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PROTEIN SYNTHESIS

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PROTEIN SYNTHESIS PROTEINS Proteins are the basic building materials of a cell, though the basic structure of proteins is linear, they are usually folded and folded ... – PowerPoint PPT presentation

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Title: PROTEIN SYNTHESIS


1
  • PROTEIN SYNTHESIS

2
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.

3
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.

4
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,

5
Ribosome
6
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.

7
PROTEIN SYNTHESIS
  • Translation proceeds in an ordered process.
  • 1- Accurate and efficient initiation occurs.
  • 2- Chain elongation.
  • 3- Accurate and efficient termination.

8
Translation
9
Termination
10
PROTEIN SYNTHESIS
11
Direction of translation
12
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.

13
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.

14
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

15
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

16
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.

17
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.

18
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

19
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.

20
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.

21
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

22
REFRENCESFURTHER READING
  • http//www.emc.maricopa.edu/faculty/farabee/biobk/
    BioBookPROTSYn.html

23
THANK YOU
THANK YOU
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