3.9 Carbohydrates
• Provide building materials and energy storage
• Are molecules that contain carbon, hydrogen
and oxygen in a 1:2:1 ratio
• Are of two main types
– Simple carbohydrates
– Complex carbohydrates
Simple Carbohydrates
• 1. Monosaccharides
– Consist of one subunit
Fig. 3.29
Glucose
Chemical formula: C6H12O6
•glucose, "blood sugar", the immediate source of energy for cellular respiration
•galactose, a sugar in milk (and yogurt), and
•fructose, a sugar found in honey.
Simple Carbohydrates
• 2. Disaccharides
– Consist of two subunits
Formed by a
dehydration
reaction
Sucrose
Fig. 3.30
sucrose - common table sugar
= glucose + fructose
lactose - major sugar in milk
= glucose + galactose
maltose - product of starch digestion
= glucose + glucose
Complex Carbohydrates
• Consist of long polymers of sugar subunits
• Also termed polysaccharides
• Examples:
– Starch provides energy storage in plants
– Glycogen provides energy storage in animals
– Cellulose is found in the cell walls of plants
– Chitin is found in the cell walls of fungi
•Because its linking bonds are flipped, and there are no side chains, cellulose molecules
lie close together with lots of hydrogen bonds.
•Cellulose (your T-shirt and textbook) is long, rigid polymer of glucose that is not sweet.
• All sugars are very soluble in water
because of their many hydroxyl groups.
• Carbohydrates provide the bulk of the
calories in most diets, and starches
provide the bulk of that.
Hydrogen bonds are weak (only 5% the
strength of a covalent bond) but important
• hold water molecules together
• hold proteins together
• hold the two strands of the DNA double helix
together
3.10 Lipids
• Large nonpolar molecules that are insoluble in water
• Lipids are hydrocarbons
hydrogen + carbon
• Three major types
– Fats are energy-storage molecules
– Phospholipids are a major component of cell membranes
– Steroids are often hormones
Fats
• Used for long-term
energy storage
• Also termed
triglycerides or
triacylglycerol
– Composed of
three fatty acid
chains linked to
glycerol
Fig. 3.33
Fats
• Fatty acids can be saturated or unsaturated
Fig. 3.33
Most plant
fats
Most animal
fats
solid at room temperature
liquid at room temperature
•
Monounsaturated fats have one double bond in the fatty acid chains.
olive, peanut, and canola oil.
•
Polyunsaturated fats have two or more double bonds in their fatty acid
chains.
corn, soy bean, cottonseed, sunflower, and
safflower oils.
Read the label!
•
5g total
- 1 g saturated fat
- 0.5 g polyunsaturated fat
-1.5 g monounsaturated fat
=2 g trans fat
•
Trans Fats have been partially
hydrogenated
•
may be worse for your health
than saturated fats
Why is the food industry sneaking in a bad fat?
•
the most abundant (least expensive) source of fat is from liquid plant
oils
•
many cooking applications, particularly baked products, need solid fats
•
the food industry uses hydrogenated oils for things like shortening
and margarine.`
-fewer double bonds
-remaining converted from cis to trans
-straightened so they get closer and
-become solid
Fats are bad for you.
True or False
or ?
• The relationship between fat in the diet and
cardiovascular disease is not proven, but the
evidence seems to indicate that:
-A diet high in fat is harmful.
-Mono and polyunsaturated fats are less
harmful
Have you heard of
omega-3 fatty acids?
• Omega-3 unsaturated fats may be GOOD for you (protective
against cardiovascular disease)
• A DRI of 1.1 grams/day for women and
1.6 grams/day for men was established in September 2002.
• These fats have at least one double bond three carbon atoms in
from the end of the fatty acid chain.
• Fish oils are a rich source of omega-3 fats.
How are fats good for you?
• Fat are our most concentrated form of energy.
Fat =9 kcal/gram Carbohydrates =4 kcal/gram
• The fats we eat give us the building material for our own fat as
well as cholesterol and various phospholipids.
• Our bodies make fat from carbohydrates
(as I know all too well!)
• Three essential fatty acids must be in our diet.
linoleic acid, linolenic acid, arachidonic acid.
Phospholipids
• A modified fat
– One of the three fatty acids is replaced by a
phosphate and a small polar functional group
Fig. 3.34a
• In water, phospholipids aggregate to form a lipid bilayer
more later when we talk about cell membranes
Steroids
• Composed of four carbon rings
• Examples:
– Cholesterol
• Found in most
animal cell
membranes
Fig. 3.34b
– Male and female sex hormones are made of cholesterol
All forms of life have common
features
All are made of cells. All have carbohydrates,
lipids, and proteins.
All forms of life have DNA as their genetic
blueprint.
Each species has its own DNA sequence