Topic 2

Question 1

DNA replication

Answer 1

• Occur in S phase of cell cycle
• In preparation of mitosis
• Before replication, the chromosome consists of one DNA molecule
• after replication, the chromosome consists of 2 DNA molecules that are a replica of each other called sister chromatids
• The sister chromatids are held together by cohesion protein at the centromere area

Question 2

what are homologous chromosomes

Answer 2

maternal and paternal copies of chromosome pairs

Question 3

what are sister chromatids

Answer 3

Sister chromatids are the two replicas of a single chromosome held together at the centromere by cohesion proteins after DNA replication

Question 4

what are kinetochores

Answer 4

• a complex protein structure
• found at the centromere region of sister chromatids
• attach to the microtubule of mitosis spindle during mitosis

Question 5

what happens during prophase

Answer 5

• chromosomes condense and become visible under microscope
• chromosomes have two sister chromatids that are helped together at the centromere
• cytoskeleton gets disassembles
• Golgi apparatus and ER disperses
• Nuclear envelope breaks down
• mitotic spindle assembles (not in plants) as 2 centrioles move at opposite ends of the cell and a radial array of micro tubules called asters form

Question 6

what happens during prometaphase

Answer 6

• chromosome attach to the microtubules at kinetochores
• the chromosomes are oriented in a way that the kinetochores of the sister chromatids are attached to microtubules of the opposite pole
• chromosomes move to the equator of cell

Question 7

what happens during metaphase

Answer 7

• all chromosomes are aligned at the equator of the cell called the metaphase plate
• chromosomes are attached to opposite poles and are under tension

Question 8

what happens during anaphase

Answer 8

• proteins (cohesins) holding the sister chromatids together at the centromere start degrading, allowing the sister chromatids to separate into individual chromatids
• the sister chromatids are pulled to opposite poles (anaphase A)
• spindle pole moves apart (anaphase B)

Question 9

what happens during telophase?

Answer 9

• spindle apparatus dissembles
• nuclear envelope forms around each set of sister chromatids (chromosomes of the daughter cell)
• chromosome starts to de coil
• ER and Golgi apparatus reforms

Question 10

Describe cytokinesis

Answer 10

cleavage of cell into two equal halves

• for animal cell: achieved by the means of constricting a belt of actin filaments , pinching the cell and forming a cleavage furrow
• for plant cell: by forming cell plate (made up membrane components) of that partitions cell into two, followed by a deposition of cellulose to for, a cell wall

Question 11

describe cytokinesis in animal cells

Answer 11

a cleavage furrow forms around a dividing cell

The completion of cytokinesis in an animal cell. the two daughter cells are still attached to each other by a thin band of cytoplasm mostly occupied by microtubules