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Organisation and Control of Prokaryotic and Eukaryotic Genome

By Ida Peters,2014-05-05 09:03
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Organisation and Control of Prokaryotic and Eukaryotic Genome

Proteins Summary

Components:

     Central ;-carbon, with H-atom

     An amino group (-NH) 2

     A carboxyl group (-COOH)

     Variable R group (Side chain)

Are zwitterions/amphoteric

    Can be classified according to R-groups

     Neutral

    o Hydrophilic

    o Hydrophobic

     Charged/Polar

    o Acidic

    o Basic

Humans just 20 amino acids

A. Polypeptide

    dehydration synthesis Peptide/amide bond

     Enzyme required for synthesis

     Water removed one molecule at a time (DEHYDRATION SYNTHESIS)

     Acid added one at a time

     Has direction (i.e. lys-cis-arg arg-cis-lys)

    o Start: amino terminal

    o End: carboxyl terminal

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    One residue

    Polypetide backbone

    Peptide bonds

     FOUR BONDS H-Bonding (usually):

     o Hydrogen bonds

    O-H-----O

    o Ionic (or electrovalent) bonds O-H-----N

    -+N-H-----O and COO ; Between NH3N-H-----N

    o Hydrophobic interactions

    ; -SH groups form S-S bonds

    o Disulphide Bridges

    B. Structure:

    Primary

     Refers to sequence of amino acids in

    a polypetide chain.

     Only covalent peptide bonds

    between successive amino acid

    residues

    QuickTime?and aSecondary TIFF (Uncompressed) decompressor

    are needed to see this picture. Refers to coiling and pleating of a

    polypeptide

     Maintained by:

    o H-bonds at regular intervals

    formed between CO and NH

    groups of backbone

    (intramolecular)

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    o *** R-GROUPS NOT INVOLVED

     A single protein can have both ;-helix and -pleated sheet

     ;-helix

    o right hand screw rule

    o e.g. keratin (in hair)

     -pleated sheet

    o when two or more regions of a single polypeptide lying side by side are linked

    together by H-bonds.

    o ***the entire sheet is one polypeptide (remember for diagrams)

    o high tensile strength

    o e.g. fibroin in silk worm silk

    QuickTime?and aTIFF (Uncompressed) decompressorare needed to see this picture.

    Tertiary

     Refers to the structure formed from extensive foldings/bendins of a single polypeptide chain,

    forming a compact chain.

     Maintained by 4 types of bonds between R-groups

    o Weak interactions: hydrogen bonds, ionic bonds, hydrophobic interactions

    o Strong covalent linkage: disulphide bonds Hydrophobic quantitatively most important

    Quaternary

     Refers to the association of 2 or more polypeptide chains into one complex, functional protein. Each polypeptide subunit

     Held together by hydrogen bonds, ionic bonds, hydrophobic interactions and disulphide bonds.

     E.g. collagen, haemoglobin

    Fibrous Protein Globular Protein

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C. Denaturation

    Agent Cause of denaturation Example

    +- of acid attaches to COO of protein COOH formed H

    -Disrupts ionic bonds formed by the COO within the Acid

    protein. Souring of milk by

    +-+bacteria. NH of protein loses a H to neutralise OH 3

    +Alkali Disrupts ionic bonds formed by the NH within the 3

    protein.

    Kinetic energy of protein molecule increases

    Heat Its atoms vibrate vigourously disrupting hydrophobic Boiling of egg white.

    interactions, ionic and hydrogen bonds

    Hair styling hydrogen Mechanical

    Physical movement may break hydrogen bonds. bonds in keratin helix are Force

    disrupted.

    Organic solvents form bonds with hydrophilic groups and Sterilisation with alcohol Organic

    disrupt hydrophobic interactions. denatures bacterial Solvents

    Thereby disrupting hydrogen bonds. proteins.

    Cytochrome oxidase

    (respiratory enzyme) is

    -Inorganic Uncharged inorganic ions form bonds with charged groups denatured by CN which

    +Chemicals of proteins and disrupts ionic bonds. combines with NH of 3

    protein to disrupt ionic

    bonds.

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D. Identification

Biuret Test

Steps:

    3 of protein solution 1. 2 cm

    2. Add equal volume of 5% KOH and mix.

    3. Add 2 drops 1% CuSO and mix. 4

Observation:

    A purple colour develops slowly if proteins are present.

Explanation:

     A test for peptide bonds.

     In the presence of dilute CuSO in alkaline solution, N atoms in peptide chain form a purple 4

    complex with copper (II) ions.

     Biuret is a compound derived from urea which also contains the CONH groups and gives a

    postive result.

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