11. Lipids

Question 1

How many carbon and C=C bonds does palmitic acid have?

Answer 1

16 C, 0 C=C

Question 2

How many carbon and C=C bonds does oleic acid have?

Answer 2

18 C, 1 C=C

Question 3

How are fatty acids metabolised after digestion?

Answer 3

1. carbon backbone oxidised in acetyl-CoA

in the presence of oxaloacetate : acetyl-CoA combines with oxaloacetate to undergo TCA cycle to produce 3 NADH, 1 FADH2, 2 CO2, 1 ATP and regenerated as oxalacetate

in the absence of oxaloacetate (due to low carb diet etc): acetyl-CoA forms ketone bodies.

Oxaloacetate is synthesised from sugars. In a low carb diet / fasting –> oxaloacetate is consumed to form glucose via gluconeogenic pathway, unavailable for reaction with acetyl CoA

Question 4

What are the names of 2 of the ketone bodies that can be formed in fatty acid metabolism?

Answer 4

acetoacetate, D-3-hydroxybutyrate

Question 5

What is the main function of lipoproteins?

Answer 5

To transport cholesterol and triacylglycerols/triglycerides

Question 6

What are the 6 types of lipoproteins, in ascending order of density?

Answer 6

1. Chylomicrons
2. Chylomicron remnants
3. Very low density lipoproteins (VLDL)
4. Intermediate-density lipoproteins (IDL)
5. Low-density lipoproteins (LDL)
6. High-density lipoproteins (HDL)

Question 7

What do chylomicrons transport?

Answer 7

Triglycerides,cholesterol and other lipids (from the diet) away from the samll intestine

Question 8

What do chylomicron remnants transport?

Answer 8

Carry cholesterol-rich residues to liver (for liver to absorb)

Question 9

What do Very low density lipoproteins (VLDL) transport?

Answer 9

Exports excess triacylglycerols and cholesterol from liver into bloodstream.

• cholesterol + fatty acids from triacylglycerols / triglycerides combine and carried as cholesteryl esters

Question 10

What do Intermediate-density lipoproteins (IDL) transport?

Answer 10

• Breaks down remnant cholesteryl esters into cholesterol and fatty acids
• fatty acids are uptaken by tissues (normal tissues)

Question 11

What do Low-density lipoproteins (LDL) transport?

Answer 11

LDL carry cholesterol in bloodstream (bad cholesterol)

Question 12

What do High-density lipoproteins (HDL) transport?

Answer 12

It packs up cholesterol released into the plasma and delivers to liver for excretion (good cholesterol)

Question 13

Biological cell membranes have several functions. 2 of the functions are:
- Prevent molecules from leaking out of the cell
- Prevent unwanted molecules from diffusing in

This function is performed by which part of the cell membrane?

Answer 13

Lipid bilayer

Question 14

Another function of biological cell membranes is that they contain transport systems to take up or remove molecules – selective permeability.

which part of the cell membrane performs this function?

Answer 14

Protein components which act as pumps/channels in cell

Question 15

Although the biological cell membrane is mainly lipid and proteins, what do they contain also/

Answer 15

carbohydrates linked to lipid and proteins (glycolipid and glycoprotein)

Question 16

Why might most unsaturated fatty acids in phospholipids be in the cis rather than the trans conformation?

Answer 16

Phospholipid bilayer – cell membrane
- Cis double bond introduces a kink that prevents packing of the fatty acid chains. Cis double bonds maintain fluidity of the cell membrane.

Question 17

What are the components of phospholipids?

Answer 17

• Glycerol backbone
• 2 fatty acids bonded to glycerol backbone
• 1 phosphate attached to glycerol backbone
• 1 alcohol group bonded to phosphate group

Can refer to notes for better visualisation

Question 18

Phospholipids are synthesised from diacylglercol (glycerol + 2 fatty acids) and phosphate-alcohol group. In this synthesis, either the diacylglucerol molecule or the alcohol group must be ____ by ____________________________

Answer 18

Activated, addition of phosphate group (phosphorylation)

Question 19

Glycolipids are sugar-containing lipids, where sugar residues are always on the ____ side of the membrane

Answer 19

extracellular

Question 20

What are glycolipids made of ?

Answer 20

• Sphingosine backbone
• 1/2 fatty acid groups
• 1 sugar group

Question 21

What is the name of the simplest glycolipid?

Answer 21

Cereboside

• 1 sphingosine, 1 fatty acid, 1 sugar

Question 22

A sphingosine molecule is made of ___ and __

Answer 22

amino acid, alcohol (amino-alcohol)

Question 24

what is the most complex sphingolipid and what do they do?

Answer 24

Gangliosides
- binding immune cells to sites of injury in inflammatory response

Question 25

What is cholesterol made of?

Answer 25

- Steroid nucleus (4 hydrocarbn chains linked together) - Long hydrocarbon tail

Question 26

What are 2 functions of cholesterol?

Answer 26

1) modulates the fluidity of animal cell membranes (cholesterol is embedded in lipid bilayer) - During low temp, Cholesterol prevents phospholipids from packing too tightly, maintaining fluidity 2) Precursor of steroid hormones such as progesterone and testosterone

Question 27

What are the 3 derivatives of cholesterol?

Answer 27

1. Bile -- breakdown product of cholesterol 2. Vitamin D 3. Steroid hormones

Question 28

Other than phospholipid bilayer, what other structure can phospholipids form, under what condition?

Answer 28

Micelle - Only forms when there is only 1 fatty acid chain (salts of fatty acids) - When there are 2 fatty acid chains, too bulky to fit into interior of micelle → steric hindrance

Question 30

# Membrane proteins Myelin contains ____% of protein. What does myelin do?

Answer 30

18% - It is high in fat, and acts as an insulator of electrical signals ## Footnote in the dendron (nerve cell), myelin sheath over the main part --> electrical signals cannot be passed through in areas with myelin over it, electrical signals “jump” → effective transfer

Question 31

Typical plasma membranes contain ____% of protein

Answer 31

50%

Question 32

Mitochondria membranes consist of ____% protein.

Answer 32

75% - Electron transport chain --> channel proteins to pump protons and electrons

Question 33

# Association of proteins with lipid bilayer What are peripheral proteins?

Answer 33

Proteins that are bound to cell membrane by electrostatic and hydrogen-bond interactions - interact with hydrophilic head of phospholipid bilayer, **on the surface of membrane**

Question 34

# Association of proteins with lipid bilayer What are integral proteins?

Answer 34

Proteins that form extensive interaction with hydrocarbon chains (hydrophobic part) of membrane lipids - **are embedded within membrane**

Question 35

The fluidity of phospholipid bilayer of cell membranes are determined by? [2]

Answer 35

1. Fatty acid composition (cis vs trans) 2. Cholesterol content

Question 37

The outer and inner surfaces of the biological membrane are structurally and functionally symmetric. True or False?

Answer 37

False - Outer and inner surfaces of biological membranes have **different components** and **different enzymatic activities**

Question 38

How is the assymetry of biological membranes preserved?

Answer 38

Insertion of membrane proteins + assymetrical distribution of lipids

Question 39

What are the 3 types of membrane proteins associated with the phospholipid bilayer?

Answer 39

1. Pumps 2. Carrier proteins 3. Channels

Question 40

Pumps use what kind of transport? (active transport/diffusion/facilitated diffusion etc)

Answer 40

*Primary* active transport involving use of *ATP*

Question 41

Pumps use what kind of transport? (active transport/diffusion/facilitated diffusion etc)

Answer 41

*Secondary* **active** transport *with no use of ATP* - utilises gradient of one ion to drive transport of another against its gradient.

Question 42

# Carrier proteins Carrier proteins can be classified into antiporters, symports and uniporters. What is an antiporter?

Answer 42

It is a carrier protein that transports 2 different ions in opposite directions at the same time

Question 43

# Carrier proteins What is a symporter?

Answer 43

(membrane) carrier proteins which carry 2 species of ions in the same direction at the same time.

Question 44

What is a uniporter?

Answer 44

(membrane) carrier proteins which carry 1 species of ions in either directions based on the concentration of the species on either side of the membrane.