Lipids

Question 1

What are some of the functions of lipids?

Answer 1

membrane structure
hormones
vitamins
energy storage
signalling
enzyme cofactors
insulation

Question 2

what are the essential fatty acids which we have to obtain from diet?

Answer 2

linoleic acid

arachidonic acid

Question 3

what is arachidonic acid derived from?

Answer 3

linoleic acid

Question 4

what are the main dietary lipids?

Answer 4

TAG
phospholipids
cholesterol esters

Question 5

what is the structure of a TAG?

Answer 5

glycerol head and three fatty acids

Question 6

what is the structure of phospholipids?

Answer 6

glycerol with two fatty acids and hydrophilic phosphate attached to glycerol

Question 7

how are lipids digested and absorbed in the gut?

Answer 7

emulsification breaks up lipid lumps
pancreatic lipase cuts up TAG into fatty acids
bile salts form micelles with long fatty acids for absorption by gut cells
free fatty acids are absorbed directly

Question 8

what happens to fatty acids once they enter the gut cells?

Answer 8

reassembled into TAG, cholesterol esters and phosphplipids for export

Question 9

what happens to fatty acids when they leave the gut cells?

Answer 9

packaged into chylomicrons with ApoB48

travel through lymph then blood to capillaries

Question 10

what is the protein that holds lipids packaged into chylomicrons for travel in the circulation?

Answer 10

apoB-48

Question 11

what happens to chylomicrons when they reach the capillaries?

Answer 11

fatty acids cleaved off by lipoprotein lipase

then used up for fuel or stored in adipose tissue

Question 12

what triggers the release or storage of TAG in adipose tissue?

Answer 12

hormone sensitive lipase (HSL) activated by epinephrine - releases TAG
high glucose in blood - inhibits release of TAG

Question 13

how are lipids transported in the blood when release from adipose tissue?

Answer 13

free fatty acids - albumin

fatty acid esters (compounds) - lipoproteins

Question 14

what are the different types of lipoproteins, what do they carry and where?

Answer 14

chylomicrons - TAG from intestine to tissues after absorption
VLDL - TAG from liver to tissues
LDL - cholesterol from liver to tissues
HDL - cholesterol from tissues to liver

Question 15

what are the three stages of fatty acid metabolism?

Answer 15

activation
transport
degradation

Question 16

what happens during fatty acid activation?

Answer 16

fatty acid is turned into fatty acyl CoA in cytosol

Question 17

what happens during fatty acid transport?

Answer 17

fatty acyl CoA transported into mitochondrion through carnitine shuttle
CoA taken off before transport, another CoA added in mitochondrion

Question 18

what are the four steps of fatty acid degradation and what happens during them?

Answer 18

Dehydrogenation - FAD to FADH2
Hydration - water added
Dehydrogenation - NAD to NADH
Thiolysis - becomes Acetyl CoA

Question 19

what happens to Acetyl CoA if there is too much of it in the mitochondria of the liver?

Answer 19

Acetyl CoA turned into Ketone bodies

pyruvate carboxylase turns pyruvate into oxaloacetate for gluconeogenesis

Question 20

what are the properties of Ketone bodies?

Answer 20

can be used for fuel by brain and muscle
can’t be used by liver
acidic compound

Question 21

what happens if there are too many ketone bodies in the circulation?

Answer 21

acidosis

fruity breath from acetone

Question 22

what are the three types of ketone bodies?

Answer 22

acetoacetate
acetone
D-betahydroxybutarate

Question 23

what molecules inhibits carnitine shuttle activity?

Answer 23

malonyl CoA

Question 24

what is the energy yield from breakdown of a 16C fatty acid chain?

Answer 24

7 FADH2
7 NADH
8 Acetyl CoA
129 ATP total

Question 25

how is a fatty acid chain broken up for metabolism?

Answer 25

two carbons at a time

Question 26

what happens if the fatty acid chain is too long?

Answer 26

shortened in peroxisome | no FADH2 comes off

Question 27

are ketone bodies water or lipid soluble?

Answer 27

water soluble

Question 28

what is the process of fatty acid metabolism called?

Answer 28

beta oxidation

Question 29

where in the cell does fatty acid synthesis occur?

Answer 29

in cytosol

Question 30

how does Acetyl CoA get transported from the liver cell mitochondrion to the cytosol?

Answer 30

through the citrate shuttle

Question 31

what is the building block of fatty acid synthesis?

Answer 31

malonyl CoA

Question 32

which molecule is used to carry H+ in fatty acid synthesis?

Answer 32

NADPH

Question 33

how is cholesterol synthesised?

Answer 33

acetyl CoA converted to HMG CoA

Question 34

what are eicosanoids and some examples?

Answer 34

long fatty acid chains derived from essential fatty acids | examples are leukotrienes, prostaglandins, thromboxane

Question 35

what are the steps involved in fatty acid synthesis and what happens in them?

Answer 35

condensation (acetyl CoA to Malonyl CoA) reduction (NADPH to NADP) dehydration (water molecule lost) reduction (NADPH to NADP)

Question 36

where are fatty acids further synthesised in the cell?

Answer 36

Endoplasmic reticulum

Question 37

what enzyme turns acetyl CoA into malonyl CoA in fatty acid synthesis?

Answer 37

Acetyl CoA Carboxylase

Question 38

where are steroids derived from?

Answer 38

cholesterol

Question 39

what is the end result of fatty acid synthesis?

Answer 39

``` palmitic acid 8 CoA 14 NADP 7 ADP 7 Pi 7 H2O ```

Question 40

how is Malonyl CoA carried through the cytosol to be added to the growing fatty acid chain?

Answer 40

through ACP

Question 41

what is the main enzyme complex used to link together malonyl CoA to turn it into palmitic acid?

Answer 41

fatty acid synthase

Question 42

how is nitrogen captured from the atmosphere?

Answer 42

through nitrogen fixation by bacteria

Question 43

how is nitrogen found in the body, and how is it passed to different molecules?

Answer 43

found in amino groups | transamination "ping-pong reaction" to bounce amino groups from one molecule to the other

Question 44

what is an amino acid called when it doesn't have a nitrogen attached to it?

Answer 44

keto acid

Question 45

what is the only molecule in the body which accepts nitrogen directly (as ammonia)?

Answer 45

glutamate

Question 46

what are the four most commonly found amino acids in the body?

Answer 46

Alanine Aspartate Glutamine Glutamate

Question 47

how is nitrogen excreted by the body?

Answer 47

through the urea cycle

Question 48

where does metabolism of nitrogen occur in the body?

Answer 48

mitochondria of liver cells

Question 49

what are the enzymes which break down proteins in the body, where do they occur and what is their function?

Answer 49

pepsin - stomach (break proteins into peptides) trypsin/chymotrypsin - small intestine (break up larger proteins into peptides) aminopeptidases - small intestine (break up peptides into amino acids)

Question 50

when are proteins broken down by the body?

Answer 50

during starvation once sugars/fats are depleted when there is excess protein from turnover when there is excess protein from diet

Question 51

what is an important co-factor for the function of transaminases, and what is it derived from?

Answer 51

pyridoxal phosphate cofactor | derived from vitamin B6

Question 52

what is a proteasome and when is it used?

Answer 52

recycling point for malfunctioning proteins | proteins "ubiquinated" and sent to proteasome for breaking up

Question 53

what is the purpose of the glucose-alanine cycle?

Answer 53

it allows pyruvate to be turned back into glucose when muscle is exercising anaerobically

Question 54

when are the two main nitrogen acquiring steps during protein metabolism?

Answer 54

when ammonia is captured by synthesis of Carbamoyl phosphate (after glutamate has been split) when aspartate enters the urea cycle

Question 55

how can the carbon chains of amino acids be used during metabolism?

Answer 55

they can be broken down for energy (CAC) they can make the citric acid cycle intermediaries they can form glucose through oxaloacetate and gluconeogenesis they can form ketone bodies through Acetyl CoA

Question 56

why are glutamine and alanine used to transport nitrogen around the body, rather than glutamate?

Answer 56

because glutamate has negative charge | alanine and glutamine are uncharged

Question 57

what is the main function of the urea cycle?

Answer 57

to introduce ammonia (which is toxic) and turn it into urea (non-toxic)

Question 58

what is an example of a metabolic urea cycle disorder?

Answer 58

ornithine transcarbamoylase deficiency

Question 59

what is an example of a metabolic amino acid disorder?

Answer 59

phenylketonuria (PKU)