Theme 3: Lecture 5 - Introduction to lipids Flashcards
What are the functions of lipids
- Phospholipids & cholesterol: cell membranes
- Triglyceride is a key energy store
- Steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids
How does creatine phosphate store energy
Creatine takes the high energy phosphate bond from ATP and stores it to rephosphorylate ADP at a later time when the cell needs the extra energy
What can Acetyl CoA be turned into
- Cholesterol (blocked by statins)
- Citric acid cycle to produce ATP
- Fatty acids, stored energy (fatty acids can also be converted back into acetyl CoA)
Fatty acid synthesis equation
Acetly-CoA + ATP + e- (ATP) -> fatty acid + CO2 + CoA
Describe fatty acid synthesis
Leads to fatty acids with even-number of carbons
Consumes ATP
Beta oxidation equation
fatty acid -> Acetyl CoA + e- (ATP)
Describe beta oxidation
- Fat Mobilization: Shortens fatty acid by 2 carbons at a time
- Produces ATP + Acetyl-CoA
Describe the structure of fatty acids
- Simple straight carbon chains + COOH
- In humans, most are 16-20 carbons long
What does it mean if it’s an essential fatty acid
It can’t be made in the body, has to be taken in by the diet
What is a triglyceride’s official name
Triacyl-glyceride
What is cholesterol an essential component of
cell membranes
What is cholesterol a precursor to
- Bile acids
- Steroid hormones
- Vitamin D
Sources of cholesterol
- Diet
- Made in liver (with a big emphasis on recycling)
How are cholesterol esters made
A cholesterol molecule is esterified by a long chain fatty acid
What are cholesterol esters broken down by
by lipases to free cholesterol and fatty acids
State cholesterol esters’ interaction with water
Hydrophobic
State cholesterol’s interaction with water
Amphipathic
What is cortisol
hormone secreted by the adrenal cortex
Structure of acetate
CH3COO-
Describe acetate
- Main energy production precursor for everything that happens in citrate cycle
- Can’t be transported in the plasma in this form so is transported by co enzyme A
What are ketone bodies
- Soluble chemicals
- Major energy source during fasting esp for brain and heart
How are ketone bodies made
-Made from acetyl-CoaA during fasting by the liver
-
How long do ketone bodies last
5 hours
Name the 3 ketone bodies
- Acetoacetic acid
- Beta-hydroxybutyric acid
- Acetone
Which ketone bodies are useful
Acetoacetic acid & beta-hydroxybutyric acid
Which ketone body is the waste product
Acetone
How is acetone made
spontaneously by decarboxylation
How is acetone eliminated
by the kidney
Are most naturally occurring unsaturated fatty acids cis or trans
cis
Describe unsaturated fatty acids
- have a lower boiling point so more liquid at body temperature
- increase fluidity of cell membranes
Why do molecules that have a cis carbon carbon double bond have a lower melting point
- The cis double bond creates a kink that saturated and trans unsaturated fat slack
- This kink lowers melting point by interfering with stacking and solidification
What are the two naming systems for unsaturated fatty acids
- Omega classification
- Alpha classification
Describe the omega naming system for unsaturated fatty acids
- Start at the methyl end and count the position of the double bonds in relation to that end
- Linoleic acid would be omega 6, 9
Describe the alpha naming system for unsaturated fatty acids
- State the number of carbons
- State the number of double bonds
- Start at the carboxyl end and count the position of the double bonds in relation to that end
- Linoleic acid would be 18:2 delta 9, 12
What do saturated fats increase
LDL
Which fats are bad for you
- Saturated fats
- Trans unsaturated fats
Why are cis unsaturated fats not bad for you
- They have a lower melting point because of the kink
- Therefore less likely to form a big globular fat and solidify
Where do the 4 lipid transport pathways transport lipids to
-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
Transport from the gut to the liver (and periphery)
What are exogenous lipids
Lipids from the diet i.e. outside the body
How are lipids transported by the exogenous pathway
- Lipids from diet packaged by small intestine into “chylomicrons”
- increased lipids in plasma after a fatty meal
- Chylomicrons taken up by liver (or by periphery)
What is the endogenous pathway
Transport from the liver to the periphery
Where are peripheral lipids stored
in muscle and adipose tissue
What are endogenous lipids
Lipids made by the body i.e. from inside
How are lipids transported by the endogenous pathway
Lipids from liver are packaged into VLDLs
What is the reverse cholesterol transport pathway
Transport from periphery to the liver
What is the reverse cholesterol transport pathway important in
recycling of lipids
When does the reverse cholesterol transport pathway occur
When lipid supplies in the liver are being exhausted
What indicates reverse path activity
HDL in blood
Which transport pathway is bile production in
Transport from liver into gut (and gall bladder)
How does cholesterol help with bile production
It is converted into bile acids
Where do bile acids go after being deposited in the gut
Most are reabsorbed by the gut and returned to the liver and recycled
Why are enzymes and receptors needed in the lipid transport pathways
to move fats in and out of blood vessels
Give an example of an enzyme used in lipid transport pathways
lipoprotein lipase
What does lipoprotein lipase do
- It is a cell surface-linked enzyme in capillary walls
- Metabolises TG to fatty acids + glycerol because TG cannot go through cell membranes
- In order to remove triglycerides from VLDL and to move the TG across the capillary membrane, TG must first be metabolised via lipoprotein lipase
What are lipoprotein particles
plasma soluble particles which can carry lipids
Why do lipids need to be packaged to be transported in the body
They aren’t plasma soluble
What are apolipoprotein particles
Proteins in lipoprotein particles that can hold lipids
What are apolipoprotein particles’ relationship with water
They are amphipathic
Example of a apolipoprotein particle
Apolipoprotein E (apoE)
What density are triglycerides
very low density
What density is cholesterol
midway between TGs and proteins
Are bigger lipoprotein particles lower or higher in density
lower in density
Why is LDL the 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
Where does LDL come from
LDL is eventually “left-over” after periphery absorbs endogenous TG from VLDL from liver
When does HDL appear
when cholesterol is being used up
What does HDL do
lipid transport from fat cells to liver (reverse cholesterol transport)
What does VLDL signify
risk of atheroma
What does VLDL do
Used to transport endogenous cholesterol and TG from Liver to adipose and muscle
What is left after TG is removed by periphery from VLDL
IDL
What is IDL
- Intermediate density lipoprotein
- IDL is intermediate step in pathway where VLDL becomes LDL
- Results from VLDL losing TG to periphery
- IDL will become LDL
What is IDL a sign of
CV risk
When are chylomicron levels high
after fat containing meals
Are chylomicrons associated with CV risk
no
What do chylomicrons do
carry lipids from gut to periphery (for exogenous lipids)
Which cells release insulin
Beta cells in pancreas
Which cells release glucagon
alpha cells in pancreas
What causes type 1 diabetes
no insulin made
What causes type 2 diabetes
absent or decreased response to insulin by target cells but insulin is still being made
What causes type 2 diabetes mellitus
obesity and genetic predisposition
What is hypercholesterolaemia
- Too much cholesterol in the blood
- A subclass of hyperlipidaemias
- High fasting levels of plasma cholesterol
What is hyperlipidaemia
Too much lipid in the blood
Example of hypercholesterolaemia
familial hypercholesterolaemia
What does hypercholesterolaemia cause
increased risk of arteriosclerosis
What is arteriosclerosis
arteries become thick and stiff, sometimes restricting blood flow
What causes hypercholesterolaemia
combination of environmental and genetic factors
What are statins
Drugs used to treat hypercholesterolaemia
How do statins work
Block endogenous cholesterol synthesis by blocking HMG-CoA Reductase (the entry step into cholesterol synthesis)
Give and example of a statin
simvastatin
What are statins prescribed for
CAD prophylaxis
What is metabolic syndrome
a group of risk factors that occur together, leading to increased risk for CAD, stroke, and type 2 diabetes
What are the causes for metabolic syndrome
- Insulin resistance
- Central obesity (waist circumference)
- high blood pressure
What does increased HDL mean
- More recycling of cholesterol
- Lower CV risk