Genetic Code Flashcards by Anifowose Olasubomi

who used fungus Neurospora to work out the relation of genes to protein

Beadle and Tatum

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protein are polymers consisting of amino acids are linked by

peptide bonds

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the linear sequence of amino acid is

the primary structure

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how is the secondary and tertiary structure developed

primary structure folds

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two or more polypeptide chains associate to form

quartenary structure

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level of structural organization of protein

1, primary
2. secondary
3. tertiary
4. quaternary

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what determines how the nucleotide sequence specifies the amino acid sequence

genetic code

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what are the examples of breaking the genetic code

use of homopolymers
use of random copolymers
use of ribosome-bound tRNAs

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what amino acid are specifies by codons composed of only one type of base?

UUU=phenylalanine

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Nirenberg and Matthaei developed a method for identifying amino acid specifies by

a homopolymer

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the use of poly (U) directs

incorporation of phenylalanine

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the use of poly (A) directs

incorporation of lysine

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use of poly (C) directs

incorporation of proline

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use of poly (G) directs

did not yield interpretable results

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effect of using random copolymers

synthesized RNAs containing 2 or 3 nucleotides which gives info about the base composition but not EXACt sequence

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what does ribosome-bound tRNAs do

provide information about genetic code

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codon GUU specifies

valine

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out of 64 codons, how many encode amino acids

61 called sense codons

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what is the initiation codon

AUG=methionine

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what are stop codons

UAA
UAG
UGA

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Why can an aminoacid be specified by more than one codon

because they are degenerate

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how is codon in an mRNA decoded

it is decoded by base pairing with its anticodon in tRNA

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what are isoaccepting tRNAs?

different tRNAs that accept the same amino acid but have different anticodons

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where is the wobble position

third (3’) position of the codon
first (5’) position of anticodon

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who proposed the wobble hypothesis

Francis Crick

THE first codon of an open reading frame is called

initiation codon or start codon

which sequence is used for initiation in a few bacterial mRNAs and encode for methionine

GUG or UUG

which sequence is used for initiation codon in eukaryotes

CUG

In bacteria, translation begina with

N-formylmethionine (fMet)

fMET is delivered to the ribosome by

a special tRNA (tRNAi Met)

initaiton codon establishes the correct or incorrect reading frame

correrect reading frame

eukaryotes begin translation with

methionine

tRNA Met is used for

elongation

genetic code is generally overlapping or non overlapping

non overlapping

alternate names for termination codons are

stop codons or nonsense codons

exceptions of each codon encodes the same amino acid is found in

Mitochondrial genes

how are amino acid are assembled into a protein through

translation

translation of an mRNA molecule takes place where

on a ribosome

protein is synthesized from which terminus

N to C

what is the first stage of translation

the attachment of a tRNA to its amino acid

------ attaches an amino acid to the 3' end of a tRNA to form an aminoacyl-tRNA

Aminoacyl-tRNA synthetase

certain positions on tRNA are recognized by the appropriate aminoacyl-tRNA synthetase. TRUE/FALSE

TRUE

step of charging tRNA

1. Amino acid reacts with atp TO PRODUCE aminocyl-AMP and 2 Pi 2. Amino acid is transfered to the tRNA forming aminoacyl-tRNA. AMP is released

what is the second step of translation

initiation

which components assemble during intiation

1. mRNA 2. the large and small ribosomal subunits 3. the initiator aminoacyl-tRNA 4. Initiation factors 5. GTP

Initiation occurs in 3 steps

1. mRNA binds to the small ribosomal subunit 2. The initiator aminoacyl-tRNA base pairs to the initiation codon 3. The large ribosomal subunit joins the initiation complex

what sequence in bacterial mRNA is required for the attachment of the small lsubunit of the ribosome

Shine-Dalgarno sequence

Eukaryotic mRNAs do not have Shine-Dalgarno sequence, so what is the alternate

5' cap play a role in initiation

describe initiation in eukaryotes

1. the small ribosomal subunit, IFs, and Met-tRNAi Met form a complex that binds to the 5'cap 2. initiation complex scan down the mRNA until reaching the initiation codon 3. Kozak sequence helps identify the initiation codon in eukaryotic mRNAs

what affects initiation of mRNA in eukaryote

The proteins that attach to the poly A tail interact with cap-binding protein and enhance binding of ribosome to 5'end of the mRNA

what is the third stage of translation

elongation

what do elongation require

70s initiation complex, Aminoacyl-tRNAS, elongation factors & GTP

tRNAs occupy which sites on ribosome

3 sites 'Exit (E) site Peptidyl (P) site Aminoacyl (A) site

3 steps in elongation stage of translation comprises

1. fMET-tRNA fMet occupies the P site of the ribosome 2. Ef-Tu, GDP and charged t-RNA form a complex that enters the A site 3. Peptide bond form between the P and A sites, and the tRNA in the P site is released. Ribosome moves down the mRNA and A is ready to receive another t-RNA

function o fRelease Factors (RF) in termination

Binds to ribosome when stop codon is reached and terminate translation

an mRNA molecule may be translated simultaneously by several ribosomes. this is called

Polyribosomes

examples of Messenger RNA surveillance

Nonsense-mediated mRNA decay (NMD) Stalled ribosomes and nonstop mRNAs No go decay

what do messenger RNA surveillance do

they detect and correct errors in mRNA

what results in the rapid degradation of an mRNA containing a premature stop codon

Nonsense mediated mRNA decay (NMD)

what does bacteria use to remove stalled ribosomes

transfer-messenger RNA (tmRNA)

how does eukaryote degrade abnormal RNA from the 3'end

process called nonstop RNA decay

what removes stalled ribosomes resulting from secondary structures or chemical damage to the mRNA, premature stop codons

NGD no-go decay

tmRNA is charged with ---- and binds to

Ala and binds to A site

which antibiotic blocks binding of aminoacyl-tRNA to A site of ribosome

Tetracycline

which antibiotic prevents the transition from initation complex to chain elongation and also causes miscoding

streptomycin

which antibiotic blocks tehpeptidyl transferase reaction on ribosomes

chloramphenicol

which antibiotic bloxks teh translocation reaction on ribosomes

cycloheximide

which antibiotic blocks initiation of transcription by binding to RNA Polymerase

Rifamycin