Chapter 5The Structure and Function of Macromolecules

AP Biology

Fall 2012

Macromolecules

Small organic molecules combine to make much larger molecules called macromolecules.

There are four classes of macromolecules:

•Carbohydrate

•Proteins

•Nucleic acids

•Lipids

Monomers and polymers

Three of the 4 macromolecules are polymers meaning that they are made of smaller units called monomers that are joined together.

Those 3 macromolecules are carbohydrates, proteins and nucleic acids

•Carbohydrate’s monomers are sugars

•Protein’s monomers are amino acids

•Nucleic acid’s monomers are nucleotides

MonomersPolymers

Monomers become polymers through a process called polymeration.

Polymeration occurs through dehydrationsynthesis.

Water is lost as the 2 monomers join together.

Polymer  Monomer

Polymers can be broken up using water.

The reaction of breaking up a polymer using water is called hydrolysis.

OH-Monomer-Monomer-H

H2O

OH-Monomer-H OH-Monomer-H

Carbohydrates

Three categories of carbohydrates:

•Simple sugars (monosaccharide)

•Double sugars (disaccharides)

•Macromolecules (polysaccharides)

Monosaccharide

•Have the molecular formula CH2O.

•Ratio of C:H:O of 1:2:1

•Most common monosaccharide is glucose.

•All simple sugars have a carbonyl group and multiple hydroxyl groups. Most common monosaccharide is glucose and has the chemical formula C6H12O6

Monosaccharide classifications

•Monosaccharides can be classified based on the following criteria:

–Location of carbonyl group (aldoses vs. ketoses)

–Number of sugars (triose, pentose, hexose)

•Glucose and other monosaccharides are major form of nutrients for cells

In an aqueous solution, monosaccharides forms rings

Disaccharide

•A disaccharide is 2 monosaccharides joined by the glycosidic linkage, which is a covalent bond formed by dehydration synthesis between to monosaccharides.

•Most common disaccharides:

–glucose + glucose  maltose

–Glucose + fructose  sucrose

–Glucose + Galactose  lactose

Glycosidic Linkages

Polysaccharides

•Polymers of sugar – chains of sugar

•Uses/functions

–Storage of energy

•Starch

•glycogen

–Building materials (structural components)

•Cellulose

•Chitin

Polysaccharides for storage

StarchGlycogen

Found only in plants. Found only in animals

Almost all linkages are various linkages

1-4 links

Helical in shapeHelical in shape

Amylose – Many branches

No branches

Amylopectin-some branching

–1. Fats

–2. Phospholipids

–3. Steroids

Fats

•Fats are made of glycerol and 3 fatty acids

•Glycerol is 3 carbons with –OH attached

•Fatty acids are 16-18 carbons with a carboxyl group at one end.

•Fatty acids are non polar and store a great deal of energy

Fats

•Three fatty acids bond to the glycerol.

•Technical term for fat is triglyceride

Fats

•Saturated fats have hydrogens attached to each carbon. They are solid at room temperature (examples would include butter and lard.)

•Unsaturated fats have doublebonds and are “missing” some hydrogens. They are liquid at room temperature (examples would include oils such as olive oil and corn oil)

Phospholipids

Phospholipids consist of a phosphate head that is polar attached to two fatty acid tails that are nonpolar.

Both of the fatty acids can be saturated fat, both can be unsaturated fat or there can be one of each

Phospholipids

•The phospholipids naturally line up in 2 layers with the hydrophobic tails pointed inward. The heads that are hydrophilic point outward

•This forms a cell membrane and is called a lipid bilayer

Steroids

•A steroid is a lipid that has 4 fused rings with varying functional groups attached.

•Cholesterol (above) is a common component of animal cell membranes and is also the framework on which many hormones are built.

Proteins

•Humans have thousands of different proteins.

•Proteins are polymers of amino acids.

•There are 20 different amino acids.

Amino Acids

•The R group is the point of variation. There are 20 different R groups. 11 are hydrophilic, 9 are hydrophobic. Of the 11 hydrophilic, 3 are basic, 2 are acidic

•The 20 amino acids are referred to by their 3 letter abbreviation.

•EX: Glycine = Gly

•All living things use these 20 amino acids to build the proteins needed.

•

Essential Amino Acids

•We need all 20 amino acids

•Humans can produce 12 of them.

•The other 8 must be included in our diet and are called “essential amino acids.”

•All but 2 of the essential amino acids can be found in plants. Tryptophan and lysine are not found in plants and vegetarians have to make sure they get these two in their diet.

Peptide bonds

•When amino acids are positioned so that the carboxyl group of one a.a. is next to the amino group of another, water is lost (dehydration synthesis) and a peptide bond is made.

•Chains of amino acids area called polypeptide chains or polypeptides.

•Chains consist of the side chain (R-groups) and the backbone (-carbon, carboxyl group and amino group.)

Peptide bonds

Functional Protein

•Polypeptide chains will twist, fold, coil and sometimes combine with other chains to make a molecule of a PRECISE and UNIQUE shape. This molecule is called a protein.

•In the architecture of a protein, there are 3 or 4 levels of structure:

–Primary, secondary, tertiary, quaternary.

•Think of a polypeptide chain as yarn and the protein as a sweater.

Primary Structure

•Arises from the sequence of amino acids.

•The sequence, or order, or the amino acids is determined by the DNA.

•Given that there are 20 amino acids, how many possible combinations are there for a chain of 100 amino acids?

Primary Structure

Changing one amino acid can radically change a protein.

Secondary Structure

•Arises from hydrogen bonds that occur between backbone molecules.

•Two types of secondary structure:

-helix – coil coming from hydrogen bonds between every 4th a.a. (EX: Human hair)

-pleated sheet – 2 or more regions of the chain are hydrogen bonded to each other. (EX: Silk)

Tertiary Structure

Arises from interactions between side chains (R groups). Causes folding (irregular contortions)

Interactions include:

•Hydrophobic interactions

•Disulfide bridges

•Hydrogen bonds

•Ionic bonds

Quaternary Structure

•Overall protein structure that results from more than one polypeptide subunits.

•Example: Collagen…fibers that result from 3 long polypeptide chains braided together.

Proteins

•

Conformation and Denaturation

•The shape a protein takes is called its conformation. The conformation is determined and maintained by the interactions taking place in primary, secondary and tertiary structure.

•However, it’s also influenced by its physical environment (pH, temperature, salt concentration,etc.)

•If you change its physical environment you can force a protein to change its conformation. This change is called denaturation.

Conformation and Denaturation

•Some causes of denaturation:

–Heat

–Organic solvents (chloroform, ether)

–Low pH

–High salt concentration

•Example: Eggs are protein and will turn hard and opaque as it cooks

•Many enzymes in the human will denature above 108 degrees F.

Nucleic Acids - Function

One kind of nucleic acid (DNA) stores the information for how to make each proteins

Another kind of nucleic acid (RNA) takes the stored information and makes it into a protein.

Analogy

DNA = Recipe, RNA = chef, protein = meal

See figure 5.28:

DNARNAprotein

Nucleic Acids - polymer

•A nucleic acid is a polymer. The monomer is a nucleotide.

•Nucleotides consist of a pentose (5-carbon) sugar, a phosphate group and a nitrogenous base

2 kinds of nucleotides

Purines Pyrimidines

2 kinds of sugar

DeoxyriboseRibose

How they fit together - DNA

•Deoxyribose sugar

•Phosphate

•Nitrogen bases Adenine, Thymine, Guanine, Cytosine

•Adenine always bonds with Thymine

•Cytosine always bonds with Guanine

•Double stranded – twists into a helix

How they fit together - RNA

•Ribose sugar

•Phosphate

•Nitrogen bases Adenine, Uracil, Guanine, Cytosine

•Single-stranded