BIO146

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Chapter 5
Chapter 5

The Structure and Function of Large Biological Molecules

5.1 - Macromolecules are polymers

macromolecules - large carbohydrates, proteins, and nucleic acids

polymer - long molecule consisting of many similar or identical building blocks linked by covalent bonds, much as a train consists of a chain of boxcars

> carbohydrates

> Proteins

> Nucleic acids (nucleotides)

monomers - the repeating units that serve as the building blocks of a polymer

The Synthesis and Breakdown of Polymers

enzymes - specialized macromolecules (usually proteins) that speed up chemical reactions

condensation reaction - a reaction in which two molecules are covalently bonded to each other with the loss of a small molecule; the reaction that connects a monomer to another monomer or a polymer

dehydration reaction (condensation) - a water molecule is lost

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→ polymers are disassembled to monomers by hydrolysis

hydrolysis (breakage) - a process that is essentially the reverse of dehydration (hydrolysis means water breakage)

→ the bond between monomers is broken by the addition of a water molecule, with a hydrogen from water attaching to one monomer and the hydroxyl group attaching to the other

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four main classes of large - carbohydrates, proteins, nucleic acids, lipid

5.2 - Carbohydrates serve as fuel and building material

Carbohydrates include sugars and the polymers of sugars

Sugars

Monosaccharides - Generally have molecular formulas that are some multiple of the unit CH2O

→ Glucose (C6H12O6) is the most common monosaccharide

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disaccharide - is formed when a dehydration reaction joins two monosaccharides

→ glycosidic linkage - a covalent bond formed between two monosaccharides

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Polysaccharides

Polysaccharides - macromolecules, polymers with a few hundred to a few thousand monosaccharides joined by glycosidic linkage

some polysaccharides serve as storage material, hydrolyzed as needed to provide monosaccharides for cells

→ starch (plants) - a polymer of glucose that enables the plant to stockpile surplus glucose

→ glycogen (animals) - a polymer of glucose that is like amylopectin but more extensively branched

- vertebrates store glycogen mainly in liver and muscle cells, by breakdown glycogen in these cells, releases glucose when the demand for energy increases

Other polysaccharides serve as a building material for structures that protect the cell or the whole organism

→ cellulose - a major component of the tough walls that enclose plant cells

→ chitin - the carbohydrate used by arthropods (insects, spiders, crustaceans, and related animals) to build their exoskeletons (the hard case that surround the soft parts of an animal)

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5.3 - Lipids are a diverse group of hydrophobic molecules

lipids - one class of large biological molecules that do not include true polymers, generally not big enough to be considered macromolecules

hydrophobic

mix poorly, with water

Fats

fat - consists of a glycerol molecule joined to three fatty acids

fatty acid - long carbon skeleton, usually 16 or 18 carbon atoms in length

→ to make a fat, each fatty acid molecule is joined to glycerol by a dehydration reaction

Phospholipids - two fatty acids and a phosphate group are attached to glycerol

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Steroids

steroids - lipids characterized b a carbon skeleton consisting of four fused rings

cholesterol - a type of steroids; a crucial molecule in animals

a common component of animal cell membranes

also the precursor from which other steroids - vertebrate sex hormones

5.4 - Proteins include a diversity of structures, resulting in wide range of functions

catalysts (enzymatic proteins) — chemical agents that selectively speed up chemical reactions without being consumed in the reaction

an enzyme can perform its function over and over again

→ each type of protein having a unique three-dimensional shape

proteins are all constructed from the same set of 20 amino acids, linked in unbranched polymers

polypeptide - a polymer of amino acids

peptide bond - the bond between amino acids

protein - a biologically functional molecule made up of one or more polypeptides, each folded and coiled into a specific three-dimensional structure

Amino Acids (Monomers)

amino acid - an organic molecule with both an amino group and a carboxyle group

the center of the amino acid is an asymmetric carbon atom called the alpha carbon

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Overview of Protein Functions

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Polypeptides (Amino Acid Polymers)

peptide bond - the bond that formed between two amino acids after joined by a dehydration reaction

polypeptide backbone - the repeating sequence of atoms in a polypeptide chain (the purple parts of the picture below)

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Protein Structure and Function

a functional protein - one or more polypeptides precisely twisted, folded, and coiled into a molecule of unique shape, which can be shown in several different types of models

→ protein’s shape or structure determines its function

a polypeptide always starts with a amine (N-terminus) and ends with carboxylic acid (C-terminus)

Four Levels of Protein Structure

Primary Structure (Linear chain of amino acids)

the primary structure of a protein is its sequence of amino acids

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Secondary Structure (regions stabilized by hydrogen bonds between atoms of the polypeptide backbone)

the result of hydrogen bonds between the repeating constituents of the polypeptide backbone (not the amino acid chains)

→ alpha helix - a delicate coil held together by hydrogen bonding between every fourth amino acid

→ beta pleated sheet - two or more segments of the

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Chapter 5Chapter 5