Week 6 Textbook Flashcards
(64 cards)
what is a codon
it is 3 nucleotides in rna that = specific amnio acids
- some nucleotide codons = stop codon
AUG = start
what are reading frames
3 different reading frames
can sequence into different AA depending on the reading frame that is used during translation
what is the purpose of tRNA
rna molecule that serves as an adaptor that reads a codon in mRNA and serves as the source of the amnio acid added to the growing polypeptide chain
- forms in the shape of a cloverleaf and then forms a compact L shape held together by H bonds
the anti codon attaches at the bottom at the amnio acid matching the anticodon is attached to 3’ end of the tRNA
what is an anticodon
3 nucleotides that bind throught base pairing to the complementary codon in an mRNA molecule
there is another end on the tRNA that is unpaired - this area at the 3’ end of the molecule is where the AA that matches the codon in covalently attached to tRNA
what is the function of the enzyme amnioacyl-tRNA synthetases
they covalently couple each amnio acid to the appropriate set of tRNA molecules
each synthetase enzyme recognizes its designated amnio acid and the anticodon area on the tRNA
what is the process called when each synthetase couples a particular amnio acid to the proper tRNA
charging
what is the ribosome and its subunits
ribsome = large complex made from small proteins = rRNA= ribosomal RNAs which form the structural and catalytic core of the ribosomes
the ribosome translates the mRNA into polypeptide chains
the small ribosomal subunt matches the tRNA to the codons of the mRNA
the large subunit catalyzes the formation of the peptide bonds that covalently link the amnio acids together in the polypeptide chain
- starts its synthesis on the 5’ end
after the polypeptide chain is made the 2 subunits of the ribosome separate
where does the tRNA enter the ribsome to grow the amnio acid peptide chain
enters to the A site by base pairing with the complementary codon on the mRNA molecule
- the amnio acid is linked to the polypeptide chain - this is held into place by the tRNA at the P site.
when the ribsomal unit shifts forward to reveal more mRNA- the tRNA moves to the E site before being ejected
- process continues until the mRNA = stop codon
the P site in the middle holds the polypeptide chain and then gives the chain to the tRNA that enters thru the A site and the middle goes to E site to leave and the A now becomes the P
what gives the ribosome its overall shape
ribosomal RNAs that are compact into the core
the ribosomal proteins are located on the surface - to help fold and stabilize the RNA core
what are ribozymes
RNA molecules that possess catalytic acitivity
what is the initiator tRNA and why is it so significant
it sets the reading frame for the entire message - one error in the nucleotide = messed up codon - nonfunctional protein
- also has a major impact on the overall rate at which proteins are synthesized
- begins with AUG = methionine
- all newly made proteins have AUG at the beginning on the N-terminal end - but it is usually removed later by a specific protease
what are translation initiation factors
proteins that promotes the proper association of ribosomes with mRNA and is required for the initiation of protein synthesis
how does the initiator tRNA start the translation process
enters into the P site (middle) of the SMALL ribosomal subunit - along with the translation initiation factors
- only a charge initator tRNA molecule is capable of binding tightly to the P site in the absence of the large ribosomal subunit
- then binds to the 5’ end of the mRNA molecule which has the 5’ gap of guanine
- the small ribosomal subunit scans the mRNA for the AUG start codon - once found, the large ribsomal subunit binds to complete the factory and start protein synthesis
- the incoming tRNA is placed in the A site
T/F bacterial mRNA’s do not have a 5’ cap
true, they dont
they cant tell the ribosome where to being searching for the AUG but htey have 6 nucleotide long specific ribosome-binding seq
a bacterial ribosome can readily bind directly to a start codon that is on the inside of the mRNA - this is necessary bc the mRNAs of bacteria are usually polycistronic (encode several different proteins on the same molecule)
UAA, UAG, UGA are ____
stop codons
the tRNAs do not specify an amnio acid for these codons but the ribosome understands to stop translation
what are release factors in the stop codons
releases factors bind to any stop codon that reaches the A site inside the ribosome - this alters the acitivity of the peptidyl transferase in the ribsosome - causing it to catalyze the addition of a water molecule instead of an AA
- this rxn frees the carboxyl end of the polypeptide chain from its attachment to the tRNA molecule
- then the ribosome breaks into its 2 parts and releases the mRNA which can be reassembled on another mRNA molecule for more protein synthesis
t/f multiple ribosomes will bind to a part of the mRNA
true
if it is being translated successfully a new ribosome will hop onto its 5’ end almost as the preceding ribosome has translated enough of the nucleotide to move out of the way
= polyribosomes /polysomes = large cytosolic assemblies that are made up of many ribosomes spaced closely tg
= boosts efficiency of the protein synthesis process
t/f some of the most effective antibiotics speed up the protein synthesis in bacteria
false - they inhibit it by either messing up the process, blocking channels
- these can be taken in high doses without being toxic to humans
- these compounds likely arose during evolution as a weapon deployed by microbes that used them to gain competitive advantage in the ecological niches they shared
why is the process of proteolysis and protease enzymes important
the proteins have different lifespans
proteolysis = breaks down proteins into its AA
they degrade the short peptides and finally to individual amnio acids = protease
they hydrolyze the peptide bonds - they do this to break down the proteins that have a short lifespan and to recognize and quickly remove the proteins that are damaged and misfolded
what are proteasomes
proteins are broken down by large machines called proteasomes
they are in the cytosol and the nucleus
each end of the cylinder has large protein complexes - act as stoppers that bind the protein subunits that need degration and then using ATP they unfold the proteins and thread them into the proteasome cylinder which uses protease to chop them into short peptides
- the protease is found in the inner part of this complex so that it doesn’t go and degrade important proteins
what is ubiquitin
this is how proteasomes select which proteins in the cell should be degraded
- they are marked for destruction by the covalent attachment of a small protein called ubiquitin
- these proteins are feed into the proteasomes
- proteins that are short lived have sequences that targets the protein for ubiquitylation as well as damaged or misfolded proteins
what are chaperone proteins
after peptide chains are made from ribosomes - they have to be folded - they don’t do this spont - they use chaperone proteins
- uses noncovalent interactions
covalently attaches phosphate group by phosphorylation
what are the post-translational modifications that are needed by proteins
needed to come fully functional
phosphorylation
T/F some codons code for more than one amnio acid
false
- none of the codons code for more than one AA but multiple codons can code for THE SAME amnio acid
