Lipids Flashcards
what are lipids?
Heterogenous organic molecules
what are uses of lipids?
They store energy. The are a structural component of cell membrane. They are needed as enzyme co-factors. Hormones. Synthesis of ADEK vitamins Used as signalling molecules.
What are fatty acids?
hydrocarbon chains with a carboxylic group at one end. can be saturated or unsaturated.
what is an essential fatty acid?
must be obtained from plants. e.g. linoleic and a-linoleic acids
What are good fats?
high in polyunsaturated fatty acids - e.g sunflower oil.
what are bad fats?
high in saturated fats, e.g stearic acid
what are really bad fats?
trans fats e.g margarine
Why must essential fatty acids be obtained through our diet?
Because we cannot introduce double bonds beyond carbon 9.
what are triglycerides ?
esters of fatty acids and glycerols .
are triacylglycerides water soluble?
nope. they coalaes into droplets in water, so they are a major component of adipose tissue and act as insulation and dietary fuel.
what are phospholipids.
Glycerol bound to two fatty acids and a phosphate group. amphipathic - form phospholipid bi layer in cell membrane
what are the main dietary lipids?
triglyceride
where does most lipid digestion take place?
small intestine through the use of pancreatic enzymes, bile salts, and emulsification.
what is TAG digested by and what it is made>
pancreatic lipase - made into monoacylglycerol and two fatty acids
what is cholesterol esters broken down into?
cholesterol and a fatty acid
what are phospholipids broken down into?
hydrolysed to a fatty acid and a lysophospholipid
What do all the products of lipid digestion form?
mixed micelles with bile salts - release their contents when they approach the brush border.
what acids don’t need mixed micelles
short and medium chain fatty acids
what cells repackage TAG, fatty acids and cholesterol esters? what do they form?
intestinal cells. form chylomicrons.
where do chylomicrons go?
into the blood via the lympathic system
What happens when chylomicrons reach the tissues?
TAG is hydrolysed to fatty acids and glycerol by lipoprotein lipase. The free fatty acids are used for energy, or re-esterfied to TAG for storage.
Free fatty acids are transported in lipoproteins in a complex with what?
serum albumin.
What lipoproteins also transport fats?
High and low density lipoproteins
what do LDLS do and is it good or bad?
LDLs carry cholesterol from the liver to other tissues which is bad.
What do HDLs do?
Pick up cholesterol from the tissues and take it to the liver for elimination.
what does the beta oxidation pathway of fatty acids do?
degrades fatty acids 2 carbons a time to form acetyl CoA, NADH and FADH2.
Where does the beta oxidation pathway occur?
the mitochondrial matrix.
what are the three stages of the beta oxidation pathway?
Activation, Transport and Degradation
Describe stage 1 - activation -of the beta oxidisation pathway?
Fatty acids are activated to form fatty acyl CoA in the cytoplasm
What transfers long chain fatty acyl CoA from the cytoplasm to the inside of the mitochondrion?
carnitine shuttle
what is carnitine?
a non-essential amino acid.
How come synthesis and degradation of fatty acids cannot occur simultaneously
because carnetine fatty - acyl transferase is inhibited by molnyl CoA - which is used in fatty acid synthesis
Explain degradation in the beta oxidation pathway.
Fatty acyl CoA is DEHYDROGENATED to form FADH2 and another intermediate.
This intermediate is hydrated (needs H20).
The intermediate made from this is dehydrogenated to form NADH.
Thiolysis (cleaved) occurs to form Acetyl CoA, that feeds into CAC
What is produced in each beta- oxidation cycle?
1 Acetyl CoA, 1NADH, 1FADH2, a and carbon species 2 carbon shorter than the original
is any fatty acid gluconeogenic?
no - cannot be used to synthesis glucose
What can excess acetyl CoA from fat metabolism be made into?? (particular during fasting or starvation)
ketone bodies
What use ketone bodies as a food source?
Cardiac and skeletal muscle - and brain during time of starvation
where does ketogenesis occur?
the liver
What is also produced during ketogeneisis but what happens to it?
acetone - expelled during expiration due to it being too volatile and unstable as a metabolite.
what are the main ketone bodies??
Acetoacetate and 3-hydroxybutarate.
how do we get carnitine?
diet
made from lysine or methionine in the liver/kidney
How many ATP molecules are formed?
129 - 32 from each glucose molecule.
where do very long chained fatty acids under a pre- b-oxidation and why is it less energy efficient?
peroxisomes -
doesn’t produce FADH2
