD — What is the key difference between metaphase and anaphase?

PPMAT

★ HIGH YIELD — What shorthand gives the order prophase, prometaphase, metaphase, anaphase, telophase?

Prophase = condense; prometaphase = envelope gone/attach; metaphase = middle; anaphase = apart; telophase = two nuclei

★ HIGH YIELD — What are the defining events of PPMAT?

Actin microfilament ring

What contractile structure drives cytokinesis?

Cleavage furrow

What structure forms when the actin-based contractile ring constricts?

Actin ring contracts → cleavage furrow deepens → plasma membranes fuse

What is the sequence of major events during cytokinesis?

A full complement of chromosomes

What chromosome complement does each daughter cell receive?

Approximately half of the parental cytoplasm and organelles

What cytoplasmic contents does each daughter cell receive?

Cyclins, CDKs, and CKIs

★ HIGH YIELD — What three major classes of cell-cycle regulators are emphasized?

Cyclin-CDK complex

What complex possesses the enzymatic activity that drives cell-cycle progression?

Cyclin-dependent kinase inhibitor (CKI)

What type of regulator inhibits cyclin-CDK complexes?

Cyclin concentrations rise and fall; CDK levels remain relatively constant.

★ HIGH YIELD — How do cyclin and CDK concentrations differ during the cell cycle?

Synthesis and degradation

Why do cyclin concentrations rise and fall during the cell cycle?

Cyclin D

G1 regulator that promotes progression through the restriction point.

Cyclins E and A

What are the S-phase regulators

Cyclins B and A

Mitotic-phase regulators

D = G1; E/A = S; B/A = M

★ HIGH YIELD — Match the major cyclin types with their cell-cycle phases.

Cyclins

What proteins are required to activate CDKs?

Serine and threonine residues

Which amino-acid residues on target proteins are phosphorylated by cyclin-CDK complexes?

CDK2

Which CDK activates target proteins involved in the S-phase transition and DNA synthesis?

CDK1

Which CDK activates target proteins needed to initiate mitosis?

Cyclin D–CDK4/6

★ HIGH YIELD — Which cyclin-CDK complex promotes progression past the G1 restriction point?

Cyclin E/A–CDK2

★ HIGH YIELD — Which cyclin-CDK combination regulates initiation of DNA synthesis/S phase?

Cyclin B–CDK1

★ HIGH YIELD — Which cyclin-CDK complex drives the G2→M transition?

D–4/6 = G1; E/A–2 = S; B–1 = M

★ HIGH YIELD — What compact cyclin-CDK map should you know for G1, S, and M?

Cell-cycle checkpoints

Control points that monitor completion of critical events and delay progression if necessary.

G1 checkpoint

Checkpoint that ensures G1 is completed before S phase begins.

Tumor suppressors

Proteins that can halt G1 progression when growth is undesirable or DNA is damaged.

Retinoblastoma (RB) protein

★ HIGH YIELD — What tumor suppressor halts cells in G1?

E2F and DP1/2

What transcription factor complex is inhibited by active RB?

Active RB binds E2F and prevents expression of genes required for S phase.

★ HIGH YIELD — How does active RB inhibit progression out of G1?

Few phosphorylated residues / relatively hypophosphorylated

What phosphorylation state characterizes active RB in resting cells?

Growth-factor signaling through the MAP kinase cascade

What upstream signal promotes RB phosphorylation in cycling cells?

Cyclin D–CDK4/6

Which complex begins phosphorylation of RB after growth-factor stimulation?

Cyclin E–CDK2

Which complex further phosphorylates RB and promotes movement out of G1?

Hyperphosphorylated RB

What form of RB can no longer inhibit E2F?

E2F binds DNA and activates genes required for S phase.

What happens after hyperphosphorylated RB releases E2F?

Low-P RB = active brake; hyper-P RB = inactive brake/E2F free.

★ HIGH YIELD — How does RB phosphorylation status relate to cell-cycle progression?

DNA damage → p53 activation

What event activates the p53 checkpoint pathway?

p53

What tumor suppressor has a major regulatory role in G1 after DNA damage?

Phosphorylation, stabilization, and activation

What happens to p53 in response to nuclear DNA damage?

p21

★ HIGH YIELD — Which CKI is transcriptionally induced by activated p53?

p53 → p21 → cell-cycle arrest → DNA repair

★ HIGH YIELD — Trace the p53 response to repairable DNA damage.

Apoptosis

What does p53 trigger if DNA damage is irreparable?

INK4A

Which CKI class prevents D-type cyclins from activating CDK4 and CDK6?

CIP/KIP

Which CKI class strongly inhibits CDK2 kinases?

p21

Which CKI belongs to the CIP/KIP family?

INK4A → CDK4/6; CIP/KIP → CDK2

★ HIGH YIELD — Match the two CKI classes with their major CDK targets.