Human metabolism ALL Flashcards
1
Q
Insulin
A
- A chain = 21aa, B chain - 30aa linked by 2 disulphide
- Preproinsulin → proinsulin
2
Q
Metabolic effects of insulin
A
- Fed state hormone
- Obese subjects secrete ↑
- T2D lose control over [glucose]
- Major anabolic hormone, stimulates uptake of nutrients
3
Q
Effects of insulin on carbohydrate metabolism
A
- Effects:
1. uptake of glucose in muscle + incorp into glycogen (GLUT4, GS, PDH)
2. Inhibits hepatic production of glucose from glycogen breakdown + gluconeogenesis (stim of GS, inhib of glycogen phosphorylase + gluconeogenic E)
4
Q
Effects on fat metabolism
A
- Stimulates synthesis of FA from glucose
- Uptake of TAG into adipose + inhibition of mobilisation of stored fat from adipose (stimulates extracellular lipoprotein lipases, inhibition of ATGL + HSL)
5
Q
GS in muscle
A
- GS (active) → GS-P (inactive)
- Phosph at many sites by PKA, AMPK or GSK3
- 3a,b,c,4,5 = GSK3
- Insulin inhibits GSK3
6
Q
Insulin receptor
A
- Tetrameric
- Insulin binds → relieves inhibition of tyrosine kinase activity → substrate recruited to IR → IRS1 is phosph + binds PI3K which catalyses PIP2 → PIP3 → PKB recruited + phosph
- Phosph GSK3 at Ser21
7
Q
GLUT4 in muscle + adipose
A
- W/o insulin, 5% of GLUT4 = at cell surface
- Insulin promotes GLUT4 from GSV to cell surface by phosph 2 Rab GTPases (Rab13 in muscle)
8
Q
PDH in muscle
A
- PDH-P (inactive)
- Activated by ↑ ratio of AcCoA : CoASH, NADH:NAD + ATP:ADP
- Different isofordms
- PDK4 phosph + inactivates PDH
- Transcription of PDK4 = controlled by FOXO1, insulin → proteolysis + exclusion of FOXO1 → PDK4 x have TF → active PDH
9
Q
HSL + adipose triacylglycerol lipase
A
- TAG = surrounded by 100s of lipid droplet proteins
- e.g. = perilipin (barrier btw lipase + substrate)
- CGI-58 = activator for ATGL
- FAB4 binds FA + transports from lipid droplet to plasma membrane
- Adrenaline → PKA stimulated → perilipin fragments barrier, HSL recruited to surface of lipid droplet → CGI-58 binds ATGL → hydrolysis of TAG, FAB4 binds FA
- Insulin ↓ cAMP, lipolysis inhibited
10
Q
Transcriptional effects of insulin on hepatic gluconeogenic E
A
- FOXO1
- insulin → PKB → Phosph FOXO1 → nuclear exclusion + degradation → x stimulate expression for G6Pase or PEPCK - Creb
- insulin → ↑ AKT which phosph Sik2
- SIK2 phosph CBP + Crtc2 → Crtc2 degraded → inhibits transcription of gluconeogenic E - PGC-1a
- Inhibits recruitment to gluconeogenic E
11
Q
Transcriptional effects of insulin on lipogenic gluconeogenic E
A
- Insulin stimulates transcription of FA synthesis
- All have TF SREBP which binds SRE
- insulin ↑ SREBP-1c by ↑ its transcription and activation via RIP
- RIP = when ER has ↓ cholesterol, SREBP2 moves from ER to Golgi by COPII, activated by Site1/2 protease → active TF, when ↑ cholesterol retained in ER
- Insulin phosph SREBP1c, has ↑ affinity for SCAP, moves to Golgi + activated
- Akt Phosphor + inactivates TSC1/2
12
Q
Diabetes
A
- Fasting hyperglycaemia + postprandial hyperglycaemia
- T1D = defect in B cells of pancreas
- T2D = insulin resistance, B cell secrete ↑
13
Q
Changes to carbohydrate metabolism
A
- Liver overproduces glucose from gluconeogenesis
- Muscle underutilises
14
Q
Change to fat metabolism
A
- Adipose overproduces FA as lipolysis x inhibited
- ↑ FA stimulates oxidation in muscle, inhibits glucose ox through glucose-FA cycle
- ↑ FA also stimulates ketone production
- ↑ TAG, ↓ HDL
15
Q
Insulin resistance
A
- E intake > expenditure = surplus E stored as TAG in adipose
- If x store more, TAG accumulate in muscle
- PKCe sensitive to stimulation by DAG, recruited to membrane + phosph IR (imparts P13K/PKB)
- But TAG accumulate not DAG
16
Q
Paradox in liver metabolism
A
- In diabetes, liver overproduces glucose
- Explained by IR in gluconeogenesis
- BUT glycogen breakdown x contribute
- BUT liver produces VLDL TAG
17
Q
Hypothesis : liver metabolism controlled by precursor supply
A
- Gluconeogenesis = controlled by glycerol from adipose + aa from muscle
- IR adipose overproduce glycerol + muscle aa
- So can be explained (x involve liver IR)
- TAG production = controlled by FA from adipose + esterification by glycerol-3-P made by IR adipose
18
Q
Hypothesis: liver insulin resistance is selective x global
A
- Insulin inhibits transcription of gluconeogenic E
- In diabetes this = IR so transcription of key E x inhibited + glucose overproduced
- Transcription of key E of FA + esterification stimulated by insulin which is overactive in IR
- But x gives inside
19
Q
Potential mechanism for IR
A
- E intake > expenditure, E stored as TAG in adipose
- When exceeded, ectopic fat causes IR
- When B cells fail to compensate, abnormal carb metabolism results
- In muscle = defective glucose uptake
- In liver = glucose overproduced + TAGs by adipose
20
Q
Glucagon
A
- 160 aa precursor made in reaction by PC2
- Hormone of starvation
- After meal glucagon ↓
21
Q
Glucagon target tissues
A
- x glucagon receptor in human adipose or skeletal
- Lots in liver
22
Q
Glucagon effect
Glycogen breakdown + glycogen synthesis
A
- Target of PKA = phosphorylase kinase b + GS
- GS phosph on site 2
- Difference liver vs muscle = site 1a+b is only in muscle, 2 is in both
- Protein phosphatase I has glycogen binding unit (G)
- Gl lacks PKA phosph site
- Phosphorylase a binds GL x Gm
- Adrenaline → PKA → GM of PPI phosph → G + C disc → small inhibitor 1-P binds PPI + inactivates (x for GL)
23
Q
Glucagon effect
Glycolysis + gluconeogenesis
A
- Glycolytic E switched off, gluconeogenic on
- PFK + F1,6BPatase
- F2,6BP = regulator, catalysed by bifunctional E
- Glucagon → PKA → phosph bifunctional E on Ser32 → hydrolyses F2,6BP → glycolysis loses activator - Pyruvate kinase (Liver)
- Phosph by PKA (inactive)
- Dephosph by PP1 (active)
- Allosterically activated by F1,6BP, inactive by Ala (stimulates/inhibits phosphorylation)
24
Q
Glucagon effect
Transcription
A
CREB
- PKA → phosph CREB on Ser133 → translocates to nucleus
- dephosph of CRTC2 → translocation to nucleus, forms complex
- E.g. PEPC = ↑ glucagon, active PKA, CREB phosph, SIK2 phosph + x phosph CRTC2 so can bind CREB + CBP → transcription of gene
- 2nd wave = PGC1a
25
Glucagon effect
| FA synthesis + oxidation
- Transport of FA to mit = mediated by CPT1/2, malonyl coA inhibits CPT1
- Active ACC = FA + malonyl coA made, FA ox inhibited
- Glucagon phosph + inhibits ACC in liver
- AMPK phosph + inhibits ACC
- 2 isofordms ACC2/ACC1
26
Liver metabolism branch points
- Acetyl coA can be fed into TCA or HMG-coA cycle
| - HMG coA synthase + citrate synthase compete for acetyl coA
27
Energy storage
- TAG = most efficient way but need mechanisms for transport
- Also glycogen, can make and degrade glycogen simultaneously
28
Tissues w/o mitochondria
- Glycolysis = entirely cytoplasmic
- RBC entirely dependent on glucose as E source
- Cori cycle (liver converts lactic acid back to glucose)
29
Starvation in tissue w/ mitochondria
- Range of fuels
- Limited availability of body carb (only small amount of glycogen)
- Best = fat
30
Inhibition of glucose utilisation
- Body glycogen used 24-48hr of starvation
- FA replace glucose in muscle, ketone in brain
- Blood brain barrier = impermeable to FA
31
PDH
- When active, pyruvate is committed to complete oxidation
- Needs to be inhibited
- PDH kinase phosph + inhibits PDH
32
PFK
- FA/ketone body ox ↑ which ↑ [citrate], inhibits PFK
| - GLUT4 inhibited
33
Ketone bodies as signals
- Antilipolytic
- Ketone bodies limit own precursor
- Inhibit supply of glycerol
34
Body protein in starvation
- Indication = N excretion
- As starvation proceeds, ↑ ammonia, ↓ urea excreted
- Alanine + glutamine = most important aa
- Sources of pyruvate for alanine (glucose, C skeletons, muscle glycogen)
- Sources of pyruvate for glutamate (C skeleton form other aa)
35
General
- Fuel = blood glucose, muscle glycogen, blood FA, muscle TAGs
36
Controlling metabolism by E status
- AMP/ATP sensed + by AMPL
- adenylate kinase amplifies small ↓ in [ATP] to ↑ in [AMP]
- glycogen phosphorylase b = stimulated by ↑ AMP/ATP
- PFK = regulated by ATP
- Bypass hexokinase so 3ATPs made per glucose
37
AMPK
- GS + HMG Coa reductase are both phosph + inhibited by AMPK
- ACC2 is phosph + inhibited
- When AMP/ATP ↑, kinase active, ACC-P inhibited, x malonyl coA made, CPT-1 de-inhib, rate of FA ox ↑
38
Controlling metabolism by nervous control
- Mediated by Ca2+
- Glycogen phosphorylase b (gamma subunit binds Ca2+, activates y subunit of phosphorylase b kinase which phosph + activates glycogen phosphorylase)
- PDH (PDH phosphatase = stimulated by Ca2+, dephosph PDH → active form)
- Isocitrate / a-ketoglut dehydrogenase
39
Adrenaline
1. glycogen breakdown in muscle + liver
- adrenaline → cAMP → activates PKA → PKA phosph phosphorylase b kinase which phosph glycogen phosphorylase → ↑ G6P + ATP
- PKA phosph + inhibits PP1
2. TAG lipolysis in adipose
- HSL phosph by PKA, ↑ activity
- Perilipin 1 phosp by PKA → fragmentation of perilipin 1 barrier
40
Types of muscle
- Type 1 (aerobic, ↑ mit density, oxidative, slow)
- SLOW = glucose → glycolysis → Krebs → Etc + can use FFA
- Type IIa (int. of type I/IIb, slow contraction)
- Type IIb (anaerobic, ↓ mit density, fast contraction)
- FAST = glucose → glut4 → glycolysis → lactate
41
Intracellular stores for exercise
- e.g. creatine, glycogen, TAG
- x need to mobilise
- Limited, ↓ E dense
42
Extracellular stores
- e.g. blood glucose, FA
- unlimited in size + ↑ E dense than glucose
- But need to mobilise
43
Muscle regulation during anaerobic exercise
- More E from glycolysis w/ glycogen than glucose
- In exercise, ↓ ATP, ↑ Pi, ↓ creatine phosphate
- Glycogen phosphorylase = activated by Ppi
- PFK regulated in parallel to glycogen breakdown
44
Fatigue in anaerobic exercise
- Lactic acid made to regenerate NAD+
- ↓ pH → less Ca2+ released by sarcoplasmic reticulum
- Inhibits PFK muscle
45
Aerobic exercise
- Type Ib muscle
- Blood glucose = 4 min, liver glycogen = 18 min, muscle glycogen = 70 min
- Adipose TAG → FA, 4018 mins
46
Fatigue in aerobic exercise
- Glycogen stores depleted
47
Chlyomicron
- Used to transport TAGS from diet to adipose (storage) or skeletal/cardiac for oxidation
48
VLDL
- Carry fat made from liver
| - As transport TAG from liver to muscle/adipose, metabolised to IDL
49
LDL
- Transport cholesterol into body
50
HDL
- Carries cholesterol out of body
51
Lipoprotein structure
- Surface = phospholipid monolayer
- Core = TAG, cholesterol esters
- Chylomicron = largest + least dense, 99:1 lipid: protein, apolipoprotein B48, A1,2,C,E
- VLDL 92:1, HDL 50:50
52
Types of apolipoprotein
- Non-exchangeble e.g. ApoB48 + ApoB100 (e.g. of mRNA editing)
- All others = exchangeable
53
LCAT
- Activated by A1
| - Converts free cholesterol to esterified cholesterol
54
TAG transport
- In starved state, body TAG mobilised as FA
| - In fed, dietary TAG is transported to adipose for storage or skeletal/cardiac for oxidation
55
Dietary fat → body fat
| Exogenous pathway
- Cholesterol is made by liver + enters circulation as a lipoprotein or is secreted into bile
- TAGs x cross cell membrane intact, need to be hydrolysed + re-synthesised
- Gastric lipases break TAG → DAG + MAG
- Pancreatic lipases → monoacylglycerol + 2FA
- Bile salts avoid product accumulation at interface
- Bile salts removed w/ collapse
- Glycerol phosphate pathway
56
Re-synthesis of TAG
- Newly made chylomicrons get exchangeable apoC11 + E from HDL in circulation
- ER, PCTVs, Golgi
- MTP
- Smooth ER + RER, core expansion
57
Lipoprotein lipase
- Chylomicron arrives at adipose, needs to be hydrolysed
- Completely hydrolyse TAG → FFA
- Glycerol 3 phosphate pathway
- Adipose x express glycerol kinase, get it from glycolysis via gly 3 P dehydrogenase
58
Insulin + body fat
- Insulin stimulates GLUT4 so glycolysis
- This ↑ supply of glyc 3 p so FA esterification
- Inhibits lipolysis by PKB phosph phosphodiesterase 3B, ↓ cAMP
- Insulin stimulates transcription of lipoprotein lipase + FA synthesis E by activating SRBEP1c
59
Endogenous pathway
- Cholesterol made by liver + enters circulation
- Dominant pathway for TAG synthesis in liver = glyc 3 phosph pathway + liver has glycerol kinase
- VLDL released into circulation → acquires ApoCII + E → lipoprotein lipase makes IDL → LDL by ApoB100 addition → IDL taken up by liver
60
Role of cholesterol
- Regulates membrane fluidity
| - Precursor for bile acids, vitamin D, steroid hormones
61
Cellular cholesterol status
Sources of cellular cholesterol
1. De novo synthesis
(20-30 E, mevalonic A = 1st unique E, similar to ketone body synthesis, 2NADPH/H+, HMG coa reductase that response to [cholesterol]
2. Circulating cholesterol carried by LDL
- ↑ LDL receptor = ↑ capacity for uptake
- Receptor mediated endocytosis, Cathrin coated pits, proton pump, pH optimum
62
NPC1/2
- NPC2 binds esterified cholesterol in lumen of ER + transfers to membrane bound NPC1
63
Transcriptional regulation
- LDL receptor + HMG CoA reductase have TF SREBP2
- ER [cholesterol] ↑, SREBP2 binds INSIG + stays in ER
- " " ↓ , SREBP2 goes to Golgi by COPII where activated by S1P/S2P, moves to nucleus
- SCAP has sterol sensing domain + binds INSIG
- ↑ cholesterol, SCAP binds cholesterol, x bind COPII, SCAP/SREBP retained in ER by INSIG
- ↓ cholesterol, SCAP binds COPII, SCAP/SCREBP move to Golgi
64
Endocytic cholesterol metabolism
- Free cholesterol enters enterocyte via NPC1L1
- Some cholesterol returns to lumen via ABCG5/8 in TICE
- Remaining cholesterol is esterified by ACAT
65
Cholesterol disposal
- Excess cholesterol excreted
- RCT, efflux of cholesterol on HDL to liver
- In liver, secreted into bile, portion reabsorbed
66
Cholesterol efflux from tissues
- 4 pathways from a macrophage (2 need diffusion by SR-B1, 2 need ATP)
- Liver + intestine make apoA1
- ApoA1 gathers cholesterol from 2 diffusion pathways
- As ApoA1 gets cholesterol, matures to HDL + LCAT
67
Good vs bad cholesterol
- Were cholesterol reaches
- Cellular cholesterol is safe
- Most carried by LDL (bad), minority by HDL (good)
- If endothelial layer damaged, LDL taken up into sub-endothelial space + oxidised (bad)
- Statins inhibit HMG CoA reductase
- ↑ LDL receptor no. → ↑ capacity for cholesterol uptake, ↓ circulating LDL
- Epidemiological studies
