Lipid metabolism

Question	Answer
Give 4 functions of lipids in the body	1. cell membranes 2. uptake of lipid soluble vitamins 3. precursors to steroid hormones 4. energy store
Fat has a much higher _____ _________ than carbohydrates or proteins	energy content
When _________ ________ exceeds __________, excess is laid down as fat.	calorific intake, consumption
Which tissue uses fat as their preferred energy source?	Cardiac muscle
Triglycerides are ______ fats consisting of a ________ molecule which 3 _______ _______ attached. It is a concentrated store of energy.	neutral, glycerol, fatty acids
What are fatty acids?	Chains of methyl groups with a terminal carboxyl group
_________ fatty acids must be obtained from the diet	essential
Humans cannot create double bonds in fatty acids less than position ___	9
Name 2 places where fatty acid synthesis can take place?	1. Hepatocytes 2. Adipocytes
Where in the cell does fatty acid synthesis take place?	Cytosol
What are 3 substrates needed in fatty acid synthesis?	1. Acetyl CoA 2. NADPH 3. ATP
How is citrate formed?	Combining Acetyl CoA with oxaloacetic acid in the TCA cycle
How is the Acetyl CoA transported from the mitochondria to the cytosol for fatty acid synthesis?	Citrate-malate antiporter
What is its mechanism?	INSIDE MITOCHONDRIA: Acetyl CoA + Oxaloacetic acid = Citrate. Citrate transported across membrane into cytosol, to be split into Acetyl CoA and Oxaloacetic acid again. Oxaloacetate converted to Malate (using NADH) then to Pyruvate (releasing NADPH) which is transported back across the membrane to be converted to oxaloacetate and begin the cycle again.
How is this transfer mechanism helpful?	It has produced 2 of the substrates needed for fatty acid synthesis - Acetyl CoA and NADPH
Where else can NADPH be obtained from?	Pentose phosphate pathway
What is the first step in fatty acid synthesis?	Acetyl CoA + ATP + HCO3- ---> Malonyl CoA + ADP + Pi
Which enzyme catalyses this reaction?	Acetyl CoA carboxylase
What stimulates and inhibits this reaction?	stimulated by: citrate inhibited by: palmitate (fatty acid)
Which vitamin is required for this reaction?	Biotin
What must Malonyl-CoA and Acetyl CoA bind to in order to be activated?	ACP - acyl carrier protein
Acetyl-ACP and Malonyl-ACP combine in a __________ reaction to give ________-____ (4C), releasing _____.	condensation, acetoacetyl-ACP, CO2
Acetoacetyl-ACP undergoes a ________ reaction, then a __________ reaction, then another _________ reaction. The product is ________-____ and 2 molecules of _______ are used.	reduction, dehydration, reduction, butyryl-ACP, NADPH
Butyryl-ACP combines with another _______-___ molecule to elongate the chain of fatty acids.	Malonyl-ACP
All the enzymes required in the elongation of the fatty acid chains form a complex called _____ _____ ________.	fatty acid synthase
Fatty acid synthase exists as a dimer. What does this mean?	Two molecules joined together. They exist in a head-to tail formation
Cholesterol is ________ and virtually ________ in water. It is the precursor of _______, ______ and _____ ______.	hydrophobic, insoluble, sterols, steroids, bile salts
How is cholesterol transported in circulation?	As cholesteryl esters
Where in the body is cholesterol synthesised?	mostly in the liver, but also in adrenal cortex
Where in the cell is cholesterol mostly synthesised?	ER
Synthesis of cholesterol is a complex process with many steps. What is the main regulatory step?	Conversion of HMGCoA to mevalonate, using HMGCoA reductase enzyme
What inhibits that enzyme and thus synthesis of cholesterol?	Cholesterol
Therefore why is it difficult to reduce circulating cholesterol levels by diet alone?	Low levels of cholesterol stimulate its synthesis
What are the 3 key steps in releasing energy from fat stores, and where do they take place?	1. Mobilisation (from adipocyte) 2. Activation (in liver cytosol) 3. Degradation (in liver mitochondria)
What happens during mobilisation?	A hormone (often glucagon) stimulates the Gs pathway to produce cAMP and PKA. PKA phosphorylates the enzyme triacylglycerol lipase, thus activating it. This breaks triacylglycerol to diacylglycerol. Other lipases break this down to glycerol and free fatty acids.
What happens to the glycerol?	It is absorbed by the liver, and converted in a series of reactions into glyceraldehyde 3 phosphate , which can enter glycolysis or gluconeogenesis.
What happens to the free fatty acids?	taken back to the liver OR resynthesised into triglycerides
In the liver cytoplasm, free fatty acids are activated by _____ to form ______ ______ ____. This is combined with ________ using the enzyme __ __ __ __, to give _____ _____ ________.	CoA, fatty acyl CoA, carnitine, CATI, fatty acyl carnitine
The _____ _____ ________ is transported into the matrix of the mitochondria in the liver by _________. In the matrix, __ __ __ __ enzyme converts ______ ______ _________ back into _____ ______ ___ and _________. This transfer process is only needed for longer chain FA.	fatty acyl carnitine, translocase, CATII, fatty acyl carnitine, fatty acyl CoA, carnitine
Once inside the matrix, _______ ____ undergoes __ __________. This process removes __ carbon units and produces _________ ____ , _____ and _____, by a series of reactions.	Acyl-CoA, beta-oxidation, 2, Acetyl CoA, FADH2, NADH
What is the fate of the FADH2 and NADH produced from beta oxidation?	Used to generate ATP
If there is carbohydrate metabolism also occuring, the ______ ____ produced will enter the ____ ______. However usually if ______ ________ of ______ _____ is taking place, there is little glucose available, so the _____ _______ is not taking place - _________________ is instead making glucose. This process uses _____________ and so _______ ____ builds up and is instead converted to ________ _______.	Acetyl CoA, TCA cycle, beta oxidation, fatty acids, TCA cycle, gluconeogenesis, oxaloacetate, acetyl CoA, ketone bodies
What are the 3 ketone bodies?	1. Acetoacetate 2. 3 beta hydroxybuterate 3. Acetone
Acetyl CoA is converted to acetoacetate in 3 stages: 1. Acetyl CoA --> _________ ____ 2. ________ ____ --> __ __ __ ____ 3. __ __ __ ____ --> Acetoacetate	acetoacetyl-CoA, acetoacetyl-CoA, HMG-CoA, HMG-CoA
Acetoacetate can then be reduced to give the other ketone bodies: __ __ _____________ _____ and ________.	3 beta hydroxybutyric acid, acetone
What causes the sweet fruity smell of people's breath who have ketosis?	Acetone
Who may be particularly susceptible to this?	Uncontrolled type 1 diabetics, or people on a low/no carb diet
Which tissues use ketone bodies as a source of energy?	Cardiac muscle and kidneys
Which tissue will use ketone bodies for energy during times of starving?	Brain
What are 4 effects of insulin in response to high levels of glucose?	1. Increased glycolysis in liver 2. Increased fatty acid synthesis in liver 3. Increased triglycerides in adipocytes 4. Decreased beta oxidation
What 2 substances stimulate mobilisation of triglycerides in adipose tissue?	1. Glucagon 2. Adrenaline

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	Created by Hannah Tribe over 10 years ago