The Molecules of LifeChapter 3

Dietary Sugars

• The average American consumes• about 45 kg of sugar (about 100 lb) per year,• mainly as sucrose and high-fructose corn syrup.

• Lactose is milk sugar• Lactose intolerance is common• Inability to break down lactose in small intestine• Transit to the large intestine where bacteria use it to produce gas

• Solutions• Avoid dairy products• Consume lactase pills along with food

Cell composition

• Mostly water• Organic (Carbon-based) molecules• Small molecules• Fuels• Raw materials

• Large molecules• Cell structure• Machinery of life

• Categories:• Proteins, lipids, nucleic acids, carbohydrates

Carbon Chemistry - 1

• Four electrons in outer shell four groups attach to each carbon atom• Endless diversity of carbon skeletons• Carbon-carbon• Carbon – hydrogen• Carbon – other functional groups• Straight or branched chains

Carbon Chemistry - 2

• Hydrocarbons• Contain only carbon and hydrogen atoms• Methane, ethane, propane, butane, pentane, hexane, heptane…• Straight or branched chains• Single or double or triple bonds• Fuels• Structural elements

Functional Groups

• Other combinations of atoms that attach to a hydrocarbon chain• Hydroxyl• Carboxyl• Amino• Phosphate• Many others

• Diverse compounds• Sugars• Amino acids• Nucleotides• Lipids

Macromolecules

• Giant• Three types:• Carbohydrates• Proteins• Nucleic Acids• (Lipids)

• Polymers• Long chains of smaller subunits

Carbohydrates

• Monomers: simple sugars; monosaccharides• simple sugars that cannot be broken down by hydrolysis into smaller sugars• Glucose• Fructose

• Disaccharides• Two sugars joined together through saccharide bonds• Dehydration reaction• Sucrose – table sugar – glucose + fructose• Lactose – milk – glucose + galactose

• Polysaccharides• Long chains• Starch: poly glucose; plant storage• Glycogen: poly glucose; animal storage• Cellulose: poly glucose; plant cell walls

Fats & Lipids - Structure

• hydrophobic, unable to mix with water.• Fats: A typical fat, or triglyceride, consists of

• a glycerol molecule,• joined with three fatty acid molecules,

• If the carbon skeleton of a fatty acid has fewer than the maximum number of hydrogens, it is unsaturated or the maximum number of hydrogens, it is saturated.

• A saturated fat has no double bonds and all three of its fatty acids saturated.• Most animal fats have a high proportion of saturated fatty acids, can easily stack, tending to be solid at room

temperature, and contribute to atherosclerosis, in which lipid-containing plaques build up along the inside walls of blood vessels.

• Most plant and fish oils tend to be high in unsaturated fatty acids and liquid at room temperature.

• Hydrogenation• adds hydrogen,• converts unsaturated fats to saturated fats,• makes liquid fats solid at room temperature, and• creates trans fat, a type of unsaturated fat that is particularly bad for your health.

Steroids

• very different from fats in structure and function• The carbon skeleton is bent to form four fused rings.• Steroids vary in the functional groups attached to this set of rings, and these chemical variations affect

their function.

• Cholesterol is• a key component of cell membranes and• the “base steroid” from which your body produces other steroids, such as estrogen and testosterone.

• Synthetic anabolic steroids• are variants of testosterone,• mimic some of its effects,• can cause serious physical and mental problems,• may be prescribed to treat diseases such as cancer and AIDS, and• are abused by athletes to enhance performance.• Most athletic organizations now ban the use of anabolic steroids because of their health hazards and

unfairness, by providing an artificial advantage.

Fats and Lipids: Uses

Fats perform essential functions in the human body including• energy storage,• cushioning, and• Insulation

• Lipids: • Essential parts of cell membranes • Hydrophobic: separates living things into compartments• Provide structural support for animal cells

• Steroids:• Critical hormones that regulate life processes• Reproductive hormones: testosterone, estrogen• Metabolic hormones

Proteins - composition

• Long strands of amino acids• 50% of the dry weight of a cell• Perform most cellular functions

• Amino acid: • Central carbon with 1 amino group (-NH2), one carboxyl group (-COOH) and

one other “R” group, along with its lone hydrogen• 20 common in living things: be able to name three

• Joined together through peptide bonds• Another dehydration reaction – yields water

Proteins - Structure

• Primary structure is the sequence of amino acids; many possibilities• a chain of 10 amino acids could be 2010 different sequences

• Secondary structure: regular folding or twisting of the chain• Held in position by hydrogen bonds

• Tertiary structure: folding this chain back on itself• More hydrogen bonds

• Some proteins contain more than one chain: quaternary structure

Proteins - uses

• Enzymes: mediate the chemical reactions in a cell• Structural proteins: support the cell’s shape and size• Chaperones protect and mediate transport of other molecules

Protein Shape (conformation)

• Depends on the sequence of amino acids• Sickle Cell Anemia

• Affected by temperature and pH• Fever – some protein denaturation• Alzheimers disease;

• Prions are small proteins that infect mammals and alter the folding of their own proteins• mad cow disease

Nucleic Acids - Composition

• Polymers of nucleotides• Nucleotide• Sugar + base + phosphate• Phosphate = PO4

-3

• Base = Nitrogenous molecule hangs attached to the sugar-phosphate backbone• adenine (A), cytosine (C), guanine (G), and either thymine (T) (DNA) or uracil

(U) (RNA)

Main Categories of Nucleic Acid

• DNA: • sugar = deoxyribose• Bases = A,C, G and T• Usually double stranded• Found in the nucleus• Very stable; carries genes

• RNA: • sugar = ribose• Bases = A, C, G and U• Usually single stranded• Found everywhere in the cell• Copied from the DNA

Nucleic Acids – Structure

• Polynucleotide• Alternating Sugar-phosphate chain• Base hangs off the chain at the sugar molecule• Chain twists to form a helix or spiral

• Structure• Primary structure: the sequence of nucleotides• Secondary structure: the spiral chain• Tertiary structure: the folding back on itself when combined with chaperone

proteins: found in chromosomes

Nucleic Acids Uses

• DNA: encodes the genome, the instructions for living things• Parts list: the sequences of all the proteins in a cell• Instruction manual for assembling and using those proteins

• RNA: • Copied from the DNA for use• Makes up the protein synthesis machinery• Some viruses use RNA as their genetic material

• Chromosomes• Long fibers in the cell nucleus• DNA + proteins + small RNAs• Gene: a specific stretch of DNA that programs the amino acid sequence of a

polypeptide