cycle 3 Flashcards
(25 cards)
purine and pyrimidine base-pairing in DNA/RNA
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
direction of movement of DNA polymerase on template strands
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’
semi-conservative
“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
leading strand and lagging strand
leading strand - new DNA strand synthesized in the direction of DNA unwinding.
lagging strand - strand synthesized si continuously in the opposite direction
general action of proteins involved in DNA replication
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
3’ vs 5’ polarity of nucleic acid chains involved in DNA replication
3’ end - has an OH (hydroxyl) group attached
5’ end - has a phosphate group attached
direction of elongation of a given DNA strand
5’ to 3’. new nucleotides are added to the 3’ end
structure of a replication bubble
two replication forks: two Ys joined together at their tops
main features of chromosomes anatomy
2 double helices
n-value and coefficient of n
n-value: number of unique nuclear chromosomes present in an organism
coefficient of n (ploidy): number of unique sets present in an organism
C-value and coefficient of C
C-value: amount of DNA in one set of an organism’s nuclear chromosomes, genome size, quantity of base pairs or mass (picograms)
changes in the coefficient of n and C throughout the cell cycle
mitosis: 2n/4C → 2n/2C
meiosis I: 2n/4C → 1n/2C
meiosis II: 1n/2C → 1n/1C
what does n imply about C, or vice versa
n implies nothing about C
the C-value paradox
there is no correlation between C and complexity
some organisms have a high C value however are not complex
how the process of gamete production and meiosis can change with ploidy (general)
changes in ploidy can disrupt the usual meiotic processes. gamete production becomes less efficient, the likelihood of producing aneuploid gametes increases
how the process of gamete production and meiosis can change with diploidy
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
how the process of gamete production and meiosis can change with triploidy
meiosis problematic, chromosomes must pair and segregates properly. leads to complex configurations where some chromosomes fail to segregate properly resulting in aneuploid gametes
how the process of gamete production and meiosis can change with tetraploidy
meiosis is more complex (4n → 2n requires multiple rounds of meiosis). unstable process - may result in production of aneuploid gametes
structure of DNA
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)
mechanisms that ensure inheritance of sameness
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)
structure of replication bubble
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
cell senescence and Hayflick limit definitions and why cells reach these stages
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)
telomere repetitive sequence
TTAGGG
why chromosomes shorten at each replication
DNA at end of lagging strand cannot be full copied (no 3’ OH)
