Cell division

Question 1

What is the cell cycle?

Answer 1

regulated cycle of division with intermediate grow periods

Question 2

Outline the stages of the cell cycle?

Answer 2

1) interphase

2) mitosis or meiosis (nuclear division)

3) cytokinesis (cytoplasmic division)

Question 3

Outline what happens during interphase?

Answer 3

G1 = proteins from which organelles are synthesised are produced, organelles replicate and cell size doubles

S = each of the chromosomes duplicate in the nucleus

G2 = the cell continues to increase in size, energy stores increase, organelles divide and duplicated DNA is checked for errors

Question 4

What is the purpose of mitosis?

Answer 4

produces 2 genetically identical daughter cells for

• growth
• cell replacement/ tissue repair
• asexual reproduction

Question 5

Name the stages of mitosis?

Answer 5

• prophase
• metaphase
• anaphase
• telophase

Question 6

Outline what happens during prophase?

Answer 6

• chromosomes condense becoming visible
• centrioles move to opposite poles of the cell and spindle fibres form
• nuclear envelope and nucleus break down meaning chromosomes are free in the cytoplasm

Question 7

Outline what happens during metaphase?

Answer 7

sister chromatids line up at the cell equator attached to the mitotic spindle by their centromeres

Question 8

Outline what happens during anaphase?

Answer 8

• energy required from ATP hydrolysis
• spindle fibres contract = centromere dividing
• sister chromosomes separate in 2 distinct chromatids and are pulled to opposite poles of the cell
• spindle fibres break down

Question 9

Outline what happens during telophase?

Answer 9

• chromosomes decondense becoming invisible
• new nuclear envelope forms around each set of chromosomes each with 1 copy of each chromosome

Question 10

What happens during cytokinesis?

Answer 10

cell membrane cleavage furrows form and the cytoplasm divides

Question 11

How is the cell cycle regulated?

Answer 11

checkpoint regulated by cell-signalling proteins ensuring damaged cells don’t progress to next stage of cell cycle

Question 12

What happens at each key checkpoint in the cell cycle?

Answer 12

G1 = cell checks for DNA damage and cell enters cycle

G2 = cell checks chromosome replication

Metaphase = cell checks sister chromatids have attached to spindle correctly

Question 13

What is meiosis?

Answer 13

Form of cell division that produces genetically different haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes

Question 14

What happens during meiosis I?

Answer 14

• homologous chromosomes pair to form bivalents
• crossing over (exchange of sections of genetic material) occurs
• cell divides in 2 and homologous chromosomes randomly separate (each cell containing a maternal or paternal copy)

Question 15

What are homologous chromosomes?

Answer 15

A chromosome pair with genes at the same locus (1 maternal and 1 paternal gene). Some alleles remain the same while others are different

Question 16

What happens during meiosis II?

Answer 16

• independant segregation of sister chromatids
• each cell divides again producing 4 haploid cells

Question 17

How does meiosis produce genetic variation?

Answer 17

• crossing over during meiosis I
• independant assortment (random segregation) of homologous chromosomes and sister chromatids
• results in new allele combinations