1. Major fuel for cells
2. Serve a structural role as parts of other molecules (proteins, DNA, RNA, tissues)
3. Short-term energy storage
1. Major fuel for cells
2. Long-term energy storage
3. Membrane assembly
(CH2O)n where n = 3 to 7
Carbohydrates are hydrated carbon skeletons
With carbonyl at end = aldehyde => "aldose"
With carbonyl in middle = ketone => "ketose"
To include number of C in backbone:
ex: aldoTRIose or ketoTRIose
Disaccharides / Oligosaccharides / Polysaccharides
2 mono saccharides
A few saccharides
(GLYCAN = polysaccharide)
Chiral Center / Stereoisomers
All carbohydrates have at least one chiral center (except dihydroxyacetone).
Possible number of stereoisomers = 2n where n is the number of chiral centers
Most hexoses of living organisms are D-isomers. But the L-isomer is possible.
Most Common Aldoses
D-Ribose, D-Arabinose, D-Xylose
D-Glucose, D-Mannose, D-Galactose
Is how the linear carbohydrate becomes a five- or six-membered ring. (It loses the carbonyl group)
Two possible isomers of the hemiacetal (or anomeric) carbon where:
Alpha: -OH is below the ring
Beta: -OH is above the ring
Hydrolysis Reaction (re: Carbohydrates)
Hydrolysis: Breaks apart a polaysaccharide using a water molecule.
Condensation Reaction (re: Carbohydrates)
Condensation: Joins 2+ saccharides together by removing an OH, H, to create a glycosidic bond.
(Water is created as a byproduct)
Note: Linkages can occur at the 1 - 1, 1 - 2, 1 - 3, 1 - 4, 1 - 6
Why are carbohydrates so diverse?
1. Many many monosaccharides and derivatives
2. Rings can be 5- or 6-membered
3. Anomeric carbon can be alpha or beta
4. Multiple positions for possible glycosidic links
(1 - 1, 1 - 4 etc.)
5. Monomers can be di, oligo, or poly- aka have various lengths
Common Carbohydrate Derivatives
Glucose + Glucose = Maltose
Galactose + Glucose = Lactose
Carbohydrates as Energy Storage in Plants/Microbes
Starch are glucose polysaccharides.
Starches are made of:
Amylose is an alpha 1-4 polymer
Amylopectin is an alpha 1-4 and alpha 1-6 polymer
Amylopectin is branched due to the 1-6 linkages.
Carbohydrates as Structural Source in Plants
Cellulose (similar to amylose):
- Found in plant cell walls.
- Packs tightly into fibers via H-bonds.
- Is a linear polymer.
Is broken down by cellulases which humans don't have, but cows and microbes do! Humans cannot hydrolyze the beta 1-4 link to break cellulose down.
Carbohydrates as Energy Storage in Human/Microbes
Glycogen is a glucose polysaccharide.
Similar to amylopectin but even more branched! Granules of glycogen are smaller than granules of amylopectin.
Glycogen is heavily weighted with H2O in the body.
Why use polymers for energy storage?
1. A large enough number of monors to supply sufficient energy would mess up osmalarity (it would be too high and water would try to push into a cell.)
2. High numbers of monomers would make the uptake of glucose from blood more difficult.
3. Storage of polymers allows for the regulation of monomers, aka the controlled release of monomers by glycogen phosphorylase.
Why don't carbohydrates have 2º or 3º structures?
Carbohydrates are hydrophillic and thus, there's no hydrophobic effect propelling internal folding.
They're also reasonably flexible because they're single bonds (no planar bonds like in peptides)
An enzyme that catalyzes hydrolysis of glycogen to produce glucose.
Where is glycogen stored?
Primarily in the liver.
As well as in muscles for short-term energy.
Composition of Biological Membranes
(which accounts for ~ 1/3 of all proteins!)
(mix of saturated and unsaturated lipids)
Cell Membrane Permeability
H2O, O2, N2, CO2, small hydrophobic molecules
any ion (+ or -), sugars - carbohydrates, amino acids, proteins, nucleotides
1. Triacylglycerol (TAG)
4. Sterols (aka cholesterol)
Saturated vs. Unsaturated lipids
Saturated lipids: (butter)
Solid at room temperature
Can pack together tightly
Unsaturated lipids (oil)
Liquid at room temperature
Have a cis or trans double bond or "kink"
Pack loosely due to the kinks
polyunsaturated fatty acid
ex: omega-3 and omega-6 fatty acids
Why use triglycerides (fat) rather than glycogen (carb) as fuel storage?
Triglycerides 1. are hydrophobic and don't have the extra weight of water; and 2. oxidation of a triglyceride provides about twice as much energy.
The body has about a day's worth of glycogen in the body, but weeks worth of triglycerides.
Lipid Structure (& Membrane Structure)
Lipids are amphiphatic.
Lipids are composed of one more fatty acid.
Each fatty acid is a hydrophillic head (COO-) and a hydrophobic tail made of hydrocarbons.
These come together to form a bilayer
where the outside layers are hydrophillic and the inside of the membrane is hydrophobic.
Fat cells that store a large amount of triglycerides (fatty acids) as fat droplets.
Additionally, lipases catalyzes the hydrolysis of triglycerides, to export the fat to other sites to be used as fuel.
5 Types of Membrane Lipids
3. Galactolipids and Sulfolipids (plants)
4. Archael tetraether lipids