Lipid digestion and synthesis Flashcards
What is the structure of a lipid?
They are three fatty acid chains which are ester linked to a glycerol backbone
what are fatty acids?
Long methyl chain hydrocarbon bound by a COOH group
What does saturated mean?
There are no double bonds
What does mono/polyunsaturated mean?
There is one double bond
There is more than one double bond.
Why do we metabolise fatty acid?
Glucose produces 17kJ/g whereas Fatty acids produce 38kg when broken down
How do we name omega fatty acids?
The number refers to how many carbons there are before a double bond
What are the names of the two enzymes which can alter fatty acid chains
Elongase- extends by 2 carbon
Desaturase- adds double bonds
What are essential fatty acids and why can’t we just make them?
Humans can’t form double bonds anywhere lower than omega 9, omega 3 and 6 are needed via diet
Why are fatty acid chains altered?
We don’t need them for energy storage so they are edited for phospholipids and other tissue composition
How are lipases digested
The ester bonds are hydrolysed by pancreatic lipases.
This produces a 2-monoacylglycerol and two free fatty acid chains
How are fatty acids absorbed?
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
How are lipids transported?
Through a lipoprotein called a chylomicron- these have a phospholipid and chol outer layer and a triglyceride and chol ester inner core
How are fatty acids taken up by adipose tissues?
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
What is the definition of lipogenesis?
This is the reconstruction of fatty acids
Where does lipogenesis occur?
In the adipose tissues
What is the first step of lipogenesis?
DHAP (dihydroxyacetone phosphate) is converted by G-3-P dehydrogenase into glucose-3-Phosphate
At the same time NADH becomes NAD+
What are activated FA?
These are fatty acid tails attached to CoA enzyme complexes
What is the second step of lipogenesis?
Acyltransferase attaches the fatty acid chains one by one
What is the name of a G-3-P complex with one fatty acid?
Lysophosphatidic acid
What is the name of a G-3-P complex with 2 fatty acids?
Phosphatidic acid
What is the third step of lipogenesis?
Phosphatase removes the Pi group leaving and alcohol group
This makes it diacylglycerol
What is the fourth step in lipogenesis?
Diglycerol acyltransferase attaches the last acylcoenzyme to form a triglyceride
how is lipolysis carried out in the adipose tissue
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
