Lipid digestion and synthesis

Question 1

What is the structure of a lipid?

Answer 1

They are three fatty acid chains which are ester linked to a glycerol backbone

Question 2

what are fatty acids?

Answer 2

Long methyl chain hydrocarbon bound by a COOH group

Question 3

What does saturated mean?

Answer 3

There are no double bonds

Question 4

What does mono/polyunsaturated mean?

Answer 4

There is one double bond
There is more than one double bond.

Question 5

Why do we metabolise fatty acid?

Answer 5

Glucose produces 17kJ/g whereas Fatty acids produce 38kg when broken down

Question 6

How do we name omega fatty acids?

Answer 6

The number refers to how many carbons there are before a double bond

Question 7

What are the names of the two enzymes which can alter fatty acid chains

Answer 7

Elongase- extends by 2 carbon
Desaturase- adds double bonds

Question 8

What are essential fatty acids and why can’t we just make them?

Answer 8

Humans can’t form double bonds anywhere lower than omega 9, omega 3 and 6 are needed via diet

Question 9

Why are fatty acid chains altered?

Answer 9

We don’t need them for energy storage so they are edited for phospholipids and other tissue composition

Question 10

How are lipases digested

Answer 10

The ester bonds are hydrolysed by pancreatic lipases.
This produces a 2-monoacylglycerol and two free fatty acid chains

Question 11

How are fatty acids absorbed?

Answer 11

The free fatty acid chains can cross plasma membrane into the intestinal cells.
Acyl CoA synthetase then attaches a CoA forming a complex.
they are then re-esterified forming a triglyceride in the gut

Question 12

How are lipids transported?

Answer 12

Through a lipoprotein called a chylomicron- these have a phospholipid and chol outer layer and a triglyceride and chol ester inner core

Question 13

How are fatty acids taken up by adipose tissues?

Answer 13

The endothelial cells have a lipoprotein lipase attached to their membrane.
FA are cleaved off from the chylomicron and absorbed into the cell.
The Remnant is then removed from circulation by the liver

Question 14

What is the definition of lipogenesis?

Answer 14

This is the reconstruction of fatty acids

Question 15

Where does lipogenesis occur?

Answer 15

In the adipose tissues

Question 16

What is the first step of lipogenesis?

Answer 16

DHAP (dihydroxyacetone phosphate) is converted by G-3-P dehydrogenase into glucose-3-Phosphate
At the same time NADH becomes NAD+

Question 17

What are activated FA?

Answer 17

These are fatty acid tails attached to CoA enzyme complexes

Question 18

What is the second step of lipogenesis?

Answer 18

Acyltransferase attaches the fatty acid chains one by one

Question 19

What is the name of a G-3-P complex with one fatty acid?

Answer 19

Lysophosphatidic acid

Question 20

What is the name of a G-3-P complex with 2 fatty acids?

Answer 20

Phosphatidic acid

Question 21

What is the third step of lipogenesis?

Answer 21

Phosphatase removes the Pi group leaving and alcohol group
This makes it diacylglycerol

Question 22

What is the fourth step in lipogenesis?

Answer 22

Diglycerol acyltransferase attaches the last acylcoenzyme to form a triglyceride

Question 23

how is lipolysis carried out in the adipose tissue

Answer 23

Embedded within the perilipin coat there are lipases
Adipose TG Lipase takes TG and removes a FA and releases it
DAG is then taken up by hormone-sensitive lipase and a second FA is released
The remaining MAG is broken down via monoglyceride lipase