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Lecture 2 Notes - Lecture 2 Chapters 2 3 Chapter 2 Water...

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Lecture 2 - Chapters 2, 3 Chapter 2 - Water accounts for about 70% of a cell’s weight & most intracellular reactions occur in an aqueous environment – life on earth began in the ocean - In each water molecule the 2 H atoms are linked to the O atom by covalent bonds – the 2 bonds are highly polar bc the O is strongly attractive for electrons, whereas the H is only weakly attractive when a positively charged region of one molecule (H) approaches a negatively charged region (O) of a second water molecule, the electrical attraction between them can result in a weak bond called a hydrogen bond – these bonds are much weaker than covalent bonds and are easily broken by the random thermal motions due to the heat and energy of the molecules – it is only because of the hydrogen bonds that link water molecules together that water is a liquid at room temperature, with a high boiling point and high surface tension, rather than a gas molecules carrying plus or minus charges (ions) likewise interact favorably w water and are hydrophilic – hydrophobic molecules, by contrast, are uncharged and form few or no hydrogen bonds, and so do not dissolve in water – in hydrocarbons, the H atoms are covalently linked to C atoms by a largely nonpolar bond; because the H atoms have almost no net positive charge, they cannot form effective hydrogen bonds to other molecules - All organic molecules are synthesized from and are broken down into the same set of simple compounds – cells contain 4 major families of small organic molecules: the sugars, the fatty acids, the amino acids, and the nucleotides o - Glucose = C 6 H 12 O 6 the way that sugars are linked together to form polymers illustrates some common features of biochemical bond formation – a bond is formed between an –OH group on one sugar & an – OH group on another by a condensation reaction, in which a molecule of water is expelled as the bond is formed – the bonds created by all of these condensation reactions can be broken by the reverse process of hydrolysis, in which a molecule of water is consumed because each monosaccharide has several free hydroxyl groups that can form a link to another monosaccharide, sugar polymers can be branched, and the number of possible polysaccharide structures is extremely large – the monosaccharide glucose is a key energy source for cells – in a series of reactions, it is broken down to smaller molecules, releasing energy that the cell can harness to do useful work – cells use simple polysaccharides composed only of glucose units – principally glycogen in animals & starch in plants – as energy stores
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o - A fatty acid molecule has 2 chemically distinct regions – one is a long hydrocarbon chain, which is hydrophobic and not very reactive chemically – the other is a carboxyl (-COOH) group, which behaves as an acid – almost all fatty acid molecules in a cell are covalently linked to other molecules by their carboxylic acid group -
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