inheritance of sameness Flashcards
Purine and pyrimidine base-pairing in DNA/RNA
guanine=cytosine
adenine=thymine(or uracil)
Direction of movement of DNA polymerase on template strands
DNA polymerase moves from 5’ to 3’ on the template strand.
Meaning of semi-conservative, leading strand and lagging strand
DNA replication is semiconservative; each stand in double helix acts as a template strand for synthesis of a new complimentary, antiparallel strand.
during DNA replication, leading strand is made as a continuous piece - other one, lagging strand is made in small pieces (due to 5’to3’ polarity).
General action of proteins
helicase: unwinds double helix.
topoisomerase: avoids twisting of DNA ahead of replication fork.
primase: synthesizes RNA primer in the 5’to3’ direction to initiate new DNA strand.
DNA polymerase III: extends RNA primer by adding DNA nucleotides to it.
DNA polymerase I:uses 5’to3’ exonucleus activity to remove/replace RNA
DNA ligase: seals nick left b/w fragmentd after RNA primer replaced with DNA.
3’ vs 5’ polarity of nucleic acid chains involved in DNA replication
phosphate group bound to 5’ carbon of deoxyribose sugar and hydroxyl group is bound to 3’ carbon of deoxyribose sugar
Direction of elongation
3’ to 5’. the 5’ end cant extend
STUDY THIS !! Structure of a replication bubble
USE SIMUTEXT!!!
Main features of chromosome anatomy
centromere at middle, telomere at ends.
Meaning of “n” and “C”
n is the number of unique chromosomes. its coefficient(ploidy) tells #of unique sets present in organism. e.g. homologous pair is 2n
c is the amount of DNA in one set of organism’s nuclear chromosome (genome size). its coefficient tells how many times entire genome is present in a cell. e.g. homologous pair is 4c
Changes in the coefficient of n and C throughout the cell cycle (i.e n vs 2n, 2C vs 4C etc.)
c duplicates during s phase and reverts near end of mitosis.
n remains constant!!
What does n imply about C, or vice versa?
nothing!!
The C-value paradox
value varies among diff species. DNA size doesn’t determine complexity of organism.
STUDY THIS!! How to solve problems when given a karyotype (can you determine ploidy, n-value, how many copies of genome…?)
Q!!
The structure of DNA
phosphate group attached to 5-carbon sugar attached to nitrogenous base.
3’to5’ end on each strand confers polarity on DNA backbone in opposite direction
Mechanisms that ensure inheritance of sameness
daughter cells inherit same DNA.
DNA polymerase only adds to free 3’OH - maintains sameness thru complementary base pairing. replisomes replicate one strand continuously, the other discontinuously.
DNA synthesizes 5’to3’ direction using 3’to5’ template.
when converting DNA to RNA, will change thymine to uracil which is still complementary to adenine.
STUDY THIS!! Structure of replication bubble (leading strand, lagging strand, placement of primers…)
Q
Cell senescence (/hayflick limit) and why cells reach this stage. what happens if it doesnt reach cell senescence?
the hayflick limit is #of times a cell can divide before cell division stops (60-70times) due to telomere running out. this leads to cell senescence (irreversible cell cycle arrest).
if cells fails to cell senescence it will undergo apoptosis or has the risk of become cancer cell.
telomere repetitive sequence
TTAGGG
Why chromosomes shorten at each replication
bc of incomplete replication of DNA molecule by DNA polymerase - ends can’t be copied.
Mechanism of telomerase action
extends template allowing new primers to be put on & so that DNA polymerase can extend it. (telomerase is not present in all cells - e.g. it is in stem, cancer, male germline, and embryonic stem cells)
telomere’s function
ends of chromosome that protects critical information
which mechanism can lead to mutation and why?
non-homologous end joining and excision repair bc they make changes in both strands
does transposition leave a copy of its transposon at original site?
not always - there are two methods, one in which they do so
how does distance of alleles affect recombination/crossing over?
alleles more likely to recombine if they’re further from one another
what is translocation?
a type of mutation. where segment of allele moved to a non-homologous chromosome
