Polymer Principles

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Transcript Polymer Principles

Polymer Principles
• Most macromolecules are polymers.
– Polymer = large molecule consisting of many identical
or similar subunits connected together.
– Monomer = subunit or building block molecule of a
polymer.
– Macromolecule = large organic polymer
• Formation of macromolecules from smaller building block
molecules represents another level in the hierarchy of
biological organization.
• Four classes
– Carbohydrates, Lipids, Proteins, Nucleic Acids
Structure of Polymers
Classes
Polymers
Subunits (monomers)
Protein
Polypeptide
Amino acid
Carbohydrate
Polysaccharide
Monosaccharide
Lipid
Triglyceride
Fatty acid, glycerol
Nucleic acid
DNA, RNA
Nucleotide
An immense variety of polymers can be built
from a small set of monomers.
• Structural variation of macromolecules is
the basis for the enormous diversity of life.
– There is unity in life as there are only about 40
to 50 common monomers used to construct
macromolecules.
– There is diversity in life as new properties
emerge when these universal monomers are
arranged in different ways.
Proteins
• Monomer = amino acid
– 20 different amino acids commonly occur in
living organisms.
– Structure: 3 parts
• Amino group
• Alpha carbon
• Carboxyl group
• Proteins are polymers of covalently bonded
amino acids.  Peptide bond
Proteins
• Wide variety of functions:
– Structure
• They compose the makeup of hair, bones, and
muscles.
• Example: Keratin found in hair; Collagen is found
in ligaments and tendons.
– Regulation
• Some hormones are proteins. Hormones act as
chemical messengers transported in the blood. They
control body processes. Insulin controls the
concentration of glucose in the blood.
Proteins
• Functions (continued)
– Transport
• Hemoglobin transports oxygen in the blood.
– Contraction
• Actin and myosin are contractile proteins in
muscles. These proteins slide together, shortening
the muscle and producing muscle contraction for
body movement.
Proteins
• Function (continues)
– Catalysts
• All enzymes, which are organic catalysts, are
mainly proteins. The digestion of starch requires an
enzyme. Every step of human metabolism requires
an enzyme in order to function rapidly enough to
support life. Metabolism is the sum of all chemical
reaction that occur in the organism.
Mechanism of Enzyme Action
• The action of an enzyme is specific.
• The substrate binds to an enzyme at the
active site.
• The shape of the active site of the enzyme
and substrate are complementary.
Mechanism of Enzyme Action
• Models of Action
– Lock and key model (older)
• The combination of substrate and enzyme is similar
to how a key (substrate) fits into a lock (enzyme).
Enzyme specificity is related to the complementary
shapes of the enzyme and substrate molecules. Each
substrate, or key, fits into a specific enzyme, or lock.
Mechanism of Enzyme Action
• Models of Action
– Induced-fit model (newer)
• It recognizes that these molecules are not rigid, they
are flexible. As they combine, each mloecule
induces the proper fit of the other one. An enzyme,
for example, can conform to the shape of the
substrate. As it does this it places a strain on the
chemical bonds in the substrate. This can chemically
change the substrate.
Mechanism of Enzyme Action
• Substrate Interactions
– When the enzyme and substrate combine, they form an
intermediate combination, the enzyme-substrate
complex.
– They ate attracted by several kinds of bonds, including
ionic attractions and hydrogen bonding. This
combination forces the substrate into a less stable
shape. This breaks some chemical bonds in the
substrate and forms new ones. In the process, the
substrate molecule is changed into a product.
Mechanism of Enzyme Action
• Substrate Interactions (continue)
– An enzyme is specific in its action.
– Example: Amylase changes the substrate
starch into maltose. This chemical change
occurs when starch is digested.
– After the product is formed and released, the enzyme
amylase can combine with another substrate molecule
and change it into a product.
– Starch is a carbohydrate. The digestion of a lipid or
protein requires different specific enzymes.
Mechanism of Enzyme Action
• Factors Affecting Enzyme Activity
– Temperature
• Enzymatic reactions have an optimum temperature
• At high temperatures, the protein part of the enzyme
denatures. Therefore, the enzyme is disrupted and
loses its activity.
– Most enzymes lose their catalytic ability at 50 to 60 degree
Celsius.
– Internal human body temperature is about 37 degrees
Celsius. The enzymes of human metabolism usually
function at an optimum around this temperature.
Mechanism of Enzyme Action
• Factors Affecting Enzyme Activity
• pH
– Each enzyme has a unique pH that is optimum.
» Salivary amylase functions best at a pH of 7 in
the oral cavity
» Pepsin has a optimal activity at a pH of 2 in the
stomach
» Trypsin works best at a pH of 8 in the small
intestine.
Carbohydrates: Fuel and
Building Materials
• Sugars, the smallest carbohydrates, serve
as fuel and carbon sources
– Carbohydrates = organic molecules made of
sugars and their polymers
• Monomers are simple sugars called
monosaccharides.
• Polymers are formed by condensation rxns.
Monosaccharides
• Simple sugar in which C, H, and O, occur in the
ratio of (CH2O).
– Are major nutrients for cells.
• Glucose is the most common.
– Can be produced by photosynthesic organisms from
CO2, H2O, and sunlight.
– Store energy in their chemical bonds which is harvested
by cellular respiration.
– Their carbon skeletons are raw materials for other
organic molecules.
– Can be incorporated as monomers into disaccharides
and polysaccharides.
Disaccharides
• A double sugar that consists of two
monosaccharides joined by a glycosidic
linkage.
– Glycosidic linkage = covalent bond formed by
a condensation rxn between two sugar
monomers.
• Example: maltose, lactose, sucrose
Polysaccharides
• The polymers of sugars, have storage and
structural.
• Polymers of a few hundred or thousand
monosaccharides.
• Are formed by linking monomers in enzymemediated condensation rxns.
• Two important biological functions:
– Energy storage (starch and glycogen)
– Structural support (cellulose and chitin)
Storage polysaccharide
• Starch = glucose polymer that is a storage
polysaccharide in plants.
– Major sources in the human diet are potatoes and grains
(e.g. wheat, corn, and friuts)
• Glycogen = glucose polymer that is a
storage polysaccharide in animals.
– Stored in the muscle and liver of humans and
other vertebrates.
Structural polysaccharides
• Cellulose
– Major structural component of plant cell walls.
Lipids
• Insoluble in water
• Include fats, oils, and waxes
• Many have three fatty acids attached to a
glycerol molecule. (Triglyceride)
• Fatty acids
– Saturated
– Unsaturated
• Monounsaturated and polyunsaturated
Lipids
• Functions:
– Triglycerides store energy efficiently
• One gram stores about 9 kilocalories.
– This is about twice the amount compared to a gram of
carbohydrate or protein.
– Triglycerides also provide insulation and
cushioning for the body.
– Waxes serve as water repellents on plant leaves,
animal fur, and bird feathers
Lipids
• Phospholipids
– Similar to triglycerides except that one of the fatty acid
chains is replaced by a phosphate group.
– Phosphates are polar.
– Function: Structural foundation of cell membranes.
• Steroids
– Backbone of four linked carbon rings
– Includes cholesterol and hormones, including
testosterone and estrogen.
Nucleic Acids
• Informational polymers
• Nucleic acids store and transmit heredity
information
• Two types of nucleic acids
– DNA- deoxyribonucleic acid
– RNA- ribonucleic acid
• Flow of information
– DNA  RNA  protein
Nucleic Acids
• A nucleic acid strand is a polymer of
nucleotides
– Monomer = nucleotide
• Three parts
– Nitrogenous base
» Pyrimidines  cytosine, thymine, and uracil
» Purines  adenine and guanine
– Pentose sugar
– Phosphate group