4. cell division_cell/tissue and stem cell

Question 1

What is the Cell Cycle?

Answer 1

• The cell cycle is the process (series of stages) that all body cells (in multicellular organisms) use to grow and divide.
• It starts with a cell that has already been produced by cell division and ends with this cell dividing to produce 2
  genetically identical daughter cells.

Question 2

mitosis

Answer 2

division into two daughter cells that are genetically identical to each other and to the parent cell.

Question 3

Meiosis

Answer 3

division into four unique daughter cells with half the chromosomes of the parent cell.

Question 4

haploid

Answer 4

Question 5

diploid

Answer 5

homologous:
Homologous chromosomes are matched pairs containing the same genes in identical locations along their length.

Question 6

Importance of the cell cycle

Answer 6

• Produces genetically identical daughter cells (i.e. clones – maintains same number of chromosomes as the parent cell).
• Growth of tissue/organism (not of cells)
• Replacement of worn out/damaged cells
• Repair of body tissues (e.g. bone, muscle etc)
• Asexual reproduction/cloning

Question 7

Stages of the Cell Cycle

Answer 7

The cell cycle has two stages:
Interphase (‘preparation phase’):
* G1 (‘Growth phase 1)
* S (DNA ‘synthesis’)
* G2 phases (‘Growth phase 2’)
M Phase (‘dividing phase’):
* Mitosis
* Cytokinesis

Question 8

G1

Answer 8

G1 – First growth phase of cell, synthesis of proteins, organelles replicate e.g. mitochondria, ribosomes etc. Cell increases in size.
End of G1 checkpoint.

Question 9

S

Answer 9

S – Synthesis phase. Replication of each chromosome in the nucleus. They are now called sister chromatids (joined at the centromere).

Question 10

G2

Answer 10

G2 – Second growth phase, cell continues to grow in size. Duplicated DNA is checked for errors. Energy stores (i.e. ATP molecules) are increased.
End of G2 checkpoint.

Question 11

Cell Cycle Checkpoints

Answer 11

• G1 Checkpoint
• G2 Checkpoint
• Spindle assembly/metaphase
  checkpoint

Question 12

G0 Phase

Answer 12

G0 – phase where the cell leaves the cell cycle either temporarily or permanently.

Question 13

what might happen if the DNA is not checked?

Answer 13

• Mutations in the DNA sequence
• Faulty DNA produced
• Error in copying daughter cells
• Daughter cells will not receive identical genetic
  information
• Proteins not made or do not function properly

Question 14

Homologous Chromosomes

Answer 14

• A pair of chromosomes – one
  maternal (from mother) and one
  paternal (from father)
• The chromosomes carry the
  same genes but may carry
  different forms of the genes. A
  alternate form of the same gene
  is called an allele.
• E.g. gene is eye colour, alleles
  could be brown, green, blue etc.

Question 15

Sister Chromatids

Answer 15

Sister Chromatids: identical, carry the same versions of all their genes because one was produced as an exact copy of the other.

Question 16

stages of mitosis

Answer 16

Question 17

interphase

Answer 17

• Before mitosis can occur, each DNA molecule (chromosome) in the nucleus is replicated
  during the interphase.
• Each chromosome is converted into two identical DNA molecules called chromatids.
• The two chromatids are joined together at a region called the centromere.
• Condensed chromosomes combined with histone proteins are called chromatids

Question 18

prophase

Answer 18

• Chromosomes condense and thicken (and therefore
  become visible)
• Consists of sister chromatids (2) joined at the
  centromere.
• Two centrioles migrate to opposite poles of the cell
  (in animal and some plant cells)
• Spindle fibres attach to specific areas on the
  centromeres and start to move the chromosomes to
  the centre (equator) of the cell.
• Nuclear envelope disappears.

Question 19

metaphase

Answer 19

• Brief phase
• Individual sister chromatids
  (chromosomes) are moved by the
  spindle fibres to align at the
  metaphase plate/equator at the
  centre of the cell.
• Sister chromatids are attached to the
  spindle fibres by the centromere.

Question 20

anaphase

Answer 20

• Centromeres holding the pairs of
  chromatids in each chromosome
  divide.
• Sister chromatids separate
• Spindle contracts (fibres shorten)
• Each chromatid is pulled by their
  centromere to opposite poles of
  the cell.

Question 21

telophase

Answer 21

• Chromatids have reached opposite poles of the cell. They
  uncoil and become long and thin again.
• They are now called chromosomes
• Spindle fibres disappear
• Nuclear envelope reforms and enclose around the
  chromosomes at each pole.

Question 22

Cytokinesis

Answer 22

• This is the phase where the cell surface membrane & cytoplasm divides.
• In animal cells a ‘cleavage furrow’ forms.
• In plant cells a ‘cell plate’ forms.
• This results in 2 genetically identical daughter cells being formed.