Topic 1 Biomolecules - Lipids

Question 1

What are lipids?

Answer 1

lipids are compounds that are insoluble in water, but soluble in an organic solvent (e.g. ether, benzene, acetone, chloroform) - most are hydrophobic

Question 2

What is a fat?

Answer 2

A lipid that is solid at room temperature

Question 3

What is an oil?

Answer 3

A lipid that is a liquid at room temperature

Question 4

What are major physiological roles of lipids?

Answer 4

Fuel molecules

Highly concentrated energy store and provide insulation

essential components of cell membrane (e.g. phospholipids, glycolipids and cholesterol)

Signal molecules and messengers in signal-transduction pathways

Used as a fuel store

Question 5

What does it mean if a compound is amphipathic?

Answer 5

Compounds which exhibit both hydrophilic (water-loving) (polar) and hydrophobic (water-hating) (non-polar) properties

Question 6

What are examples of types of lipids?

Answer 6

fatty acids

triacylglycerols

phospholipids - glycerophospholipids, sphingolipids

Glycosphingolipids

Cholesterol - steroid hormones, bile acids

Question 7

What does a fatty acid consist of?

Answer 7

a hydrocarbon chain with a terminal carboxylic acid group

Question 7

Give examples of lipids are membrane lipids (polar)

Answer 7

phospholipids, glycolipids

Question 7

Give examples of storage lipids (neutral)

Answer 7

Triacylglycerols

Question 7

Are fatty acids weak or strong acids?

Answer 7

they are weak acids due to carboxylic group, and they have a pKa of around 4.5

Question 7

Describe saturated fatty acids

Answer 7

No double bonds between carbons e.g. animal fats, solid at room temperature

they have higher melting points than unsaturated fatty acids.

Question 7

Fatty acids in biological systems usually contain an even number of carbon atoms. fatty acids vary in chain length. describe these different chain lengths?

Answer 7

Short= 2-8 (or less than 6) carbons (volatile and smelly)

Medium= 10-14 (or 6-12 ) carbons

Long = 16-18 (or more than 12) carbons

Question 7

How do chain lengths and degree of saturation affect fatty acid properties?

Answer 7

short chain length and unsaturation enhance the fluidity of fatty acids and their derivatives

Question 7

What fatty acid chain lengths are considered amphiphillic?

Answer 7

medium and long

Question 8

In most naturally occurring fatty acids, what is the orientation/conformation around the double bonds?

Answer 8

cis conformation

Question 8

Describe unsaturated fatty acids

Answer 8

contain one or more double bonds e.g. vegetable oils, liquid at room temperature

have lower melting points than saturated fatty acids

Question 8

describe triglycerides structure?

Answer 8

Triglycerides are uncharged (neutral) esters where glycerol is bonded to three fatty acids

Question 8

Why is the cis conformation of double bonds in fatty acids important?

Answer 8

important for structure because each cis double bond inserts a bend/kink into the hydrocarbon tail.

Question 8

What are triglycerides?

Answer 8

Triglycerides are a class of lipids commonly referred to as FATS, and are an important part of our diet.

Question 9

What are triglycerides function?

Answer 9

they are highly concentrated stores of metabolic energy because the are reduced and anhydrous (i.e containing no water)

Question 10

What are lipid droplets?

Answer 10

large globules formed by the coalescence (joining or merging) of triacylglycerols

They may occupy most of the adipocyte volume and are surrounded by a phospholipid monolayer and proteins required for lipid metabolism

Question 11

What is adipose tissue ?

Answer 11

adipose tissue is a major site of triglyceride accumulation and specialised for triglyceride synthesis, storage and mobilisation into fuel.

Question 12

Describe phospholipids structure?

Answer 12

one or more fatty acids

a platform to which the fatty acids are attached

a phosphate

an alcohol or choline attached to the phosphate

Question 13

What are phospholipids function?

Answer 13

major component of cell membrane

Question 14

What are glycerophospholipids?

Answer 14

Major class of phospholipids which make up a large proportion (50-75%) of the membrane in mammals, bacteria and plants

they contain a glycerol backbone

Question 15

What are glycerophospholipid function?

Answer 15

crucial for structural integrity and fluidity of lipid bilayer

Question 16

What is the amphiphilic nature of glycerophospholipids crucial for?

Answer 16

membrane formation

Question 17

what is membrane fluidity controlled by?

Answer 17

fatty acid composition and cholesterol content

Question 18

Describe fatty acid composition?

Answer 18

• Straight hydrocarbon chains of saturated fatty acid residues interact favourably with one another.
  – favours the rigid state
• Long hydrocarbon chains interact more strongly than do short ones.
  – Each additional CH2 group contributes about −2 kJ mol−1 to the free energy of interaction of two adjacent hydrocarbon chains.
• A cis double bond produces a bend in the hydrocarbon chain interferes with a highly ordered packing of fatty acid chains

Question 19

Describe the structure of sphingolipids?

Answer 19

backbone of sphingolipids is sphingosine, an amino alcohol that contains a long, unsaturated hydrocarbon tail

Question 20

what is sphingolipids function?

Answer 20

role in membrane structure, cell signalling and cell recogniton

Question 21

what are glycolipids?

Answer 21

a class of lipids that have a carbohydrate (sugar) moiety attached to their hydrophilic head groups

Question 22

describe glycolipids struture?

Answer 22

Lipids containing a sphingosine backbone with 1+ sugars attached to the primary –OH group
– sugar residues are always on the extracellular side of the membrane

Question 23

what is glycolipids function?

Answer 23

cell recognition and adhesion, and cell signaling

Question 24

What is cholesterol?

Answer 24

cholesterol is a member of a large group of substances called steroids.

so cholesterol is a steroid ig

Question 25

Describe cholesterol (steroid) structure

Answer 25

Steroid built from 4 linked hydrocarbon rings
– contains a linked hydrocarbon tail at one end and an
–OH group at the other end
– oriented parallel to fatty acid chains of phospholipids in membranes
– –OH group interacts with phospholipid head groups

Question 26

what is cholesterol (steroid) function?

Answer 26

stabilises cell membrane

– the bulky steroid nucleus of cholesterol disrupts the regular interactions between fatty acid chains – helps maintain proper membrane fluidity in membranes in animals

Question 27

What are derivatives of cholesterol?

Answer 27

steroid hormones

sex hormones

corticosteroids

mineralocorticoids

bile salts - polar derivatives of cholesterol, act as detergents in the small intestine to aid digestion of fats, the major mammalian bile salt is glycocholate