Chapter #5 The structure And Function Of Large Biological Molecules Notes
Introduction: The Molecules of Life
1. The critically important large molecules of all living things—from bacteria
to elephants—fall into just four main classes:
a) carbohydrates
b) lipids
c) proteins
d) nucleic acids
2. Members of three of these classes are huge and are thus called macro-
molecules:
a) carbohydrates
b) proteins
c) nucleic acids
I. Macromolecules Are Polymers, Built From Monomers
1. The macromolecules in three of the four classes of life’s organic com-
pounds – carbohydrates, proteins & nucleic acids are polymers.
2. A polymer is a long molecule consisting of many similar or identical
building blocks linked by covalent bonds.
3. The repeating units that serve as the building blocks of polymers are
smaller mnolecules called monomers.
A. The Synthesis & Breakdown of Polymers
1. Monomers are connected by a reaction in which two molecules are co-
valently bonded to each other through loss of a water molecule: this
is known as a condensation reaction, specifically a dehydration reaction .
a) in the reaction one molecule provides a hydroxyl group, while the other
provides a hydrogen.
2. The dehydration process is facilitated by enzymes, special macromolecules
that speed up chemical reactions in cells.
3. Polymers are disassembled to monomers by hydrolysis.
4. Hydrolysis is a process whereas bonds between the monomers are broken
by the addition of water. Example - digestion in our bodies.

B. The Diversity of Polymers
1. The inherent differences between human siblings reflect variations in
polymers, particularly DNA and proteins.
2. The key to variation is arrangement of monomers in different ways.
II. Carbohydrates Serve as Fuel and Building Material
1. Carbohydrates are organic molecules which include both sugars and poly-
mers of sugars.
2. Monomers or building block molecules are simple sugars called mono-
saccharides.
3. Disaccharides are double sugars, consisting of two monosaccharides joined
by a covalent.
4. Carbohydrates also include macromolecules called polysaccharides, polymers
composed of many sugar building blocks.
A. Sugars
1. Monosaccharids – Single sugars which generally have molecular formulas
that are some multiple of the unit CH
2
O.
a) Glucose is the most common, it is of central importance in the chemistry
of life. (It is the major nutrient for cells)
b) Store energy in their chemical bonds which is harvested by cellular
respiration. Major fuel for process.
c) Can be incorporated as monomers into disaccharides & polysaccharides.
2. Classification of Sugars (Criteria for Classifying Sugars)
a) The trademarks of a sugar: The molecule has a carbonyl group & multiple
hydroxyl groups. Depending on the location in the carbon skeleton – the
sugar is either a ketose or aldose. (Most names for sugars end in ose ).

b) Size of the carbon skeleton which range from 3 to 7 carbons long.
Class. # of Carbons Example
3 Glyceraldehyde Triose
Pentose 5 Ribose
Hexose 6 Glucose
3. Spatial arrangement around asymmetric carbon my vary.
Example: glucose & galactose
4. In aqueous solutions, many monosaccharides form rings.
5. Disaccharides
a) Disaccharides consists of two monosaccharides joined by a glycosidic
linkage.
b) Glycosidic linkage is a covalent bond formed between two mono-
saccharides by a dehydration reaction. Examples:
Glucose + glucose ------ Maltose
Glucose + fructose ----- Sucrose
Ingredient used in brewing beer
Table sugar
Sugar present in milk Glucose + galactose ---- Lactose
B. Polysaccharides
1. Polysaccharides are macromolecules, polymers with a few hundred to a
few thousand monosaccharides joined by glycosidic linkages.
2. Polysaccharides have two important functions:
a) Energy storage
Example: starch & glycogen
b) Structural support
Example: cellulose & chitin
C. Storage Polysaccharides
1. Starch – A glucose polymer that is a storage polysaccharide in plants.
2. Most animals, including humans, also have enzymes that can hydrolyze
plant starch, making glucose available ass a nutrient for cells.

3. Starch is a helical glucose polymer with a 1-4 linkage.
4. Amylose, the simplest form, is an unbranched polymer.
5. Amylopectin is a branched polymer with 1-6 linkages at the branch point.
6. Starch is stored in granules within plant organelles called plastids.
7. Animals store a polysaccharide called glycogen .
a) Glycogen is more extensively branched than amylopectin.
b) Glycogen is stored in the muscle and liver cells of humans and other
vertebrates.
C. Structural Polysaccharides
1. The polysaccharide called cellulose is a major component of the tough
walls that enclose plant cells.
2. Cellulose is a linear unbranched polymer of D glucose in beta 1-4 linkage (beta
configuration make every other glucose monomer upside down with
respect to its neighbors).
3. Cellulose differs from starch in its glycosidic linkages. Thus the two differ in
shapes and properties as a result.
4. Cellulose cannot be digested by most organisms, including humans because
they lack an enzyme that can hydrolyze the beta 1-4 linkage. However,
some microbes can digest cellulose.
5. Another important structural polysaccharide is chitin.
6. Chitin is a structural polysaccharide that is a polymer of an amino sugar
a) Chitin is used by arthropods to build their exoskeletons.
b) Chitin is found in many fungi, which use it as a building material for their
cell wall.
c) The monomer for chitin is an amino sugar.
III. Lipids are a Diverse Group of Hydrophobic Molecules
1. Lipids are a diverse group of organic compounds that are insoluble in
water, but will dissolve in nonpolar solvents. (Example- ether, chloroform,
benzene).
2. The hydrophobic behavior of lipids is based on their molecular structure.

3. The most important families of lipids—fats, phospholipids & steroids.
A. Fats
1. Fats are constructed from two kinds of smaller molecules: glycerol & fatty
acids.
a) Glycerol – (3 carbon alcohol)
b) Fatty acid – (carboxylic acid – composed of carboxyl group at one end &
an attached hydrocarbon chain tail – 16 – 18 carbons). The relatively
nonpolar C-H bonds in the hydrocarbon chains of fatty acids are the
reason fats are hydrophobic.
2. The type of linkage which join three fatty acid molecules to glycerol is an
ester linkage.
3. Two other names for a fat is a triacylglycerol & triglyceride.
4. Fatty acids vary in length & in the number & locations of double bonds.
Thus, fats maybe categorized as saturated fats & unsaturated fats.
5. A diet rich in saturated fats is one of several factors that may contribute
to the cardiovascular disease known as atherosclerosis. However, trans fats
may contribute more than saturated fats to atherosclerosis.
6. The major function of fats is energy storage.
B. Phospholipids
1. Phospholipids are major components of cell membranes.
2. Phospholipids are compounds with molecular building blocks of
a) glycerol
b) 2 fatty acids
c) a phosphate group
d) usually an additional small chemical group attached to the phosphate
3. Phospholipids show ambivalent behavior toward water.
a) The hydrophilic head has an affinity for water
b) The hydrophobic tail does not have an affinity for water & point toward
the interior , away from the water.

C. Steroids
1. Steroids include cholesterol & certain hormones.
2. Steroids are lipids which have four fused carbon rings with various functional groups attached.
3. Cholesterol is the precursor from which other steroids including vertebrate
sex hormones.
4. Is a common component of animal cell membrane.
5. High level of cholesterol in the blood may contribute to atherosclerosis.
IV. Proteins Have Many Structures, Resulting In A Wide Range Of Functions
1. Nearly every dynamic function of a living being depends on proteins.
2. Proteins account for more than 50% of dry mass of most cells, & they are
instrumental in almost everything organisms do.
a) Examples: Enzymes, most of which are proteins- selectively accerlerate
chemical reactions.
b) Transport Proteins – Transport of other substances. Ex. Hemoglobin
c) Storage Proteins – Storage of amino acids
3. Proteins are the most structurally sophisticated molecule known.
4. Proteins vary extensively in structure, each type of protein have a unique
three-dimensional shape.
A. Polypeptides
1. Proteins are diverse & are constructed from the same set of 20 amino acids.
2. Polymers of amino acids are called polypeptides .
3. A protein consists of one or more polypeptides, each folded and coiled into
a specific three-dimensional structure.

B. Amino Acid Polymer
1. All amino acids share a common structure.
a) an asymmetric carbon
b) a hydrogen atom
c) a carboxyl group
d) an amino group
2. Amino acids are organic molecules possessing both carboxyl & amino groups
3. The twenty amino acids are grouped according to the properties of their side
chains (R groups). They are nonpolar, polar, electrically charged (acidic or
basic).
C. Amino Acid Pollymers
1. Peptide bonds formed by dehydration synthesis the link carboxyl group of one
amino acid to the amino group of the next in making a polypeptide chain.
2. The repeating sequence of the atoms – N –C-C-N-C-C forms the backbone
of a protein.
D. Protein Structure & Function
E. Four Levels of Protein Structure
1. The levels of protein structure are as follows:
a) Primary Structure - is the unique sequence of amino acids.
b) Secondary Structure – is the repeated coiling & folding of the backbone.
1. The two types are a) alpha helix, and b) beta pleated sheet
c) Tertiary Structure - is the overall shape which involves the interactions
between the side chains (R groups) of the various amino acids.
d) Quaternary Structure – is the overall protein structure that results from
the aggregation of two or more polypeptide chains aggregated into one
functional macromolecule.
F. Sickle-Cell Disease: A change in Primary Structure
1. Sickle-cell disease is caused by the substitution of one amino acid (valine) for
the normal one (glutamic acid) at a particular position in the primary sequence
structure of hemoglobin, the protein that carries oxygen in red blood cells.

2. Normal RBC’s are biconcave disk- shaped, but sickle-cell disease, the
abnormal hemoglobin molecules tend to crystallize, deforming some of the
cells into a sickle shape.
G. What Determines Protein Structure?
1. The primary structure is only one of the factors in determining protein
structure. Protein structure also depend on the physical & chemical con-
ditions of the protein’s environment.
a) pH
b) salt concentration
c) temperature
2. If the above factors are altered, the protein may unravel & lose its native shape.
H. Protein Folding in the Cell
V. Nucleic Acids Store and Transmit Hereditary Information
1. The amino acid sequence of a polypeptide is programmed by a unit of in-
heritance known as a gene.
2. Genes consist of DNA, a polymer belonging to the class of compounds known as
nucleic acids.
I. The Roles of Nucleic Acids
1. The two types of nucleic acids, deoxyribonucleic acid (DNA) & ribonucleic acid
(RNA), enable living organisms to reproduce their complex components from
one generation to the next.
2. DNA provides directions for its own replication.
3. DNA directs RNA synthesis and, through RNA, controls protein synthesis.
4. Encoded in the structure of DNA is the information that programs all the cell’s
activities.
5. The site of protein synthesis are structures called ribosomes.
J. The Structure of Nucleic Acids
1. Nucleic acids are macromolecules that exist as polymers called polynucleotides.
2. Each polynucleotide consists of monomers called nucleotides.

3. A nucleotide is composed of three parts:
a) a nitrogenous base
b) a five carbon sugar
c) a phosphate group
4. A nucleoside is composed two parts:
a) a nitrogenous base
b) a five carbon sugar (pentose)
B. Nucleotide Monomers
1. There are two families of nitrogenous bases:
a) pyrimidine - a six membered ring of carbon and nitrogen atoms.
1. Examples: thymine, cytosine, & uracil
2. Thymine is in DNA & uracil is in RNA, cytosine is in both nucleic acids.
b) purines – a larger molecule, with a six-membered ring fused to a five-
membered ring.
Examples: adenine & guanine
2. The nitrogenous bases in DNA are – thymine, adenine, cytosine & guanine.
3. The nitrogenous bases in RNA are – uracil, adenine, cytosine & guanine.
4. The sugar connected to the bases in DNA is deoxyribose.
5. The sugar connected to the bases in RNA is ribose.
C. Nucleotide Polymers
D. The DNA Double Helix
1. The RNA molecules of cells consist of a single polynucleotide chain.
2. DNA molecules consist of two polynucleotides that spiral around an
imaginary axis , forming a double helix (a twisted ladder).
3. Only certain bases in the double helix are compatible with each other. Example:
Adenine (A) always pairs with thymine (T), and guanine (G) always pairs
with cytosine (C).