module 2 - 3.10 protein synthesis Flashcards
what is the central dogma of molecular biology?
DNA —transcription–> / <–reverse transcription– RNA –translation–> polypeptide
what is transcription?
- the process of making a copy of something
- info held on DNA molecule is transcribed into info held on mRNA molecule
how is a copy of the DNA base sequence made?
made as an mRNA molecule by RNA polymerase
what does mRNA do?
moves genetic information and genes from nuclear pores to ribosomes
what is translation?
the process of conversion of something from one form into another e.g. language
what is the sequence of codons on the mRNA translated into?
a sequence of amino acids, making a polypeptide
what does translation use to transfer tRNA molecules?
ribosomes
what is 1 language?
what is 2 language?
- codons
- amino acids
why is information in DNA transcribed into mRNA?
so it can be used multiple times
what is the first stage of transcription?
initiation
what is the promoter region?
RNA polymerase binding site for DNA
what is the sense strand of DNA?
holds the triplet code for the sequence of amino acids
what is the antisense strand of DNA?
does not code for the sequence of amino acids but is complementary in base sequence to the sense DNA strand
what does the antisense strand act as?
acts as the template DNA strand for RNA polymerase so that the mRNA has the same base sequence as the sense DNA strand
what is the second stage of transcription?
elongation
what is RNA polymerase’s error rate from its proof reading ability?
1 in 10^4 to 10^6
what is the fidelity of RNA polymerase making mRNA?
high fidelity
how many nucleotides can RNA polymerase synthesize per second?
40-80 nucleotides per second
what is the third stage of transcription?
termination
what do all polypeptides have as their first amino acid?
methionine
why don’t all proteins start with methionine?
because some polypeptides go through post translational modification from the golgi
if methionine (ATG) is the start codon, what is the codon and anticodon for methionine?
codon - AUG
anticodon - UAC
what does a tRNA molecule consist of?
a single RNA strand - 80 nucleotides long
where is the anticodon on a tRNA molecule?
at the end (bottom) 3 single stranded bases that are complementary to a codon on mRNA
what is the amino acid acceptor site?
a short sequence of bases that can bind to the only amino acid that the anticodon is complementary to on the mRNA
what do tRNA molecules serve as?
the physical link between mRNA and amino acids used to make a polypeptide
how many tRNA molecules are there compared to codons?
the same amount - there is a tRNA molecule for every codon
where are tRNA molecules coded?
in the nucleolus
what 2 components are ribosomes made from?
- ribosomal RNA (rRNA)
- proteins
what are ribosomes?
- complex macromolecular machines, found within all living cells
- site of biological protein synthesis
what are the 2 subunits of ribosomes?
- small ribosomal subunit that ‘reads’ the mRNA
- the large ribosomal subunits that has 2 binding sites for tRNA molecules and catalytic site for joining amino acids together
which bonds join amino acids?
peptide bonds
what is the first stage of translation?
initiation by forming an initiation complex
how does the tRNA anticodon UAC bind to the complementary codon AUG?
complimentary base pairing
how many tRNA’s are there with the anticodon UAG? and why is this?
- one
- it can only bind to the amino acid methionine (at he amino acid acceptor site)
what is formed when a large ribosome subunit is joined to the party?
a ribosome
what is the second stage of translation?
elongation of the polypeptide
what is the second amino acid that is brought into the second tRNA binding site on the ribosome during elongation of the polypeptide?
valine
what is the catalytic site on the polypeptide called/
peptidyl transferase
what is peptidyl transferase made of?
rRNA
what does the catalytic site on the ribosome create?
a peptide bond between methionine and valine by a condensation reaction
what happens to the first tRNA (UAC/ valine)?
it detaches to the ribosome and will be bound to the fresh amino acid of methionine
how many does the ribosome move along the mRNA strand after the first tRNA molecule detaches?
moves along by one codon, the second tRNA bind site is now clear
what type of bond is formed from the peptidyl transferase between valine and histidine?
peptide bond through a condensation reaction
how many amino acids are joined by the ribosome per second?
60
what is the third stage of translation?
termination of a polypeptide
how long does the termination of a polypeptide continue for?
until ribosome encounters a stop codon on the mRNA
what are the stop codons in RNA?
UAG
UAA
UGA
what are the stop codons in DNA?
TAG
TAA
TGA
what do stop codons do?
cause the ribosomal subunits to detach from each other and from the mRNA
when the polypeptide folds up into its final shape, what may it undergo?
post translational modification to form a protein (from the golgi)
