Cell Cycle: Lect 3

Question 1

Labile cells

Answer 1

Multiply throughout life. Cells of skin, GIT, epithelial cells.

Question 2

Stable cells

Answer 2

quiescent(Go phase). Divide if stimulate. Liver cells.

Question 3

Permanent cells

Answer 3

lost the capacity to divide. Permanently in Go phase. Neurons/Cardiac muscle cells.

Question 4

Stages of cell cycle:

G1 phase:
-important proteins?

Answer 4

10-12 hrs -
-46 chrom & 46 chromatids
Cell increases in size. Cell undergoes differentiation and performs its function. Cell check for size, nutrients, GFs and damage. Some cells enter Go phase “permanent and stable cells”.
G1->S check pt: p53 and Rb proteins.

Question 5

S phase

Answer 5

6-8 hrs
Phase of DNA synthesis and replication. Entire chrom replicates and chromatid number doubles. Each chrom has two sister chromatids 46 chrom & 92 chromatids.

Question 6

G2 phase

Answer 6

2-4hrs
Cell size increases; entire genome is scanned for any mistakes. Post-replication DNA repair. Chromatid number is doubled.

Question 7

Stages of Mitosis:

Answer 7

Prophase - nuclear envelope dissolves, spindle forms and chrom start condensing.

Metaphase - chrom maximally visible and align in equator. Visualized by karyotyping.

Anaphase - separation of sister chromatids and they move to the centrioles.

Telophase - sister chromatids move to opposite poles. Nuclear envelope starts forming. Chrom less condensed and cytokinesis occurs.

Question 8

Meiosis

Answer 8

final stage of gametogenesis; formation of four gametes each w/ 23X/Y chrom.
-Hom. chrom undergo recombination therefore each game is unique.

Meiosis I: Hom. chrom separate
Meiosis II: Sister chromatids of a chrom separate.

Male meiosis produce 4 sperm cells and female produce 1 egg and 3 polar bodies.

Question 9

Nondisjunction M I:

Answer 9

Homologous chrom do not separate. Most frequent in females and more dangerous.

• Results in 2 trisomies and 2 monosomies = incompatible w/ life.
• Turner’s and Klinefelter’s

Question 10

Nondisjunction M II:

Answer 10

Hom chrom separate but sister chromatids do not separate.

• Results in 1 trisomy, 1 monosomy and 2 normal gametes.
• XYY syndrome, Turners and XXX superfemale.

Question 11

Meiosis female/males

Answer 11

oogenesis begins during prenatal development.
-Primary oocytes arrest at prophase-I

In males, begins at puberty.

Question 12

At the beginning of meiosis, there are ____ chromosomes & _____ sister chromatids
•At the end of meiosis I, each cell has _____ chromosomes & ______ sister chromatids (reduction division)
•At the end of Meiosis II, there are _____ chromosomes & ______ chromatids

Answer 12

46, 92.

23, 46

23, 23