Lipid metabolism

Question 1

Which lipids are used as fuel

Answer 1

Triacylglycerols

Question 2

Which lipids are used in membranes

Answer 2

Glycerophospholipids

Cholesterol

Question 3

Which lipids are used in lipid digestion

Answer 3

Bile salts (from cholesterol)

Question 4

Which lipids are used in communication

Answer 4

Steroid hormones (from cholesterol)

Question 5

Which lipids are used in vision, growth

Answer 5

Vitamins

Question 6

Triacylglycerols composed of

Answer 6

Glycerol and three fatty acids

Question 7

Triacylglycerols joined by

Answer 7

Ester bonds

Question 8

Triacylglycerols efficient form to

Answer 8

Store energy
Body has almost unlimited ability to store these
Can be saturated or unsaturated

Question 9

Fatty acids

Answer 9

Have variable length

Question 10

Sources of lipids

Answer 10

Diet

Carbohydrates (in liver)

Question 11

Major dietary lipid

Answer 11

Triacylglycerols

Question 12

Digestion of dietary lipids: what emulsifies

Answer 12

Bile salts

Question 13

Digestion of dietary lipids: what breaks down fatty acids from triacylglycerols

Answer 13

Lipases

Question 14

Digestion of dietary lipids: fatty acids form

Answer 14

Micelles, absorbed by epithelial cells, packaged as chylomicrons

Question 15

Chylomicrons

Answer 15

Comprised of layer of phospholipids (hydrophilic head, hydrophobic tails)
Apoproteins added in RER, packaged together in golgi and then become part of chylomicron

Question 16

What happens to chylomicrons?

Answer 16

Triacylglycerols digested by lipoprotein lipase (LPL)
LPL produced by adipose, muscle and lactating mammary gland cells
Regulated by insulin
Fatty acids absorbed by cells; other remnants absorbed by liver

Question 17

HDL (high density lipoprotein)

Answer 17

Mature them into final chylomicrons by adding components

Question 18

Lipoprotein lipase sat on surface of cells

Answer 18

Recognise apoproteins (e.g. C2)
Receptor and enzymes
Digesting fatty acids, remnants back into blood stream, apoproteins recognised by liver

Question 19

Endogenous lipids

Answer 19

Fatty acids synthesised in liver
Glucose is source of carbons
Reactions occur in cytosol
Fatty acids can be stored as triacylglycerols, oxidised as fuel or used to make components of membranes
Packaged with proteins to form VLDL

Question 20

Endogenous lipids

Answer 20

Fatty acids synthesised in liver
Glucose is source of carbons
Reactions occur in cytosol
Fatty acids can be stored as triacylglycerols, oxidised as fuel or used to make components of membranes
Packaged with proteins to form VLDL (released to blood)

Question 21

Functions of TCA cycle except for to produce energy

Answer 21

To make fats

e.g. Citrate –> fatty acid synthase

Question 22

VLDL

Answer 22

Newly formed triaglycerides packaged into lipoproteins for secretion
Very low density lipoprotein
In this form they are transported to other tissues
Similar structure to chylomicron

Question 23

VLDL Fate

Answer 23

Triacylglycerols digested by lipoprotein lipase (LPL)
LPL produced by adipose, muscle and lactating mammary gland cells
Regulated by insulin
Fatty acids absorbed by cells
VLDL remnant remains

Question 24

Fatty acid oxidation

Answer 24

Fatty acids are important fuel source
During fasting, fatty acids become main energy source
Long chain fatty acids released from adipose tissue, stimulated by < insulin and > glucagon
Taken up by other tissues e.g. muscle
Several different pathways but main one is beta-oxidation

Question 25

Beta-oxidation

Answer 25

Fatty acids enter tissues by diffusion Then activated to acetyl CoA, producing NADH and FAD2H Repeated until all Cs have been converted to acetyl CiA (2C) Acetyl CoA can enter TCA cycle *Fatty acids can be very long, containing many carbons, producing a lot of energy*

Question 26

Beta-oxidation

Answer 26

Fatty acids enter tissues by diffusion Then activated to fatty acyl CoA using ATP Fatty acyl-CoA transported into mitochondria Then activated to acetyl CoA, producing NADH and FAD2H Repeated until all Cs have been converted to acetyl CiA (2C) Acetyl CoA can enter TCA cycle *Fatty acids can be very long, containing many carbons, producing a lot of energy*

Question 27

Fed vs fasting

Answer 27

Fed: triacylglycerols being taken up into tissues Fasting: released to bloodstream

Question 28

Cholesterol

Answer 28

``` Can be synthesised or obtained from diet Major component of blood lipoproteins Important as: -component of cell membranes -precursor of bile salts -precursor of steroid hormones -precursor of vitamin D ```

Question 29

Cholesterol absorption

Answer 29

Enters gut enterocytes predominantly by diffusion Cholesterol cannot be fully metabolised - entry must be regulated Enterocytes transport excess back into gut lumen -cholesterol and bile salts excreted in faeces Defects in proteins which transport cholesterol out of leads to chlolesterol accumulation and cardiovascular disease

Question 30

Cholesterol synthesis

Answer 30

``` Occurs in cytosol (mainly liver) 4 stages: 1. Acetyl-CoA --HMG-CoA reductase --> mevalonate 2. Mevalonate --> isoprenes 3. Isoprenes (5C) --> Squalene (30C) 4. Squalene ---> Cholesterol ```

Question 31

Cholesterol fate

Answer 31

Secreted from liver as: - bile salts - ->stored in gallbladder - ->secreted into gut - ->aid digestion by emulsifying fat - biliary cholesterol - ->secreted into gut - ->can be reabsorbed - cholesterol ester - ->packaged in VLDL and transported to tissues

Question 32

Bile salts

Answer 32

Charged molecules, effective as detergents | Predominantly recycled to liver

Question 33

Cholesterol transport

Answer 33

Cholesterol and cholesterol esters transported in lipoproteins Cholesterol helps to stabilise lipoprotein

Question 34

Cholesterol cell entry

Answer 34

When triglycerides removed from VLDL and absorbed, VLDL 'remnant' remains Converted to IDL and then LDL LDL contain a lot of cholesterol and cholesterol esters This can be: -returned to liver to make more VLDL -taken up by other cells needing cholesterol (membrane synthesis and steroid hormone synthesis) Excess LDL can be endocytosed by macrophages This can cause inflammation and contribute to atherosclerosis

Question 35

What happens to excess LDL?

Answer 35

Excess cholesterol taken up by macrophage --> foam cell Creates turbulence/ narrowing Damages blood vessel Thrombus develops whilst trying to heal BV Major cause of cardiovascular disease

Question 36

How is cholesterol taken up by cells

Answer 36

LDL particle containing apoprotein and cholesterol ester recognised by cell membrane --> receptor-mediated endocytosis Useful stuff absorbed by endosome, digested by lysosome, used by cell LDL receptor recycled out of cell and used again

Question 37

Statins

Answer 37

Used to combat high cholesterol levels in the blood Competitively inhibit HMG Co-reductase, an enzyme required for cholesterol synthesis Structural analogues of natural substrate, compete for binding - have higher affinity -mimic part of substrate that fits into active site of enzyme to inhibit it

Question 38

What affects action of HMG-CoA reductase?

Answer 38

Cholesterol, glucagon and cholesterol lowering drugs inhibit it. Insulin increases its action