DNA Flashcards
What makes up a nucleotide
- nitrogenous organic base (A+T C+G)
- sugar
- phosphate
Who discovered the double helix
Watson and crick in 1953
what type of backbone is DNA
Sugar phosphate backbone
what bonds hold the helix together
hydrogen bonds
how are the subunits linked
covalently
what are the purines
adenine and guanine
what are the pyrimidines
uracil, thymine, cytosine
where is uracil found
RNA
when is DNA formed
condensation reaction
what is polymerisation
subunit addition to the chain
how does DNA encode infromation
in the order of sequences of base pairs in the DNA strand
what do DNA strands form
Linear messages- they spell out the sequence of amino acids in proteins
do the 2 woven strand mirror each other
yes, but they are antiparallel
is DNA stable
yes but is bulky
what groove does the double helix have
a major or minor groove
can the 2 DNA strands be separated
they can be separated by melting or deannealing and they can be reannealled when in close proximity
when can DNA form circular molecules
when their ends are joined e.g. bacteria or ribosomes
what is the pros of the double helix
- chemically stable
- easily unwound for transcription
- mirror imaging excellent for replication and repair
what are the cons of the double helix
- can only replicate 5’-3’ which causes difficulties
- difficult to fold into nucleus- torsional effects
what occurs in replication
- 1 strand of the double helix acts as a template for the complementary strand
- the double helix is opened by initiator protein
- the newly synthesised strands have opposite polarity
- 2 identical daughter duplexes are produced
what are two DNA replication theories
conservative (2 different coloured strand)
semi-conservative (2 different coloured strands woven- contains one of the original strands)
where does DNA replication start
at A=T rich regions called replication origins
what is the function of DNA polymerase
adds new nucleotides and proofreads DNA
what do the leading and lagging strands do
DNA strands can only extend in 5’-3’ direction so the lagging strand is made in small pieces (okasaki fragments) which are joined
