DNA Structure & Replication Flashcards
what is a nucleotide monomer made of?
a phosphate group, ribose, nitrogenous base
which nucleotides are purines?
adenosine & guanosine
which nucleotides are pyrimidines?
thymidine & cytidine
how are single strands of DNA formed?
connecting nucleotides via covalent bonds from the phosphate groups to the deoxyribose sugars
within our body, when is DNA single stranded and not double stranded?
during replication
what does it mean for DNA to be “anti-parallel”
single strands are upside down compared to eachother, 5’ and 3’ ends are opposite from one another
how are single strands bound in double-stranded DNA?
by many weak hydrogen bonds between nitrogenous bases
what is “base-pairing”
binding between specific nucleotides
which base-pair is easier to break? G-C or A-T?
A-T (2 hydrogen bonds) whereas G-C has 3
describe the Watson and Crick “semi-conservative model” for DNa replication
double stranded DNA parent strand is separated into two single strands, each of which is used as a template to synthesize another strand of DNA, the resulting daughter DNA molecules consist of one parent strand and one newly synthesized strand
Double stranded DNA molecules are wrapped up with proteins inside the cell in order to form what structures?
chromosomes
What phase does DNA replication occur during?
interphase
What structures does DNA replication result in?
two sister chromatids
Where does DNA replication start? What does this create?
at multiple origins of replication, creating replication bubbles
What is the purpose of having multiple origins of replication?
makes replication go significantly faster, it is more efficient
purpose of helicase
separates dsDNA into single strands at the origin of replication
purpose of single strand binding protein
keeps strands apart and prevent rewinding of the double helix
purpose of topoisomerase
releases mechanical stress in front of helicase
purpose of primase
makes the RNA primer (small section of dsDNA) that allows the DNA polymerase to start synthesizing
how is the RNA primer removed
via a nuclease
How does DNA polymerase add nucleotides?
creates a new covalent bond between the last deoxyribose sugar group and the phosphate group of a free floating nucleotide monomer
How is the leading strand synthesized?
continuously in the 5’ to 3’ direction
How is the lagging strand synthesized?
in Okazaki fragments because DNA polymerase can only synthesize in the 5’ to 3’ direction, uses multiple RNA primers that the DNA polymerase jumps to
How many base pairs in the human genome?
3.1 billion
What is a byte? What is a bit?
byte = 8 bits
bit = one digital piece of info (0 or 1)
How many bits are needed to encode (A, T, C, G)?
Two: A(0,0) T(0,1) C(1,0) G(1,1)
How many GB in the human genome?
0.775 GB (7 powerpoints)
How does DNA polymerase detect errors?
mismatch is sensed as a bulge, DNA polymerase backs up and breaks the covalent bond cutting out incorrect nucleotide, then DNA polymerase resynthesizes correct nucleotide
If DNA polymerase doesn’t catch the errors, what enzyme does?
nucleases cut out incorrect nucleotides and DNA polymerase resynthesizes
structure of dsDNA of prokaryotes
circular
structure of dsDNA in eukaryotes
linear
How do eukaryotes solve the issue of a 3’ overhang after a round of replication?
telomerase uses its own RNA template to extend the 3’ end and then DNA polymerase can make a new Okazaki fragment
What happens to telomere length as humans age?
telomere length declines due to decreased telomerase activity, which increases mortality
What problem does having short telomeres present?
ends of telomeres can’t form protective T loop, the cell detects the free end as a dsDNA break and so it puts a stop to cell division and the cell gets old
Which strand poses the 3’ overhang issue?
lagging strand
which enzyme connects the Okazaki fragments of the lagging strand?
ligase
