Chapter 5 The Mitotic Cell Cycle

Question 1

Structure of chromosomes

Answer 1

• DNA
• Histone proteins
• Sister chromatids
• Centromere
• Telomere

Question 2

Importance of mitosis

Answer 2

• growth of multicellular organisms
• repairment and replacement of damaged or dead cells
• asexual reproduction

Question 3

Phases of the mitotic cell cycle

Answer 3

• Interphase
• Mitosis
• Cytokinesis

Question 3

Interphase

Answer 3

• G1 phase: cells make the RNA, enzymes and other proteins needed for growth
• S phase: DNA replication occurs. Each chromosome is duplicated, forming two genetically identical sister chromatids joined at the centromere
• G2 phase: final checks are made for DNA errors before entering mitosis

Question 4

Stages of Mitosis

Answer 4

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 5

Prophase

Answer 5

• Chromosomes condense and become visible
• The nuclear envelope begins to break down, and nucleolus disappears
• Spindle fibers form from centrioles

Question 6

Metaphase

Answer 6

• Chromosomes align at the equator of the cell
• Spindle fibers attach to the centromeres of chromosomes

Question 7

Anaphase

Answer 7

• Sister chromatids are pulled apart to opposite poles of the cell by the shortening of spindle fibers

Question 8

Telophase

Answer 8

• Chromosomes reach the poles and begin to decondense
• Nuclear envelopes form around each set of chromosomes
• Spindle breaks down

Question 9

What is cytokinesis?

Answer 9

The division of the cytoplasm between daughter cells

Question 10

The role of telomeres

Answer 10

Prevent the loss of genes from the ends of the chromosomes during DNA replication

• During DNA replication, the enzyme DNA polymerase cannot fully replicate the very ends of the lagging strand. As a result, a small portion of DNA is lost with each round of replication. Telomeres act as protective caps, so this loss affects the telomeric DNA rather than essential coding genes. This prevents the loss of important genetic information and maintains genome stability

Question 11

The role of stem cells

Answer 11

Cell replacement and tissue repair

• Stem cells are undifferentiated cells that can divide by mitosis to produce more stem cells or differentiate into specialized cell types

Question 12

Formation of a tumour

Answer 12

• If mutation occurs in genes controlling cell division, control of the cell cycle can be lost
• Cells begin to divide uncontrollably, even when new cells are not needed.
• These rapidly dividing cells can form a mass of abnormal cells called a tumor

Question 13

Behaviour of chromosomes in plant and
animal cells during the mitotic cell cycle

Answer 13

PROPHASE:
- In animal cells, centrioles move to opposite poles and begin to form the spindle (microtubules)

• In plant cells, there are no centrioles, but spindle fibers still form from microtubule-organising centres

CYTOKINESIS:
- In animal cells, the cell surface membrane forms a cleavage furrow that pinches the cytoplasm in two, forming two daughter cells

• In plant cells, a cell plate forms from vesicles produced by the Golgi apparatus; this develops into a new cell wall and cell membranes, separating the two daughter cells