3.2 - From one to many: the cell cycle

Question 1

What happens in Interphase?

Answer 1

New cell organelles are synthesised and DNA replication occurs.By the end of interphase the cell contains enough cell context to produce 2 new cells.

Question 2

What is the order of the stages in mitosis?

Answer 2

prophase, metaphase, anaphase, and telophase.

Question 3

What happens in Prophase?

Answer 3

The chromosomes condense becoming shorter and thicker, with each chromosome visible as two strands called chromatids. Apart from the occasional mutation, the two strands are identical copies of each other , produced by replication. They are effectively two chromosomes joined at one region called centromere

Question 4

What happens in Metaphase?

Answer 4

The chromosomes centromeres attach to spindle fibres at the equator.

Question 5

What happens in Anaphase?

Answer 5

The centromeres split. The spindle fibres shorten, pulling the two halves of each centromere in opposite directions. One chromatid of each chromosome is pulled to each of the poles. Anaphase ends when the separated chromatids reach the poles and the spindle breaks down.

Question 6

What happens in Telophase?

Answer 6

This is effectively the reverse of prophase. The chromosomes unravel and the nuclear envelope reforms, so that the two sets of genetic information become enclosed in separate nuclei.

Question 7

What is Cytoplasmic division?

Answer 7

After nuclear division (mitosis) , the cell surface membrane constricts around the centre of the cell. A ring of protein filaments bound to the inside surface of the cell is divided into two new cells. It has been proposed that the proteins actin and myosin, responsible for muscle contraction, may also be the proteins responsible for cytoplasmic division. Plant cells synthesize a new cell plate between the two new cells.

Question 8

What is Cell division?

Answer 8

Mitosis and meiosis involves division of the nucleus which is followed by the division of the cytoplasm called cytokinesis.

Question 9

What is Mitosis used for?

Answer 9

• Growth and repair of an organism
• Repair of tissues (replacement of cells)
• Reproduction

Question 10

What is cytokinesis?

Answer 10

Cytoplasmic division of all the other materials in the cell (cytoplasm,cell membrane and organelles)
Results in the formation of 2 new daughter cells with the correct number of chromosomes

Question 11

What is G1 in the cell cycle?

Answer 11

cell grows and prepares for DNA replication

G = GROWTH

Question 12

What is G2 in the cell cycle?

Answer 12

cell finishes growing and prepares for mitosis

Question 13

How is DNA organised in chromosomes?

Answer 13

• DNA contains a single long double stranded DNA molecule.
• These molecules are much longer than the diameter of the nucleus.
• They are packaged into the nucleus by winding around proteins known as histones, which help to coil the DNA.
• This complex of DNA and proteins is known as chromatin.
• DNA is most tightly condensed in mitotic chromosomes just before cell division where they can be seen easily under a light microscope.
• At other times individual chromosomes are not visible by light mcircopsly because they are less condensed

Question 14

What is the nucleolus and the function?

Answer 14

• The nucleolus is where the ribosomes are assembled.
• Under a microscope,the nucleoli appear as large round patches.
• Ribosomes are composed of protein and RNA molecules and the genes needed for the production of the ribosomal RNA components are located in clusters on several of the chromosomes.
• The relevant sections of these chromosomes loop into the nucleolus.

Question 15

What is the difference between plant and animal cell differentiation?

Answer 15

• Plant cells remain totipotent unlike animal cells.
• In animals,cell differentiation is irreversible.
• However,plant cells that are differentiated are able to be de-differentiated and then develop into a new plant.

Question 16

Why can plants be reproduced using tissue culture?

Answer 16

• Plants can be reproduced using tissue culture because of the totipotency of the plant cells.
• These embryos develop into complete plants that are genetically identical clones.

Question 17

Summarise the uses of stem cells in medicine

Answer 17

• Stem cells offer great hope to medicine particularly in regenerative medicine.
• This is the branch of medicine concerned with replacing,engineering or regenerating human cells.

Question 18

What is therapeutic cloning (process and result)?

Answer 18

In therapeutic cloning ,the patient needing a transplant would have one of their diploid cells removed.This could simply be acell from the base of of a hair or any other tissue.This cell or its nucleus would then be fused with an ovum from which the haploid nucleus had been removed.The result would be a diploid cell rather like a zygote.

Question 19

What are adult stem cells and how are they used?

Answer 19

• Adult stem cell have been used for a long time.
• The adult stem cells move into bone marrow and produce healthy blood cells.
• Adult stem cells have also been used to produce cells for transplantation To treat patients with burns

Question 20

What are reprogramming somantic cells/how are they used?

Answer 20

• Reprogramming somatic cells are known as pluripotent stem cells.
• Reprogramming somatic cell would overcome the problem of cell rejection and dress the ethical concerns with the use of embryonic stem cells.