5. THE MITOTIC CELL CYCLE

Question 1

What is the key to precise nuclear division

Answer 1

the fact that the two DNA molecules in sister chromatids, and hence their genes, are identical

Question 2

How do histones and DNA interact

Answer 2

histones are basic while DNA is acidic

Question 3

When is the DNA most tightly coiled

Answer 3

right before nuclear division in the cell cycle

metaphase during mitosis

Question 4

Two features essential for successful nuclear division

Answer 4

centromeres

telomeres

Question 5

Functions of telomeres

Answer 5

• permits continued replication of cells (stem/meristematic)
• prevents loss of genes/ prevents chromosome shortening
• length of telomeres determine life span
• prevents ends of chromosomes attaching to each other
• prevents cell death

Question 6

Cytokinesis in animal cells

Answer 6

• cell membrane forms
• cleavage furrow forms
• cytoplasm constricts

Question 7

Cytokinesis in plant cells

Answer 7

• cell membrane forms
• cell plate/middle lamella forms as cellulose is laid down
• cytoplasm divides into two
• vesicles move to equator

Question 8

Centromere

Answer 8

• needed for the separation of sister chromatids during mitosis
• visible as a constriction
• is the site of attachment of spindle microtubules
• every chromosome has two kinetochores at its centromere

Question 9

Kinetochore

Answer 9

• each chromosome has two kinetochores at its centromere
• made of proteins which specifically bind to the DNA in the centromere and also bind to microtubules
• spindle fibers extend from the kinetochore to the poles of the spindle during mitosis
• construction of the kinetochores begins in S phase of the cell cycle and they are lost again afterwards
• the microtubules attached to a given kinetochore pull the kinetochore, with the rest of its chromatid dragging behind, towards the pole
• this is achieved by shortening of the microtubules, both from the pole end and the kinetochore end

Question 10

How do sister chromatids move to opposite poles of the cell

Answer 10

• the microtubules attached to a given kinetochore pull the kinetochore, with the rest of its chromatid dragging behind, towards the pole
• this is achieved by shortening of the microtubules, both from the pole end and the kinetochore end

Question 11

Differences between euchromatin and heterochromatin

Answer 11

• heterochromatin is more tightly coiled

- heterochromatin contains inactive genes

Question 12

What is semi-conservative replication

Answer 12

• synthesis of two identical DNA molecules

- each new molecule consists of one original strand and one new strand