Cell division and cell death

Question 1

Cell cycle

Answer 1

Consists of interphase and mitotic phase.

Question 2

Interphase

Answer 2

G1 phase: Physical growth (G0 phase: Inactivity).
S phase: DNA replication.
G2 phase: Preparation for division.

Question 3

Mitotic Phase

Answer 3

M phase.
Mitosis
Cytokinesis.

Question 4

DNA replication

Answer 4

After DNA replication each chromosome is made of two identical copies: Sister chromatids.
Two types:
Semi-conservative
Semi-discontinous

Question 5

Semi-conservative (Exam)

Answer 5

As the DNA double helix is unwound by helicase, replication occurs separately on each template strand in antiparallel directions resulting in each copy having 1 parental strand and 1 newly synthetized strand.

Question 6

Semi-discontinuous (Exam)

Answer 6

1 strand is synthetized continuously (leading strand). The other synthetized in fragments, okazaki fragments, (Lagging strand).

Question 7

How does the DNA replication work?

Answer 7

Helicase breaks the hydrogen bonds between the nitrogenous base pairs.
RNA primer produced by RNA primase sticks to the split DNA to start synthesis, extends from 5’ end to 3’ end.
In semi-discontinuous, the strands are replicated in opposite direction. Leading strand is replicated normally while the lagging strand can only replicate fragments (okazaki) at a time, needing multiple primers.
Exonuclease removes the RNA primers.
A specific DNA polymerase fills the gaps.
DNA ligase joins DNA fragments.

Question 8

Helicase

Answer 8

Unwind DNA (exposing template)

Question 9

Primase

Answer 9

Synthetize RNA primer (necessary for DNA polymerase to start)

Question 10

DNA polymerase

Answer 10

Synthesis DNA (5’ -> 3’)
Fills gaps left by RNA primers.

Question 11

EXONUCLEASE

Answer 11

Removes RNA primers

Question 12

DNA LIGASE

Answer 12

Closes the gaps.

Question 13

Mitosis

Answer 13

4 phases:

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 14

What is the purpose of Mitosis?

Answer 14

Growth/repair tissue.
Replace worn out cells.
Maintainance of tissue.

Question 15

What is the results of Mitosis? (Exam)

Answer 15

Two genetically identical diploid cells.

Question 16

Diploid Cell

Answer 16

Has two copies of each chromosome. Homologous pair.

Question 17

Chromatids

Answer 17

Two sister chromatids make 1 chromosome.

Question 18

Prophase

Answer 18

Nuclear envelope disappears.
Chromatin condenses.
Centrosomes migrate to opposite poles.
Formation of mitotic spindle (microtubules).
Chromosomes captured by spindle fibers.

Question 19

Metaphase

Answer 19

Chromosomes align at the equatorial plate (metaphase plate).
Bound to microtubules from opposite poles.

Question 20

Anaphase

Answer 20

Separation of chromosomes, sister chromatids go on opposite poles.

Question 21

Telophase

Answer 21

Nuclear envelope appears
Chromatin decondense
Spindle disappears.

Question 22

Cytokinesis

Answer 22

Splitting of the cytoplasm (Microfilaments).

Question 23

What is the difference between mitosis and cytokinesis?

Answer 23

Mitosis divides the nuclea.

Cytokinesis divides the cytoplasm.

Question 24

Necrosis

Answer 24

Trauma/infection
cells explode
inflammation and tissue damage.

Question 25

What are the two types of cell death?

Answer 25

Necrosis and apoptosis

Question 26

Apoptosis

Answer 26

Planned
Physiological
No inflammation, no tissue damage.
Cells collapse, break up into fragments called apoptotic bodies that are reabsorbed (phagocytosis).
Triggered in two ways:
Intrinsic pathway
Extrinsic pathway

Question 27

How do cells die in apoptosis?

Answer 27

Initiator caspases start proteolytic cascade:
Activating executioner caspases.
Cleavage of structural proteins
Activation of DNA-degrading enzymes

Question 28

Intrinsic pathway

Answer 28

Cellular stress/damage
Release of cyt c from mitochondria to cytosol.
Apoptosome assembly.
Activation of initiator caspases.

Question 29

Extrinsic pathway

Answer 29

Immune system kills the cell.
Extracellular stimulation of death receptors.
Disc: death inducing signaling complex.
Activation of initiator caspases.