Lecture 10: Cell Division

Question 1

What are the three possible destinies of a cell?

Answer 1

Live and function without dividing
Grow and divide
Die

Various signals tell a cell which path to take

Question 2

What is homeostasis in the context of cell proliferation?

Answer 2

Balance between cell proliferation and cell death (Apoptosis)

Question 3

What is mitosis?

Answer 3

The process in which the nucleus turns into two nuclei

Question 4

What does the cell theory state?

Answer 4

All organisms are made of cells and all cells come from pre-existing cells

Question 5

What is somatic cell division?

Answer 5

Mitosis – diploid (2n) to diploid (2n)

Question 6

What is reproductive cell division?

Answer 6

Meiosis - diploid (2n) to haploid (1n)

Question 7

What is the primary reason somatic cells divide?

Answer 7

Growth and development, tissue renewal

Question 8

What is the result of somatic cell division?

Answer 8

Two daughter cells that are genetically and functionally identical to the parent cell.

Question 9

Do all somatic cells divide?

Answer 9

Many, but not all; some divide more than others

Question 10

What phase are somatic cells in most of the time?

Answer 10

Interphase

Question 11

What is M Phase (Mitotic Phase)?

Answer 11

Mitosis + Cytokinesis

Question 12

What is the length of interphase dependent on?

Answer 12

Cell type

Question 13

What occurs during the G₁ phase of interphase?

Answer 13

Cell grows larger, metabolically active, duplicates organelles and cytosolic components

Question 14

What happens during the S (Synthesis) phase of interphase?

Answer 14

DNA replication occurs, strands are separated at the hydrogen bonds holding the nucleotides together, new strand of DNA is synthesized opposite each of the old strands.

Question 15

What happens during the G₂ phase of interphase?

Answer 15

Checks for correct DNA synthesis

Prepares for the Mitotic phase (synthesis of the proteins and enzymes required,
gathering of reactants)

Replication of centrosomes is completed

Question 16

What is a sister chromatid?

Answer 16

Identical chromatids formed during DNA replication that are cross at the centromere

Question 17

What checks occur at the G₁ checkpoint?

Answer 17

• Is the DNA undamaged?
• Is cell size and health/nutrition OK?
• Are appropriate signals present?

Question 18

What happens if a cell does not pass the G₁ checkpoint?

Answer 18

May exit to G₀

Question 19

What occurs during prophase of mitosis?

Answer 19

Nuclear membrane dissolves and DNA thickens; centrosomes move to opposite ends and form spindle fibers (microtubules)

Question 20

What occurs during metaphase of mitosis?

Answer 20

Chromosomes “line” up in the center of the cell

Spindle Fibers grow towards the DNA chromosomes and the other centrosome

The Spindle Fibers attach to the centromeres on the chromosomes and pull/push them into the middle of the cell

Question 21

What occurs during anaphase of mitosis?

Answer 21

Sister chromatids separate, each now considered an independent chromosome

Chromomeres are now called kinetochores

Chromosomes are pulled apart by spindle fiber, to opposite ends of the cell before the nuclear envelope reforms in telophase

Question 22

What occurs during telophase in mitosis?

Answer 22

Two new nuclei form and chromosomes unwind
Cleavage furrow as the cells divide

Question 23

What is cytokinesis?

Answer 23

Cell divides into two, happens in parallel to mitosis

Question 24

Where does meiosis occur?

Answer 24

In the gonads (ovaries and testes)

Question 25

What is produced during meiosis?

Answer 25

Gametes which are haploid (a single set of 23 chromosomes) Cells genetically different from the parent cell

Question 26

What is synapsis in meiosis?

Answer 26

Pairing of homologous chromosomes during prophase I

Question 27

What occurs during crossing over in meiosis?

Answer 27

Non-sister chromatids exchange genetic material

Question 28

How many haploid cells are produced at the end of meiosis II?

Answer 28

4

Question 29

What is the difference between meiosis I and meiosis II?

Answer 29

Meiosis I separates homologous chromosomes; Meiosis II separates sister chromatids

Question 30

What are homologous chromosomes?

Answer 30

Pairs of chromosomes that have the same genes in the same order, but may have different alleles

Question 31

What is the number of divisions in mitosis?

Answer 31

One, including prophase, prometaphase, metaphase, anaphase, and telophase

Question 32

What is the number of divisions in meiosis?

Answer 32

Two, each including prophase, metaphase, anaphase, and telophase

Question 33

What are sources of genetic variation in meiosis?

Answer 33

* independent assortment at metaphase I (2²³ >8 million possible combinations) * crossing over at prophase 1 (~1-3 crossover events per pair) * fusion between two gametes (> 2²³ times 2²³ combinations!!!)

Question 34

What are the steps of the eukaryotic cell cycle?

Answer 34

Mitotic phase -> G₁ phase -> S phase -> G₂ phase -> mitotic phase

Question 35

What is interphase?

Answer 35

G₁ phase, S phase, and G₂ phase Most cells of the body are performing there functions in interphase

Question 36

What occurs in the G1 phase?

Answer 36

Most cellular activities - the duration varies from cell to cell

Question 37

What occurs in the S phase?

Answer 37

DNA replication - 23 sets of chromosomes before exist as single chromatids, they become 23 sets of chromosomes which are formed from two sister chromatids pairing up

Question 38

What occurs in the G2 phase?

Answer 38

Checks for correct DNA synthesis Preparation for mitosis (synthesis of proteins and enzymes, gathering of reactants) Replication of centrosomes (made up of centrioles which organise microtubules)

Question 39

Crossover between homologous chromosomes occurs during...?

Answer 39

metaphase I