Notes: Cell Division & the Cell Cycle (Ch. 12)

• One of the major characteristics of a

living thing is the ability to GROW.

• What does growth mean in terms of

the cell? Bigger cells or more cells?

Why more cells?

• cell size is limited by its surface area to volume ratio (SA:V)– if a cell gets too large, it wouldn’t

be possible for it to get oxygen/nutrients in and wastes out by diffusion

Cell Division

• In simple terms: 1 cell divides into 2 new cells

3 main stages of the Cell Cycle

1. Interphase• longest stage (90%); preparation for

cell division

2. Mitosis (10%)• nucleus divides into 2 nuclei, each

with the same # and kind of chromosomes (DNA) as the parent cell

3. Cytokinesis• cytoplasm divides forming 2 distinct

cells

Cell Cycle G1 = growth (producing proteins & organelles)

S = DNA Synthesis (duplicated) & more growth

G2 = growth & completes preparation for division

• MITOSIS = the division of the nucleus

• Why is it important that the nucleus divides?– it stores the DNA (information of life)

– all new cells need this information

• Chromosomes = tightly coiled chromatin (DNA); consist of 2 identical chromatids (sister chromatids); which are connected in the center by a CENTROMERE

**a human cell entering mitosis contains 46 chromosomes (=DIPLOID

number)

centromere

DNA

chromatin

chromosome

How Does Chromatin Coil so Tightly?

• Chromatin wraps around 8 histone proteins

• A second type of histone (H1) holds the nucleosome “beads” together to increase compaction further

Mitosis is one, continuous event, but it can be described as happening in 5

phases:

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

**Remember, the cell is coming out of

Interphase…

PROPHASE• chromatin

condenses & chromosomes become visible

• Centrosomes/ centrioles separate and start to move to the opposite sides of the nucleus;

PROMETAPHASE

• nuclear envelope breaks down and the nucleolus disappears

• spindle fibers (from centrioles) connect to chromosomes at their centromeres (kinetochore);

METAPHASE• **chromosomes line up

in the center of the cell (metaphase plate);

  **fibers connect from

the poles (end) of the spindle to the centromere/kinetochore of each chromosome

ANAPHASE

• centromeres split, causing the sister chromatids to separate, becoming individual chromosomes

 • chromosomes are

pulled apart to opposite ends of the cell

TELOPHASE• chromosomes uncoil

into chromatin; • new nuclear envelope

forms around the chromatin

 • spindle breaks apart • nucleolus reappears in

each new nucleus

Finally… CYTOKINESIS

• in animal cells: cell membrane pinches in & divides (cleavage furrow)

• in plant cells: a cell plate (new cell wall) forms

Then the cell returns to Interphase… and the

process continues

Which of the following processes take place during interphase?

A. Cell division

B. Cell division & Active Transport

C. Active Transport & Protein Synthesis

D. Active Transport, Protein Synthesis, Replication of DNA

SL

How are all cells formed?A. By cell division

B. By mitosis

C. By fragmentation

D. By cytokinesis

Chromatids areA. Made of microtubules

B. Bacterial chromosomes

C. Strands of duplicate genetic material

D. Supercoils of protein

What is the correct order for Mitosis?A. Interphase, Prophase, Prometaphase, Metaphase, Anaphase,

Telophase

B. Prophase, Prometaphase, Metaphase, Anaphase, Telophase

C. Telophase, Anaphase, Metaphase, Prometaphase, Prophase

D. Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis

This cell is in which phase of Mitosis?A. Prophase

B. Prometaphase

C. Anaphase

D. telophase