fat metabolism 1/2 WF

Question 1

fatty acids structure?

Answer 1

straight chain
saturated or unsaturated
carboxyl group is C1
carbon chain
double bonds can be cis (naturally occuring) or trans (synthetic)

Question 2

triacylglycerol structure

Answer 2

fatty acids stored as esters with glycerol

Question 3

triacylglycerols features?

Answer 3

water insoluble
liquid at body temp
digestion begins in intestine
converted mechanically into lipid droplets in the stomach

Question 4

digestion of triacylglycerol in the intestine?

Answer 4

bile salts (natural detergents) break down triacylglycerol droplets forming mixed micelles.

pancreatic lipase on triacylglycerol leads to 2 fatty acids and monoacylglycerol.

Question 5

what inhibits pancreatic lipase

Answer 5

orlistat

Question 6

how are triacylglycerols transported? what do these particles contain?

Answer 6

in chylomicrons
contain triacylglycerol, phospholipids, cholesterol + esters, vitamins A/D/E/K

Question 7

where are chylomicrons secreted

Answer 7

from mucosal cells in intestine into lymphatic system, then enter blood through thoracic duct.

Question 8

what class are chylomicrons a member of

Answer 8

plasma lipoproteins

Question 9

structure of chylomicrons

Answer 9

core of triacylglycerol and acyl-cholesterol (hydrophobic)
surrounded in hydrophilic components - phospholipids, cholesterol, apoproteins

Question 10

half life of chylomicrons in the plasma?

Answer 10

~5mins

Question 11

degradation process of chylomicrons?

Answer 11

collect apoprotein C-II which activates degradation enzyme lipoprotein lipase (endothelial cell surfaces).
this hydrolyses triacylglycerol to free fatty acids and glycerol.
free fatty acids taken up by cells.
glycerol remains in plasma and metabolised by liver.
chylomicrons converted to chylomicron remnants which are taken up by the liver.

Question 12

what is the start point for synthesis of long chain fatty acids? what is the first reaction controlled by? what does it involve?

Answer 12

acetyl-CoA
first reaction controlled by acetyl-CoA carboxylase (important control point for synthesis and degradation). requires ATP and CO2 (from bicarbonate)

Question 13

what is acetyl-CoA carboxylase inactivated by?

Answer 13

phosphorylated form = inactive

phosphorylation promoted by glucagon, AMP-activated protein kinase, long chain fatty acyl-CoA

Question 14

what is acetyl-CoA carboxylase activated by?

Answer 14

dephosphorylated form = active
dephosphorylation promoted by insulin

Question 15

fatty acid synthase complex structure, features?

Answer 15

multi-enzyme complex, 2 identical subunits
each subunit has 7 different activities.

converts acetyl-CoA to long chain fatty acids (16 carbon, saturated)

Question 16

7 activities in fatty acid synthase complex?

Answer 16

priming
loading
condensation
two reductions
acyl transfer
reloading

Question 17

hormonal control of triacylglycerol synthesis?

Answer 17

insulin - promotes glucose uptake, acetyl-CoA formation and exportation from mitochondria

glucagon - inhibits glucose conversion, inhibits acetyl-CoA carboxylase

Question 18

malonyl-CoA features?

Answer 18

precursor for fatty acid synthesis
inhibitor of fatty acid oxidation

Question 19

unsaturated fatty acids structure?

Answer 19

1 to 4 double bonds
some can be made, some are essential

Question 20

fatty-acid desaturase system?

Answer 20

removal of 2 hydrogens (reduces O2 to H2O)
other oxygen atom reduced by reduced NAD
insertion of double bonds begins at carbon 9

Question 21

why does essential fatty acid deficiency take a long time to develop?

Answer 21

large reservoir in the body

Question 22

mobilisation of triacylglycerol in adipose tissue done by which enzyme? how is this hormonally controlled?

Answer 22

hormone-sensitive lipase hydrolyses triacylglycerol in adipose tissue

inhibited by insulin
promoted by adrenaline/glucagon/growth hormone

Question 23

eventual product of triacylglycerol in adipose tissue?

Answer 23

glycerol and free fatty acids

Question 24

features of fatty acids?

Answer 24

low solubility
capable of diffusing through biological membranes

Question 25

what are fatty acids transported with?

Answer 25

fatty acids are transported bound to serum albumin

Question 26

how do fatty acids enter cells?

Answer 26

via fatty acid transporters

Question 27

how are fatty acids prevented from leaking back into the plasma once they’ve entered a cell?

Answer 27

attached to coenzyme A (large hydrophilic enzyme)

Question 28

what do fatty acids become once they’ve entered the cell?

Answer 28

acyl-CoA (long chain fatty acids esterified onto coenzyme A)