Biologi Protein Synthesis

8/3/2019 Biologi Protein Synthesis

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PROTEIN SYNTHESIS


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PROTEINS

Proteins are the basic buildingmaterials of a cell, though thebasic structure of proteins is

linear, they are usually foldedand folded again into complexstructures. Different proteinsperform different functions. LikeDNA, proteins are polymers, thatis, complex molecules made upof simple subunits.


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PROTEINS

THE PROTEIN CONTENT OF THE CELL

A typical' mammalian cell, for example a liverhepatocyte, is thought to contain 10 000 20 000different proteins, representing approximately 0.5

ng of protein or 1820% of the total cell weight.The copy numbers of individual proteins vary:

< 20 000 molecules per cell for the rarest types.

100 million copies for the commonest ones.

N.B. >50 000 per cell is considered to be relativelyabundant.


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PROTEIN SYNTHESIS

Protein synthesis inside the cells is acomplicated biochemical process,begins with transcription, the

separation of a DNA molecule intotwo strands, a section of one strandacts as a template to produce a newstrand called messenger RNA. ThemRNA leaves the cell nucleus andattaches 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 arelinked 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 byaminoacyl-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 finalproduct of genome

expression and constitute allthe proteins present in a cellat a particular time, It is

considered as the central linkbetween the genome and thecell.


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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 theinhibition of translation. Inhibition can be

affected at all stages of translation from

initiation to elongation to termination.


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Several Antibiotic and Toxin inhibitors ofTranslation:

Chloramphenicol: inhibits prokaryotic peptidyl

transferaseCycloheximide: inhibits eukaryotic peptidyltransferase

Diptheria toxin catalyzes ADP-ribosylation of

and inactivation of eEF-2Erythromycin: inhibits prokaryotic translocationthrough the ribosome large subunit


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Fusidic acid: similar to erythromycin only by preventingEF-G from dissociating from the large subunit

Neomycin: similar in activity to streptomycin

Puromycin: resembles an aminoacyl-tRNA, interfereswith peptide transfer resulting in prematuretermination in both prokaryotes and eukaryotes

Ricin: found in castor beans, catalyzes cleavage of theeukaryotic large subunit Rrna

Streptomycin: inhibits prokaryotic peptide chaininitiation, also induces mRNA misreading

Tetracycline: inhibits prokaryotic aminoacyl-tRNAbinding 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. These triplets are callednucleotides

codons.Genetic code is required to account for all 20amino acids found in proteins. A two-lettercode would have only 42 = 16 codons, which

is not enough to account for all 20 aminoacids, whereas a three-letter code would give43 = 64 codons.

The 64 codons fall into groups, the members ofeach group coding for the same amino acid.


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THE GENETIC CODE

all amino acid are coded by two, three,Degeneracyfour or six codons except tryptophan and methioninehave just a single codon each.

, whichpunctuation codonsThe code also has four

indicate the points within an mRNA where translationof the nucleotide sequence should start and finish.

, which also3-AUG-5is usuallyinitiation codonThespecifies methionine (so most newly synthesizedpolypeptides start with methionine), with a fewmRNAs other codons such as 5-GUG-3 and 5-

UUG-3 are used.3-UAA-5,3-UAG-5aretermination codonsThe three

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:

.translationIt signals the start of

It codes for the incorporation of the amino acid

(Met) into the growing polypeptidemethionine

chain.The genetic code can be expressed as either

RNA codons or DNA codons:


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THE GENETIC CODE

RNA codons:

messenger RNAOccur in

(mRNA) and are the codonsthat are actually read during thesynthesis of polypeptides. Buteach mRNA molecule acquires

its sequence of nucleotides byfrom thetranscription

corresponding gene.


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THE GENETIC CODE

The DNA Codons: (genes at the levelof DNA):

These are the codons as they are read

') strand of DNA.3' to5(senseon theExcept that the nucleotide thymidine(T) is found in place of uridine (U),they read the same as RNA codons.

However, mRNA is actuallyantisensesynthesized using the') as the5' to3(strand of DNA

template.


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REFRENCES&FURTHERREADING

en.wikipedia.org/wiki/Genetic_Code:CGeneticode

Genetic Code:

www.accessexcellence.org/AB/GG/genetic.html

http:/www.med.uottawa.ca/patho/devel/index.html

Protein Synthesis:http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Codons.html#rna_codons


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REFRENCES&FURTHERREADING

http://www.emc.maricopa.edu/faculty/farabee/bi

obk/BioBookPROTSYn.html


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THANK YOU

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Biologi Protein Synthesis