Topic 1 - Year 1 - Biological Molecules - Lipids

Question 1

What are Lipids?

Answer 1

Lipids are commonly known as fats or oils.

Question 2

Why do lipids differ from carbohydrates

Answer 2

Lipids are different from carbohydrates as they are not polymers formed from long chains of monomers (repeating units ) rather they are made of a variety of different components.

Question 3

Name a component found in all lipids

Answer 3

Hydrocarbons (molecules that contain carbon and hydrogen only)

Question 4

Name 2 types of Lipid

Answer 4

Triglyceride

Phospholipid

Question 5

What is meant by hydrophobic?

Answer 5

Something that is hydrophobic repels water

Question 6

How many fatty acids are found in one triglyceride ?

Answer 6

3

Question 7

Why are lipids different from carbohydrates and proteins ?

Answer 7

Lipids are different form carbohydrates and proteins as they are not polymers made up of repeating units. Lipids are made from a variety of different components.

Question 8

What do all lipids contain?

Answer 8

All lipids contain hydrocarbons (molecules that contain hydrogen and carbon only).

Question 9

Name two lipids

Answer 9

Phospholipid

Triglycerides

Question 10

How many molecules are in a Triglyceride?

Answer 10

There are 4 molecules in a triglyceride , 1 molecule of glycerol chemically bonded by ester bonds formed in condensation reactions to 3 fatty acids.

Question 11

What makes Triglycerides insoluble in water?

Answer 11

Fatty acids have long tails made of hydrocarbons . The hydrocarbon tails are hydrophobic this means they repel water . These tails consequently make triglycerides insoluble in water.

Question 12

Hydrophobic

Answer 12

Repel water

Question 13

Hydrophilic

Answer 13

Attracts water

Question 14

Describe the structure of a Fatty Acid

Answer 14

A fatty acid has an O atom that has a double bond to the central carbon atom , then a OH group which has a single bond to the central carbon atom , and then an R group which also makes a single bond to the central carbon atom. The R group is a variable group , it changes between different fatty acids , the R group is normally he hydrocarbon chain.

Fatty Acid

O
  \\
   C --- R 
   /
HO

Sometimes fatty acids can be shortened to RCOOH

Question 15

Name the two catagories of fatty acid

Answer 15

Saturated Fatty Acid

Unsaturated Fatty Acid

Question 16

Describe the structure of a saturated fatty acid

Answer 16

A saturated fatty acid has no carbon to carbon double bonds in its hydrocarbon chain, all bonds between carbons are singular.

Question 17

Describe the structure of an unsaturated fatty acid

Answer 17

An unsaturated fatty acid contains 1 (mono unsaturated) or several (polyunsaturated) carbon to carbon double bonds , in its hydrocarbon tail , this can cause a kink in the chain.

Question 18

How are triglycerides formed?

Answer 18

Triglycerides are formed in condensation reactions. An ester bond forms between two molecules releasing 1 molecule of water. This process happens 3 times to produce 1 triglyceride hence 3 molecules of water are produced for every one triglyceride made and 3 ester bonds are contained within the single triglyceride.

Question 19

How many ester bonds are made in 1 triglyceride?

Answer 19

3

Question 20

How many molecules of water are produced as a result of condensation reactions in the formation of a triglyceride?

Answer 20

3

Question 21

Which two groups of the glycerol molecule and fatty acid molecule undergo a condensation reaction to form the Ester bond?

Answer 21

The two OH groups on the molecules bond in the condensation reaction.

GLYCEROL FATTY ACID

   H             
    | H -- C --- OH                              O
    |                                            \\ H -- C --- OH                                 C --- R
    |                                             / H -- C --- OH              +           HO
    |
   H

Question 22

Draw the structure of a Triglyceride

Answer 22

H
| O
| //
H – C ——– O ———- C — R
| O
| //
H – C ——– O ———- C — R
| O
| //
H – C ——– O ———- C — R
|
|
H

Question 23

What are the lipids found in cell membranes called?

Answer 23

The lipids found in cell membranes are called phospholipids.

Question 24

How many molecules are found in a phospholipid?

Answer 24

4 molecules are found in a phospholipid , 2 fatty acids , 1 molecule of glycerol and one phosphate group.

Question 25

Which part of a phospholipid are hydrophobic?

Answer 25

The fatty acids (hydrocarbon chains) are hydrophobic so repel water.

Question 26

Which part of the phospholipid is hydrophilic?

Answer 26

The phosphate group is hydrophlic as it has a negative charge , being hydrophilic means it attracts water .

Question 27

What is the difference between triglycerides and phospholipids?

Answer 27

Triglycerides have three fatty acids within them where as a phospholipid only has two fatty acid molecules in them.

Phospholipids have a phosphate group attached where as triglycerides don’t.

Question 28

What are some similarities between phospholipids and triglycerides?

Answer 28

They both contain one molecule of glycerol (glycerol back bone)

They both make ester bonds between glycerol and fatty acids in condensation reactions

They are both insoluble in water.

Question 29

What are triglycerides used for?

Answer 29

Triglycerides are mainly used as an energy storage molecule. they are good for this as their fatty acid tails contain lots of energy- loads of energy is released when the hydrocarbon chain is broken down.

Lipids contain about twice as much energy per gram than carbohydrates.

Question 30

What is a benefit of triglycerides being insoluble?

Answer 30

Triglycerides are storage molecules , as they do not dissolve they do not affect the water potential of the cell. This is essential as if the lipids did effect the water potential of the cell water would flood in by osmosis to even the water potential on either side of the membrane which would cause the cell to swell and potentially burst.

Question 31

How do Triglycerides behave in cells?

Answer 31

In cells triglycerides bundle together in insoluble droplets . They do this because the fatty acid tails are hydrophobic so point inwards shielding them from the water with their glycerol backbones.

Question 32

How do phospholipids arrange themselves?

Answer 32

Phospholipids arrange themselves in a bilayer, in this bilayer the hydrophilic heads of the phospholipids point outward as they have an affinity for the water where as the tails point inwards as they are hydrophobic, the tails are shielded by the phosphate heads. As the centre of the bilayer is hydrophobic water soluble materials cannot easily pass through.
O O O O O O O O O O
II II II II II II II II II II
II II II II II II II II II II
O O O O O O O O O O

Question 33

What is the test called used to decide whether lipids are present in a sample?

Answer 33

The emulsion test

Question 34

Explain what steps are taken in the emulsion test.

Answer 34

To test for the presence of lipids in a sample

1. put the sample into solution by maybe crushing it
2. shake the test tube substance with ethanol for about a minute
3. pour the solution mixed with ethanol into water
4. the positive test result will be a cloudy white suspension

the more lipid that is present the more noticeable the milky colour will be