Introduction to lipids Flashcards
Give some examples of lipids and their functions
Phospholipids & cholesterol: cell membranes
Triglyceride is a key energy store
Steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids
How is energy stored short term in cells?
ATP, redox agents, ionic transmembrane agents and creatine phosphate
How is energy stored long term?
Stored as carbohydrates and fats
Give an overview of how acetyl Co-A acts as an energy mediator
Sugars and starches turn into glucose which can be reversibly converted to form glycogen.
Glucose can either form lactic acid or acetyl CoA
The acetyl CoA form citric acid and ATP or reversibly into fatty acids. Acetyl CoA can be prevented from turning into cholesterol by statins
What does the brain constantly require form the plasma?
Glucose or ketone bodies
What happens in the citric acid cycle?
Acetyl CoA combines with oxaloacetate to form citric acid which then combines with oxygen to release energy and CO2
Describe fatty acid synthesis
Leads to fatty acids with an even number of carbon atoms and consumes ATP
Describe beta oxidation
A way of breaking down fats by fat mobilization
Shortens fatty acids by 2 carbons at a time and produces acetyl CoA and ATP
Describe the structure of a fatty acid
Carbon chain with a COOH group attached
Most are 16-20 carbons long
50% have carbon carbon double bonds
Why are essential fatty acids required?
Mammals lack the ability to make double bonds so some double bonded fatty acids are taken in through the diet
Which chemical group does a fatty acid contain before bound to glycerol?
Acyl group
What is cholesterol?
Essential component of the cell plasma membrane
Precursor of steroid hormones, bile salts and vitamin D
Where is cholesterol obtained?
Liver or diet
There is major emphasis on the recycling of cholesterol. State 2 ways in which it is recycled
Bile salts
Endogenous pathway
How is cholesterol amphipathic as the free alcohol?
Both hydrophobic and hydrophilic
Is a cholesterol ester hydrophilic or hydrophobic?
Hydrophobic
What percentage of cholesterol is esterified?
75%
How is cholesterol broken down?
By lipases to form glycerol and fatty acids
List some steriods
Cholesterol
Vitamin D
Cortisol
Testosterone
What is acetyl CoA?
Main energy production precursor
What are ketone bodies? State them
Soluble chemicals made by acetyl CoA during fasting
Acetoacetic acid & beta-hydroxybutyric acid
Acetone is eliminated as waste
Cis carbon-carbon double bonds create a kink. What does this kink do?
Lowers melting temperatures
State the 4 pathways of lipid transport
From gut (digestive tract) to liver & periphery
(Periphery for lipids = muscle and adipose tissue)
From liver to periphery
From periphery to liver
From liver into digestive tract
What is the exogenous pathway?
From gut to liver. Lipids are packaged into chylomicrons in the small intestine and these are taken up by the liver or periphery
What is the endogenous pathway?
From liver to periphery
Lipid from liver packaged into VLDL
What is reverse cholesterol transport?
From periphery to liver
Occurs when lipid supplies in liver are being exhausted
Thus a sign of reduced body lipid
HDL in blood indicates reverse path activity
Describe bile production
From liver into gut
Cholesterol converted into bile acids
Most bile acids are reabsorbed by gut
Returned to the liver and recycled
Describe LDL
Most Dangerous lipoprotein
LDL contents get incorporated into atheromas
LDL in blood may be “storage” for cholesterol that “cannot be stored elsewhere”
Excess LDL accumulates in atheromas
LDL is eventually “left-over” after periphery absorbs endogenous TG from VLDL from liver
What is HDL?
The good lipoprotein
Increased HDL and lower CV risk
Give the name for when lipids are transported from fat cells to the liver
Reverse cholesterol transport
Describe VLDL
Signifies risk of atheroma
Used to transport endogenous cholesterol and TG from Liver to adipose and muscle
After TG is removed by periphery from VLDL, leaves over IDL
IDL is intermediate step in pathway where VLDL becomes LDL
Describe chylomicron
Not usually associated with CV risk
Normally high after fat-containing meals
Carries lipids from gut to periphery
For exogenous lipids
