PROTEIN SYNTHESIS
Proteins determine the physical and chemical characteristics
of the cell and therefore of the organism formed from them. Some proteins help
assemble cellular structures such as the plasma membrane, the cytoskeleton, and
other organelles. Others serve as hormones, enzymes, antibodies, and contractile
elements in muscular tissue.
Proteome: all the
protein of an organism
Gene expression:
Gene’s DNA is used as a template for the synthesis of specific protein
Protein synthesis happens in 2 steps
A) Transcription
B) Translation
Transcription
Transcription process through which the information encoded
in a specific region of DNA is copied to produce a specific molecule of RNA.
Transcription happens in Nucleus. During transcription
process the genetic information represented by the sequence of base triplets in
DNA serves as a template for copying the information into complementary
sequence of codons.
The enzyme RNA polymerase catalyzes the transcription of
DNA.
Promoter: the
specific nucleotide where the transcription begins.
Terminator:
specific nucleotide where the transcription ends.
Transcription leads to 3 types of RNA molecules
Ribosomal RNA (rRNA):
Helps form the ribosomes
Messenger RNA (mRNA):
Carries the instructions from the nucleus to the ribosome for building a protein
Transfer RNA (tRNA):
Transfers appropriate amino acids to the ribosome for building the protein
Translation:
Translation process through which the information encoded by
mRNA is translated to amino acid sequence of protein
Translation is carried in the Cytosol of the cell.
Translation occurs in many steps as following
a) Binding of mRNA to the small ribosomal unit, Binding of
tRNA to the specific site
b) Attachment of large-ribosomal unit to small unit- mRNA
complex
c) The anticodon on the tRNA pairs with the codon on mRNA
d) Large ribosomal subunit catalyzes the formation peptide
bond which detaches the tRNA and the process of anticoding the codon is
continued.
e) Protein synthesis ends when the ribosome reaches the
terminator codon.
Formed protein detaches from the tRNA. tRNA vacates the
ribosomal unit and ribosome splits into
its large and small subunits.