Lipids Flashcards
What is a lipid?
It is an ester of a long hydrocarbon FA that is insoluble in water and is found in all living cells and tissues
What are the functions of lipid?
Energy storage, signalling molecules, enzyme cofactors, structural component of cell membranes, synthesis of vitamins and hormones
What are FAs?
They are hydrocarbon chains with a carboxylic group at one end, they can be saturated or unsaturated and their nutritional value can vary
What are the 4 types of fats?
Essential, good, bad and really bad
What are essential fats?
Fats that must be obtained from the diet as we can not produce C=C structures beyond C9 e.g. Linoleic acid
What are good fats?
Polyunsaturated e.g. plant oils
What are bad fats?
Unsaturated e.g. steric acid
What are really bad fats?
Trans fats e.g. margarine
What do gluconeogenic substances not contain?
FAs
What does the FA nomenclature of 12:1 and 16:2(2,8) mean?
12: 1- 12xC’s and 1xC=C
16: 2(2,8)- 16xC’s and 2xC=C (at C2 and C8)
What are the 3 major classes of lipids?
FA, triacylglycercide (TAG) and phospholipid
What are TAGs?
Main dietary lipid consisting of esters of FAs and glycerol
What are the properties of TAG?
It is anhydrous, highly reduced, combine in to water droplets and are major components of adipose tissue
What are the functions of TAG?
Energy storage (best), insulators, and forms depot fat in adipose tissue
What do phospholipids consist of?
Glycerol, 2xFA and a phosphate group
What are the properties of phospholipids?
Anhydrous
What are the functions of phospholipid?
Basic structure of cell membranes
What diseases are lipids involved in?
Atherosclerosis and steatorrhea
What is atherosclerosis?
Increases blood pressure due to an imbalance in lipid metabolism
What is steatorrhea?
Lipid malabsorption which leads to excess fat in pool and causes stool to float due to excess fluid. It has an oily appearance and foul smell
What causes steatorrhea?
Problems in bile secretion, pancreatic function and intestinal cell uptake
Where does digestion take place?
In the mouth and small intestine (mainly)
What is involved in digestion?
All lipids (mainly TAG), pancreatic enzymes, bile salts which cause emulsification and peristalsis
How are TAGs digested?
By pancreatic lipase which forms monoacylglycerol and 2xFAs
How are cholesterol esters digested?
Broken down to cholesterol and 1xFA
How are phospholipids digested?
Hydrolysed to lysphophospholiid and 1xFA
When are FAs releases from fat stores?
When energy supply is low
How are lipids absorbed?
The products of digestion form mixed micelles with bile salts and their contents are released when a brush border membrane is crossed
Do all FAs need micelles?
No, only long chain FAs
What are bile salts?
Derivatives of cholesterol that are biological detergents that form emulsions with mixed micelles and prevent lipids from combining in an aqueous environment
What is the brush border membrane?
Enterocytes that release the products of lipid into cells via diffusion
How are lipids transported?
Chylomicrons, lipoprotein and albumin
What is the function of chylomicrons?
They store TAG, FAs and cholesterol esters which are then releases by exocytosis into the blood via the lymphatic system
What happens to TAG after it has been transported?
It is hydrolysed to FAs and glycerol by lipoprotein lipase when it reaches tissues
What happens to FAs after they are transported?
They are used a energy or er-esterfired into TAG for storage
What is the most dense out of chylomicrons, HDL and LDL?
Most- HDL
Least- Chylomicrons
What are lipoproteins?
They have hydrophilic surfaces and hydrophobic cores and are transport free FAs
Why are lipoproteins in a complex with serum albumin?
As serum albumin is the most abundant plasma protein with many binding sites
How is cholesterol transported?
LDL- liver -> tissue
HDL- tissue -> liver
What is VLDL?
Very low density lipoprotein
What is albumin?
A protein which is used to transport unesterified carboxylic acids by binding to them
How is excess carbohydrate and C from protein stored?
As FA residues and TAG in adipose tissue due to metabolism through acetyl CoA
Where are FAs synthesised?
Liver, lactating memory gland, adipose tissue and kidney
How are FAs synthesised from TAG?
They are released by hormone sensitive lipase (HSL) which is activated by adrenaline and inhibited by high plasma glucose and insulin
Where does FA synthesis take place?
In the cytosol from acetyl CoA which uses ATP and NADPH
What is acetyl CoA?
It is transported to cytosol by citrate shuttles. It is formed in mitochondria
Why are citrate shuttles used to transport acetyl CoA?
It can’t cross the mitochondrial membrane, only the acetyl bit can
When do citrate shuttles occur?
When mitochondrial [citrate] is high
What are the products of FA synthesis?
Palmitic acid- C16
What is elongation and desaturation?
The further modification of palmitate (ester of palmitic acid) in the mitochondria by digestive enzymes
What is the function of Acetyl carrier protein (ACP)?
It links intermediates
What is the catalyst involved in FA synthesis?
A multi enzyme complex
What is the fate of FAs?
Acetyl CoA -> FA (in liver) -> TAG -> VLDL -> adipose tissue
What is an example of an essential FA?
Omega 3, which is derived from linoleic acid and lowers cholesterol
What are the effects of deficiencies in essential amino acids?
Growth retardation, reproductive failure and chronic intestinal disease
What is B-oxidation?
The metabolism of FAs, by degrading 2xC at a time in the mitochondria matrix
What are the products of B-oxidation?
1xacetyl CoA, 1xNADH, 1xFADH2
What are the 3 stages involved in B-oxidation?
Activation, transport and degradation
What is the process of activation in B-oxidation?
FAs are activated in the cytoplasm and forms acyl CoA
What is acyl CoA?
A temporary compound formed when acetyl CoA binds to a long-chain FA
What is involved in the transport phase of B-oxidation?
Carnitine shuttles
What is the process of transport in B-oxidation?
Long chain FAs are transported from cytoplasm -> inside the mitochondrion, catalysed by carnitine fatty-acyl transferase
What type of amino acid is carnitine?
Non-essential
What is the function of molnyl CoA?
It inhibits carnitine fatty-acyl transferase in FA synthesis
Can FA synthesis and degradation occur at the same time?
Nope
What is the process of degradation in B-oxidation?
FA acyl CoA is dehydrogenated to form FADH2 and another intermediate, which is then hydrated and dehydrated to form NADH. Thylosis then occurs
What is thylosis?
Forms acetyl CoA form dehydrogenated NADH
What are steroid hormones?
They are chemical substances that serve as chemical messengers. Steroids are major lipid class
What is the function of cholesterol?
It is the main starting material for steroid hormone synthesis, and is a component of cell membranes
Where does cholesterol synthesis occur?
Liver
What is the structure of cholesterol?
27xC and 4x benzene rings
What are ketone bodies?
Water soluble compounds produced from excess acetyl CoA that are transported through the blood to peripheral tissues
What are the functions of ketone bodies?
They can be re-converted into acetyl CoA or enter the CAC
What is ketosis?
Metabolic process that burns stored fats when there is not enough glucose, due to starvation as TAGs aren’t being mobilised. The [ketone body] increases
What is ketogenesis?
The production of ketone bodies which occurs in the liver and also produces acetone
Why must acetone be expelled by respiration?
It is too unstable
What are the 2 main types of ketone bodies?
Actetoacetate and 3-hydroxylbutarate
