TOPIC A: REGULATION OF METABOLISM Flashcards
(156 cards)
1
Q
In which conditions is the glycolytic pathway active?
A
- ATP LOW
- ADP HIGH
- AMP relatively HIGH (up to 20 fold)
- NADH/NAD+ ratio LOW
2
Q
What is the first ( first regulatory) reaction of glycolysis and what are the enzyme/cofactors involved?
A
- Glucose–> Glucose-6-Phosphate
-ATP–> ADP - Mg2+ takes part
Enzyme is Hexokinase
3
Q
What is the second regulatory reaction in glycolysis and what are the enzymes./cofactors involved?
A
- Fructose-6-Phosphate–> Fructose 1,6-Bisphosphate
- PFK-1 is enzyme (PhosphoFructoKinase-1)
- ATP–> ADP
4
Q
What is the third regulatory step in glycolysis and what are the cofactors involved?
A
(2) PEP (phosphoenolpyruvate)–> (2) Pyruvate
- Enzyme is Pyruvate Kinase
- (2)ADP–> (2)ATP
5
Q
What is the function of ‘kinase’ enzymes?
A
- Catalyses phosphorylation (ADDS phosphate)
6
Q
What is the function of ‘mutase’ enzymes?
A
- takes functional group from one location to another
7
Q
What is the function of ‘phosphatase’ enzymes?
A
- Takes the phosphate group off molecule
8
Q
What is the definition of gluconeogenesis and when is it most likely to occur?
A
- Formation of glucose from non carbohydrate precursors (like oxaloacetate and pyruvate)
- During times of fast (low blood glucose levels)
9
Q
What are the two methods to boost blood glucose levels?
A
- GNG
- Glycogenolysis
10
Q
What is the delta G value for the 7 reversible reactions of glycolysis?
A
- Almost 0
11
Q
What is the delta G value for the 3 irreversible (regulatory) reactions of glycvolysis?
A
- Very negative
12
Q
What is the overall equation for GNG?
A
- 2 pyruvate + 4ATP + 2GTP + 2NADH + 2H+ + 4H20——-> Glucose + 4ADP + 2GDP + 6Pi + 2NAD+
13
Q
What are the two different pathways for the first bypass reaction in GNG?
A
- Lactate present (lactate–> pyruvate)
- No lactate present (just pyruvate)
14
Q
What is the rough comparison for the (pyruvate–> PEP) lactate pathway for the 1st regulatory step in GNG?
A
lactate–> cystolic NADH formed
- In mitochondria oxaloacetate–> PEP via mitochondrial PEP carboxykinase
- Oxaloacetate travels out of mitochondria
(no malate shuttle needed)
15
Q
What is the rough comparison for the first regulatory reaction (pyruvate–> PEP) with no lactate present?
A
- Malate shuttle needed yo convert oxaloacetate–> malate then back to oxaloacetate OUT of mitochondria
- PEP converted to via CYTOSOLIC PEP carboxykinase
16
Q
What is the first part of the GENERAL reaction for the GNG conversion pyruvate–> PEP?
A
- (2) Pyruvate–> (2)oxaloacetate
- via ‘pyruvate carboxylase enzyme
- (2)ATP–> (2) ADP
- Biotin required
17
Q
What is the second part of the GENERAL reaction for the GNG conversion of pyruvate–> PEP?
A
- (2) oxaloacetate——> (2) PEP
- Via PEP carboxykinase enzyme (mitochondrial or cytosolic depending on lactate or pyruvate as starting material)
18
Q
What substrate MUST be available for GNG?
A
- NADH !!
19
Q
What is added to pyruvate to get oxaloacetate?
A
- CO2
20
Q
What occurs in bypass reaction 2 of GNG?
A
Fructose 1,6-bisphospate—-> Fructose-6-phosphate
- Via fructose 1,6-bisphosphatase enzyme
- H20–> Pi
21
Q
What occurs in bypass reaction 3 of GNG?
A
- Glucose-6-Phosphate—-> Glucose
- Via Glucose-6-Phosphatase enzyme
- H20—> Pi
22
Q
When is the Gluconeogenesis pathway active?
A
ATP HIGH
ADP LOW
AMP LOW
NADH/NAD+ ratio HIGH
23
Q
What is the end product of GNG (quantity of glucose from…) ?
A
- 1 molecule of glucose from 2 pyruvate
24
Q
Roughly how long does it take for the glycogen stores to be used up?
A
- 10-18 hours
25
What does AMP stand for?
- Adenosine Mono Phosphate
26
What are inhibitory substrates in the second bypass reaction? (Fructose-6-p--> Fructose 1,6-bisphosphate)
- Citrate (increases inhibitory action of ATP--> signals to cell it's meeting energy needs)
- ATP (inhibits PFK-1 allosterically--> allosteric inhibitor when ATP is high)
27
What are the activators of the Fructose-6-P --> Fructose1,6-bisphospate reaction?
- Fructose 2,6 bisphosphate (decreases affinity for citrate and ATP and activates PFK-1)
- AMP and ADP
28
How is fructose 2,6-bisphosphate controlled?
- Under hormonal control (glucagon and insulin)
29
What does 2,6-bisphosphate (also AMP) inhibit in GNG?
- Fructose 1,6-bisphosphatASE-1
30
What is pyruvate kinase allosterically activated by?
- Fructose-1,6-bispohsphate
31
How many izozymes of pyruvate kinase are there?
-3 izozymes
32
What is pyrivate kinase allosterically inhibited by?
- Signs of abundant energy supply
| e. g. ATP, AcetylCoA + long chain FAs, Alanine (amino acids)
33
What is pyruvate kinase M (muscle) regulated by?
- Adrenaline (epinephrine)
34
When is adrenaline released in terms of energy and what does this cause?
- When more energy is required---> in crease in cAMP--> Activates glycolysis
35
What is the pathway when blood glucose levels are low?
- Glucagon released
- Increased cAMP
- PKA activated (protein Kinase A)
- Phosphorylases
- Inactivates pyruvate kinase-L
- Decrease in use of glucose by liver cells (so glucose can be sent to places that need it i.e. brain)
36
What is the enbd product for the phosphorolysis of glyocgen?
- G-1-P
37
What does glycogen phosphorylase do in glycogenolysis?
-Breaks the alpha 1-4 linkages
38
In glycogenolysis, which enzyme breaks the branch points (1-6 linkages) down?
- Debranching enzyme
39
What does phosphoglutomutase catalyse?
- Conversion of g-1-p--> g-6-p (mutase moves the P group from position 1--> 6)
40
What is insulin produced by?
- Beta pancreatic cells
41
What are the 4 outcomes of ligand-receptor interaction?
1. Second messenger (cAMP,cGMP) insidecell is ALLOSTERIC regulator of enzymes
2. Receptor TYROSINE KINASE activated by extracellular hormone
3. Change in mempot occurs from OPENING or CLOSING of hormone gated ion channel.
4. Steroid causes change in level of expression (DNA-->mRNA) of genes (nuclear hormone receptor protein)
42
What effect will metabotropic receptors have on enzymes?
-Change will ACTIVATE or INHIBIT enzyme after receptor in pathway.
43
What do ionotropic receptors act as?
- Signal AMPLIFIER and TRANSDUCER
44
What type of cascade occurs in regulation of glycogen synthesis and adrenaline breakdown?
- Signal amplified--> a catalyst (protein kinase) activates another protein kinase ---> LARGE amplifications of original signal
e. g. One A causes many G-1-P molecules to be made from GLYCOGEN
45
Which hormones trigger very rapid responses and what change does it cause in enzymes?
- Hormones that act on membrane receptors
| - Cases change in activity of PRE-EXISTING enzymes (allosteric mechanisms or covalent modifications)
46
What is the mode of action of thyroid and sex hormones (steroid) and is this a fast or slow mechanism?
- They upregulate (synthesise) or downregulate of the REGULATED PROTEIN
- Alter gene expression
- Much slower response (hours or days)
47
What are examples of peptide hormones and where are they synthesised? -
- All hypothalamus and pituitary hormones
- Pancreatic--> Insulin, glugagon, Somatostatin
- Synthesised in ribosomes
48
What are the catecholamine hormones?
- Adrenaline and NA
49
What are examples of eicosanoid hormones and when are they produced
Prostoglandins, thromboxones, Leukotrines, Lipoxins
| - Only produced WHEN NEEDED
50
How can some antiinflammatory drugs work?
- By BLOCKING steps in prostoglandin synthesis pathways
51
What is the function of thromboxones?
- Regulate platelet function (blood clotting)
52
What is the effect of cortisol?
- To increase the rate of gluconeogenesis
53
What does AMPK in the hypothalamus do?
- Integrates signals and influences feeding behavior + energy yielding metabolism in tissues.
54
What do hepatocytes do with a diet rich in protein?
- Supply themselves with HIGH levels of enzyme (for amino acid catabolism and G.N.G)
55
What happens (hepatocytes) when there is a shift from a protein rich diet to carb rich diet?
- Levels of a.a. catabolism and G.N.G DROP
| - There is INCREASE in synthesis of enzymes essential to carb metabolism and fat synthesis
56
Which transporter is involved in the transport of glucose into the hepatocytes?
- GLUT2
| Glucose---> GLUT2---> Glucose--> G-6-P via glucokinase (IV) enzyme
57
What does the high Km of Hexokinase IV (glucokinase) ensure?
- Phospohrylation of glucose is MINIMAL when conc. of glucose is LOW (so liver doesn't use glucose as a fuel in glycolysis and so it can be used for OTHER TISSUES)
58
Which fuels does RESTING muscle use?
- Free FAs (adipose) + Ketone bodies (liver)
| - These then form AcetylCoA-> CA cycle--> oxidative phosphorylation (ATP formed)
59
What fuels does somewhat active (moderate) muscle activity use?
- BLOOD GLUCOSE (pyruvate--> CA cycle--> ox.phosp.--> ATP
| - FAs + Ketone bodies
60
Which fuels does extremely active muscle (maximally) use and how many ATP is formed from each ____ molecule?
- Glycogen--> Lactate
- Each glucose forms 3 ATP
- ADRENALINE secreted
61
In highly active muscle when Adrenaline is secreted, what does it stimulate?
- Release of glucose from liver
| - Breakdown of glycogen in muscle tissue
62
What is the other source of ATP that skeletal muscle contains?
- PHOSPHOCREATINE
63
What is the equation for muscle activity -active contraction and gylcolysis (creatine) ?
Phosphocreatine + ADP---> ATP + Creatine
64
What is the equation for recovery from muscle activity?
Creatine + ATP ---> Phosphocreatine + ADP
65
What is creatine's role?
- Shuttles ATP equivalents from mitochondrion to places where ATP is being used
66
What can be the LIMTING factor in development of NEW muscle tissue?
- CREATINE!!!
67
After exercise, what is the extra O2 used for?
- Oxidative phosphorylation
| - ATP from lactate is used for G.N.G in liver
68
What is the Cori cycle?
-A pathway for recycling lactate to form glucose again (then glycogen) - it is a cycle
69
Which factors mediate allosteric regulation?
- Substrates of pathways (e.g. glucose--> glycolysis)
- Product in pathway (ATP from glycolysis)
- Key metabolite or cofactor (NADH)
70
What are two examples of second messengers from extracellular signals?
- cAMP and Ca2+
71
What is compartimentalisation in enzyme regulation?
- A way to alter the effects that an enzyme has
| - Enzyme and substrate get put into different compartments
72
What is an example of compartimentalisation?
- Hexokinase enzyme can't act on glucose UNTIL sugar enters myocyte (blood--> myocyte)
73
Do glucose transporters determine the RATE of entry of glucose?
- YES!
74
Which 4 factors can change the activity of a single enzyme molecule?
- Concentration of substrate
- Allosteric effector presence
- Covalent modification (phosphorylation)
- Binding of regulatory proteins
75
What are the effects of phosphorylation (by a protein kinase)? (4 effects)
1. Alter electrostatic features of an enzymes active site
2. Cause movement of inhibitory region of enzyme OUT of active site
3. Alter enzyme's interaction with OTHER proteins
4. Force CONFORMATIONAL changes that cause Vmax or Km to change
76
What is the difference between 'metabolic regulation' and 'metabolic control' ?
- METABOLIC REGULATION: Process that MAINTAINS homeostasis
METABOLIC CONTROL: Process that leads to CHANGE in OUTPUT of metabolic pathway overtime (response to signal OR change in circumstances)
77
Is AMP are more or less sensitive indication of the cell's energetic state than ATP?
- MORE SENSITIVE
78
What does AMPK do?
- Responds to increase in AMP
| - Phosphorylates IMPORTANT PROTEINS and results in regulation
79
How is AMPK activated?
- By AMP binding allosterically
80
How does AMP slow glycogen synthesis?
- Inhibiting glycogen synthase enzyme
81
Which hexokinase izozyme is in myocytes, and does it have low or high affinity for substrate?
- Hexokinase II
| - Has HIGH affinity for glucose
82
What are muscle hexokinase I and II inhibited by?
- Allosterically inhibited by product; G-6-P
83
Is hexokinase IV (liver) inhibited by G-6-P?
- NO! So it can continue to operate more than the others in muscle (high Km value--> low affinity for substrate)
84
What are potential sources of G.N.G?
- Pyruvate
- Lactate
- Glycerol
- Amino Acids
85
What is hormonal regulation of glycolysis and gluconeogenesis MEDIATED by?
- Fructose 2,6-bisphosphate
| - Acts allosterically on PFK-1 and Fructose bisphpsphatase enzymes
86
What happens when fructose 2.6-bisphosphate binds to allosteric site on PFK-1?
- There is INCREASED affinity for Fructose-6-P and REDUCED affinity for ATP and Citrate (these are allosteric inhibitors)
87
Is PFK-1 active without fructose 2,6-bisphosphate?
- NO!!
88
Which factors allosterically inhibit ALL forms of pyruvate kinase?
- High ATP
- AcetylCoA
- Long chain FAs
- Alanine (enough Amino acids)
(i. e. When the energy supply is high these act)
89
If there is a lot of isulin (and you want to form glycogen), what do you need to INACTIVATE?
- Glycogen phosphorylase needs to be inactivated (remove the Phosphate group)
90
What types of regulation is glycogen under in glycogen breakdown?
- Hormonal: glucagon/Adrenaline (cause the stimulation of glycogen breakdown)
- Allosteric: cAMP
- Glycogen phosphorylase (which is regulated by covalent modification)
91
In the muscle, what do AMP and Ca2+ activate?
- They activate the kinase to phosphorylate
92
What is Glucose-6-Phosphate an allosteric activator of?
- The phosphate (PP1) that is responsible for activating Glycogen synthase A
93
What are the purines?
- Adenine + Guanine (A+ G)
94
What are the pyrimidines?
- Cytosine (C)
- Thymine (T)
- Uracil (U)
95
What does a nucleoSIDE consist of?
- The base and the sugar (NO phosphate)
96
What does a nucleotide consist of ?
- Sugar, base AND phosphate group
97
What are the FOUR ways our body uses nucleotides? -
1. Building blocks of RNA and DNA
2. NuscleoSide triphosphates (ATP and GTP) to carry energy
3. Cofactors (NAD+, FAD and CoA) and activated intermediates like UDP glucose
4. cAMP and cGMP acting as signalling molecules
98
Is there a direct nutritional requirement for nucleotides?
NO
99
What is the name for purine nucleoSide RNA and DNA adenine?
RNA: Adenosine
DNA: Deoxyadenosine
100
What is the name for the purine nucleoSide for cytosine?
RNA: Cytidine
DNA: Deoxycytidine
101
What is the name for the purine nucleoTide for Adenine?
RNA: Adenylate (RNA)
DNA: Deoxyadenylate
102
In general terms, what is the de novo pathway for nucleotide metabolism?
- Metabolic precursors are used for synthesis
| e. g. aa's, ribose-5-p, CO2, NH3
103
Which form are 2'deoxy-D-ribose (DNA) and D-ribose (RNA) in?
- Their Beta furanose closed 5-ring form
104
In general terms, what is the salvage pathway for nucletodie* metabolism?
- Synthesis from BASES from the DIET and degradation of nucleic acids
105
Are the purine rings synthesised with precursor compartments?
- YES!!! e.g. N's are from the amide N in glutamate
106
In de novo synthesis, which molecule is the purine ring structure built onto?
- PRPP (Phosphoribosyl pyrophosphate)
107
Is the De novo synthesis of purines energy requiring?
- YES! 5 ATP are used
108
After the first step in de novo purine synrthesis, what is formed (i.e. after the 11 steps)?
- Inosinate (IMP) which is GMP and AMP precursor
| First intermediate with COMPLETE purine ring
109
Which two molecules are formed from IMP in the purine de novo synthesis pathway?
- GMP and AMP
110
Where do GMP and AMP act as negative regulators ? (in de novo synthesis purine pathway)?
- Act on glutamine-PRPP amindotransferase enzyme to block pathway in FIRST STEP
- Both inhibit conversion of IMP to GMP and AMP
111
What are the steps that occur in purine metabolism degradation?
- Phosphate group removed
- Ribose group removed
- Amino group removed (deamination)
- URIC ACID FINAL PRODUCT
112
What is the final product of purine degradation?
URIC ACID
113
What are the two purine salvage pathways?
Guanine---> GMP via HGPRT enzyme(also PRPP lets off phosphate)
Hypoxanthine--> IMP via HGRPT enzyme (also PRPP lets off phosphate)
114
What is the enzyme that catalyses the adenine salvage pathway?
- Adenine phosphoribosyltransferase
| Adenine +PRPP----> AMP + PPi
115
What is PRPP the source of in the salvage pathways for purine metabolism?
- The ribose and phosphate
116
What is gout caused from?
- build up of uric acid from faults in ENZYMES in purine degradation metabolism pathway
- Results in arthritis in joints from build up of uric acid crystals
117
Which enzyme is deficient in SCID (Severe Combined Immunidefficiency)?
ADA deaminase defficiency
118
What does the ADA enzyme do?
- Converts Adenosine ----> Inosine
119
What is the biochemistry of SCID?
- Loss of ADA enzyme activity
- Increased dATP levels
- dATP is feedback inhibitor of ribonucleotide reductase
- High dATP reduces synthesis of other dNTP's
- reduced dNTP pool effects T and B cell proliferation
120
What are the symptoms of SCID?
- No immunity
| - Lots of infections
121
What is the most common treatment for SCID?
- Gene therapy
| - Good but WBCs have a short lifespan so not permanent
122
Which enzyme is defficient and which pathway is this part of in Lech-Nyan syndrome, also what does this lead to mainly?
- HGPRT enzyme (genetic lack)
- Purine degradation pathway
- High PRPP and uric acid levels
- Increased de novo synthesis of purines (the body only relies on this pathway
123
What are the symptoms of Lesch-Nyan syndrome?
- CNS damaged
- Self mutilation
- Mental retardation
- Gout arthritis
124
How is the pyrimidine ring synthesized?
- Oratate
125
What are constitutive enzymes and what pathways are they involved in?
- Enzymes present in constant concentrations in cell
- Have LONG lifetimes
- Glycolysis + CA cycle
126
What are inducible/repressible enzymes and what substances can they be affected by?
- Enzymes that are only synthesised when the cell REQUIRES them
- Metabolites, Hormones, Growth factors can affect them (increased rate of synthesis or degradation (induced) or decreasd (repressed)
127
Which glycolysis enzymes can insulin induce?
- Liver hexokinase (Glu---> G-6-P)
| - Liver PFK-1
128
What is an example of repression of synthesis in glycolytic pathway?
- End product in pathway; ATP represses PFK
| - So when ATP levels are high, PFK-1 inhibited
129
What is an example of two enzymes that are compartmentalised?
- G-6-Phosphatase
- Found in glucoNEOgeic tisues (LIVER and kidneys) not fond in muscle, brain or fat
- Pyruvate kinase occurs in different tissues (izozymes)
- strucutral differences
130
Are RBCs also a form of comparmetalisation?
- YES! As they have NO mitochondria thus NO enzymes for CA cycle and ETC
131
Are izozymes the product of different genes?
- YES!
132
Do izozymes catalyse the same reaction?
- YES! But different primary structures
133
What does glucokinase (hexokinase IV)'s high Km (i.e. Low affinity for substrate) mean for the enzyme activity?
- Allows enzyme in liver to last for MUCH longer and continue operating without saturation(compared to muscle hexokinase which cannot)
134
Which 4 ways is the AMOUNT of enzyme affected?
1. Lifespan of enzyme
2. Synthesis of enzyme (induced or repressed)
3. Compartmentalisation of synthesised enzymes
4. Izozymes (compartmetalisation result)
135
In allosteric modulation, what is the role of a negative modulator?
- Bind to active site and PREVENT activity of enzyme
136
Are allosteric enzymes inhibitors and activators reversible and non covalent?
- YES!`
137
What effect can having too much alcohol (ethanol) have on the metabolic pathways?
- Breakdown of ethanol---> NADH produced
| - High NADH levels inhibit CA cycle (becasue NAD+ is required for CA cycle)
138
Are enzymes regulated by regulatory proteins?
- YES!
139
Is hormonal control of enzymes (inTERcellular) faster than regulation by allosteric activation/inhibition & covalent modiciation (inTRAcellular)?
- NO!!! Hormonal control is SLOWER
140
What effect does adrenaline have on tissues?
- Prepares them for BURSTS of activity
141
Is glucose uptake in the brain and RBCs dependent on insulin?
NO!!!! It is independent (doesn't rely on insulin)
142
Is glucose uptake by muscle and adipsoe tissue dependent on insulin?
- YES! Require insulin to signal glucose uptake
143
IS there mobilisation of the GLUT4 transporter with type I diabetes?
- NO!
144
In myocytes and adipose cells, what does the interaction of insulin cause (when insulin levels are high)?
- Insulin interacts with receptor
- Glucose transporters in vescile membranes move to SURFACE of cell
- Glucose can now be transported INTO cell via GLUT 4 transporters
145
What hapens to the glut 4 transporters after the insulin levels drop?
- They form an endosome again inside cell and are ready for next insulin interaction
146
In what state does glycogen synthesis take place?
- FED state
147
when does glycogenolysis occur?
- In the fasting state(liver) or rapid exercise (muscle)
148
What does UTP (iridine Tri Phosphate) do?
- Activates glucose
149
If there is lots of insulin in body, (want to form glycogen) do you need to activate or inactivate glycogen phosphorylase?
- INACTIVATE glycogen phosphorylase a(active)
(So remove the phosphate group)
- Prevents glycogen breakdown and glyocgen phosphorylase b will be less active
150
If there is high levels of gluacagon in bdsy, which enzyme would you want active to promote glycogen breakdown?
- Kinase enzyme to phosphorylate
151
What type of regulation does the glycogen phosphorylase enzyme undergo?
- Covalent modification (reversible phosphorylation)
| - Allosteric enzyme
152
What happens to the phopsphorylase enzyme a (active) when glucoese levels return to normal?
- Glucose enters liver cel
- Binds to allosteric site on phopshorylase a---> inhibits enzyme
- Thus less breakdown of glycogen to glucose
153
WHat are the twowayas in which gylcogen synthase is controlled?
- Hormonally + phosphorylation and dephosphorylation
154
What does the insulin signalling pathway cause?
- Increases glucose IMPORT into muscle
- STIMULATES activity of MUSCLE hexokinase
- ACTIVATES glycogen synthase
155
What does increased hexokinase activity enable?
-Activation of glucose
156
What is the GENERAL function of glycogen synthase?
- Elongates chain to form glycogen
