This document provides information about genetic information and protein synthesis. It discusses genes located in the cell nucleus and DNA structure. The genetic code and process of protein synthesis through transcription, post-transcriptional processing, translation, and post-translational modification are described. Regulation of gene expression can occur at transcription, translation, and through local chromatin modification.

1. Genetic Information
and
Protein Synthesis

2. Outline
• Genes in the Cell Nucleus
– DNA
– Genetic Code
• The process of Protein synthesis
– Transcription
– Post-transcriptional processing
– Types of RNA
– Translation
– Post-translational modification
• Regulation of Gene Expression
– Control of gene expression at:
– Transcription
– Translation of mRNA
– local chromatin-modification
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3. Objectives
At the end of this session the students will able to:
• Describe structure and characteristics of DNA & genetic
code.
• List steps of protein synthesis
• Identify the functions of RNAs in protein synthesis
• Describe post-transcriptional and translational
modifications.
• Describe the general mechanisms of regulation of gene
expression.
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4. Genes in the Cell Nucleus
• Genetic materials in the nuclei of all cells of the body
control:-
heredity from parents to off spring
day-to-day function of all the body’s cells
• The genes control cell function by determining
synthesis of substances within the cell.
• This can be possible through formation of a specific
cellular protein.
• Some of the cellular proteins are structural proteins,
enzymes, chemical messengers.
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5. DNA
• In the cell nucleus, large
numbers of genes are arranged
in double-stranded helix of
DNA molecules.
• The nucleotides in DNA contain
the following basic chemical
compounds:-
1. Phosphoric acid,
2. A sugar called deoxyribose,
and
3. One of four nitrogenous bases
(two purines-adenine and
guanine, and two pyrimidines-
thymine and cytosine).
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6. DNA...
 The phosphoric acid and
deoxyribose form the two helical
strands that are the backbone of
the DNA molecule.
• Joined by 3’,5’ phosphodiester
bond
 The nitrogenous bases lie
between the two strands and
connect them.
• Hydrogen bonds between the
purine and pyrimidine bases
attach the two strands
– Two H-bonds b/n A & T
– Three H-bonds b/n G &C
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8. DNA...
• Double helix of DNA can
be denatured by
application of heat (at 85-
1000c ) or high alkaline
pH.
• No covalent bonds are
broken in this process.
• It can return to double
strand if the denaturing
condition is slowly
removed (renaturation).
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9. Genetic Code
• Molecules of DNA contain information, coded in the
sequence of nucleotides.
• Each three successive bases “triplet” is considered as
a code word.
• Successive “triplets” of bases in DNA are known as
genetic code.
• Four bases in the DNA can be arranged in(444=64)
different three-letter combinations.
• A given amino acid is usually specified by more than
one code word (exceptions are methionine and
tryptophan).
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10. Genetic...
• Only 61 of the 64 possible code words are used to specify
amino acids.
• The code words that do not specify amino acids are
known as “stop” signals.
• The genetic code is universal (the same in all organism).
• Some minor exceptions such as:
 Stop-codon, UAA, can encode a tryptophan in some
lower eukaryotic organisms such as Paramecium and
Tetrahymena
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11. Genetic...
• A gene is a sequence of DNA nucleotides containing
the information that specifies the amino acid
sequence of a single polypeptide chain.
• A single molecule of DNA contains many genes.
• The total genetic information coded in the DNA of a
typical cell in an organism is known as its genome.
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12. Genetic...
• The human genome contains between 50,000 and
100,000 genes, the information required for
producing different proteins.
• During protein synthesis DNA does not directly
participate in the assembly of amino acid molecules.
• The transfer of information from DNA to the site of
protein synthesis is the function of RNA molecules.
• Genetic information flows from DNA to RNA and
then to protein.
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13. The Process of Transcription
• The process of transferring genetic information from
DNA to RNA in the nucleus is known as transcription.
• It is the mechanism by which a template strand of DNA is
utilized by specific RNA polymerases to generate one of
the three different classes of RNA.
Synthesis of RNA
• The enzymes responsible for the synthesis of RNA, using
DNA as a template are RNA polymerases.
RNA polymerase I -synthesizes the rRNAs;
RNA polymerase II -synthesizes mRNA. It is
extremely sensitive to inhibition by α-amanitin.
RNA polymerase III -synthesizes the small nuclear
RNAs & tRNAs.
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14. The Process...
• All RNAs are synthesized by these enzymes, in a
direction of 5' to 3' of RNA strand, but in the 3' to 5'
direction of DNA template strand.
• Gene transcription is initiated by a class of proteins
known as transcription factors.
• The two strands of the DNA molecule separate
temporarily; one of these strands is used as a template
for synthesis of an RNA molecule.
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15. The Process...
• The process of transcription can be divide it into 3
separate steps:
– Initiation,
– Elongation and
– Termination.
I. Initiation of transcription
• Initiation involves the interaction of the RNA
polymerase with DNA in a specific site, known as
promoters.
– The RNA polymerase has an appropriate complementary
structure that recognizes this promoter and becomes
attached to it.
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16. The Process...
• Promoters are groups of nucleotides sequences in DNA,
usually located in front of the gene that is to be
transcribed.
- the TATA and the CAAT box
• Transcription factors are required to identify & separate
the DNA strands at the promoter region of a gene.
– Basal transcription requires, in addition to pol II, a number
of GTFs [general transcription factor]called TFIIA, TFIIB,
TFIID, TFIIE, TFIIF, and TFIIH
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17. The Process...
II. Elongation
• DNA topoisomerase I & II cause unwinding
of the DNA helix and separation of the two
strands.
• RNA polymerase adds a complementary
RNA nucleotide (ATP, GTP, CTP or UTP )
to the growing RNA chain in a direction of
3' to 5` of DNA strand by the following
steps:
 First, it causes a hydrogen bond to form b/n
the end base of the DNA strand and the base
of an RNA nucleotide.
 Breaks two of the three phosphate group
away from each of these RNA nucleotides.
 This energy is used to cause phosphodiester
bridges between nucleotides in the growing
RNA chain.
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18. The Process...
III. Termination
• RNA polymerases have a defined site at which to stop
RNA synthesis, so that the appropriate size of
transcript is produced.
• The three RNA polymerases work in different
mechanisms to terminate transcription.
• For example:-
RNA polymerase I uses a specific protein to
terminate the transcription of rRNAs.
RNA polymerase III uses a specific termination
sequence.
RNA polymerase II uses both sequence and protein
factors to facilitate termination of transcription.
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19. The Process...
• As the new RNA strand is formed  the RNA
polymerase dislodge from DNA template rebinding
of complementary DNA strand.
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20. Post-transcriptional processing
• All three classes of RNA (tRNAs, rRNAs, and
mRNAs) are synthesized as primary transcripts.
• Processing may involve :-
– Adding of sequences to the primary transcript,
– Removal and rejoining of segments of the
transcript.
5' caps and poly(A) tails
• A 7-methyl guanine residue is added to the 5' end
mRNAs.
• It is essential for ribosomal binding
• It protects the mRNA from attack by 5'
exonucleases.
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21. Post-transcriptional processing
• A poly(A) tail of (100-300 residues) is added to the 3'
end of mRNAs.
• The A residues are added by the action of poly(A)
polymerase using ATP as a substrate.
• These tails help stabilize the mRNA and facilitate
their exit from the nucleus.
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22. Post-transcriptional processing
Splicing mRNA
• The removal of an intron
(non-coding sequences)
and rejoining of two
exons (expression
regions) to their 5' and 3'
ends.
• Accomplished by
spliceosome (snRNAs &
large complex of protein)
that facilitate base-pairing
interactions, with the sites
on the mRNA that
represent intron/exon
boundaries.
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23. Types of RNA
• During transcription three different types of RNA
synthesised, each of which play different role in
protein synthesis:
– Messenger RNA ,
– Transfer RNA &
– Ribosomal RNA
1. Messenger RNA
• Carries genetic code to the cytoplasm for protein
synthesis.
• Composed of several hundred to thousands RNA
nucleotides in single strand.
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24. Types of RNA
• Contain codons that are exactly complementary to the
triplets of the DNA genes.
• One or more codons represent a single amino acid.
• There are a sort of codons known as:
• Start codon AUG-methionine and
• Stop codons UAA UAG UGA
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25. Types of RNA
2. Transfer RNA
• Transfer RNA molecules contain
about 80 nucleotides forming four
distinct loops.
• The acceptor arm:- is the site of
attachment of the specific amino
acid.
• The anticodon region:-consists of
nucleotides, and it recognizes the
three-letter codon in mRNA
• The thymidine-pseudouridine-
cytidine (TΨC) arm:-is involved in
binding of the aminoacyl-tRNA to
the ribosomal surface at the site of
protein synthesis.
• The D arm:-sites for the proper
recognition of a given tRNA species
by its proper aminoacyl-tRNA
synthetase.
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D arm
TΨC arm
Acceptor arm

26. Types of RNA
• tRNA transports activated amino acids to the
ribosomes to be used in assembling the protein
molecule.
– aa ATP (aminoacyl-tRNA synthetases) aa-AMP
(activated aa)
– aa-AMP + tRNA  aa-tRNA (charged tRNA).
• Each type of tRNA combines specifically with 1 of
the 20 amino acids that are to be incorporated into
proteins.
• tRNA recognize a specific codon by specific code in
the tRNA known as anti-codons.
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27. Types of RNA
3. Ribosomal RNA
• Along with different proteins, forms ribosomes,
which are the site of protein assembly.
• rRNA transcript has a size of 45S (about 13 kb long).
• This large primary transcript is processed into 28S,
18S, 5.8S, and 5S.
• The 28S, 5.8S, and 5S rRNAs associate with
ribosomal proteins to form the large ribosomal
subunit (60S).
• The 18S rRNA associates with other proteins to form
the small ribosomal subunit (40S).
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28. Types of RNA
• The functional ribosome has a size of 80S.
• The protein part of ribosomes has both structural and
enzymatic functions.
 The large ribosomal subunit catalyzes formation of the
peptide bonds that link amino acid residues in a protein.
 The small subunit binds mRNA and is responsible for the
accuracy of translation.
• The ribosome has three binding sites for tRNA
molecules—the A, P and E sites.
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29. Types of RNA
• During translation, the A site binds an incoming
aminoacyl-tRNA as directed by the codon currently
occupying this site.
– This codon specifies the next amino acid to be added to the
growing peptide chain.
• The P-site codon is occupied by peptidyl-tRNA.
• This tRNA carries the chain of amino acids that has
already been synthesized.
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30. The Process of Translation
• Translation is a process that involves the interaction
of enzymes, tRNAs, ribosomes, and mRNA in
specific ways to produce a protein molecule.
• Has three steps: initiation, elongation & termination.
A. Initiation of protein synthesis
• Initiation of translation requires a specific initiation
factors(eIFs).
• eIFs recognize & bring the 7-methylguanine cap of
mRNAs to the small sub unit of ribosomes.
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31. The Process of Translation
• The ribosome first binds at the 5' end of the mRNA,
and then moves down the molecule until it
encounters the first AUG codon.
• Methionyl-tRNA (met-tRNA) molecule enter the
ribosomal subunit to incorporate the initial
methionine residue into all proteins .
• This process needs hydrolysis of ATP & GTP
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32. The Process of Translation
B. Elongation
• Begins with the binding of a
charged tRNA to the A site
(site 2) of the ribosome.
• The charged tRNA molecule
is brought to the ribosome
by the action of an
elongation factor called EF-
1α.
• Peptidyl transferase
catalyzes the formation of a
peptide bond between the
amino acid in the site A (site
2) and the amino acid at the
end of the growing peptide
chain in the P (site1).
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33. The Process of Translation
C . Termination
• Termination of protein synthesis occurs when the
ribosome encounters a termination codon on the
mRNA.
• Protein factors called releasing factors recognize
these codons, and cause the protein that is attached to
the last tRNA molecule in the site1 to be released.
• The ribosome, mRNA, and tRNA will dissociate from
each other.
• Molecules of mRNA eventually broken down into
nucleotides by cytoplasmic enzymes.
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34. Post-translational modification
• Many proteins must be altered by chemical
modification of amino acids before the proteins
become biologically active.
• Post-translational modifications occurs within the
rER and Golgi apparatus.
• It may include:
1. Amino-terminal modification, e.g. amino acid
methionine cleaved from the end of most proteins.
2. Modification of individual amino acids-by
methylation or combining with lipids or CHOs,
binding of phosphate group to serine, threonine,
tyrosine side chains.
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35. Post-translational modification
3. Proteolytic processing-
conversion of
preprohomones 
prohormones 
hormones.
4. Formation of disulfide
bridges & hydrogen
bond between peptide
chains – to fold in to
three-diamentional
conformation.
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36. Regulation of Gene Expression
• Gene expression is the ability of a gene to produce a
biologically active protein.
• Why control of gene expression?
– Both prokaryotic and eukaryotic cells adapt to
changes in their environment by turning the
expression of genes on and off.
– Cells conserve fuel by making proteins only when
they are needed.
– During development, physical and physiological
changes result from variations in gene expression
and therefore of protein synthesis.
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37. Regulation of Gene Expression...
• Gene expression refers to the multistep process that
results in the production of a functional gene product
(RNA or protein).
• The first step in gene expression(transcription) is the
primary site of regulation in both prokaryotes and
eukaryotes.
• However, control of gene expression also involves:
– Chromatin-modifying activities,
– Post-transcriptional,
– Translational processes.
• Each of these steps can be regulated to provide
additional control over the kinds and amounts of
protein produced.
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38. 1.Regulation of transcription
• The process of gene transcription is the major site for
control of gene function.
• Controlled by two set of interacting regulatory
components:
–Cis-acting regulatory elements
–Trans-acting molecules
Cis-acting regulatory elements
• The DNA sequences to which activator/inhibitor proteins
bind.
• These DNA sequences flanking a gene are called cis-
acting regulatory elements because they influence
expression of genes only on the same chromosome.
• Usually embedded in the non-coding regions of the
genome.
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39. Regulation of transcription...
• The DNA regulatory base sequences form:
• The promoter region
• Enhancer region or
• Silencers that allows control of gene expression by
multiple signals
I. Promoters
• DNA nucleotide sequences that are relatively close to the
start point for transcription of a gene and control its
expression are collectively known as the promoter.
• Few response elements are located with in the
promoter region.
• Those factors, bound to promoter sequences, determine
how actively the RNA pol II copies the DNA into RNA.
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40. Regulation of transcription...
II. Enhancers
• Enhancers may lie upstream or downstream of a promoter.
• Enhancers contain DNA sequences that bind specific
transcription factors known as activators.
• Can regulate the level (rate) of transcription of a gene.
• Important in conferring tissue-specific transcription.
• Enhancers may be brought close to the basal promoter region
by bending of the DNA molecule.
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41. Regulation of transcription...
III. Silencers
• Silencers are similar to enhancers in that they lie
upstream or downstream of start point of a gene.
– Bind repressor proteins
• They reduce the rate of gene transcription.
Trans-acting molecules
• DNA-binding proteins that can function as
transcription activators or specific transcription
factors.
• Can diffuse through the cell from its site of synthesis
to its DNA-binding site.
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42. Regulation of transcription...
• They have at least two binding domains:
– the DNA-binding domain, and
– the transcription activation domain.
• The transcription activation domain allows the
binding of other proteins, such as co-activators or co-
repressors.
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43. Regulation of transcription...
• Interact with RNA polymerases to stabilize the
formation of the initiation complex.
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44. Regulation of transcription...
• There are two types transcription factors, general transcription
factors and specific transcription factors.
General Transcription Factors
• General transcription factors are common to most genes.
• Bind to the promoter to allow RNA polymerase II to bind and
form the initiation complex at the start site for transcription.
• Examples, TFII , NF-1 that modulate basal transcription of
many genes.
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45. Regulation of transcription...
Specific Transcription Factors
• Specific transcription factors bind to enhancer regions
or, in a few cases, to silencers.
• Each gene contains a variety of enhancer or silencer
sequences in its regulatory region.
• Specific transcription factors determines which genes
will be transcribed at what rates.
• Specific transcription factors are cell-type specific.
– Examples include steroid receptors and the CREB
protein.
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46. Regulation by post-transcriptional
processes affecting mRNA
• Splice-site choice & mRNA stability are some of post
transcriptional factors that affect gene expression.
Splice-site choice
• Tissue-specific protein products (protein isoforms) can be
made from the same pre-mRNA through use of alternate splice
sites.
• For example, tropomyosin isoforms, antibody production by
B-lymphocytes.
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47. Regulation by post-transcriptional...
mRNA stability
• Life time of mRNA in
the cytosol influences
how much protein
product can be produced.
• mRNA stability control
gene expression by
affecting the life time of
mRNA
• Example , in the
metabolism of iron iron
conc. in the cell  the
IRPs bind to the IREs
and stabilize the mRNA
for TfRTfR synthesis.
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48. Control of gene expression at
translation of mRNA
– Regulation of gene
expression can also occur at
the level of translation.
– One mechanism by which
translation is regulated is
through phosphorylation of
the eukaryotic translation
initiation factor, eIF-2 .
– Phosphorylation of eIF-2
inhibits its function and so
inhibits translation at the
initiation step.
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49. Regulation through local chromatin-
modification
• Chromatin-modifying activities include:
Histone acetylation
• Acetylation of amino terminal of protein histone
• Histone acetylation more open chromatin structure
transcrptionally active chromatin.
• Underacetylation of histone is associated with closed
chromatin favour inactive chromatin.
DNA methylation
• DNA methylating enzymes favour inactive chromatin.
• There are several proteins that bind to methylated CGs but not
to unmethylated CGs the DNA takes open chromatin
structure transcrptionally active chromatin.
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50. Thank you