Lecture 4 molecules of life

You are What You Eat: Macromolecules of Life & Their Relationship to

Diet and NutritionText Reading: Chapter 2 (p35-40), Chapter 3 (p53-62, 70-75)

Learning Objectives

• Name the four major classes of biological macromolecules. Describe the composition and function of each. Provide examples of each.

• Distinguish between steroids and anabolic steroids, and explain how the use of anabolic steroids can be dangerous to a person’s health.

• Apply this information to interpreting a food label and categorize the food as either healthful or junk food.

Organic Molecules

• A cell is mostly water.

• Rest of the cell consists mostly of carbon-based molecules.

• Organic chemistry is the study of carbon compounds.

Carbon

• Carbon (atomic number = 6) is a versatile atom.• Four electrons in valence shell.• Can share its electrons with other atoms to form

up to four covalent bonds.

• Carbon can use its bonds to• Attach to other carbons.• Form an endless diversity of carbon skeletons.

Diversity of Carbon Skeletons

• Simplest organic compounds are hydrocarbons.• Organic molecules containing only carbon and

hydrogen atoms.• Simplest hydrocarbon = methane.

Hydrocarbons

Hydrocarbons (cont’d)• Larger hydrocarbons are the main molecules in the

gasoline.

• The hydrocarbons of fat molecules provide energy for our bodies.

• Composition of a molecule determines its– shape– function

• Molecules recognize one another based on their shapes.

• Properties of an organic molecule depend on – its carbon skeleton– the atoms attached to the skeleton

The Composition and Shape of a Molecule is Important for its Function

Giant Molecules from Smaller Building Blocks

– On a molecular scale, many of life’s molecules are gigantic.

• Biologists call them macromolecules.• Examples: DNA, carbohydrates, proteins, lipids

– Most macromolecules are polymers.• Polymers made by stringing together many

smaller molecules (monomers/subunits).• Similar to train cars being linked together to

form a train.

Biological Macromolecules

– There are four categories of macromolecules in cells:• Carbohydrates• Lipids• Proteins• Nucleic acids

Carbohydrates– Major source of energy

for cells

– Carbohydrates include• Simple sugar molecules

(fructose, glucose, sucrose) – enter system quickly

• Complex carbohydrates contain branched chains of simple sugars (starch, glycogen) – digested slowly

Carbohydrates (cont’d)

Figure 2.12

– 3 classes of carbohydrates:• Monosaccharides• Disaccharides• Polysaccharides

Monosaccharides

– Monosaccharides are simple sugars.

– Examples: glucose, fructose• Glucose found in sports drinks• Fructose found in fruit, corn syrup• Honey contains both glucose and fructose

– Monosaccharides are the main fuel that cells use for cellular work.

Disaccharides

– A disaccharide is a double sugar.• Constructed from two monosaccharides.

– Examples: maltose, lactose, sucrose

• Maltose is used to make beer, malted milk shakes, & malted milk ball candies.

– Lactose is another type of disaccharide.• Found in milk products.• lactose intolerance: inability to digest lactose• These people don’t make enough lactase, the

enzyme the breaks down lactose.

Disaccharides (cont’d)

– Most common disaccharide is sucrose (table sugar)• Consists of a glucose linked to a fructose.• Extracted from sugar cane and roots of sugar

beets.

Disaccharides (cont’d)

– USA is one of the world’s leading markets for sweeteners.

• Average American consumes ~64 kg (>140 lbs!!!) of sugar/year

Polysaccharides– Complex carbohydrates are called polysaccharides.

• Long chains of sugar units.• Polymers of monosaccharides.

– Examples: starch, glycogen, cellulose– Fiber is an indigestible complex carbohydrate

Proteins– Proteins perform most of the tasks the body needs to

function.Structure

Storage

Contractile Proteins

Transport

Defense (Antibodies)

Enzymes

Hormones

Signaling Proteins

The Monomers: Amino Acids– Proteins are polymers of amino acids.

– All proteins are constructed from a common set of 20 kinds of amino acids.

– Each amino acid consists of• A central carbon atom bonded to four

covalent partners.• Side group is variable among all 20.• The side group gives each amino acid

its properties.

Proteins as Polymers– Cells link amino acids together to form proteins.

• The resulting bond between them is called a peptide bond.

• String of amino acids sometimes called polypeptide.

Figure 2.13

Protein Diversity– Your body has tens of thousands of different kinds of

proteins.– Different combinations of amino acids give proteins

different properties.– Most proteins are at least 100 amino acids in length.– Many different sequences possible with 20 amino

acids.– Analogy: 26 letters can make many different words

– Primary structure• Sequence of amino acids in a

protein

Protein Structure

– A slight change in the primary structure of a protein affects its ability to function.

• The substitution of one amino acid in hemoglobin causes sickle-cell disease.

Protein Shape– Proteins have four levels of structure.

Sequence of amino acids

Local folding patterns

Examples: alpha helix, beta pleated sheet

Overall three-dimensional shape

Overall shape when two or more polypeptides bind each other

What Determines Protein Structure?– A protein’s amino acid sequence dictates its structure.

– A protein’s shape is also sensitive to the surrounding environment.• Unfavorable temperature and pH changes can cause a

protein to unravel and lose its shape.• This is called denaturation.

Proteins as Nutrients– Our bodies can make several amino acids.– Essential amino acids: amino acids our bodies cannot make,

must obtain from food.– Complete proteins: contain all essential amino acids.– Animal proteins (meat) more likely to be complete than plant

proteins. Plant proteins can be combined to make complete.

Figure 3.2

Lysine Valine

(a) Lentils are high in lysine and low in valine. (b) Rice is low in lysine and high in valine.

Lysine Valine

The side groups oflysine and valineare different.

Lipids– Lipids are hydrophobic (water-fearing).

• They do not mix with water.– Oil and vinegar salad dressing separates into layers.

– Examples: fats, oils, steroids, wax, cholesterol, phospholipids

Figure 2.14

Fats– Dietary fat consists largely of the molecule

triglyceride. • Triglyceride is a combination of glycerol and three fatty

acids.

– Fats perform essential functions in the human body:• Energy storage• Cushioning • Insulation

Fats (cont’d)

– Unsaturated fatty acids• Have less than the maximum number of hydrogens bonded to the

carbons (ie they have double bonds). Greatest called polyunsaturated.

– Saturated fatty acids• Have the maximum number of hydrogens bonded to the carbons.

– If all three fatty acids in a fat are saturated, it is a saturated fat.If any are unsaturated, it is an unsaturated fat.

Saturated vs Unsaturated FatsSaturated fat Unsaturated fat

Figure 3.4

– Most animal fats have a high proportion of saturated fatty acids, which can be unhealthy.

• Examples: butter, lard• Usually solid at room temperature• Contribute to atherosclerosis and cardiovascular disease

– Most plant and fish oils tend to be low in saturated fatty acids.

• Example: corn oil, canola oil, cod liver oil• Usually liquid at room temperature

Saturated vs Unsaturated Fats (cont’d)

Hydrogenation and Trans Fats• Hydrogenation:

Conversion of unsaturated fats to saturated fats by adding hydrogen.– Production of margarine

and peanut butter

• Fats created by hydrogenation are unhealthy because trans fats are produced.– Trans fats: type of unsaturated fat (shortening, margarine)– Found in many fast food products, although now banned– No nutritional value– Increase risk of cardiovascular disease– Even more unhealthy than saturated fats.

Steroids– Another type of lipid.

– Different from fats in structure and function.• Carbon skeleton is bent to form four fused rings.

– Cholesterol is the “base steroid” from which your body produces other steroids.

• Example: sex hormones (testosterone, estrogen)

– Synthetic anabolic steroids are controversial.• They are variants of testosterone.

Anabolic Steroids

– Some athletes use anabolic steroids to build up their muscles quickly.

• However, these substances can pose serious health risks.• Mood swings• Depression• Liver damage• High cholesterol• Shrunken testicles, reduced sex drive, infertility

Nucleic Acids– Information storage molecules.

• Provide the directions for building proteins.

– Two types of nucleic acids:• DNA, deoxyribonucleic acid• RNA, ribonucleic acid

– The genetic instructions in DNA• Must be translated from “nucleic acid language” to

“protein language.”

Flow of Genetic Information in Cells

Nucleotides: Building Blocks of Nucleic Acids

– Nucleic acids are polymers of nucleotides: sugar + a phosphate + a nitrogenous base

– DNA nucleotides have one of 4 bases:

• Adenine (A)• Guanine (G)• Thymine (T)• Cytosine (C)

Sugar in DNA = deoxyriboseSugar in RNA = ribose

– RNA contains uracil (U) instead of thymine

– Nucleotide monomers are linked into long strands.

DNA as Polymers

– Two strands join together to form DNA double helix.

– Looks like twisted ladder

Figure 2.15a

– Bonding between bases on opposite strands follow strict rules:

DNA Base-Pairing Rules

A with T

G with C

Figure 2.15a,b

– RNA, ribonucleic acid, is different from DNA.• Its sugar has an extra OH group.• It has the base uracil (U) instead of thymine (T).• It is usually single-stranded.

RNA

Review: Complete the Table

Biological Molecule (Polymer)

Subunits (Building Blocks)

Functions Examples

Carbohydrates

Proteins

Nucleic acids

Lipids (Fats)

You Are What You Eat

ProteinSteak Structural proteins, enzymesand energy

Amino acids

(a) Structural Proteins

(b) Carbohydrate breakdown

ATP

FatButter Glycerol and fatty acids

CarbohydratesApple

Structural components

Energy production

Build membranes

Stored energy

(c) Fat breakdown

Fat droplet

ATP

ATPFigure 3.14

Reading Food Labels

Unsaturated fats?

Complex carbs?

1 g fat = 9 calories1 g carb = 4 calories1 g protein = 4 calories Check out the website links

posted on MyGateway!

READ

Read end of Chapter 3 (p70-75):– Body fat– BMI– Obesity– Health effects: diabetes, hypertension, heart

attack, stroke, high cholesterol– Eating disorders