Eukaryotic Cell Cycle and Chromosomes

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Questions and Answers

What is the diploid number of chromosomes in humans?

46 (correct)

What characterizes a haploid cell?

It consists of sister chromatids.

It has two sets of chromosomes.

It contains 46 chromosomes.

It represents one set of chromosomes. (correct)

What makes up a homologous chromosome pair?

Sister chromatids

Two identical chromosomes

Two different chromosomes

Two chromosomes of the same kind (correct)

What occurs prior to DNA replication in chromosomes?

Each chromosome is composed of a single DNA molecule. Signup and view all the answers

What holds together sister chromatids after replication?

Cohesin proteins Signup and view all the answers

During which phase of the cell cycle does primary growth occur?

G1 Phase Signup and view all the answers

How many sister chromatids are present in a replicated chromosome?

Two Signup and view all the answers

What distinguishes replicated homologous chromosomes from non-replicated homologous chromosomes?

Number of chromatids Signup and view all the answers

What is the primary role of the G1/S checkpoint in the cell cycle?

To determine if the cell should commit to DNA replication Signup and view all the answers

Which condition will NOT cause the cell cycle to halt at the G1/S checkpoint?

Presence of growth factors Signup and view all the answers

At which checkpoint does the cell confirm that DNA replication has been successfully completed?

G2/M checkpoint Signup and view all the answers

What is assessed at the late metaphase/spindle checkpoint?

The attachment of chromosomes to the spindle Signup and view all the answers

What can cause the G2/M checkpoint to halt the cell cycle?

DNA damage Signup and view all the answers

What is the significance of growth factors at the G1/S checkpoint?

They signal the cell to enter the S phase Signup and view all the answers

Which of the following describes 'genomic fidelity' as related to the G2/M checkpoint?

The accuracy of DNA replication Signup and view all the answers

What happens at the spindle checkpoint if not all kinetochores are attached to spindles?

The cell cycle halts Signup and view all the answers

What primarily occurs during the G2 phase of the cell cycle?

Organelles replicate and microtubules organize Signup and view all the answers

How long does the M phase typically last in the cell cycle?

1 hour Signup and view all the answers

Which statement accurately describes the duration of the cell cycle across different organisms?

Liver cells can take more than a year to complete a cell cycle. Signup and view all the answers

What is a major event occurring during the S phase of interphase?

Replication of DNA Signup and view all the answers

Cells that enter the resting phase G0 are characterized by what?

Permanent exit from the cell cycle Signup and view all the answers

Which phase of the cell cycle is primarily responsible for the actual division into two daughter cells?

M phase Signup and view all the answers

During which phase of the cell cycle does the most variation in length occur?

G1 phase Signup and view all the answers

What defines the relationship between sister chromatids after the S phase?

They are identical copies joined at the centromere. Signup and view all the answers

What is the primary role of cyclin-dependent kinases (Cdks) in the cell cycle?

Phosphorylate proteins to regulate the cell cycle Signup and view all the answers

How are Cdks activated?

Through binding with cyclins and phosphorylation Signup and view all the answers

What does the term 'mitosis-promoting factor' (MPF) refer to?

The complex of Cdk and cyclin that regulates the cell cycle Signup and view all the answers

What effect does phosphorylation at one site on Cdk have?

It inactivates the Cdk Signup and view all the answers

Which Cdk-cyclin pair is associated with the G1/S checkpoint in mammalian cells?

Cdk2/Cyclin E Signup and view all the answers

What is the function of the Anaphase-Promoting Complex (APC)?

To mark securin for destruction and trigger anaphase Signup and view all the answers

What role do growth factors play in the regulation of the cell cycle?

They trigger intracellular signaling systems to stimulate cell division Signup and view all the answers

Which checkpoint does the APC/c operate at during the cell cycle?

Spindle checkpoint Signup and view all the answers

What is a common misconception regarding the role of cyclins in the cell cycle?

Cyclins solely determine the timing of cell cycle phases Signup and view all the answers

Which of the following is NOT true about cyclin-dependent kinase (Cdk) regulation?

Cdks operate independently without external signals. Signup and view all the answers

How does the spindle checkpoint relate to Cdk activity?

It relies on APC activity for proper functioning. Signup and view all the answers

What is one of the consequences of losing control of the cell cycle?

Increased likelihood of cancer development Signup and view all the answers

What ensures the proper timing and progression through the cell cycle in eukaryotic cells?

Interaction between Cdks and cyclins along with phosphorylation Signup and view all the answers

In multicellular eukaryotes, what is the impact of external signals on the cell cycle?

They allow more complex control of the cell cycle. Signup and view all the answers

What role does the p53 protein play in the cell cycle?

Monitors DNA integrity Signup and view all the answers

What is the function of tumor-suppressor genes in the cell cycle?

Prevent the development of mutated cells Signup and view all the answers

What is required for a cancerous phenotype to develop related to tumor-suppressor genes?

Both copies of the gene must lose function Signup and view all the answers

How does the Rb protein function in controlling the cell cycle?

Inhibits signals from growth factors Signup and view all the answers

What happens when proto-oncogenes mutate?

They can cause uncontrolled cell division Signup and view all the answers

What is the initial trigger for developing retinoblastoma linked to the Rb gene?

Inherited a single mutant copy of Rb Signup and view all the answers

What is NOT a characteristic of proto-oncogenes?

They function as tumor-suppressor genes Signup and view all the answers

What is a consequence of p53 being absent or damaged in cells?

Failure to halt damaged cell division Signup and view all the answers

What type of mutation in growth factor receptors can lead to cancer?

Mutations that render the receptor 'on' Signup and view all the answers

Which of the following accurately describes the nature of tumor-suppressor genes?

They inhibit cell division Signup and view all the answers

What is the role of repair enzymes when DNA damage is detected by p53?

To attempt repair of the damaged DNA Signup and view all the answers

Why do mutations in both copies of a tumor-suppressor gene increase cancer risk?

They remove checkpoints in the cell cycle Signup and view all the answers

What dual role does the p53 protein play in relation to the cell cycle?

Monitors DNA integrity and induces apoptosis Signup and view all the answers

Study Notes

Eukaryotic Chromosomes

Humans are diploid (2n), meaning they have two complete sets of chromosomes, totaling 46.
Humans are also haploid (n), meaning they have one set of chromosomes, totaling 23.
Homologous chromosomes are pairs of the same kind of chromosome, each one being a homologue.

Replication

Each chromosome is composed of a single DNA molecule before replication occurs.
After replication, each chromosome consists of two identical DNA molecules.
These identical molecules are held together by cohesin proteins, appearing as two strands bound together as the chromosome condenses.
One chromosome is composed of two sister chromatids.

Overview of Eukaryotic Cell Cycle

The eukaryotic cell cycle can be broken down into two main phases: interphase and M phase.
Interphase is the longest phase of the cell cycle and is further divided into G1, S, and G2 phases.
G1 is the primary growth phase
S is the phase in which DNA replicates.
G2 is the phase in which organelles replicate and microtubules organize.
M phase is the separation of the nucleus into two daughter cells, further divided into five phases.
C is the division of the cytoplasm for two new cells.

Duration of Cell Cycle

The time required for a cell cycle can vary greatly and depends on the type of cell.
Embryonic cells, such as those of a fruit fly, may complete a cycle in just 8 minutes.
Mature cells take significantly longer to grow, with mammalian cells taking about 24 hours, and liver cells taking an entire year.
Growth occurs during G1, G2, and S phases, with M phase lasting only about an hour.
G1 is typically the longest phase, and some cells enter a resting phase known as G0 where they may pause for longer periods.

Interphase

The G1/S checkpoint determines whether a cell will commit to DNA replication and, consequently, cell division.
The G1/S checkpoint is the primary point of external signal influence, particularly responding to growth factors.
Growth factors are peptides that signal cells to grow and divide when the environment is favorable.
The G1/S checkpoint can halt the cell cycle if there is DNA damage, starvation conditions, or a lack of growth factors (GFs).
The G2/M checkpoint ensures DNA replication is successful before allowing the cell to proceed into mitosis.
This checkpoint halts the cell cycle in the presence of DNA damage or inaccuracies in DNA replication.
The spindle checkpoint confirms all chromosomes are attached to the spindle before committing to the separation of the chromosomes in anaphase.
The spindle checkpoint halts the cell cycle if any kinetochores are not attached to spindles.

Control of Cell Cycle

Cyclin-dependent kinases (Cdks) are enzymes that phosphorylate proteins and play a crucial role in cell cycle control
These enzymes work in conjunction with cyclins at different points in the cell cycle.
Cdk's activity is also controlled by phosphorylation.

Cdk - cyclin complex

Cdk enzymes form complexes with cyclins and regulate the cell cycle.
This complex is also known as mitosis-promoting factor (MPF).
The activity of the Cdk-cyclin complex is regulated by a pattern of phosphorylation. Phosphorylation at specific sites, either activates or inactivates the complex.

Control in Multicellular Eukaryotes

Multiple Cdks regulate the cell cycle.
Animal cells are more responsive to external signals, allowing for more complex control of the cell cycle.
Each checkpoint is controlled by a particular Cdk-cyclin (or MPF).
Key mammalian MFPs include:
G1/S- Cdk2/Cyclin E
G2/M- Cdk1/Cyclin B
Spindle Checkpoint- APC

Anaphase-Promoting Complex (APC)

The anaphase-promoting complex (APC), or cyclosome (APC/C), is a protein complex that triggers anaphase.
Its function is to mark securin for destruction, which allows separase to destroy cohesin, initiating the separation of sister chromatids.
APC is composed of many proteins, making it a complex structure for memorization.

Growth Factors

Growth factors trigger intracellular signaling processes.
Platelet-derived growth factor (PDGF), one of the first identified growth factors, activates its receptor, a receptor tyrosine kinase (RTK), which initiates a MAP kinase cascade to stimulate cell division.
Growth factors can override cellular controls that normally inhibit cell division.

Cell cycle and cancer

Cancer is characterized by unrestrained and uncontrolled cell growth, resulting from a failure in cell cycle control.
Cancer-causing mutations occur in two types of genes: tumor suppressor genes and proto-oncogenes.

Tumor-Suppressor Genes

P53 plays a vital role in the G1 checkpoint.
It monitors the integrity of DNA, halting cell division if damage is detected.
P53 allows repair enzymes to act on the damaged DNA and triggers cell death if the damage is irreparable.
Tumor suppressor genes prevent the development of mutated cells carrying mutations.
Many cancerous cells lack or have damaged p53.
The retinoblastoma susceptibility gene (Rb), identified as the first tumor suppressor, predisposes individuals to a rare form of cancer affecting the retina of the eye.

Retinoblastoma

Inheriting a single mutant copy of the Rb gene leaves individuals with only one functional copy.
If the remaining functional gene is damaged during the many cell divisions required to produce the retina, a cancerous cell can arise.
A single cancerous cell within the retina can eventually develop into a retinoblastoma tumor.
The Rb protein integrates signals from growth factors, binding to essential regulatory proteins to prevent cyclin and Cdk production.

Proto-Oncogenes

These are normal cellular genes that can transform into oncogenes when mutated, potentially causing cancer.
Some encode receptors for growth factors, leading to uncontrolled cell division if the receptor is mutated to a constitutive “on” state, rendering the cell independent of growth factors.
Others encode proteins involved in signal transduction.
Only one copy of a proto-oncogene needs to have a mutation for uncontrolled cell division to occur.

Cell Division/Cycle Videos

Several videos are provided:
Chromosomal Compaction: Illustrates the process of chromosome compaction.
Binary Fission: Visualizes the process of binary fission, including bidirectional DNA replication.
FtsZ Protein: Briefly explains the function of the FtsZ protein in bacterial cell division.
Bacterial Cell Cycle: A more detailed view of the bacterial cell cycle.
Cell Division Review: Provides a comprehensive overview of cell division.
Cytokinesis: Focuses on the process of cytokinesis.
Control of the Cell Cycle: Explains the different checkpoints and the mechanisms that regulate the cell cycle.
Stimulation of Cell Replication: Illustrates the steps involved in the stimulation of cell replication.
Cell Proliferation Signaling Pathway: Explores the signaling pathway involved in cell proliferation.
Two Examples of How Tumor Suppressor Genes Block Cell Division: Demonstrates the mechanisms by which tumor suppressor genes can block cell division.

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Description

This quiz covers the structure and function of eukaryotic chromosomes, focusing on diploid and haploid states, homologous chromosomes, and the process of replication. Additionally, it explores the phases of the eukaryotic cell cycle, including interphase and its subdivisions. Test your knowledge on these fundamental concepts of cell biology!