Macromolecules – Structure and Function
Within cells, small organic molecules (monomers) are joined together to form larger molecules (polymers).
Macromolecules are large molecules composed of thousands of covalently connected atoms.
Three of the four classes of life’s organic molecules are polymers:
▪ Carbohydrates▪ Proteins▪ Nucleic acids
An immense variety of polymers can be built from a small set of monomers.
Monomers form larger molecules by condensation reactions called dehydration reactions.
Polymers are disassembled to monomers by hydrolysis, a reaction that is the reverse of the dehydration reaction.
Short polymer Unlinked monomer
Dehydration removes a watermolecule, forming a new bond
Dehydration reaction in the synthesis of a polymer
Longer polymer
Hydrolysis adds a watermolecule, breaking a bond
Hydrolysis of a polymer
Carbohydrates include sugars and the polymers of sugars.
The simplest carbohydrates are single sugars, or monosaccharides.• Monosaccharides have molecular formulas
that are usually multiples of CH2O.
• Glucose is the most common monosaccharide.
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks.
Triose sugars(C3H6O3)
GlyceraldehydeAld
ose
sK
eto
s es
Pentose sugars(C5H10O5)
Ribose
Hexose sugars(C5H12O6)
Glucose Galactose
Dihydroxyacetone
Ribulose
Fructose
Monosaccharides serve as a major fuel for cells and as raw material for building molecules.
Though often drawn as a linear skeleton, in aqueous solutions they form rings.
Linear andring forms
Abbreviated ringstructure
A disaccharide is formed when a dehydration reaction joins two monosaccharides.
This covalent bond is called a glycosidic linkage.
Glucose
Maltose
Fructose Sucrose
Glucose Glucose
Dehydrationreaction in thesynthesis of maltose
Dehydrationreaction in thesynthesis of sucrose
1–4glycosidic
linkage
1–2glycosidic
linkage
Polysaccharides, the polymers of sugars, have storage and structural roles.
The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages.• Storage polysaccharides: starch & glycogen• Structural polysaccharides: cellulose & chitin
Starch, a storage polysaccharide of plants, consists entirely of glucose monomers.• Plants store surplus starch as granules
within chloroplasts and other plastids.Glycogen is a storage polysaccharide
in animals.• Humans and other vertebrates store
glycogen mainly in liver and muscle cells.
Chloroplast Starch
1 µm
Amylose
Starch: a plant polysaccharide
Amylopectin
Mitochondria Glycogen granules
0.5 µm
Glycogen
Glycogen: an animal polysaccharide
Starch & Glycogen
Cellulose is a major component of the tough wall of plant cells.
Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ.
The difference is based on two ring forms for glucose:
alpha () and beta ()
a Glucose
a and b glucose ring structures
b Glucose
Starch: 1–4 linkage of a glucose monomers.
Cellulose: 1–4 linkage of b glucose monomers.
Cellulosemolecules
Cellulose microfibrilsin a plant cell wall
Cell walls Microfibril
Plant cells
0.5 µm
Glucosemonomer
Enzymes that digest starch by hydrolyzing alpha linkages can’t hydrolyze beta linkages in cellulose.
Cellulose in human food passes through the digestive tract as insoluble fiber.
Some microbes use enzymes to digest cellulose. Many herbivores, from cows to termites, have
symbiotic relationships with these microbes.
Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods.
Chitin also provides structural support for the cell walls of many fungi.
Chitin can be used as surgical thread.
Which of these polysaccharide/function pairs are INCORRECTLY matched:
A.starch/storage in plantsB.chitin/structure in plantsC.glycogen/storage in animalsD.cellulose/structure in plants
fungi/arthropods
Lipids are the one class of large biological molecules that do not form polymers.
All lipids have little or no affinity for water.
The most biologically important lipids are fats, phospholipids, and steroids.
When lipids are mixed with water, the water molecules bond to each other and exclude the lipid molecules. What causes lipids to be hydrophobic?
A.They are extremely polar molecules.B.They consist mostly of water
molecules.C.They consist mostly of hydrocarbons
which form polar covalent bonds.D.They consist mostly of hydrocarbons
which form nonpolar covalent bonds.
Dehydration reaction in the synthesis of a fat
Glycerol
Fatty acid(palmitic acid)
The major function of fats is energy storage. Fats are constructed from two types of smaller
molecules: glycerol and fatty acids. Glycerol is a three-carbon alcohol with a
hydroxyl group attached to each carbon. A fatty acid consists of a carboxyl group
attached to a long carbon skeleton.
Animation: Fats
• In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride.
Ester linkage
Fat molecule (triacylglycerol)
Fatty acids vary in length (number of carbons) and in the number and locations of double bonds.
Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds (straight chains – solids at room temperature).
Unsaturated fatty acids have one or more double bonds (bent chains – liquids at room temperature).
Saturated fat and fatty acid.
Stearic acid
Unsaturated fat and fatty acid.
Oleic acid
cis double bondcauses bending
Trans fats are unsaturated, but the hydrogens around the double bonds are arranged in such a way that the fatty acid chains are still straight.
Trans fats are known to raise bad cholesterol and lower good cholesterol.
Which of the following statements about fats is FALSE?
A.Most animal fats are saturated fats.B.Saturated fats are liquids at room
temperature.C.Plant fats and fish fats are usually
unsaturated.D.A diet rich in saturated fats may
contribute to cardiovascular disease through plaque deposits.
In a phospholipid, two fatty acids and a phosphate group are attached to glycerol.
The two fatty acid tails are hydrophobic and the phosphate group forms a hydrophilic head.
Structural formula Space-filling model Phospholipid symbol
Hydrophilichead
Hydrophobictails
Fatty acids
Choline
Phosphate
Glycerol
Hyd
rop
ho
bic
tai
lsH
ydro
ph
i lic
hea
d
When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior.
Phospholipid bilayers are the major component of all cell membranes.
WATERHydrophilichead
Hydrophobictails
WATER
Steroids are lipids characterized by a carbon skeleton consisting of four fused rings.
Cholesterol, an important steroid, is a component in animal cell membranes.
Although essential in animals, high levels of cholesterol in the blood may contribute to cardiovascular disease.
Which of the following statements about proteins/polypeptides is FALSE?
A. Polypeptides are polymers of amino acids.B. All proteins consist of more than one
polypeptide.C. Amino acids in a polypeptide are linked by
peptide bonds.D. Each polypeptide has a unique linear
sequence of amino acids.
Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions.
Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life.
Substrate(sucrose)
Enzyme(sucrase)
Fructose
Glucose
Amino acids are organic molecules with carboxyl and amino groups.
Amino acids differ in their properties due to differing side chains, called R groups.
Cells use 20 amino acids to make thousands of proteins.
Aminogroup
Carboxylgroup
carbon
Isoleucine (Ile)
Methionine (Met) Phenylalanine (Phe) Tryptophan (Trp) Proline (Pro)
Leucine (Leu)Valine (Val)Alanine (Ala)
Nonpolar
Glycine (Gly)
Asparagine (Asn) Glutamine (Gln)Threonine (Thr)
Polar
Serine (Ser) Cysteine (Cys) Tyrosine (Tyr)
Electricallycharged
Aspartic acid (Asp)
Acidic Basic
Glutamic acid (Glu) Lysine (Lys) Arginine (Arg) Histidine (His)
A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape.
The sequence of amino acids determines a protein’s three-dimensional conformation, which determines its function.
A ribbon model
Groove
Groove
A space-filling model
Both ribbon models and space-filling models can be used to depict a protein’s conformation.
Amino acidsubunits
pleated sheet+H3N
Amino end
helix
Primary structure is a protein’s unique sequence of amino acids.
Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain.
Tertiary structure is determined by interactions among various side chains (R groups).
Quaternary structure results when a protein consists of multiple polypeptide chains.
Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word.
Primary structure is determined by inherited genetic information.
Amino acidsubunits
Carboxyl end
Amino end
The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone.
Typical secondary structures are a coil called an alpha helix and a folded structure called a beta pleated sheet.
Amino acidsubunits
pleated sheet
helix
Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents.
These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions.
Strong covalent bonds called disulfide bridges may reinforce the protein’s conformation.
Hydrophobicinteractions andvan der Waalsinteractions
Polypeptidebackbone
Disulfide bridge
Ionic bond
Hydrogenbond
Quaternary structure results when two or more polypeptide chains form one macromolecule.
Collagen is a fibrous protein consisting of three polypeptides coiled like a rope.
Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains.
Chains
ChainsHemoglobin
Iron
Heme
CollagenPolypeptide chain
Polypeptidechain
Which of these factors can affect protein conformation?
A.temperatureB.alternations in pHC.salt concentrationD.all of the above
The loss of a protein’s native conformation is called denaturation.
Denaturation
Renaturation
Denatured proteinNormal protein
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