The Molecules of Cells Chapter Three

Classes of Compounds Inorganic compounds Organic compounds Water, salts, and many acids and bases Do not contain carbon Organic compounds Carbohydrates, fats, proteins, nucleic acids Contain carbon, usually large, covalently bonded Life’s molecular diversity is based on the properties of carbon

Characteristic chemical groups help determine the properties of organic compounds Functional Groups: affect a molecules function by participating in chemical reactions in a characteristic way

Cells make a huge number of large molecules from a small set of small molecules Monomers: Building blocks of polymers Polymers: Large molecules formed from smaller monomers There are four classes of Biological macromolecules, three are polymers: Carbohydrates Lipids (not polymers) Proteins Nucleic Acids

Polymers Around Us

Making and Breaking Polymers Dehydration (synthesis) reactions: Form polymers by removing a molecule of water Hydrolysis: Polymers are broken down using water The reverse of dehydration reactions

Carbohydrates Functions Major source of cellular fuel (glucose) Sugars and starches Contain C, H, and O [(CH20)n] Three classes Monosaccharides-Simple sugars containing three to seven C atoms Disaccharides-Double sugars/too large to pass through cell membranes Polysaccharides-Polymers of simple sugars, e.g., starch and glycogen Functions Major source of cellular fuel (glucose) Structural molecules (ribose sugar in RNA)

(a) Monosaccharides Monomers of carbohydrates Example Hexose sugars Example Pentose sugars Glucose Fructose Galactose Deoxyribose Ribose

(b) Disaccharides Consist of two linked monosaccharides Example Sucrose, maltose, and lactose Glucose Fructose Glucose Glucose Galactose Glucose Sucrose Maltose Lactose

Lipids Contain C, H, O (less than in carbohydrates), and sometimes P Insoluble in water Several Classes of Lipids: Triglycerides Phospholipids Steroids

Triglycerides Triglycerides—solid fats and liquid oils Composed of three fatty acids bonded to a glycerol molecule Main functions Energy storage Insulation Protection

Phospholipids Modified triglycerides: Glycerol + two fatty acids and a phosphorus (P)-containing group “Head” and “tail” regions have different properties Main component of cellular membranes

Steroids Lipids composed of fused ring structures Cholesterol, vitamin D, steroid hormones, and bile salts

Proteins Contain C, H, O, N, and sometimes S Polymers of amino acids All 20 amino acids have same basic structure Amino acids are held together by peptide bonds (polypeptides)

Proteins are made from amino acids linked by peptide bonds

Natural Folding Denaturing

Nucleic Acids DNA and RNA Contain C, O, H, N, and P Building block = nucleotide, composed of N-containing base, a pentose sugar, and a phosphate group

Sugar-phosphate backbone Nucleotide Base pair Base pair Figure 3.16C DNA double helix. Sugar-phosphate backbone

Deoxyribonucleic Acid (DNA) Four bases: adenine (A), guanine (G), cytosine (C), and thymine (T) Double-stranded, helical Replicates before cell division, ensuring genetic continuity Provides instructions for protein synthesis

Ribonucleic Acid (RNA) Four bases: adenine (A), guanine (G), cytosine (C), and uracil (U) Uracil replaces thymine in RNA Single-stranded Mainly active outside of nucleus