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What is a triglyceride? The structure of glycerol and fatty acids

Composed of 3 fatty acids linked to a glycerol molecule. Glycerol has 3 carbons, each with an OH group. Fatty acids have a carboxylic acid group (COOH) at one end and a long hydrocarbon tail (composed of only carbon and hydrogen) at the other.

1

What is the structure of saturated and unsaturated fatty acids?

Saturated fatty acids have no double bonds between carbon atoms in their tails. This means that a saturated fatty acid has the maximum number of hydrogen atoms that can be attached - so it is 'saturated' with hydrogens. Unsaturated fatty acids have at least one double bond between the carbon atoms and so have fewer hydrogen atoms than the maximum possible.

2

What links glycerols and fatty acids?

They are linked by enzyme-catalysed reactions. These are condensation reactions between the OH of the fatty acid and the Oh of the glycerol, resulting in the removal of a water molecule . The bond that is formed between the glycerol and the fatty acid is an esterbond.

3

What types of triglycerides are found in fatty acids?

Triglycerides that are mainly composed of saturated fatty acids are solid at room temperature; they are fats. Oils are mainly composed of unsaturated fatty acids and are liquid at room temperature. The double bonds between carbons stop unsaturated fatty acids being packed to close together and so oil remains liquid at room temperature.

4

What is phospholipid?

They are like a triglyceride but they have a phosphate group in place of one of the fatty acids. This means that they are composed of glycerol, two fatty acids and phosphate. The fatty acids and the phosphate are joined by ester bonds to the glycerol. Usually, one of the fatty acids is saturated and the other is unsaturated. Other charges groups, such choline, maybe attached to the phosphate.

5

What is the head of the phospholipid?

The 'head' of the phospholipid is formed by the phosphate and the choline groups. Both of these groups are electrically charged which makes them hydrophilic - they are attracted to water.

6

What is the 'tail' of the phospholipid?

It is formed by the fatty acids, one of which is unsaturated. The fatty acids are uncharged and non-polar, which makes them hydrophobic- they are repelled by water.

7

What is the phospholipid bilayer?

It is in membranes forms because the hydrophilic heads stay in contact with aqueous solutions (extracellular fluids in the cytosol) and the hydrophobic tails stay in the middle of the bilayer, away from the water. The unsaturated fatty acids in the tails keep the membrane fluids preventing the phospholipids packing closely together.

8

What are steroids?

They are a four ring structure of 17 carbons. Varying side chains attached to this structure gives different steroids. Many steroids play a role in cell signalling as hormones; they are hydrophobic molecules so they are able to diffuse across membranes and bind to receptors inside cells.

9

What is the structure of the cholesterol?

It has an OH at the bottom left and C8H17 at the top right.

10

What is the structure of testosterone?

It is double-bonded oxygen (C=O) at the bottom left and an OH at the top right.

11

What is testosterone used in?

Muscle development and in male puberty. Cholesterol fits into the hydrophobic part of the phospholipid bilayer and reduces phospholipid movement in the membrane. It also helps to prevent solidification of the membrane at low temperatures.