fatty acid synthesis

Question 1

. Know the differences between saturated and unsaturated fatty acids.

Answer 1

Saturated fatty acids: contain no double bond. Unsaturated: fatty acids contain one or more
double bonds. Almost all double bonds in fatty acids are in cis configuration.Saturated fatty acids: contain no double bond. Unsaturated: fatty acids contain one or more
double bonds. Almost all double bonds in fatty acids are in cis configuration.

Question 2

how do double bonds affect characteristics of a fatty acid

Answer 2

Cis double bonds cause the fatty acid to bend at that position. Addition of double bonds decreases the melting temperature and increases membrane fluidity if it is a component of cell membrane

Question 3

name essential fatty acids

Answer 3

Linoleic acid (the precursor of arachidonic acid that is the substrate for prostaglandin synthesis) and linolenic acid (the precursor of other omega-3 fatty acids important for growth) can only be obtained from diet b/c we lack the enzyme to introduce double bonds btw carbon 9 and methyl group end

Question 4

naming mechanisms for fatty acids`

Answer 4

1. ie. 20:4(5, 8, 11, 14) where there are 20 carbons in the chain and 4 double bonds at locations 5,8,11 and 14. 2. carbon atoms are named as alpha, beta…omega

Question 5

2. Describe how and why fatty acid synthesis is favored when energy sources are in excess.

Answer 5

Excess carbs and proteins are converted to pyruvate and Acetyl-CoA whch are converted to palmitic acid and other fatty acids

Question 6

3. List the three phases of fatty acid synthesis and know the substrates for fatty acid synthesis.

Answer 6

1. Production of cytosolic acetyl CoA. 2. conversion of acetyl CoA to malonyl CoA (via acetyl CoA carboxylase). 3. Conversion of malonyl CoA into palmitate (via fatty acid synthase)

Question 7

describe production of cytosolic Acetyl CoA in FAA synthesis

Answer 7

Oxidation of pyruvate/ catabolism of fatty acids, ketone bodies and aa > acetyl CoA in mitochondria > acetyl CoA is condensated with OAA to form citrate (citrate synthase) > transported into cytosol > citrate cleaved by ATP-citrate lysate > cytosolic Acetyl CoA and OAA

Question 8

Describe production of malonyl CoA in FAA synthesis

Answer 8

Acetyl CoA carboxylase converts Acetyl CoA to malonyl CoA. This is the rate limiting step for FAA synthesis and requires bicarb, ATP and biotin (coenzyme).

Question 9

structure of actyl CoA carboxylase

Answer 9

three functional regions- the Biotin Carrier Protein, Biotin Carboxylase and the Transcarboxylase that transfers the carboxyl group to acetyl CoA to make malonyl CoA. Biotin moves from one active site to the other via a flexible arm.

Question 10

describe production of palmitate in FAA synthesis

Answer 10

Fatty acid synthase performs 4 steps: malonyl CoA to 3-ketoacyl ACP (acyl carrier protein) > reduce keto group to alcohol > dehydration to introduce double bond > reduce double bond to saturated bond. NADPH is used for two reduction steps, supplied by hexose monophosphate pathway.

Question 11

What is the final product of fatty acid synthesis

Answer 11

palmitic acid (16:0)- the first two carbons are from Acetyl CoA and the rest are from malonyl CoA

Question 12

discuss how palmitate is converted into other fatty acids

Answer 12

Palmitate can be further elongated by the addition of two carbon units in the ER and the mitochondria (by fatty acid elongases) to form other long chain fatty acids. Enzymes in the ER, called mixed-function oxidase, can desaturate fatty acids by introducing cis double bonds.

Question 13

How is fatty acid synthesis regulated

Answer 13

diet/metabolic conditions and by regulating acetyl CoA carboxylase

Question 14

How does high carb diet affect FAA synthesis

Answer 14

Stimulates FAA synthesis. Increases pyruvate and Acetyl coA in mitochondria, favoring production and translocation of citrate from mitochondria to cytosol

Question 15

How does high fat/ low carb diet affect FAA synthesis

Answer 15

Reduces FAA synthesis- leads to low pyruvate flux in mitochondria and elevated acyl CoA in cytoplasm

Question 16

How does high insulin or glucagon affect FAA synthesis

Answer 16

high insulin favors FAA synthesis. High glucagon favors lipolysis (beta oxidation)

Question 17

how does long term diet affect FAA synthesis

Answer 17

Prolonged consumption of a diet containing excess calories causes an increase in transcriptional expression of acetyl CoA carboxylase and fatty acid synthase; in contrast, fasting causes a reduction of expression of acetyl CoA carboxylase and fatty acid synthase

Question 18

Regulators of acetyl CoA carboxylase

Answer 18

1. citrate- activates this enzyme by causing polymerization and increasing Vmax. 2. Palmitoyl CoA- inhibits enzyme. 3. insulin- activates enzyme by activating protein phosphatase which dephosphorylates ACC. 4. glucagon- inhibits ACC by activating cAMP-dependent protein kinase which phosphorylates ACC

Question 19

How are fatty acids stored

Answer 19

as Triacylglycerols- 3 fatty acids esterified to a glycerol molecule. Occurs in liver and adipose tissue

Question 20

How are triacylglycerols stored

Answer 20

Packaged with cholesterol, phospholipids, and apoB-100 into VLDL particles which are secreted into blood.

Question 21

5. Explain how chronic alcoholism causes hyperlipidemia in both the liver and serum.

Answer 21

ethanol oxidized to fatty acids in liver > elevated NADH/NAD slows TCA cycle and and fatty acid oxidation promotes glycerol-3-phosphate production > glycerol-3-P + fatty acids forms triacylglycerols > liver secretes abnormally high VLDL but as liver function is impaired, protein synthesis decreases and liver becomes unable to produce/secrete VLDL. Hepatic fat builds up