Matthews content semester 2 Flashcards
1
Q
where does glycose come from ?
A
first 4 hours after meal, exogenous so in blood. the glycogen is used when glucose levels drop.
2
Q
what is the composition of glycogen
A
'’Animal starch’’ as its a branched polymer of glucose. main chain is alpha 1-4 linkages between glucose molecules. side chain of aplha 1-6 linkage.
3
Q
what are the name of the linkages between glucose molecules?
A
glyosidic bonds
4
Q
what is glycogens structure
A
Helical structure. 12-14 glucose per chain. branch every 8-12 glucose. each chain has 12-14 glucose residues. up to 120,000 glucose per glycogen molecules. 10-40 nm diameter
5
Q
how is glycogen stored
A
glycogen granules (20-40 molecules) up to 10% of liver mass and 1-2% of muscle.
6
Q
what is glycogenolysis
A
the breaking down of glycogen to release glucose
7
Q
what is the 2 step process of glycogenolysis?
A
- glycogen is converted into Glucose-1-phosphate using glycogen phosphorylase
- this is then converted by phosphoglucomutase into glucose-6-phosphate which is a apart of glycolysis cycle.
8
Q
what is a phosphorylase enzyme?
A
a enzyme that uses phosphate to make or break bonds
9
Q
how does phosphorylis work
A
glycogen is broken into glucose 1-phosphate and glycogen using a HPO4 2-
10
Q
what are the equations for hydrolysis and phosphorolysis?
A
Hydrolysis: R-OR’+HOH = R-OH +R’-OH
phosphorolysis: R-O-R’ + HOPO3 2- = R-OH + R’-OPO3 2-
11
Q
Why use phosphorolysis?
A
glycogen - glucose - glucose-6-phosphate requires ATP. If you can go in at the second step (G6P) it means you don’t use an ATP
12
Q
what is the structure of the phosphorylase active site?
A
Deep cleft to active site, pyridoxal phosphate prosthetic group.
13
Q
what are the three different versions of the phosphorylase enzyme? (isozymes)
A
Muscle (mGP)
Brain (bGP)
Liver (lGP)
14
Q
what does does phosphorylase being processive mean?
A
it doesn’t let go of the substrate making the process more efficient. so procession + branched structure = rapid mobilisation of glucose.
15
Q
what cant phosphorylases do?
A
proceed past branch points. so cant break 1-6 bonds, or break any 1-4 bonds that are within 4 units of the branch point. this leaves y shaped glycogen called limit dextrin’s
16
Q
how are branch points broken?
A
debranching enzyme, made up of transferase enzyme which transfers 3 glycosyl units from the side chain to the main chain. Also made up of alpha -1-6 glucosidase enzyme which hydrolyses the single 1,6 glucose unit to free it
17
Q
what is the second step of glycogen catabolism
A
a 2 step reaction:
- phosphate attached to serine in active site attacks OH on carbon 6 of glucose-1-phosphate leaving a phosphorylated carbon 6
- phosphate on 1 position attacks OH on serine restoring the phosphate leaving glucose-6-phosphate
18
Q
what are the different uses for glycogen catabolism in the muscles and liver?
A
muscle: glycogen = glycolysis = ATP
Liver: Glycogen = Glycogenesis = increased blood glucose.
19
Q
how does the liver undergo glycogenesis?
A
transported takes glucose-6-phosphate into the lumen and cleaves of phosphate which gets transported out along with free glucose.
20
Q
what happens if there is a build up of glucose?
A
glucose needs to be stored as glycogen in the liver. this is glycogen anabolism
21
Q
why cant glucose catabolism work backwards to generate glycogen stores?
A
(McArdle’s disease. so glycogen phosphorylase isnt being used.) Concentration of Pi is too high so more G-1-P would be required. also co-operative binding of Pi
22
Q
what is the process of glycogenesis?
A
glucose to G-1P using phosphoglucomutase, then UTP-Glucose Pyro phosphorylase converts G-1-P into UDP-glucose (activated glucose) in presents of UTP and PPi which then breaks into 2 Pi (this is energy that drives reaction) Glycogen synthase converts UDP into glycogen
23
Q
what are the different ways energy can be broken down
A
ATP = ADP+Pi ATP = ADP ATP = AMP+PPi ATP = PPi
24
Q
what is happening in the glucose activation step?
A
the end 2 phosphates from UTP leave and G-1-P and UTP react together.
25
how does glycogen synthase work
adds to existing chains, creates alpha 1-4 bonds. A UDP and H+ are removed to form glyosidic bond.
26
what are the problems with glycogen synthase?
cant start chains.
| cant make alpha 1-6 branches
27
how are the problems of glycogen synthase solved?
1. Glycogenin - build initial 8 unit primer chain, which can then be extended by glycogen synthase.
2. branching enzyme (glycosyltransferase) - binds to chains 11 units long and then cuts off heptamer (7) glucose units and reattaches via 1-6 bond. reattachment site >4 units from existing branch.
28
what are lipids?
fats (solid), oils(liquid), waxes and other hydrophilic molecules such as cholesterol. for storage
29
what is the structure of triglycerides/triglycerols?
3 fatty acid chains that are ester linked to glycerol. Fatty acyl acid chains (COOh group at end) are named Sn1 sn2 (on opposite side to 1 and 3) and sn3
30
what is the difference between saturated and unsaturated?
S: no double bonds
Mono/poly saturated: 1/more than 1 double bond
U: double bonds
more double bonds =lower melting point (oil rather than fat)
31
what are the effects of 2 different forms of fatty acids?
Cis and Trans.
Cis - creates kink in chain, (possibly remain liquid)
Trans - chain straight
32
how are fatty acids named?
common name: oleic acid (number from COO-)
systematic name: Cis-delta9 (position of carbon 9) octadecenoic acid (18 carbons)
omega or n system: C18:1 (n-9) (number CH4, if multiple n is the first bond )
33
how can humans convert fatty acids? (limited)
Elongases - increase chain length by 2 carbons
| Desaturases - add double bond, humans cant add a double bond lower than omega 9
34
where do we get the essential fatty acids?
Omgea 3 or omgea 6 come from diet and are termed essential. they can be elongated and desaturated.
35
why do we need to alter fatty acids?
no need for energy storage purposes.
membrane phospholipids: fatty acid length-bilayer thickness, degree of unsaturated-membrane fluidity, tissue-specific membrane composition e.g brain has omega 3,6, some FA are precursors to signalling molecules e.g. prostaglandins, leukotrienes, thromboxanes
36
how are fats and oils (lipids - triglycerides) digested?
digested by pancreatic lipases. by hydrolysis of 1 and 3 chain at the ester bond. leaving 2-monoacylglyerol and 2 free fatty acid chains. con now cross plasma membrane into intestinal cells.
37
what happens to digester triglycerides? lipogenesis
re-estified in gut mucosa. Fatty acids have to be activated first using Coenzyme A + ATP. Acyl CoA synthetase joins them. and H2O AMP and PPi are produced. sulfer from CoA will remove hydrogen and ester bond will reform.
38
how do triglycerides move about?
packages into lipoproteins for transport in the tissues as they are too hydrophobic otherwise. transport from gut to tissue using chylomicrons (1um diameter) e.g ApoB48, ApoC2 (docking at capillaries), ApoE
39
what is the structure of a lipoprotein?
lipid and protein. phospholipids monolayer and cholesterol hydrophilic groups. with apolipoproteins embedded. inside is triglycerides and chol ester inner core ,hydrophobic
40
how are fatty acids taken up into the adipose tissue
endothelial cells have lipoprotein lipase attached on the lumenal side, the active site cleaves off the fatty acids that can diffuse into the cells. when chlomicron has offloaded most of the TG it is called a remnant and is removed from circulation by the liver
41
what is the process of triglycerides synthesis in the adipose tissue (WAT)?
different from intestinal synthesis.
Starts as 1 glycerol-3-phosphate (comes from DHAP glycolysis) and 3 activated fatty acids.. G-3-P dehydrogenase attached H (from NADH) to give 2 Oh groups. Activated fatty acids are added, 1 by G-3-P acyltransferase and 2 by 1-acylG-3-P acyltransferase. giving phosphatidic acid. Phosphatidic acid phosphatase removes phosphate for sn3, and a 3rd
chain can be added by Diacylglycerol acyltransferase leaving a triglycerol.
42
why do we need to metabolise fatty acids?
they contain alot of energy. (Fatty acid -palmitic, 38kj/g 9kcal/g where as glucose is 17kj/g or 4 kcal/g).
They form a dense energy store. glucose=glycogen + 2x masses of water. but fatty acids=triglycerides +no water.
43
what surrounds the lipids?
perilipin coat (phosphorylated, arranged with gaps important for enzymes to get in)
44
how many enzymes are required to remove fatty acid tails?
3. Adipose TG Lipase(ATGL.
| Hormone-sensitive Lipase (HSL). Monoacylglycerol lipase (MGL)
45
what transports fatty acids in the blood
Human serum albumin (HSA). carries form adipose tissue to the rest of the body , travelling to the outer membrane of the mitochondria where they are activated
46
how are fatty acids activated in the mitochondria?
Fatty acids + Coenzyme A = Acyl CoA, ATP consuming process that catalysed by Acyl Co Synthetase. (AMP + PPi produced) conversion of AMP to ADP requires another ATP
47
how does fatty acid get into the matrix of the mitochondria?
1. Acyl-CoA synthetase attaches CoA to free fatty acid to make Acyl-CoA and this crosses through the outer membrane
2. Carnitine Acyltransferase I swaps CoA for a carnitine this allows it to cross inner membrane.
3. Translcase antiporter lets it cross across the bilayer and a carnitine leaves
4. Acyl chain is reattached to CoA once inside the matrix
48
what is the process of breaking down fatty acids ? Beta oxidation
FAs are catabolised in 2C units. First cleavage point is next to beta Carbon. of Acyl CoA. (in order of alpha beta gamma after carboxyl group), produces Acetyl CoA (TCA Cycle) and Acyl CoA (Round 2 of beta oxidation). four step process to release 2C from each fatty acid
49
what is step one of beta oxidation
Acyl CoA is oxidised (alpha and beta) by dehydrogenase using FAD to FADH2 to trans-delta2-Enoyl CoA. FADH2 goes into the electron transport chain.
50
what are steps 2 and 3 of beta oxidation?
hydration of trans-delta2-Enoyl CoA by hydratase to produce L-3-Hydroxyacyl CoA. this is then oxidised (beta) by dehydrogenase and NADH is formed (ETC) as well as 3-ketoacyl CoA
51
what is step 4 of beta oxidation
3-ketoacyl CoA is split into Acyl CoA and Acetyl CoA (TCA cycle) by thiolysis using thiolase and CoA
52
what is a summary of the 4 steps of beta oxidation?
```
oxidation.
Hydration
Oxidation
Cleavage
repeated until fatty acid is broken down
```
53
what is produced in each cycle?
1 x Acytyl CoA
1 x FADH2
1 X NADH
(Final clevage gives 2x acytyl CoA)
54
how do you work out the number of cycles needed to break down a fatty acid?
number of carbons / 2 -1.
55
beta oxidation.
longer chain fatty acids have more cycle e.g. stearic acid - 8 cycle - 146 ATP.
PUFA need additional isomerase enzymes to convert cis double bond to trans double bond
56
what are ketone bodies? comes after beta oxidation which is fatty acid degradation. leads into TCA cycle.
under conditions of prolonger fasting/starvation a high level of TG hydrolysis occurs and free FA level rise. when actyl CoA build up in the liver beyond the capacity of the TCA cycle to use it, Ketone bodies are made. These are released into the blood and used as fuel by other cells eps. heart. They require little conversion to enter TCA cycle so are rapid source of energy .
57
what is the process of ketogenesis?
taking three acytyl CoAs and joining them together. KB used as fuel are Acetoacetate, beta hydroxybutrate, Acetone is lost in breath/sweat/urine (energy lost)
58
what happens in destination tissue?
Acetoacetyl-CoA is recreated, then split into 2 Acetyl CoA
59
what enzyme isn't found in the liver?
Beta-Ketoacyl-CoA transferase
60
why metabolise fatty acids?
they contain a lot of energy, they form a dense energy store
61
what is the start and end point of fatty acid anabolism?
starting point is Acetyl CoA (2C), Endpoint is palmitic acid (16 C)
62
what is the difference between fatty acid catabolism and anabolism?
use of NADPH / NADP+ rather than NAD+/NADH.
| use of Malonyl CoA as basic unit - not Acetyl CoA
63
how is malonyl CoA formed?
Acetyl CoA + ATP + HCO3- =Acetyl CoA carboxylase= Malonyl CoA (3C) + ADP + Pi + H+
64
how is Acetyl CoA regulated ?
Citrate, Insulin - simulates allosterically
| Palmitic acid, Glucagon, adrenaline - inhibits allosterically
65
how does fatty acid anabolism work?
chain grows 2C at a time. 3+2 = 4 + 1 Carbon, release of CO2 is driving process.
66
what is the process of fatty acid anabolism?
fatty acid synthase joins Acetyl CoA + malonyl CoA using ATP to add chains.
67
what is the process of exporting Acetyl CoA to the cytoplasm?
Acetyl CoA is converted to citrate which diffuses out down conc gradient. this is then split into Acetyl CoA and OAA. OAA is converted to malate to pyruvate with the production of a CO2 and NADPH. Pyruvate diffuses into cell matrix and is converted to OAA, consuming a CO2.
68
what is NADPH
Nicotinamide Adenine Dinucleotide Phosphate
69
what is the structure of fatty acid synthase?
272kDa multidomain enzyme - 6 active sites and a ACP(Acyl carrier protein)
70
what are the 4 steps of fatty acid anabolism?
Condensation (active site 1,2)
Reduction (active site 4)
Dehydration (active site 3)
Reduction (active site 5)
71
what is the first step of fatty acid anabolism?
Acetyl group transferred to KS via ACP and MAT. Malonyl transfered onto ACP by MAT. KS joins acetyl and Malonyl (loss of CO2)
72
what is the equation for step one of fatty acid anabolism?
Acetyl-KS (2 carbon)+ Malonyl-ACP (3C) = Acetoacetyl-ACP (4C)+ CO2
73
what are steps 2, 3, 4 of fatty acid anabolism?
2. C=O to CHOH
3. C-C to C=C
4. CH to CH2
NADPH used to reduce unwanted carbonyl group.
74
when can the fatty acid chain move on to the final enzyme
Cycle is repeated 6x until enough 2C has been added to make palmitic acid (16 C) which is then released (thioesterase)
75
what tissue uses a different thioesterase
mammary tissue expresses a different thioesterase, which cleaves off shorter fatty acids to go into milk TG
76
what are the similarities between fatty acid synthesis and protein synthesis?
a condensation and translocation reaction
77
how are fatty acids stored?
in anabolic state they will be converted to Triglycerides and stored. if they are synthesised in the liver, lipoproteins used to export Triglycerides to adipose and other tissue
78
what are the 5 types of lipoproteins?
```
Chylomicrons
VLDL - very low density lipoprotein.
IDL - intermediate density lipoprotein
LDL -low density Lipoprotein
HDL - high density lipoprotein
(listed in order of size). conversion of VLDL-IDL-LDL
```
79
how does the lipoprotein composition vary?
VLDL-50% triglycerides rest phospholipids, cholesterol, apoproteins.
IDL similar but les triglyceride.
LDL - small amount of triglyceride, lots of cholesterol.
HDL- tiny amount triglyceride, losts of apoproteins
80
what is the life span of lipoproteins?
```
chylomicrons- 5min
VLDL- min/hours
IDL-min/hours
LDL-3 days
HDL-3-6 days
```
81
what is an example of a defect in the LDL-R gene? hyperlipidaemias
heterozygous- 50% reduction in LDL-R, double normal plasma LDL (2500-5000mg/L), 1 in 2 chance of myocardinal infarction by 50 yrs
homozygous- no LDL-R at all, Plasma LDL >6000mg/L. High chance of death before age of 20
82
why do we need amino acid metabolism ?
excess aren't stored.
| excess are't simply excreted.
83
what is nitrogen balance?
body keeping balance by getting rid of or taking in amino acids. mix of available animo acids in an amino acid pool.
84
what is the movements of amino acids entering and leaving the amino acid pool?
Biosynthesis: 250-300g/day body protein
Degradation: 250-300g/day return to pool.
Diet: 100g/day entering. 100g/day breakdown
85
what are the uses for the amino acids in the pool?
1. protein synthesis
2. direct use/minor modification
3. Breakdown and redeployment
86
what is direct use of amino acids? in neurotransmitters and hormones?
```
N: 1. Glutamate, Aspartate and glycine.
2. Glutamate=GABA. 3.Tyrosine=Dopamine, Noradrenaline, Adrenaline. 4.Tryptophan = serotonin
5. arginine = NO
H: 1. Tyrosine = thyroxine.
Tryptophan = melatonin
```
87
what is the breakdown of amino acids
Amino group splits and form NH3 (Ammonia - toxic) and a carbon skeleton broken to CO2 H2O energy production or biosynthetic pathways (purines, pyrimidines, haem ect.)
88
what is an overview o the break down of Amino acids?
1. Amino acids undergo transamination using alpha ketoglutarate (formed from glutamate), to form glutamate.
2. deamination of glutamate occurs to produce ammonia.
3. ammonia is converted to urea in the liver
89
what is the process of transamination?
amino acid (NH2) and alpha ketoglutarate (C=O), an aminotransferase turns amino acid to a alpha keto acid (C=O) and Glutamate (NH2). no energy consumption
90
what are the products of transamination of aspartate and alanine?
```
aspartate= OAA + glutamate
Alanine = pyruvate + glutamate
```
91
what is the structure of the aminotransferase active site?
Vit B6-derived prosthetic group called pyridoxal phosphate (PLP) to do amino group transfer
92
what is the process of amino group transfer in terms of chemical structure?
1. PLP - NH2 group removed and amino acid is joined by N double bonds to carbon.
2. H2O attacks and swaps nitrogen for oxygen leaving a NH2 group on the PMP. reverse
93
what is the process on deamination?
in the mitochondria, glutamate undergoes hydrolysis and NH4+ is removed to get alpha ketoglutarate. glutamate dehydrogenase catalyses and NAD+ is reduced to NADH.
Inhibited by GTP and activated by ADP
94
why does deamination occur in the mitochondria?
contain production of NH4+
95
what is the process of urea synthesis?
Mitochondria : NH+ (from deamination) + CO2 + H2O + 2ATP = carbamoyl phosphate + 2ADP + Pi. catalysed by carbamoyl phosphate synthetase I.
96
what is the urea cycle? cytoplasm.
occurs in cytoplasm.
Carbamoyl phosphate goes in and citrulline is formed, this incorporates amino group from Asp (ATP required) to form argino-succinate. this is cleaved to produce Fumarate and Arg. H2O helps metabolise Arg to produce urea
97
how many amino groups are used to form urea?
2
98
in order what are the enzymes involved in the urea cycle?
1. Ornithine carbamoyl transferase
2. Arginino-succinate synthetase
3. Arginino-succinate lyase
4. Arginase
99
what is the structure of urea?
NH2-CO-NH2.
| small and hydrophilic.
100
what is the overall energy cost of urea cycle?
4 ATP
101
what happens in Extra-hepatic tissues (outside liver)
catabolise AA to NH3 but cant make urea e.g. Branched chain AA catabolism for energy in muscles.
alpha-KG + NH3 = Glutamate
Glu + NH3 = Glutamine (export of 2 amino into the blood).
In kidney Glutamine can be deaminated back to Glu to release NH3 into urine for acid neutralisation
102
what can the carbon skeleton end up as ?
```
Pyruvate
Acetyl CoA
Acetoacetyl CoA
alpha-ketoglutarate
Fumarate
(link to TCA cycle)
```
103
what happens to cystine and methionine?
contain sulfur. it ends up as pyruvate vitB6 is involved
104
how is cystine converted to pyruvate?
1. converted to cysteinesulphinate using O2 and NADPH. it is transaminated to beta-sulphinylpyruvate. SO2 (urea) is cleaved off to pyruvate
2. or cystine can be transaminated to beta mercaptopyruvate. have a thiol as hydrogen sulphate gas leaving pyruvate.
105
what are the essential 9 amino acids that carbon skeletons cant be synthesised?
FHILKMTVW, other amino acids can made from these/TCA cycle.
106
what are two example of amino acid being used to form components?
pyrimidines - de novo synthesis
| purines - combine carbon skeleton from three amino acids.
107
what is gluconeogenesis?
the synthesis of glucose from other molecule (Amino Acids)
108
why does gluconeogenesis occur?
In absence of insulin, most of the body utilises fatty acid for energy, but the brain and red blood cells use glucose.
Between meals blood glucose levels drop.
Glycogen stores in liver are limited and muscles can't release glucose (from glycogen) into the blood.
109
what is the solution to low glucose
synthesize new glucose molecules to release into blood. Best solution would be to convert fatty acids to glucose, but we don't have the enzymes (glycerol can be converted). simplest way is to reverse glycolysis but 3 steps are irriversable delta G = +84kj/mol
110
how do you reverse converting EP to Pyruvate (irreversible)
Enzymes Pyruvate carboxylase and PEP carboxykinase. ATP, CO2 GTP, with OAA intermediate
111
how do you reverse F-1,6-Phosphate to F-6 phosphate?
enzyme F-1,6-biphosphatase
112
how do you reverse G-6 phosphate to glucose?
enzyme G-6-phosphtase
113
what is the whole process of reversing glycolysis?
1. 2 ATPs convert Pyruvate to EP
2. EP - 2phosphate glycerate - 3 phosphate glycerate - ATP converts it to 1,3-Glycerate - DHA + Gly-3-phosphate - F 1,6 - F6 - G6 - glucose
114
how many ATPs are required to reverse glycolysis?
6
| Delta G = 38 kj/mol
115
what is the 2 step process of converting pyruvate to PEP?
1. pyruvate carboxylase (biotin prosthetic group)
HCO3- + ATP = HOCO2-P + APD,
-Biotin + HOCO2-P = -biotin-CO2 + Pi,
Biotin-CO2 + pyruvate (3c) = Biotin + OAA (4c) mitochondrion.
2. PEP carboxykinase (PEPCK), OAA + GTP = PEP (3C) + GDP + CO2, Co2 drives reaction
116
what is the overall equation for converting pyruvate to PEP?
pyruvate + CO2 + ATP + GTP = PEP +CO2 + ADP + GDP
117
how is fructose 1,6-bisphophate turned into F-6-P?
Hydrolysis. F-1,6-biphosphatase.
| F 1,6-bisP + H2O = F-6-P + Pi. cytoplasm
118
how is glucose-6-phosphate converted to glucose?
hydrolysis. Glucose-6-phosphatase.
Glucose-6-phosphate + H2O = Glucose + Pi. endoplasmic reticulum (G-6-P cannot cross plasma membrane so tissues without Glucose-6-phosphatase cannot export glucose.
119
what is the problem with gluconeogenesis? what are the solutions
no stores of pyruvate to maintain gluconeogenesis. get it from Lactate-Cori cycle or Glucogenic amino acids
120
what is the Cori cycle?
in blood Glucose-pyruvate-lactate using LDH.
in liver lactate turns to pyruvate (NADH generated) using LDH and then pyruvate goes to glucose to be released into blood
121
how is glycogenic Amino acids produce pyruvate?
anything that can be turned into oxaloacetate can be turned to glucose. TCA cycle.
122
what two amino acids can not be used to make glucose?
ketogenic amino acids , leucine and lysine.
123
what is the most important amino acid in gluconeogenesis?
alanine - muscle catabolism releases Ala into blood, converted to pyruvate. conc of alanine goes up in liver and alanine aminotransferase reacts alanine with alpha ketoglutarate to make glutamate and pyruvate.
124
how is glycerol used to make Glucose?
Glycerol converted to Glycerol-3-phosphate by glycerol kinase. glycerol phosphate dehydrogenase converts this to dihydroxyacetone phosphate this can then enter gluconeogenesis to form glucose, or be converted into glyceraldehyde-3-phosphate and go into glycolysis.
125
where are the entry points for gluconeogenesis?
Alanine & lactate enter at pyruvate.
| other amino acids enter at OAA. Glycerol enters at DHA
126
where do other non-glucose carbohydrates enter glycolysis?
fructose: non-liver tissues at F-6 phosphate, liver tissues at Gly-3-phosphate
Galactose: G-6 phosphate
Mannose: F-6 phosphate
127
how does fructose turn to F-6-phosphate?
hexokinase. break down of ATP
128
How does mannose get turned into F-6-phosphate?
hexokinase. using ATP. gets turned into M-6 phosphate which gets turned into F-6-phosphate by phosphomannose isomerase
129
how does galactose get turned into G-6-Phosphate.
Galactokinase uses ATP to turn galactose to Gal-1-phosphate. this reacts with UDP-Glucose to make UDP-galactose. G-1-Phosphate is converted into G-6-phosphate by phosphoglucomutase.
130
what is a metabolic pathway?
the enzymatic route that a metabolite molecule takes
131
what is the rate limiting step?
1. slowest reaction in pathway
2. determines overall flux through a pathway by acting as a bottleneck
3. usually the first unique enzyme in a pathways. in a branched pathway it will occur after a branch so products can be made independetly.
132
how do you identify the rate limiting step of a pathway?
1. measure Vmax for enzymes in pathway. lowest = RLS
2. compare Keq and mass action ratio (MAR). ratio of P to S within cell.
3. test if at a cross over point - peturb system
133
how do you determine the RLS using MAR.
if reaction is close to equilibrium in the cell MAR is close to equilibrium constant. If the reaction is rate-limiting in the cell MAR
134
what is the perturb system?
flux through a pathway e.g. treat tissue with hormone. if pathway flux increases, activity of enzyme controlling flux must have increased, resulting in increase in [P] and decrease in [S]
135
why do we need to control? regulating metabolism
1. ensure a given metabolic pathway is active when its product is needed
2. ensure competing pathways aren't simultaneously active.
3. ensure co-ordinated activity in multiple related pathways
136
why is it important to ensure competing pathways aren't simultaneously active
glycolysis and gluconeogenesis happen at same time, this leads to futile cycling. in the cycle of f-6-phospahte to f-1,6-diphosphate atp is used up.
137
what are types of enzyme regulation?
1. intrinsic control by metabolites: allosterism/inhibitors
2. fast extrinsic control via hormones: covalent modifications e.g. phosphorylation
3. slow extrinsic control via hormones: gene expression
138
what are types of control by metabolites?
product inhibition-e.g. hexokinase, build up of glucose-6-phosphate, so one stays in active site blocking others being made.
allosterism - inhibition and activation
139
what enzymes can ATP inhibit and AMP/ADP activate?
```
PFK1,
Pyruvate kinase,
Pyruvate dehydrogenase,
Citrate synthase,
isocitrate dehydrogenase,
alpha-ketoglutarate dehydrogenase
```
140
what are the effects of hormones on enzymes?
alter Activity of enzymes - rapid via (de)phosphorylation or short lived. Number of enzymes- slow via gene expression change or longer lived effect. opposing metabolic pathways up or down in concert.
141
how does enzyme control by phosphorylation work?
protein kinase, adds phosphate to enzyme, phosphoprotein phosphatase returns enzyme to its normal state. Phosphorylation - conformational change - activation or inactivation.
Phosphorylation overrides any allosterism.
142
what are the allosteric regulators of phosphorylase ?
In muscle - + AMP, ATP G-6-P.
| In liver Glucose
143
what are the glycogen synthase phosphorylation sites?
in muscle: 9
in liver: 7
6 different kinases = inhibition
144
what is the signalling cascade
hormones bind to receptor allowing G protein to bind and become activated, which causes activation of adenylasecyclase. this converts ATP to Cyclic AMP. this activated Protein kinase A (also activates glycogen synthase a which reduces glycogenesis) which adds a phosphate to phosphorylase kinase. converts phosphorylase b to phosphorylase a which is the active form. this leads to increase in glycogenolysis.
145
what is an example process of control by phosphorylation, insulin.
protein kinase B adds a phosphate group to GSK3 which stops glycogen synthesise working. PP1 removes Phosphate to activate G.Synthase and increase glycogenesis. Insulin sensitive protein kinase, adds phosphate to PP1, deactivating phosphorylase kinase and glycogen phosphorylase. leads to drop in glycogenolysis
146
control of phosphorylation - glycogen metabolism.
levels of phosphorylase rapidly drop as glucose is added, and levels of glycogen synthase climbs
147
what are some examples of hormone sensitive lipases
Insulin - dephosphorylated, cant breakdown fat with insulin around, Triglyceride droplet has impenetrable barrier of perilipin.
Adrenaline - phosphorylated. (protein kinase A) perilipin changes conformation when phosphorylated allowing hormone sensitive lipase to bind and break down fatty acids. can lose weight
148
what are the enzymes that allow conversions between F-6-P and F-2, 6-P2
Phosphofructokinase-2 forward
Fructosebiphosphtase-2
reverse.
both enzymes are in the same polypeptide, coming from one gene (PFK2/FBPase2)
149
if insulin or adrenaline is active what happens to the enzymes controlling F-6-P to F-2,6-P2
Insulin: PFK2 is active so F-2,6-P2 is formed,
speed up glycolysis.
Adrenaline: FBPase2 is active.
phosphate is used as a switch
150
what is the link reaction (enzyme regulation) pyruvate dehydrogenase.
the three levels of control
1. PDH kinase acts on enzyme that converts pyruvate to Acetyl CoA adding a phosphate and deactivating it, this is reversed by PDH Phosphatase.
2. ATP NADH and Acetyl CoA feed back negatively on enzyme.
3. CoA ADP NAD+ simullates enzyme and ATP and NADH stimulate the kinase that switches of PDH
4. release of Ca2+ in muscles inhibits kinase and stimulates PDH phosphatase
151
what is the enzyme that links together allosterism to phosphorylation ? and what does it do?
AMP-activated Protein Kinase (AMPK), called energy sensor. AMP binds cooperativly and allosterically - 1000 fold increase in activity of AMPK.
Phosphorylates multiple targets (Enzymes & TF), Activated by Metformin (diabetic drug)
152
what is the signally done by AMPK?
fuel sensor and regulator.
153
what is control of enzymes by gene expression?
transcription factors bind genes and increase or decrease expression. so [enzyme] V and V max increase and decrease.
154
how are transcription factors activated?
some are metabolite receptors - gene binding occurs after metabolite binds. phosphorylation of transcription factors lead to gene binding .
155
what is CREB?
Cyclic AMP Responsive Element Binding Protein
156
control of expression by glucagon?
1.glucagon causes production of cyclic AMP which activates protein kinase A
2. PKA can phosphorylate inactive CREB
3. phosphate becomes a binding site for CREB binding proteins.
4. this pair of proteins then binds to CREB-binding element on DNA
5. this induces transcription etc.
glucagon causes phosphorylation and transcriptional regulation.
157
example of control of expression?
during exercise upregulation in expression of enzyme lipoprotein lipase which cleaves off fatty acid. more lipase expressed so more fatty acids tails removed.
158
summarise the different metabolic control mechanisms via enzyme regulation.
1. allosterism/inhibitors - very quick, graded, but limited effect.
2. Phosphorylation - quite quick on/off effect.
3. gene expression - slow but sustained effect increase and decrease V max. mutations lead to Vmax=0
159
what is the effects of dietary deficiencies on enzyme regulation?
```
B1: thiamine - TPP e.g PDH
B2: Riboflavin - FAD/FMN - 50+ enzymes
B3: Niacin - NAD/NADP - 200+ enzymes
B5 Pantothenic acid - CoA
B6: Pyridoxine - PLP -phosphorylase, aminotransferases
B7: Biotin - PEP carboxykinase, PDH
```
even if the [enzyme] is normal the amount that is functional will be subnormal i.e. low V max
160
what are 2 examples of deficiency diseases?
beriberi B1
| Pellagra B3
161
what is the effect of dietary additions ? caffeine
inhibits cAMP phosphodiesterase.
| so levels of cAMP levels stay high. more protein kinase A, increase in glycogenolysis and lipolysis
162
what are altered metabolic states?
```
Fed (anabolic state)
High fructose
Alcoholism
Fasting (catabolic state)
starvation
Exercise
Thermogenesis
```
163
what is the link between food molecules and storage molecules?
food molecules - anabolic pathways - storage molecules - catabolic pathways - ATP. ATP inhibits catabolic pathways and stimulates anabolic pathways.. ADP stimulates catabolic pathways and inhibits anabolic pathways
164
metabolic profile of brain tissue?
1000kj/kg/day energy. none stored.. substrate: glucose. no substrate exported
165
metabolic profile of liver
835kj/kg/day glycogen, triglycerides. substrate: glucose, fatty acids, amino acids. exports glucose and triglycerides
166
metabolic profile of adipose tissue
19kj/kg/day triglycerides
| substrate: fatty acids. exports fatty acids and glycerol
167
metabolic profile of muscle
54kj/kg/day glycogen, triglycerides.
| substrates: rest=fatty acids, exports none active=glucose exports lactate
168
what are metabolic oddities?
heart: preferred fuel =ketone bodies
Erythrocytes: glycolysis only - generate lactate.
Cancer: Aerobic lactate production (warburg effect)
kidneys: use 8g day of lactate for ATP production.
Intestines: preferred fuel = glutamine
Immune cells: preferred fuel source = glutamine
Spermatozoa: fructose
169
what triggers insulin release into the blood?
increase in glucose or Leu.
| Produces glycogen
170
what triggers glucagon relase?
a drop in blood glucose and increase in glucogenic amino acids
171
what does glucose end up as?
50-60% glycolysis
10% glycogen
30-40% Triglycerides
172
what do amino acids end up as?
Protein
| Carbon Skeletons
173
what do fatty acids end up as ?
Triglycerides
174
where are molecules stored?
Liver: glycogen, triglycerides
Adipose tissue: triglycerides
muscle: triglycerides, glycogen, amino acids
175
what does glucose inhibit and stimulate? in the liver - and enzyme activty
stimulates: glycogen synthase- glycogenesis, Pyruvate kinase and PFK2-[f-2,6,p2]-pfk1 - Glycolysis.
Inhibits: Phosphorylase - glycogenolysis, F-16-Biphosphatase - gluconeogenesis
176
what do fatty acids stimulate? in the liver enzyme activity
Acetyl CoA carboxylase - FA synthesis
177
what do fatty acids stimulate in adipose tissue? enzyme actvity
Pyruvate dehydrogenase - Acetyl CoA increased Fatty acids
178
what do triglycerides inhibit in the adipose tissue? enzyme activity
decrease HS lipase - lipolysis
179
what does glucose stimulate and inhibit in the liver in terms of enzyme levels?
stimulates: Glucokinase - Gluc-G-6-P-Glycolysis
Inhibits: PEPE carboxykinase - OAA-TCA cycle not PEPE
180
What do fatty acids stimulate in terms of enzyme levels in thee liver?
malic enzyme-generates NADPH for FAS.
| ATP-Citrate lyase - Increase cytoplasmic Acetyl CoA
181
what does glucose stimulate in adipose tissue in terms of enzyme levels?
increase Phosphfructokinase-1 - F-6-P to F1,6p2 increased glycolysis.
182
what do triglycerides stimulate in the adipose tissue in terms of triglycerides?
lipoprotein lipase for Fatty acid entry
| Glycerol-3-P acyltransferase for lipogenesis
183
what do most tissue in the body contain?
GLUT1+3 - Low Km
| Hexokinase I-II -low Km
184
what do the liver and beta cells in pancreas contain?
```
GLUT2 - High Km
Hexokinase IV (Glucokinase) -High Km not inhibited by G-6-P
```
185
What are isozymes?
different enzymes, same substrate
186
what do muscle and adipose tissues contain?
GLUT4 -medium Km
induced by by insulin.
Hexokinase II - Low Km
187
what is the effect of insulin on fat stores
Insulin turns glucose to fat, and blocks fat breakdown so fat stores swell as more fat is made and is not being used
188
what is High fructose corn syrup?
Sweetener in food, less glucose than sugar (sucrose), less insulin release, less fat storage, but fructose is metabolised faster than glucose so this doesnt work.
189
how does fructose enter glycolysis?
Fructose converted by fructosekinase to F-1-phosphate, F-1phosphate aldolase converts this to glyceraldehyde and DHA phosphate. triose kinase converts this to Glyc-3-phosphate to enter glycolysis.
190
what is the effect of fructose entering glycolysis
bypasses 2 control points in glycolysis.
F-1-P stimulates pyruvate kinase speeding up whole pathways, leading to excess pyruvate-excess acetyl CoA-fatty acid and triglyceride synthesis
191
what is effects of artificial sweeteners?
sweet taste in mouth leads to increased insulin that causes hypoglycaemia resulting in hunger and over eating
192
what is aspartame broken up into?
aspartate, Phenyalanine, Methanol. so isnt 0 cal
193
what is the pathway for dealing with ethanol?
ethanol converted to Acetaldehyde using alcohol dehydrogenase and NADH production. this is converted to acetate by aldehyde dehydrogenase (NAD++H20-NADH + H+). acetate is converted to Acetyl CoA by Acetyl CoA synthetase using energy from GTP
194
what is the problems of ethanol (alcohol) consumption?
no regulation of ethanol metabolism
ethanol oxidised in preference to other nutrients. leads to build up of lots of NADH+H+ and little NAD+ which inhibits TCA cycle, and lactate isnt converted to pyruvate. the results in metabolic acidosis.
lots of ATP produced can inhibit glycolysis allosterically.
195
what is the effect of low pyruvate and NAD+ levels caused by ethanol ? and high levels of Acetyl CoA
low Pyruvate means gluconeogenesis is low and hypoglycaemia occurs.
low NAD+ means beta-oxidation doesn't occur (build up of fatty acids)
High Acetyl CoA means increased Triglyceride synthesis
196
what is the catabolic state? not eaten for a while
breakdown of stored molecules to release glucose (brain + blood) or fatty acids (everything else)
197
what is the first metabolic priority
maintain blood glucose: job of Adrenaline and glucagon leading to increase in glycogenolysis and gluconeogenesis and lipolysis to increase glycerol for gluconeogenesis.
Cortisol - causes protein degradation to give increase in Gluconeogenesis
198
what is the response of different organs during fasting
adrenal glad releases adrenaline. glucagon released from pancreas. these target the liver so glycogen is broken into glucose.
Adipose tissue breaks down triglycerides, fatty acids travel in blood, and glycerol go to liver to be broken into glucose.
Cortisol is released by adrenal glad and reinforces these changes.
Muscle amino acids are broken down and taken to the liver for gluconeogenesis
199
in terms of adrenaline what does glucose stimulate and inhibit during the catabolic state? in muscle enzyme activity
stimulates: Glycogen synthase - glycogenesis
Inhibits: Phosphorylase - glycogenolysis, PFK2 - F-2,6,P2 - PFK1. - glycolysis
200
in terms of adrenaline what does triglycerides stimulate during the catabolic state? in muscle and adipose tissue? enzyme activity
M: lipoprotein lipase - Fatty acid intake
A: HS lipase - lipolysis
201
in the presence of adrenaline (or glucagon) what is the effect of glucose on enzyme activity in the liver?
inhibits: Glycogen synthase - glycogenesis,
PFK2 - F-2,6,P2 - PFK1 - glycolysis
stimulates: Phosphorylase - glycogenolysis, F-1,6-bisphosphatase - gluconeogenesis
202
in the presence of adrenaline (or glucagon) what is the effect of fatty acids on enzyme activity in the liver?
inhibition: Acetyl CoA carboxylase - decreased fatty acid synthesis
203
in the presence of glucagon what are the effects of glucose on enzyme levels in the liver?
reduced: glucokinase, pyruvate kinase.
Increased: PEP carboxykinase, F-1,6-Biphosphatase, G-6-phosphatase
204
in the presence of glucagon what are the effects of fatty acids on enzyme levels in the liver?
reduced: acetyl CoA carboxylase - stops malonyl CoA.
Increased: Carnitine acyltransferase-1 - fatty acids to mitochondria for oxidation
205
in the liver what are the increased enzyme levels in the presence of cortisol?
Glucose: PEP carboxykinase, Amino Acid catabolising enzymes, Urea cycle enzymes, Glycogen synthase - increased glycogenesis.
triglycerides: HS lipase - increased fatty acids and glycerol.
Muscle: increased protein degradation (transamination-increased Ala-gluconeogenesis)
206
what are the second metabolic priority's? starvation
1. preserve functional protein by decreasing glucose requirements.
207
how does the body decrease glucose requirements when starving?
Brain converts to ketone body usage (70% ATP) - reduced need for gluconeogenesis- reduced need for protein catabolism. liver exports ketone bodies, and at rest muscles export amino acids.
208
what are the equations for rapid short term replenishment of ATP?
ADP + Creatine P = ATP + Creatine (creatine kinase)
| ADP + ADP = ATP + AMP 9Adenylate kinase)
209
what is used during long duration. low intensity exercise?
Fatty acids and Glycogen
210
what is supermouse?
overexpression of PEP-carboxykinase in muscle:
| low lactate production, increased fatty acid use, increased triglyceride in muscles, more mitochondria
211
how is heat generates from metabolic processes?
1. shivering
| 2. uncoupled respiration,-thermogenin, fatty acyl amino acids
212
what is brown adipose tissue?
modified adipocytes which generate heat by wasting energy stored in fats. (important in babies)
213
what is the structure of brown adipose tissue?
Numerous small triglyceride droplets, more mitochondria. sympathetic innervation (noradrenaline)
214
what is the role of brown adipose tissue?
activates uncoupling protein 1 (a thermogenin) which leads to uncoupling of electron transport chain and ATP synthesis so energy is lost as heat (ETC has sped up so energy cannot be captured)
215
what does sympathetic innervation do?
releases into blood of N-acyl amino acid synthase, leads to the joining of fatty acids+amino acids to make an N-acyl amino acid
216
how sympathetic intervention works - occurs in all mitochondria not just brown adipose
ADP is swapped with ATP through transporter (ATP/ADP carrier - translocase). presences of acyl amino acid turn it into a proton transporter. energy is not captured as ATP so lost as heat
217
what is dinitrophenol
has the property of being able o transport protons across a membrane, so the proton isn;t used to make ATP so enrgy is not captured and heat is created and ETC speeds up
218
what is the difference between healthy tissue and insulin resistant tissue?
healthy: glucose goes to muscle, liver and adipose.
Insulin resistant: muscles stop glucose uptake, liver stays in state of releasing glucose and glycogen isn't formed. adipose tissue takes up excess tissue
219
mouse model for diabetes
transgenic mouse that has no adipose tissue.
eats 5x quantity of food/day, blood glucose and triglycerides 3x normal, insulin 50-400x normal (and ineffective)
diabetes cured by transplanting in adipose tissue
