Lipid Metabolism Flashcards
What are simple lipids
Fatty acids/ building blocks
What are compound lipids
Triacylglycerols/ energy stores (triglycerides and Phosphoacylglycerols – membranes (phospholipids)
What are derived lipids
Steroids – e.g., cholesterol
What are fatty acids composed of
Composed of a hydrocarbon “tail” and a carboxyl group (-COOH) “head”.
They are carboxylic acids.
The carboxyl group head has two polar groups: C=O and O-H
Hydrocarbon tail is made up of hydrogen and carbon and is non-polar
How many carbons a can fatty acids vary in
1-30
How many C do SCFA have
<8 carbons
How many carbons do MCFA have
8-14 carbons
How many carbons so LCFA have
> 14
Where are short chain fatty acids typically found in
found in milk fat – produced from undigested CHO in the colon
Where are MCFA often found
Milk fat and coconut
Which type of FA is most common in our diet
LCFA are the most common in our diet – they are either saturated or unsaturated
Why are high saturated fat foods solid at room temperature
No C=C so molecule is straight and tightly packed
What is a monounsaturated fat
One C=C double bond
What is a polyunsaturated fat
More than one C=C
How are lipids stored in the body
Stored as triacylglycerides or triglycerides in adipose tissue and muscle
Can be un- or saturated fatty acids attached to the glycerol backbone
What are lipoproteins
Lipids surrounded by a protein (because lipids don’t like water; hydrophobic!)
What are the functions of lipoproteins
After digestion (or the breakdown of TAGs) they are used to transport lipids around the body to different tissues
What are examples of lipoproteins
Chylomicrons, VLDL, LDL, HDL
Why are lipids not metabolised immediately after a meal containing fat
Lipids aren’t metabolized until 1-2 h after a meal or even up to 6 h if the meal is particularly rich in CHO. This is because CHO releases insulin and insulin inhibits lipolysis.
What stores can lipids can be broken down from
Adipose tissue and skeletal muscle
What hormone activates lipolysis at rest
Glucagon
What is the main hormone that activates lipolysis during exercise
Adrenaline
What is lipolysis
Lipolysis is the breakdown of a TAG into 1 glycerol and 3 free fatty acid molecules
What three different enzymes break down the three different fatty acids
Adipose triglyceride lipase (ATGL)
Hormone sensitive lipase (HSL)
Monoacylglycerol lipase (MGL)
Which enzyme breaks down the triacylglycerol to a diacylglycerol
Adipose triglyceride lipase (ATGL)
Which enzyme breaks down the diacylglycerol to a monoacylglycerol
Hormone sensitive lipase (HSL)
What enzyme breaks monoacylglycerol into fatty acid and glycerol
Monoacylglycerol lipase (MGL)
When does breakdown typically occur
In fasting conditions or upregulated during exercise
What hormones regulate lipolysis by stimulating the lipase enzymes to split the TAGS into glycerol and FFA
Glucagon and epinephrine ect.
Why is lipid metabolism important during endurance exercise
Lipid oxidation (aerobic), so fats used to produce ATP increases as endurance exercise does
Why with increased duration of exercise is their a higher utilisation of lipids and why is there a higher utilisation in trained athletes
Because the carbohydrates store is depleted (muscle and liver glycogen)
And endurance trained people are better able to utilise oxygen for lipid oxidation
How are FA transported in the blood
FA are hydrophobic so have to be bound to albumin to travel in the blood
Which enzyme is primary regulator of lipolysis rate
Hormone sensitive lipase (HSL)
How is glycerol transported
Glycerol is hydrophilic so can go straight to the liver
How many FA molecules can albumin carry
10 FA molecules
What happens to FA after lipolysis
can either be remade into TAGS or taken to tissues for oxidation
How many transporter proteins are used to transport albumin to the cell cytosol
3
What are the three transporter proteins that transport albumin into the cell cytosol (transport FA across the membrane for beta oxidation)
Fatty acid binding protein, fatty acid transport protein and fatty acid translocase(CD36)
How can you increase the number of transport proteins
The number of transport proteins can be increased by aerobic exercise and/or a HF diet
What happens to FA once they have been transported into tissues
Once transported to tissues, FA can be used to generate energy via a process called beta-oxidation
What is beta oxidation
beta oxidation is a process whereby the carbon chains of the FA are removed, therefore shortening the molecule
The aim of beta-oxidation is to derive acetyl CoA for use in the TCA cycle
Where does beta oxidation occur
in the mitochondrial matrix and requires oxygen
Why do we need to transport FA from the cytoplasm to the mitochondrial matrix
The enzymes needed to generate ATP from the mitochondria are located in the MM
What are FA activated into and why
FA will not be transported if it is not activated
To activate, FA reacts with coenzyme A to form ACYL COA – NOT acetyl coA
What catalyses FA activation
fatty acyl CoA synthetase
What is needed for FA activation and what is produced
requires ATP. 2 ATP are required so AMP and two PPi are produced.
What happens to the activated FA
Carnitine forms a bond with the C group on the Acyl CoA molecule to form Acyl carnitine
Acyl carnitine diffuses into inter membrane space via porins on the outer MM
Protein transporter called acyl carnitine translocase transports acyl carnitine to the MM
remove this carnitine from the the Acyl group
Acyl coA however goes through the process of Beta oxidation
What enzyme catalyses the formation of Acyl carnitine
carnitine acyl transferase 1 (on outer MM)
What enzyme removes carnitine from the Acyl group
carnitive acyl transferase II
What happens to the carnitine after
The carnitine can then be transported back to the cytoplasm to repeat the process via the translocase enzyme
Summarise how FA are transported to the MM
carnitine has to shuttle acyl coa into the MM for beta oxidation.
How many carbon chains are removed from the FA on each cycle of beta oxidation
2 carbon chains (More C chains = more cycles until only acetyl CoA is left)
