EXAM2_L21_The_Cell_Cycle

Question 1

What are MITOGENS?

What are 4 phases of Cell cycle?
What is considered INTERPHASE?
What is considered M phase?

Answer 1

Mitogens are Growth Factors (signaling molecules)

• Stimulate mitosis
• alter proteins that control initiation of cell cycle

-G1, S, G2, M
Interphase: G1, S,G2
M phase: Mitosis (physical division of the cell)

Question 2

What is a resting state?

What is a non-proliferating cell called?

Answer 2

• Normal functioning cell (NOT DIVIDING)
  -IN ABSENCE OF MITOGEN
  if non proliferating cell -“Arrested” in G0

Question 3

Cells that terminally enter G0?

Answer 3

Neurons

Question 4

Gap 1 Phase events

Answer 4

-Stimulated by a mitogen– enters G1:
Replicates PROTEINS, ENZYMES, METABOLITES

• cellular components required for survival
• **-Proteins required for DNA replication

not chromosomes!

Question 5

S Phase events

Answer 5

DNA REPLICATION

• 46 chromosomes (23 maternal 23 paternal) is duplicated
• Daughter stays attached to parent chromosome by centromere

-DNA is Euchromatin state (uncondensed)

After S phase- Cell has 92 chromatids and is 4n.

Question 6

G2 Phase events

Answer 6

-Cell Growth in size
-makes proteins, organelles, cytoplasm
Makes everything needed so it can DIVIDE in mitosis
(including proteins needed to condense & separate chromatin)

• DOUBLE CHECKS for errors in duplicated Chromosomes
• makes any needed repairs- then enters mitosis

Question 7

Mitosis Phase events

Answer 7

Cell enters M phase with DOUBLE EVERYTHING
PMAT
Cell divides

Question 8

Haploid Cell

Answer 8

Cell with ONE version of each chromosome (ie: egg/sperm)

• haploid number is 23 (1-22, plus either X or Y)
• ploidy number represented as “n”

Question 9

Diploid Cell

Answer 9

Cell with TWO versions of ea. Chromosome
-one copy maternal & one copy paternal

• initially occurs at fertilization of egg/sperm then diploid state maintained in all SOMATIC (body) cells
• 46 chromosomes (23 maternal 23 paternal)
• ploidy number is “2n”

Question 10

Homologous Chromosomes

Answer 10

DIPLOID

Maternal and Paternal chromosomes comprised of the same genes/DNA sequences

Question 11

Microtubules

Answer 11

in INTERPHASE or G0- microtubules used for organelle and vesicular transport

During M-phase_MT’s undergo HUGE transformation to sort mitotic chromosomes

Question 12

Centrosomes, centromeres, centrioles WHAT ARE THESE?

Answer 12

Centrosomes- MTOC’s

• organelles made from centrioles and other proteins
• Move to ends of cell & form MITOTIC SPINDLE

Centrioles- make centrosomes

Centromeres- attach sister chromatids

Question 13

How are chromosomes pulled to opposite ends of the cell?

Answer 13

MT’s pull chromosomes apart via kinetochore

Question 14

Kinetochore
Centromere

What does interphase look like?

Answer 14

Protein complex- HANDLE for MT’s
-connects each sister chromatid to the mitotic spindle

Centromere joins sister chromatids and to kinetochore

Interphase( g1,s,g2)

• Microtubules dispersed throughout cell
• Chromosomes loosley dispersed
• Chromosomes begin to condense at end of g2

Question 15

PMAT

Answer 15

P: Chromosomes condensed; MT’s organize (tubulin used in mitotic spindle)

PM: nuclear membrane breaks down (MTs extend in) ea. ch has one kinetochore on each side.

M: metaphase plate; line up parallel to MP.
A: shortest: separate chromatids- cytokinesis begins
T: nucleus reforms; chromosomes decondense- cytokinesis

Question 16

When does cytokinesis begin and end?
What causes cleavage?
What formed?
what direction is cleavage? Why?

Answer 16

starts anaphase ends telophase

• Contractile Ring (actin microfilaments inner cell surface)
• cleavage furrow- forms perpendicular to mitotic spindle to ensure equal splitting

Question 17

Mitosis vs Meiosis
asking number of cells and what they turn into:
2n n etc

Answer 17

Mitosis- 1 diploid cell makes two diploid daughter cells

Meiosis- 1 diploid germ cell makes 4 haploid gametes

Question 18

Spermatogonia develop into..

Oogonia divide to form…

Answer 18

four haploid sperm cells
One haploid egg, and three polar bodies

• *In humans only 2 polar bodies
• **(1st doesn’t go through meiosis II)

Question 19

Tetrad

What happens in S of a cell undergoing meiosis?

Answer 19

One Maternal chromosome (two chromatids)
One Paternal chromosome (two chromatids)
bundled together for Homologous recombination

Diploid 2n cell replicated to 4n state then starts meiosis 1

Question 20

MEIOSIS I

Answer 20

4n (46 chromosomes; 92 chromatids)–

• Tetrads undergo homologous recombination
• TETRADS separate into DYADS and cell splits into two diploid 2n cells (23 recombined and duplicated pairs)

Question 21

MEIOSIS II

What 2 events cause genetic variability?

Answer 21

TWO diploid 2n Cells divide into FOUR haploid n cells

1. Crossing over/Recombination
2. Random arrangements of chromosomes during metaphase lineup (2^23= 8 million combinations)

Question 22

Synaptonemal complex

Answer 22

Protein that zips all four maternal/paternal chromatids together into a TETRAD

Formation of tetrad stimulates crossing over

Question 23

Chiasmata in human oogenesis

Answer 23

7th month of development female fetus oogonia begin meiosis I and arrest after replication & before division of prophase I (now called primary oocytes 4n).

Now crossing over occurs and synaptonemal complex breaks down.

Primary oocytes contain chiasmata for years b/c primary oocyte paused until puberty/ovulation.