Biology 112 Chapter 5 Macromolecules
Dec 18, 2015
Biology 112Chapter 5
Macromolecules
MacromoleculesAll living things are made up of four classes
of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids
Molecular function relates to molecular structure
Diversity of molecular structure is the basis for the diversity of life.
Most macromolecules are PolymersPolymer = Large molecule consisting of
many identical or similar subunits (monomers) connected together.
Three of the four classes of life’s organic molecules are polymers:CarbohydratesProteinsNucleic acids
Synthesis of PolymersCondensation (dehydration) reactions =
polymerization reactions during which monomers are covalently linked. This produces a net removal of one water molecule for each covalent linkage formed.
Breakdown of PolymersHydrolysis = reaction process that breaks
covalent bonds between monomers by the addition of water molecules.
Unity and DiversityA limitless variety of polymers
can be built from a small set of monomer building blocks.
Each cell has thousands of different kinds of macromolecules
Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species.
Unity…only about 40-50 common monomers are used
Diversity…emerges as these universal building blocks are arranged in different ways.
CarbohydratesCarbohydrates include sugars and the
polymers of sugarsThe simplest carbohydrates are
monosaccharides, or single sugarsMonosaccharidesMajor nutrient for cells. Glucose is most
common.Can be produced by photosynthesis from CO2,
H2O and sunlight.Energy stored in their chemical bonds which is
harvested by cellular respiration.Their carbon “skeletons” are the raw material
for other organic moleculesAre the monomers for polysaccharide polymersMany form ring structures in aqueous solutions
DisaccharidesA disaccharide is formed when a
dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidic linkage.
PolysaccharidesStorage
PolysaccharidesStarchGlycogen
Structural PolysaccharidesCelluloseChitin
LipidsLipids are the one class of large biological
molecules that do not form polymersThe unifying feature of lipids is having little
or no affinity for water. They are hydrophobic. They are nonpolar.
Lipids are hydrophobic becausethey consist mostly of hydrocarbons, which form nonpolar covalent bonds
The most biologically important lipids are fats, phospholipids, and steroids
FatsFats are constructed from two types of
smaller molecules: glycerol and fatty acidsGlycerol is a three-carbon alcohol with a
hydroxyl group attached to each carbonA fatty acid consists of a carboxyl group
attached to a long carbon skeletonIn a fat, three fatty acids are joined to
glycerol by an ester linkage, creating a triacylglycerol, or triglyceride
Fat synthesis
SaturationFatty 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
Unsaturated fatty acids have one or more double bonds
Fats made from saturated fatty acids are called saturated fats, and are solid at room temperature. (Most animal fats are saturated)
Fats made from unsaturated fatty acids are called unsaturated fats or oils, and are liquid at room temperature. (Plant fats and fish fats are usually unsaturated)
A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen
Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds
These trans fats may contribute more than saturated fats to cardiovascular disease
Functions of Fats:
Energy storage!A high energy compact form of fuel
storage.Insulates against heat lossCushions some vital organs in mammals
(Kidneys)
PhospholipidsComposed of glycerol, 2 fatty acids and a
phosphate group ( and usually an additional chemical group attached to the phosphate.
Hydrophilic headsHydrophobic tails
Spontaneously form a phospholipid bilyer in an aqueous environment
Major constituents of biological membranes.
Phospholipids
SteroidsSome hormones are steroids. (estrogen,
testosterone)Steroids are common components of
animal membranes (cholesterol)
ProteinsPolypeptides = polymers
of amino acids in a specific sequence that are linked by peptide bonds.
Amino acids Carboxyl groupAmino groupA variable R group specific
to each amino acid. The physical and chemical properties of these groups give the uniqueness to each amino acid. (polar/nonpolar ; charged/uncharged ; acidic/basic)
20 common amino acids
Amino Acids
Peptide bonds
Protein structureA protein’s function depends upon its unique
conformation!!!!4 levels of protein structure
Primary --unique A.A. sequenceSecondary-- regular repeated coiling or folding
Alpha helixBeta pleated sheet
Tertiary -- irregular contortions due to bonding between side chains (R groups)Weak interactions
Hydrogen bonds Ionic bondsHydrophobic interactions
Covalent bonds – Disulfide bridgesQuaternary -- results when two or more
polypeptide chains form one macromolecule
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
DenaturationDenaturation = a process that alters a
protein’s native conformation and biological activity.
Protein Functions
Sickle-Cell DiseaseA slight change in
primary structure can affect a protein’s structure and ability to function
Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
Nucleic AcidsNucleic acids are polymers of nucleotides
linked together by condensation reactions. (DNA and RNA)
NucleotidesNucleotides are composed of :
5-carbon sugarphosphate group nitrogenous base
PyrimidinesCytosineThymineUracil
PurinesAdenineGuanine
Nucleotide functions:monomers for nucleic acidstransfer of chemical energy (ATP)act as electron acceptors
The Roles of Nucleic Acids
There are two types of nucleic acids:Deoxyribonucleic acid
(DNA)Ribonucleic acid
(RNA)DNA provides directions
for its own replicationDNA directs synthesis of
messenger RNA (mRNA) and, through mRNA, controls protein synthesis
Protein synthesis occurs in ribosomes
Inheritance is based on the precise replication of DNA
EvolutionDNA and Proteins can serves as
measures of evolutionThe more closely related species have
more similar sequences of DNA and therefore also more similar proteins.