lecture 18 Flashcards by Jillian Kucey

how many possible codons are there

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what are the 4 properties of the genetic code

redundant
conservative
unambiguous
universal

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what does redundant mean

most amino acids are coded by more than one codon

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conservative

multiple codons specify same amino acid because of identical first 2

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unambiguous

one codon codes for only one amino acid

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universal

all codons specify the same amino acid across species

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what direction are codons read in

5’ to 3’

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whats the start codon ? what does it code for

AUG - methionine

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what are the 3 stop codon

UAA
UAG
UGA

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what is the genetic code

translating nucleotides to amino acids

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what Is the anticodon on

tRNA

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where is the amino acid on the tRNA

the 3’ end (amino acid acceptor arm with a C-C-A sequence)

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how many nucleotides is the anticodon loop

7 NTs

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what explains why multiple codons can code for a single amino acid

wobble hypothesis

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can a tRNA bind to more than one codon

yes ! but only one amino acid

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whats unique about tRNA and Watson crick base pairing

the 3rd position (wobble hypothesis) may not always be Watson crick pairing

the first 2 will be though

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what enzyme links amino acids to tRNA

aminoaceyl-tRNA synthetases

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how are amino acids linked to tRNA

covalently linked to 3’ end

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is aminoacyl-tRNA specific to amino acids

yes

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where is methionine in proteins

N terminal

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whats the first residue in bacteria

formyl-methionine

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whats the only amino acid that can bind to P site when large ribosomal subunit is not present

methionine

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what is protein synthesis also called

translation

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what does the small subunit (40S) do in translation

decodes the genetic message

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what does the large subunit (60S) do in translation

catalyzes peptide bond formation

what are the 3 steps of translation

initiation elongation termination

1st step of initiation in translation

40S subunit (+TFs) bind to tRNA-Met to form the 43S complex

what does the 43S complex bind to? what does that make

the 5' cap of mRNA makes the 48S complex

whats the 2nd step of initiation in translation

43S complex binds to mRNA complex to form 48S complex

what complex searches for AUG codon

48S complex (small ribosomal subunit+mRNA+tRNA)

43S complex + mRNA complex =

48S complex

what gets hydrolyzed to allow for IFs to leave to make space for large subunit

the GTP on the tRNA-Met

what does translation of our mRNA

80S complex

48S complex + 60S complex =

80S complex

when does the mRNA bind the small subunit in translation

early in translation

when does the mRNA bind the large subunit in translation

not until the very end

what are the 3 tRNA binding sites on a ribosome

A (aminoacyl) P (peptidyl) E (exit)

what does the A site do

binds incoming aminoacyl-tRNA carrying new amino acid

what does the P site do

holds the tRNA with the polypeptide

what the E site do

holds the tRNA without the amino acid which is then released by ribosome

where do the tRNA anticodons connect to

the mRNA in the 80S ribosome

what starts elongation

introduction of the first tRNA

what are the 4 steps of elongation

1. aminoacyl-tRNA selection 2. peptide bond formation 3. translocation 4. release of deacylated tRNA

what does binding aminoacyl to A site require

GTPase

whats the elongation factor for aminoacyl-tRNA for bacteria

EF-Tu

whats the elongation factor for aminoacyl-tRNA in eukaryotes

eEF1A

what does anything eukaryotic usually have in front of it

"e"

why does GTP get hydrolyzed in the 1st step of elongation

to release the elongation factors once its tRNA is bound to mRNA

does the peptide bond formation need input of energy to create

what is the peptide bond formation catalyzed by

peptidyl transferase within the large subunit (it has its own enzymatic activity)

what moves in translocation

the ribosome shifts

what causes translocation of the ribosome relative to the mRNA

binding of an elongation factor + GTP hydrolysis

whats the elongation factor for translocation in eukaryotes

EF-2

whats the elongation factor for translocation in prokaryotes

EF-G

how much does the ribosome move in translocation

three nucleotides (1 codon)

what direction does the ribosome move during translocation

5' to 3'

how many hydrolysis of GTP in each cycle of elongation? where?

2 once to connect the tRNA to the A site once during translocation

how many positions does each tRNA go through in the ribosome? which one is an exception?

all 3 positions except for initiator tRNA with Met

what does termination require

release factors

what recognizes the stop codon

release factors

what do release factors actually do

they bring in a water molecule and precipitates the association of the polypeptide from our tRNA molecule to release it

whats the final step of translation

dissociation of the mRNA from the ribosome and disassembly of the ribosome

what is a non sense mediated decay

mRNA surveillance mechanism that detects messages with premature termination codons

what are the 4 point mutations

silent nonsense missense (conservative) missense (non conservative)

whats a silent mutation

mutation in 3rd position of codon but there's no change in what it codes for

whats a synonymous mutation? example?

mutation in codon sequence but there's no change in what it codes for (silent)

whats a nonsense mutation

stop codons presenting anywhere

whats a conservative missense

mutation but resulting in an amino acid with similar chemical properties so its a functional protein

whats a non-conservative missense

mutation results in a different amino acid that is not the same at all and results in a non functional protein

what do antibiotics often target

sites of protein synthesis (ribosomes)