Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 27 Translation Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
Translation
1
? Objectives
? Mutation
? Steps of Protein synthesis
? Prokaryotes
? Eukaryotes
? Post translational Modification
? Clinical implications
2
Case 1
? A 3-year-old Caucasian boy is brought to the clinic for a chronic
productive cough not responding to antibiotics given recently. He
has no fever or sick contacts. His medical history is significant for
abdominal distention, failure to pass stool, and emesis as an infant.
He continues to have bulky, foul-smel ing stools. No diarrhea is
present. He has several relatives with chronic lung and "stomach"
problems, and some have even died at a young age. The
examination reveals an il appearing, slender male in moderate
distress. The lung exam reveals poor air movement in the base of
lungs bilateral and coarse rhonchi throughout both lung fields. A
chloride sweat test was performed and was positive, indicating
cystic fibrosis (CF).
? What is the mechanism of the disease?
? How might gel electrophoresis assist in making the diagnosis
3
Case 2
? An 8-year-old boy is brought to his pediatrician by his
mother because she was concerned that he was having
language-speech problems, was hyperactive, and was told
by teachers that he may have mental retardation. The
mother reports a strong family history of mental
retardation in males. The boy on exam is found to have a
large jaw, prominent ears, and enlarged testes
(macroorchidism). The mother was told her family had a
genetic problem causing the mental retardation. The
patient underwent a series of blood tests and was
scheduled to see a genetic counselor, who expressed that
the etiology of the genetic defect was likely transmitted
from his mother. The genetic counselor states that his
mother likely has a silent mutation.
4
? What is the most likely diagnosis?
? Which chromosome is likely to be
affected?
? What are some types of biochemical
mutations?
? What is the biochemical basis of the
different types of mutations?
5
Case 3
? A 15-year-old African-American female presents to the emergency
room with complaints of bilateral thigh and hip pain. The pain has
been present for 1 day and is steadily increasing in severity.
Acetaminophen and ibuprofen have not relieved her symptoms.
She denies any recent trauma or excessive exercise. She does report
feeling fatigued and has been having burning with urination along
with urinating frequently. She reports having similar pain episodes
in the past, sometimes requiring hospitalization. On examination,
she is afebrile (without fever) and in no acute distress. No one in
her family has similar episodes. Her conjunctiva and mucosal
membranes are slightly pale in coloration. She has nonspecific
bilateral anterior thigh pain with no abnormalities appreciated. The
remainder of her examination is completely normal. Her white
blood cel count is elevated at 17,000/mm3, and her hemoglobin
(Hb) level is decreased at 7.1 g/dL. The urinalysis demonstrated an
abnormal number of numerous bacteria.
6
? What is the most likely diagnosis?
? What is the molecular genetics behind this
disorder?
? What is the pathophysiologic mechanism
of her symptoms?
7
Sickle cel disease (pain crisis).
? CLINICAL CORRELATION
? This 15-year-old female's description of her pain is typical of a sickle cell
pain crisis.
? infection is a trigger, most commonly pneumonia or a urinary tract
infection. This case is consistent with a urinary tract infection, indicated by
her symptoms of urinary frequency, and burning with urination (dysuria).
? Her white blood cell count is elevated in response to the infection.
? The low hemoglobin level is consistent with sickle cell anemia.
? Since she is homozygous (both genes coding for sickle hemoglobin), both
her parents have sickle cell trait (heterozygous) and thus do not have
symptoms.
? The diagnosis can be established with hemoglobin electrophoresis.
? Treatment includes searching for an underlying cause of crisis (infection,
hypoxia, fever, excessive exercise, and extreme changes in temperature),
administration of oxygen, intravenous fluids for hydration, pain
management, and consideration of a blood transfusion.
8
Proteome:
complete set of proteins expressed in a cell
Genetic code:
A dictionary that identifies the correspondence
between a sequence of nucleotide bases and
a sequence of amino acids.
9
10
Features of the Genetic Code
? Degenerate
? Unambiguous
? Nonoverlapping
? Not punctuated
? Universal
In mitochondria: AUA= Met, UGA= trp;
AGA&AGG= stop codon
11
Recognition of the codon by the anticodon
Involved in binding
tRNA to ribosome
Serves as the
recognition site for enzyme:
adds amino acid
Complimentary and antiparal el binding
12
Adapted from Harper's Biochemistry
Point mutation: Single nucleotide change in coding region
1. Silent mutation
2. Missense mutation
3. Nonsense mutation
13
14
Adapted from Lippincott,s Biochemistry
Missense mutations resulting in abnormal hemoglobin chains
15
Other mutations
16
1. Trinucleotide repeat expansion
17
Adapted from Lippincott,s Biochemistry
Fragile X
? Fragile X is the most common inherited form of
mental retardation,
? Affecting primarily males
? moderate to severe mental retardation,
hyperactivity, typical facies such as large jaw and
large ears. Pigmented skin lesions (cafe au lait)
can also be seen.
? The fragile X mental retardation (FMR) gene
product is affected and, through a little-
understood mechanism, leads to mental
retardation.
18
Fragile X syndrome
? Molecular basis of disease:
Mutation resulting in an increased number of
CGG repeats on the X chromosome. When the
number of repeats reaches a critical size, it can be
methylated and inactivated resulting in the
disorder. Individuals who carry 50 to 199 repeats
are phenotypical y normal and carry a
premutation. If repeats exceed 200, the patient
has a full mutation; and if methylation occurs, he
or she wil be affected.
19
? 2. Splice site mutation
? 3. Frameshift mutation
? Deletion
? Addition
20
Effects of deletions in a gene on the sequence of the mRNA
transcript and of the polypeptide chain translated therefrom
21
Adapted from Harper,s Biochemistry
The effects of insertions in a gene on the sequence of the mRNA
transcript and of the polypeptide chain translated therefrom
22
The effects of deletions and insertions in a gene on the sequence of the mRNA
transcript and of the polypeptide chain translated there from
23
Cystic fibrosis
? is an inherited condition affecting approximately 1 in 2500
white individuals.
? Affected patients usually have abnormal mucus secretion
and eccrine sweat glands leading to respiratory infections,
gastrointestinal obstruction, pancreatic enzyme dysfunction
leading to malabsorption of nutrients, and excessive
electrolyte secretion.
? The protein cystic fibrosis transmembrane conductance
regulator (CFTR) is defective, leading to abnormal chloride
transport.
? Approximately 70 percent of mutations are accounted for
by deletion of three specific base pairs at the F 508 position
of the CFTR.
24
Case 4
? A 40-year-old male returned from a deer-hunting trip approximately 6
weeks ago, and presents to clinic with multiple complaints. He states that
recently he has had worsening joint pain and "arthritis" in multiple joints
that seems to move to different spots. Patient also complains of some
numbness in his feet bilaterally.
? The patient denies any medical problems and he had a normal annual
physical prior to hunting trip. On further questioning, he remembered
having a rash on his body and the lesions were circular and appeared to be
resolving in the center. He noted that he felt really bad once he got home
with muscle ache (myalgias), joint ache (arthralgias), stiff neck, and severe
headache. He also remembered that many of his hunting friends had
experienced flea and tick bites and is quite sure he was bitten as well. The
physical exam is essentially normal except some joint tenderness of left
knee and right shoulder. After making your diagnosis you gave him a
prescription for erythromycin.
? What is the most likely diagnosis?
? What is the biochemical mechanism of action of erythromycin?
25
Steps of protein synthesis
Sequences of signal for initiation (Prokaryote and Eukaryote)
Peptide bond formation does not require energy? How it is possible
26
DIFFERENCES IN PROKARYOTIC AND
EUKARYOTIC PROTEIN SYNTHESIS
PROKARYOTE
EUKARYOTE
Start
fMet-tRNA
Met-tRNA
Recognition
Shine-Dalgarno
5 caps direct e-IFs
sequence
sequence
Initiation factors
IF-1, IF-2, IF-3
multiple e-Ifs (>10)
Elongation factors EF-Tu, EF-G, EF-Ts
Multi-subunit
eEF-1, eEF-2, eEF-3
27
Components required for translation
? Amino acids
? tRNA
? Aminoacid attachment site
? Anticodon
? DHU loop
? Pseudouridine loop
? Codon recognition by tRNA
? Antiparal el binding between codon and anticodon
? Wobble hypothesis
? Aminoacyl tRNA synthetase
28
Activation of Amino acid
29
? Messenger RNA
? Functional y competent ribosome
? rRNA
? Ribosomal protein
? A,P and E sites
? Cel ular location
? Free in the cytosol
? Associated with endoplasmic reticulum
? Protein factors for initiation, elongation and
termination
30
? Energy sources
? Four high energy bonds cleavage for addition of
one amino acid to the polypeptide chain
? 2 from ATP- aminoacyl tRNA synthetase reaction
? 2 from GTP
? 1 for binding aminoacyl tRNA to the A site
? 1 for translocation
? AT P and GTP molecules for initiation in eukaryotes
? GTP required for termination in both pro and Eu
31
Steps of protein synthesis
? Initiation
? Elongation
? Termination
32
Adapted from Lippincott,s Biochemistry
34
Adapted from Lippincott,s Biochemistry
Video on Prok translation
35
Eukaryotic translation
? Initiation:
? (1) dissociation of the ribosome into its 40S and 60S
subunits;
? (2) binding of a ternary complex consisting of the
initiator methionyl-tRNA, (met-tRNAi), GTP, and eIF-2
to the 40S ribosome to form the 43S preinitiation
complex;
? (3) binding of mRNA to the 40S preinitiation complex
to form the 48S initiation complex; and
? (4) combination of the 48S initiation complex with the
60S ribosomal subunit to form the 80S initiation
complex.
36
37
38
39
Adapted from Harper,s Biochemistry
The circularization of mRNA through protein-protein interactions
between 7meG cap-bound elF4F and poly A tail-bound poly A binding protein
40
Adapted from Harper,s Biochemistry
Activation of eIF-4E by insulin and formation
of the cap binding eIF-4F complex
41
Adapted from Harper,s Biochemistry
Elongation
? (1) binding of aminoacyl-tRNA to the A site,
? (2) peptide bond formation,
? (3) translocation of the ribosome on the
mRNA, and
? (4) expulsion of the deacylated tRNA from the
P- and E-sites.
42
Diagrammatic representation of the peptide elongation
process of protein synthesis
43
Adapted from Harper,s Biochemistry
Peptide elongation process of protein synthesis
Adapted from Harper,s Biochemistry
Peptide elongation process of protein synthesis
Adapted from Harper,s Biochemistry
Diagrammatic representation of the
termination process of protein synthesis
46
Adapted from Harper,s Biochemistry
The termination process of protein synthesis
47
Adapted from Harper,s Biochemistry
The termination process of protein synthesis
48
Adapted from Harper,s Biochemistry
Comparison between Prokaryotes and Eukaryotes
Cel
Factor
Function
Initiation
P
IF2 GTP
Bring charged initiating tRNA to P
E
eIF2-GTP
site
P
IF3
Prevent association of subunits
E
eIF3
Elongation
P
EF-Tu-GTP
Bring al other charged tRNA to A site
E
EF-1-GTP
P
EF-Ts
Guanine nucleotide exchange factor
E
EF-1
P
EF-G-GTP
Translocation
E
EF-2-GTP
Termination
P
RF-1,2
Recognize stop codon
E
eRF
P
RF-3-GTP
Release of other RF
E
eRF-3-GTP
49
Video on EUK translation
50
Clinical implication
51
52
Adapted from Lippincott,s Biochemistry
53
Adapted from Lippincott,s Biochemistry
Post translational modification
A. Trimming
B. Covalent attachment
Methylation
Acetylation
Glycosylation
N glycosidic linkage
O glycosidic linkage
Lipidation
GPI (glycosyl phosphatidyl inositol)
S palmitoylation
54
Post translational modification
Phosphorylation
Formation of disulphide bonds
Gammacarboxylation----glutamic residue
Hydroxylation ----Proline and lysine
C. Protein degradation
Ubiquitination
Proteolysis
55
MCQ1
? The 6-year-old son of a migrant worker is brought to a clinic with
chil s, headache, nausea, vomiting, and sore throat. The examining
physician notes a persistent grayish colored membrane near the
tonsils. History reveals that the patient has not been immunized
against diphtheria. Diphtheria toxin is potential y lethal in this
unimmunized patient because it causes which of the following?
? A. Inactivates an elongation factor required for translocation in
protein synthesis
? B. Binds to the ribosome and prevents peptide bond formation
? C. Prevents binding of mRNA to the 60S ribosomal subunit
? D. Inactivates an initiation factor
? E. Inhibits the synthesis of aminoacyl-charged tRNA
56
MCQ2
? Many antimicrobials inhibit protein translation. Which
of the following antimicrobials is correctly paired with
its mechanism of action?
? A. Tetracyclines inhibit peptidyltransferase.
? B. Diphtheria toxin binds to the 30S ribosomal subunit.
? C. Puromycin inactivates EF-2.
? D. Clindamycin binds to the 30S ribosomal subunit.
? E. Erythromycin binds to the 50S ribosomal subunit.
57
MCQ3
? Translation of a synthetic polyribonucleotide containing the
repeating sequence CAA in a cell-free protein- synthesizing
system produces three homopolypeptides: polyglutamine,
polyasparagine, and polythreonine. If the codon for
glutamine and asparagine are CAA and AAC, respectively,
which of the following triplets is the codon for threonine?
? A. AAC.
? B. CAA.
? C. CAC.
? D. CCA.
? E. ACA.
58
MCQ4
? A tRNA molecule that is supposed to carry cysteine (tRNAcys) is
ischarged, so that it actual y carries alanine (ala-tRNAcys). Assuming
no correction occurs, what wil be the fate of this alanine residue
during protein synthesis?
? A. It wil be incorporated into a protein in response to an alanine
codon.
? B. It wil remain attached to the tRNA, as it cannot be
used for protein synthesis.
? C. It wil be incorporated randomly at any codon.
? D. It wil be chemical y converted to cysteine by cel ular enzymes.
? E. It wil be incorporated into a protein in response to
a
cysteine codon
59
This post was last modified on 05 April 2022