Amino Acids

  • Created by: Jenny Le
  • Created on: 06-04-14 00:47

Interaction of Amino Acids with Water

  • Non-polar amino acids: NEUTRAL - hydrocarbon side group (hydrophobic)
  • Polar amino acids: NEUTRAL - side groups form H-bonds (hydrophilic)
  • Acidic amino acids: NEGATIVE CHARGE - contain carboxylate groups
  • Basic amino acids: POSITIVE CHARGE - form ionic bonds with acidic amino acids
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Essential/Non-essential Amino Acids

ESSENTIAL AMINO ACIDS - cannot be made by the body; must be supplied by food

(Isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Histidine is semi-essential because the body does not always require dietary sources of it.)

NON-ESSENTIAL AMINO ACIDS - made by the body from the essential amino acids or normal breakdown of proteins.

(arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamate, glycine, proline, serine and tyrosine.)

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Complete/Incomplete Proteins

COMPLETE PROTEINS - proteins that contain all NINE of the essential amino acids.

(Typically proteins from animal foods such as meats, poultry, fish, dairy and eggs are complete.)

INCOMPLETE PROTEINS - sources usually include nuts and vegetables.

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Mood Food

High-carbohydrate meals can increase the brain's TRYPTOPHAN levels and therefore the SEROTONIN that promotes contentment and normal sleep.

A high-protein meal increases TYROSINE levels causing neurons to produce NOREPINEPHRINE and DOPAMINE (neurotransmitters that promote alertness and activity).

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  • Tyrosine is required for your body to make active THRYOID hormones. Low levels of tyrosine in the blood is associated with an underactive thyroid gland.
  • Extreme thyroid deficiency causes severe mental retardation known as CRETINISM
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  • Lysine is an essential amino acid and so must be replenished often as it cannot be stored or made in the body. 
  • Within 6 to 8 weeks of lysine deficiency, the amino acid imbalance causes a deficiency in the B Vitamin NIACIN and symptoms begin to develop such as bloodshot eyes, fatigue, dizziness, nausea, loss of appetite, anaemia and kidney stones.
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  • Amino acids exist in either L (levo) or D (dextro) form. The L and D refer to the absolute confirmation of optically active compounds.
  • With the exception of GLYCINE, all other amino acids are mirror images that cannot be superimposed.
  • Most of the amino acids found in nature are of the L-type.
  • Therefore eukaryotic proteins are always composed of L-amino acids.
  • Howevere, D-amino acids are found in bacterial cell walls and in some peptide antibiotics.
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Modified amino acids

Derivatives act as chemical messengers - neurotransmitters.

  • Glutamate derivative - y-amino butyric acid (GABA)
  • Tryptophan derivative - serotonin, melatonin

Hormonal action - thyoxine (tyrosine derivative)

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Almost all peptide bonds are in the TRANS position

  • Steric clashes (exlusion) between side groups in CIS position attached to the α-carbon
  • Rotation about the α-carbon, degrees of freedom allows protein folding - angle restriction (phy and psi)
  • The shape will depend on the type of side chain interaction, R group, and environmental factors, energy efficiency - limits the number of structures possible.
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Secondary structure

Twisting and folding of amino acid chain into:

  • helices with H-bonds (includes α-helix)
  • extended regions that H-bond together (b structures)
  • loops and turns that link the helices and extended regions together
  • random coil
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Classification by Shape

  • GLOBULAR PROTEINS - roughly spherical, usually water-soluble. e.g. myoglobin, lysozyme, insulin, enzymes, antibodies.
  • FIBROUS PROTEINS - elongated, fibre-like shape, usually water-insoluble. e.g. collagen, keratins, actin.
  • INTEGRAL MEMBRANE PROTEINS - have water-soluble ends and loops, interspersed with water-insoluble membrane - spanning sequences. e.g. rhodopsin, glycophorin, ATP synthase.
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Classification by Composition

  • SIMPLE PROTEINS - made up only of amino acids. e.g. albumin, collagen, keratins, histones.
  • CONJUGATED PROTEINS - made up of amino acids plus other compounds called prosthetic groups. e.g. lipoproteins, glycoproteins, haemoproteins, flavoproteins.
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Levels of protein structure

  • PRIMARY - sequence of amino acids
  • SECONDARY - twisting and folding of chain, (alpha-helix & beta-pleated sheet structures)
  • TERTIARY - arrangement of the secondary structures with respect to each other in space. Can consist of motifs and domains.
  • QUARTERNARY - packing arrangement of polypeptide subunits in oligomeric proteins.
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