DNA Translation

RNA TRANSLATION

process in which a sequence of nucleotide triplets in a messenger RNA give rise to a specific sequence of amino acids during the synthesis of a polypeptide chain or protein

RIBOSOMES

translate the genetic message of mRNA into proteins

5’-3'

The mRNA is translated _______, producing a corresponding N-terminal → C-terminal polypeptide

N-TERMINAL→ C-TERMINAL POLYPEPTIDE

The mRNA is translated 5'→3', producing a corresponding

AMINO ACIDS BOUND TO TRNAs

• Specific binding of each amino acid to its tRNA.

• Specific base pairing between the mRNA codon and tRNA anticodon

TRANSLATIONAL MACHINERY

• mRNAs

• tRNAs

• Aminoacyl tRNA synthetase

• Ribosome

MESSENGER RNA

Provides an intermediate that carries the copy of DNA sequence that represents protein

MESSENGER RNA

3 modifications for the recruitment of ribosome to mRNA

KOZAK SEQUENCE

presence of a purine 3 bp upstream of AUG and presence of a guanine immediately downstream

METHYLATED GUANINE CAP

5’

POLY A TAIL

3’

CODONS

ordered series of three nucleotides specific for amino acids

TRANSFER RNA

Acts as adaptor between codons and the amino acids they specify

TRANSFER RNA

There are many types of tRNA but each is attached to a specific amino acid and each recognize a particular codon

75-95

ribonucleotides in length

5’-CCA-3’

Terminus is ______ which is the binding site of amino acid

5’-CCA-3’

binding site of amino acid

TRANSFER RNA

Contains unusual or modified bases- uridine, thymine, pseudouridine, methylguanine, hypoxanthine etc

ACCEPTOR ARM

the site of attachment of the specific amino acid

TΨC ARM

involved in binding of the aminoacyl-tRNA to the ribosomal surface at the site of protein synthesis

D ARM

recognition of a given tRNA species by its proper aminoacyl-tRNA synthase

ANTI-CODON LOOP

recognizes the three-letter codon in mRNA

ANTI-CODON LOOP

base pair complementary to mRNA codons

ACCEPTOR STEM

– 5’-CC—3’ which is the binding site of amino acids

AMINO ACYL TRNA SYNTHETASE

Provide specificity in joining amino acids to their RNAs

AMINO ACYL TRNA SYNTHETASE

Linkage is an endergonic process that occurs at the expense of ATP, which loses two phosphate groups, becoming AMP

ADENYLATION

Amino acid with the ATP to become adenylated

CHARGING

Carbonyl group of adenylated aa react with 3'OH of tRNA. A high energy bond and the release of AMP

AMYNOACYLATION

produces a charged tRNA (aminoacyl-tRNA), using energy from ATP hydrolysis

AMINO ACID and ATP

bind to the specific aminoacyl- tRNA synthetase enzyme

AMINOACYL-AMP

ATP loses two phosphates and the resulting AMP is bound to the amino acid, forming

3’r ADENINE

Every tRNA has a

3'r-OH or 2'r-OH

the amino acid is attached to the _________ of this nucleotide

AMINO ACID

attached by carboxyl group to ribose of last ribonucleotide of tRNA chain

-C-C-C-A-3’

Last 3 nucleotides of all tRNAs

RIBOSOME

It directs the synthesis of proteins

LARGE SUBUNIT

contains the peptidyl transferase center

SMALL SUBUNIT

contains the decoding center

PEPTIDYL TRANSFERASE CENTER

which is responsible for the formation of peptide bonds

DECODING CENTER

which charged tRNAs read or decode the codons of mRNA

LARGE SUBUNIT and SMALL SUBUNIT

undergo association and dissociation during each cycle of translation

PROKARYOTIC RIBOSOME

70S

EUKARYOTIC RIBOSOME

80S

POLYRIBOSOME/POLYSOME

An mRNA bearing multiple ribosome is known as

A-SITE

-binding site for the first aminocylated tRNA

P-SITE

binding site for the first peptidyl tRNA

E-SITE

binding site for the first uncharged tRNA

SMALL SUBUNIT

has two narrow tunnels:

• Entry Channel for mRNA

• Exit channel for mRNA

LARGE SUBUNIT

has an exit channel for newly synthesized polypeptide chain

START CODON

First codon of an ORF present at the 5’ end

STOP CODON

Last codon of an ORF at the 3’end which define the signal termination of protein synthesis

FIRST CODON

5’-AUG-3'

STOP CODON

5'-UAG-3'

5'-UGA-3'

5'-UAA-3

61 CODONS

Even though there are only 20 amino acid exists, there are ________ available

FEATURES OF GENETIC CODE

• Degenerate

• Unambiguous

• Non-overlapping

• Not punctuated

• Universal

DEGENERATE

• Multiple codons must decode the same amino acid

• In general, the third nucleotide in a codon is less important than the first two in determining the specific amino acid to be incorporated

UNAMBIGUOUS

Given a specific codon, only a single amino acid is indicated

NON-OVERLAPPING

The reading of the genetic code during the process of protein synthesis does not involve any overlap of codons

NO PUNCTUATION

Once the reading is commenced at a specific codon, the message is read in a continuing sequence of nucleotide triplets until a stop codon is reached

UNIVERSAL

The code is the same in all organisms from viruses and bacteria to humans with few exceptions

WOBBLE BASE PAIRS

Two nucleotides that does not following Watson-Crick base pair rules

WOBBLE BASE PAIRS

One tRNA molecule can recognize and bind to more than one codon due to the less precise base pairs between the 3rd base of the codon and the base at the 1st position on the anticodon

METHIONINE

The initiator tRNA is charged with

elF4G

binds to elF4E

elF4A

binds to mRNA

SMALL SUBUNIT

eIF, eIFA, eIF2, eIF5

4 INITIATION FACTORS

elF4E, elF4G, elF4B, elF4A

48S PREINITIATION COMPLEX

This 43S complex with mRNA is called

SMALL SUBUNIT

attaches near the start codon (AUG)

INITIATOR TRNA

binds to the start codon (AUG)

LARGE SUBUNIT

joins the complex

ELONGATION

• Correct aminoacyl-tRNA is loaded to the A site of the ribosome as dictated by the A site codon

• Peptidyl transferase reaction

• Translocation of peptidyl tRNA from A site of ribosome to the P site of ribosome

ELONGATION

Once the correctly charged tRNA has been placed in the A site and has rotated in the peptidyl transferase center, peptide bond formation takes place

TERMINATION

• Stop codons are recognized by proteins called release factors(RF)

• These activate the hydrolysis of of polypeptide from the peptidyl tRNA

RELEASE FACTOR

Stop codons are recognized by proteins called

CLASS 1 RFs

recognize stop codon and trigger the hydrolysis of peptide chain from the peptidyl tRNA

CLASS 2 RFs

stimulate the dissociation of class 1 RFs from the ribosome after the release of polypeptide

OPEN READING FRAME

Protein coding region of mRNA is composed of a contiguous, nonoverlapping string of codons