Lecture 12 - DNA Replication And Mitosis

Question 1

What are the two major phases of the cell cycle?

Answer 1

Interphase and cell division

Question 2

What is interphase?

Answer 2

the period from cell formation to cell division and has three subphases.

During interphase, nuclear material is in uncondensed chromatin state

Question 3

Subpahases of interphase

Answer 3

G1 or gap 1: the cell is synthesizing proteins and actively growing
S phase: DNA is replicated
G2 or gap 2: enzymes and other proteins are synthesized and distributed throughout the cell

Question 4

DNA replication

Answer 4

Takes place when the DNA helix uncoils and the hydrogen bonds between its base pairs are broken.

Two identical “daughter” DNA molecules are formed from the original.

Question 5

What is DNA polymerase’s role?

Answer 5

DNA polymerase attaches to the primer and adds nucleotides to form new strand.

synthesizes both new strands at one time (one leading strand and one lagging strand).

works only in one direction, so leading strand is synthesized continuously.

Because the lagging strand is “backwards,” it is synthesized discontinuously into segments (Okazaki fragments)
DNA ligase, then splices short segments of lagging strand together.

Question 6

What is a centrosome?

Answer 6

an organelle in the cytoplasm that serves as the microtubule organizing centre for the cell.
It is composed of two centrioles and a mass of protein to use as microtubule building supplies.

Question 7

What is a centriole?

Answer 7

a tubulin cylinder that is part of the centrosome and form the base of flagella or cilia.

Question 8

What is a centromere?

Answer 8

the region of a chromosome that links two sister chromatids together. It is also the site of assembly of the kinetochore

Question 9

What is the kinetochore?

Answer 9

the structure that allows microtubules to connect each chromatid to the polar centrosomes for mitosis to complete.

Question 10

What is DNA made of?

Answer 10

two anti-parallel strands, arranged in a double helix.

Question 11

What are chromosomes made of?

Answer 11

composed of DNA. Before the S phase of interphase, there is one copy of each chromosome in the cell.

Question 12

What are replicated chromosomes made of?

Answer 12

also composed of DNA. They are found after the S phase, so there are two copies of each chromosome held together by a centromere.

Question 13

Chromatids

Answer 13

Sister chromatids are each of the two copies of a replicated chromosome

Daughter chromosomes are single chromosomes that were previously sister chromatids but have now been pulled apart by their kinetochores during anaphase of mitosis.

Question 14

Mitosis

Answer 14

the process of nuclear division in which cells contain all genes.

DNA must be replicated in S phase before mitosis can occur

Question 15

Cytokinesis

Answer 15

the process of dividing the cytoplasm.

Question 16

What does control of cell division depend on?

Answer 16

surface-volume relationships, chemical signaling, and contact inhibition.

Question 17

What are the four stages of mitosis?

Answer 17

Prophase (early and late)
Metaphase
Anaphase
Telophase

Question 18

What happens during Early prophase?

Answer 18

Chromatin condenses, forming visible chromosomes

Each chromosome and its duplicate (called sister chromatids) are held together by a centromere

The centrosome and its duplicate begin synthesizing microtubules that push each centrosome to the opposite poles of the cell. This is called the mitotic spindle. Other microtubules called asters radiate from the centrosome.

Question 19

What happens during late prophase?

Answer 19

The nuclear envelope breaks up.

Special microtubules attach to a specific area on the centromeres called the kinetochore (protein handle) and pull the chromosomes to the centre (equator) of the cell.

Question 20

What happens during metaphase?

Answer 20

centromeres of chromosomes line up at metaphase plate

Question 21

What happens during anaphase?

Answer 21

centromeres of chromosomes split

Chromosomes are Pulled to opposite sides of cell

Anaphase is the shortest of all mitotic phases.

Question 22

What happens during telophase?

Answer 22

Nucleoli reappear and the spindle disappears.

Cytokinesis begins during late anaphase and continues through mitosis. cleavage furrow forms until the two daughter cells are pinched apart.