Chapter 5 The Structure and Function of Macromolecules

Introduction cells join smaller organic molecules together to form larger molecules the four main classes of macromolecules are: carbohydrates,lipids,proteins, and nucleic acids

Large molecules formed by joining many subunits together Macromolecules also known as “polymers”

Monomer a building block of a polymer repeated linked units

Condensation Synthesis or Dehydration Synthesis the chemical reaction that joins monomers into polymers covalent bonds are formed by the removal of a water molecule between the monomers

one monomer provides the hydroxyl group and the other provides a hydrogen together these form water

Hydrolysis the reverse of condensation synthesis (dehydration synthesis) Hydro = waterLysis = to split the covalent bonds connecting monomers in a polymer are disassembled by hydrolysis

in hydrolysis, as the covalent bond is broken a hydrogen atom and hydroxyl group from a split water molecule attaches where the covalent bond used to be

hydrolysis will break polymers into monomers by adding water hydrolysis reactions dominate the digestive process, guided by specific enzymes

An immense variety of polymers can be built from a small set of monomers each cell has thousands of different macromolecules these monomers can be connected in various combinations, like the 26 letters in the alphabet can be used to create a great diversity of words

Four Main Types of Macromolecules carbohydrates lipids proteins nucleic acids

Carbohydrates include both sugars and the polymers of sugars used for fuel, building materials, and receptors made of C, H, O general formula is CH 2 O most names for sugars end in -ose

Types of Carbohydrates 1. monosaccharides 2. disaccharides 3. polysaccharides

Monosaccharides mono = single (one) saccharide = sugar simplest of all carbohydrates 3 to 7 carbons

monosaccharides are also classified by the number of carbons in the backbone can be in linear or ring forms

Disaccharides two monosaccharides can join with a glycosidic linkage to form a disaccharide via dehydration

maltose, malt sugar, is formed by joining two glucose molecules sucrose, table sugar, is formed by joining glucose and fructose and is the major transport form of sugars in plants

Polysaccharides the polymers of sugars, have storage and structural roles many joined simple sugars (can be hundreds to thousands of monosaccharides joined by glycosidic linkages)

one function of polysaccharides is as an energy storage macromolecule that is hydrolyzed as needed

other polysaccharides serve as building materials for the cell or whole organisms

Starch a storage polysaccharide composed entirely of glucose monomers made of linkages of α glucose linkage makes the molecule form a helix

fuel storage in plants α glucoseβ glucose

Cellulose made of 1 – 4 β glucose linkage makes the molecule form a straight line used for structure in plant cell walls

most organisms can digest starch (1 – 4 α linkage), but very few can digest cellulose (1 – 4 β linkage)

Glycogen “animal starch” similar to starch, but has more linkages or branches

humans and other vertebrates store glycogen in the liver and muscles but only have about a one- day supply

Chitin another structural polysaccharide found in the exoskeletons of arthropods and cell walls of many fungi

similar to cellulose, except that it has a nitrogen-containing appendage on each glucose monomer

Lipids The unifying feature of lipids is that they all have little or no affinity for water this is because their structure are dominated by nonpolar covalent bonds

lipids are diverse hydrophobic molecules made of C, H, O lipids store large amounts of energy unlike other macromolecules, lipids do not form polymers

Fats and Oils Fats – solid at room temperature Oils – liquid at room temperature

Fats and Oils Made of two kinds of smaller molecules 1. glycerol 2. fatty acids

Fatty Acids A long carbon chain (12 – 18 carbons) with a –COOH (acid) on one end and a –CH 3 (fat) at the other

Triglycerides (Triacylglycerols) three fatty acids joined to one glycerol

joined by an ester linkage between the –COOH of the fatty acid and the –OH of the alcohol

Saturated Fats saturated – no double bonds most animal fats

Unsaturated Fats unsaturated – one or more C=C bonds double bonds cause “kinks” in the molecule’s shape (can accept more hydrogen)

Why do fats usually contain saturated fatty acids and oils usually contain unsaturated fatty acids? The double bond pushes the molecules apart, lowering the density, which lowers the melting point

Fats differ in which fatty acids are used used for energy reserve (adipose tissue), cushion for vital organs, insulation

Which has more energy, a kg of fat or a kg of starch? Fat – there are more C – H bonds which provide more energy per mass (2x as much energy) (2x as many calories)

Phospholipids similar to fats, but have only two fatty acids the third –OH of glycerol is joined to a phosphate containing molecule are major components of cell membranes (arranged as a bilayer)

Phospholipids have a hydrophobic tail, but a hydrophilic head

The hydrophilic heads are on the outside in contact with the aqueous solution and the hydrophobic tails form the core

the phospholipid bilayer forms a barrier between the cell and the external environmental

Steroids lipids with four fused rings differ in the functional groups attached to the rings

cholesterol – a component in animal cell membranes Examples of Steroids: sex hormones – estrogen and testosterone

Proteins made of C, H, O, N, and sometimes S proteins are the most structurally complex molecules known each type of protein has a complex 3-D shape or conformation

Uses of Proteins structure enzymes antibodies transport movement receptors hormones

Proteins all protein polymers are constructed from the same set of 20 monomers – amino acids polymers of proteins are called polypeptides polypeptide chains of amino acids linked by peptide bonds

a protein consists of one or more polypeptides folded and coiled into a specific conformation

Amino Acids All have a carbon with four attachments: - COOH (acid) - NH 2 (amine) - H - R (some other side group)

R Groups 20 different kinds:

The properties of the R groups determine the properties of the protein

Polypeptide Chains Amino acids are joined together when a dehydration reaction removes a hydroxyl group from the carboxyl end of one amino acid and a hydrogen from the amino group of another the resulting covalent bond is called a peptide bond

(N-C-C) is the polypeptide backbone

Levels of Protein Structure Organizing the polypeptide into its 3-D functional shape primary secondary tertiary quaternary

Primary sequence of amino acids in the polypeptide chain many different sequences are possible with 20 amino acids

Secondary 3-D structure formed by hydrogen bonding between the R groups two main secondary structures: α helix pleated sheets

secondary structure of a protein results from hydrogen bonding at regular intervals along the polypeptide backbone

Tertiary bonding between R groups Examples: Hydrogen bonds among polar and/or charged areas Ionic bonds between charged R groups

Hydrophobic interactions and van der Waals interactions among hydrophobic R groups

while these bonds are relatively weak, disulfide bridges, strong covalent bonds that form between the sulfhydryl groups, stabilize the structure

Quaternary when two or more polypeptides unite to form a functional protein Example: hemoglobin

Is Protein Structure Important?

Denaturing of a Protein events that cause a protein to lose structure (and function) Examples: pH shifts high salt concentrations heat

These forces disrupt the hydrogen bonds, ionic bonds, and disulfide bridges that maintain the protein’s shape

some proteins can return to their functional shape after denaturation, but others cannot, especially in the crowded environment of the cell

Nucleic Acids informational polymers made of C, H, O, N, and P Examples: DNA and RNA polymers of nucleotides

DNA provides direction for its own replication DNA also directs RNA synthesis and, through RNA, controls protein synthesis

Nucleotides Three parts to a nucleotide: 1. nitrogenous base 2. pentose sugar 3. phosphate group

Nitrogenous Bases rings of C and N the N atoms tend to take up H + (base)

Two types: 1. Pyrimidines (single ring) Cytosine (C), Thymine (T), and Uracil (U)

2. Purines (double rings) Adenine (A) and Guanine (G)

Pentose Sugar 5 – C sugar ribose – RNA deoxyribose - DNA RNA and DNA differ in an – OH group on the 2 nd carbon

polynucleotides are synthesized by connecting the sugars of one nucleotide to the phosphate of the next with a phosphodiester link

this creates a repeating backbone of sugar- phosphate units with the nitrogen bases as appendages

A always pairs with T and G always pairs with C