Structure and Function of Structure and Function of MacromoleculesMacromolecules

Chapter 5Chapter 5

Most macromolecules are polymersMost macromolecules are polymers PolymerPolymer -- (Poly = many; mer = part) Large molecule consisting of many -- (Poly = many; mer = part) Large molecule consisting of many

similar subunits connected together.similar subunits connected together. MonomerMonomer -- Subunit or building block molecule of a polymer. -- Subunit or building block molecule of a polymer. MacromoleculeMacromolecule -- (Macro = large) Large organic polymer. -- (Macro = large) Large organic polymer.

Four classes of macromolecules in living organisms:Four classes of macromolecules in living organisms: 1. Carbohydrates.1. Carbohydrates. 2. Lipids.2. Lipids. 3. Proteins.3. Proteins. 4. Nucleic acids.4. Nucleic acids.

Most polymerization reactions Most polymerization reactions in living organisms are in living organisms are condensation condensation reactions.reactions.

Polymerization reactionsPolymerization reactions -- Chemical reactions that link two or more small -- Chemical reactions that link two or more small molecules to form larger molecules.molecules to form larger molecules.

Condensation reactionsCondensation reactions -- Monomers are covalently linked, resulting in -- Monomers are covalently linked, resulting in removal of a water molecule.removal of a water molecule.

• • One monomer loses a hydroxyl (OH), and the other monomer loses a One monomer loses a hydroxyl (OH), and the other monomer loses a hydrogen (H).hydrogen (H).

HydrolysisHydrolysis -- (Hydro = water; lysis = break) A reaction process that breaks -- (Hydro = water; lysis = break) A reaction process that breaks covalent bonds between monomers by the addition of water molecules.covalent bonds between monomers by the addition of water molecules.

Organisms use carbohydrates for fuel and Organisms use carbohydrates for fuel and building materialbuilding material

CarbohydratesCarbohydrates -- Organic molecules made of sugars -- Organic molecules made of sugars and their polymers.and their polymers.

A. A. Monosaccharides Monosaccharides (“single sugar”) Simple sugars (“single sugar”) Simple sugars with C, H and O in the ratio of 1:2:1.with C, H and O in the ratio of 1:2:1.

B. B. DisaccharidesDisaccharides (“two sugars”) Consists of two (“two sugars”) Consists of two monosaccharides joined by a monosaccharides joined by a glycosidic linkage.glycosidic linkage. Glycosidic linkageGlycosidic linkage = Covalent bond formed by a = Covalent bond formed by a

condensation reaction between two sugar monomers. condensation reaction between two sugar monomers.

C. C. PolysaccharidesPolysaccharides (“many sugars”) Polymers of a (“many sugars”) Polymers of a few hundred or thousand monosaccharides.few hundred or thousand monosaccharides.

MonosaccharidesMonosaccharides

Are major nutrients for cells (glucose). Are major nutrients for cells (glucose). Store energy in their chemical bonds which is harvested by Store energy in their chemical bonds which is harvested by

cellular respiration.cellular respiration. Can be incorporated as monomers into disaccharides and Can be incorporated as monomers into disaccharides and

polysaccharides.polysaccharides.

Characteristics of a sugar:Characteristics of a sugar: 1. An -OH group is attached to each carbon except one, 1. An -OH group is attached to each carbon except one,

which is double bonded to an oxygen (carbonyl).which is double bonded to an oxygen (carbonyl). Terminal carbon forms a double bond with oxygen --aldehyde Terminal carbon forms a double bond with oxygen --aldehyde

sugar or aldose (glucose).sugar or aldose (glucose). Inside carbon bonds with oxygen -- ketone sugar or ketose Inside carbon bonds with oxygen -- ketone sugar or ketose

(fructose).(fructose). 2. Size of the carbon skeleton varies from 3 to 7 carbons. 2. Size of the carbon skeleton varies from 3 to 7 carbons. 3. In aqueous solutions, many monosaccharides form rings. 3. In aqueous solutions, many monosaccharides form rings.

DisaccharidesDisaccharides

Glycosidic linkageGlycosidic linkage -- Covalent bond -- Covalent bond formed by a condensation reaction formed by a condensation reaction between two sugar monomers.between two sugar monomers.

ExExamples of Disaccharides:amples of Disaccharides:Maltose (malt sugar) glucose + glucose.Maltose (malt sugar) glucose + glucose.Lactose (milk sugar) glucose + galactose.Lactose (milk sugar) glucose + galactose.Sucrose (table sugar) gSucrose (table sugar) glucose + fructose.lucose + fructose.

PolysaccharidesPolysaccharides Have two important biological functions:Have two important biological functions: 1. Energy storage (starch and glycogen).1. Energy storage (starch and glycogen). 2. Structural support (cellulose and chitin).2. Structural support (cellulose and chitin).

Storage PolysaccharidesStorage Polysaccharides Cells hydrolyze storage polysaccharides into sugars as Cells hydrolyze storage polysaccharides into sugars as

needed. Two most common storage polysaccharides needed. Two most common storage polysaccharides are are starch starch and and glycogen.glycogen.

StarchStarch -- Glucose polymer that is a storage -- Glucose polymer that is a storage polysaccharide in plants.polysaccharide in plants.

Helical glucose polymer with a 1-4 linkages (aHelical glucose polymer with a 1-4 linkages (amylose mylose and amylopectin).and amylopectin).

Most animals have digestive enzymes to hydrolyze Most animals have digestive enzymes to hydrolyze starch (amylase in saliva).starch (amylase in saliva).

GlycogenGlycogen -- Glucose polymer that is a storage -- Glucose polymer that is a storage polysaccharide in animals.polysaccharide in animals.

Stored in the muscle and liver of humans and other Stored in the muscle and liver of humans and other vertebrates.vertebrates.

More branched than amylopectin.More branched than amylopectin.

Polysaccharides (cont)Polysaccharides (cont) Structural PolysaccharidesStructural Polysaccharides Include Include cellulose cellulose and and chitin.chitin. CelluloseCellulose -- Linear unbranched polymer of -- Linear unbranched polymer of ββ (beta) (beta)

glucose in 1-4 linkages (-OH group on carbon one is glucose in 1-4 linkages (-OH group on carbon one is above above the ring's plane).the ring's plane). A major structural component of plant cell walls.A major structural component of plant cell walls. Starch has Starch has αα (alpha) glucose configuration (alpha) glucose configuration (-OH group on (-OH group on

carbon one is carbon one is below below the ring's plane)the ring's plane).. Hydrogen bonds hold together parallel cellulose Hydrogen bonds hold together parallel cellulose

molecules in bundles ofmolecules in bundles of microfibrils. microfibrils. Cellulose cannot be digested by most organisms Cellulose cannot be digested by most organisms

because they lack an enzyme to hydrolyze the because they lack an enzyme to hydrolyze the ββ 1-4 1-4 linkage. linkage.

ChitinChitin -- Polymer of an amino sugar. -- Polymer of an amino sugar. Forms exoskeletons of arthropods.Forms exoskeletons of arthropods. In cell walls of some fungi.In cell walls of some fungi. Amino sugar Amino sugar similar to similar to beta glucose beta glucose with a nitrogen-with a nitrogen-

containing group replacing the hydroxyl on carbon 2.containing group replacing the hydroxyl on carbon 2.

Lipids are hydrophobic molecules with Lipids are hydrophobic molecules with diverse functionsdiverse functions

Insoluble in water, but will dissolve in Insoluble in water, but will dissolve in nonpolar solvents (e.g. ether, chloroform, nonpolar solvents (e.g. ether, chloroform, benzene). benzene).

Important groups are:Important groups are: A.A. FatsFats -- Constructed from glycerol and -- Constructed from glycerol and

fatty acid.fatty acid.B. B. PhospholipidsPhospholipids -- Glycerol, two fatty -- Glycerol, two fatty

acids, phosphate group.acids, phosphate group.C.C. SteroidsSteroids -- Four fused carbon rings -- Four fused carbon rings

with various functional groups attached.with various functional groups attached.

FatsFats Glycerol (a three-carbon alcohol) + Fatty acid Glycerol (a three-carbon alcohol) + Fatty acid

(carboxylic acid).(carboxylic acid). Fatty acids composed of a carboxyl group at one Fatty acids composed of a carboxyl group at one

end and an attached end and an attached hydrocarbon chain hydrocarbon chain ("tail"), ("tail"), usually 16-18 carbons.usually 16-18 carbons.

Nonpolar C-H bonds make the tail hydrophobic Nonpolar C-H bonds make the tail hydrophobic and not water soluble.and not water soluble.

Three fatty acids can bond to one glycerol Three fatty acids can bond to one glycerol (triglyceride).(triglyceride).

Ester linkageEster linkage -- -- condensation reaction linking condensation reaction linking glycerol to fatty acids; bond formed between glycerol to fatty acids; bond formed between hydroxyl group and carboxyl group.hydroxyl group and carboxyl group.

Fats (cont)Fats (cont) SATURATED FATSATURATED FAT No double bonds No double bonds

between carbons in fatty between carbons in fatty acid tail.acid tail.

Carbon skeleton of fatty Carbon skeleton of fatty acid is bonded to acid is bonded to maximum number of maximum number of hydrogens hydrogens (saturated (saturated with with hydrogens).hydrogens).

Usually a solid at room Usually a solid at room temperature.temperature.

Most animal fats.Most animal fats. Bacon grease, lard and Bacon grease, lard and

butter.butter.

UNSATURATED FATUNSATURATED FAT One or more double bonds One or more double bonds

between carbons in fatty acid tail.between carbons in fatty acid tail. Tail kinks at each C=C, so Tail kinks at each C=C, so

molecules do not pack closely molecules do not pack closely enough to solidify at room enough to solidify at room temperature.temperature.

Usually a liquid at room Usually a liquid at room temperature.temperature.

Most plant fats.Most plant fats. Corn, peanut and olive oils.Corn, peanut and olive oils. In many commercially prepared In many commercially prepared

food products, unsaturated fats are food products, unsaturated fats are artificially hydrogenated to prevent artificially hydrogenated to prevent them from separating out as oil them from separating out as oil (e.g. peanut butter and margarine).(e.g. peanut butter and margarine).

Fats (cont)Fats (cont)

Functions:Functions:Energy storage -- One gram of fat stores Energy storage -- One gram of fat stores

twice as much energy as a gram of twice as much energy as a gram of polysaccharide. polysaccharide.

Animals store more energy with less Animals store more energy with less weight than plants which use starch.weight than plants which use starch.

Cushions vital organs in mammals Cushions vital organs in mammals (kidney).(kidney).

Insulates against heat loss (mammals Insulates against heat loss (mammals such as whales and seals).such as whales and seals).

PhospholipidsPhospholipids Differ from fat in that the third carbon of glycerol is Differ from fat in that the third carbon of glycerol is

joined to a joined to a negatively charged negatively charged phosphate group.phosphate group. Hydrocarbon tails are hydrophobic.Hydrocarbon tails are hydrophobic. Polar head (glycerol/phosphate) is hydrophilic.Polar head (glycerol/phosphate) is hydrophilic. Cluster in water as their hydrophobic tails turn away Cluster in water as their hydrophobic tails turn away

from water (from water (micelle).micelle). Major constituents of cell membranes. Phospholipids Major constituents of cell membranes. Phospholipids

form a bilayer held together by hydrophobic form a bilayer held together by hydrophobic interactions among the hydrocarbon tails. interactions among the hydrocarbon tails.

Hydrophilic heads -- Hydrophilic heads -- point towards exterior of bilayer.point towards exterior of bilayer. Hydrophobic tails -- Hydrophobic tails -- point towards interior of bilayer.point towards interior of bilayer.

SteroidsSteroids

Cholesterol, an Cholesterol, an important steroid:important steroid:

Is the precursor to Is the precursor to many other steroids many other steroids including vertebrate including vertebrate sex hormones and sex hormones and bile acids.bile acids.

Is a common Is a common component of animal component of animal cell membranes.cell membranes.

Nucleic acids store and transmit hereditary information

Two types of nucleic acids.Two types of nucleic acids. 1. Deoxyribonucleic Acid (DNA)1. Deoxyribonucleic Acid (DNA) • • Contains coded information that programs all cell Contains coded information that programs all cell

activity.activity. • • Is copied and passed from one generation of cells to Is copied and passed from one generation of cells to

another.another. • • In eukaryotic cells, is found primarily in the nucleus.In eukaryotic cells, is found primarily in the nucleus.

2. Ribonucleic Acid (RNA)2. Ribonucleic Acid (RNA) • • Functions in the actual synthesis of proteins coded for Functions in the actual synthesis of proteins coded for

by DNA.by DNA. • • Messenger RNA (mRNA) carries encoded genetic Messenger RNA (mRNA) carries encoded genetic

message from the nucleus to the ribosomes in the message from the nucleus to the ribosomes in the cytoplasm.cytoplasm.

The flow of genetic information goes from DNA —> RNA The flow of genetic information goes from DNA —> RNA ——> > protein.protein.

DNA strand is a polymer made up of DNA strand is a polymer made up of nucleotidesnucleotides

Nucleic acidNucleic acid -- Polymer -- Polymer of nucleotides of nucleotides linked together by linked together by condensation reactions.condensation reactions.

NucleotideNucleotide -- Building block molecule of a nucleic acid -- Building block molecule of a nucleic acid made of: made of:

1. 1. PentosePentose (5-Carbon Sugar): ribose or deoxyribose. (5-Carbon Sugar): ribose or deoxyribose. 2. 2. Phosphate groupPhosphate group attached to the number attached to the number 5 5 carbon of carbon of

the sugar.the sugar. 3. 3. Nitrogenous Base: Nitrogenous Base: Adenine, Guanine, Cytosine, Adenine, Guanine, Cytosine,

Thymine (DNA only), Uracil (RNA only).Thymine (DNA only), Uracil (RNA only). Nucleotides are joined into a polymer by Nucleotides are joined into a polymer by phosphodiester phosphodiester

linkages linkages between the phosphate of one nucleotide and between the phosphate of one nucleotide and the sugar of the next.the sugar of the next.

PyrimidinePyrimidine -- Nitrogenous base characterized by a six- -- Nitrogenous base characterized by a six-membered ring made up of carbon and nitrogen atoms membered ring made up of carbon and nitrogen atoms (C, T, U).(C, T, U).

PurinePurine -- Nitrogenous base characterized by a five- -- Nitrogenous base characterized by a five-membered ring fused to a six-membered ring (A, G).membered ring fused to a six-membered ring (A, G).

Inheritance is based on precise Inheritance is based on precise replication of DNAreplication of DNA

In 1953, J. Watson and F. Crick (with help of M. Wilkins In 1953, J. Watson and F. Crick (with help of M. Wilkins and R. Franklin) proposed the and R. Franklin) proposed the double helix double helix as the three as the three dimensional structure of DNA. dimensional structure of DNA.

Consists of two nucleotide chains wound in a double Consists of two nucleotide chains wound in a double helix.helix.

Sugar-phosphate backbones are on the outside of the Sugar-phosphate backbones are on the outside of the helix.helix.

Nitrogenous bases are paired in the interior of the helix Nitrogenous bases are paired in the interior of the helix and are held together by hydrogen bonds.and are held together by hydrogen bonds.

Base-pairing rules are that adenine (A) always pairs with Base-pairing rules are that adenine (A) always pairs with thymine (T); guanine (G) always pairs with cytosine (C).thymine (T); guanine (G) always pairs with cytosine (C).

Two strands of DNA are complimentary and thus can Two strands of DNA are complimentary and thus can serve as templates to make new complementary serve as templates to make new complementary strands. It is this mechanism of precise copying that strands. It is this mechanism of precise copying that makes inheritance possible.makes inheritance possible.

Most DNA molecules are long — with thousands or Most DNA molecules are long — with thousands or millions of base pairs.millions of base pairs.