The Structure and Function of

MacromoleculesChapter 5

• Macromolecules - larger molecules made from smaller ones.

• 4 major classes of macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

• 3 of these are polymers because they are made from individual building blocks called monomers.

• Monomers - joined together through condensation or dehydration reaction (form macromolecules)

• Requires energy; uses covalent bonds (links together monomers)

• Water produced.

Water produced as by-product

• Hydrolysis breaks polymers into monomers.

• Water added to polymer; breaks bonds, creates monomers (i.e. digestive process in animals)

Carbohydrates

• 1Carbohydrates - sugars (monomers) and polymers.

• AMonosaccharides - simple sugars.• BDisaccharides - double sugars

(monosaccharides linked together)• CPolysaccharides - polymers of

monosaccharides.• Sugars named with –ose.

• Monosaccharides needed for cellular work.

• Help to synthesize other macromolecules.

• 2 monosaccharides joined by glycosidic linkage to form disaccharide via dehydration.

• Maltose - 2 glucose molecules.• Sucrose - 1 glucose, 1 fructose.

• Polysaccharides - energy storage.

• Starch - energy storage polysaccharide for plants.

• Starch stored in plants plastids.• Herbivores access starch for

energy.

• Animals store energy as glycogen.• Humans - in liver and muscles.• Cellulose – polysaccharide; plant

cell walls.• Many herbivores cannot digest

cellulose (develop relationships with microbes)

• Chitin - polysaccharide - makes up exoskeleton of arthropods (like crustaceans).

• Chitin - found in fungi; functions as structural support.

Chitin is used in surgery

Lipids• Lipids - no polymers (exception)• Lipids nonpolar (no affinity for

water)• Fat made from glycerol and fatty

acids.• Glycerol - 3 carbon molecule with

hydroxyl group and fatty acid; consists of carboxyl group attached to long carbon skeleton.

• The 3 fatty acids in a fat can be same or different.

• No carbon-carbon double bonds, molecule is saturated fatty acid (hydrogen at every possible position)

• Form bad fats - solid at room temperature (butter, lard)

No double-double bonds

• 1+ carbon-carbon double bonds - molecule is unsaturated fatty acid - formed by removal of hydrogen atoms from carbon skeleton.

• Form good fats - liquid at room temperature (oils)

• Purpose of fat - energy storage. • Gram of fat stores 2X as much

energy as gram of polysaccharide.

• Fat also cushions vital organs.• Layer of fat can also function as

insulation.

• Phospholipids - 2 fatty acids attached to glycerol, phosphate group at 3rd position.

• Fatty acid tails are hydrophobic, phosphate group and attachments form hydrophilic head.

• When phospholipids added to water, self-assemble with hydrophobic tails pointing toward center, hydrophilic heads on outside.

• Phospholipids in cell form bilayer; major component of cell membrane.

Hydrophilic

Hydrophobic

• Steroids - lipids with carbon skeleton consisting of 4 fused carbon rings.

• Cholesterol - component in animal cell membranes.

• Cholesterol – also forms hormones (i.e. testosterone, estrogen)

Cholesterol

Proteins

• Proteins - support, storage, transport, defenses, and enzymes.

• Made in ribosomes in cell.• Proteins - amino acids linked

together to form polymer.• 20 different amino acids that can

be linked together to form thousands of different proteins.

• Amino acids link - polypeptides - combine to form proteins.

• Amino acids made of hydrogen atom, carboxyl group, amino group, variable R group (or side chain).

• R group makes amino acids different from one another.

• Amino acids joined by peptide bonds when dehydration reaction.

• Shape of protein determines function.

• Shapes - 3 dimensional - determined by sequence of amino acids.

• Primary structure of protein - linear sequence of amino acids.

• Secondary structure - hydrogen bonds at regular intervals along polypeptide backbone.

• Two shapes are usually formed: alpha coils or beta sheets.

• Tertiary structure determined by the interactions among R groups.

• Interactions include hydrogen bonds, van der Waals forces, and ionic bonds.

• Disulfide bridges help stabilize form.

• Quarternary structure - joining of 2+ polypeptide subunits.

• Collagen and hemoglobin examples.

• Protein’s shape can change due to environment.

• pH, temperature, or salinity (salt concentrations) change - protein can denature (starts to fall apart)

• Some proteins can return to functional shape after denaturation, others cannot, especially in crowded environment of cell.

Nucleic acids

• Amino acid sequence of polypeptide programmed by a gene (regions of DNA, polymer of nucleic acids)

• 2 types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

• DNA gives information so RNA can create proteins.

• Flow of genetic information - DNA -> RNA -> protein.

• Protein synthesis occurs in ribosomes.

• Monomers of nucleic acids - nucleotides.

• Nucleotides made up of 3 parts: nitrogen base, five-carbon sugar, and phosphate group.

• Nitrogen bases, rings of carbon and nitrogen, come in 2 types: purines and pyrimidines.

• Pyrimidines - cytosine (C), thymine (T), and uracil (U in RNA only).

• Purines - adenine (A) and guanine (G).

• Pyrimidines - single six-membered ring; purines - five-membered ring.

• In RNA - sugar is ribose; DNA - sugar is deoxyribose.

• Difference between sugars is lack of oxygen atom on carbon two in deoxyribose.

• RNA single-stranded - linear shape.

• DNA forms double helix.• Sugar and phosphate forms

backbone of double helix while nitrogen bases form connection between backbones.

• Adenine (A) always pairs with thymine (T) guanine (G) with cytosine (C).

• Know sequence of one side of double helix - figure out other.

• Two strands are complementary.

http://www.emunix.emich.edu/~rwinning/genetics/pics/dna2.gif

• DNA used to show evolutionary similarities between species.

• Two species that appear to be closely-related based on fossil and molecular evidence also more similar in DNA and protein sequences than more distantly related species.