CELS 191 Lecture 12 Flashcards
how many codons code for amino acids
61 of 64 - most amino acids have more than one codon
how many codons specify stop (translation)
3
how many codons specify start
one - AUG specifies methionine which is always the first amino acid when we synthesise the amino acid polypeptide chain - it can be broken off before it becomes a protein
what molecule turns mRNA into a polypeptide chain - also known as an adaptor molecule
a small RNA molecule called transfer RNA (tRNA)
what is the structure of tRNA
it is a small molecule that is a single strand of RNA roughly 70-80 nucleotides in length
how many tRNA are there for each amino acid
at least one
what are the three key features of tRNA
the amino acid attachment site at the three prime end which is mportant if you are going to carry and amino acid onto the mRNA
the three dimensional shape that allows it to fit into the machinery that will make the polypeptide
the anticodon that interacts with the condone of the mRNA
how are tRNA molecules ‘charged’
an enzyme recognises both a specific amino acid and the correct tRNA for this amino acid and joins them together
what is translation
the synthesis of proteins by ribosomes using mRNA as a set of instructions
what are the 2 locations ribosomes can be found and their functions
bound to the rER - synthesise proteins that are used within the plasma membrane or are exocytosed from the cell
free in the cytosol - synthesise proteins that are released into the cytosol and used within the cell
what are the three stages of translation and which of the sages require energy
initiation, elongation and termination and all three stages require energy
in the first step of initiation (in translation) a specific initiation tRNA binds to the small ribosomal subunit - what is the tRNA carrying
methionine
in the second step of initiation (in translation) the small ribosomal subunit/initiator tRNA identifies the ____ and attaches to the mRNA
5’ G cap
in the third step of initiation (in translation) the small ribosomal subunit/initiator tRNA complex moves along the mRNA (5’-3’ direction) until it finds the _____
initiation AUG codon
in the fourth step of initiation (in translation) the complex stops, with the initiator tRNA carrying the first methionine positioned in the ____
P site
what is step five of initiation in translation
the large ribosomal subunit attaches
in step one of elongation a ‘charged’ tRNA with an anticodon complementary to the ____ site codon lands in the ___ site
A site
in the second step of elongation (in translation), the ribosome will break the bond the binds the _____ to the _____ in the P site
amino acid - tRNA
in the second step of elongation (in translation) the amino acid in the P site is transferred to the newly arrived ____ (attached to the tRNA in the A site) and form a ____bond between them
amino acid - peptide
at the end of the initial part second step of elongation (in translation) what are we left with
A tRNA with the growing amino acid side chain in the A site
an empty/’uncharged’ tRNA in the P site
in the second step of elongation (in translation) while the ____ are bound to the mRNA (in the p and a sites) the ribosome moves ____ nucleotides down the mRNA
tRNAs - three
in the second step of elongation (in translation) what are we left with after the mRNA has moved down three nucleotides
the tRNAs with the growing amino acid chain moves to the P site (was in the A site) so that the chain of amino acids can exit through the tunnel located above the P site
uncharged tRNA in the E site (was in the P site)
in the third step of elongation (in translation) in the E site, the anticodon of the tRNA detaches from the _____ and the uncharged ___ is expelling
mRNA codon - tRNA
in the fourth step of elongation (in translation) a new ‘charged’ ____ with an anticodon complementary to the next A site ___ enters the ribosome at the __ and the elongation process repeats itself
tRNA - codon - A site
