cycle 2

Question 1

location of DNA in eukaryotic and prokaryotic cells

Answer 1

in the nucleus

Question 2

phases and main characteristics of the cell cycle for prokaryotic cells

Answer 2

B period - from birth to the initiation of DNA replication. cell grows in size
C period - replication in middle of cell where DNA enzymes are located. chromosome is replicated (begins at ori) and the resulting daughter chromosomes move to opposite ends
D period - cell division begins. new cell wall is synthesized. cell divides by binary fission and forms two daughter cells

Question 3

phases and main characteristics of the cell cycle for eukaryotic cells

Answer 3

G1 - period of growth before DNA replicates. gap where no DNA is synthesized, cell continues to function.
S - DNA replication and chromosome duplication occur. continues synthesis
G2 - second gap where cell growth continues and cell prepares for mitosis. no DNA synthesis, continues to synthesize RNAs and proteins. marks the end of interphase
M - mitosis

Question 4

stages and main characteristics of mitosis

Answer 4

prophase - chromosomes condense
prometaphase - nuclear envelope disappears, spindle fibre enters, microtubules from opposite poles attach to the kinetochores of each chromosome
metaphase - chromosomes align at midpoint
anaphase - sister chromatids separate and move to opposite poles
telophase - chromosomes unfold, return to interphase state, nuclear envelopes form, cytoplasm divides by furrowing
interphase - two daughter cells are genetic duplicates

Question 5

stages and main characteristics of meiosis I

Answer 5

prophase I - chromosomes condense, homologous chromosomes pair together
prometaphase I - nuclear envelope breaks down, spindle enters the former nuclear area. chromosomes attach to kinetochore microtubules
metaphase I - random alignment of chromosomes (independent assortment)
anaphase I - two chromosomes of each homologous pair separate and move to opposite spindle poles
telophase I - transitory stage, little or no change in the chromosomes. cell division (cytokinesis) in telophase I creates truly haploid cells

Question 6

stages and main characteristics of meiosis II

Answer 6

prophase II - chromosomes condense
prometaphase II - nuclear envelope breaks down. spindle enters the former nuclear area, spindle microtubules leading to opposite spindle poles attach to the two kinetochores of each chromosomes
metaphase II - movements of the spindle microtubules align the chromosomes on the metaphase plate. independent assortment
anaphase II - sister chromatids of each chromosomes separate from each other and move to opposite spindle poles. separated chromosomes (now chromatids) have been segregated to the two poles
telophase II - chromosomes begin decondensing, spindles disassemble, new nuclear envelopes form around the masses of chromatin. cells divide. result is four haploid cells with half the number of chromosomes.

Question 7

basic mechanism of DNA recombination in prophase of meiosis

Answer 7

homologous chromosomes pair
crossover between non-sister chromatids
takes place at random

Question 8

randomness of alignment of homologous pairs in metaphase I

Answer 8

accounts for the second major source of genetic variability

Question 9

reason why G1 and G2 phases exist

Answer 9

gap for growth. no DNA synthesis. synthesis of RNAs and proteins

Question 10

location of actively cycling cells in multicellular animals

Answer 10

specialized tissues that produce gametes and spores respectively

Question 11

purpose of cell division and risk if cells grow too large in size

Answer 11

needs a high SA:V ratio
able to satisfy demands of the cell - easier diffusion

Question 12

main role of cell cycle checkpoints

Answer 12

ensure accurate cell division by preventing critical phases from beginning until the previous phases are completed correctly (no replication or division of mutations

Question 13

positive regulation at cell cycle checkpoints

Answer 13

cyclins and CDKs
phosphorylation cascade - cyclin binds to CDK. cyclin-CDK complex is phosphorylated. activated cyclin-CDK complex phosphorylates target protein. phosphorylated target protein changes to active form. moves cell into next stage of cell cycle.

Question 14

negative regulation at cell cycle checkpoints

Answer 14

p53, p21, Rb
p53 detects DNA damage and increases p21 (cyclin-DCK inhibitor) production by binding to p21 promoter. cyclin-CDK complex inactivated, cannot phosphorylate proteins involved in cell cycling
inhibits the cell cycle
apoptosis - if DNA damage can be repaired, positive regulation pathway stimulated. if DNA damage cannot be repaired, p53 triggers apoptosis

Question 15

risk of any protein involved at the cell cycle checkpoints not functioning properly

Answer 15

mutations replicate and divide - cancer

Question 16

why p53 is considered the guardian of the genome

Answer 16

prevents mutations from replicating

Question 17

examples of situations in which cells would be programmed to die by apoptosis

Answer 17

if DNA damage cannot be repaired
cells between fingers

Question 18

what the process of mitosis ensures in subsequent generations

Answer 18

genetically identical DNA sequences

Question 19

main differences between mitosis and meiosis

Answer 19

mitosis - one cell division, produces 2 genetically identical daughter cells, 2n→2n
meiosis - two cell divisions produces 4 not genetically identical cells, 2n→n

Question 20

why meiosis I is “reductional” and meiosis II is “equational”

Answer 20

I - 2n→n
II - n→n

Question 21

characteristics of homologous chromosomes

Answer 21

one paternal one maternal
same genetic info and size

Question 22

mechanism of recombination during prophase. how do homologues pair in order for all non-sister chromatids to participate in recombination

Answer 22

crossover between non-sister chromatids. homologous chromosomes pair together. undergo recombination by exchanging segments (crossover) resulting in new combinations of alleles.

Question 23

mechanism by which recombination creates novel combinations of alleles

Answer 23

independent assortment
crossover

Question 24

relationship between distance between alleles and the likelihood that they will be inherited together; linked genes

Answer 24

higher probability of being inherited together if closer together

Question 25

other mechanisms giving rise to variation in meiosis

Answer 25

homologous recombination
independent assortment
random fertilization

Question 26

mechanisms giving rise to aneuploid products of meiosis

Answer 26

non-disjunction - chromosomes do not separate properly

Question 27

relationship between age of an oocyte and the risk of offspring having down syndrome

Answer 27

accumulating mutations over time

Question 28

products of mitosis and meiosis in animals

Answer 28

gametes arise by meiosis
zygote divides by mitosis

Question 29

products of mitosis and meiosis in plants and most fungi

Answer 29

gametes arise by mitosis
spores are formed by meiosis

Question 30

products of mitosis and meiosis in other fungi and algae

Answer 30

gametes arise by mitosis
zygote divides by meiosis