PROTEIN SYNTHESIS

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• PROTEIN SYNTHESIS

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PROTEINS

• Proteins are the basic building materials of a
  cell, though the basic structure of proteins is
  linear, they are usually folded and folded again
  into complex structures. Different proteins
  perform different functions. Like DNA, proteins
  are polymers, that is, complex molecules made up
  of simple subunits.

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PROTEINS THE PROTEIN CONTENT OF THE CELL

• A typical' mammalian cell, for example a liver
  hepatocyte, is thought to contain 10 000 20 000
  different proteins, representing approximately
  0.5 ng of protein or 1820 of the total cell
  weight.
• The copy numbers of individual proteins vary
• lt 20 000 molecules per cell for the rarest types.
  
• 100 million copies for the commonest ones.
• N.B. gt50 000 per cell is considered to be
  relatively abundant.

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PROTEIN SYNTHESIS

• Protein synthesis inside the cells is a
  complicated biochemical process, begins with
  transcription, the separation of a DNA molecule
  into two strands, a section of one strand acts as
  a template to produce a new strand called
  messenger RNA. The mRNA leaves the cell nucleus
  and attaches to the ribosomes,

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Ribosome
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RIBOSOMES

• Specialized cellular structures that are the
  sites of protein synthesis. Amino acids are
  carried to the ribosomes by transfer RNA (tRNA)
  (translation) the amino acids are linked
  together in a particular sequence, dictated by
  the mRNA, to form a protein. Activation of amino
  acids is carried out by a two step process
  catalyzed by aminoacyl-tRNA synthetases and
  requires energy in the form of ATP.

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PROTEIN SYNTHESIS

• Translation proceeds in an ordered process.
• 1- Accurate and efficient initiation occurs.
• 2- Chain elongation.
• 3- Accurate and efficient termination.

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Translation
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Termination
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PROTEIN SYNTHESIS
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Direction of translation
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PROTEOME

• The proteome is the final product of genome
  expression and constitute all the proteins
  present in a cell at a particular time, It is
  considered as the central link between the genome
  and the cell.

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Protein Synthesis Inhibitor

• Many of the antibiotics utilized for the
  treatment of bacterial infections as well as
  certain toxins function through the inhibition of
  translation. Inhibition can be affected at all
  stages of translation from initiation to
  elongation to termination.

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Protein Synthesis Inhibitor

• Several Antibiotic and Toxin inhibitors of
  Translation
• Chloramphenicol inhibits prokaryotic peptidyl
  transferase
• Cycloheximide inhibits eukaryotic peptidyl
  transferase
• Diptheria toxin catalyzes ADP-ribosylation of and
  inactivation of eEF-2
• Erythromycin inhibits prokaryotic translocation
  through the ribosome large subunit

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Protein Synthesis Inhibitor

• Fusidic acid similar to erythromycin only by
  preventing EF-G from dissociating from the large
  subunit
• Neomycin similar in activity to streptomycin
• Puromycin resembles an aminoacyl-tRNA,
  interferes with peptide transfer resulting in
  premature termination in both prokaryotes and
  eukaryotes
• Ricin found in castor beans, catalyzes cleavage
  of the eukaryotic large subunit Rrna
• Streptomycin inhibits prokaryotic peptide chain
  initiation, also induces mRNA misreading
• Tetracycline inhibits prokaryotic aminoacyl-tRNA
  binding to the ribosome small subunit

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THE GENETIC CODE

• Genetic code is degenerate, unambiguous, none
  overlapping
• The genetic code consists of 64 triplets of
  nucleotides. These triplets are called codons.
• Genetic code is required to account for all 20
  amino acids found in proteins. A two-letter code
  would have only 42 16 codons, which is not
  enough to account for all 20 amino acids, whereas
  a three-letter code would give 43 64 codons.
• The 64 codons fall into groups, the members of
  each group coding for the same amino acid.

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THE GENETIC CODE

• Degeneracy all amino acid are coded by two,
  three, four or six codons except tryptophan and
  methionine have just a single codon each.
• The code also has four punctuation codons, which
  indicate the points within an mRNA where
  translation of the nucleotide sequence should
  start and finish.
• The initiation codon is usually 5'-AUG-3', which
  also specifies methionine (so most newly
  synthesized polypeptides start with methionine),
  with a few mRNAs other codons such as 5'-GUG-3'
  and 5'-UUG-3' are used.
• The three termination codons are 5'-UAG-3',
  5'-UAA-3' and 5'-UGA-3' these are sometimes
  called amber, opal and ochre, respectively.

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THE GENETIC CODE

• The code is not uambiguous because a given codon
  designates only one amino acid.
• One codon, AUG serves two related functions
• It signals the start of translation.
• It codes for the incorporation of the amino acid
  methionine (Met) into the growing polypeptide
  chain.
• The genetic code can be expressed as either RNA
  codons or DNA codons

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THE GENETIC CODE

• RNA codons
• Occur in messenger RNA (mRNA) and are the codons
  that are actually read during the synthesis of
  polypeptides. But each mRNA molecule acquires its
  sequence of nucleotides by transcription from the
  corresponding gene.

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THE GENETIC CODE

• The DNA Codons (genes at the level of DNA)
• These are the codons as they are read on the
  sense (5' to 3') strand of DNA. Except that the
  nucleotide thymidine (T) is found in place of
  uridine (U), they read the same as RNA codons.
  However, mRNA is actually synthesized using the
  antisense strand of DNA (3' to 5') as the
  template.

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REFRENCESFURTHER READING

• GenetiCCodeen.wikipedia.org/wiki/Genetic_code
• Genetic Code www.accessexcellence.org/AB/GG/genet
  ic.html
• http/www.med.uottawa.ca/patho/devel/index.html
• Protein Synthesis
• http//users.rcn.com/jkimball.ma.ultranet/BiologyP
  ages/C/Codons.htmlrna_codons

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REFRENCESFURTHER READING

• http//www.emc.maricopa.edu/faculty/farabee/biobk/
  BioBookPROTSYn.html

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