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Biochemistry II > Ch. 15 Metabolic Regulation > Flashcards

Ch. 15 Metabolic Regulation Flashcards

1
Q

Why is metabolic regulation complex and difficult to follow? (3)

A

There is lots of interplay, convergence, and divergence.

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2
Q

How are metabolites in a pathway described/thought of?

A

Metabolites in a pathway are in a “pool”. The carbon can flow down these “rivers” in any direction.

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3
Q

What two things must happen to metabolic pathways?

A
  1. Pathways MUST be regulated
  2. Pathways MUST work in conjunction with each other to maintain a middle ground of [metabolite]
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4
Q

What is the interplay of pathways to maintain [metabolite] also known as and why is it complicated?

A

Metabolism. It is complicated because cells must do this under constantly changing conditions.

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5
Q

How can metabolic flow be maintained? (8)

A
  1. increasing or decreasing enzyme activity
  2. enzyme regulatory subunits
  3. kinase and phosphotase activity
  4. allosteric regulation/interactions
  5. substrate level control
  6. sequestering enzymes
  7. protein-protein interactions
  8. targeted protein degredation
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6
Q

What are examples of increasing or decreasing enzyme activity? (3)

A

Transcriptional control (# of enzyme copies)
Number of receptors on cell surface
mRNA half life

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7
Q

What is an example of an enzyme with regulatory subunits?

A

PKA

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8
Q

What is an example of kinase and phosphotase activity?

A

Enzyme phosphorylation and/or dephosphorylation

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9
Q

How does substrate level control work?

A

When [metabolite] is high, the pathway will work at a high velocity

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10
Q

What is an example of sequestering enzymes?

A

Sequestering GLUT4 receptors in vesicles until insulin is released.

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11
Q

What is an example of protein-protein interactions?

A

GPCRs

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12
Q

What is an example of targeted protein degredation?

A

tagging with ubiquitin

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13
Q

Where do pathways exist dynamically? Why?

A

Pathways NEVER exist at equilibrium because the pathway is continually drawing off products.

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14
Q

What is a characteristic pathways must have in terms of the cellular environment?

A

Pathways must be able to adjust to changing conditions and deal with convergence and divergence.

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15
Q

What is an example of a divergence in glycolysis?

A

Carbons in glycolysis go to other things besides energy like alanine production.

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16
Q

How are pathways regulated in regards to maintaining homeostasis? (2)

A

Pathways are regulated based on the energy needs of the cell and according to where the carbon has/wants to flow. (aka: cells must have the right “rivers” running at the right time to meet needs)

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17
Q

What kind of energy must cells use in metabolic pathways?

A

Cells must use the best energy available at the time.

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18
Q

What is an example of cells using the best energy available to them?

A

Muscle cells prefer to use fats, but if working anaerobically (sprinting) cells can only use glucose and glycolysis.

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19
Q

What things are two big factors in metabolism?

A

Time and Oxygen

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20
Q

Why is an understanding of metabolic regulation and processes important? (3)

A

An understanding of metabolic regulation and processes is necessary for treatment of metabolic conditions, creating pharmaceuticals that target metabolic pathways, and agricultural GMOs.

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21
Q

Outline the steps of an experiment studying reaction mechanics with liver cells.

A
  1. made a liver total homogenate
  2. figured out flux (overall rate)
  3. added purified phosphohexose isomerase (phosphoglucomutase) and measured flux
    - flux of pathway reaction didn’t change
  4. added PFK and measured flux
    - flux was a little higher, but didn’t really change
  5. added hexokinase and measured flux
    - flux skyrocketed = MAIN REGULATORY ENZYME
    OF GLYCOLYSIS
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22
Q

Are all enzymes in a pathway of the same importance?

A

No.

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23
Q

What does it mean that pathways are reciprocally regulated?

A

Something that stimulates one pathway inhibits another.

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24
Q

How is catabolism (i.e. glycolysis) generally regulated?

A

Catabolism inhibited by high energy molecules.
Catabolism stimulated by low energy molecules

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25
How is anabolism (i.e. gluconeogenesis) generally regulated?
Anabolism inhibited by low energy molecules. Anabolism stimulated by high energy molecules
26
What is glucose-6-phosphotase?
A gluconeogenesis enzyme and transport protein that converts glucose-6-phosphate to glucose.
27
What is the Kₘ of glucose-6-phosphotase and what does it mean?
Very high Kₘ which means it doesn't bind substrate well. [substrate] must be pretty high for the enzyme to be active.
28
How is glucose-6-phosphotase regulated?
Substrate level control. low [G6P] = not "on" and glycolysis is happening high [G6P] = "on" and gluconeogenesis happening
29
What is hexokinase?
The first enzyme involved in glycolysis and converts glucose to G6P. Has six isozymes.
30
How is hexokinase inhibited? How does this compare to glucose-6-phosphotase?
ALLOSTERICALLY inhibited by high [G6P] - opposite of gluconeogenesis and glucose-6-phosphotase
31
When do G6P levels rise?
G6P levels only rise when glycolysis is blocked downstream.
32
Where is Hexokinase IV found?
liver
33
What is the Kₘ of Hexokinase IV?
high Kₘ so it doesn't bind substrate well
34
How is Hexokinase IV regulated? (2)
NOT inhibited by G6P ONLY active when blood glucose concentrations are high
35
How are all hexokinase isozymes regulated?
all are transcriptionally regulated
36
What is phosphofructokinase?
The third enzyme in glycolysis that phosphorylates F6P to F16BP.
37
What is PFK ALLOSTERICALLY inhibited by?
PFK is allosterically inhibited by ATP because ATP lowers PFKs affinity to substrate (increases Kₘ)
38
What else is PFK inhibited by and what does it mean?
PFK is also inhibited by citrate which ties glycolysis to the citric acid cycle (citrate present = citric acid cycle not running = high energy state)
39
What is PFK stimulated by? (2)
Stimulated by AMP and ADP. They higher the affinity to substrate (lowers Kₘ)
40
What is fructose-1,6-bisphosphotase?
A gluconeogenesis enzyme that converts F16BP to F6P.
41
What is fructose-1,6-bisphosphotase inhibited by?
Inhibited by AMP. This is reciprocal regulation between F-1,6-BPase and PFK.
42
What is fructose-2,6-bisphosphate?
A molecule that binds to PFK allosterically and increases its affinity for substrate (lowers Kₘ)
43
What effect does fructose-2,6-bisphosphate have on PFK kinetics?
PFK will be active at low substrate concentrations when it is present.
44
What is the other half of reciprocal regulation for fructose-2,6-bisphosphate?
When fructose-2,6-bisphosphate is present, F-1,6-BPase will have decreased affinity for substrate and only be active at high substrate concentrations.
45
What is pyruvate kinase?
The tenth glycolysis enzyme that converts PEP to pyruvate and produces one ATP.
46
What is pyruvate kinase inhibited by and how? (4)
Inhibited by... 1. ATP via feedback inhibition 2. Acetyl-CoA via feedback inhibition 3. fatty acids because they are high in energy (don't need anymore acetyl-CoA) 4. alanine because its precursor is pyruvate (divergence)
47
What is pyruvate kinase stimulated by?
Stimulated by fructose-1,6-bisphosphate because if its concentration is high, it needs to be drawn off (aka: "flow down the river")
48
How can pyruvate kinase be inactivated?
Phosphorylating pyruvate kinase inactivates it.
49
Where can the carbon in pyruvate flow? (3)
1. back to glucose (high energy) 2. towards the citric acid cycle (low energy) 3. make amino acids
50
What is the general purpose of the citric acid cycle? Why would pyruvate flow there?
It is where we crank energy production out. Completely oxidize carbon and release energy.
51
Where does Acetyl-CoA go/what does it do? (2)
Acetyl-CoA can enter into the citric acid cycle, but it is also feed-stocked into fatty acid synthesis.
52
Where will acetyl-CoA flow if you are on your ass? Active?
If you are on your ass, acetyl-CoA will build up and be drawn off into fatty acid synthesis. If you are active it will be used to produce energy (citric acid cycle).
53
What does acetyl-CoA stimulate?
pyruvate carboxylase
54
What does acetyl-CoA inhibit?
pyruvate dehydrogenase
55
What does high energy state mean for acetyl-CoA?
lots of energy = citric acid cycle inhibited = acetyl-CoA and citrate build up = gluconeogenesis turns "on"
56
What does a high [acetyl-CoA] lead to?
high [acetyl-CoA] = high glycogen OR high fatty acid concentrations (for storage)
57
What is an example of transcriptional control of metabolic pathways?
RTK signaling turns on transcription of enzymes that consume glucose (insulin signaling). Either store or use glucose.
58
What happens to Vmax as copy number of enzymes changes?
As copy number increases, so does Vmax.
59
What is glycogen?
A very large polymer of glucose for storage.
60
What link of linkages make up glycogen and describe each. (2)
glucose (ɑ1→4) glucose are the major linkage present glucose (ɑ1→6) glucose occur at branch points
61
Where is glycogen stored?
liver and muscle cells
62
What is glycogen phosphorylase?
an enzyme that breaks down glycogen by cleaving the most non-reducing glucose molecule and phosphorylating it to glucose-1-phosphate
63
What is the ΔG of glycogen phosphorylase?
﹣ΔG because there is a lot of inorganic phosphate around
64
What type of bonds can glycogen phosphorylase break?
Only (ɑ1→4) bonds. It CANNOT get a branch point into its active site or break an (ɑ1→6) bond.
65
What is debranching enzyme?
An enzyme that breaks glucose (ɑ1→6) glucose bonds
66
What is phosphoglucomutase?
An enzyme that catalyzes the conversion of G1P to G6P
67
What does the conversion of G1P to G6P by phosohoglucomutase mean for glucose?
Glucose can either go into glycolysis or go to the liver for gluconeogenesis (for maintaining BGL)
68
Is glycogen high or low energy?
Glycogen is a high energy form of glucose. You must put energy into glucose to make glycogen. (glycogen → G1P → G6P)
69
What is the chemical equation of glycogen breakdown?
glucose + glycogen (n-1) → glycogen (n) with a "+" ΔG
70
What are the steps of making glycogen from glucose? (4)
1. glucose converted to G6P by hexokinase (burn ATP) 2. G6P isomerized to G1P by phosphoglucomutase 3. G1P + UTP → UDP-glucose by UDP-glucose phosphorylase (burn UTP) 4. glycogen synthase takes UDP-glucose and attaches it to glycogen to make glycogen (n+1)
71
What two things must happen to glucose for it to be converted to glycogen?
Glucose must be activated (add energy) Glucose is covalently attatched to uradine (UTP)
72
What kind of bonds does glycogen synthase make?
Only catalyzes (ɑ1→4) bonds which are linear.
73
What is glycogen branching enzyme?
An enzyme that cuts a string of (ɑ1→4) bonds on a linear glycogen molecule and moves it to a new location on glycogen where it is reattached via an (ɑ1→6) bond. Now a branch.
74
Why is glycogen branched? (2)
It is easier to pack into granules while branched. *It allows for thousands of glycogen phosphorylases and syntheses to be active at the same time (speed!)*
75
What is glycogen phosphorylase?
a regulatory enzyme that breaks down glycogen
76
How is glycogen phosphorylase activated?
It is active once phosphorylated. It is phosphorylated by glycogen phosphorylase kinase via an enzyme cascade.
77
How does glycogen phosphorylase kinase get phosphorylated?
Glycogen phosphorylase gets phosphorylated by PKA via the epinephrine/β-adrenergic GPCR
78
How is glycogen phosphorylase inactivated?
Inactivated by phosphoprotein phosphotase 1 (PP1). It is dephosphorylated.
79
How is glycogen phosphorylase allosterically activated?
ALLOSTERICALLY activated by AMP (ATP prevents activation by AMP)
80
What other allosteric binding site does glycogen phosphorylase have and what does it do when its ligand binds?
It has an ALLOSTERIC binding site for glucose because when glucose is abundant you don't need to produce any more from glycogen. glucose binding → glycogen phosphorylase becomes succeptible to PP1 activity → inactivaition
81
What is glycogen synthase?
a regulatory enzyme that synthesizes glycogen by taking UDP-glucose and linking it to glycogen
82
When is glycogen synthase active?
it is active when dephosphorylated (kinase=inactivates and phosphotase=activates)
83
How does insulin impact glycogen synthase? (3)
1. insulin phosphorylates GSK3 2. phosphorylated GSK3 is inactive 3. results in an increase in PP1 concentration
84
What ALLOSTERICALLY activates glycogen synthase?
Glucose-6-phosphate ALLOSTERICALLY activates it. (high [G6P] = high [glucose] = store glucose)
85
Why is phosphorylation of glycogen synthase unique? (2)
Several kinases will phosphorylate it. It has nine different amino acids that can be phosphorylated.
86
Where is insulin made and where does it go?
Insulin is made and secreted by pancreas β-cells. Pancreas dumps insulin into portal vein which does to the liver (where glycogen is stored).
87
What does insulin stimulate? Inhibit?
Insulin stimulates glycogen synthase. Insulin inhibits glycogen phosphorylase.
88
When will insulin be secreted?
After eating because the BGL will increase rapidly.
89
What does insulin do for carbohydrate metabolism? (3 pathways/roles)
1. glucose binds insulin receptor → GLUT4 moves from vesicles to p.m. → cells take up glucose → glucose converted to G6P → G6P stimulates glycogen synthase 2. G6P from the above mechanism also feedstocks UDP-glucose 3. insulin inactivates kinase and stimulates PP1
90
What is glucagon?
low blood glucose level signal secreted by the pancreas
91
What is epinephrine?
a signal that the cell needs energy NOW
92
What do glucagon and epinephrine both do in terms of regulation? (3)
Stimulate a signal transduction cascade Stimulate glycogen phosphorylase Inhibit glycogen synthase
93
What two enzymes are important for blood glucose level regulation?
Glycogen phosphorylase and glycogen synthase are important reciprocal regulators for maintaining BGL.

Biochemistry II (11 decks)

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