Mol bio lecture 2 pt1

Questions and Answers

What is the primary purpose of the G1 phase in the cell cycle?

To prepare for DNA replication and monitor external signals (correct)

To divide the nucleus and cytoplasm into two daughter cells

To ensure accurate DNA replication has occurred

To perform apoptosis and eliminate damaged cells

Which checkpoint is critical for determining whether a cell proceeds to DNA replication?

G2 checkpoint

M checkpoint

G1 restriction point (correct)

Cytokinesis checkpoint

In which phase does the cell ensure all DNA has been accurately replicated before division?

M Phase

S Phase

G1 Phase

G2 Phase (correct)

What happens during cytokinesis?

The cytoplasm divides, resulting in two separate daughter cells Signup and view all the answers

Which regulatory molecules are primarily involved in the checkpoint processes of the cell cycle?

Cyclins and cyclin-dependent kinases (CDKs) Signup and view all the answers

What triggers G1 senescence in a cell?

Changes in chromosomes or DNA damage Signup and view all the answers

During which phase does DNA replication occur?

S Phase Signup and view all the answers

What is the consequence of a cell entering the G0 phase?

The cell remains metabolically active but can no longer divide Signup and view all the answers

Which of the following correctly matches a phase with its activity?

G1 Phase: Protein synthesis and preparation for DNA replication Signup and view all the answers

Which statement about checkpoints in the cell cycle is accurate?

Checkpoints ensure genomic stability by regulating cell growth and division Signup and view all the answers

What is the primary function of hyperphosphorylated Rb in the cell cycle?

To enable cell entry into the S phase Signup and view all the answers

How does E2F-dependent transcription influence the cell cycle?

It initiates transcription of genes necessary for DNA replication Signup and view all the answers

Which statement correctly contrasts cyclins and CDKs?

Cyclins activate CDKs only during specific phases, while CDKs are always active. Signup and view all the answers

What happens as a result of increased activity of CDK2?

Phosphorylation of target proteins occurs to promote replication Signup and view all the answers

What is the role of cyclins in the cell cycle?

They regulate the timing of CDK activation during specific phases. Signup and view all the answers

During which phase do cyclins specifically trigger the activity of CDK2?

S phase Signup and view all the answers

Which enzyme is directly responsible for the phosphorylation events that drive the cell cycle forward?

Cyclin-dependent kinase (CDK) Signup and view all the answers

What is the consequence of blocking E2F-dependent transcription?

Inhibition of DNA synthesis and cell cycle progression Signup and view all the answers

Which of the following statements about cyclins is false?

Cyclins are stable proteins that do not change throughout the cell cycle. Signup and view all the answers

What triggers the upregulation of CDK2 during the cell cycle?

The activation of E2F-dependent transcription Signup and view all the answers

What is the initial step in E2F promoter repression during the cell cycle?

Binding of pRb to E2F transcription factors Signup and view all the answers

Which protein complex is primarily responsible for the phosphorylation of pRb?

Cyclin D/CDK4 complexes Signup and view all the answers

In which phase of the cell cycle is hypophosphorylated pRb predominantly found?

G1 phase Signup and view all the answers

What is the consequence of pRb hyperphosphorylation during cell cycle progression?

Release of E2F transcription factors Signup and view all the answers

What defines the activity of transcription factor complexes in cell cycle regulation?

Binding to specific DNA sequences at target gene promoters Signup and view all the answers

What is the role of E2F transcription factors in the cell cycle?

Activating genes necessary for DNA replication Signup and view all the answers

Which of the following is a characteristic of pRb in its hypophosphorylated state?

It prevents E2F from binding to promoters Signup and view all the answers

What mechanism leads to E2F activation during the cell cycle?

Phosphorylation of pRb by cyclin/CDK complexes Signup and view all the answers

Which cyclin-CDK pair is primarily involved in the G1/S transition?

Cyclin E + CDK2 Signup and view all the answers

What is the primary role of the p53 molecule in the cell cycle?

Inducing cell cycle arrest or apoptosis in response to DNA damage Signup and view all the answers

At which phase does Cyclin A + CDK1/2 have its maximum activity?

S phase and early G2 phase Signup and view all the answers

Which effect does the phosphorylation of Rb (Retinoblastoma protein) have on cell cycle regulation?

Releases E2F to promote DNA synthesis Signup and view all the answers

What primarily regulates the activity of CDKs?

Phosphorylation events Signup and view all the answers

What is the function of p21 in the context of cell cycle regulation?

Inhibits cyclin/CDK activity in response to DNA damage Signup and view all the answers

Which statement correctly describes CDK levels throughout the cell cycle?

CDK levels remain constant throughout the cell cycle. Signup and view all the answers

How do cyclins contribute to cell cycle progression?

By activating CDKs to control different phases of the cell cycle Signup and view all the answers

Which cyclin-CDK pair is involved in the increase of activities during the G1 phase?

Cyclin D + CDK4, CDK6 Signup and view all the answers

What role does the E2F transcription factor play in cell cycle regulation?

It supports the transition from G1 to S phase by promoting DNA synthesis Signup and view all the answers

When are cyclins typically degraded?

When their function is no longer needed. Signup and view all the answers

Which cyclin peaks during G2 and M phases?

Cyclin B Signup and view all the answers

How is the expression of cyclins characterized throughout the cell cycle?

It is highly variable and regulated. Signup and view all the answers

What is the relationship between cyclins and CDKs in terms of action?

Cyclins activate CDKs and regulate cell cycle progression. Signup and view all the answers

Which factor is responsible for the timing of cyclin availability during the cell cycle?

Specific regulatory proteins Signup and view all the answers

Study Notes

E2F Promoter Activation and Repression

Repression Mechanism: In G1 phase, hypophosphorylated pRb binds to E2F transcription factors, preventing gene activation necessary for S phase.
Additional Repressors: Proteins p107 and p130 further inhibit E2F activity.
Activation Process: Cyclin/CDK complexes phosphorylate pRb, allowing release of E2F transcription factors.
E2F Function: Once released, E2F binds to promoters, stimulating transcription of genes for DNA replication.

pRb Phosphorylation States

Hypophosphorylated pRb:
- Binds tightly to E2F, repressing its activity; associated with early G1 phase.
Hyperphosphorylated pRb:
- Released E2F enables activation of genes for DNA replication; occurs during late G1 and S phase.

Role of Transcription Factor Complexes in Cell Cycle Regulation

Overview: Transcription factor complexes regulate gene expression critical for cell cycle progression.
Key Players: E2F transcription factors are vital for activating genes required for DNA synthesis and S phase entry.

Cell Cycle Stages and Steps

G1 Phase:
- Cell growth, preparation for DNA replication, normal functions, external signal monitoring.
S Phase:
- DNA replication occurs, ensuring that chromosomes are duplicated accurately.
G2 Phase:
- Continued cell growth, ensuring complete and correct DNA replication, final preparations for mitosis.
M Phase (Mitosis):
- Division of the nucleus and cytoplasm into two daughter cells; includes prophase, metaphase, anaphase, and telophase.
Cytokinesis:
- Final cytoplasmic division resulting in two separate daughter cells.
Checkpoints:
- Regulate cell growth, DNA integrity, and division to maintain genomic stability.

G0 Phase

Description: Exit from the cell cycle; cells remain metabolically active but do not divide.
Characteristics: Cells can become senescent and require changes to return to active division.
Triggers for Senescence: G1 senescence due to chromosome changes or DNA damage; G2 only from DNA damage.

Activities During Cell Cycle Stages

G1 Activities:
- Growth, protein and organelle synthesis, preparation for DNA synthesis.
S Phase Activities:
- DNA replication and chromosome duplication; controlled by E2F activity and CDK regulation.

Cyclins and Cyclin-Dependent Kinases (CDKs)

Cyclins:
- Regulatory proteins synthesized and degraded at specific cell cycle points, determining CDK activation.
CDKs:
- Enzymes phosphorylating target proteins to drive cell cycle progression; require cyclin binding for activity.

Cyclin-CDK Pairs and Cell Cycle Stages

Cyclin D + CDK4, CDK6: Active in G1 phase.
Cyclin E + CDK2: Peaks at G1/S transition.
Cyclin A + CDK1/2: Active during S phase and early G2 phase.
Cyclin B + CDK1: Peaks in G2 and M phase.

Key Molecules in Cell Cycle Regulation

p53: Induces cell cycle arrest or apoptosis in response to DNA damage; activates p21.
pRb: Inhibits E2F to prevent transition to S phase; releases E2F upon phosphorylation.
p21: Inhibits cyclin/CDK complexes, halting cell cycle progression for DNA repair.
E2F: Transcription factor promoting S phase genes; regulated by pRb.
Cyclins: Activate CDKs to regulate the cell cycle phases; specific cyclins serve distinct phases.

Consequences of Changes in Regulation

E2F Binding: Impacted by pRb phosphorylation status, affecting DNA replication.
Cyclin/CDK Activity: Changes can lead to premature or delayed cell cycle progression.
Fatty Acid Metabolism: Influenced by cell cycle regulatory processes.
Transcription Factor Complexes: DREAM complex binding can suppress transcription, influencing cell cycle control.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on cyclins and their role in cell cycle regulation. Understand how cyclins activate CDKs and the mechanisms involved in their degradation. This quiz will help you explore the various regulators and phases of the cell cycle.