Cell Cycle

The cell cycle

The series of events that take place in a cell that causes it to divide into 2 daughter cells.

What processes are involved in the cell division cycle?

• Cell growth

• DNA replication

• Distribution of the duplicated chromosomes to daughter cells

• Cell division

How long do most cell cycles take?

15-20 minutes on average. Definitely under 40 minutes.

Which process occupies the most time in prokaryotic cell division?

The chromosome process

Binary fission

A type of asexual reproduction method / cell division used only for bacteria.

What are the stages in binary fission?

• B-period

• C-period

• D-period

B-period

Before replication. The end of cell replication up until the start of DNA replication.

C-period

Chromosome replication. The whole period for chromosomal replication.

D-period

Division. From the end of chromosomal replication until the very end of the cell cycle.

Mitosis

The process in which a eukaryotic cell nucleus splits into 2. It evolved from an early form of binary fission.

Origin of replication

Where binary fission starts. Reactions are catalyzed here by enzymes located in the middle of the cell.

What happens when the ori is duplicated?

The 2 origins actively migrate to the 2 ends of the cell.

How does the cell separate into 2 parts in binary fission?

The cytoplasm divides through a partition in the cell wall material that grows inward until the cell is split.

What are the four parts of eukaryotic cell division?

• G1 phase

• S phase (synthesis)

• G2 phase

• M phase

What parts in eukaryotic cell division make up interphase?

• G1 phase

• S phase (synthesis)

• G2 phase

What is the M phase classified as?

Mitosis and cytokinesis.

How long does interphase extend to?

From the end of one mitosis to the beginning of the next mitosis.

Chromosomes

Nuclear units of genetic information that are divided and distributed by mitotic cell division.

Chromatid

The replication of DNA of each individual chromosome creates 2 identical molecules called sister chromatids.

Chromatin

A complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.

Ploidy

The number of chromosome sets in a cell or species.

Diploid

2n; has 2 sets of chromosomes.

→ includes somatic cells (every cell minus haploid cells such as sperm and egg cells).

Haploid

1n; has 1 set of chromosomes.

What marks the beginning of the cell cycle?

The formation of a new daughter cell.

What order is the cell cycle in?

Since it is a cycle, it can typically occur at any point in the cycle because it is all connected. From beginning to end, it starts with G1 and ends with M.

G1 Phase

Gap 1 / Growth 1. The cell carries out its functions and may grow.

S Phase

Synthesis phase. This is when DNA replication and chromosome duplication occur.

G2 phase

Gap 2 / Growth 2. A brief gap in the cell cycle when cell growth continues and the cell prepares for mitosis and cytokinesis.

After interphase, what are the next stages of mitosis?

• Prophase

• Prometaphase

• Metaphase

• Anaphase

• Telophase

Chromosome segregation

The equal distribution of daughter chromosomes into each of the 2 daughter cells that result from cell division.

Spindle

The cytoskeletal structure that forms during cell division to separate sister chromatids between daughter cells.

What are spindles composed of?

Hundreds of proteins and microtubules.

Centrosome

The main microtubule organizing center of a cell which organizes the microtubule cytoskeleton during interphase and positions many cytoplasmic organelles.

Centromere

The region of a chromosome at which the kinetochore forms and attaches to spindle microtubules during cell division.

Kinetochore

Large protein assemblies that connect chromosomes to microtubules of the mitotic and meiotic spindles in order to distribute the replicated genome from a mother cell to its daughters.

Cleavage furrow

A groove that girdles the cell and gradually deepens until it cuts the cytoplasm into 2.

What part of mitosis does the cleavage furrow occur in?

Cytokinesis

Cell plate

The new cell wall that forms during cytokinesis in terrestrial plants.

Cell plate formation

The process where golgi-derived and endosomal vesicles carrying cell wall and cell membrane components to the plane of cell division and the subsequent fusion of these vesicles within the plate.

Prophase

Chromosomes condense into compact, rod-like structures, and each chromosome is doubled as a result of replication.

What happens to the centrosome in prophase?

It splits into 2 parts and move apart toward opposite poles of the cell which are developing spindles in the cytoplasm.

Prometaphase

The nuclear envelope breaks down and the spindle enters the former nuclear area. Kinetochores form on each chromosome and microtubules from opposite spindle poles attach to 2 kinetochores of each chromosome.

Metaphase

The spindle is fully formed and the chromosomes align at the spindle midpoint. Each sister chromatid pair is held in position by opposing forces.

→ The kinetochore microtubules pulling to the poles

vs

→ The cohesins binding the sister chromatids together

Anaphase

Separase cleaves the cohesion ring holding the sister chromatids together. The spindle separates the sister chromatids and moves them to opposite spindle poles.

At what point is chromosome segregation complete?

Anaphase

Telophase

The chromosomes decondense and there is a return to the extended state that is typical of interphase. A new nuclear envelope forms around the chromosomes and the cytoplasm is beginning to divide by furrowing.

Cytokinesis

The physical process of cell division, where the cytoplasm of a parent cell is divided into 2 daughter cells.

What is cytokinesis like in animal cells?

Involves the formation of a cleavage furrow, which constricts like a drawstring to separate the cells.

What is cytokinesis like in plant cells?

Vesicles from the GA move along the microtubules to the center of the cell and coalesce to form a cell plate, where a cell wall forms between the 2 daughter cells.

Prokaryote cell division

Bacterial chromosomes attach to the PM.

A ring of Ftsz proteins (that are evolutionarily related to tubulins) are present.

Dinoflagellate cell division

The nuclear envelope is intact.

The chromosomes are attached to the nuclear membrane.

Microtubules passing through tunnels in nuclear envelope.

Diatom cell division

The nuclear envelope is intact.

The chromosomes are attached to the kinetochore microtubule.

Most eukaryotic cell division

The nuclear envelope isn’t present during nuclear division.

Chromosomes are attached to kinetochore microtubules.