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Biochem > Module 7 - Metabolism > Flashcards

Module 7 - Metabolism Flashcards

1
Q

How is energy produced

A

From metabolish of carbohydrate susch as sugar in our diet or glycogen storage in muscles or liver

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2
Q

Define Glycolysis

A
  • highly regulated pathways that control the breakdown of carbs according to need
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3
Q

Gluconeogenesis

A

process to synthesise glucose de novo, glucose preferred by brain

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4
Q

What is the Pentose Phosphate pathway

A

an alternate pathway by which glucose is broken down to generate NADPH (for reductive biosynthetic processes such as fat synthesis) as well as providing ribose-5-phosphate (for nucleotide synthesis)

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5
Q

What is the structure of Glycogen

A

Highly branched
Alpha 1-4 bonds link to form subunits linear
Alpha 1-6 are branching points
single reducing end and several non-reducing ends

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6
Q

What is the fxn of non reducing ends

A

●Glucose resides are sequentially removed from several non-reducing ends during glycogen degradation, providing a rapid surge of glucose release when it is needed by the body.

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7
Q

what does Glygogen phosphoylase do

A

Glycogen Breakdown by catalyzing the phosphorylation of glycogen with the addition of PI (inorganic phosphate) which releases a glucose residue in the form glucose-1-phosphate

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8
Q

What does Glycogen synthase do

What energy source

A
  • converts glucose-1-phosphate → Glycogen using Glycogen synthase
    ○ Catalyzes the synthesis of glycogen from glucose-1-phosphate using UTP as energy to drive this reaction forward
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9
Q

What does Phosphoglucomutase enzyme do.. using…

A
  • converts glucose-1-phosphate → glucose-6-phosphate
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10
Q

How is Glycogen phosphorylase and glycogen synthase regulated

A

these enzymes are controlled by allosteric regulation and covalent regulation by phosphorylation

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11
Q

Describe the Allosteric Regulation of Glycogen Synthase

A

Glycogen synthase is activated by high concentrations of glucose-6-phosphate → signals there are plenty of carbs available for storage as glycogen

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12
Q

Describe the Allosteric Regulation of Glycogen Phosphorylase

A
  • is activated by high concentrations of AMP, - indicates that the energy status of the cell is low (low ATP) signals an increase in glycogen phosphorylase to recluse more glucose residues for glycolysis to produce ATP
  • is inhibited by high concentrations of ATP → - signals to the cell that there is an energy supply to meet the demand, and no further substrate needs to be broken down and utilized.
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13
Q

What does phosphorylation do

A

Covalent addition of a phosphate group to an enzyme can act as switch that turns the enzyme on and off depending on the enzyme in question

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14
Q

Covalent Regulation of Glycogen phosphorylase

A
  • phosphorylation by an enzyme called kinase converts it to its active form
    ○Removal of the phosphate group by an enzyme called a phosphatase converts it back to its inactive form
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15
Q

Covalent Regulation of Glycogen synthase

A

Phosphorylation of glycogen synthase converts to its inactive form while removal of the phosphate group converts back to active form

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16
Q

Covalent Regulation of Glycogen synthase

A

Phosphorylation of glycogen synthase converts to its inactive form while removal of the phosphate group converts back to an active form

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17
Q

What signals regulate phosphorylation and dephosphorylation

A

●Hormonal signals regulate the phosphorylation and dephosphorylation by the kinase and phosphatase
○Insulin stimulates dephosphorylation by phosphate
○Glycogen and epinephrine stimulate phosphorylation by kinase

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18
Q

Glycogen Metabolism regarding Insulin

A
  • Insulin elevates blood sugar which signals the glucose to be taken up to tissue for energy or be stored away
  • Insulin binds to the receptor at the cell surface, signals for activation of glycogen synthase and inactivation of glycogen phosphorylase
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19
Q

Glycogen Metabolism regarding Glucagon

A

● Glucagon is counter regulatory to insulin
glycogen is released when glucose levels in the bloodstream drop and signals more glucose to be released from liver glycogen = glucagon inactivates glycogen synthase and activates glycogen phosphorylase

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20
Q

What can pyruvate and NADH do

A

Can be used to produce more ATP

21
Q

How many reactions does Glycolysis have, what does it do, where does it take place

A

10 Reactions
converts sugar into pyruvate (3 C molecule)
Takes place in the cytosol

22
Q

What happens during Step 1-5 of Glycolysis

A
  • Converts a 6C sugar glucose into 2 3C sugars called glyceraldehyde-3-phosphate by consuming 2 ATP
  • These reactions are catalyzed by kinase and are irreversible
  • Called preperatory phase
23
Q

What happens during Step 6-10 of Glycolysis

A
  • one ATP is made per glyceraldehyde-3-phosphate in both reaction 7 and 10 (so 4 ATPS are produced by glycolysis)
  • carried out by kinase reaction
    Step 6: forms NADH called dehydrogenase which is an electron carrier with the potential to produce more ATPS through oxidative phosphorylation
    Step 7: Reversible + ATP
    Step 8: Irrreversible
    STEP 10: ATP
  • 2 NADH, 4ATP are made
24
Q

How is energy concerved in pay off phoase

A

By formation of 2 molecules of e- carrier NADH per molecule of glucose

25
Q

What is the total and net rxn of glycolysis

A

Total: 4 ATP, 2 NADH, 2 Pyruvate
Net: 2 ATP, 2 NADH, 2 Pyruvate

26
Q

What happens to Pyruvate and NADH

A
  • pyruvate which oxidized in the mitochondria

- NADH can be oxidized by the electron transport chain of mitochondria

27
Q

What are good points of regulation for Flux in Glycolysis

A

●Enzymes that catalyze reactions 1 and 3 are targets for the control of flux through glycolysis as these reactions have the largest change in free energy and are irreversible

28
Q

How is Flux controlled in glycolysis through Step 1?

A

Step 1 is catalyzed by hexokinase, inhibited by its product, glucose-6-phosphate, via end-product inhibition
○ High concentrations of glucose-6-phosphate signal there is enough substrate for glycolysis to proceed and addition glucose does not need to be broken down

29
Q

What is end product inhibition

A

the process whereby the end products of a pathway feedback and inhibit flux through an enzyme

30
Q

How is Flux controlled in glycolysis through Step 3?

A
  • Step 3: catalyzed by phosphofructokinase, inhibited by high concentrations of ATP and citrate
  • ATP signals enough levels of ATP and flux through glycolysis can be down regulated
  • Citrate (first product in the tricarboxylic acid cycle) signals not enough substrate for the tricarboxylic acid cycle and further glucose does not need to be broken down
  • phosphofructokinase UPREGULATED by high concentrations of AMP and ADP which signal low energy status
  • allosterically upregulated by Fructose-2,6-bisphosphate
31
Q

What must be regenerated for glycolysis to occur

A

NAD+ must be regenerated from NADH

O2 is present its done in the transport chain in mitocondria

32
Q

What happesns to NAHD when there is no O2

wats the net oxidation?

A

NADH is not converted back to NAD+ in mitochondria

  • Fermentation occurs when O2 is absent and can regenerate NAD+
  • It produced ATP w/ no net oxidation of C
33
Q

What are the two strategies regarding fermentation

A

Strategy 1: Formation of Lactate

Strategy 2: Formation of Ethanol

34
Q

Describe Strategy 1 of Fermentation

A

Strategy 1: Formation of Lactate
●Enzyme lactate dehydrogenase oxidizes

NADH pyruvate becomes lactate which allows dor regenerating NAD+ which will continue to allow for glycolysis
●Intense exercise forms lactate which can contribute to soreness and fatigue
- 2Lactate + 2ATP

35
Q

Describe Strategy 2 of Fermentation

A

Strategy 2: Formation of Ethanol
●Occurs in yeast and other microorganisms
●In yeast, ethanol (from pyruvate) is produced rather than lactate during fermentation which regenerates NAD+ and allows glycolysis to continue
- CO2 is also produced
- 2 ethanol + 2CO2 + 2ATP

36
Q

What is the net reaction of fermentation

A

●Under conditions where O2 is absent, fermentation can still produce 2 molecules of ATP to meet the cell’s demands for ATP

37
Q

What is gluconeogenesis an what are some precursors

A

● Gluconeogenesis is de novo synthesis of glucose
● Supplies glucose to the body when glycogen stores are low
● Precursors like some amino acids, citric acid cycle intermediates and lactate-via-pyruvate is converted to oxaloacetate which is converted to glucose through gluconeogenesis

38
Q

Is gluconeogeneis the reverse of glycolysis and is energy required

A

No, not exactly the reverse’

Yes input is required

39
Q

Is gluconeogenesis Energetically Favourable

A

● The 3 non-equilibrium reactions in glycolysis with large changes in free energy are by-passed in gluconeogenesis
● The near-equilibrium reactions are shared btwn the two pathways
● Concentrations of substrates are different under the metabolic circumstances that occur when gluconeogenesis is required thus driving near-equilibrium rxns in reverse direction
● Non-equilibrium reactions proceed differently in reverse direction

40
Q

Net reaction of Gluconeogenesis

A

4 ATP + 2 Pyruvate + 2GTP + 2 NADH

41
Q

Glycolysis vs Gluconeogenesis

A
  • not exactly reverse
  • Step 1,3 and 10 (Enzymes: glucokinase, phosphofructokinase and pyruvate kinase) need to be bypassed
  • The rxns are by-passed by glucose-6-phosphatase, fructose bisphosphatase, PEP carboxykinase and pyruvate carboxylase
42
Q

How is Flucx controlled through Gluconeogenesis

A
  • Flux regulated reciprocally to flux through glycolysis to avoid futile cycling
  • Key point in regulation occurs at fructose bisphosphatase
    ● the fructose bisphosphatase is inhibited by high concentrations of AMP and fructose-2,6-bisphosphatase
  • This is in contrast to phosphofructokinase (which catalyzes opposite rxn)
43
Q

How are F6P (fructose-6-phosphate) and F1,6P (fructose-1,2-bisphosphate) regulated

A

Fructose-6-Phosphate
-High concentration of AMP and F2,6P inhibits fructose bisphosphatase from making Fructose-6-Phosphate in gluconeogenesis

Fructose-1,6-bisphosphate

  • High ATP and Citrate inhibit phosphofructokinase needed to make F1,6P
  • High AMP & ADP activate phosphofructokinase needed to F1,6P
44
Q

What is the pentose phosphate pathway

A

is an alternate pathway where glucose is broken down to generate NADPH for reductive biosynthetic processes like fat synthesis or providing ribose-5-phosphate for the biosynthesis of nucleotides depending on cell needs
● The oxidative phase where glucose-6-phosphate is oxidized generates NADPH and waste product CO2

45
Q

How does PPP makes ribose 5 phosphate

A

● Under conditions where ribose-5-phosphate is required for nucleotide synthesis, pentose phosphate pathway diverts carbons to its production

46
Q

One pathway of PP makes ribose-5-phosphate what is the alternative?

A
  • the C’s are further metabolized to two fructose-6-phosphate and one glyceraldehyde-3-phosphate from 3 original glucose-6-phosphate molecules
  • also made 3CO2 + 6NADPH
    ●These intermediates then feed into glycolysis and are further metabolized for energy generation
47
Q

What is the total cost of making glucose De Novo (gluconeogenesis)

A

at the cost of 6 ATP equivalents per glucose
- not reverse of glycolysis
4 ATP 2 GTP

48
Q

What is Fermentation

A

○Glycolysis can proceed in the absence of oxygen under anaerobic conditions called fermentation in which lactate production and in yeast ethanol is generated as a byproduct

49
Q

How are the high energy steps (1,3,10) in glycolysis overcome in gluconeogenesis

A
  • The rxns are by-passed by glucose-6-phosphatase, fructose bisphosphatase, PEP carboxykinase and pyruvate carboxylase

Biochem (7 decks)

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