Lipid Metabolism and Ketones

Question 1

consequences of increased fat intake without appropriate energy expenditature

Answer 1

increase in number of adipocytes
more fat in adipocytes
obesity

Question 2

what is the energy balance dependent on

Answer 2

genetically linked factors - protein messengers regulating appetite
environmental factors - food abundance, fashionable food

Question 3

requirements for fat

Answer 3

energy source
essential fatty acids - polyunsaturated fats cannot be made in the body (deficiencies lead to membrane disorders, increased skin permeability, mitochondrial damage)
soluble vitamins - A, D, E, K stored in body fat

Question 4

structure of lipids

Answer 4

predominantly hydrocarbon
long chain fatty acid
insoluble in water - important for biological function

Question 5

examples of lipids

Answer 5

simple
compound
steroids

Question 6

describe triglycerides

Answer 6

simple lipid - glycerol and 3 fatty acids
main energy storage form in adipose tissue
compact - doesn’t require concomitant storage of water
hydrophobic
high energy yield per gram

Question 7

structure of fatty acids

Answer 7

mainly straight chains
aliphatic - no rings
even number of carbon atoms - branched and odd numbers of carbon atoms are rare

Question 8

saturated fatty acid

Answer 8

no double bond

Question 9

unsaturated fatty acid

Answer 9

double bond - cis figuration

Question 10

polyunsaturated fatty acid

Answer 10

multiple double bond
lower the melting point
occur in small amounts - cannot be synthesised by body but is essential for living
e.g. linoleic acid

Question 11

examples of natural fatty acids

Answer 11

palmitic acid - saturated
stearic acid - saturated
oleic acid - unsaturated

Question 12

melting point of fatty acids

Answer 12

fatty acids with <8 carbon atoms - liquid at room temp
plants contain large proportions of unsaturated fatty acids - liquid
animal fats contain mostly palmitic and stearic acid - solid

Question 13

products of fat digestion

Answer 13

glycerol - readily absorbed in intestinal epithelial cells
fatty acids
monoglycerides

Question 14

fat absorption

Answer 14

absorbed into mucosal cells of intestine;
short and medium length fatty acids enter portal blood
longer chain fatty acids and monoglycerides are re-synthesised to triglycerides

Question 15

chylomicrons

Answer 15

fat coated with a layer of protein, phospholipid and cholesterol

Question 16

action of a chylomicron

Answer 16

enter lymph then enter the blood stream
at muscle and adipose tissue, chylomicrons are attacked and cleaved by lipoprotein lipases
there, fatty acids are;
re-synthesised into triacylglycerols (in adipose tissue, for storage)
oxidised to provide energy (in muscle)
depends on amount available

Question 17

describe lipolysis

Answer 17

breakdown of lipids - initial cleavage by hormone sensitive lipases e.g. adrenaline-sensitive - releasing free fatty acids and glycerol, occurs when energy is needed
fat stored as adipose tissue

Question 18

activation of fatty acids prior to oxidation

Answer 18

they have to first be converted to CoA derivatives - fatty acid + CoA –> acyl-CoA –> carnitine
occurs in cytoplasm
requires energy - 2ATP

Question 19

how and why are fatty acids transported to mitochondrial matrix

Answer 19

for further oxidation, first they have to be transferred from acyl-CoA –> carnitine
transported via acyl-carnitine transport (carnitine shuttle) in inner membrane to mitochondrial matrix

Question 20

beta-oxidation of fatty acids

Answer 20

occurs in mitochondrial matrix

4 steps in each cycle

Question 21

products of beta oxidation

Answer 21

acetyl-CoA
FADH2
NADH + H+
fatty acyl-CoA - shortened by 2 carbon atoms

products then go to TCA cycle

Question 22

how to calculate the number of oxidations required for complete catalysis of a saturated fat

Answer 22

(x/2) - 1

Question 23

breakdown of glycerol

Answer 23

glycerol is activated to glycerol-3-phosphate by glycerol kinase - present in liver and kidney but absent from adipose tissue, skeletal and heart muscle
glycerol kinase then dehydrogenated to dihydroxyacetone phosphate

Question 24

where are ketone bodies formed

Answer 24

formed in liver mitochondria - from acetyl-CoA from beta oxidation

Question 25

ketosis

Answer 25

diffuse into the blood stream and to peripheral tissues
important for energy metabolism for heart muscle renal cortex - converted back to acetyl-CoA via fatty acid oxidation and enters TCA cycle
dependent on C4 compound (oxaloacetate) for formation of citrate

Question 26

ketosis in starvation and diabetes

Answer 26

oxaloacetate is consumed for gluconeogenesis
fatty acids are oxidised to provide energy
acetyl-CoA is converted to ketone bodies
high levels in blood
too much for extrahepatic tissue (i.e. heart, brain, etc.)
ketone bodies are moderate acids
accumulation leads to severe acidosis (blood can’t buffer any more)
impairs tissue function, particularly central nervous system
smell of acetone can be detected in breath