The Cell Cycle Flashcards
List the main phases of the cell cycle and correlate them with the changes in DNA content that occur throughout the cycle:
G1 phase - DNA content remains constant at 2n meaning there is a single set of chromosomes
S phase - DNA content increases from 2n to 4n as each chromosome is copied
G2 phase - check for DNA replication errors
M phase - phase of cell division, cytokinesis occurs
Summarise cell cycle control system driven by cyclin-dependent kinases (Cdk)
Central Mechanism: Driven by Cyclin-Dependent Kinases (Cdks).
Cdks are activated by binding to specific cyclins and phosphorylate target proteins to progress the cycle.
Checkpoint Regulation: Ensures proper completion of key events (e.g., DNA replication, spindle assembly).
Correlate different cyclin-Cdk complexes with each phase of the cell cycle
G1 Phase: Cyclin D-Cdk4/6 → Drives progression through G1 and prepares for S phase.
S Phase: Cyclin E-Cdk2 → Initiates DNA replication.
G2 Phase: Cyclin A-Cdk2 → Prepares for mitosis.
M Phase: Cyclin B-Cdk1 (Cdc2) → Triggers mitotic entry.
Identify reversible phosphorylation of proteins as the central signalling mechanism employed by the subsystems of cell cycle control
Key Mechanism: Central signaling mechanism in cell cycle control.
Kinases: Add phosphate groups to proteins (e.g., Cdks).
Phosphatases: Remove phosphate groups, reversing effects.
Importance: Allows rapid and reversible regulation of protein activity.
Recognise the importance of transcriptional control of the cell cycle through regulated expression of genes involved in cycle progression and DNA replication.
Key Concept: Regulated expression of genes ensures proper cycle progression.
E.g., Cyclin expression peaks at specific phases.
Transcription factors like E2F regulate genes for DNA replication and cycle progression.
Importance: Synchronises gene expression with phase-specific activities.
Discuss cycle control through proteolysis directed by the ubiquitin-ligases APC/C and SCF
Ubiquitin Ligases:
APC/C (Anaphase-Promoting Complex/Cyclosome): Targets cyclin B and securin for degradation to exit mitosis.
SCF (Skp, Cullin, F-box complex): Degrades cyclin E and Cdk inhibitors (e.g., p27) for G1/S transition.
Process: Proteins tagged with ubiquitin are degraded by the proteasome.
Outline roles of Cdk inhibitory proteins and transcriptional suppressor protein Rb1
Cdk Inhibitory Proteins (CKIs):
p21, p27, p16 - block Cdk activity to halt cell cycle progression under stress or damage.
Retinoblastoma Protein (Rb1):
Binds E2F transcription factors in its hypophosphorylated state to inhibit progression from G1 to S phase.
Phosphorylation by Cyclin D-Cdk4/6 inactivates Rb1, releasing E2F for transcription of S phase genes.
Describe eukaryotic chromosomes:
Function - genetic information storage
46 chromosomes (23 homologous pairs)
Chromatin - when chromosomes aren’t dividing
Chromatids - duplicated chromosomes
Centrosome - kinetochore and microtubule spindle attachment
Describe interphase:
G1 phase - increase in size
S phase - DNA replication, Two sister strands of DNA produced
G2 phase - Organelles double
New cytoplasm forms
Mitotic structure forms
What is the G0 phase ?
Resting or quiescent phase in the cell cycle where cells exit the regular cycle of division
Cells in the G₀ phase are metabolically active but do not actively prepare for DNA replication or cell division
Quiescence is a reversible state in which cells can re-enter the cell cycle in response to specific signals
Sensence - cells remain in G₀ and cannot re-enter the cell cycle
What are the stages of M phase ?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
What are the 3 types of spindle used in metaphase ?
Aster microtubules
Kinetochore microtubules
Interpolar microtubules
Describe metaphase:
Centrosomes localise to opposite ends of the cell
Chromosomes line up on the metaphase plate
Microtubules finish attaching to kinetochores
Describe prophase and prometaphase:
Prophase;
Chromatin begins to condense and centrosomes duplicate
Nuclear envelope begins to dissolve
Mitotic spindle begins forming
Duplicated chromosomes condense under the control of protein complexes called condensins regulated by M-Cdk
Prometaphase;
Chromosomes completely duplicate
Microtubules begin to attach to kinetochores
Non-kinetochore microtubules begin to extend
Describe anaphase
Chromosomes break apart
Sister chromatids are pulled apart toward opposite poles
The cell elongates as non-kinetochore microtubules lengthen
Shortest stage
