Chapter 6 Expression of Biological Information (Part IV)
By : Biology Unit Kedah Matriculation College
DNA & genetic information DNA structure DNA as a carrier Gene concept
Expression of Biological Information
DNA replication Protein synthesis Transcription Definition Models of DNA replication DNA replication process Enzyme involved Gene regulation & expression concept Components Mechanism Translation
Explain translation in protein synthesis Describe the stages involved: i . initiation ii. elongation (codon recognition, peptide bond formation and translocation) iii. termination
Translation - a process - whereby the genetic information in mRNA strand - is translated into sequence of amino acids to form polypeptide/protein
Occurs in cytoplasm
RNA direct the synthesis of polypeptide.
cell interprets a genetic message and builds a protein accordingly.
The message is a series of codons along an mRNA molecule and interpreter is transfer RNA
Structures that involve in translation
triplet bases on tRNA: anticodon
Structures that involve in translation:
tRNA transfer amino acid from cytoplasm to ribosome
tRNA can be used repeatedly.
Each type of tRNA molecule associates a particular mRNA codon with a particular amino acid.
Shape: 2 dimensional – cloverleaf shape.
tRNA includes the anticodon , the specialized base triplet that binds to a specific mRNA codon.
e.g.: mRNA codon UUU has AAA as its anticodon.
From the other end of the L shaped tRNA molecule protrudes its 3’end; the attachment site for amino acid.
tRNA with amino acid; aminoacyl tRNA.
2. Aminoacyl-tRNA synthetase
Catalyze the matching up of amino acid with the correct tRNA and using energy of ATP ( activation of amino acids )
Catalyzes the covalent attachment of amino acid to the 3’- OH of tRNA.
Resulting aminoacyl tRNA
Activation of aminoacyl tRNA
Facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis.
A large and small subunit join to form a functional ribosome only when they attach to mRNA molecule.
Each ribosomal subunit is consist proteins and ribosomal RNA (rRNA).
Ribosome has TWO binding site for mRNA: P site (peptidyl-tRNA site)
Holds the tRNA carrying the growing polypeptide chain.
A site (aminoacyl-tRNA site)
Holds the tRNA carrying the next amino acid to be added to the chain.
of translation process, synthesis of a polypeptide chain : 1.
Bring together mRNA and tRNA bearing the first amino acid of polypeptide and two subunits of ribosome.
Small ribosomal subunit binds to mRNA that being
read from 5’ to 3’.
Then initiator tRNA base-pairs with the start codon
Arrival of a large subunit completes the
required to bring all the translation components together Initiator tRNA site in the P site of ribosome and vacant A site is ready for next tRNA.
initiation complex of translation
Ribosome (large) tRNA mRNA Ribosome (small)
Amino acid are added one by one to the initial amino acid. Each addition, occurs in 3 steps cycle.
Codon recognition Formation od peptide bond Translocation
i . Codon recognition
mRNA codon in A site forms hydrogen bonds with the anticodon of an incoming molecule of tRNA carrying its appropriate amino acid.
Elongation factors lead the tRNA into A site.
ii. Peptide bond formation
Polypeptide detaches from tRNA (in P site) to which it was bond and is link to amino acid carried by the tRNA (in A site)
large ribosomal subunit
catalyzes the formation of peptide bond
between polypeptide extending from P site and newly arrived amino acid in A
2. Peptide bond Formation 3. Translocation
tRNA in P site dissociates from ribosome.
tRNA in A site now attached to the growing polypeptide, is translocated the P site to
as the tRNA changes sites, its anticodon remains hydrogen bonded to the mRNA codon, allowing the mRNA and tRNA molecules to move as a unit.
This movement, in turn, brings the next codon to be translated into A site.
Elongation is repeated as each amino acid is added to the chain until the polypeptide is completed.
Peptide bond formation
Elongation continues until A site reaches
do not code for amino acids and
No aminoacyl tRNA recognize
Protein called ‘ release factor ’ binds to the termination codon in A site.
freeing the polypeptide - mRNA detaches from the ribosome.
- ribosome separates
Initiation Initiation codon AUG
UAC Large Unit P A 5’
UAC AUG GAA GAG CAU … UGA
3’ Small Unit Initiation Complex
UUG UGG UAC
AUG GAA GAG CAA ….UGA
3’ Elongation CUC
UUG UGG UAC AUG GAA GAG
3’ ACU Termination UAA STOP codon UAG UGA
Messenger RNA (mRNA)
mRNA A start codon U G G G C U C C A U C G G C G C A U A A codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 protein methionine glycine serine isoleucine glycine alanine stop codon aa1 Primary structure of a protein aa2 aa3 aa4 aa5 peptide bonds
mRNA U C C A U C A U G G G C U C C A U C G G A Codon 1 methionine
A group of several ribosomes attached to, and translating the same messenger RNA simultaneously
Increase the rate of same protein synthesis/protein produced rapidly more of same protein can be made simultaneously Animation
RNA polymerase DNA Can you tell the story?
pre-mRNA exon intron 5' GTP cap mature mRNA poly-A tail large ribosomal subunit polypeptide amino acids tRNA aminoacyl tRNA synthetase 3' 5' small ribosomal subunit E P A tRNA ribosome