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Biochem 2EE3 > Mod 8 > Flashcards

Mod 8 Flashcards

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1
Q

The mitochondria

A

Specializes in energy production in terms of ATP generation

has a double membrane

Outer mem surrounds entire structure
- Highly permeable with porin channels
- Lets things smaller than 5000 daltons big to pass

intermembrane space

Inner mem has cristae to increase surface area
- Relatively impermeable, allow only small uncharged compounds like CO2 and water to pass

mitochondrial matrix

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2
Q

What doe the permeability difference of the two mito matrices allow for

A

Difference in permeabilities allow proton gradient to be established for the ETC

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3
Q

Where are most CA cycle enzymes located

A

in the mito matrix

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4
Q

Pyruvate oxidation - what is it

A
  • in mitochondria
  • conversion of the three-carbon pyruvate to a two-carbon molecule of acetylCoA
  • catalyzed by enzyme pyruvate dehydrogenase (PDH)
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5
Q

Two stages of pyruvate oxidation

A
  1. Decarboxylation of pyruvate to form acetyl-CoA
  2. Oxidation of the acetyl group of acetyl-CoA to form carbon dioxide
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6
Q

Pyruvate dehydrogenase reaction

A

step 1 of pyruvate oxidation

Catalyzed by pyruvate dehydrogenase

Causes irreversible oxidative decarboxylation of pyruvate to acetyl-CoA

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7
Q

Pyruvate dehydrogenase net reaction

A

pyruvate + CoA-SH + NAD+
–> (using PDH)
NADH + CO2 + acetyl-CoA

pyruvate loses CO2 and instead binds with S-CoA

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8
Q

Oxidative processes

A

draw e- away (LEO)

reduce things

ex. NAD+ to NADH

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9
Q

CoASH enzyme

A

In reduced form, coenzyme A is also referred to as CoASH

Derivative of pantothenic acid which is a B vitamin

Reactive part is the free thiol group

Forms an energy-rich thioester bond with the two-carbon acetyl group that will be derived from pyruvate

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10
Q

Pyruvate Dehydrogenase structure

A

Multi-enzyme complex

Made up of three core enzyme subunits = E1, E2, E3

and two regulatory enzymes = PDH kinase and PDH phosphatase

Lipoic acid coenzyme is covalently attached to the E2 enzyme and acts as a ‘swinging arm’ for the acetyl group as it goes from one enzymatic complex to the next

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11
Q

PDH kinase and PDH phosphatase

A

When phos by PDH kinase = inactivated

When dephos by PDH phosphatase = activated

(like glycogen synthase)

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12
Q

PDH 5 co-factors required

A
  1. NAD+
  2. TPP
  3. Lipoic acid
  4. CoA
  5. FAD
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13
Q

3 advantages of multienzyme complexes (such as pyruvate dehydrogenase)

A
  1. increased rate/efficiency (due to reduction in diffusion distance for intermediates)
  2. complex channels intermediates between successive enzymes in a pathway, minimizing side reactions
    (like the swinging arm)
  3. Reactions catalyzed by multienzyme complexes can be coordinately regulated
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14
Q

PDH kinase allosteric regulation

done by effectors

A

activate PDH kinase
AcetylCoA, ATP, and NADH
= inactivate PDH

deactivate it
Pyruvate and ADP
= activate PDH

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15
Q

PDH phosphatase allosteric regulation

done by effectors

A

Insulin and Ca2+
Activate PDH phosphatase

= activate PDH

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16
Q

Competitive inhibition of PDH

A

AcetylCoA and NADH are competitive inhibitors when in high concentration

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17
Q

What form of PDH is active

A

a-form

b-form phos = inactive

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18
Q

CA cycle (gen)

A

2-carbon acetylCoA is broken down into two molecules of CO2

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19
Q

CA cycle net reaction

A

3 NAD+, FAD, GDP, Pi, acetylCoA
–>
3 NADHs, 1 FADH2, 1 GTP, 2 CO2s, 1 free CoA (no acetyl)

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20
Q

How many enzymes in CA cycle and where are they located

A

Eight enzymes in the cycle, compartmentalized within the mitochondria

All soluble within the matrix EXCEPT succinate dehydrogenase which is a membrane protein in the inner mitochondrial membrane

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21
Q

Why is the CA cycle aka the tricarboxylic acid cycle aka the krebs cycle

A

named after scientist krebs

product of first reaction is citrate

citrate is a tricarboxylic acid

cycle begins and ends with oxaloacetate

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22
Q

NADH/FADH2 etc in the CA cycle

A

Drawing electrons away from the AcetylCoA and passing them to reducing equivalents NAD+ and FAD

ETC regenerates NADH and FADH2

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23
Q

What happens to the CA cycle CO2

Study These Flashcards
A

CO2 waste product will eventually leave cell → bloodstream → exhaled

24
Q

Three things that regulate key CA cycle enzymes

SCA

Study These Flashcards
A
  1. Availability of substrates
    - Need 1:1 ratio of oxaloacetate and acetylCoA for reaction 1
    - Adequate free NAD+
  2. Competitive inhibition by products
    Ex. accumulation of NADH inhibits key enzymes like dehydrogenases that generate these reducing equivalents
  3. Allosteric regulation
    - Positive or negative
25
CA cycle allosteric regulation done by three things
Allosteric effectors (ex. Ca2+) - positive regulation - bc signals muscle contraction = fuel will be needed ATP - negative regulation - signals high energy = doesn’t need to oxidize any more acetylCoA ADP - positive regulation - Signals low energy so more ATP needed = increased CA cycle flux
26
3 Common themes in CA cycle metabolic regulation ERF
1. Energy status of the cell (ADP/ATP) 2. Redox state of the cell (NADH/NAD+) 3. Feedback inhibition by products
27
Amphibolic
both catabolic and anabolic in nature
28
In what way is the CA cycle amphibolic
both catabolic and anabolic in nature Catabolic bc they break down and oxidize acetylCoA that originated from glucose or fat to generate ATP and reducing equivalents Anabolic citric acid cycle intermediates are also the starting materials for biosynthetic pathways
29
Examples of where CA intermediates go
citrate for the production of fatty acids and steroids succinylCoA for the synthesis of heme and chlorophyll alpha-ketoglutarate and oxaloacetate for aa synthesis and purines (ak) and pyrimidines (ox)
30
Anaplerosis
the process of replenishing citric acid cycle intermediates (siphoned off) so the cycle can begin again
31
Synthesis of oxaloacetate from pyruvate
quantitatively the most important anaplerotic reaction pyruvate + CO2 + ATP + H2O --> oxaloacetate + ADP + Pi
32
Regulation of pyruvate dehydrogenase and pyruvate carboxylase to ensure a 1:1 ratio of oxaloacetate:acetylCoA need to coordinate pd and pc
If acetylCoA > oxaloacetate, citrate synthase will not function maximally due to substrate limitation = Excess acetylCoA inhibits PDH, diverting pyruvate to the pyruvate carboxylase reaction = forms oxaloacetate
33
Fat breakdown
When low glucose levels (at rest or between meals)... * Glucagon released stimulates lipase to breakdown fats to provide energy * Process of beta oxidation * Lipase enzyme hydrolyzes the ester bonds and therefore releases the fatty acids from the glycerol = fatty acids + glycerol
34
Fatty acid journey after separation from triacylglycerol
- Leave the adipose tissue and enter the bloodstream carried by albumin - Taken up by the liver and muscle for energy but NOT by the brain - Activated - Then broken down into acetyl-CoA via beta oxidation
35
Glycerol journey after separation from triacylglycerol
- Leaves the adipose tissue to be taken up by the liver Liver = site of gluconeogenesis Glycerol = substrate for gluconeogenesis - enters the gluconeogenic pathway at the midpoint - Converted to glucose via gluconeogenesis and released back into the bloodstream to be taken up by tissues for energy
36
Fatty acid activation in cytosol
Activate by attaching a long chain hydrocarbon's acyl group to CoA (_S-CoA) Catalyzed by enzyme acylCoA synthetase uses ATP and forms AMP + PPi
37
Beta oxidation of fatty acids in the matrix
Carbons are removed from fatty acid (acyl group) two at a time adjacent to the beta carbon Cleaving the C-C bond = generates an acetylCoA molecule 1 round of B-oxy is 4 reactions - One rxn generates a FADH2 - One generates NADH Oxidative process so generates reducing agents so like 16 carbon chain --> 8 acetylCoA, 7 FADH2 and NADH
38
Beta oxidation net reaction
fatty acid, FAD, NAD+, CoASH --> many rounds acetyl-CoA, FADH2, NADH
39
Fate of beta oxidation products
AcetylCoA either enters CA cycle or (in liver) converted to ketone bodies = energy production FADH2/NADH will donate their e- to the ETC to generate ATP through oxidative phosphorylation
40
Ketogenesis
Glucose will be low bc the liver glycogen stores have been depleted Brain can’t use fatty acids for energy, so converts them to ketone bodies in the liver
41
Ketone bodies
- once carb stores in liver are used up, liver will convert fats to ketone bodies via an acetylCoA intermediate Ketone bodies enter bloodstream cross the blood-brain barrier, are then taken up by the brain and broken back down into acetylCoA which enters the CA cycle and produces energy
42
What ketone bodies can our body produce (3)
Acetone Acetoacetate Beta-hydroxybutyrate
43
Fat storage as+in
* Stored as triacylglycerols aka triglycerides * Made of three fatty acids esterified with glycerol * Made of 2+ different types of fatty acids * Stored in adipocytes = specialized cells
44
Is fat storage just reverse beta oxidation
basically but doesn't share any of the beta oxidation enzymes 2 carbons originating from acetylCoA are added (one at a time) to an elongating fatty acyl chain
45
When does fat storage occur
* Fat comes from excess carb intake High glucose will be first used to replenish glycogen stores Then the rest will be broken down through glycolysis and pyruvate dehydrogenase to generate acetylCoA * When acetylCoA not needed to generate energy, it will do fat synthesis instead of the CA cycle
46
Are anabolic processes ox or red specifically fatty acid synthesis
reductive We need to donate e- to the newly synthesized fatty acids E- come from reducing equivalents (NADP+ is the reducing equivalent of the reduced form NADPH) - so from NADP+
47
Where does fat synthesis occur
cytosol Tricarboxylate transport system must move acetylCoA out of the mito matrix into the cytosol via a citrate intermediate
48
What does fatty acid synthesis use + example
enzyme fatty acid synthase NADPH 1 ATP / acetylCoA round ex. Takes 8 acetylCoA molecules and condenses them bit by bit into a 16-carbon fatty acid called palmitate
49
Enzymes called elongases and desaturases
make longer chain fatty acids and create double bonds in unsaturated fatty acids
50
Triacylglycerol synthesis
Once the fatty acids are synthesized, they are esterified with glycerol to form triacylglycerols or are used to make membrane lipids
51
Fatty acid synthesis net reaction with palmitate
8 acetylCoA, 14 NADPH, 7 ATP --> palmitate, 8 CoA, 14 NADP+, 7 ADP, 7 Pi
52
Fatty acid metabolism → high glucose Ex. after a carb-rich meal
Insulin (hormone) is released Activates fat synthesis in the liver and inhibits fat breakdown in adipose tissue
53
Fatty acid metabolism → low glucose Ex. when fasting or between meals
Glucagon released ⇒ glucagon is the counter regulatory hormone to insulin Glucagon stimulates fat breakdown by stimulating lipase in adipose tissue Fats then broken down to acetylCoA and used for energy AcetylCoA can be diverted to ketone body synthesis during starvation/extended fasting
54
AcetylCoA --> cholesterol
all cholesterol carbons are derived from acetyl-CoA uses HMG-CoA reductase
55
Those with high LDL cholesterol
Enzyme HMG-CoA reductase is the target of statin drugs help lower cholesterol
56
Amino acids --> pyruvate or acetylCoA
The breakdown of amino acids derived from protein can lead to the production of pyruvate or acetylCoA as well as to other intermediates in glycolysis or the citric acid cycle So body breaks down protein for energy

Biochem 2EE3 (10 decks)

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