Protein Synthesis

Human life is impossible without proteins. Why?
Proteins are of two Kinds
1. Structural
Actin & Myosin: muscle proteins
Keratin: nails, hair, horns, feathers
Collagen: bones, teeth, cartilage, tendons,
ligament, blood vessels, skin matrix
2. Functional
 Enzymes
Antibodies
Haemoglobin
Protein Synthesis takes place on two major steps:
1. Transcription
2. Translation
Transcription:
 Takes place inside the nucleus
 DNA unzips (one gene) and a complimentary copy of
this gene called mRNA (messenger RNA) is formed from
RNA nucleotides
 The newly formed mRNA leaves the nucleus through the
a nuclear pore
Translation:
 Takes place in the cytoplasm
 The freely floating ribosomes or the ones sticking to the
RER start reading the message on the mRNA
 Reading the message takes place three nitrogenous
bases at a time (triplets), each triplet is called a codon
 tRNA (transfer RNA) which is found in the cytoplasm
has the appropriate anti-codon for each codon which is
equivelant to one specific amino acid
 There are 20 different amino acids that enter in the
synthesis of polypeptides (proteins)
Translation:
Mutations
1. Chromosomal mutations
All or part of a chromosome.
e.g.: Down's Syndrome
2. Gene mutations
• Deletion: deletion of one
nitrogenous base
• Addition: adition of one
nitrogenous base
• Substitution: one
nitrogenous
base is replaced
* Any of such mistakes results in
by another
a wrong protein being synthesized.