Metabolic Pathways: Lipid Catabolism

Question 1

fat and lipid metabolism

Answer 1

increased fat intake without appropriate energy expenditure leads to….

increase in number of adipocytes
more fat in adipocytes

Question 2

control of energy balance depends on

Answer 2

genetically linked factors

environmental factors

Question 3

fat is required

Answer 3

energy source
essential for fatty acids
fat-soluble vitamins

Question 4

lipids

Answer 4

collection of different compounds - simple, compound, steroids

predominately hydrocarbon
usually contain long chain fatty acids
insoluble in water

important for their biological function

Question 5

triglycerides

Answer 5

triacylglycerols

main energy storage from in adipose tissue

compact - dont require concomitant storage of water

hydrophobic

high energy yield per gram

Question 6

triglycerides - structure

Answer 6

consist of glycol and 3 fatty acids

Question 7

fatty acids

Answer 7

mainly straight chains
aliphatic (no rings)
usually contain an even number of C atoms
branded chains and add numbers of C are rare

saturated - no double bonds
unsaturated - one double bond
polyunsaturated - multiple double bonds

double bonds usually in cis configuration

Question 8

main natural fatty acids

Answer 8

palmitic acid

stearic acid

oleic acid

Question 9

polyunsaturated fatty acids

Answer 9

occur only in small amounts

Manny cannot be synthesised by the body
essential fatty acid

Question 10

fatty acids - nomenclature

Answer 10

carboxyl group
C-1
C adjacent to group is alpha carbon
C furthest away is w carbon

Question 11

fatty acids - melting point variation

Answer 11

fatty acids with up to 8 C atoms are liquid at room temperature - longer ones are solid

double bonds lower melting point

plant fats contain large proportion of unsaturated fatty acids - liquid

animal fats contain palmitic and stearic acid - solid

Question 12

main products of fat digestion

Answer 12

glycerol, fatty acids, monoglycerides

Question 13

fat absorption

Answer 13

absorbed into mucosal cells of intestine

coated with a layer of protein, phospholipid, cholesterol - chylomicrons

Question 14

chylomicrons

Answer 14

enter lymph, then the blood stream

at muscle and adipose tissue, chylomicrons are attacked and cleaved by lipoprotein lipase

fatty acids are resynthesises into triacylglycerols and oxidised to provide energy
depends on amount available

Question 15

lipolysis of stored fat

Answer 15

lipolysis = breakdown of lipids

fat is stored in adipose tissue

initial cleavage by hormone sensitive lipases

Question 16

fatty acid oxidation

Answer 16

before oxidisation, converted to CoA derivatives

occurs in cytoplasm

requires 2 ATP

further oxidation of fatty acids occurs in mitochondrial matrix

need to be transported into mitochondria by special carrier mechanism

Question 17

carnitine shuttle

Answer 17

in the cytoplasm

fatty acids are transferred from acyl-CoA to carnitine

acyl-carnitine transporter in inner membrane

net result: acyl-CoA located in the mitochondrial matrix

Question 18

beta oxidisation

Answer 18

cycle of reactions in mitochondrial matrix

four steps in each cycle

PRODUCTS:
1 acetyl-CoA
1 FADH2
1 NADH + H+
1 fatty acyl-CoA, shortened by 2 carbon atoms

Question 19

additional pathways

Answer 19

unsaturated fatty acids - already partially oxidised, yield less FADH2

odd-chain fatty acids - yields propionyl-CoA in last step, converted to succinylcholine-CoA and enters TCA cycle directly

branched-chain fatty acids - C-1 carbon oxidised to CO2, acetyl- and propionyl-CoA released in equal numbers

requires several additional enzymes

Question 20

breakdown of glycerol

Answer 20

activated to glycerol-3-phosphate by glycerol kinase

dehydrogenated to dihydroxyacetone phosphate

Question 21

ketone bodies

Answer 21

formed in liver mitochondria

diffuse into the blood stream and to peripheral tissues

important molecules of energy metabolism for heat muscle and renal cortex