Transcript Macromolecules

Macromolecules and Nutrition
 Macro means large
 Macromolecules are large complex
molecules essential for life
 Carbohydrates
 Lipids
 Proteins
 Nucleic Acids
Human Nutrition
 Human Nutrition, study of how food affects the
health and survival of the human body.
 Human beings require food to grow, reproduce, and
maintain good health. Without food, our bodies could
not stay warm, build or repair tissue, or maintain a
heartbeat.
 Eating the right foods can help us avoid certain
diseases or recover faster when illness occurs.
Human Nutrition
 These and other important functions are fueled by
chemical substances in our food called nutrients.
 Nutrients are classified as carbohydrates,
proteins, fats, vitamins, minerals, and water.
 When we eat a meal, nutrients are released from
food through digestion.
Human Nutrition: Digestion
 Digestion begins in the mouth by the action of
chewing and the chemical activity of saliva, a
watery fluid that contains enzymes, certain proteins
that help break down food.
Human Nutrition: Digestion
 Further digestion occurs as food travels through
the stomach and the small intestine, where
digestive enzymes and acids liquefy food and
muscle contractions push it along the digestive tract.
Holt, Modern Biology
Human Nutrition: Digestion
 Nutrients are absorbed from the inside of the
small intestine into the bloodstream and carried
to the sites in the body where they are needed.
 At these sites, several chemical reactions occur that
ensure the growth and function of body tissues.
 The parts of foods that are not absorbed continue
to move down the intestinal tract and are
eliminated from the body as feces.
Human Nutrition: Digestion
 Once digested, carbohydrates, proteins, and fats
provide the body with the energy it needs to
maintain its many functions.
 Scientists measure this energy in kilocalories, the
amount of energy needed to raise 1 kilogram of water
1 degree Celsius.
 In nutrition discussions, scientists use the term
calorie instead of kilocalorie as the standard unit of
measure in nutrition.
Nutrition: Nutrients
 Nutrients are classified as essential or
nonessential.
 Nonessential nutrients are manufactured in the
body and do not need to be obtained from food.
 Examples include cholesterol, a fatlike substance
present in all animal cells.
Nutrition: Nutrients
 Essential nutrients must be obtained from food
sources, because the body either does not
produce them or produces them in amounts too
small to maintain growth and health.
 Essential nutrients include water, carbohydrates,
proteins, fats, vitamins, and minerals.
Nutrition: Nutrients
 An individual needs varying amounts of each
essential nutrient, depending upon such factors as
gender and age.
 Specific health conditions, such as pregnancy,
breast-feeding, illness, or drug use, make unusual
demands on the body and increase its need for
nutrients.
 Dietary guidelines, which take many of these factors
into account, provide general guidance in meeting
daily nutritional needs.
Nutrition: Nutrients
 If the importance of a nutrient is judged by how long
we can do without it, water ranks as the most
important.
 A person can survive only eight to ten days
without water, whereas it takes weeks or even
months to die from a lack of food.
Nutrition: Water
 Water circulates through our blood and lymphatic
system, transporting nutrients to cells and
removing wastes through urine and sweat.
 Water also maintains the natural balance between
dissolved salts and water inside and outside of
cells.
 Our joints and soft tissues depend on the
cushioning that water provides for them.
Nutrition: Water
 While water has no caloric value and therefore is
not an energy source, without it in our diets we
could not digest or absorb the foods we eat or
eliminate the body’s digestive waste.
 The human body is 65 percent water, and it takes
an average of eight to ten cups to replenish the
water our bodies lose each day.
Nutrition: Water
 How much water a person needs depends largely on
the volume of urine and sweat lost daily, and water
needs are increased if a person suffers from diarrhea
or vomiting or undergoes heavy physical exercise.
 Water is replenished by drinking liquids, preferably
those without caffeine or alcohol, both of which
increase the output of urine and thus dehydrate the
body.
Nutrition: Water
Many foods are also a good source of water—fruits and
vegetables, for instance, are 80 to 95 percent water;
meats are made up of 50 percent water; and grains,
such as oats and rice, can have as much as 35
percent water.
Nutrition: Carbohydrates
 Carbohydrates are the human body’s key source
of energy, providing 4 calories of energy per gram.
 When carbohydrates are broken down by the
body, the sugar glucose is produced; glucose is
critical to help maintain tissue protein, metabolize
fat, and fuel the central nervous system and body
cells.
Nutrition: Carbohydrates
 Glucose is absorbed into the bloodstream
through the intestinal wall.
 Some of this glucose goes straight to work in our
brain cells and red blood cells, while the rest
makes its way to the liver and muscles, where it
is stored as glycogen (animal starch), and to fat
cells, where it is stored as fat.
 Glycogen is the body’s auxiliary energy source,
tapped and converted back into glucose when we
need more energy.
Nutrition: Carbohydrates
 Although stored fat can also serve as a backup
source of energy, it is never converted into
glucose.
 Fructose and galactose, other sugar products
resulting from the breakdown of carbohydrates,
go straight to the liver, where they are converted
into glucose.
Nutrition: Carbohydrates
 Starches and sugars are the major
carbohydrates.
 Common starch foods include whole-grain
breads and cereals, pasta, corn, beans, peas, and
potatoes.
 Naturally occurring sugars are found in fruits
and many vegetables; milk products; and honey,
maple sugar, and sugar cane.
Nutrition: Carbohydrates
 Foods that contain starches and naturally occurring
sugars are referred to as complex carbohydrates,
because their molecular complexity requires our
bodies to break them down into a simpler form to
obtain the much-needed fuel, glucose.
 Our bodies digest and absorb complex
carbohydrates at a rate that helps maintain the
healthful levels of glucose already in the blood.
Nutrition: Carbohydrates
 In contrast, simple sugars, refined from naturally
occurring sugars and added to processed foods,
require little digestion and are quickly absorbed by
the body, triggering an unhealthy chain of events.
 The body’s rapid absorption of simple sugars
elevates the levels of glucose in the blood, which
triggers the release of the hormone insulin.
Nutrition: Carbohydrates
 Insulin reins in the body’s rising glucose levels,
but at a price: Glucose levels may fall so low
within one to two hours after eating foods high in
simple sugars, such as candy, that the body
responds by releasing chemicals known as antiinsulin hormones.
 This surge in chemicals, the aftermath of eating a
candy bar, can leave a person feeling irritable and
nervous.
Nutrition: Carbohydrates
 Many processed foods not only contain high levels of
added simple sugars, they also tend to be high in fat
and lacking in the vitamins and minerals found
naturally in complex carbohydrates.
 Nutritionists often refer to such processed foods as
junk foods and say that they provide only empty
calories, meaning they are loaded with calories from
sugars and fats but lack the essential nutrients our
bodies need.
Nutrition: Carbohydrates
 In addition to starches and sugars, complex
carbohydrates contain indigestible dietary fibers.
 Although such fibers provide no energy or building
materials, they play a vital role in our health.
 Found only in plants, dietary fiber is classified as
soluble or insoluble.
Nutrition: Carbohydrates
 Soluble fiber, found in such foods as oats, barley,
beans, peas, apples, strawberries, and citrus fruits,
mixes with food in the stomach and prevents or
reduces the absorption by the small intestine of
potentially dangerous substances from food.
 Soluble fiber also binds dietary cholesterol and
carries it out of the body, thus preventing it from
entering the bloodstream where it can accumulate
in the inner walls of arteries and set the stage for high
blood pressure, heart disease, and strokes.
Nutrition: Carbohydrates
 Insoluble fiber, found in vegetables, whole-grain
products, and bran, provides roughage that speeds
the elimination of feces, which decreases the time
that the body is exposed to harmful substances,
possibly reducing the risk of colon cancer.
 Studies of populations with fiber-rich diets, such as
Africans and Asians, show that these populations have
less risk of colon cancer compared to those who eat
low-fiber diets, such as Americans.
Nutrition: Carbohydrates
 In the United States, colon cancer is the third most
common cancer for both men and women, but
experts believe that, with a proper diet, it is one of the
most preventable types of cancer.
 Nutritionists caution that most Americans need to eat
more complex carbohydrates.
Nutrition: Carbohydrates
 In the typical American diet, only 40 to 50 percent of
total calories come from carbohydrates—a lower
percentage than found in most of the world. To make
matters worse, half of the carbohydrate calories
consumed by the typical American come from
processed foods filled with simple sugars.
Nutrition: Carbohydrates
 Experts recommend that these foods make up no
more that 10 percent of our diet, because these foods
offer no nutritional value.
 Foods rich in complex carbohydrates, which provide
vitamins, minerals, some protein, and dietary fiber
and are an abundant energy source, should make up
roughly 50 percent of our daily calories.

"Human Nutrition," Microsoft® Encarta®
Encyclopedia 99. © 1993-1998 Microsoft Corporation.
All rights reserved.
IPS: Chemistry Review
 Atom- basic unit of matter
 Protons- positive charge, located in the nucleus
 Neutrons- neutral, located in the nucleus
 Electrons- negative charge, located outside the
nucleus
IPS - Chemistry Review
 Element- made of only one kind of atom. The number of
protons determines what the element is called. In an atom,
the number of protons and electrons are equal.
 The same element will always have a set number of
protons.
 The number of neutrons may vary. These are called
isotopes.
 Electrons may also vary. These are called ions.
IPS - Chemistry Review
 The ion is determined by the number of electrons in the
outer shell or orbit. These are called valence electrons.
 If an atom gains electrons, it becomes negatively
charged.
 If an atom loses electrons, it becomes positively charged.
IPS - Chemistry Review
Bonds- joining two or more atoms together
Ionic bond- formed by joining two ions together
Example: NaCl
Co-Valent bond-formed by the sharing of electrons
Example: C6H12O6
Common molecules
Macromolecules: Carbohydrates
Carbohydrates
made of C,H,O
Sugar
Starch
The ratio of hydrogen to oxygen is 2:1
Cellulose
Carbohydrates
Sugar- manufactured in green plants.
Provides the basic fuel for both plant
and animal life.
Carbohydrates
Sugar
Monosaccharides
Mono = one
saccharide = sugar
Disaccharide
Di = two
Polysaccharide
Poly = many
Carbohydrates
Sugar
Monosaccharides- simple sugars that may contain 5 or 6
carbon atoms. Examples: Glucose, Fructose, Galactose
These simple sugars are made in plant cells. They have the
same empirical or molecular formula: C6 H12 O6.
Their structural formulas are different.
Monosaccharides
Monosaccharides
Glucose
Fructose
Galactose
Monosaccharides
Structural formulas allow you to visualize the molecule.
Notice, even though these molecules all have the same number
of each atom, they look different.
Holt, Modern Biology
Disaccharides
 Disaccharides
Di = two
 Two simple sugars form one molecule of a double sugar.
One molecule of water is given off. This is called a
dehydration synthesis reaction.
 De = away
 hydro = water
 synthesis = put together
Disaccharides
Disaccharides
Maltose
Sucrose
Lactose
Disaccharides
Glucose + glucose
C6H12O6 + C6H12O6
maltose + water
C12H22O11 + H2O
Dehydration synthesis- take away water to put a molecule together
Holt, Modern Biology
Disaccharides
Dehydration synthesis- take away water to put a molecule together
Glucose + fructose
sucrose + water
C6H12O6 + C6H12O6
C12H22O11 + H2O
Sucrose is common table sugar. It is found in sugar cane and
sugar beets.
Dehydration Synthesis
Prentice Hall, Biology
Review
Disaccharides
Dehydration synthesis- take away water to put a molecule together
Glucose + galactose
C6H12O6 + C6H12O6
lactose + water
C12H22O11 + H2O
Lactose is milk sugar, found in the milk of mammals.
Disaccharides
Can these reactions be reversed to break the disaccharide apart into
two monosaccharides?
Yes. What must be added? What is the process called?
Water must be added. The process is called hydrolysis.
Hydro = water
lysis = break apart or to break down
Disaccharides
This is an example of Hydrolysis. Water is added to maltose in
order to break it down into two glucose molecules. Of course,
enzymes would control this process.
Holt, Modern Biology
Hydrolysis
Prentice Hall, Biology
Hydrolysis
Prentice Hall, Biology
Review
Polysaccharides
 Polysaccharides are large molecules formed
by joining monosaccharides.
 Poly = many
How to Make a Polysaccharide
 Slap together three or more mono’s

Keep on condensing (or dehydrating)
(From a plant)
Carbohydrates: Starch
 Starch is a polysaccharide made up of glucose units in
branched chains.
 Each time a glucose molecule is added, one water
molecule is removed (dehydration synthesis).
 There may be 500 to many thousands of glucose
molecules joined to form a starch molecule.
 Examples: potatoes,corn, rice, wheat, and other grains.
Carbohydrates
Nutrition
 When we eat carbohydrates, the molecules
are broken apart to form simple sugars.
 Water must be added for this process to
occur (hydrolysis).
Carbohydrates: Glycogen
 Glycogen is animal starch.
 It is made of highly branched chains of
glucose molecules.
 It is produced in the liver and stored in the
liver and muscles.
 When extra energy is needed, the liver
converts glycogen into glucose.
Polysaccharide: Glycogen
(From an animal)
Carbohydrates: Cellulose
 Cellulose is a large polysaccharide made of
chains of glucose molecules.
 It may contain as many as 3,000 glucose
molecules.
 Cellulose forms a strong fibrous structure in
plant cell walls. It gives the walls support.
Polysaccharide: Cellulose
Lipids
Carbohydrates
Macromolecules
Proteins
Nucleic Acids
Network Tree
Starch
Cellulose
Glycogen
Carbohydrates
(C,H,O)
1
Sugar
Monosaccharide
Glucose
3+
Polysaccharide
Galactose
Fructose
2
Disaccharide
Lactose
Maltose
Sucrose
Monosaccharides
Structural formulas allow you to visualize the molecule.
Notice, even though these molecules all have the same number
of each atom, they look different.
Holt, Modern Biology
Disaccharides: How are they put together?
Dehydration synthesis- take away water to put a molecule together
Glucose + glucose
maltose + water
Glucose + fructose
sucrose + water
Glucose + galactose
C6H12O6 + C6H12O6
lactose + water
C12H22O11 + H2O
Dehydration Synthesis:
What does it look like?
Prentice Hall, Biology
Disaccharides:
How do we digest them?
Hydrolysis. Water is added to maltose in order to break it down
into two glucose molecules. Of course, enzymes would control
this process.
Holt, Modern Biology
Compare and Contrast
Starch
Plants
Glycogen
Stored for later,
converted into
glucose for
respiration..
Branched chains
of glucose
Big
Animals
Compare and Contrast
Starch
Branched chains
Stored for later,
converted into
glucose for
respiration.
Cellulose
Carbohydrates
Polysaccharides
glucose
Big
Straight Chains
Found in plant
cell walls
Used for support
Nutrition: Lipids
 Fat stored in the body cushions vital organs and
protects us from extreme cold and heat.
 Fat consists of fatty acids attached to a
substance called glycerol.
 Dietary fats are classified as saturated,
monounsaturated, and polyunsaturated
according to the structure of their fatty acids (see
Fats and Oils).
Nutrition: Lipids
 Fats, which provide 9 calories of energy per gram,
are the most concentrated of the energyproducing nutrients, so our bodies need only
very small amounts.
 Fats play an important role in building the
membranes that surround our cells and in
helping blood to clot.
 Once digested and absorbed, fats help the body
absorb certain vitamins.
Nutrition: Lipids
 Animal fats—from eggs, dairy products, and
meats—are high in saturated fats and cholesterol,
a chemical substance found in all animal fat.
 Vegetable fats—found, for example, in avocados,
olives, some nuts, and certain vegetable oils—are
rich in monounsaturated and polyunsaturated fat.
 As we will see, high intake of saturated fats can be
unhealthy.
Nutrition: Lipids
 To understand the problem with eating too much
saturated fat, we must examine its relationship to
cholesterol.
 High levels of cholesterol in the blood have been
linked to the development of heart disease, strokes,
and other health problems.
 Despite its bad reputation, our bodies need
cholesterol, which is used to build cell membranes,
to protect nerve fibers, and to produce vitamin D
and some hormones, chemical messengers that
help coordinate the body’s functions.
Nutrition: Lipids
 We just do not need cholesterol in our diet. The
liver, and to a lesser extent the small intestine,
manufacture all the cholesterol we require.
 When we eat cholesterol from foods that contain
saturated fatty acids, we increase the level of a
cholesterol-carrying substance in our blood that
harms our health.
Nutrition: Lipids
 Cholesterol, like fat, is a lipid—an organic
compound that is not soluble in water.
 In order to travel through blood, cholesterol
therefore must be transported through the body in
special carriers, called lipoproteins.
 High-density lipoproteins (HDLs) remove
cholesterol from the walls of arteries, return it to the
liver, and help the liver excrete it as bile, a liquid
acid essential to fat digestion.
 For this reason, HDL is called "good" cholesterol.
Nutrition: Lipids
 Low-density lipoproteins (LDLs) and very-lowdensity lipoproteins (VLDLs) are considered
"bad" cholesterol.
 Both LDLs and VLDLs transport cholesterol from
the liver to the cells.
 As they work, LDLs and VLDLs leave plaqueforming cholesterol in the walls of the arteries,
clogging the artery walls and setting the stage for
heart disease.
Nutrition: Lipids
 Almost 70 percent of the cholesterol in our
bodies is carried by LDLs and VLDLs, and the
remainder is transported by HDLs.
 For this reason, we need to consume dietary fats
that increase our HDLs and decrease our LDL and
VLDL levels.
Nutrition: Lipids
 Saturated fatty acids—found in foods ranging from
beef to ice cream, to mozzarella cheese to
doughnuts—should make up no more than 10
percent of a person’s total calorie intake each day.
 Saturated fats are considered harmful to the heart
and blood vessels because they are thought to
increase the level of LDLs and VLDLs and decrease
the levels of HDLs.
Nutrition: Lipids
 Monounsaturated fats—found in olive, canola, and
peanut oils—appear to have the best effect on blood
cholesterol, decreasing the level of LDLs and VLDLs
and increasing the level of HDLs. Polyunsaturated
fats—found in margarine and sunflower, soybean,
corn, and safflower oils—are considered more
healthful than saturated fats.
 However, if consumed in excess (more than 10
percent of daily calories), they can decrease the blood
levels of HDLs.
Nutrition: Lipids
 Most Americans obtain 15 to 50 percent of their daily
calories from fats.
 Health experts consider diets with more than 30
percent of calories from fat to be unsafe, increasing
the risk of heart disease.
 High-fat diets also contribute to obesity, which is
linked to high blood pressure and diabetes mellitus.
Nutrition: Lipids
 A diet high in both saturated and unsaturated fats has
also been associated with greater risk of developing
cancers of the colon, prostate, breast, and uterus.
 Choosing a diet that is low in fat and cholesterol is
critical to maintaining health and reducing the risk of
life-threatening disease.

"Human Nutrition," Microsoft® Encarta® Encyclopedia 99. ©
1993-1998 Microsoft Corporation. All rights reserved.
Macromolecules: Lipids
 Lipids are macromolecules made of carbon,
hydrogen, and oxygen.
 The ratio of hydrogen to oxygen is much
greater than 2:1.
 Lipids are made of fatty acids attached to
alcohol.
 Examples: fats, oil, waxes and cholesterol.
Macromolecules: Lipids
Fat molecule = 3 fatty acid molecules plus one alcohol
(glycerol).
3 Hydrogen ions are removed from glycerol and 1 hydroxide (OH)
ion is removed from each fatty acid to make 1 fat molecule (C-O-C
bonds are formed) + 3 water molecules. This process is called….
Dehydration Synthesis.
Lipids
 Composed of fatty acids and glycerol
Dehydration Synthesis of Fat
Prentice Hall, Biology
Lipids
Excess food is stored as fat in animals. It is found in
tissues and as butterfat in milk and other dairy products.
Recall Carbohydrates, to answer the following:
To break down the fat molecule to use it for energy, we
would add ….., in the process called...
Water…….Hydrolysis.
Lipids: Triglycerides
 Useful for long-term storage of energy;
warmth; organ protection (cushion)
 What reaction took place?
Lipids: Phospholipids
 Cell membranes, remember?
Lipids: Steroids
 Many animal hormones are steroids

E.g., testosterone
Lipids: Cholesterol
 Cholesterol is a large lipid molecule located
in the cell membranes of animals.
 Cholesterol- needed by nerve cells
 In excess, it can form deposits on the inner
walls of blood vessels making them less
elastic and leaving less room for blood flow.
Lipids: Unsaturated Fats
 Too much fat = bad (heart disease)


Unsaturated better than saturated
Unsaturated –> increase HDLs over LDLs
Lipids: Oils/Waxes
Oils
Oils are lipids that are liquid at room temperature.
Examples: vegetable oils such as, corn, peanut, soybean.
Waxes
Waxes are made of fatty acids joined to an alcohol other than
glycerol. They are solid at room temperature.
Nutrition: Proteins
 Dietary proteins are powerful compounds that build
and repair body tissues, from hair and fingernails to
muscles.
 In addition to maintaining the body’s structure,
proteins speed up chemical reactions in the body,
serve as chemical messengers, fight infection, and
transport oxygen from the lungs to the body’s tissues.
Nutrition: Proteins
 Although protein provides 4 calories of energy per
gram, the body uses protein for energy only if
carbohydrate and fat intake is insufficient.
 When tapped as an energy source, protein is
diverted from the many critical functions it performs
for our bodies.
Nutrition: Proteins
 Proteins are made of smaller units called amino
acids.
 Of the more than 20 amino acids our bodies require,
eight (nine in some older adults and young children)
cannot be made by the body in sufficient quantities to
maintain health.
 These amino acids are considered essential and
must be obtained from food.
Nutrition: Proteins
 When we eat food high in proteins, the digestive tract
breaks this dietary protein into amino acids.
 Absorbed into the bloodstream and sent to the cells
that need them, amino acids then recombine into the
functional proteins our bodies need.
Nutrition: Proteins
 Animal proteins, found in such food as eggs, milk,
meat, fish, and poultry, are considered complete
proteins because they contain all of the essential
amino acids our bodies need.
 Plant proteins, found in vegetables, grains, and
beans, lack one or more of the essential amino acids.
 However, plant proteins can be combined in the diet
to provide all of the essential amino acids.
Nutrition: Proteins
 A good example is rice and beans.
 Each of these foods lacks one or more essential
amino acids, but the amino acids missing in rice are
found in the beans, and vice versa. So when eaten
together, these foods provide a complete source of
protein.
 Thus, people who eat only vegetables (see
Vegetarianism) can meet their protein needs with
diets rich in grains, dried peas and beans, rice, nuts,
and tofu, a soybean product.
Nutrition: Proteins
 Experts recommend that protein intake make up only
10 percent of our daily calorie intake.
 Some people, especially in the United States and
other developed countries, consume more protein
than the body needs.
 Because extra amino acids cannot be stored for later
use, the body destroys these amino acids and
excretes their by-products.
Nutrition: Proteins
 Alternatively, deficiencies in protein consumption,
seen in the diets of people in some developing
nations, may result in health problems.
 Marasmus and kwashiorkor, both life-threatening
conditions, are the two most common forms of
protein malnutrition.
Nutrition: Proteins
 Some health conditions, such as illness, stress, and
pregnancy and breast-feeding in women, place an
enormous demand on the body as it builds tissue or
fights infection, and these conditions require an
increase in protein consumption.
 For example, a healthy woman normally needs 45
grams of protein each day.
 Experts recommend that a pregnant woman consume
55 grams of protein per day, and that a breast-feeding
mother consume 65 grams to maintain health.
Nutrition: Proteins
 A man of average size should eat 57 grams of protein
daily.
 To support their rapid development, infants and
young children require relatively more protein than do
adults.
 A three-month-old infant requires about 13 grams of
protein daily, and a four-year-old child requires about
22 grams.
Nutrition: Proteins
 Once in adolescence, sex hormone differences
cause boys to develop more muscle and bone than
girls; as a result, the protein needs of adolescent
boys are higher than those of girls.

"Human Nutrition," Microsoft® Encarta® Encyclopedia 99. ©
1993-1998 Microsoft Corporation. All rights reserved
Macromolecules: Proteins
 Proteins are the most common organic
molecule in living cells.
 They are made of carbon, hydrogen,
oxygen, nitrogen and sometimes sulfer.
CHON(S)
 Proteins are made of amino acids. There
are approximately 20+ amino acids.
Macromolecules: Proteins
Proteins are large complex polypeptides.
Prentice Hall,
Biology
Think of the amino acids as letters and proteins as words in
making up a sentence.
Proteins may contain as few as 50 or as many as 3,000 amino
acid molecules. The number of possible combinations of amino
acids is staggering. We have tens of thousands of different
proteins.
Macromolecules: Proteins
 Amino acids are joined by means of dehydration synthesis.

An OH from the acid group of one amino acid joins to
an H from the amino group of the other amino acid.
 A water molecule is formed, and a C-N bond is formed
between the two amino acids.
 The C-N bond is called a peptide bind.
 Dipeptide: 2 amino acids joined
 Polypeptide: 3 or more amino acids joined.
Proteins
 Composed of amino acids
 Amino acids are joined by peptide
bonds
 The string of peptides is also called
a polypeptide
 Needed for muscles, skin, cell
membranes, and enzymes
Proteins: Structure
 The protein you end up with depends on:



which amino acids were chosen,
their order (sequence), and
how many of each
 Who decides?

The DNA
Proteins: Structure
 Amino acids have three parts:
 The 20+ amino acids differ only in their R-group
Generalized Formula for Amino Acid
H
R
C
Acid group
COOH
NH2
Rest of the molecule
Amino group
Amino Acid Groups
H
NH2
=
N
H
O
COOH =
C O H
Macromolecules: Proteins
 Proteins taken in as food are different than our proteins.
 They must be broken down into amino acids by adding
water. Recall Carbohydrates and Lipids
 The process is…
 Hydrolysis.
 To build proteins water must be removed in the process
of….
 Dehydration Synthesis.
Dehydration Synthesis
Prentice Hall, Biology
Proteins: Structure
 Compare 3 amino acids:
Category 1
Category 2
Let’s Review
What is the name of
this unit?
Category 3
Category 4
Proteins: Enzymes
 Enzyme, any one of many specialized organic
substances, composed of polymers of amino acids,
that act as catalysts to regulate the speed of the many
chemical reactions involved in the metabolism of living
organisms.
 The name enzyme was suggested in 1867 by the
German physiologist Wilhelm Kühne (1837-1900); it is
derived from the Greek phrase en zymç, meaning "in
leaven.”
 Those enzymes identified now number more than 700.
Proteins: Enzymes
 Enzymes are classified into several broad categories,
such as hydrolytic, oxidizing, and reducing,
depending on the type of reaction they control.
 Hydrolytic enzymes accelerate reactions in which a
substance is broken down into simpler compounds
through reaction with water molecules.
Proteins: Enzymes
 Oxidizing enzymes, known as oxidases, accelerate
oxidation reactions; reducing enzymes speed up
reduction reactions, in which oxygen is removed.
 Many other enzymes catalyze other types of
reactions.
Proteins: Enzymes
 Individual enzymes are named by adding ase to the
name of the substrate with which they react.
 The enzyme that controls urea decomposition is
called urease; those that control protein hydrolyses
are known as proteinases.
 Some enzymes, such as the proteinases trypsin and
pepsin, retain the names used before this
nomenclature was adopted.
Proteins: Enzymes
 Some enzymes, such as pepsin and trypsin, which
bring about the digestion of meat, control many
different reactions, whereas others, such as urease,
are extremely specific and may accelerate only one
reaction.
 Still others release energy to make the heart beat
and the lungs expand and contract.
Proteins: Enzymes
 Many facilitate the conversion of sugar and foods into
the various substances the body requires for tissuebuilding, the replacement of blood cells, and the
release of chemical energy to move muscles.
Proteins: Enzymes
 As a class, enzymes are extraordinarily efficient.
 Minute quantities of an enzyme can accomplish at
low temperatures what would require violent reagents
and high temperatures by ordinary chemical means.
 About 30 g (about 1 oz) of pure crystalline pepsin, for
example, would be capable of digesting nearly 2
metric tons of egg white in a few hours.
Proteins: Enzymes
 The kinetics of enzyme reactions differ somewhat
from those of simple inorganic reactions.
 Each enzyme is selectively specific for the
substance in which it causes a reaction and is most
effective at a temperature peculiar to it.
 Although an increase in temperature may accelerate
a reaction, enzymes are unstable when heated.
Proteins: Enzymes
 The catalytic activity of an enzyme is determined
primarily by the enzyme's amino-acid sequence and
by the tertiary structure—that is, the threedimensional folded structure—of the macromolecule.
 Many enzymes require the presence of another ion
or a molecule, called a cofactor, in order to function.
Proteins: Enzymes
 As a rule, enzymes do not attack living cells. As soon
as a cell dies, however, it is rapidly digested by
enzymes that break down protein.
 The resistance of the living cell is due to the
enzyme's inability to pass through the membrane of
the cell as long as the cell lives.
Proteins: Enzymes
 When the cell dies, its membrane becomes
permeable, and the enzyme can then enter the cell
and destroy the protein within it.
 Some cells also contain enzyme inhibitors, known as
antienzymes, which prevent the action of an enzyme
upon a substrate.

"Enzyme," Microsoft® Encarta® Encyclopedia 99. © 1993-1998
Microsoft Corporation. All rights reserved.
Proteins: Enzymes
 Enzymes are proteins that act as a catalyst.
(Catalysts are substances that increase the rate of a
chemical reaction.)
 Enzymes are not used up or changed by a reaction.
 Enzymes are specific in their actions.
 Enzymes work best under specific conditions.
Substrate: The substance that the enzyme causes to react.
Enzymes
Nucleic Acids: DNA
4. Nucleic Acids
 DNA or RNA
 Composed of nucleotides
 Each nucleotide has a



Phosphate group
Sugar (deoxyribose or ribose)
Nitrogen base
 4 bases

A, G, C, T (or U in RNA)
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