Macromolecules — Energy Yielding Nutrients
I. 3 Energy Yielding Nutrients (Macromolecules)
A. Carbohydrates
B. Proteins
C. Lipids
II. Carbohydrates
A. Composed of Carbon and Water (CH2O)n
B. Simple Sugars
1. Monosaccharides and Disaccharides
Glucose + Glucose ————– Maltose
Fructose + Glucose ————– Sucrose
Galactose + Glucose ————- Lactose
a. Glucose
1. most common
b. Fructose
1. Sweetest
2. Isomer of glucose – same atoms, but different
arrangement
3. Shape determines sweetness
a. taste buds
4. Fruits, honey, corn syrup, sweeteners, semen
c. Galactose
1. Isomer of glucose and fructose; least sweet
2. Milk sugar (lactose)
d. Maltose
1. beer and malt liquors
e. Sucrose
1. most abundant disaccharide
2. table sugar, fruits, vegetables, natural sweeteners,
junk food
3. fructose is the sweetest monosaccharide
f. Lactose
1. carbohydrate of milk; about 5% of milk’s weight
2. Chemistry of Glucose (C6H12O6)
a. a.k.a. dextrose
b. 6 carbons, 12 hydrogens, 6 oxygens
c. carbons always have 4 bonds
d. carbons are numbered 1 thru 6
3. Chemistry of Maltose
a. two glucose molecules
b. (14) linkage
c. dehydration synthesis or condensation
d. hydrolysis
1. – amylase
C. Polysaccharides (Complex carbohydrates)
1. Many monosaccharides linked together
2. Starch
a. glucose storage in plant cells
b. wheat, rice, potatoes, legumes (peas and beans)
3. Glycogen
a. glucose storage in animal cells (liver and muscle cells)
4. Cellulose
a. plant cell walls, structure
b. fruits, vegetables, legumes (peas and beans)
c. linear polymer of glucose
d. (14) linkage
e. – amylase cannot recognize this bond
1) humans cannot digest cellulose
2) dietary fiber
f. energy source for
1) bacteria in large intestine
a) production of gases
2) ruminants (cows)
a) guts contain special bacteria that produce
cellulases
3) termites
a) guts contain cellulose digesting protozoans
4) fungi
a) produce enzymes and can live on wood
D. Digestion and Absorption of CHO’s
1. Dietary CHO’s
a. mainly polysaccharides and disaccharides
b. free monosaccharides (glucose and fructose) are rare
1) honey, certain fruits, added sugars to processed
food
c. The cellular use of CHO’s depends on the absorption from
the GI tract to the blood; restricted to monosaccharides
2. Enzymes
Starches — – amylase—– maltose & isomaltose — isomaltase—- glucose
Sucrose —sucrase——— fructose + glucose
Lactose —lactase——— galactose + glucose
Maltose —maltase——— glucose + glucose
NOTES on enzymes:
– – amylase found in saliva and pancreas
– Starch has (14) and (16) linkages
– – amylase breakdown yields maltose and isomaltose
– isomaltose is a disaccharide with a (16) linkages
-isomaltase, sucrase, lactase, and maltase are brush border enzymes
(microvilli)
3. Absorption of monosaccharides
a. occur across enterocytes
b. glucose, galactose, and fructose are absorbed
4. Following absorption of monosaccharides across gut wall, they
enter circulation – carried to the liver via hepatic portal system
5. Liver takes up fructose and galactose and converts them to
some glucose derivative
6. Glucose is taken up by liver, but not completely. Glucose can
pass liver and be distributed to other cells (muscle and
adipose)
7. Liver uptake of glucose is not insulin dependent, but muscle and
adipose take up of glucose is insulin dependent
8. Insulin allows glucose to enter muscle and adipose tissue, this
lowers blood glucose levels
E. Sugars and Health Issues
1. No dietary requirement for CHO’s
a. There are requirements for amino acids and fatty acids
2. Foods that contain high amounts of added sugars
a. Cakes, candies, and soda (junk foods)
b. Empty calorie foods – still get calories but without
vitamins and minerals
1) this can either result in deficiencies of essential
nutrients, or force the individual to eat additional foods with essential nutrients which can lead to too many overall calories (weight gain)
2) You spend 150 of your days calories on one can of
soda which has no other nutrients
3. CHO in fruits, vegetables, and grains generally have vitamins
and minerals
4. Caution: Just because something is natural does not mean it is
nutritious
a) honey is glucose, fructose and sucrose with little vitamins
and minerals
G. Glycemic index
1. Ranking of foods based on the postprandial
blood glucose levels (glucose levels 1-2 hours after meal)
**How fast glucose is absorbed**
2. Presence of nonabsorbable CHO’s such as fibers in
vegetables and fruits slow the rate of absorption of monosaccharides
a) fats and oils also slow the rate of CHO absorption
4.. Eat foods high in fiber
1) fiber cannot be broken down, therefore cannot be
absorbed, therefore do not count as calories
2) also high fiber will slow the absorption of glucose
a)controls insulin levels
H. Food Labels
-Total CHO 23.0 g
-Dietary Fiber 3.0 g
-Sugars 10.0 g
**How much starch? 10.0 g
III. Proteins
A. Composed of 20 common amino acids
B. Amino acid structure
1. Central carbon – four bonds
2. Hydrogen (-H)
3. Carboxylic acid (-COOH)
4. Amino group (-NH2)
5. Side chain (-R group)
C. Side chains make amino acids different
D. Nonessential (dispensable) amino acids
1. Body cells can produce these from other amino acids, CHO, and
fats
E. Essential (indispensable) amino acids
1. nine amino acids that must be supplied by the diet
2. our cells need all amino acids for protein synthesis
F. Quality of Protein
1. Complete proteins – contain all essential amino acids
a. Meat, fish, poultry, eggs, soy
2. Incomplete (poor quality proteins)
a. plant proteins (don’t contain all essential a.a.’s)
*vegetarians can get all essential amino acids by eating a variety of
incomplete proteins in vegetables, nuts, legumes, etc.
G. Peptide Bonds
1. Links –COOH of one amino acid to the -NH2 of another
2. dipeptide, tripeptide, polypeptide
H. Amino acid sequence determines shape and function of protein
1. Hydrophilic amino acids
2. Hydrophobic amino acids
I. Denaturation
1. protein unfolds – shape changes therefore function changes
2. pH, temperature
J. Protein Digestion
1. No chemical digestion in mouth or esophagus
2. Stomach
a. gastrin stimulates release of pepsinogen and HCl
b. HCl denatures proteins and activates pepsinogen to
pepsin
c. pepsin breaks peptide bonds and yields oligopeptides and
polypeptides which end up in chyme
3. Small Instestine
a. Chyme stimulates release of CCK and secretin
b. bicarbonate juice and proenzymes are sent to duodenum
from pancreas
c. Trypsinogen —-enterokinase—– trypsin
e. enterokinase is a brush border enzyme
f. trypsin activates the other proenzymes
g. brush border peptidases
1) yield free amino acids
h. Final product of protein digestion that can absorbed
1) free amino acids
2) di and tripeptides
K. Absorption in small intestines
1. free amino acids and di and tripeptides are absorbed across
brush border into enterocyte
a. Inside enterocyte the peptides are hydrolyzed to free
amino acids
2. Amino acids to hepatic portal vein to liver
a. liver is primary uptake site for ingested amino acids
b. liver monitors absorbed amino acids and adjusts their rate
of metabolism to meet the needs of the body
IV. Lipids
A. Classes
1. Triglycerides
2. Sterols (steroids)
3. Phospholipids
B. Functions
1. structure of cell and organelle membranes
a. phospholipids and cholesterol
2. energy (calories)
3. hormones (steroids)
4. vitamins (fat soluble)
5. digestion of fat (cholesterol)
C. Triglycerides
1. majority of dietary fat (95%)
2. stored in adipose tissue for energy, protection, heat insulation
3. 3 fatty acids and 1 glycerol
D. Fatty Acids (FA’s)
1. hydrocarbon chain with carboxylic acid end
2. range from 4 to 24 carbons long
3. saturated fatty acids (SFA)
a. all single bonds, C-C
4. monounsaturated fatty acids (MUFA)
a. one double bond, C=C
5. polyunsaturated fatty acids (PUFA)
a. two or more double bonds, C=C
6. FAT – triglycerides with long, saturated fatty acids tend to be
solid at room temperature (higher melting point)
7. OIL – triglycerides with short, unsaturated fatty acids tend to be
liquid at room temperature
8. double bonds, C=C, can have cis (U-shape bend) or trans
(linear) configuration
a. most natural FA’s are cis, but some are trans
b. partial hydrogenation
1) process used to make margarine
2) add hydrogen to double bonds to solidify vegetable
oils
3) those cis double bonds not hydrogenated are
converted to trans bonds
4) possible adverse effects of trans fatty acids;
cardiovascular disease
9. linoleic and linolenic FA’s are essential FA’s
a. absence in diet results in retarded growth,
dermatitis, early death
b. omega–3 FA’s in fish oils have been found to decrease
cardiovascular disease
E. Sterols
1. 4 ring core structure (steroid nucleus)
2. Cholesterol is most common
a. only in animals
b. meats, egg yolk
c. essential for life
1. cell membrane structure
2. precursor for sex steroids and Vitamin D
F. Digestion
1. Pancreatic lipase – majority of digestion occurs in small intestine
2. Undigested fats in stomach slow gastric motility and slow gastric
emptying; fats have “high satiety value”
3. Bile emulsifies fat and increases surface area for lipase
6. Triglycerides are broken into monoglycerides and fatty acids
7. Olestra – sucrose molecules linked with long-chain fatty acids
a. taste is essentially indistinguishable from fat
b. not hydrolysable by pancreatic lipase
c. no caloric value
G. Absorption
1. monoglycerides and fatty acids are absorbed into enterocytes
2. In the enterocyte, triglycerides are reformed (using fatty acids
greater than 10-12 C)
3. short chain fatty acids (<10-12 C) can enter into portal blood
4. Chylomicrons are formed within enterocytes
a. lipoprotein – lipids covered with protein coat
b. water soluble
IV. Calorie
A. Unit that measures energy
B. 1 Calorie is the amount of heat necessary to raise the temperature of 1
kilogram (1 liter) of water 1 degree Celsius
C. The amount of energy a food provides depends on its amount of CHO, lipid,
and protein
1. 1 g of CHO —- 4 Cal
2. 1 g of fat — 9 Cal
3. 1 g of protein ——- 4 Cal
4. 1 slice of bread w/ tablespoon of peanut butter
ex) 16 g CHO x 4 kcal/g = 64 kcal
7 g protein x 4 kcal/g = 28 kcal
9 g fat x 9 kcal/g = 81 kcal
——————
173 kcal
To determine the amount of kcal from fat
81 kcal / 173 kcal = .47 x 100 = 47%
47% of the kcal comes from fat
