Protein structure


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Protein structure

  1. 1. Primary Structure – the sequence of amino acidsPROTEIN STRUCTURE
  2. 2. PRIMARY STRUCTURE Sequence of amino acids in protein linked by covalent amide (peptide) bonds
  3. 3. CONDENSATION AMINO ACIDS: AMIDES ORPEPTIDE BONDS O O O H2N C + H2N C + H2N C Amino acids condense HC OH CH OH CH2 OH to form amides – or CH3 alanine glycine glutamine CH2 H2C peptide bondsPeptide or amide bond C H2N O O + O Protein chain made up H3N C H O HC N C of amino acids H HC N C - covalently bonded by CH3 CH O CH3 CH2 amide bonds H2C C H2N O
  4. 4. SEQUENCE MATTERS  Functioning proteins have O O O unique primary structure – H2N C + H2N C + H2N C sequence of amino acids HC OH CH2 OH CH OH CH3 alanine glycine glutamine CH2 in the chain H2C  This primary sequencePeptide or amide bond C determines how the H2N O O protein folds into 3-D O H3N + C H O shape required for protein HC N C H HC N C - function CH3 CH O CH3  Sequence has a freeN-terminal amino acid CH2 C-terminal amino acid H2C amino end (N-terminalalanine (free amino end) glutamine (free carboxyl end) C amino acid) H2N O  Sequence has free carboxyl end (C-terminal amino acid
  5. 5. SEQUENCE MATTERS O O OH2N C + + H2N  When 3 amino acids H2N C C HC OH CH2 OH CH OH reacted together, 6 CH3 alanine glycine glutamine CH2 possible different H2C tripeptides result C H2N O Possible sequences  Sequence of amino acids in proteins determined by ala-gly-gln sequence of nucleotides ala-gln-gly on m-RNA, which is gly-ala-gln transcribed from DNA gly-gln-ala gln-ala-gly gln-gly-ala
  6. 6. Vasopressin (antidiuretichormone• 9 amino acid polypeptide forms cyclic structure• N terminal amino acid: glycine• No C terminal amino acid (due to ring structure)• Conserves body fluids , reduces loss of water in urine• Leads to constriction of blood vessels, increase in blood pressurePOLYPEPTIDE HORMONES
  7. 7. Oxytocin• 9 amino acid polypeptide with cyclic structure• N-terminal amino acid: glycine• No C-terminal amino acid• Well studied effects: • Stimulates milk production • Stimulates muscle contraction for birth • Promotes maternal behavior• Possible association with development of human bonding an interpersonal relationships• Compare structure to vasopressin: 2 amino acids different – very different physiological effects!POLYPEPTIDE HORMONES
  8. 8. Lysozyme• Enzyme breaks down bacterial cell walls• Found in egg whites, human tears• Single polypeptide chain of 129 amino acids• N-terminal amino acid is lysine• C-terminal amino acid is leucineDisulfide bonds consideredto be part of tertiarystructure.PROTEIN PRIMARY STRUCTURE