Lecture 6: Sugars and Lipids Flashcards Preview

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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



• 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
- results in starch: moderately branched, amylopectin in plants
highly branched, glycogen in animals (used for energy storage in animal cells)


Beta 1,4 Linkage

- 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



• 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)



- 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



• 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*