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biochemistry > lipid metabolism > Flashcards

lipid metabolism Flashcards

1
Q

what are lipids? what are the three main types?

A
  • diverse biological compounds> low solubility in water
  • steroids, triglycerides and phospholipids
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2
Q

what are the roles of steroids?

A
  • cell signalling
  • membrane function
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3
Q

what are the roles of fatty acids and triglycerides?

A
  • high ATP yield
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4
Q

what do phospholipids form?

A
  • form membranes
  • present at interface between lipids and water
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5
Q

how do lipids differ to carbohydrates?

A
  • lipids= hydrophobic
  • longer the chain and fewer double bonds= lower solubility
  • diff structural properties alters digestion, absorption and metabolism
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6
Q

what makes up phospholipids? what do they affect?

A
  • consists of a glycerol unit connected by 2 FA’s and a phosphoric bond via ester bonds
  • affect cell signalling
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7
Q

what are membrane lipids referred to as?

A
  • amphipathic
  • because one end is hydrophobic while other is hydrophilic
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8
Q

describe triacylglycerol

A
  • 90-95% of dietary fat
  • energy store in adipose tissue & muscle
  • one glycerol unit and 3 FFA’s connected by ester bonds
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9
Q

what do lipid hydrolases involve?

A
  • lipoprotein lipase, hormone- sensitive lipase and adipose TAG lipase
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10
Q

what fibres are TAG stores greater in?

A
  • greater in type 1 muscle fibres compared to type 2
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11
Q

what needs to happen before TADs goes through the membrane?

A
  • must be broken down in order to pass through
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12
Q

describe the first step of digestion and absorption regarding the lipid droplets

A
  • lipid droplets are reduced in size via bile acids made in the liver and released in the gallbladder
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13
Q

what happens in the intestinal lumen during step 2 of digestion and absorption

A
  • pancreatic lipid hydrolyses the ester bonds to yield 2FA’s and 2 monoglycerol
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14
Q

what do the fatty acids and monoglycerols do in step 3?

A
  • enter the intestinal cells and reform triacylglycerols
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15
Q

describe step 4 in relation to chylomicrons

A
  • lipids are packaged into chylomicrons
  • exported into lymph nodes and into the bloodstream
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16
Q

what are chylomicrons?

A
  • class of lipoprotein that transports insoluble triacyclglycerol
  • single layer of phospholipids w a hydrophobic core
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17
Q

what happens once chylomicrons are formed?

A
  • pass into extracellular space
  • then lymphatic vessels and into the bloodstream
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18
Q

where is fat stored in the human body?

A
  • mainly stored in adipose tissue & muscle (0.2-0.8%)
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19
Q

where is adipose tissue found? what percentage is in males/ females?

A
  • subcutaneous fat (under skin)
  • visceral fat (around organs)
  • 15% in man, 23% in women
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20
Q

what is the cytoplasm of an adipocyte dominated by?

A
  • large lipid droplet filled with triacylglycerol (80%)
  • serves as huge energy reserve
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21
Q

where are triacylglycerol stores? why are they here?

A
  • contained in lipid droplets w/ in adipocytes/ muscle fibres near mitochondria
  • reduce distance for ATP production
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22
Q

what does exercise speed up?

A
  • Fatty acids degradation in adipose tissue and muscle via beta- oxidation
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23
Q

what does beta oxidation produce? what does this enter?

A
  • produces acetyl- coA
  • enters the krebs cycle
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24
Q

what enzymes catalyse the breakdown of triacylglycerol?

A
  • adipose TAG
  • Lipase Hormone
  • Sensitive Lipase
  • monoacylglycerol
  • acyltransferase
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25
Q

where does synthesis of triacylglycerol occur? what forms the TAG glycerol breakdown?

A
  • occurs in cytosol
  • glycerol generated from dietary glucose forms the TAG glycerol backbone
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26
Q

how are the three fatty acids added during the synthesis of triacylglycerols?

A
  • added in 2 steps via enzyme Glycerol Phosphate Acetyltransferase
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27
Q

is synthesis or breakdown more predominant in fed state?

A
  • synthesis of TAG> breakdown
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28
Q

is synthesis or breakdown more dominant during exercise?

A
  • breakdown> synthesis of TAG
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29
Q

how do fatty acids circulate in the blood?

A
  • attached to albumin
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30
Q

when does the lipolysis rate increase during exercise?

A
  • within 5-10 minutes of exercise
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31
Q

what is the rate of lipolysis influenced by?

A
  • epinephrine increases lipolysis via B- adrenergic pathway
  • decreases lipolysis via a- adrenergic pathway
  • insulin decreases pathway
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32
Q

what hormones are involved in low intensity exercise? what pathway does this drive?

A
  • ^ epinephrine and decreases insulin
  • drives the cAMP pathway activating AGTL, HSL + MGL
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33
Q

what hormones are involved in high intensity exercise? what does this suppress?

A
  • ^ epinephrine and insulin
  • supresses cAMP pathway
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34
Q

describe the fate of lipolysis products during exercise

A
  • FFA’s in muscle remain& FFA’s from adipose tissue are imported into the muscle via FABP-PM
  • boost available energy
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35
Q

what are fatty acids primarily used for?

A
  • beta oxidation and ATP provision
36
Q

what are fatty acids primarily used for in the liver?

A
  • gluconeogenesis and some FFA may enter for triacylglycerol synthesis
37
Q

how does fatty acid degradation in the muscle occur?

A
  • occurs through beta oxidation in the mitochondria
38
Q

how many steps does fatty acid degradation include? What do the steps do?

A
  • 3 step process of activating FFA’s & transporting across the membrane
39
Q

how are fatty acids activated in step 1?

A
  • activated by a reaction with CoA forming Acyl- coA
  • passes to the inter-membrane space
40
Q

what happens in step2 of FFA degradation regarding the acyl group?

A
  • carnitine takes the Acyl group allowing transport into the mitochondrial matrix
41
Q

what happens to the acyl chain in the last step of degradation?

A
  • acyl chain is then taken from carnitine to reform Acyl-coA in the matrix
42
Q

what does beta- oxidation involve?

A
  • oxidation of the B- carbon in the acyl chain
43
Q

how does acyl- coA enter the beta oxidation pathway?

A
  • in the mitochondrial matrix
44
Q

how many reactions does 1 cycle of beta oxidation involve?

A
  • 1 cycle involves 4 reactions that degrade acyl- coA
45
Q

what are the products of beta oxidation? what do they enter?

A
  • produces 8 acetyl-coA, 7FADH2 and 7NADH
  • enter krebs cycle and ETC
  • krebs cycle and ETC pull B- oxidation and yield a large amount of energy
46
Q

what happens if there is an odd number of carbons in FFA’s?

A
  • occurs when beta oxidation removes 2 carbons at a time
  • once a 5 carbon acyl- coA molecule is reached it is broken down into acetyl- coA & a 3 carbon propionyl CoA molecule
47
Q

what does 3 carbon propionyl CoA undergo to form?

A
  • undergoes 3 reactions forming succincylCoA
  • enters at reaction 5 of the KC
  • then fully oxidised to generate ATP
48
Q

how does exercise speed up fatty acid oxidation in muscles?

A
  • stimulates lipolysis
    ^ blood flow= ^ FFA delivery
  • enhance translocation of FA binding protein at the plasma membrane
    ^ muscle uptake of FFA’s
49
Q

what does exercise increase? what does this enzyme do?

A
  • increased AMP- activated protein kinase
  • deactivates acetyl-CoA carboxylase
  • reduces FFA synthesis & favours lipolysis
50
Q

what is the blood plasma fatty acid profile during low intensity exercise?

A
  • slight initial increase which is maintained throughout
  • post exercise small increase before returning to baseline
51
Q

what is the blood plasma fatty acid profile during moderate intensity exercise?

A
  • initial decrease before a gradual increase throughout
  • large increase post exercise before baseline return
52
Q

what is the blood plasma fatty acid profile during high intensity exercise?

A
  • large initial decrease (reliant on anaerobic sources)
  • sustained low throughout due to release of insulin
  • post exercise large ^
53
Q

what does ingesting carbohydrates during a prolonged exercise bout maintain?

A
  • maintains plasma glucose
54
Q

what would someone with a high fat and low carbohydrate diet have ?

A
  • high plasma triacylglycerol use
55
Q

what is FatMAX?

A
  • max % of V02 where fat can be oxidised
56
Q

what is max fat oxidation?

A
  • rate of fat oxidation at a given intensity
57
Q

what happens as exercise intensity increases?

A
  • there is an increase of fat oxidation up to 60%
58
Q

what are the points where carb and lipid connect?

A
  • glycerol
  • fatty acids
  • oxaloacetate
59
Q

describe how glycerol connect carbohydrate and lipid metabolism

A
  • can be converted to glucose in the liver
  • forms a minor part of triacylglycerol
60
Q

describe how fatty acids connect carb and lipid metabolism

A
  • meet at acetyl- coA but can’t be converted back to pyruvate
  • can not replenish carbs
61
Q

describe how oxaloacetate connects carb & lipid metabolism

A
  • can be used to reform glucose through beta oxidation into acetyl- coA through the KC
  • no conversion of acetyl- coA so it is lost as C02
62
Q

can fatty acids be converted into glucose?

A
  • no but glucose can be converted into FFA’s through acetyl-coA and through L-glycerol- 3-phosphate
63
Q

what are plasma lipoproteins?

A
  • carriers of TAG and cholesterol esters coated by phospholipids
64
Q

what are apolipoproteins?

A
  • signal sites on the outside> ratio of lipid to apolipoprotein mass determines property and function
65
Q

what is rate of LDL: HDL a measure of?

A
  • a measure of cardiovascular health
66
Q

what are the measurements of the different lipoproteins?

A

chylomicrons= 0.92-0.94 g/mL
VLDL= 0.96-1.00g/mL
LDL= 1.02- 1.06g/mL
HDL= 1.06- 1.21g/mL

67
Q

which lipoprotein contains the most cholesterol?

A
  • low density lipoproteins
68
Q

what do chylomicrons and VLDL carry?

A
  • carry TAG
69
Q

what do LDL and HDL carry?

A
  • carry cholesterol but HDL carries it towards the liver
70
Q

what is a healthy lipidemic profile?

A
  • low triacylglycerols, total cholesterol and LDL with high HDL
71
Q

where do chylomicrons enter from?

A
  • enter the blood from the small intestine
72
Q

how are chylomicrons broken down?

A
  • broken down by lipases into TAGs for energy provision
73
Q

where are chylomicron fragments transported to? what are they converted to?

A
  • chylomicron fragments are transported to the liver & converted to VLDL
74
Q

what happens to the VLDL?

A
  • recirculated into the blood to then form LDL offloading more TAD
75
Q

how many apolipoprotein isomers are there?

A
  • 3 APOE
  • w each persons carrying 2 alleles
76
Q

describe Alzheimer’s disease risk factors

A
  • risk is either ^ or decreased depending on how apolipoprotein E signals in the body
77
Q

what is pathogenesis of obesity?

A

^ in energy uptake& decrease in EE
- adipose tissue dysfunction
- decreased adiponectin
- altered blood lipid profile
- increased inflammatory
- decreased risk

78
Q

how is the effect of acute exercise on plasma lipids tested?

A
  • by a fat tolerance test> pts ingest a high fat meal
  • measure the response of plasma lipids to the meal
79
Q

what can an acute bought of exercise lead to?

A
  • can suppress TAG appearance in the blood plasma & improve lipid profile
80
Q

what are the benefits of chronic exercise on lipids?

A
  • shown to improve lipid profile
  • increases adiponectin levels
81
Q

what does adiponectin increase? what other benefits are there?

A
  • increases lipid oxidation, improves insulin sensitivity and is linked to lower inflammation
82
Q

is adiponectin higher or lower in obese people?

A
  • lower
83
Q

what does exercise lower in obese people?

A
  • lowers inflammation
  • however, unclear if it directly related to weight loss
84
Q

what have lab studies demonstrated?

A
  • exercise can match diet- induced weight loss however it is very complicated
85
Q

what is the respiratory exchange ratio?

A
  • volume of exhaled C02 divided by the volume of 02 consumed

biochemistry (15 decks)

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