Lecture 6: Sugars and Lipids Flashcards
Sugar Functions
- storage (ex. starch)
- structure (ex. cellulose; plant cell wall)
- modifies proteins (They modify the part of the membrane protein that face outwards of the cell)
Types of Carbohydrates
Monosaccharides: monomer of glucose
Disaccharides: consist of two monosaccharides
Polysaccharides: are composed of hundreds to hundreds of thousands of monosaccharides
General formula for carbohydrate monomer
- multiples of CH2O, e.g. glucose C6H12O6
- always have same amount of C and O
• A monomer can be either:
1. An aldose: Carbonyl group at
end of carbon chain
2. A Ketose: Carbonyl group in
middle of carbon chain
Isomers
- In many isomers a group is attached to different carbon atoms.
- In Optical isomers (aka stereoisomers) a group is attached in different ways to the same carbon atom. Optical isomers are mirror images of each other.
- Optical isomers occur whenever a carbon has four different atoms or groups attached to it.
Glucose vs. Galactose
- 2^4 = 16 possible stereoisomer combinations
Linear glucose vs. ring form
- sugars can also be in ring form when in water (Oxygen from the 5-C bonds to the 1-C, resulting in a ring structure)
- Can form 2 stereoisomers, alpha and beta.
Glycosidic linkage
- Happens between C#1 and OH group
- Lots of combinations (11)
- Only two are important
- B1-4 linkage and A1-4 linkage
Alpha 1,4 Linkage
- Creates Maltose
- Not easily broken (stable)
- The swiggle bond denotes that it can still open and close (denotes unknown or unspecified orientation)
- free OH on C#1 allows conversion to aldehyde
- BELOW SEA LEVEL
- results in starch: moderately branched, amylopectin in plants
highly branched, glycogen in animals (used for energy storage in animal cells)
Beta 1,4 Linkage
- ABOVE SEA LEVEL
- Makes cellobiose, which gives rise to cellulose (always unbranched)
- In reality you have to flip second molecule around 180 so that HO-CH2 is pointing down, and the covalent bond is straight.
- The flipping of the second glucose molecule gives rise to different property (symmetrical), then the molecules is very linear and stable structure (lots of H-bonds)
- Found in plant cell walls, and wood
Lipids
• Insoluble in water •Roles for lipids in organisms include: - Energy storage (fats and oils) - Cell membranes (phospholipids) - Capture of light energy (carotenoids) - Hormones and vitamins (steroids and modified fatty acids) - Thermal insulation - Electrical insulation of nerves - Water repellency (waxes and oils)
Beta- Carotene
- found in carrots, split into vitamin A (important for eyesight)
Steroids
- Vitamin A and D are added to milk because they are lipid soluble (only take up vitamins with the fat)
Fatty Acid
- has carboxyl group
- has hydrocarbon chain
- depending on how long the chain is, determines how water soluble it is
Fats from via..
- dehydration reactions: Glycerol molecule + three fatty acids which form 3 ester linkages
Phospholipids
- have two hydrophobic fatty acids (tails) and one hydrophilic head group attached to glycerol
- consist of choline & phosphate group (hydrophilic)
- Fatty Acid (2) (hydrophobic)
Lipid Bilayers
• Hydrophilic heads interacts with water
• Hydrophobic tails interact with one another
- form this on their own
- depends on temperature
How do bilayers seal?
- It is energetically favorable for bilayers to seal, that is to form an enclosed space
- still have edges that are exposed
- If they close, they form a ball
- If you have phospholipids, it just happens on its own
Phospholipids; lateral motion
- Phospholipids are in constant lateral motion, but rarely flip to the other side of the bilayer
Double bonds
- cause kinks in phospholipid tails (means they can move around more freely- liquid at room temp; oils, unsaturated fats)
- no kink; saturated fat
- the shorter the HC chain, the more liquid
Lipid Bilayer with NO unsaturated fatty acids
Lower permeability, less fluid
the number of double bonds you have determines the fluidity
Lipid Bilayer with MANY unsaturated fatty acids
Higher permeability, more fluid
the number of double bonds you have determines the fluidity
