Chapter_3_Proteins_Carbs_Lipids

Chapter_3_Proteins_Carbs_Lipids - Macromolecules...

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Macromolecules (polysaccharides, proteins, and nucleic acids) are formed by covalent bonds between monomers (the building blocks) (monosaccharides, amino acids, and nucleotides). For example, a polypeptide (or protein) is a linear string of amino acids, linked together by peptide bonds. Macromolecules
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From monomer to polymer Macromolecules are formed by covalent linking between monomers (the building blocks): polysaccharides from monosaccharides, proteins from amino acids, and nucleic acids from nucleotides. All organisms are ~70% water and ~25% macromolecules, and even the amounts of each type of macromolecule are nearly the same! H 2 0
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Monomers are joined by condensation (a.k.a. dehydration) reactions. In condensation (dehydration) reactions, one molecule of water is released. +Energy +Energy
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Polymers are broken down into monomers in hydrolysis reactions.
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Peptide linkage Amino acids, the building blocks for proteins, have an amino (NH 3 + ) group at one end, a carboxyl (COO - ) group at the other, and a side chain R. R may be of any of 20 different kinds. At pH 7.4, the amino group has a + charge and the carboxyl group a – charge, giving a net charge of 0. The charge on an amino acid depends on the charge of the side chain R. +Energy Grows from N terminus to C. The peptide bond is inflexible—no rotation is possible.
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Proteins A typical amino acid has a molecular weight of ~100. Therefore, a protein with a molecular weight of 100,000 is composed of ~1,000 amino acids. Functions of proteins include support, protection, catalysis ( enzymes !), transport, defense (antibodies), hormones, receptors, regulation, and movement. They sometimes require an attached prosthetic group. Twenty different amino acid residues are found in proteins. As noted above, all amino acids have an amino end , a carboxyl end , a hydrogen, and a side chain bonded to the alpha carbon atom. These side chains of amino acids may be positively or negatively charged , polar , or hydrophobic .
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Types of amino acids Amino acids (Do NOT memorize their names) can be classified based on the characteristics of their R groups. Five have charged hydrophilic side chains. Five have polar but uncharged side chains. Seven have nonpolar hydrophobic side chains. Cysteine has a terminal disulfide (—S—S—). Glycine has a hydrogen atom as the R group. Proline has a modified amino group that forms a covalent bond with the R group, forming a ring.
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Negatively charged amino acids, hence polar
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Positively charged amino acids, hence polar
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Uncharged but polar amino acids These amino acids are hydrophilic and form hydrogen bonds , so they coat the exterior of proteins that reside in an aqueous environment and can bind water-soluble molecules.
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Hydrophobic amino acids These amino acids cluster together, avoiding water. They also line the exterior of proteins that reside inside the oil-like interior of membranes.
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Glycine has the smallest R, just a hydrogen. Proline is stiff; it is the most common
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Chapter_3_Proteins_Carbs_Lipids - Macromolecules...

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