Sept 6 Central Dogma of Molecular Biology Flashcards
what is the central dogma and the steps? (language analogy)
DNA synthesis –> replication
making a perfect copy
RNA synthesis –> transcription
rewriting in a different nucleotide font
Protein synthesis –> translation
rewriting in a different language (nucleotide to amino acid)
what are the 3 phosphates called on the rNTP
alpha, beta and gamma
what is the template in transcription?
exposed DNA strand
what enzyme is involved in transcription and what does it do?
RNA polymerase
catalyses the attack of the 3’ OH on the alpha phosphate of the rNTP
what happens to the other two phosphates of the rNTP?
they are “dropped”
to what end of the growing RNA strand are nucleotides added? and what is the direction relative to the DNA strand
the 3’ end
antiparallel
how do rNTPs come in contact with the growing RNA strand?
they diffuse randomly
to which strand of DNA is the new RNA strand identical with?
the non template strand
except for the substitution of T for U
where does transcription start? (where RNA polymerase starts its action)
at the promoter region
which enzymes unfolds the DNA molecule?
DNA helicase
what is formed when the RNA polymerase enzyme binds to a promoter and causes two DNA strands to detach?
the transcription bubble
moves along the DNA
unidirectionally!!
what happens as RNA polymerase advances along the strand?
the DNA duplex reforms behind the enzyme
“kicks out” the newly synthesised RNA strand, which exits through a channel in the polymerase
5’ end first
when does RNA polymerase stop?
certain DNA sequences destabilise the attachment of the enzyme to the DNA as it moves
RNA polymerase falls off DNA and releases RNA chain
what are the similarities between DNA transcription and DNA replication? (7)
- the template is the DNA
- DNA duplex locally unwound by helicase at initiation sites to expose templates
- chain growth at 3’ end, antiparallel to template
- monomers are dNTPs
- direct interaction (base pairing) between template DNA and incoming monomer
- attack of the 3’ OH on alpha phosphate of the incoming NTP
- beta and gamma phosphates dropped
what are the differences between DNA replication and transcription? (4 categories)
transcription:
monomers –> rNTPs
start and stop sites on template
newly synthesised strand (RNA) separates from template strand
only one of the original DNA strands is a template strand
start with one double strand DNA and end with that plus the RNA produced
replication:
monomers –> dNTPs
start sites (origins) but no stop sites
newly synthesised strand never separates from template
both of the original DNA strands independently serve as template strands
start with one molecule of DNA and end with two
what are the “words” for translation?
codons, made of three nucleotides
how many codons are there?
64
what does it mean when we say that the genetic code is degenerate?
several different codons code for the same amino acid
what are the three “stop” codons?
UAA, UAG, UGA
what is the “start” codon and what amino acid does it code for?
AUG
codes for methionine