The genetic code defines how sequences of nucleotide triplets (codons) in DNA and RNA specify which amino acid will be added during protein synthesis. The genetic code is nearly universal across all organisms, with some exceptions being redundant as single amino acids can be specified by multiple codons. During translation, anticodons in transfer RNA pair with messenger RNA codons to deliver the correct amino acids to the ribosome for polymerization into a protein chain, directed by the genetic code.

2. Presented by
Tabinda shahid

4. Genetic code and components of
protein synthesis

5. Contents

6. Genetic code
The set of DNA and RNA sequences that
determine the amino acid sequences used in the
synthesis of an organism's proteins. It is the
biochemical basis of heredity and
nearly universal in all organisms.

7. • The genetic code is highly similar
among all organisms and can be
expressed in a simple table with
64 entries.

9. Cont……………………………..
The code defines how sequences of these
nucleotide triplets, called codons, specify
which amino acid will be added next
during protein synthesis. With some
exceptions a three-nucleotide codon in a
nucleic acid sequence specifies a single amino
acid.

10. Cont……………………………
The genetic code is described as degenerate, or
redundant, because a single amino acid may
be coded by more than one codon.

15. Anti codon
The anticodon region of a
transfer RNA is a sequence of
three bases that are
complementary to a codon in
the messenger RNA. During
translation , the bases of the
anticodon form
complementary base pairs with
the bases of the codon by
forming the appropriate
hydrogen bonds.

18. The start codon is the first codon of a messenger
RNA (mRNA) transcript translated by a
ribosome. The start codon always codes for
methionine in eukaryotes and a modified Met
(fMet) in prokaryotes. The most common start
codon is AUG.
Start codon
18

19. STOP CODON
 In the genetic code, a stop codon (or
termination codon) is a nucleotide triplet
within messenger RNA that signals a
termination of translation.
 Proteins are based on polypeptides, which
are unique sequences of amino acids.

20. Stop codons signal the termination of this
process by binding release factors, which
cause the ribosomal subunits to
disassociate, releasing the amino acid
chain.

22. THE CHARACTERISTICS OF THE
GENETIC CODE
1. Only 61 triplets or codons code for amino
acids
3 stop codons (aka nonsense codons or
terminator codons) UUA UAG UGA.

23. 1. The code is a degenerative code
Several codons code for the same amino acid.
The first two letters seem to be the most important the third one
tends to be interchangeable
Examples

24. • The reading of mRNA is always in the same
direction 5’ to 3’ (the same way as
transcription and replication).
• The code is universal for all organisms.

25. • Similar amino acids have similar codons.
Example
Aspartic acid codons GAU and GAC. Glutamic
acid codons GAA and GAG. Both are acidic
amino acids.

26. Components of protein synthesis
• Protein synthesis is one of the most fundamental biological
processes by which individual cells build their specific
proteins.
• The process is initiated in the cell’s nucleus, where specific
enzymes unwind the needed section of DNA, which makes the
DNA in this region accessible and a RNA copy can be made.
• This RNA molecule then moves from the nucleus to the cell
cytoplasm, where the actual the process of protein
synthesis take place.

27. Components of protein synthesis
The following "ingredients" are required for protein
synthesis:
 Aminoacylated tRNAs
 Ribosomes
 An mRNA
 Ancillary Protein "Factors"
 A special tRNA for Initiation

28. Aminoacylation of Transfer RNA
The addition of the correct amino acid to the correct
tRNA is possibly the most critical step in gene
expression. If this is not done correctly, then the
Genetic Code would effectively be meaningless.

29. Once the amino acid has been added to
the tRNA, it will be used for protein
synthesis according to the specificity
dictated by the anticodon sequence in
the tRNA.

30. Ribosomes
The ribosomes are complex ribo nucleo
protein complexes. They consist of two
ribo nucleo protein subunits: a smaller
subunit and a larger subunit. The sizes and
exact composition of each subunit is
basically the same in all organisms.

32. The messenger RNA
The mRNA must contain some
feature that allows its 5' end to be
recognized by and positioned
correctly on the ribosome during
the assembly of the protein
synthesizing apparatus.

33. Ancillary Protein "Factors"
• Each of the steps of protein synthesis requires
the participation of a number of additional special
protein factors.
• Some of the factors are G-proteins -- they bind
GTP and GTP hydrolysis is an important part of
their function.

34. A special tRNA for Initiation
• In bacteria, protein synthesis starts with a
special amino acid: N-formyl-methionine.
• Addition of the formyl group to the N-
terminal methionine effectively provides it with
a peptide bond.
• This amino acid is synthesized by modifying
methionine after it has been attached to a
special tRNA -- tRNAf
Met.