Biochemistry of Nucleic Acid Flashcards
What is the genome
total DNA in each cell
carries genetic information which is stored in the nucleotide sequence
the sequence determines the amino acid sequence of polypeptide chain
What is DNA
polymer
2 complimentary antiparallel helices that contain a sugar phosphate backbone on outside and bases on inside
what elements is DNA composed of
C, H, N, O, P
2 types of nucleotide shape
purines and pyrimidines - join together by hydrogen bonds
where does transcription take place
nucleotide to nucleotide in nucleus formation of RNA from DNA
pre-mRNA formed then undergoes splicing to form RNA
where does translation occur
nucleotide to amino acid
RNA to polypeptide chain
occurs in cytoplasm
difference between DNA and RNA
RNA has a hydroxyl group on second carbon whereas DNA only has a hydrogen atom
what is a nucleoside
base and sugar
what is a nucleotide
nucleoside + phosphate group
what bases occur in DNA
adenosine
cytosine
guanine
thymine
what bases are pyrimidines
uracil
thymine
cytosine
what bases occur in RNA
adenosine
cytosine
guanine
uracil
what bases are purines
adenosine
guanine
during polymerisation off DNA/RNA what is a phosphodiester bond formed between
a free 3’ OH group and 5’ triphosphate
consumes 2 high energy bonds
what does each gene produce
number of different proteins
only small number of genes are expressed
what does carbon 1 have attached
a base
what does carbon 5 have attached
a phosphate
where can new nucleotides only be added to
free 3’ OH group forming phosphodiester bond
how do nucleotide analogies work as drugs
ZDV and AZT = retrovir
analogue of thymidine
incorporated into growing viral of DNA
Lachs 3’ OH group therefore chain elongation is terminated, prevents transcription
How does ZDV work as a drug
reverse transcriptase has a higher affinity for ZDV than human DNA polymerase so turn RNA into DNA infecting host cell and uses DNA to make products which makes new viral cell
why is DNA antiparallel
one 5’ to 3’
one 3’ to 5’
what must take place before cell division/mitosis
DNA must replicate so daughter cells have complete compliment of genome
replication is semi-conservative
what is DNA replication catalysed by
DNA polymerase
what is the role of DNA polymerase
adds nucleotides to growing DNA strand
cannot start DNA synthesis on its own
requires an RNA primer to start replication
why do eukaryotic genomes have many origins of replication
replication starts simultaneously at several points in genome
bidirectional
ensures replication can be finished in reasonable time
why is DNA replication discontinuous
nucleotides can only be adde to the free 3’ end therefore synthesising in a 5’ to 3’ direction
what is the leading strand
always has a free 3’ end
what is the lagging strand
as DNA can only be added to 3’ end the 5’end being replicated must be replicated in short segments called Okazaki fragments
primer binds as DNA unwinds then nucleotides added
as more template unwinds more primers bind and catch up with itself
what is the role of helicase
unwinds DNA, stops It rewinding
what is the role of DNA ligase
primers distend, then DNA ligase joins nucleotides by forming phosphodiester bonds between them in the lagging strand
what is RNA primer synthesised by
primase
what is the replication fork
unwound DNA
leading template strand (3’ to 5’)
lagging template strand (5’ to 3’)
what are the building blocks for DNA replication
dATP, dTTP, dCTP, dGTP
what do they 3 phosphates do
one phosphate group forms phosphdiester bond
leaves two phosphates as pyrophosphate - energy supply
what can incorporation of the wrong nucleotide result in
can create mutations
can be deleterious
errors occur once every 10000-100000 base pairs
what activity does DNA polymerase have
3’ -> 5’ exonuclease activity
removes incorrect nucleotide
improves error rate
proofreads and repairs
