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3.3.13 Amino Acids, Polymers, DNA (Amino acids (zwitterions: ions that…
3.3.13 Amino Acids, Polymers, DNA
Amino acids
zwitterions: ions that have a permanent positive charge and a permanent negative charge but remain neutral overall
positive ion forms in strongly acidic conditions when the amino group gains a hydrogen ion and becomes protonated
negative ion forms in strongly alkaline conditons when the carboxylic acid group loses a hydrogen ion and becomes deprotonated
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Amino acids can be located on a chromatogram using developing agents such as ninhydrin or ultraviolet light and identified by their Rf values.
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Proteins
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secondary structure
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bonds present:
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hydrogen bonds: between -NH of one amino acid, and -CO of another
tertiary structure
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bonds present:
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hydrophobic and hydrophilic interactions: hydrophobic R groups in the centre of the peptide chains to avoid water, and hydrophilic R groups found at the edge of the structure, close to water; case twisting of amino acid chain; stable structure
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hydrolysis reaction
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dipeptide molecule is broken down into two amino acids, and a water molecule is lost
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Enzymes
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has a very specific active site that only a complementary substrate molecule can bind to; form intermolecular forces with the active site temporarily which promotes movement of electrons that lower activation energy for the reaction
enzyme inhibition: inhibitor has a structure similar to the substrate molecule and therefore complementary to the active site of an enzyme, so binds to the active site instead of the substrate and stops the reaction
active site can only bind to one or the other from a pair of enantiomers (stereoisomers); the active site is stereospecific
computer modelling can predict the shape of a protein before synthesis, so can predict their properties and how it will act; can design drugs
DNA
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A single strand of DNA (deoxyribonucleic acid) is a polymer of nucleotides linked by covalent bonds between the phosphate group of one nucleotide and the 2-deoxyribose of another nucleotide.
This results in a sugar-phosphatesugar-phosphate polymer chain with bases attached to the sugars in the chain.
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cell division
hydrogen bonds of the double helix breaks and the strands unravel, but nucleotides are still covalently bonded to each other so bases are in correct order
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