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BIOL 3421 - molecular biochem > lipid synthesis: palmitate modification > Flashcards

lipid synthesis: palmitate modification Flashcards

1
Q

list 5 things we can do with palmitate

A

elongate it, desaturate it, make eicosanoids, make TAGs, make membrane phospholipids

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2
Q

list the 4 basic steps of FA elongation

A

condensation, reduction, dehydration, reduction

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3
Q

what do you get after elongating palmitate once

A

stearate (18:0)

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4
Q

where does FA elongation occur in the cell (2)

A

smooth ER and mitochondria

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5
Q

what two things serve as precursors for desaturation

A

palmitate and stearate

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6
Q

name the two most common MUFAs

A

palmitoleate and oleate

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7
Q

what is the shorthand of palmitoleate

A

16:1(Δ9)

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8
Q

what is the shorthand of oleate

A

18:1(Δ9)

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9
Q

what enzyme family is involved in adding double bonds to FAs

A

desaturases

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10
Q

name the process of converting palmitate to palmitoleate

A

desaturation

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11
Q

name the processes of converting palmitate to oleate

A

elongation (=stearate) followed by desaturation

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12
Q

describe the process of adding double bonds via desaturase

A

both FA-CoA and NADPH lose 2 electrons, and molecular oxygen receives them and is reduced to water (water acts like an electron acceptor so the double bond can be made)

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13
Q

which end of the FA chain are double bonds added to via desaturases

A

the methyl end

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14
Q

T or F: mammals do not have desaturases to add double bonds to the methyl end

A

true

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15
Q

because mammals don’t have desaturases, which 2 important molecules are we unable to produce

A

linoleic acid and a-linolenic acid (the omegas)

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16
Q

what is the shorthand name for linoleic acid?

A

18:2 (Δ9,12)

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17
Q

what is the shorthand name for linolenic acid?

A

18:3 (Δ9,12, 15)

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18
Q

T or F: plants do not have desaturases

A

false; they do

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19
Q

how do mammals obtain linoleic and linolenic acid?

A

from the diet

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20
Q

sources of linoleic acid?

A

vegetable oils

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21
Q

sources of linolenic acid?

A

green leafy veggies, flax and chia seeds, canola and soybean oils

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22
Q

how is linoleate produced from oleate

A

desaturation

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23
Q

how is linolenate produced from linoleate

A

desaturation

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24
Q

list the omega 6 derivatives of linoleate (3)

A

y-linolenate, eicosatrienoate, and arachidonate

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25
Q

list the omega 3 derivatives of linoleate (3)

A

a-linolenate, EPA, DHA

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26
Q

T or F: we directly ingest the omegas

A

false; we indirectly ingest them

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27
Q

describe how mammals obtain omegas via indirect ingestion

A

we must ingest linoleic and a-linolenic acid, and then those can be further desaturated and elongated to make PUFAs

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28
Q

which part of the brain heavily relies on PUFAs

A

grey matter membranes

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29
Q

list some benefits of FAs to grey matter membranes of the brain

A

enhances synaptic plasticity and memory, inhibits the production of neurotoxic cytokines, stimulates neurite outgrowth, increases cognition for people with alzheimer’s, lowers heart disease, lowered inflammatory response

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30
Q

list two groups of people that have been found to have low PUFAs in the blood

A

people with schizophrenia/depression, children with autism spectrum disorders

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31
Q

what are the three eicosanoids derived from

A

arachidonic acid

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32
Q

T or F: several hormones stimulate eicosanoid synthesis

A

true

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33
Q

where is arachidonic acid in regards to phospholipids

A

it serves as the FA tails

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34
Q

describe how eicosanoid synthesis is triggered while arachidonic acid is serving as the FA tail in phospholipids

A

hormones will trigger A2 phospholipases to cleave a membrane phospholipid, freeing arachidonic acid

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35
Q

what frees arachidonic acid from phospholipids

A

A2 phospholipases

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36
Q

after arachidonic acid is freed from phospholipids during eicosanoid synthesis, what occurs?

A

enzymes will convert it to an initial prostaglandin (PGH2) in a two step process

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37
Q

which enzyme converts freed arachidonic acid to PGH2? what is a special characteristic of this enzyme?

A

the conversion occurs via a multi-functional enzyme called cyclooxygenase

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38
Q

describe how cyclooxygenase (COX) is multifunctional. What types of activity does it have?

A

cyclooxygenase activity: COX introduces 2 oxygens to form an intermediate ringed peroxide
peroxidase activity: COX reduces one peroxide to alcohol to form PGH2

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39
Q

how many forms of the COX enzyme do mammals have

A

2

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40
Q

what two forms of the COX enzyme do mammals have

A

COX1 and COX2

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41
Q

which eicosanoid’s synthesis is blocked during the use of asprin?

A

prostaglandin

42
Q

describe how aspirin blocks prostaglandin synthesis

A

it acetylates a serine residue in the active site to inhibit COX2, which reduces pain and inflammation. It also inhibits COX1, leading to some side effects

43
Q

describe how aspirin may cause side effects

A

it inhibits COX2 (blocks prostaglandin synthesis), but also inhibits COX1 = side effects. COX1-synthesized prostaglandins regulate mucus levels in the stomach, so aspirin can cause stomach lining irritation

44
Q

what enzyme generates thromboxanes from PGH2

A

thromboxane synthase

45
Q

where is thromboxane synthase located in the body? link this location to the function of thromboxanes

A

thromboxanes assist in platelet aggregation + blood vessel constriction. Thromboxane synthase is located in platelets

46
Q

what is the effect of aspirin reducing thromboxane production

A

low doses of aspirin reduces the probability of heart attack/stroke by reducing thromboxane synthesis

47
Q

what happens to made FAs during periods of growth (where do they go)

A

they’re incorporated into the PM as phospholipids

48
Q

what happens to made FAs during periods of no growth (where do they go)

A

they’re incorporated into TAGs for energy storage

49
Q

what two precursors are needed for TAG synthesis

A

glycerol-3-phosphate and fatty acyl-CoA

50
Q

how is glycerol-3-phosphate made (to be used in TAG synthesis) (2 ways)

A

formed from a glycolysis intermediate, or from glycerol in the liver/kidney in an ATP-depended reaction by glycerol kinase

51
Q

how is fatty acyl-CoA made (to be used in TAG synthesis)

A

made by acyl-CoA synthetase enzymes (this costs ATP)

52
Q

write out the reaction of fatty acyl-CoA production

A

fatty acid + CoA + ATP –> fatty acyl-CoA + AMP + 2Pi

53
Q

how many ATP equivalents does it take to add a CoA onto a FA (in TAG synthesis)

A

2 ATP equivalents

54
Q

once the precursors of TAG synthesis have been made (glycerol-3-phosphate and fatty acyl-CoA), what is the first step/product of TAG synthesis

A

phosphatidic acid aka diacylglycerol-3-phosphate

55
Q

how is phosphatidic acid made during TAG synthesis

A

two free OH groups on glycerol-3-phosphate are acylated via acyl transferases

56
Q

what enzyme acylates the two free OH groups on glycerol-3-phosphate to make phosphatidic acid (in TAG synthesis)

A

acyl transferase

57
Q

how much ATP does it take to acylate the 2 free OH groups of glycerol-3-P to make phosphatidic acid

A

2 ATP equivalent (per acyl chain)

58
Q

once phosphatidic acid is made (during TAG synthesis), what is the next step + what enzyme does the step

A

it’s hydrolyzed by phosphatidic acid phosphatase to make 1,2-diacylglycerol

59
Q

once 1,2-diacylglycerol is made during TAG synthesis, what is the next step

A

the final acyl group is added to generate the triacylglycerol

60
Q

what is the cost of adding the final acyl group to 1,2-diacylglycerol to form TAG

A

2 ATP to add, but remember it also costs 2 ATP to FORM this fatty acyl-CoA

61
Q

what is the final ATP cost of TAG synthesis

A

12 ATP

62
Q

how might insulin regulate the TAG synthesis pathway

A

insulin is present after we eat, so we don’t want to be making fats but storing them. insulin promotes acetyl-CoA formation and the eventual formation of TAGs. This is because we want to store what we have eaten, so we store the TAGs that get made

63
Q

describe TAG synthesis regulation for a diabetic

A

a diabetic person wouldn’t be getting enough acetyl-CoA, so we wouldn’t want TAGs to be made because TAGs are for storage. Instead, acetyl-CoA will be used to make ketone bodies instead of making TAGs

64
Q

where in the body does the TAG cycle take place (3)

A

adipose tissue, blood, and liver

65
Q

what percentage of free FAs released from TAG breakdown are used for fuel

A

25%

66
Q

what percentage of free FAs released from TAG breakdown are used to regenerate TAGs

A

75%

67
Q

list the basic steps of the TAG cycle, staring in the adipose tissue

A

from the adipose tissue, starvation causes it to release free FAs into the blood, and some of these will be used for fuel. Most free FAs go back to the liver to be re-packaged into TAGs, go back to the blood, then back to adipose tissue

68
Q

why does the body use the “futile” TAG cycle

A

the cycle keeps some free FAs in the blood for immediate breakdown in a sudden energy need

69
Q

what molecule is required in high amounts for the TAG cycle to occur? where is this molecule located (2)

A

glycerol-3-phosphate is needed in adipocytes and hepatocytes

70
Q

list 3 ways to generate glycerol-3-phosphate

A

from glucose (via glycolysis), from glycerol (after phosphorylation by glycerol-kinase), and from pyruvate (via glyceroneogenesis)

71
Q

for the TAG cycle specifically, where do we get the glycerol-3-phosphate from

A

pyruvate (glyceroneogenesis)

72
Q

describe glycerol-3-phosphate production from glucose

A

glucose undergoes some steps of glycolysis but stops when DHAP is produced. From here, glycerol-3-phosphate dehydrogenase and NADH are used to make glycerol-3-phosphate

73
Q

describe glycerol-3-phosphate production from pyruvate (when fasting)

A

pyruvate undergoes glyceroneogenesis to produce DHAP. From here, glycerol-3-phosphate dehydrogenase and NADH are used to make glycerol-3-phosphate

74
Q

which enzyme controls TAG cycle flux

A

PEP carboxykinase

75
Q

what reaction does PEP carboxykinase mediate

A

pyruvate –> PEP

76
Q

where is PEP carboxykinase located in the body

A

adipose tissue and the liver

77
Q

what does it mean for the TAG cycle to have PEP carboxykinase in both the adipose tissue and the liver

A

PEP carboxykinase is able to create lots of flux via the back and forth of fatty acids between adipose and liver

78
Q

describe what occurs when PEP carboxykinase is expressed in the liver

A

lots of glyceroneogenesis, which makes more TAGs. The TAGs are exported back to adipose tissue, and this promotes much flux through the TAG cycle. This is important during starvation so you get that 25% of free FAs to the muscle

79
Q

describe what occurs when PEP carboxykinase is expressed in adipose tissue

A

increased glyceroneogenesis makes more TAGs which cycle WITHIN adipose tissue = not much flux through the cycle. This is useful when there is other fuel around (ie glucose)

80
Q

which steroid hormone regulates levels of PEP carboxykinase in the liver/adipose

A

cortisol

81
Q

describe how cortisol affects PEP carboxykinase levels

A

it causes an increase in PEP carboxykinase levels in the liver, and a decrease in adipose tissue = maximum TAG cycle flux

82
Q

what do high levels of TAG cycle flux cause in the body? (4)

A

promotes insulin resistance –> type II diabetes, increases blood pressure, increases risk of liver disease and atherosclerosis, overexpression of PEP-related genes promotes obesity

83
Q

where do we WANT PEP carboxykinase to be active

A

adipose tissue only (low flux)

84
Q

T or F: A group of drugs used to treat type II diabetes promotes synthesis of PEP carboxykinase in adipose tissue only

A

true

85
Q

T or F: PEP carboxykinase activity in adipose tissues ONLY lowers the amount of free FAs in the blood

A

true

86
Q

T or F: PEP carboxykinase activity in adipose tissues ONLY decreases a person’s insulin sensitivity

A

false; it increases a person’s insulin sensitivity

87
Q

describe the steps of phospholipid synthesis starting with phosphatidic acid

A

make phosphatidic acid and then DAG by cleaving off a P. Add an initial headgroup to the backbone through a phosphodiester linkage. When DAG, P and headgroup all come together, 2 waters will be released. Modify the headgroup (if needed)

88
Q

what type of bond links the head group to DAG (during phospholipid synthesis)

A

phosphodiester linkage

89
Q

describe how to add a head group during phospholipid synthesis

A

form a phosphodiester bond with the OH on the 3C of DAG and an OH on the head group. One of these alcohols first needs to be activated

90
Q

in phospholipid synthesis, what activates the OH to form the phosphodiester bond that attaches the head group

A

cytidine diphosphate (CDP)

91
Q

in phospholipid synthesis, what does the other OH do after the first was activated by CDP

A

the second OH completes nucleophilic attack to displace cytidine monophosphate (CMP)

92
Q

in bacteria phospholipid synthesis, which OH does CDP attach to; the one on DAG or the one on the head group

A

the one on DAG

93
Q

in eukaryotic phospholipid synthesis, which OH does CDP attach to; the one on DAG or the one on the head group

A

CDP can attach to both

94
Q

in phospholipid synthesis in BACTERIA, what is the head group

A

serine

95
Q

in phospholipid synthesis in YEAST, what is the head group

A

serine or inositol

96
Q

in phospholipid synthesis in MAMMALS, what is the head group

A

choline or ethanolamine

97
Q

list 3 potential head group modifications of the yeast serine headgroup (in phospholipid synthesis)

A

-CDP-DAG condenses with serine to make phosphatidylserine
- decarboxylation of PS to from phosphatidylethanolamine
- adding 3 methyl groups onto the PE amine to make phosphatidylcholine

98
Q

where are lipids made

A

smooth ER

99
Q

after lipids are made in the smooth ER, where are they transported to

A

to the golgi

100
Q

how are synthesized lipids transported from the smooth ER to the golgi

A

via vesicles

101
Q

after arriving to the golgi after synthesis, where do lipids go?

A

they move to membranes via vesicles in specific proportions

BIOL 3421 - molecular biochem (20 decks)

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