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1. HARAMAYA UNIVERSITY
COLLEGE OF HEALTH AND
MEDICAL SCIENCES
SCHOOL OF MEDICINE
Module Title: Introduction to Medicine
Course Title: Biochemistry
Topics to be covered: Translation and Mutation
Target students: Preclerkship-I
Instructor: Teka Obsa (Asst. Prof.
of Medical Biochemistry, MSc, BSc in MLT)
6/1/2024 1

2. Translation and Mutation
Outline
•Definition of translation
•Genetic code
•Components required for translation
•Codon recognition by tRNA
•Steps of protein synthesis
•Modification of Polypeptide Chains
•Mutation
•Classification ofmutation
•Mutagens
By: Teka O. 2

3. Translation and Mutation
•Module: Introduction to Medicine
•Course: Biochemistry
•Students: PC-I
•Instructor: Teka Obsa (MSc, Asst. Prof. of Medical
Biochemistry, BSc in MLT)
By: Teka O. 3

4. The Central Dogma of Life.
4By: Teka O.

5. Translation/Protein synthesis
Translating the genetic information from nucleotide sequence of
mRNA into the amino acid sequence of the corresponding
polypeptide or protein.
•The pathway of protein synthesis is called translation because
the “language” of the “nucleotide sequence” on the mRNA is
translated into the language of “amino acid sequence” in the
protein.
5By: Teka O.

6. Genetic code:is a genetic dictionary.
•Individual “word” in the code is composed of three
nucleotide bases (codon/triplet).
•There is at least one codon or more for all 20 AAs.
•There are (4)
3
= 64codons in genetic code.
•The 3 codons are nonsense/stop/termination codons.
•Include UAA, UAGand UGA.
•AUG is the initiation codon.
6By: Teka O.

7. Features of Genetic Code
A.Triplet
B.Degeneracy /redundancy
E.g. Isoleucine coded by AUU, AUC, AUA.
C.Specificity or unambiguity:
D.Universality: Exception: in AUG –Met (in eukaryotes
& N-Fmet).mitochondrial DNA, (UGA -Try).
E.Non-overlapping
F.Commaless
G.Collinearity
7By: Teka O.

8. By: Teka O. 8
The genetic code table

9. Components required for translation
1.Amino acids
2.tRNA
3.mRNA
4.Ribosomes
5. Protein factors
6. Energy sourceATP, GTP
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10. A. Amino acids
•All the amino acids that eventually appear in the finished
protein must be present at the time of protein synthesis.
•All the essential amino acids should present in sufficient
quantities in the diet
B. tRNA
•At least one specific tRNA molecule per amino acid.
•In humans around 50 species of tRNA and in bacteria
contain 30-40 species.
10By: Teka O.

11. C. Aminoacyl-tRNA synthetases
•This family of enzymes is required for attachment of amino
acids to their corresponding tRNAs.
•Each member of this family recognizes a specific aa.
•Aminoacyl-tRNA synthetasescatalyze a two-step reaction
that results in the covalent attachment of the carboxyl group
of an amino acid to the 3'-end of its corresponding tRNA
(cognate) .
•The overall reaction requires ATP.
•Also have aa “proofreading” or “editing” activity
11By: Teka O.

12. D. Messenger RNA
•Contains specific information required for translation.
E. Ribosomes
•Ribosomes are the centres or factories for protein synthesis.
•Ribosomes are huge complex structures (70S for prokaryotes
and 80S for eukaryotes) of proteins and ribosomal RNAs.
•They consist of two subunits—one large and one small.
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13. Ribosome binding sites
A-site (for Aminoacyl)
P-site (for Peptidylsite)
E-site (for Exit site)
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14. E. Protein factors
•Initiation, elongation, and termination (or release) factors.
•Have catalytic and stabilizing function.
G. ATP and GTP :
•Cleavage of four high-energy bonds is required for the
addition of one amino acid to the growing polypeptide
chain:
•two from ATP in the aminoacyl-tRNA synthetase reaction:
•one in the removal of PPi,
•one in the subsequent hydrolysis of the PPito
inorganic phosphate by pyrophosphatase.
•two from GTP-one for binding the aminoacyl-tRNA to the
A site and one for the translocation step.
14By: Teka O.

15. Codon recognition by tRNA
•Correct pairing of the codon in the mRNA with the anticodon
of the tRNA is essential for accurate translation.
A. Antiparallel binding of codon and anticodon
•Binding of the tRNA anticodon to the mRNA codon follows
the rules of complementary and antiparallel binding.
15By: Teka O.

16. B. Wobble hypothesis
•Describes the mechanism by which tRNAs can
recognize more than one codon for a specific aa.
•The base at the 5'-end of the anticodon (the first base)
is not as spatially defined as the other two bases.
•Movement of the first base allows nontraditional base-
pairing with the 3'-base of the codon (the last base).
•This movement is called “wobble” and allows a single
tRNA to recognize more than one codon.
By: Teka O. 16

17. Wobble base pairs are shown in red
By: Teka O. 17

18. Steps of protein synthesis
Activation of Amino acids
•A group of enzymes aminoacyl tRNA-synthetasesare
required this process.
•These enzymes are highly specific for the AA & tRNA.
18By: Teka O.

19. Steps of protein synthesis
Translation proper divided into three steps:
1.Initiation
2.Elongation
3.Termination
19By: Teka O.

20. 1.Initiation
Assembly of the components of the translation:
•2 ribosomal units
•mRNA to be translated
•Amino-acyl-tRNA
•GTP
•Initiation factors to facilitate the
assembly
•In prokaryotesIF-1,IF-2 and IF-3
•In eukaryotesAt least 10 initiation
factors are required.
20By: Teka O.

21. 30S ribosomal subunit
•In prokaryotesIn the mRNA a sequence of bases (5’-
UAAGGAGG-3’) known as Shine-Dalgarnosequence located
6-10 bases before AUG near 5’end.
•16S ribosomal RNA has a nucleotide sequence
complementary to all bases of Shine-Dalgarnosequence.
•This facilitates binding and positioning of the mRNA on the
30S subunit
3’-AUUCCUCC---------------------------5’
5’-UAAGGAGG------------AUG-------3’
SDS
21By: Teka O.

22. Initiationcodon:
•The codon AUGis responsible for the initiation of protein
synthesis.
•It is found at the 5’ end close to Shine-Dalgarnosequence.
•tRNA carrying methionine is converted to formylmethionine
(N
10
-formyl THFdonates formylgroup).
•In eukaryotes, methionineis not formylated.
•The initiator tRNA with anticodonUAC recognizes the
initiation codon AUG and starts protein synthesis.
22By: Teka O.

23. Initiation codon...
•At the beginning, the initiation tRNA occupies the ‘P site’ of
the ribosome.
•The incoming next amino acid (as aminoacyltRNA)
corresponding to the codon on mRNA is deposited at ‘A site’
of the ribosome.
•This process depends on the elongation factors and the energy is
derived from the hydrolysis of GTP.
•Free tNRAexits through E site
•Translation and transcription are coupledin prokaryotes.
23By: Teka O.

24. 2. Elongation:
•Ribosomes elongate the polypeptide chain by a
sequential addition of amino acids to the growing carboxyl end.
•About 20 aa/second are added to the growing polypeptide
chain.
•The ribosome moves from 5’ end to 3’ end of the mRNA.
Formation of peptide bond
•The enzyme peptidyltransferasecatalyses the formation of
peptide bond.
24By: Teka O.

25. 3.Termination
•One of the 3 codons (UAA, UAG and UGA) acts as stop signal.
•The stop codons do not have specific tRNAs
•As the termination codonoccupies the ribosomal A site, the
release factors (RF-1, RF-2 and RF-3) bind with codon.
•These factors cause the hydrolytic breakdown of the peptidyl-
tRNA and release the newly synthesized protein.
•They are also responsible for the dissociation of ribosomes from
mRNA.
25By: Teka O.

26. Polysomes
•Translation begins at the 5'-end of the mRNA, with
the ribosome proceeding along the RNA molecule.
•Because of the length of most mRNAs, more than
one ribosome at a time can translate a message.
•Such a complex of one mRNA and a number of
ribosomes is called a polysomeor polyribosome.
26By: Teka O.

27. Animation for translation
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28. Posttranslational Modification of Polypeptide Chains
•Many polypeptide chains are modified, either co-translationallyor
post-translationally.
•These modifications may include removal of part of the translated
sequence, or the covalent addition of one or more chemical groups
required for protein activity.
•Some types of post-translational modifications are listed below.
28By: Teka O.

29. A. Trimming
•Many proteins destined for secretion from the cell are
initially made as large, precursor molecules that are not
functionally active.
•Portions of the protein chain must be removed by
specialized endoproteases, resulting in the release of an
active molecule.
•The cellular site of the cleavage reaction depends on
the protein to be modified.
•Endoplasmic reticulum, Golgi apparatus or secretory
vesicles.
29By: Teka O.

30. B. Covalent attachments
•Proteins may be activated or inactivated by the covalent
attachment of a variety of chemical groups.
Examples include:
•1. Phosphorylation: Phosphorylation occurs on the
hydroxyl groups of serine, threonine, or, less frequently,
tyrosineresidues in a protein.
•This phosphorylation is catalyzed by one of a family of
protein kinasesand may be reversed by the action of
phosphatases.
•The phosphorylation may increase or decrease the
functional activity of the protein.
30By: Teka O.

31. 2. Glycosylation: In endoplasmic reticulum (ER)
3. Hydroxylation:
-catalyzed by 2-oxoglutarate-dependent dioxygenases
Proline and lysine residues of the α chains of collagen
(vitamin C-dependent)
C. Protein folding:spontaneous & chaperone facilitated
D. Protein degradation: misfolded
•Ubiquitination
31By: Teka O.

32. Inhibitors of Translation
Translation is the favouritetarget for inhibition by antibiotics, which
inhibit the protein synthesis and growth of pathogens
Streptomycin: Initiation is inhibited causes misreading of mRNA
for normal pairing of codon and anticodon.
Tetracycline: Inhibits the binding of aminoacyl tRNA to the
ribosomes.
Chloramphenicol: competitive inhibitor of the enzyme peptidyl
transferseand prevents the elongation.
Erythromycin:inhibits translocation of bacterial ribosomes.
Puromycin: It is derived from mold. It has structure very similar
to that of 3' end of aminoacyl-tRNA. Blocks further addition
of amino acids
32By: Teka O.

33. TunicamycinIt prevents attachments of
oligosaccharide side chains to certain glycoproteins.
Cycloheximide: It inhibits protein biosynthesis in
eukaryotes by blocking peptidyltransferase activity
of 60S eukaryotic ribosome.
Diptheriatoxin: It is produced by bacteria that cause
diptheriain children.
•It inhibits protein synthesis in eukaryotes. It
inactivates elongation factor of eukaryotes.
33By: Teka O.

34. 15. Mutation
•Any change in genetic makeup
•Ultimate effect of mutation is on translation
•Out of every 10
6 cell divisions-1 mutationoccurs.
•Mayoccurin
•somaticcells
•Gametes
•Main causes:
•Mistake in cell replication
•Environmental factors
34By: Teka O.

35. Characteristics ofMutation
•Generally mutant alleles are recessive to their wild
type or normalalleles.
•Most mutations have harmful effect, but some
mutations arebeneficial.
•Some genes shows high rate of mutation(mutable).
•Highly mutable sites within a gene (hotspots).
35By: Teka O.

36. Classificationofmutation
Basedoncausesofmutation
1.Spontaneousmutation:occursnaturallywithout
anycause.Therateofspontaneousmutationisvery
slow.eg-Methylationfollowedbydeaminationof
cytosine.
2.InducedMutation:causedbyexposureto
mutagens(chemical,physicalorbiological).
36By: Teka O.

37. Based on tissue oforigin
1.Somaticmutation
•A mutation occurring in somatic cell.
•Inasexuallyreproducingspeciessomaticmutations
transmits from one progeny to the nextprogeny
2. GerminalMutation
•When mutation occurs in gametic cells.
•Insexuallyreproductivespeciesonlygerminal
mutationaretransmittedtothe nextgeneration.
37By: Teka O.

38. Basedondirectionofmutation
1.Forwardmutation:Whenmutationoccursfromthe
normal/wildtypealleletomutantallele.
Reverse mutation:When mutation occurs in reverse
direction (from mutant allele to the normal/wild type allele).
Based on trait affected
1.Visible mutation:Those mutation which affects
phenotypic character and can be detected by normal
observation.
2.Biochemical mutation: mutation which affect the
production of biochemicals and which does not show any
phenotypic character.
38By: Teka O.

39. Based on patterns of inheritance
•Autosomal Dominant
•Autosomal Recessive
•X-linked Dominant
•X-linked Recessive
•Y-linked disorder
•Mitochondrial disorder
39By: Teka O.

40. MUTAGENS
•Are agents which cause DNA damage
TYPES OF MUTAGENS
Biological agents
•Viruses
•Bacteria
Chemical agents
•Baseanalogs
•(5BU,2AP)
•Alkylatingagents
•alkylsulfonates
•intercalatingagents
•Ethidiumbromide
•Deaminatingagents
•nitrousacid
Physical agents
•UVlight
•Heat
•Radiations
(X-rays,gamma
rays)
40By: Teka O.

41. EFFECTS OF MUTATION
Effects
Beneficial
Harmful
Neutral
•Produce new version
of protein
•Essential forevolution
•Enhance thesurvival
and reproductive
success
•Turn off harmfulgenes
•Proteinmalfunction
•Lethal tolife
•Sometimes stopsthe
development offetus.
•Cause genetic disorder
•Not significantly harm
or
benefitbody
41By: Teka O.

42. TYPES OF GENEMUTATION
GENEMUTATION
•Silentmutation
•Missensemutation
•Nonsensemutation
Pointmutation Frame shiftmutation
Basesubstitution
mutation
•Insertion
•Deletion
•Transitionmutation
•Transversionmutation
42By: Teka O.

43. Base Substitution mutation
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44. Summary of pointmutation consequences
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45. One or more base pairs are inserted inor deleted
from the DNA.
Frameshift mutations
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46. Chromosomal mutation oraberrations
•The change involving morphological or
numerical alterationofchromosome.
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47. Structure of Chromosome
By: Teka O. 47

48. Definition of terms
•Locus-specific fixed location where a particular
gene is located.
•Gene–a region of DNA that determines a trait.
•Allele–is a specific gene responsible for the
variationin which a given trait can be expressed.
Homologous chromosomes –chromosomepairs
similar in length, gene and centromere position.
48By: Teka O.

49. Definition of terms
•Genotype: refers to an individual’s genes.
•Phenotype: refers to an individual’s physical
•appearance.
•Heterozygous: having two different alleles at a
given gene locus.
•Homozygous: having identical alleles at a given
gene locus.
By: Teka O. 49

50. Karyotyping:
•Pairing and ordering all the chromosomes of an
organism.
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51. Structural changes inchromosome
Types of structural changes inchromosome
1.Deletion ordeficiency
2.Duplication
3.Inversion
4.Translocation
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52. By: Teka O. 52

53. Typesof inversion:
There are two types of inversion
mutation in chromosomes:
•ParacentricInversions.
•PericentricInversions.
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54. 4.Translocation
•The transfer of a part of a chromosome of to a
non-homologous one.
•Threetypes.
1.Simpletranslocations:
•The brokenpiecegets attached to one end of a
nonhomologouschromosome.
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55. 2.Shifttranslocation
•Thebrokensegmentofone
chromosomegetsinsertedinterstitially
inanonhomologouschromosome.
3.Reciprocaltranslocations.
•Asegmentfromonechromosomeis
exchangedwithasegmentfromanother
nonhomologousone.
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56. 56By: Teka O.

57. Numerical change in chromosome
1. Aneuploidy 2. Euploidy
1.Aneuploidy: Loss or gain of a single
chromosome set.
•Nullisomy 2n-2 hypoploidy
•Monosomy 2n-1
•Trisomy 2n+1 hyperploidy
•Tetrasomy 2n+2
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58. 2. Euploidy:Loss or gain of whole
chromosome set.
•Monoploidy
•Triploidy
•Polyploidy
•Autopolyploidy
•Allopolyploidy
58By: Teka O.

59. Common Autosomal trisomies
•Down Syndrome (Trisomy 21)
•Edward’s Syndrome (Trisomy 18)
•Patau’s Syndrome (Trisomy 13)
59