Biology Chapter 8 - The Cell Cycle

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Questions and Answers

What is the correct sequence of phases in the eukaryotic cell cycle?

S, G1, M, G2

M, G2, S, G1

G1, S, G2, M (correct)

G1, G2, M, S

Which phase in binary fission is characterized by the formation of a septum?

Division phase (correct)

Replication phase

Interval phase

Termination phase

During which phase does DNA replication occur in the eukaryotic cell cycle?

M phase

G2 phase

G1 phase

S phase (correct)

What initiates the division phase in binary fission?

FtsZ protein formation Signup and view all the answers

Which of the following is not a checkpoint phase in the cell cycle?

S checkpoint Signup and view all the answers

What characterizes the G0 phase in the cell cycle?

Cellular resting phase Signup and view all the answers

Which protein complex is essential for cyclin-dependent kinase (CDK) activation?

Cyclin Signup and view all the answers

What is the main outcome of the G1 phase in the eukaryotic cell cycle?

Preparation for DNA synthesis Signup and view all the answers

What defines a quiescent cell in the context of the cell cycle?

It is temporarily dormant but can re-enter the cell cycle. Signup and view all the answers

What role do cyclin-dependent kinases (CDKs) play in the cell cycle?

They are stable in concentration and activate various cyclins. Signup and view all the answers

Which checkpoint is primarily responsible for ensuring adequate cell size and that DNA is undamaged before DNA replication?

G1/restriction checkpoint Signup and view all the answers

What is the primary function of the p53 protein during the cell cycle?

Inducing apoptosis in response to extensive DNA damage. Signup and view all the answers

What distinguishes nucleotide excision repair (NER) from other DNA repair mechanisms?

It targets DNA damage from environmental factors like UV rays. Signup and view all the answers

Which of the following cell cycle phases is characterized by DNA replication?

S phase Signup and view all the answers

What is the main consequence of defective double-strand break (DSB) repair mechanisms?

Chromosomal instability and rearrangements. Signup and view all the answers

At which checkpoint is the integrity of chromosomes primarily assessed before entering mitosis?

G2-phase checkpoint Signup and view all the answers

Which repair mechanism is strand-specific and primarily corrects DNA replication errors?

Mismatch repair (MMR) Signup and view all the answers

How do cyclins affect CDKs during the cell cycle?

Cyclins stabilize CDKs' kinase activity. Signup and view all the answers

Which condition is associated with mutations in mismatch repair genes?

Hereditary nonpolyposis colorectal cancer Signup and view all the answers

During which phase of the cell cycle is homologous recombination repair (HR) most active?

S phase Signup and view all the answers

Which phase marks the transition from G0 to G1 and is influenced by CDK3 and cyclin-C?

G1 phase Signup and view all the answers

What is the primary role of the ATM protein in DNA damage repair?

Facilitating repair of double strand breaks Signup and view all the answers

Which pathways are primarily involved in cellular senescence?

p53/p21 and p16/pRB Signup and view all the answers

What happens during the intrinsic pathway of apoptosis when a cell is damaged?

Mitochondrial substances are released into the cytoplasm Signup and view all the answers

What triggers the extrinsic pathway of apoptosis?

Signals from other cells Signup and view all the answers

What is a key characteristic of apoptosis compared to necrosis?

Cell death occurs without damaging neighboring cells Signup and view all the answers

What occurs after the activation of the apoptosis pathway?

Cytoskeleton collapses Signup and view all the answers

Which of the following describes cellular senescence?

Irreversible arrest of cell proliferation Signup and view all the answers

In what phase of the cell cycle do checkpoint pathways regulate DNA repair mechanisms?

Throughout all phases of the cell cycle Signup and view all the answers

Which statement about apoptotic caspases is true?

They are synthesized as inactive precursors called procaspases Signup and view all the answers

How does damage to DNA lead to cell cycle progression arrest?

Activation of checkpoint pathways Signup and view all the answers

Study Notes

Lecture 8 - The Cell Cycle

The cell cycle is the period between successive cell divisions.
Binary fission is the normal life cycle of bacterial cells.
Binary fission involves three phases: Replication phase (R-phase/C-period), Division phase (D-phase/D-period), and Interval phase (I-phase/B-period).
Replication phase is the time taken to replicate the bacterial genome.
Division phase involves the segregation of daughter chromosomes and cell components to daughter cells. This is initiated by FtsZ proteins forming a Z-ring at the midpoint of the cell, leading to septum formation.
Interval phase is the period between the division process and initiation of chromosome replication.
Prokaryotic cells divide by binary fission.

Cell Cycle in Eukaryotes

Interphase includes G1, S, and G2 phases.
G1 phase is the gap phase after cell division, with variable duration depending on cell type. Cells check for sufficient resources before entering the S phase.
S phase is DNA synthesis, where DNA replication occurs.
G2 phase is the gap after DNA synthesis, where cells check for complete replication.
M phase (mitosis) is the phase where the cell actually divides.
GO phase is a resting phase where some cells exit the cell cycle. Some GO cells can re-enter the cell cycle and others cannot. Quiescent cells are in a dormant state, and senescent cells are aging or deteriorating.
Cyclins-CDK complexes regulate the eukaryotic cell cycle.
G1, S, and M-phase cyclins-CDK complexes have specific functions.
Cell cycle checkpoints monitor cell cycle progression, ensuring that the cell is in a suitable state for the next stage. Checks are done for appropriate cell size, DNA replication, integrity of chromosomes, and accurate segregation during mitosis.

CDKs and Checkpoints

CDKs (cyclin-dependent kinases) and cyclins regulate progression through the cell cycle.
Cell cycle checkpoints are surveillance mechanisms that monitor the order, integrity, and fidelity of cell cycle events.
There are different checkpoints that regulate the different phases of the cell cycle.
G1/restriction checkpoint
G2/M checkpoint
Intra-S-phase checkpoint
Spindle assembly checkpoint

DNA Repair

DNA repair mechanisms deal with endogenous and exogenous factors that damage DNA.
There are multiple DNA repair mechanisms, including Nucleotide Excision Repair (NER) and Mismatch Repair (MMR).
NER repairs distortions in the DNA double helix, especially those caused by UV light.
MMR corrects errors in DNA replication.
Defects in NER or MMR pathways can cause human diseases like Xeroderma pigmentosum (XP) and hereditary nonpolyposis colorectal cancer (HNPCC), respectively.

Cell Aging and Apoptosis

Cellular senescence is an irreversible arrest of cell proliferation. Two main pathways are involved - p53/p21 and p16/pRB.
Apoptosis (programmed cell death) is a natural process in multicellular organisms.
Apoptosis leads to fragmentation of DNA, shrinkage of cytoplasm, and membrane changes without lysis or damage.
Apoptosis involves a cascade of caspase activation.
Apoptosis can be triggered by internal or external signals, and its regulation contributes to normal tissue homeostasis.

Base Excision Repair (BER)

BER is responsible for removing small, non-helix-distorting errors that occur during DNA replication, such as oxidized or alkylated bases.
This is a crucial mechanism to maintain genomic integrity.

Homologous Recombination Repair (HR) and Non-Homologous End Joining (NHEJ)

Both HR and NHEJ repair double-strand breaks (DSBs) in DNA.
HR uses a homologous template for accurate repair, while NHEJ is a quicker but potentially less accurate method.
The choice of repair pathway often depends on the cell cycle stage.

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Description

Explore the intricate details of the cell cycle, including both prokaryotic and eukaryotic cell division. Delve into binary fission and the phases of interphase, examining how cells replicate and divide. This quiz covers essential concepts in cellular biology and the life cycle of cells.