2- eukaryotic cell cycle and division

Question 1

cell cycle definition

Answer 1

a regulated process in which cells divide into two identical daughter cells

Question 2

three stages of the cell cycle

Answer 2

• interphase: G1, S and G2
• mitosis: prophase, metaphase, anaphase and telophase
• cytokinesis

Question 3

chromatin

Answer 3

• DNA packaged with histones
• DNA + histones -> nucleosomes -> chromatin -> chromosomes

Question 4

homologous chromosome

Answer 4

• pair of chromosomes with the same sequence of genes, but different alleles
• one is inherited from each parent

Question 5

chromatid

Answer 5

one of two identical halves of a chromosome replicated for cell division

Question 6

sister chromatids

Answer 6

two identical halves of a chromosome, joined at the centromere

Question 7

centromere

Answer 7

it is the restricted region of a chromosome, linking a pair of sister chromatids

Question 8

centrosome

Answer 8

it consists of two centrioles, arranged at right angles to each other

Question 9

purpose of the cell cycle

Answer 9

• growth of multicellular organisms
• replacement of cells and repair of tissues
• asexual reproduction

Question 10

purpose of meiosis

Answer 10

• production of haploid gametes
• maintenance of chromosome numbers

Question 11

mitotic index

Answer 11

the amount of cell division occurring in a tissue is quantified using the mitotic index

Question 12

mitotic index =

Answer 12

number of cells containing visible chromosomes/ total cells in field of view

Question 13

cell counts

Answer 13

the number of cells in each stage of mitosis

Question 14

what does the cell count show

Answer 14

the relative duration of each stage in the cell cycle. the longer a phase, the more cells are likely to be going through the phase

Question 15

steps in the cell cycle

Answer 15

interphase (gap 1 -> synthesis -> gap 2) -> mitosis (prophase -> metaphase -> anaphase -> telophase) -> cytokinesis

Question 16

interphase- gap 1

Answer 16

• cells increase in size
• transcription occurs
• organelles replicate
• biosynthesis occurs: the generation of natural products through enzymatic reactions

Question 17

interphase- synthesis

Answer 17

• DNA replicates by semi- conservative replication
• each chromosome now consists of 2 sister chromatids
• the amount of DNA has doubled
• this is rapid because exposed DNA base pairs are more susceptible to mutations

Question 18

interphase- gap 2

Answer 18

• cells continue to increase in size and prepare for mitosis
• DNA is checked for errors
• energy stores (ATP content) are increased

Question 19

mitosis- prophase

Answer 19

• chromosomes supercoil
• the nuclear membrane breaks down, and the nucleolus disappears
• centrioles divide into two and move to opposite ends of the cell

Question 20

mitosis- metaphase

Answer 20

• chromosomes align at the metaphase plate at the equator of the cell
• chromosomes are joined to spindle via the centromere

Question 21

mitosis- anaphase

Answer 21

• centromeres divide
• spindle fibres shorten, and split the centromere to separate sister chromatids
• motor proteins walking along tubular

Question 22

mitosis- telophase

Answer 22

• chromosomes detach from spindle fibres and start to uncoil
• nuclear envelopes begin to form around each group of chromosomes
• there are now two nuclei
• spindle fibres break down and the nucleolus reforms

Question 23

cytokinesis- animal cells

Answer 23

• the plasma membrane is pulled inwards by the cytoskeleton
• it forms a cleavage furrow in the middle of the cell

Question 24

cytokinesis- plant cells

Answer 24

• vesicles from the golgi line up where the metaphase plate was to form a cell plate
• vesicles secrete a layer of calcium pectate called the middle lamella
• onto this, a primary cell wall made of cellulose microfibrils is laid down
• then a secondary cell wall at right angles is deposited
• the cell wall may be impregnated with lignin

Question 25

meiosis results in

Answer 25

genetic variation

Question 26

what are the two ways genetic variation can be achieved

Answer 26

- crossing over (meiosis 1, prophase 1) - independent assortment (meiosis 1, metaphase 1)

Question 27

crossing over

Answer 27

the exchange of sections of DNA between homologous chromosomes

Question 28

independant assortment

Answer 28

there are various combinations of maternal and paternal chromosome arrangement

Question 29

chromosome mutations are

Answer 29

changes to the number or structure of chromosomes

Question 30

types of chromosome mutations

Answer 30

- translocations - duplications - deletions - inversions - nondisjunctions

Question 31

translocations

Answer 31

part of one chromosome breaks off and reattaches to a different one

Question 32

deletions

Answer 32

a section of chromosome is removed, resulting in a loss of a large number of genes

Question 33

inversions

Answer 33

a part of a chromosome flips it’s orientation

Question 34

nondisjunctions

Answer 34

homologous chromosomes or sister chromatids fail to separate

Question 35

nondisjunctions can result in

Answer 35

- polysomy - monosomy

Question 36

polysomy

Answer 36

the presence of extra copies of chromosomes

Question 37

example of polysomy

Answer 37

down’s syndrome- there are 3 copies of chromosome 21

Question 38

monosomy

Answer 38

the absence of one member of a pair of chromosomes

Question 39

monosomy example

Answer 39

turner’s syndrome- monosomy of the sex chromosome, where only one sex chromosome is present in a cell (X chromosome)