Cell Cycle and Mitosis Overview
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Questions and Answers

What protein is maintained at constant levels throughout the cell cycle and requires cyclin to become catalytically active?

cdk

Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle?

G1

Which of the following triggers the cell's passage past the G2 checkpoint into mitosis?

MPF

Why do neurons and some other specialized cells divide infrequently?

<p>They have been shunted into G0.</p> Signup and view all the answers

Which of the following most accurately describes a cyclin?

<p>It activates a Cdk molecule when it is in sufficient concentration.</p> Signup and view all the answers

The cyclin component of MPF is destroyed toward the end of which phase?

<p>M</p> Signup and view all the answers

Which is the first checkpoint in the cell cycle where a cell will be caused to exit the cycle if this point is not passed?

<p>G1</p> Signup and view all the answers

What are proteins that regulate the cell cycle and show fluctuations in concentration called?

<p>cyclins</p> Signup and view all the answers

What statement predicts a natural phenomenon that could occur to prevent cell growth?

<p>As cells become more numerous, the amount of required growth factors and nutrients per cell becomes insufficient to allow for cell growth.</p> Signup and view all the answers

What part of the cell cycle produces two new identical cells?

<p>Cytokinesis</p> Signup and view all the answers

What is observed through a microscope in a plant cell during cytokinesis?

<p>a cell plate beginning to develop</p> Signup and view all the answers

What describes the interphase portion of the cell cycle?

<p>During interphase, a cell is metabolically active.</p> Signup and view all the answers

Who discovered that in DNA from any species, the amount of adenine equals thymine, and guanine equals cytosine?

<p>Chargaff</p> Signup and view all the answers

If cytosine makes up 42% of the nucleotides in a sample of DNA, what percentage of the nucleotides will be thymine?

<p>8</p> Signup and view all the answers

What will be found in an analysis of nucleotide composition of DNA?

<p>A + C = G + T</p> Signup and view all the answers

What is the function of helicase in DNA replication?

<p>It untwists the double helix and separates the two DNA strands.</p> Signup and view all the answers

What does 'antiparallel' refer to in the context of DNA strands?

<p>The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.</p> Signup and view all the answers

What are the repetitive DNA sequences at the ends of eukaryotic chromosomes called?

<p>telomeres</p> Signup and view all the answers

What does semiconservative DNA replication mean?

<p>Each new double helix consists of one old and one new strand.</p> Signup and view all the answers

What is the role of DNA ligase during DNA replication?

<p>It joins Okazaki fragments together.</p> Signup and view all the answers

Which enzyme separates the DNA strands during replication?

<p>helicase</p> Signup and view all the answers

Which enzyme covalently connects segments of DNA?

<p>ligase</p> Signup and view all the answers

What enzyme excises damaged DNA in nucleotide excision repair?

<p>nuclease</p> Signup and view all the answers

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

<p>DNA polymerase III</p> Signup and view all the answers

How do the leading and lagging strands differ?

<p>The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.</p> Signup and view all the answers

Why does a new DNA strand elongate only in the 5' to 3' direction?

<p>DNA polymerase can only add nucleotides to the free 3' end.</p> Signup and view all the answers

What is the function of topoisomerase?

<p>Relieving strain in the DNA ahead of the replication fork.</p> Signup and view all the answers

Which enzyme removes RNA nucleotides from the primer and adds DNA nucleotides to Okazaki fragments?

<p>DNA polymerase I</p> Signup and view all the answers

What does the action of helicase create?

<p>Replication forks and replication bubbles.</p> Signup and view all the answers

Why is the new DNA strand assembled in short segments?

<p>DNA polymerase can only assemble DNA in the 5' to 3' direction.</p> Signup and view all the answers

The synthesis of a new strand begins with the synthesis of a(n) _____

<p>RNA primer</p> Signup and view all the answers

During which phase of mitosis do the chromatids become chromosomes?

<p>anaphase</p> Signup and view all the answers

At which phase are centrioles beginning to move apart in animal cells?

<p>prophase</p> Signup and view all the answers

Which phase of the cell cycle matches with its description: follows cell division?

<p>G1</p> Signup and view all the answers

Where do the microtubules of the spindle originate during mitosis in animal cells?

<p>centrosome</p> Signup and view all the answers

If a group of cells has an average of 8 picograms of DNA immediately after mitosis, how much would be found at the end of S and G2?

<p>16, 16</p> Signup and view all the answers

What happens if colchicine is added to cells in G2?

<p>The chromosomes would coil and shorten but have no spindle to which to attach.</p> Signup and view all the answers

During _____ the cell grows and replicates both its organelles and its chromosomes.

<p>interphase</p> Signup and view all the answers

Which of the following are primarily responsible for cytokinesis in plant cells but not in animal cells?

<p>golgi derived vesicles</p> Signup and view all the answers

What would most affect the movement of chromosomes during anaphase?

<p>shortening of microtubules.</p> Signup and view all the answers

Which measurements in animal cells would you expect to increase from M to G1?

<p>organelle density and enzymatic activity</p> Signup and view all the answers

What effect does Taxol have on animal cells?

<p>Taxol disrupts microtubule formation, affecting mitotic spindle.</p> Signup and view all the answers

What is a cleavage furrow?

<p>a groove in the plasma membrane between daughter nuclei</p> Signup and view all the answers

What results from cells undergoing the cell cycle repeatedly without cytokinesis?

<p>large cells containing many nuclei</p> Signup and view all the answers

Nucleoli are present during _____

<p>Interphase</p> Signup and view all the answers

Cytokinesis often, but not always, accompanies _____

<p>telophase</p> Signup and view all the answers

When do chromosomes become visible?

<p>prophase</p> Signup and view all the answers

When do centromeres divide and sister chromatids become full-fledged chromosomes?

<p>anaphase</p> Signup and view all the answers

During which phase do spindle fibers attach to kinetochores?

<p>prometaphase</p> Signup and view all the answers

During prophase, a homologous pair of chromosomes consists of _____

<p>two chromosomes and four chromatids</p> Signup and view all the answers

Density-dependent inhibition is explained by which of the following?

<p>As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells and they stop dividing.</p> Signup and view all the answers

How are all cell cycle checkpoints similar?

<p>They give the go-ahead signal to progress to the next checkpoint.</p> Signup and view all the answers

What describes cyclin-dependent kinase (Cdk)?

<p>Cdk is present throughout the cell cycle and is an enzyme that attaches phosphate groups to other proteins.</p> Signup and view all the answers

What occurs at the M phase checkpoint?

<p>Separase enzyme cleaves cohesins and allows chromatids to separate.</p> Signup and view all the answers

Study Notes

Cell Cycle Overview

  • Cdk (cyclin-dependent kinase) is a protein that requires cyclin to become active; levels remain constant throughout the cell cycle.
  • The G1 checkpoint is crucial for cells to receive signals that permit division.
  • MPF (M-phase promoting factor) triggers the cell's transition from G2 to mitosis.

Cell Division and Checkpoints

  • Neurons and specialized cells divide infrequently due to being in the G0 phase.
  • Cyclins activate Cdk molecules when present in adequate amounts.
  • The G1 checkpoint is the first critical point where cells can exit the cycle if not passed.

Cell Cycle Regulators

  • Density-dependent inhibition halts cell division once optimal density is reached, sending growth-inhibiting signals through cell-surface protein interactions.
  • Cytokinesis occurs when the cytoplasm divides, resulting in two new identical cells.

Mitosis Process

  • During cytokinesis in plant cells, a cell plate develops across the middle and nuclei form on either side.
  • Interphase is characterized by metabolic activity and preparation for division.

DNA and Nucleotide Facts

  • Chargaff's rule states equal amounts of adenine to thymine, and guanine to cytosine in DNA.
  • If cytosine makes up 42% of nucleotides, thymine will be approximately 8%.
  • Nucleotide composition follows A + C = G + T.

DNA Replication Mechanics

  • Helicase unwinds the double helix, separating DNA strands during replication.
  • DNA replication is semiconservative, producing one old and one new strand in each double helix.
  • Lagging strands are synthesized in short segments because DNA polymerase can only add nucleotides to the 3' end.

Enzymatic Functions in DNA Replication

  • DNA ligase connects Okazaki fragments on the lagging strand.
  • Topoisomerase relieves strain ahead of the replication fork.
  • Nuclease excises damaged DNA in nucleotide excision repair.

Mitosis Phases

  • During anaphase, sister chromatids become separate chromosomes.
  • Prophase marks the time when centrioles begin to move apart, and chromosomes become visible.

Cellular Responses and Drug Interference

  • Addition of colchicine halts spindle formation in G2 phase, leading to unanchored coiling and shortening of chromosomes.
  • Taxol disrupts microtubule formation, affecting the mitotic spindle, halting mitosis despite increasing assembly rates.

Cytokinesis in Different Cells

  • In plant cells, Golgi-derived vesicles are primarily responsible for cytokinesis, unlike animal cells.
  • Cleavage furrows indicate the division groove forming between daughter nuclei in animal cells.

Unique Cell Cycle Considerations

  • Cells can undergo repeated divisions without cytokinesis in certain fungi and algae, leading to large, multinucleated cells.
  • Nucleoli are present during interphase, while cytokinesis may not occur with every telophase.

Checkpoints and Regulation

  • All checkpoints in the cell cycle function similarly by issuing go-ahead signals for progression.
  • Cdk is an enzyme consistently present throughout the cell cycle that modifies other proteins by attaching phosphate groups.
  • At the M phase checkpoint, the separase enzyme cleaves cohesins to facilitate chromatid separation.

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Description

Test your knowledge on the cell cycle, focusing on the roles of Cdk, cyclins, and checkpoints. This quiz also covers the processes of mitosis and cytokinesis, including their regulatory mechanisms. Ideal for students studying cell biology.

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