cycle 3

Question 1

purine and pyrimidine base-pairing in DNA/RNA

Answer 1

purine - adenine and guanine. built from a pair of used rings of carbon and nitrogen atoms
pyrimidines - thymine and cytosine. built from a single carbon ring

Question 2

direction of movement of DNA polymerase on template strands

Answer 2

DNA polymerase moves along the template strand towards its 5’ end
DNA polymerase assemble nucleotides from 5’ to 3’
template strand is “read” from 3’ to 5’

Question 3

semi-conservative

Answer 3

“old” strand is template for synthesis of its partner. results in two double helices each with one strand derived from the parental DNA. consists of the identical base-pair sequences as the parental DNA

Question 4

leading strand and lagging strand

Answer 4

leading strand - new DNA strand synthesized in the direction of DNA unwinding.
lagging strand - strand synthesized si continuously in the opposite direction

Question 5

general action of proteins involved in DNA replication

Answer 5

Helicase - unwinds DNA
Topoisomerase - prevents twisting ahead of the replication fork as DNA unwinds
Single-stranded binding proteins - coat single-stranded DNA segments, keeping the two strands from pairing back together
Primase - lays down RNA primer
DNA polymerase III - extends primer by adding DNA nucleotides
DNA polymerase I - replaces RNA primer with DNA nucleotides
Ligase - repairs gap in phosphate sugar backbone

Question 6

3’ vs 5’ polarity of nucleic acid chains involved in DNA replication

Answer 6

3’ end - has an OH (hydroxyl) group attached
5’ end - has a phosphate group attached

Question 7

direction of elongation of a given DNA strand

Answer 7

5’ to 3’. new nucleotides are added to the 3’ end

Question 8

structure of a replication bubble

Answer 8

two replication forks: two Ys joined together at their tops

Question 9

main features of chromosomes anatomy

Answer 9

2 double helices

Question 10

n-value and coefficient of n

Answer 10

n-value: number of unique nuclear chromosomes present in an organism
coefficient of n (ploidy): number of unique sets present in an organism

Question 11

C-value and coefficient of C

Answer 11

C-value: amount of DNA in one set of an organism’s nuclear chromosomes, genome size, quantity of base pairs or mass (picograms)

Question 12

changes in the coefficient of n and C throughout the cell cycle

Answer 12

mitosis: 2n/4C → 2n/2C
meiosis I: 2n/4C → 1n/2C
meiosis II: 1n/2C → 1n/1C

Question 13

what does n imply about C, or vice versa

Answer 13

n implies nothing about C

Question 14

the C-value paradox

Answer 14

there is no correlation between C and complexity
some organisms have a high C value however are not complex

Question 15

how the process of gamete production and meiosis can change with ploidy (general)

Answer 15

changes in ploidy can disrupt the usual meiotic processes. gamete production becomes less efficient, the likelihood of producing aneuploid gametes increases

Question 16

how the process of gamete production and meiosis can change with diploidy

Answer 16

meiosis reduces chromosomes number by half. two sequential divisions result in four haploid gametes. essential for maintaining genetic diversity and ensuring that offspring have the same diploid chromosome number as parents

Question 17

how the process of gamete production and meiosis can change with triploidy

Answer 17

meiosis problematic, chromosomes must pair and segregates properly. leads to complex configurations where some chromosomes fail to segregate properly resulting in aneuploid gametes

Question 18

how the process of gamete production and meiosis can change with tetraploidy

Answer 18

meiosis is more complex (4n → 2n requires multiple rounds of meiosis). unstable process - may result in production of aneuploid gametes

Question 19

structure of DNA

Answer 19

deoxyribose (from 1’ to 5’), phosphate, nitrogenous bases (AGTC)
double helix - purine and pyrimidine paired together fill the space between backbone chains (complementary base-paring)

Question 20

mechanisms that ensure inheritance of sameness

Answer 20

DNA replication (ensures that each daughter cell receives and identical copy of the genetic info from parent cell)
mitosis (results in the production of two daughter cells, each with the same genetic material as parent cell)

Question 21

structure of replication bubble

Answer 21

two replication forks created from ori
DNA polymerase synthesizes from 5’ to 3’ on leading strand. grows continuously in the same direction as the replication fork moves
DNA polymerase synthesizes in series of short discontinuous fragments (Okazaki fragments) from 5’ to 3’
each Okazaki fragment requires a primer to initiate synthesis

Question 22

cell senescence and Hayflick limit definitions and why cells reach these stages

Answer 22

senescence: irreversible cell cycle arrest (will not replicate)
Hayflick limit: number of times a cell divides before cell division stops (60-70). telomere is too short for DNA to replicate (shoelace cap)

Question 23

telomere repetitive sequence

Answer 23

TTAGGG

Question 24

why chromosomes shorten at each replication

Answer 24

DNA at end of lagging strand cannot be full copied (no 3’ OH)

Question 25

mechanism of telomerase action

Answer 25

telomerase restore length of telomeres, extends the template