Polymer Principles

• Most macromolecules are polymers.– Polymer = large molecule consisting of many identical

or similar subunits connected together.– Monomer = subunit or building block molecule of a

polymer.– Macromolecule = large organic polymer

• Formation of macromolecules from smaller building block molecules represents another level in the hierarchy of biological organization.

• Four classes– Carbohydrates, Lipids, Proteins, Nucleic Acids

Structure of Polymers

Classes Polymers Subunits (monomers)

Protein Polypeptide Amino acid

Carbohydrate Polysaccharide Monosaccharide

Lipid Triglyceride Fatty acid, glycerol

Nucleic acid DNA, RNA Nucleotide

An immense variety of polymers can be built from a small set of monomers.

• Structural variation of macromolecules is the basis for the enormous diversity of life.– There is unity in life as there are only about 40

to 50 common monomers used to construct macromolecules.

– There is diversity in life as new properties emerge when these universal monomers are arranged in different ways.

Proteins

• Monomer = amino acid– 20 different amino acids commonly occur in

living organisms.

– Structure: 3 parts• Amino group

• Alpha carbon

• Carboxyl group

• Proteins are polymers of covalently bonded amino acids. Peptide bond

Proteins

• Wide variety of functions:– Structure

• They compose the makeup of hair, bones, and muscles.

• Example: Keratin found in hair; Collagen is found in ligaments and tendons.

– Regulation• Some hormones are proteins. Hormones act as chemical

messengers transported in the blood. They control body processes. Insulin controls the concentration of glucose in the blood.

Proteins

• Functions (continued)– Transport

• Hemoglobin transports oxygen in the blood.

– Contraction• Actin and myosin are contractile proteins in

muscles. These proteins slide together, shortening the muscle and producing muscle contraction for body movement.

Proteins

• Function (continues)– Catalysts

• All enzymes, which are organic catalysts, are mainly proteins. The digestion of starch requires an enzyme. Every step of human metabolism requires an enzyme in order to function rapidly enough to support life. Metabolism is the sum of all chemical reaction that occur in the organism.

Mechanism of Enzyme Action

• The action of an enzyme is specific.

• The substrate binds to an enzyme at the active site.

• The shape of the active site of the enzyme and substrate are complementary.

Mechanism of Enzyme Action

• Models of Action– Lock and key model (older)

• The combination of substrate and enzyme is similar to how a key (substrate) fits into a lock (enzyme). Enzyme specificity is related to the complementary shapes of the enzyme and substrate molecules. Each substrate, or key, fits into a specific enzyme, or lock.

Mechanism of Enzyme Action

• Models of Action– Induced-fit model (newer)

• It recognizes that these molecules are not rigid, they are flexible. As they combine, each mloecule induces the proper fit of the other one. An enzyme, for example, can conform to the shape of the substrate. As it does this it places a strain on the chemical bonds in the substrate. This can chemically change the substrate.

Mechanism of Enzyme Action

• Substrate Interactions– When the enzyme and substrate combine, they form an

intermediate combination, the enzyme-substrate complex.

– They ate attracted by several kinds of bonds, including ionic attractions and hydrogen bonding. This combination forces the substrate into a less stable shape. This breaks some chemical bonds in the substrate and forms new ones. In the process, the substrate molecule is changed into a product.

Mechanism of Enzyme Action

• Substrate Interactions (continue)– An enzyme is specific in its action.

– Example: Amylase changes the substrate starch into maltose. This chemical change occurs when starch is digested.

– After the product is formed and released, the enzyme amylase can combine with another substrate molecule and change it into a product.

– Starch is a carbohydrate. The digestion of a lipid or protein requires different specific enzymes.

Mechanism of Enzyme Action

• Factors Affecting Enzyme Activity– Temperature

• Enzymatic reactions have an optimum temperature

• At high temperatures, the protein part of the enzyme denatures. Therefore, the enzyme is disrupted and loses its activity.

– Most enzymes lose their catalytic ability at 50 to 60 degree Celsius.

– Internal human body temperature is about 37 degrees Celsius. The enzymes of human metabolism usually function at an optimum around this temperature.

Mechanism of Enzyme Action

• Factors Affecting Enzyme Activity• pH

– Each enzyme has a unique pH that is optimum.

» Salivary amylase functions best at a pH of 7 in the oral cavity

» Pepsin has a optimal activity at a pH of 2 in the stomach

» Trypsin works best at a pH of 8 in the small intestine.

Carbohydrates: Fuel and Building Materials

• Sugars, the smallest carbohydrates, serve as fuel and carbon sources– Carbohydrates = organic molecules made of

sugars and their polymers• Monomers are simple sugars called

monosaccharides.

• Polymers are formed by condensation rxns.

Monosaccharides

• Simple sugar in which C, H, and O, occur in the ratio of (CH2O).– Are major nutrients for cells.

• Glucose is the most common.

– Can be produced by photosynthesic organisms from CO2, H2O, and sunlight.

– Store energy in their chemical bonds which is harvested by cellular respiration.

– Their carbon skeletons are raw materials for other organic molecules.

– Can be incorporated as monomers into disaccharides and polysaccharides.

Disaccharides

• A double sugar that consists of two monosaccharides joined by a glycosidic linkage.– Glycosidic linkage = covalent bond formed by

a condensation rxn between two sugar monomers.

• Example: maltose, lactose, sucrose

Polysaccharides

• The polymers of sugars, have storage and structural.

• Polymers of a few hundred or thousand monosaccharides.

• Are formed by linking monomers in enzyme-mediated condensation rxns.

• Two important biological functions:– Energy storage (starch and glycogen)– Structural support (cellulose and chitin)

Storage polysaccharide

• Starch = glucose polymer that is a storage polysaccharide in plants.– Major sources in the human diet are potatoes and grains

(e.g. wheat, corn, and friuts)

• Glycogen = glucose polymer that is a storage polysaccharide in animals.– Stored in the muscle and liver of humans and

other vertebrates.

Structural polysaccharides• Cellulose

– Major structural component of plant cell walls.

Lipids

• Insoluble in water• Include fats, oils, and waxes• Many have three fatty acids attached to a

glycerol molecule. (Triglyceride)• Fatty acids

– Saturated– Unsaturated

• Monounsaturated and polyunsaturated

Lipids

• Functions:– Triglycerides store energy efficiently

• One gram stores about 9 kilocalories.– This is about twice the amount compared to a gram of

carbohydrate or protein.

– Triglycerides also provide insulation and cushioning for the body.

– Waxes serve as water repellents on plant leaves, animal fur, and bird feathers

Lipids

• Phospholipids– Similar to triglycerides except that one of the fatty acid

chains is replaced by a phosphate group.

– Phosphates are polar.

– Function: Structural foundation of cell membranes.

• Steroids– Backbone of four linked carbon rings

– Includes cholesterol and hormones, including testosterone and estrogen.

Nucleic Acids

• Informational polymers• Nucleic acids store and transmit heredity

information• Two types of nucleic acids

– DNA- deoxyribonucleic acid– RNA- ribonucleic acid

• Flow of information– DNA RNA protein

Nucleic Acids

• A nucleic acid strand is a polymer of nucleotides– Monomer = nucleotide

• Three parts– Nitrogenous base

» Pyrimidines cytosine, thymine, and uracil

» Purines adenine and guanine

– Pentose sugar

– Phosphate group