Cell Cycle, Mitosis and Meiosis

Question 1

What are the 2 types of Chromosomes?

Answer 1

• Circular (bacteria)

- Linear (most organisms)

Question 2

What expends the most energy in cells?

Answer 2

Dividing up their chromosomes

Question 3

What is Chromatin? Why is it necessary?

Answer 3

Chromatin is the combination of protein and DNA. Chromosomes are visible once condensed by a protein.
During cell division, DNA wraps around proteins (histones), they help keep the DNA tightly packed.

Question 4

Do all species have the same amount of chromosomes? How does number of chromosomes vary within a species?

Answer 4

• Number of chromosomes is always the same for a given species
• Number of chromosomes varies from species to species

Question 5

What are the “identical pairs” that chromosomes often come in?
How many do humans have?

Answer 5

• Homologs

- Humans have 22 homologs and 2 sex chromosomes.

Question 6

What is a chromatid? What holds them together?

Answer 6

Chromatids are the duplicates made for cell
division.
They are held together by a centromere.

Question 7

What makes up the centromere?

Answer 7

Centromere is a conglomeration of proteins.

Question 8

List the 3 major steps in cell division

Answer 8

• S Phase (DNA replication)
• Mitosis OR Meiosis
• Cytokinesis

Question 9

What are the four stages of the cell cycle? What happens in each one?

Answer 9

• G1 phase (rest)
• S phase (DNA replication)
• G2 phase (preparation for division)
• M phase (Mitosis or Meiosis)

Question 10

Why is a proper cell cycle important? How is the cell cycle regulated? What happens if it is not?

Answer 10

• A cell cycle is like “quality control” - ensures everything happens sequentially
• It has checkpoints at end of each phase before allowing next phase to begin
• Unregulated cell division causes cancer.

Question 11

List all steps in Mitosis- explain them

Answer 11

1) Interphase: DNA replication
2) Prophase: chromosomes condense, centromeres move to poles
3) Prometaphase: Nuclear envelope breaks down, kinetochores attached to kinetochores
4) Metaphase: Chromosomes lineup at metaphase plate
5) Anaphase: Chromosomes seperate, microtubules shorten
6) Telophase: Daughter chromosomes reach poles, chromosomes decondense

Question 12

What is the spindle? What are they made of?

Answer 12

• Spindle is what separates the chromosomes

- Made of microtubules

Question 13

Explain cytokinesis in animals

Answer 13

• In animals, actin and myosin form a “purse string” that constricts and divides the cell

Question 14

Explain cytokinesis in plants

Answer 14

• Vesicles fuse to form a membrane- form a cell wall

Question 15

What does Syncytial division mean? Where does it often happen?

Answer 15

When cells go through division without cytokinesis

Happens in muscle cells, they have multiple nuclei

Question 16

Explain Meiosis- where does it differ from mitosis?

Answer 16

• It is split into meiosis 1 and 2. Meiosis 1 is the division of homologs.
  - Results in 2 cells with 2 copies of each homolog.
• Meiosis 2 is similar to mitosis.
  - Results in 4 haploid cells

Question 17

Where in Meiosis can issues happen that cause down syndrome?

Answer 17

During anaphase 1 there is a non-disjunction event where both chromosome 21 end up in the same gamete. Causes egg to have 3 21 chromosomes.