1. Chapter 6 Expression of Biological Information (Part IV)
By :
Biology Unit
Kedah Matriculation College

2. DNA & genetic information Gene regulation & expression
Concept review…
Expression of Biological Information
DNA & genetic information
Gene regulation & expression
DNA replication
Protein synthesis
DNA structure
DNA as a carrier
Gene concept
concept
Components
Mechanism
Transcription
Definition
Models of DNA replication
DNA replication process
Enzyme involved
Translation

3. Learning outcome Explain translation in protein synthesis
Describe the stages involved:
i. initiation
ii. elongation (codon recognition, peptide bond
formation and translocation)
iii. termination

4. Translation

5. Translation Definition Translation Occurs in cytoplasm - a process
- whereby the genetic information in
mRNA strand
- is translated into sequence of amino
acids to form polypeptide/protein
Occurs in cytoplasm 5

6. Translation 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

7. Structures that involve in translation
Ribosome tRNA
mRNA
triplet bases on tRNA: anticodon 7

8. Structures that involve in translation:
1. tRNA
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.

9. 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.

10. 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.

12. 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

13. Activation of aminoacyl tRNA

14. 3. Ribosomes
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).

15. P site (peptidyl-tRNA site) A site (aminoacyl-tRNA site)
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.

17. Translation process

18. Overall Process…

19. Overall Process…

20. 3 steps of translation process,
synthesis of a polypeptide chain :
Initiation
Elongation
Termination

21. 1. Initiation
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’.

22. Initiation Then initiator tRNA base-pairs with the start codon
Arrival of a large subunit completes the initiation complex

23. Initiation
initiation factor: 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.

24. initiation complex of translation
Ribosome (large)
tRNA
mRNA
Ribosome (small) 24

25. Formation od peptide bond Translocation
2. Elongation
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

27. Elongation factors lead the tRNA into A site.
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.
hydrogen bonds

30. 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 site.

31. 2. Peptide bond Formation
3. Translocation

32. iii. Translocation tRNA in P site dissociates from ribosome.
tRNA in A site now attached to the growing polypeptide, is translocated to the P site

33. iii. Translocation
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.

34. Peptide bond formation

36. 3. Termination
Elongation continues until A site reaches termination codon.
do not code for amino acids and stop translation.
No aminoacyl tRNA recognize

37. Termination
Protein called ‘release factor’ binds to the termination codon in A site.
- freeing the polypeptide from the ribosome.
- mRNA detaches
- ribosome separates

38. Initiation Initiation Complex Large Unit P A Small Unit Small Unit UAC
Met
Large Unit
Initiation codon
AUG P A
5’ UUG UGG UAC AUG GAA GAG CAU … UGA 3’
Small Unit
Initiation Complex
Small Unit

39. Elongation CUU UAC 5’ UUG UGG UAC AUG GAA GAG CAA ….UGA 3’ CUC ACU UUU
Met
UAC
5’ UUG UGG UAC AUG GAA GAG CAA ….UGA 3’
CUC
Elongation

40. Termination ACU 5’ UUG UGG UAC AUG GAA GAG CAU UGA 3’ GUG STOP codon
UAA UAG UGA

41. Messenger RNA (mRNA) Primary structure of a protein A U G C mRNA start
codon
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1
methionine
glycine
serine
isoleucine
alanine
stop
codon
protein
Primary structure of a protein
aa1
aa2
aa3
aa4
aa5
aa6
peptide bonds
copyright cmassengale

42. 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

43. Polyribosomes

44. Polyribosomes/polysome
A group of several ribosomes attached to, and translating the same messenger RNA simultaneously

45. Significance of polyribosome
Increase the rate of same protein synthesis/protein produced rapidly
more of same protein can be made simultaneously
Increase the rate of same protein synthesis
More of same protein can be made simultaneously
More of same protein in a shorter time / rapidly
Animation

47. Can you tell the story? RNA polymerase DNA amino acids exon intron
tRNA
pre-mRNA
5' GTP cap
mature mRNA
aminoacyl tRNA synthetase
poly-A tail
large ribosomal subunit 3'
polypeptide 5'
tRNA
small ribosomal subunit E P A
ribosome