Eukaryotic Cell Biology Exam 5

Vocabulary Terms

G1 phase

Gap phase for cell growth; cell responds to social and environmental cues

G0 phase

Specialized resting state where cells stop dividing

Restriction point

Commitment point in late G1 where the cell becomes committed to division

S phase

DNA synthesis phase; chromosomes and centrosomes duplicate

G2 phase

Second growth phase; prepares for mitosis

M phase

Mitosis phase where chromosomes segregate

Cytokinesis

Division of the cytoplasm following mitosis

Prophase

Chromosomes condense; sister chromatids held by cohesin

Prometaphase

Mitotic spindle attaches to sister chromatids

Metaphase

Sister chromatids align at the cell center

Anaphase

Cohesin disintegrates; sister chromatids separate

Telophase

Spindle disassembles; nuclear envelope reforms

EdU/BrdU staining

Thymidine analog labeling used to detect cells in S-phase

Flow cytometry

Technique to measure DNA content per cell

Fucci system

Fluorescent cell cycle reporter system based on protein degradation

Geminin

Green fluorescent marker active from early S phase to mitosis

Cdt1

Red fluorescent marker expressed from end of mitosis through G1

Checkpoint

Control mechanism verifying proper progression through cell cycle

Cyclin-dependent kinases (CDKs)

Kinases that regulate cell cycle progression; constant levels

Cyclins

Regulatory proteins that bind CDKs; synthesized and degraded cyclically

G1 cyclins

Cyclins controlling progression through early G1

G1/S cyclins

Cyclins controlling the G1→S transition

S cyclins

Cyclins required for DNA replication

M cyclins

Cyclins required for mitosis

CAK (Cdk-activating kinase)

Phosphorylates and activates CDK–cyclin complexes

Wee1 kinase

Adds inhibitory phosphate to CDKs, inactivating them

Cdc25 phosphatase

Removes inhibitory phosphate from CDKs, activating them

CKIs (p27, p16, p21)

Cdk inhibitor proteins that block CDK–cyclin activity

Proteolysis

Protein degradation, often via ubiquitylation and proteasome

PP2A-B55

Phosphatase that counteracts M-Cdk activity; high in interphase

Greatwall kinase

Kinase activated by M-Cdk; inhibits PP2A-B55 through Ensa

Ensa

Protein phosphorylated by Greatwall that inhibits PP2A-B55

Positive feedback loop

A system where M-Cdk activates Cdc25 and inhibits Wee1, amplifying activation

APC/C (Anaphase-Promoting Complex)

Ubiquitin ligase that targets securing and cyclins for degradation

Securin

Protein that protects cohesin linkages between sister chromatids

Cdc20

Activator of APC/C during metaphase→anaphase transition

Cdh1

Late mitosis/early G1 APC/C activator keeping cyclin levels low

Ubiquitylation

Addition of ubiquitin to proteins to mark them for proteasomal degradation