Mitosis and meiosis + experimental evidence

Question 1

Cell cycle definition

Answer 1

Repeated cycles of macromolecular synthesis (growth) and division (mitosis)- the regular sequence of events that produces new cells.

Question 2

Two main phases of the cell cycle

Answer 2

Interphase and mitosis

Question 3

What periods are within interphase?

Answer 3

G1, G2 and S phase

Question 4

G1 length

Answer 4

Longest of the phases

Question 5

G1 explained

Answer 5

Period of active RNA and protein synthesis, including proteins controlling progress through the cell cycle.
Cell volume, that was halved in mitosis, is restored

Question 6

S phase explained

Answer 6

Characterised by DNA replication, histone synthesis and centriole duplication

Question 7

G2 length and explained

Answer 7

Relatively short, proteins required for mitosis accumulate

Question 8

What is the overall function of the gap phases?

Answer 8

Allow time delays for cell growth

Question 9

What does the length of G1 depend upon?

Answer 9

How favourable the extracellular conditions are. If conditions are unfavourable then the cells delay progress through G1.

Question 10

What happens if conditions are unfavourable?

Answer 10

If conditions are unfavourable then the cells delay progress through G1.

May enter a specialised resting state known as G0, in which the cells can remain for days, weeks or months before resuming proliferation.

Question 11

What activates postmitotic G0 cells + process?

Answer 11

Growth factors or signals from the extracellular environment called mitogens bind and to the cell surface receptors and trigger a cascade of kinase signalling in the cell.

Cells are maintained at the restriction point at the G1/S boundary until sufficient enzymes and nutrients are required for DNA synthesis have accumulated.

Question 12

Checkpoint function and locations

Answer 12

Entry or progression into the next phase of the cell cycle is monitored at specific checkpoints before the beginning of each phase. Certain conditions must be met to continue

Question 13

What regulates the checkpoints +function?

Answer 13

Cyclins. Different cyclins present during different cell cycle phases each activating one or more specific cyclin-dependent kinases.

Question 14

How do CDK work?

Answer 14

Phosphorylate specific proteins including enzymes, transcription factors and cytoskeletal subunits triggering activities in the phase.

Question 15

What happens after the phase is completed?

Answer 15

CDKs are ubiquitinated and broken down by proteasomes and a new cyclin for the next phase takes over.

Question 16

Gene that encodes for an important CDK?

Answer 16

CDC2

Question 17

Why is CDC2 important?

Answer 17

Codes for a CDK that appears both at G1 and G2 phase

Question 18

How was CDC2 proven to checkpoint two phases?

Answer 18

Lee and Nurse

Known already that CDC2 mutants

Question 19

6 stages of mitosis

Answer 19

Prophase, pro metaphase, metaphase, anaphase, telophase and cytokinesis

Question 20

Explain each stage of mitosis and their appearance

Answer 20

prophase- nucleolus disappears, replicated chromatin condenses, into threadlike chromosomes, with the sister chromatids attached to one another at the centromere. Two centrosomes with their duplicated centrioles move to opposite poles. Late in prophase lamina and inner nuclear membrane are phosphorylated causing the nuclear envelope to disappear into vesicles

Prometaphase- Late in prophase lamina and inner nuclear membrane are phosphorylated causing the nuclear envelope to disappear into vesicles

metaphase- chromosomes condense further into large protein complexes called kinetochores. Microtubules produced by centrioles move the chromosomes to the equatorial plate

anaphase- sister chromatids (bound by cohesin protein) separate and move to opposite poles- by a combination of microtubule motor proteins and dynamic changes in length of the spindle.

Telophase- two sets of chromosomes begin reverting to their uncondensed state. Microtubules depolymerise, two nuclear envelopes begin to reform.

Cytokinesis- belt like contractile ring of actin filaments forms at the cell’s equator. Constriction of the ring produces a cleave furrow and progresses until organelles and cytoplasm are divided, with each daughter cell containing a nucleus.

Question 21

Meiosis definition

Answer 21

Specialised process involving two closely associated cell divisions that occurs only in the cells that will form sperm and egg cells

Question 22

What are sperm and egg cells called?

Answer 22

Gametes

Question 23

What occurs during sexual reproduction?

Answer 23

Two gametes fuse to form offspring with a new gene combination, derived from both parents.

Question 24

Two features that characterise meiosis

Answer 24

Early in meiosis, homologous chromosomes of each pair come together in a process known as synapsis where double stranded breaks and repairs may result in DNA exchange known as crossovers.

Cells produced are haploid, meaning they have half the genetic material of a diploid cell (23 chromosomes in humans)

Question 25

What is the benefit of crossovers?

Answer 25

Produce new combinations of genes in the chromosomes increasing genetic diversity.

Question 26

Two stages of meiosis

Answer 26

Meiosis 1 and meiosis 2

Question 27

Meiosis 1 explained

Answer 27

Division where homologous pairs are pulled to separate poles.-producing two identical diploid cells

Question 28

What is a tetrad?

Answer 28

Term used to describe synaptic chromosomes, as there are 4 copies of each genetic sequence present in each homologous pair (due to the sister chromatid formation)

Question 29

Meiosis 2 explained

Answer 29

Each of the cells divide again- chromatids separate- form 4 haploid cells in total. Resembles mitosis

Question 30

S phases in both meiosis 1 and 2

Answer 30

meiosis 1- normal S phase

meiosis 2- no intervening s phase

Question 31

How is cell proliferation measured?

Answer 31

Radioactively tag DNA using 3H-labeled thymidine. Able to see the formation of new DNA molecules, which occurred in S phase. Increase in S phase is synonymous with increase cell proliferation.

Question 32

What did Walther Flemming do?

Answer 32

Used aniline dyes to see structures that absorbed basophilic dyes, which he named chromatin. Studied cell division in vivo and in stained preparation using material from the fins and gills of salamanders. Drew out the different stages of mitosis.