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TRANSCRIPTION,TRANSLATION
&EFFECT OF MUTATION ON PROTEIN STRUCTURE &
FUNCTION
Punjab EDUSAT Society {PES}
FUNCTION
By – Surinder Kaur
DIET Ropar
Surinder-1998@ yahoo.in
Mob No 9988530775
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The process by which a molecule of DNA is copied
into a complementary strand of RNA.
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thymine
adenine
cytosine
guanine
Hydrogen bond
(H-bonds)
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phosphate
DNA nucleotide
Deoxyribose sugar
phosphate
Nitrogenous base
(guanine)
RNA nucleotide
ribose sugar
phosphate
Nitrogenous base
(uracil)
Sugar / phosphate “strand”
Nitrogenous base
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Step 1: Hydrogen bonds
between complimentary
bases break
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DNA “unzips”
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Step 2: DNA strands
pull apart from each other
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pull apart from each other
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Step 3:
RNA nucleotides
in the cell match
up with only one
side of the
RNA nucleotide
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side of the
“unzipped” DNA
each “unzipped’
strands forms a
template for a
mRNA strand
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Step 4:
RNA nucleotides
continue to match
up with
“unzipped” DNA
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“unzipped” DNA
until the message
is completely
transcribed
mRNA strand
One side of DNA strand
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mRNA strand
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Step 4:
mRNA strand
breaks off
from the DNA
strand
One side of DNA strand
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Step 5:
mRNA strand
leaves the
nucleus for
the ribosome
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Step 6: Once the mRNA
leaves, the DNA “zips”
back together
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Transcription Graphics
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RNA and Protein SynthesisRNA and Protein Synthesis
• RNA is a Single
Stranded Nucleic Acid
• RNA Acts as a
Messenger between
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Messenger between
DNA and Ribosomes
• Process Takes Amino
Acids and Forms
Proteins
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TRANSLATIONTranslation is the mechanism by which the triplet base sequence of an mRNA guides the linking of a specific sequence of amino acids to form a polypeptide (protein) on ribosomes.
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(protein) on ribosomes.
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Requirements for proteins synthesis
1. Amino acids as raw materials
2. DNA as specificity control.
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2. DNA as specificity control.
3. RNAs as intermediaries.
4. Ribosomes as protein factories.
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Mechanism of Protein synthesis
1. Activation of amino acids.
2. Charging of tRNA
3. Activation of ribosomes.
4. Assembly of amino acids (polypeptide
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formation).
a) Initiation of polypeptide chain
b) Elongation of polypeptide chain
c) Termination and release of polypeptide chain
d) Modification of released polypeptide chain
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Activation of amino acids
Activating enzyme, Mg 2+
Amino acids + ATP
Amino acid-AMP-Enzyme complex+ PPi
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Amino acid-AMP-Enzyme complex+ PPi
(Activated amino acid)
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Charging of tRNA
Enzyme
Amino acid-AMP-Enzyme complex + tRNA
tRNA- Amino acid complex + ATP + Enzyme
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RNA Used in Protein Synthesis
• Messenger RNA (mRNA).
• Ribosomal RNA (rRNA).
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• Ribosomal RNA (rRNA).
• Transfer RNA (tRNA).
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Proteins
• Proteins are composed of one or
more polypeptides.
• Polypeptides are linear chains of
amino acids.
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amino acids.
• The sequence of amino acids in a
polypeptide is known as its “primary
structure”.
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Amino Acids and Peptide Bonds
• There are 20 different
amino acids coded in
DNA.
• When polypeptides are
synthesized, the acid
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synthesized, the acid
group of one amino acid
is attached to the amino
group of the next amino
acid, forming a peptide
bond.
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Translation
• Translation of mRNA into protein is accomplished by the ribosome, an RNA/protein hybrid. Ribosomes are composed of 2 subunits, large and small.
• Ribosomes bind to the translation initiation
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• Ribosomes bind to the translation initiation sequence on the mRNA, then move down the RNA in a 5’ to 3’ direction, creating a new polypeptide.
• Each group of 3 nucleotides in the mRNA is a “codon”, which codes for 1 amino acids.
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Initiation of Translation
• In prokaryotes, ribosomes bind to specific translation initiation sites. There can be several
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sites. There can be several different initiation sites on a messenger RNA:
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.• In eukaryotes, ribosomes bind to the
5’ cap, then move down the mRNA until they reach the first AUG, the codon for methionine. Translation starts from this point. Eukaryotic mRNAs code for only a single gene.
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• Note that translation does not start at the first base of the mRNA.
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More Initiation• The initiation process
involves first joining the
mRNA, the initiator
methionine-tRNA, and the
small ribosomal subunit.
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small ribosomal subunit.
Several “initiation factors”--
additional proteins--are also
involved.
• The large ribosomal subunit
then joins the complex.
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Elongation• The ribosome has 2 sites for tRNAs, called P
and A.
The initial tRNA with attached amino acid is in the P site. A new tRNA, corresponding to the next codon on the mRNA, binds to the A site.
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next codon on the mRNA, binds to the A site. The ribosome catalyzes a transfer of the amino acid from the P site onto the amino acid at the A site, forming a new peptide bond.
The process is then repeated:
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Elongation
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Termination• Three codons are called “stop codons”. (UAA,
UAG & UGA) They code for no amino acid, and
all protein-coding regions end in a stop codon.
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Post-Translational Modification
• New polypeptides usually fold themselves spontaneously into their active conformation.
• Many proteins have sugars, phosphate groups, fatty acids, and other molecules
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groups, fatty acids, and other molecules covalently attached to certain amino acids.
• Many proteins are targeted to specific organelles within the cell.
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Why are DNA & Ribosomes located at different sites
Location of instruction centre (DNA) and manufacturing centre (ribosomes) at different sites in a
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(ribosomes) at different sites in a cell is advantageous.
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