Lecture 7 - Lipids 1

Question 1

Lipids are an:
___ if it is liquid at RT
___ if it is solid at RT

Answer 1

Oils - liquid

Fat - solid

Question 2

How many kJ and calories per g of lipid?

Answer 2

37kJ, 9 calories

Question 3

Dietary fat is comprised mostly of what 3 things?

Answer 3

1. Triglycerides (90% of total dietary lipids)
2. Phospholipids
3. Sterols

Question 4

Triglycerides are made up of ____ + _____.

Answer 4

3 fatty acids + a glycerol backbone

Question 5

What are the 3 types of FAs (which are what comprise triglycerides)?

Answer 5

Saturated, monounsaturated, polyunsaturated

Question 6

What are the 3 main series of unsaturated FAs? What is the name based on?

Answer 6

Omega-9 (aka n-9), omega-6 (n-6) and omega-3 (n-3). Based on first double bond counting from methyl carbon (omega/n).

Question 7

3 common SATURATED FAs?

Answer 7

Palmitic (palm oils), stearic (animal fats), myristic (butter, coconut oil)

Question 8

2 common MONOUNSATURATED FAs?

Answer 8

Oleic (olive oil), palmitoleic (fish/animal fats, vege oils)

Question 9

3 common POLYUNSATURATED FAs?

Answer 9

Linoleic (sunflower/corn/soybean oil), alpha-linoleic (chia/flax oil), pentanoic (fish/fish oils)

Question 10

What are the 5 main dietary sources of saturated fat?

Answer 10

1. Dairy
2. Butter, margarine, vege oils
3. Meat products
4. Poultry
5. Desserts e.g. cake

Question 11

What are the only 2 essential FAs to humans? What biochemical process happens when we ingest them?

Answer 11

Linoleic (n-6) and alpha-linoleic (n-3) acid. They undergo transformation into other FAs using enzymes

Question 12

What are trans fatty acids?
What is a benefit of it?
What is a source of naturally occurring trans FAs?

Answer 12

1. Hydrogen is added across a double bond in a polyunsaturated FA (‘hydrogenated’). This causes the configuration to change from cis to trans.
2. Prolongs shelf life as fat remains solid at RT
3. Small amount in milk and dairy products

Question 13

What are 2 main types of PHOSPHOLIPIDS?
What are 2 functions of phospholipids?
What are 2 sources?

Answer 13

1. Phosphatidylserine, phosphatidylcholine
2. Emulsifier, a component of cell membranes
3. Egg yolk, peanuts

Question 14

Main type of STEROL in animals?

Main type of STEROL in plants?

Answer 14

Cholesterol

Phytosterols (then further subcategories)

Question 15

4 key steps in the absorption of fat?

Answer 15

1. Triglycerides mixed with ampipathic compounds (bile acids, phospholipids) in which it is EMULSIFIED (broken down from large droplets to small droplets)
2. Pancreatic lipase removes 2 FAs (increases SA)
3. Phospholipase + cholesteryl ester hydrolase help to further break down the droplet into monoglycerides + FAs.
4. These monoglycerides + FAs can diffuse across enterocytes (mucosal cells of small intestine)

Question 16

Are lipids soluble in plasma? Why/why not? To combat this lipids are bound with ____ for transport and this unit is termed _____?
This unit can be formed using 2 pathways, what are they each called?

Answer 16

No - plasma is an aqueous solution. Lipids are hydrophobic.
Bound with protein to form lipoproteins.
Exogenous pathway: lipoproteins formed in mucosal cells after the fat has being absorbed (chylomicrons)
Endogenous pathway: lipoproteins are formed in the liver and then transported (via VLDLs) to the tissues

Question 17

In a lipoprotein, what comprises the:
Outer layer?
The core?

Answer 17

OL: apolipoproteins, cholesterols + phospholipids
C: triglycerides + cholesterol ester rich

Question 18

LDL-c is positively/negatively associated with _______. Is the relationship linear or non-linear?

Answer 18

Positively atherosclerosis, non-linear

Question 19

Doctors commonly prescribe meds that target the rate limiting step of cholesterol synthesis. What is this step and what are the meds called?

Answer 19

HMG-CoA reductase

Statins - HMG-CoA reductase inhibitors

Question 20

HDL-c is positively/negatively associated with _______.

HDL-c is positively/negatively/not associated with _______.

Answer 20

Negatively, atherosclerosis.

No association, CVD (still used as a risk marker though).

Question 21

Triglycerides are positively/negatively/no associated with _______.
What 3 things lower triglycerides?

Answer 21

Not associated (still used as a risk marker though) with CVD.
Niacin, omega-3 FAs, fibrates.

Question 22

SFAs and MUFA + PUFAs affect LDL levels through the endogenous pathway. What is the mechanism behind this for:
SFAs?
MUFA + PUFAs?

Answer 22

SFA: downregulates LDL receptors on both liver and body tissues hence higher amounts of LDL is left circulating. Saturated fat is the main dietary driver of LDL-c
M/PUFA: upregulates LDL receptors on both liver and body tissues but this is coupled with an increase in endogenous cholesterol synthesis hence these 2 mechanisms cancel eachother out.

Question 23

SFAs increase LDL-c. So does dietary cholesterol and trans-fats. Which of the 3 increases it the most, which increases it the least.

Answer 23

Trans fats > SFAs > dietary cholesterol

• ** Trans fats do this by increasing endogenous cholesterol synthesis
• ** Dietary cholesterol and SFAs co-inhabit/they are found together

Question 24

Phytosterols decreases blood cholesterol by ___% at highest dose.
What is the mechanism behind this?
What are some dietary sources of phytosterols?

Answer 24

10%
Competes with cholesterol for absorption in the gut hence less cholesterol is absorbed.
Margarine, brekkie cereals, low-fat yoghurt + milk.

*** There is a dose-dependent reduction in LDL-c and phytosterol concentration in margarine. Greater reduction seen in higher [phytosterol]. There is an increase in LDL-c when butter is used (butter contains SFAs).