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Micro Topic 5 - TOPIC 5 BACTERIAL GENETICS I...

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TOPIC 5: BACTERIAL GENETICS I. PROTEINS (chapter 2) 1. INTRODUCTION a) Proteins are organic molecules containing carbon, hydrogen, oxygen, nitrogen, sometimes sulfur. b) They make up 50% of cell dry weight. c) They are essential for cell structure and function – enzymes, carrier proteins, bacteriocins, toxins etc. A. AMINO ACIDS (Figure 2.12 –2.14 pg 43-45) a) These are the building blocks of proteins. b) They contain one carboxyl group (-COOH) and one amino group (-NH 2 ) attached to an alpha carbon (C α ). c) Also contain a side group (R group): many different possible side groups, the distinguishing feature of the amino acid, which affect the structure and thus the function of the protein. d) Amino acids exist in either of two configurations (stereoisomers), called D or L isoforms. B. PEPTIDE BONDS a) Amino acids bond between the –COOH group of one amino acid and the -NH 2 of another. b) When a peptide bond is formed, 1 H 2 O molecule is released (dehydration synthesis). c) Two joined amino acids form a dipeptide; three joined amino acids form a tripeptide; many joined amino acids form a polypeptide. C. LEVELS OF PROTEIN STRUCTURE (Figure 2.15 pg 46) a) Proteins vary in structure, depending on function. b) Proteins fold into 4 levels of organization: a. Primary – chain of linked amino acids b. Secondary – repeated twisting or folding of the polypeptide chain. c. Tertiary – three-dimensional structure of a polypeptide chain. d. Quaternary – the relationship between several polypeptide chains that make up a protein. c) In non-optimal temperatures, pH or osmolarity, proteins become denatured (becomes unfolded and loses its shape). 1
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2. ENZYMES (Chapter 5) (Figure 5.2 pg 113) a) For a reaction to occur, molecules must collide. The collision creates the energy (activation energy) needed to make the reaction happen. b) Enzymes are proteins that catalyze (speed up) chemical reactions by lowering the activation energy. a. In other words, enzymes are catalysts (a catalyst is a substance that speeds up a chemical reaction without being affected itself). c) The substance on which an enzyme acts is the substrate. d) Enzymes have characteristic three-dimensional shapes, which includes an active site, where the enzyme and the substrate interact. e) The shape of an enzyme and its active site confers specificity. f) Enzymes are efficient, can operate at relatively low temperatures, and are under various cellular controls. A. NAMING ENZYMES a) Enzyme names usually end in -ase. b) All enzymes are grouped into 6 classes, defined on the basis of the types of reactions they catalyze, e.g dehydrogenases and oxidases. B. ENZYME COMPONENTS (Figure 5.3 pg 115) a) Most enzymes are holoenzymes, consisting of a protein portion (apoenzyme) and a nonprotein portion (cofactor). The apoenzyme cannot function without the cofactor.
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