chapter 16- dna replication Flashcards
what is transformation
change in genotype and phenotype due to the assimilation of foreign dna
what is a virus/bacteriophage
dna or rna enclosed in a protective coat made of protein
how do viruses work
they infect their dna in the host cell, take over the machinery and make more viruses, the host cell bursts and releases the viruses
what are chargaff’s rules
base composition of dna varies between species
[A] = [T] and [C] = [G] in all species
how are dna strands built
antiparallel from 5’ to 3’
what group is at the 3’ and 5’ ends
free hydroxyl at the 3’ end
free phosphate at the 5’ end
how much space is present between the strand
enough for one purine and one pyrimidine (3 rings)
what is the diameter of the helix
2 nm
how many hydrogen bonds are between bases
adenine and thymine have 2
cytosine and guanine have 3
what is the semi conservative model
when the double helix replicates each daughter molecules will have one parental strand and one newly made strand
where does replication start
at specific sites called origins of replication
what happens at origins of replication
two dna strands are separated and a replication bubble is formed
what is a replication fork
the y shaped region at the end of the bubble where dna strands are separating
what does the helicase do
enzyme that unzips the double helix at the replication forks
what stabilizes the separated dna strands
single strand binding proteins
what do topoisomerase do
breaks, twists and rejoins the dna strands when they are too coiled ahead of the forks
what does primase do
puts down rna nucleotides to make rna primer which starts the replication strand
how many nucleotides are present in the rna primer
5-10
what enzyme elongates the new strand
dna polymerase
what is the rate of elongation in human cells
50 nucleotides per second (slow)
what is added to the new dna strand and what happens to it when it binds
nucleoside triphosphate
loses two phosphate groups as pyrophosphate
what supplies nucleotides to dna and whats different about it
datp, dgtp, dctp and dttp
has deoxyribose sugar unlike atp which has ribose
what is the difference between the leading strand and the lagging strand and why does it happen
leading is built continuously
lagging makes okazaki fragments that need to be joined
strand can only be built 5’ to 3’
what joins okazaki fragments together
ligase enzyme
