Genetic code describes codons that code amino acids. Contents are well defined according to process central dogma specially Translation mechanism.

1. GENETIC CODE
GUIDED BY-
DR. DHNANJAY
SHUKLA
PRESENTATION BY-
CHANDRA SHEKHAR
DHIRENDRA KUMAR
KUSHAL KANT PANT
UDYAN SHARMA

2. Central dogma

3. • The central dogma of molecular biology
describes the two-step process, transcription
and translation, by which the information in
genes flows into proteins: DNA → RNA →
protein.

4. Translation
The pathway of protein synthesis is called
Translation because the language of
nucleotide sequence on mRNA is translated in
to the language of an amino acid sequence.
The process of Translation requires a Genetic
code, through which the information
contained in nucleic acid sequence is
expressed to produce a specific sequence of
amino acids.

11. tRNA
• Transfer RNAs or tRNAs are molecules that act as
temporary carriers of amino acids, bringing the
appropriate amino acids to the ribosome based on the
messenger RNA (mRNA) nucleotide sequence. In this
way, they act as the intermediaries between nucleotide
and amino acid sequences.
• tRNAs are ribonucleic acids and therefore capable of
forming hydrogen bonds with mRNA.
• They pair with mRNA in a complementary and
antiparallel manner, and each tRNA can base pair with
a stretch of three nucleotides on mRNA.

12. tRNA Structure and Function

13. • The anticodon loop, which pairs with mRNA, determines which
amino acid is attached to the acceptor stem. The anticodon loop is
recognized by aminoacyl tRNA synthetase (AATS), the enzyme that
chemically links a tRNA to an amino acid through a high-energy
bond. AATS ‘reads’ the anticodon and also recognizes the D-arm
located downstream from the 5’ end of the tRNA.
• The D-arm is made of a double-stranded stem region formed by
internal base pairing as well as a loop structure of unpaired
nucleotides. The D-arm is a highly variable region and plays an
important role in stabilizing the RNA’s tertiary structure and also
influences the kinetics and accuracy of translation at the ribosome.
• T-arm, Similar to the D-arm, it contains a stretch of nucleotides that
base pair with each other and a loop that is single stranded. The
paired region is called the ‘stem’ and mostly contains 5 base pairs.
The loop contains modified bases and is also called the TΨC arm.

15. GENETIC CODE
 Written in linear form of ribonucleotide
bases (mRNA).
 Each word consists of 3 ribonucleotide letters
which (triplet codon) specifies one amino
acids.
 The code is unambiguous – each triplet
specifies only a single amino acid.
 The code is degenerate , one amino acid can
be specified by more than one triplet codon.

16.  The code is comma less ;once translation beings the
codons read one after the other with no breaks
between them (until the stop signal is reached)
 The codon contain 1 start codon and 3 stop codons
 The code is non overlapping
 The code is (nearly) universal with only minor
exception a single coding dictionary is used by all
most all viruses, prokaryotes ,archaea and eukaryotes
.

17.  The initiation codon AUG is the most common signal
for the beginning of a polypeptide in all cells in
addition to coding for Met residues in internal
positions of polypeptides.
 The termination codons (UAA, UAG, and UGA),
also called stop codons or nonsense codons, normally
signal the end of polypeptide synthesis and do not
code for any known amino acids.
 In general, a reading frame without a termination
codon among 50 or more codons is referred to
as an open reading frame (ORF).
 When several different codons specify one amino acid,
the difference between them usually lies at the third
base position (at the 3 end). For example, alanine is
coded by the triplets GCU, GCC, GCA, and GCG.

19. Wobble Allows Some tRNAs to Recognize
More than One Codon
• If the anticodon triplet of a tRNA recognized only one
codon triplet through Watson-Crick base pairing at all
three positions, cells would have a different tRNA for
each amino acid codon. This is not the case, however,
because the anticodons in some tRNAs include the
nucleotide inosinate (designated I), which contains the
uncommon base hypoxanthine . Inosinate can form
hydrogen bonds with three
different nucleotides.

20. The first two bases are
identical (CG) and
form strong Watson-Crick
base pairs with the
corresponding bases of the
anticodon, but the third base
(A, U, or C) forms rather weak
hydrogen bonds with the I
residue at the first position of
the anticodon.

21. • Crick concluded that the third base of most
codons pairs rather loosely with the corresponding base of its
anticodon; to use his picturesque word, the third base of such
codons (and the first base of their corresponding anticodons)
“wobbles.” Crick proposed a setof four relationships called the
wobble hypothesis:
1. The first two bases of an mRNA codon always form strong
Watson-Crick base pairs with the corresponding bases of the tRNA
anticodon and confer most of the coding specificity.
2. The first base of the anticodon (reading in the 5’-3’ direction; this
pairs with the third base of the codon) determines the number of
codons recognized by the tRNA. When the first base of the
anticodon is C or A, base pairing is specificand only one codon is
recognized by that tRNA. When the first base is U or G, binding is
lesspecific and two different codons may be read.When inosine (I) is
the first (wobble) nucleotide of an anticodon, three different codons
canbe recognized—the maximum number for any tRNA.

22. • 3. When an amino acid is specified by several
different codons, the codons that differ in either
of the first two bases require different tRNAs.
•
4. A minimum of 32 tRNAs are required to translate all 61
codons (31 to encode the amino acids and1 for initiation)

23. History
• Paul Zamecnik discovered
ribosome .
• Robert Holley discovered
transfer RNA (tRNA).

24. • In 1961 Marshall Nirenberg
and Heinrich Matthaei
found that the 3 codons of
genetic code in mRNA
codes for amino acids.
• In 1964 Nirenberg and
Philip Leder found that
each amino acid codes for
only specific amino acid.

25. • H. Gobind Khorana, developed
chemical methods to synthesize
polyribonucleotides with
defined,repeating sequences of two
to four bases. The polypeptides
produced by these mRNAs had one
or a few amino acids in repeating
patterns. These patterns, when
combined with information from the
random polymers used by Nirenberg
and colleagues, permitted
unambiguous codon assignments.

26. Mutations and the genetic code
There are two kinds of mutations which played a
very significant role in the study of the genetic
code in living systems. These are:
(i) frame shift mutations and
(ii) base substitutions.

28. Base substitution mutation