cell cycle phases

What is the cell cycle?

A series of events within a eukaryotic cell that prepare it to divide into two new cells.

Who named the process of nuclear division “mitosis”?

Flemming in 1882.

What does the term “mitosis” mean?

It comes from Greek “mito,” meaning “thread,” describing the appearance of condensed chromosomes.

What was the initial belief about interphase?

It was thought to be a resting stage when cells were inactive.

What did Howard and Pelc’s experiment show?

DNA is synthesized only during a specific portion of interphase, not continuously.

What is the generation time in onion root tip cells?

About 30 hours.

How long is the DNA synthesis phase (S phase) in onion root tip cells?

About 6 hours.

What are the main functions of the cell cycle?

Growth, tissue repair, renewal, and reproduction in unicellular organisms.

What are the two main stages of the cell cycle?

Interphase and Mitotic (M) phase.

What happens during interphase?

The cell grows and duplicates its DNA.

What happens during the mitotic phase?

The cell divides its DNA and cytoplasm to form two new cells.

List the 5 main phases of the eukaryotic cell cycle.

G1, S, G2, M, and C (cytokinesis).

What occurs during the G1 phase?

Intense biosynthetic activity and cell growth.

List key functions of the G1 phase.

Cell growth, synthesis of RNA and proteins, organelle duplication, and response to growth signals.

What regulates the G1 phase?

Integration of extracellular signals, metabolic cues, and DNA surveillance.

What happens if a cell doesn’t reach sufficient size?

It cannot divide (as shown in the amoeba microsurgery experiment).

What is the G0 phase?

A resting (quiescent) phase where cells exit the cycle.

Give examples of cells in G0 phase.

Neurons and cardiac muscle cells.

Can G0 cells re-enter the cycle?

Yes, under specific signals like liver regeneration.

What occurs during the S phase?

Chromosomes replicate, forming two sister chromatids joined at the centromere.

Why must DNA replication be exact?

To prevent mutations (errors in genetic code).

What is semiconservative replication?

Each new DNA molecule has one old strand and one new strand.

Who proposed semiconservative replication?

Watson and Crick.

What enzyme unwinds the DNA helix?

Helicase (breaks hydrogen bonds).

What enzyme synthesizes RNA primers?

Primase.

What enzyme adds new nucleotides?

DNA polymerase.

What enzyme joins DNA fragments?

Ligase.

What is the result of DNA replication?

Two identical DNA molecules, each half-old and half-new.

What happens during G2 phase?

Cell continues to grow, produces proteins, and prepares for mitosis.

What does the G2 checkpoint ensure?

DNA is fully replicated and undamaged before mitosis.

Why are cell cycle gaps important?

They allow time for the cell to assess its condition before division.

What are checkpoints in the cell cycle?

Control mechanisms ensuring accurate DNA replication and division.