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STEP TO PG-MD/MS - DR.AKIF A.B
MOLECULAR BIOCHEMISTRY- I & II
- DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
NUCLEIC ACID-Made up of monomer units called Nucleotides.
-Nucleotides are linked to each other by 3’-5’ Phosphodiester bond
-Backbone of nucleic acid = Sugar + Phosphate
NUCLEOTIDES
1) Nitrogen Bases : Purines and pyramidines
2) Pentose sugar
3) Phosphate group
Nucleoside
STEP TO PG-MD/MS - DR.AKIF A.B
Beta-N-Glycosidic bond-C1 of Pentose Sugar is linked to N9 of Purines or N1 of Pyramidines
-Most nucleotides are 5’ Nucleotides
-Base sequence og Nucleic Acid is written in 5’-3’ direction
STEP TO PG-MD/MS - DR.AKIF A.B
1) At the physiological PH, the DNA molecules are:
A Positively charged.
B Negatively charged
C Neutral.
D Amphipathic
STEP TO PG-MD/MS - DR.AKIF A.B
B) Negatively charged
DNA is negatively charged because of phosphate group
STEP TO PG-MD/MS - DR.AKIF A.B
2) Nucleoside is made up of (PGI)
A. Pyramidine
B. Histone
C. Purine
D. Sugar
E. Phosphate
STEP TO PG-MD/MS - DR.AKIF A.B
C. Purine
D. Sugar
A. Pyramidine
NUCLEOTIDES
1) Nitrogen Bases : Purines and pyramidines
2) Pentose sugar
3) Phosphate group
Nucleoside
Ans.
STEP TO PG-MD/MS - DR.AKIF A.B
3. Apart from occuring in Nucleic acids, Pyramidines are also present in
A. Theophylline
B. Theobromine
C. Flavin mononucleotide
D. Thiamine
STEP TO PG-MD/MS - DR.AKIF A.B
D. Thiamine
Purine ring is present in
Pyramidine ring is present in
Theobromine Thiamine
Theophylline
Flavin Mononucleotide
STEP TO PG-MD/MS - DR.AKIF A.B
3. Which one of the following procedures as routine technique for karyotyping using light microscopy:
A C-banding
B G-banding
C Q-banding
D Brd V-standing
STEP TO PG-MD/MS - DR.AKIF A.B
Ans. B) G-Banding
a. “The most commonly employed staining method uses a Giemsa stain and hence is called G banding”
b. A Karyotype is a standard arrangement of a photographed or image stained chromosomes, where chromosomes are in metaphase stage.
c. Mitosis is arrested in dividing cells in metaphase stage by use of colchicine.
d. In metaphase stage individual chromosomes take the form of two chromatids connected at the centromeres.
i. Chromosomes are arranged in pairs
ii. Chromosome pairs arranged in decreasing order of length.
STEP TO PG-MD/MS - DR.AKIF A.B
Staining allows identification of each individuals chromosome on the basis of distinctive and reliable pattern of alternating light and dark bonds. One of the following banding technique may be used.
STAINING OF CHROMOSOME
G—Banding Q— Banding C-Banding R-Banding
Giemsa bonding
Quinacrine- banding
Constitutive-banding
Reverse stainingGiemsa banding
Most commonly used
Demonstrates bandsalong chromosome
Demonstrate constitutivehetero chromatin
Gives pattern opposite to G-banding
STEP TO PG-MD/MS - DR.AKIF A.B
4. Which of the following is not a nitrogenous base
A. Adenine
B. Guanosine
C. Cytosine
D. Thymine
STEP TO PG-MD/MS - DR.AKIF A.B
B. Guanosine
-Guanosine is a nucleoside
-Remaining are nitrogenous bases
-Guanine is a nitrogen base
STEP TO PG-MD/MS - DR.AKIF A.B
5. On complete hydrolysis of DNA we will get all the following except
A Deoxy pentose sugar
B Phosphoric acid
C Adenosine
D Purine bases
STEP TO PG-MD/MS - DR.AKIF A.B
C) Adenosine- Nucleoside = Deoxy - Adenosine or adenosine = Base (Adenine) + sugar
- Adenosine = ribose + Adenine
-Deoxyadenosine = Deoxyribose + Adenine
Therefore Adenosine is present in RNA, not present DNA.
STEP TO PG-MD/MS - DR.AKIF A.B
-DNA is a Polymer of deoxyribonucleotides
i. Adenine deoxyribonucleotideii. Thymine deoxyribonucleotideiii. Guanine deoxyribonucleotideiv. Cytosine deoxyribonucleotide
- Nucleotides joint by covalent 3’-5’ phosphodiester linkage
-Right handed Double helix structure of DNA is given by Waston and Crick
-A combine with T (A = T) by two H2 bond C combines with G(C =G) by three H2 bond
-Chargaff’s Rule — Ratio of purine (G+A) to pyrimidine (T+C) bases in the DNA is always around 1. - i.e. G + A / T + C = 1
-Antiparallel i.e one strand in 5’-3’ direction and other in 3’-5’ direction
DNA
-
STEP TO PG-MD/MS - DR.AKIF A.B
DNA - 6 types of DNA : A to E and Z
- most common TYPE of DNA is B-DNA
B-DNA-10 base pair per turn
-Most stable
-This was actually explained by watson and crick
-Length of one turn = 34 A* or 3.4nm
-Diameter oe width = 20 A* or 20nm
-Right handed helix ( Z-DNA is left handed)
DNA STRANDSTEMPLATE STRAND CODING STRAND
Non coding strand
Antisense strand Sense strand
-ve strand +ve strand
3’-5’ direction 5’-3’ direction
This strand is copied during m-RNA synthesis
STEP TO PG-MD/MS - DR.AKIF A.B
6. Thermostability of DNA is provided by
A G-C bonds
B A-T paining
C N-glycosolic bond
D Antiparallel arrangement
STEP TO PG-MD/MS - DR.AKIF A.B
Ans. A G-C Bonds
- ‘A’ combines with ‘T’ by 2 hydrogen bonds i.e A = T while ‘C’ combines with ‘G’ by 3-Hydrogen bondsi.e. C = G
Since it has 3 bonds it is responsible for its stability
STEP TO PG-MD/MS - DR.AKIF A.B
Melting (Denaturation) of DNA
- Separation of 2 strands of DNA by breaking of Hydrogen Bonds
- DNA separated into two components strands either by:
1) increasing temperature or 2) decreasing salt concentration.
- Phosphodiester bond is not broken
- Primary structure is not disrupted, only secondary and tertiary structure is disrupted.
- After denaturation (melting), of DNA, there is an increase in the optical absorbance of purine and pyrimidine bases à a phenomenon referred as Hyperchromicity of denaturation.
- DNA rich in G=C melt at higher temperature than that rich in A=T pairs.
- Formamide is used commonly in recombinant DNA experiments, Lowers the ‘Tm’ by destabilizing H bonds.
STEP TO PG-MD/MS - DR.AKIF A.B
Melting (Denaturation) of DNA-Melting Temperature (Tm) = Temperature at which half of strand is denatured
-Normal Tm = 85-95*C
-Tm = 2*no. of A=T Pairs + 3 * no. of C=G pairs
STEP TO PG-MD/MS - DR.AKIF A.B
TRIPLEX DNA-3rd strand binds at major groove of B-DNA by Hydrogen bonding
-k/a Hoogsten Pairs
STEP TO PG-MD/MS - DR.AKIF A.B
4-STRANDED DNA-High in Guanine content
- G –Quarlet DNA
STEP TO PG-MD/MS - DR.AKIF A.B
TOPOISOMERASE- Regulates overwinding or underwining of DNA.
Topoisomerase I Topoisomerase II
Makes Single Stranded Nick In DNA
Makes double stranded Nick
Removes –ve supercoils Removes –ve supercoils
Cant insert supercoils Can insert supercoils
ATP is not requires ATP is required
E.g.: Helicase DNA gyrase
STEP TO PG-MD/MS - DR.AKIF A.B
TOPOISOMERASE
STEP TO PG-MD/MS - DR.AKIF A.B
DRUGS ACTING ON TOPOISOMERASEBacterial Topoisomerase
Human topoisomerase
Ciprofloxacin Etoposide
Nalidixic acid Adriamycin
Daunorubocin
STEP TO PG-MD/MS - DR.AKIF A.B
NUCLEOSOME-DNA + Histone Protein
-Most abundant chromatin protein = Histone protein
-5 Types :
H1 Lysine rich
Linker proteinH2A, H2B
Arginine rich
H3 Lysine richH4
-Beads of String appearance
-Nucleosomes are linked to each other by 30bp k/a Linker.
- Basic protein
STEP TO PG-MD/MS - DR.AKIF A.B
NUCLEOSOME
STEP TO PG-MD/MS - DR.AKIF A.B
REGIONS IN DNAEUCHROMATIN HETEROCHROMATIN
Regions in DNA which is transcriptionally active.
transcriptionally inactive
Chromatin is Less densely packed Densely packed
Stains less densely Stains densely
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
TYPES OF HETEROCHROMATIN
Constitutive Facultative Always condensed At times condensed but other times
it is actively transcribed and thus uncondensed and appears as euchromatin
-Inactive-Seen in centromere and ends of telomere
X- chromosome
One X CHROMOSOME is inactive in females (barr body) but at time of embryogenesis it becomes active
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
-Y chromosome is Acrocentric
-X chromosome is submetacentric
-Telocentric chromosome is not seen in humans
-MC chromosome = Submetacentric
STEP TO PG-MD/MS - DR.AKIF A.B
HYPERCHROMATISM-It is increase of absorbance
-Measured by absorbance at 260nm
-It occurs when DNA is denatured
-ssDNA is more Hyperchromatic than dsDNA.
STEP TO PG-MD/MS - DR.AKIF A.B
DNA REPLICATION
STEP TO PG-MD/MS - DR.AKIF A.B
DNA REPLICATION-Occurs in S phase of cell cycle
-Each DNA strands separates and acts as template strand on which complementary strand is synthesised
-Base pairing rule is obeyed
-Semiconservative nature
-New strand is synthesised in 5’-3’ direction
-Synthesis of DNA in both strands is not similar :
- Leading strand : DNA is continuosly polymerised
- Lagging strand : DNA is discontinuosly polymerised (semi discontinuous)
STEP TO PG-MD/MS - DR.AKIF A.B
DNA REPLICATION-Replication proceeds from multiple origin in each chromosomes in eukaryotes including humans
-Replication obeys polarity
-Replication occurs in both directions along all of chromosome
-Both strands are replicated simultaneously
-Replication process generates ‘replication bubbles’
STEP TO PG-MD/MS - DR.AKIF A.B
Common features between prokaryotic and eukaryotic DNA replication:
1) Semiconservative
2) Bidirectional
3) Semi discontinuous
STEP TO PG-MD/MS - DR.AKIF A.B
DNA POLYMERASEIN EUKARYOTES
TYPES FUNCTION
DNA Polymerase Alpha Primase
DNA Polymerae Beta DNA repair
DNAP gamma Mitochondrial DNA synthesis
DNAP delta Lagging strand synthesis
DNAP epsilon Leading strand synthesis
STEP TO PG-MD/MS - DR.AKIF A.B
DNA POLYMERASEIN PROKARYOTES
Polymerase I Gap filling following DNA replication, repair and recombination
Polymerase II Proof reading and repair
Polymerase III Leading strand synthesis, Okazaki fragment synthesis
STEP TO PG-MD/MS - DR.AKIF A.B
PROTEINS INVOLVEDIN DNA REPLICATION
PROTEINS FUNCTIONDNA polymerases Deoxynucleotide polymerizationHelicases Unwinding of DNATopoisomerase Relieves torsional strain that
results from helicase induced unwinding
DNA Primase Initiates synthesis of RNA primers
Single stranded binding proteins
Prevents premature reannealing of dsDNA
DNA ligase Seals the broken ends between nascent chain and okazaki fragments
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
TELOMERASE-Telomeres are present at the end of eukaryotic chromosome
-Telomeres consist of TG repeats
-During each replication telomere shortens and thus cell dies later
-Early shortening of telomere is associated with early aging and malignancy
-Telomerase lengthens telomere and it is RNA dependent DNA polymerase(Reverse Transcriptase)
STEP TO PG-MD/MS - DR.AKIF A.B
Q. Highly repetitive DNA is seen in (PGI)
A. Cloning of DNA
B. Microsatellite DNA
C. Telomere
D. Centromere
STEP TO PG-MD/MS - DR.AKIF A.B
Ans. C. Telomere
D. Centromere
-In human DNA around 30% of genome consists of repeatitive sequence
-The sequence are clustered in centromere and telomere
-They are transcriptionally inactive
-They mostly have structural role in chromosome.
STEP TO PG-MD/MS - DR.AKIF A.B
An enzyme called Helicase breaks the hydrogen bonds between the bases of the two antiparallel strands.
The strands are initially split apart in areas that are rich in A-T base pairs forming a replication fork.
DNA Gyrase (also called Topoisomerase) relieves tension that builds up as a result of unwinding.
Single strand binding proteins (SSBs) help to stabilise the single stranded DNA.
STEP-1
STEP TO PG-MD/MS - DR.AKIF A.B
RNA polymerase (also known as RNA Primase) synthesizes short RNA nucleotides sequences that act as primers (starters).
These essentially provide a starting point for DNA replication.
STEP-2
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3DNA Polymerase III can now start synthesising the new DNA strand using free DNA nucleotides.
However, DNA polymerase can only read the original template (parent strand) in the 3’ → 5’ direction (making DNA 5’ → 3’).
This is not a problem on the leading strand, because the DNA polymerase can simply continue to read along as the two parent stands continue to unzip.
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-4On the lagging strand DNA polymerase moves away from the replication fork.
As the strands continue to unzip more DNA is exposed and new RNA primers must be added.
As a result the lagging strand is synthesised in short bursts as DNA polymerase synthesizes DNA in-between each of the RNA primers.
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-5The newly synthesised lagging strand now consists of both RNA and DNA fragments.
The DNA fragments are known as Okazaki fragments, after a Japanese scientist who noticed that heating DNA during replication, which separates the strands, gave many small fragments of DNA.
From this he concluded that one stand must be synthesized in short bursts of DNA.
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-6DNA Polymerase I now removes the RNA primers and replaces them with DNA
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-7DNA Ligase joins the DNA fragments of the lagging strand together to form one continuous length of DNA.
STEP TO PG-MD/MS - DR.AKIF A.B
DNA REPAIRDNA damaging agents
Defects in DNA
Repair mechanism
Disorder associated
UV lightsChemicals
Pyrimidine dimers
Nucleotide excision repair
Xeroderma pigmentosa
Replication errors
Mismatch repair
HNPCC
Ionising radiation
Homologous recombination
Ataxia telangiectasia
MOLECULAR BIOCHEMISTRY- II
TRANSCRIPTION
STEP TO PG-MD/MS - DR.AKIF A.B
Key points:
Transcription is the process in which a gene's DNA sequence is copied (transcribed) to make an RNA molecule.
RNA polymerase is the main transcription enzyme.
Transcription begins when RNA polymerase binds to a promoter sequence near the beginning of a gene (directly or through helper proteins).
RNA polymerase uses one of the DNA strands (the template strand) as a template to make a new, complementary RNA molecule.
Transcription ends in a process called termination. Termination depends on sequences in the RNA, which signal that the transcript is finished.
TRANSCRIPTION
STEP TO PG-MD/MS - DR.AKIF A.B
(a)To initiate the transcription process, RNA polymerase, shown as a large green blob, binds to a promoter sequence shown in dark green on a double-stranded DNA molecule.
(b)Once bound, RNA polymerase and its associated proteins bend the DNA to separate the two strands.
(c) A DNA sequence downstream of the promoter region is labeled the termination site, and it indicates where the transcription process will end.
STEP TO PG-MD/MS - DR.AKIF A.B
RNA POLYMERASERNA POLYMERASE DNA POLYMERASE
No Primer is needed Primer is needed
No proof reading activity
proof reading activity
TYPE OF RNA POLYMERASE
MAJOR PRODUCTS
RNA Polymerase I rRNA
RNA Polymerase II mRNA, miRNA, SnRNA
RNA Polymerase III tRNA, 5s rRNA
-In Prokaryotes there is only one type of RNA Polymerase
-Eukaryotes :3 Types
STEP TO PG-MD/MS - DR.AKIF A.B
PROMOTERS OFTRANSCRIPTION
Bacterial Promoters
Eukaryotic promoters
1) TATA Box 10 bp upstream of start site of Transcription
1) Golberg Hogness Box
-Similar to TATA Box
-25-35 bp upstream
2) TGG Box 35 bp upstream 2) CAAT Box 70-80 bp upstream
STEP TO PG-MD/MS - DR.AKIF A.B
PROMOTERS OFTRANSCRIPTION
-Usually Promoters are located upstream of start site of Transcription
- But Promoters for RNA Polymerase III is located Downstream
-Promoters lie on the coding strand of DNA but not on Template strand
STEP TO PG-MD/MS - DR.AKIF A.B
(b) During the elongation phase, RNA polymerase adds nucleotides to a growing mRNA chain.
The nucleotides of the mRNA are represented here as pink T-shaped molecules; a curved red arrow indicates that they are added to the three-prime end of the growing mRNA transcript.
Blue arrows show that the DNA is wound back up at the left side and is unwound at the right side as RNA polymerase moves along the template strand from left to right, as indicated by a green arrow.STEP TO PG-MD/MS - DR.AKIF A.B
DNA STRANDSTEMPLATE STRAND CODING STRAND
Non coding strand
Antisense strand Sense strand
-ve strand +ve strand3’-5’ direction or 5’-3’ direction
5’-3’ direction or 3’-5’ direction
This strand is copied during m-RNA synthesis
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
(c) When RNA polymerase reaches the termination site on the template DNA strand, the mRNA transcript is separated from the DNA.
Here, the synthesized mRNA is shown as a separate molecule below the double-stranded DNA, and a red arrow above the double-stranded DNA shows the release of the RNA polymerase from the DNA.
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
POST TRANSCRIPTIONALPROCESSING
- Primarily occurs at nucleus
1) 7-methylguanosine capping at 5’ end
3) Removal of Introns and Joining of Exons called splicing
2) Addition of Poly A tail at 3’ end
STEP TO PG-MD/MS - DR.AKIF A.B
RNARNA DNA
Mostly seen in cytoplasm Nucleus
Destroyed by alkali Not destroyed
Single stranded Double stranded
STEP TO PG-MD/MS - DR.AKIF A.B
NON CODING RNAs1)Transfer RNA (tRNA)
2)Ribosomal RNA (rRNA)
3) mi RNA
4) Si RNA
STEP TO PG-MD/MS - DR.AKIF A.B
RIBOSOMAL RNA-Most abundant RNA
-40S Ribosome = 18 SrRNA + 30 Proteins
-60S Ribosome = 5S rRNA + 5.8 + 28S
-Synthesised in Nucleolus
-Some rRNA acts as Ribozymes
STEP TO PG-MD/MS - DR.AKIF A.B
tRNA-Transfer RNA
-Transfers Amino acids from Cytoplasm to Ribosomes
Acceptor arm -Amino acid binding site- CCA at 3’end
Anticodon arm Binds with mRNAD-ARM Dihydrouridine arm
- Detects aminoacyl tRNA Synthase
ARM - Ribothymidine and Pseudouridine
STEP TO PG-MD/MS - DR.AKIF A.B
MODIFIED tRNA1) Dihydrouridine = One of double bond is
decreased
2) Pseudouridine : Ribose and N2 base is linked by C-C bond instead of C-N bond
3) Ribothymidine : methylation of one of uracil to form Thymine
- Only RNA to contain Thymine is : Ribothymidine tRNA
4) Inosine : Contain Hypoxanthine
STEP TO PG-MD/MS - DR.AKIF A.B
1) Reverse Transcriptase : RNA dependent DNA Polymerase
2) DNA Polymerase : DNA dependent DNA Polymerase
3) Primase: DNA dependent RNA Polymerase
4) RNA Polymerase : DNA dependent RNA Polymerase
STEP TO PG-MD/MS - DR.AKIF A.B
Replication Transcription
Deoxyribonucleotides are added
Ribonucleotides are added
Adenine pairs with Thymine Adenine pairs with Uracil
Both strands of DNA acts as Template
One strand act as template and other as Coding strand
A Primer is involved as DNA polymerase cannot initiate DNA synthesis on its own
Primer is not required
DNA dependent DNA Polymerase is the enzyme
DNA dependet RNA polymerase is the enzyme
STEP TO PG-MD/MS - DR.AKIF A.B
TRANSLATION
STEP TO PG-MD/MS - DR.AKIF A.B
CODON-Triplet nucleotide sequence present in mRNA representing specific Amino Acid.
-If 1 base represents 1 amino acid = then Total 4 Amino Acids (4 )
-If 2 base represents 1 amino acids = 4 = 16 amino acids
-If 3 base = 4 = 64 Amino Acids
-If 4 base = 4 = 256
1
2
3
4
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
TRANSLATIONEUKARYOTIC PROKARYOTIC
mRNA is monocistronic PolycistronicTranslation occurs only once transcription is complete
Translation can occur even before transcription is complete
Initiating Amino Acid = Methionione
N-Formyl Methionine
- mRNA is always translated from 5’ to 3’ direction.
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-1Charging of t-RNA
-Specific Amino acid is attached to acceptor arm(3’) of t-RNA by Amino-acyl-t-RNA synthase
-2 ATPs are used
-Amino acyl t-RNA synthase is specific for a Amino acid and t-RNA
-Responsible for high fidelity of Translation of Genetic message
STEP TO PG-MD/MS - DR.AKIF A.B
There is no t-RNA for Hydroxylysine and Hydroxyproline since they are
formed by post translation modification of Lysine and Proline
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-2INITIATION
STEP TO PG-MD/MS - DR.AKIF A.B
STEP 2ARIBOSOMAL DISSOCIATION
80S Ribosome = 60S + 40 S
-2 sites for t-RNA on Ribosomes = P site( Peptidyl) + A site (Amino acyl)
-Initially t-RNA bind to P-site
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-2BEIF2 + GTP
EIF2 - GTP
EIF2 –GTP-t-RNA
43 S preinitiation
complex Binds to AUG on m-RNA at 5’
end
48S initiation complex
Binds with 60S
ribosomes
Forms 80S initiation complex
Release of all
elongation factors(Eif2-
GTP)
Methionine-t-RNA
Binds to 40S ribosomes
T-RNA is at P site
STEP TO PG-MD/MS - DR.AKIF A.B
SHINE –DALGARNO SEQUENCE
-In Prokaryotes
- Codon sequence near initiator codon which facilitates binding of Pre-Initiator complex with m-RNA
KOZAK-COSENSUS SEQUENCE
-In Eukaryotes
- Codon sequence near initiator codon which facilitates binding of Pre-Initiator complex with m-RNA
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3ELONGATION PHASE
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3A
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3B-New amino acid binds with t-RNA and then this forms complex with GTP to attach to A site of Ribosome on m-RNA
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3 C,D,E
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3F
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-3G
STEP TO PG-MD/MS - DR.AKIF A.B
STEP-4TERMINATION
There are three termination codons that are employed at the end of a protein-coding sequence in mRNA: UAA, UAG, and UGA.
No tRNAs recognize these codons.
Thus, in the place of these tRNAs, one of several proteins, called release factors, binds and facilitates release of the mRNA from the ribosome and subsequent dissociation of the ribosome.
STEP TO PG-MD/MS - DR.AKIF A.B
INITIATOR CODONS
-AUG
-In Eukaryotes= AUG codes for Methionine
-In prokaryotes = AUG codes for N-Formyl-Methionine
STEP TO PG-MD/MS - DR.AKIF A.B
ENERGY REQUIREMENTSDURING TRANSLATION
Charging of t-RNA 2 Phosphates
Formation of 48 S Pre initiation complex
1 ATP
Formation of 80 S initiation complex
1 GTP
Binding of fresh Aminoacyl t-RNA @ A- SITE
1 GTP
During Translocation 1 GTP
During Termination 1 GTP
STEP TO PG-MD/MS - DR.AKIF A.B
TERMINATOR CODONSUAG UGA UAA
Amber Opal Ochre
EXCEPTIONSUAG can be recoded to
PyrollysineUGA can be recoded to
Selenocysteine
UGA also codes for Tryptophan in Mitochondrial DNA
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
POST-TRANSLATIONALMODIFICATIONS
1) Trimming2) Glycosylation -N-Glycosylation occurs in Endoplasmic
Reticulum
-O-Glycosylation occurs in Golgi Apparatus
3) Hydroxylation Of proline and Lysine gives Hydroxyproline and Hydroxy Lysine
4) Gamma Carboxylation
Of Vit. K dependent clotting factors ( 2,7,9,10)
5) Protein folding Chaperons6) Protein degradation
UbiquitinSTEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B
STEP TO PG-MD/MS - DR.AKIF A.B