The Cell Cycle and Mitosis

Question 1

Diploid (2n)

Answer 1

Contain two copies of each chromosome

Question 2

Haploid (n)

Answer 2

Containing only one copy of each chromosome

Question 3

Interphase

Answer 3

First 3 stages of cell cycle: contains G1, S, and G2 –> longest part of the cell cycle; actively dividing cells spend about 90% of their time in interphase.

Question 4

G0 phase

Answer 4

Cell is simply living and carrying out its functions, without any preparation for division

Question 5

G1 stage

Answer 5

Cells create organelles for energy and protein production (mitochondria, ribosomes, and endoplasmic reticulum) while also increasing their size.

Question 6

Restriction point

Answer 6

Occurs in G1 stage. Certain criteria, such as containing the proper complement of DNA, must be met for the cell to pass the restriction point and enter the synthesis stage.

Question 7

S stage

Answer 7

Cell replicates its genetic material so that each daughter will have identical copies.

Question 8

Does cell ploidy change after replication in synthesis stage?

Answer 8

No: chromatids have doubled, so twice as much DNA is present, but ploidy is still the same.

Question 9

G2 stage

Answer 9

Cell checks to ensure that there are enough organelles and cytoplasm for 2 daughter cells.

Question 10

p53`

Answer 10

The main protein in control of the restriction checkpoint, and also at the G2/M checkpoint.

Question 11

Molecules responsible for the cell cycle

Answer 11

Cyclins and Cyclin-dependent kinases (CDK)

Question 12

How do CDKs work

Answer 12

During the cell cycle, concentration of the various cyclins increase and decrease during specific stages. These cyclins bind to CDKs, creating an activated CDK-cyclin complex, which can then phosphorylate transcription factors –> then promote transcription of genes required for next stage of cell cycle.

Question 13

List the phases of mitosis and describe briefly

Answer 13

Prophase – chromosomes condense, spindle forms
Metaphase – chromosomes align
Anaphase – sister chromatids separate
Telophase – new nuclear membranes form

Question 14

Meoisis I

Answer 14

Results in homologous chromosomes being separated, generating haploid daughter cells; this is known as reductional division.

Question 15

Meiosis Ii

Answer 15

Similar to mitosis: results in separation of sister chromatids without a change in ploidy –> therefore known as equational division

Question 16

How is Prophase I meiosis different than Prophase in mitosis

Answer 16

In meiosis, in prophase I, homologous chromosomes come together and intertwine in a process called synapsis. Then crossing over occurs during genetic recombination

Question 17

Tetrad

Answer 17

In prophase I of meiosis, each chromosome consists of 2 sister chromatids –> each synaptic pair contains 4 chromatids

Question 18

Synaptonemal complex

Answer 18

The group of proteins that hold together homologous chromosomes in prophase I of Meiosis

Question 19

Chiasma (plural chiasmata)

Answer 19

Point of contact between homologous chromosomes, where they may break and exchange equivalent pieces of DNA –> crossing over.

Question 20

Mendel’s second law of independent assortment

Answer 20

States that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes, explained by crossing over.

Question 21

How is Metaphase I in meiosis different than metaphase in mitosis

Answer 21

In mitosis, each chromosome is lined up on the metaphase plate by two spindle fibers (one from each pole).
In meiosis, homologous chromosomes are lined up across from each other at the metaphase plate and are held by one spindle fiber

Question 22

How is Anaphase I in meiosis different than anaphase in mitosis

Answer 22

Process is called disjunction, accounts for Mendel’s first law (of segregation). Each chromosome of paternal origin separates from its homologue of maternal origin –> either chromosome can end up in either daughter cell –> this random separation is called segregation

Question 23

How is Telophase I different than telophase in mitosis

Answer 23

Cells are now haploid in meiosis: e.g in humans, only 23 chromosomes are now found in each daughter cell.

Question 24

Hemizygous

Answer 24

Describes the characteristic way males inherit genes on the X chromosome, as they only have one copy.

Question 25

SRY (sex-determining region Y)

Answer 25

One notable gene on the Y chromosome, which codes for a transcription factor that initiates testis differentiation and , thus, the formation of male gonads.