bio 2. cell life cycle/PMAT/cytokensis

CELL LIFE CYCLE

The cell cycle consists of:

Interphase

• G₀

• G₁

• S

• G₂

followed by:

M phase

• Prophase

• Metaphase

• Anaphase

• Telophase

Then:

Cytokinesis

• Cytoplasm divides

• Produces daughter cells

Interphase

Interphase is the period when the cell:

• Performs normal functions

• Grows

• Copies DNA

• Prepares for cell division

Interphase includes:

G₀ → G₁ → S → G₂

G₀ phase

The cell is not actively progressing through the cell cycle.

It performs its normal specialized functions.

Some cells can remain in G₀ for long periods.

Example:

Many mature neurons remain in G₀.

G₀ = resting/non-dividing state

G₁ phase

G₁ phase

The cell:

• Grows

• Performs normal cellular activities

• Produces proteins

• Produces organelles

• Prepares for DNA replication

Remember:

G₁ = growth

S phase

S = DNA synthesis/replication

The cell replicates its DNA.

By the end of S phase:

➡ Each chromosome has been copied.

Each duplicated chromosome consists of two sister chromatids joined together.

Process of DNA replication.

Purpose: make an accurate copy of the cell’s DNA before division.

DNA replication must happen before mitosis so each daughter cell receives the necessary genetic information.

Basic process:

1. The DNA double helix unwinds/unzips.

2. The two DNA strands separate.

3. Each original strand serves as a template.

4. New complementary nucleotides are added.

5. Two DNA molecules are produced.

Each new DNA molecule contains:

• One original strand

• One newly synthesized strand

Base pairing

DNA follows complementary base pairing:

A ↔ T

C ↔ G

So:

• Adenine pairs with thymine.

• Cytosine pairs with guanine.

Semiconservative replication

Produces two Copies; DNA molecule contains:

• One original strand

• One newly synthesized strand

G₂ phase

The cell:

• Continues growing

• Produces proteins

• Prepares for mitosis

• Checks/prepares replicated DNA

Remember:

G₂ = prepare for division

MITOSIS

Mitosis divides the nucleus and separates duplicated chromosomes.

The four major phases are:

Prophase → Metaphase → Anaphase → Telophase

Memory:

PMAT

Prophase

Major events:

• Chromatin condenses into visible chromosomes.

• Each chromosome consists of two sister chromatids.

• The mitotic spindle begins forming.

• Spindle fibers interact with chromosomes.

• The nucleolus disappears.

• The nuclear envelope breaks down as mitosis progresses.

What to recognize:

Chromosomes become visible and the spindle develops.

Metaphase

Major event:

Chromosomes line up in the middle of the cell.

This arrangement is called the:

Metaphase plate

Spindle fibers attach to chromosomes and help position them.

What to recognize:

Chromosomes lined up across the center.

Anaphase

The sister chromatids separate.

Once separated, each chromatid is considered an individual chromosome.

Spindle fibers pull the chromosomes toward opposite poles of the cell.

What to recognize:

Chromosomes moving apart.

Telophase

Chromosomes arrive at opposite ends of the cell.

Major events:

• Chromosomes begin to decondense.

• New nuclear envelopes form around each set of chromosomes.

• Nucleoli reappear.

• The spindle breaks down.

What to recognize:

Two nuclei beginning to form.

Cytokinesis

Cytokinesis is the division of the cytoplasm.

It usually occurs toward the end of mitosis/overlaps with late telophase.

Result:

Two daughter cells

Each daughter cell receives a nucleus containing a complete set of chromosomes.

Chromatid

A duplicated chromosome contains two sister chromatids.

• Stages: Prophase and Anaphase

• Details: Chromatids condense and become visible during prophase. They separate into individual chromosomes during anaphase.

Spindle fibers

• Stages: Prophase, Metaphase, and Anaphase

• These protein ropes start growing in prophase.

• hold the chromosomes in metaphase

• pull the chromatids apart in anaphase.

Metaphase plate

• Stage: Metaphase

• Details: This is the imaginary center line where chromosomes line up before they split.

Daughter cells

• Stages: Telophase and Cytokinesis

• Details: These two identical new cells appear at the very end of the division process.

Cytokinesis

• Stage: Cytokinesis (follows Telophase)

• Details: The main cell body splits in half to completely finish \

• creating the two new daughter cells.

Cell Division

Normal cells have mechanisms that regulate:

• Cell growth

• DNA replication

• Cell division

• Cell death

This prevents cells from dividing uncontrollably.

Cancer

Cancer occurs when cells acquire genetic changes that disrupt normal control of cell division.

The cells may:

• Divide too frequently.

• Ignore signals telling them to stop dividing.

Cancer cell division = uncontrolled/abnormally regulated

Why mutations matter

Genes help regulate cell growth and division.

Mutations can affect genes that:

• Stimulate cell division

• Stop cell division

• Repair DNA

• Control programmed cell death

If these control systems become abnormal, cells can continue dividing when they shouldn’t