Carbohydrate Metabolism Study Set - Key Terms & Definitions

Stages of Cellular Respiration

(1) Acetyl-CoA Production

(2) Acetyl-CoA Oxidation via Citric Acid Cycle

(3) Electron Transfer & Oxidative Phosphorylation

Acetyl-CoA can be produced from what 3 substances?

- Amino Acids: Transamination + Oxidation

- Fatty Acids: β-Oxidation

- Glucose: Glycolysis

What are the 3 fates of Glucose?

- Glycogen: Storage

- Ribose-5-Phosphate via Pentose Phosphate Pathway

- Pyruvate via Glycolysis

What are the 2 phases of Glycolysis?

(1) Energy Investment/Preparatory Phase

(2) Energy Payoff Phase

The breakdown of 6C Glucose into two 3C Pyruvates occurs in 10 steps. The first ____ constitute the Preparatory Phase of Glycolysis.

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Energy Investment/Preparatory Phase

(1) Glucose + ATP --> G6P

(2) G6P --> Fructose 6-Phosphate (F6P)

(3) F6P + ATP --> Fructose 1,6-Bisphosphate (F1,6P)

(4) F1,6P --> Glyceraldehyde 3-Phosphate (G3P) + Dihydroxyacetone Phosphate (DHAP)

(5) G3P + DHAP --> 2 G3P

Priming Stage

Conversion of Glucose into FBP with the investment of 2 ATP

Splitting Stage

Splitting of FBP into two G3P

Payoff Phase

(6) G3P + 1 NAD+ --> 1,3-Bisphosphoglyverate (1,3-BPG) + NADH

(7) 1,3-BPG + ADP --> 3-Phosphoglycerate (3-PG) + ATP

(8) 3-PG --> 2-Phosphoglycerate (2-PG)

(9) 2-PG --> Phosphoenol Pyruvate (PEP)

(10) PEP + ADP --> Pyruvate + ATP

This process occurs TWICE per Glucose so, overall, 4 ATP and 2 NADH are produced

G3P Dehydrogenase

Enzyme that catalyzes G3P to 1,3-BPG, with NADH as a by-product

Phosphoglycerate Kinase

Enzyme that catalyzes 1,3-BPG to 3-PG, with ATP as a by-product

Substrate-Level Phosphorylation

An enzyme-catalyzed reaction that yields ATP/GTP

Enolase

Enzyme that catalyzes 2-PG to PEP via elimination of water

Pyruvate Kinase

Enzyme that catalyzes PEP to Pyruvate, with ATP as a by-product

Irreversible

NADH Cycle

Recycling of NAD+ and NADH between G3P Dehydrogenase and Lactate Dehydrogenase so that Glycolysis can continue

Lactate Dehydrogenase

Enzyme that catalyzes Pyruvate to Lactate, with NAD+ as a by-product

What are the 3 main regulatory enzymes of the Glycolytic Pathway?

- Hexokinase

- Phosphofructokinase (PFK)*

- Pyruvate Kinase

* - Most important regulatory/rate-limiting enzyme of Glycolysis

Hexokinase is considered to be the regulator of ____.

Glucose Breakdown

PFK1 and Pyruvate Kinase are considered to be the regulators of ____.

Glycolysis

These 2 are more specific to Glycolysis, but all 3 are regulators of Glycolysis

Most allosteric effectors of Glycolysis regulate ____.

PFK1

What are the most important Negative allosteric effectors of Glycolysis?

- Citrate

- ATP

- H+ (low pH)

Products of Metabolism

What are the most important Positive allosteric effectors of Glycolysis?

- AMP

- F2,6BP

- Inorganic Phosphate

Glycolysis takes place in the ____.

Cytosol

Citric Acid Cycle takes place in the ____.

Mitochondria

Oxidative Phosphorylation takes place in the ____.

Mitochondria

Pyruvate Dehydrogenase Complex

3 Enzymes that convert Pyruvate to Acetyl-CoA in the Mitochondria

The Pyruvate Dehydrogenase Complex requires ____ Coenzymes to be assembled.

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Citric Acid Cycle

(1) Acetyl CoA

(2) Citrate

(3) Isocitrate

(4) α-Ketoglutarate + CO2 + NADH

(5) Succinyl-CoA + CO2 + NADH

(6) Succinate + GTP/ATP

(7) Fumarate + FADH2

(8) Malate

(9) Oxaloacetate + NADH

- Pyruvate from Glycolysis is oxidatively decarboxylated to Acetate

- 2 CO2 + 1 ATP + 1 FADH2 + 3 NADH

NADH goes on to make ATP in ____ and ____.

electron transport/oxidative phosphorylation

Isocitrate Dehydrogenase

Enzyme that catalyzes the β-decarboxylation of Isocitrate to α-Ketoglutarate

Rate-Limiting Enzyme of the Krebs Cycle

α-Ketoglutarate Dehydrogenase

Enzyme that catalyzes Oxidative Decarboxylation of α-Ketoglutarate to Succinyl-CoA

α-Ketoglutarate Dehydrogenase is nearly identical to ____ mechanistically and structurally.

Pyruvate Dehydrogenase

What 5 Coenzymes are required for α-Ketoglutarate Dehydrogenase activity?

- TPP

- CoASH

- Lipoic Acid

- NAD+

- FAD

Succinyl-CoA Synthetase

Enzyme that catalyzes Succinyl-CoA to Succinate, with GTP/ATP as a by-product

Succinyl-CoA is a ____.

high-energy intermediate

Makes Substrate-Level Phosphorylation possible

What are the 3 main regulatory enzymes of the Citric Acid Cycle?

- Citrate Synthase

- Isocitrate Dehydrogenase

- α-Ketoglutarate Dehydrogenase

Electron Transport

Electrons carried by Coenzymes (NADH/FADH2) are brought to the inner mitochondrial membrane to generate a proton gradient

Oxidative Phosphorylation

The production of ATP using energy derived from the redox reactions of the Electron Transport Chain (ETC)

Occurs at the Inner Mitochondrial Membrane

What is the difference between Substrate-Level Phosphorylation and Oxidative Phosphorylation?

Oxidative Phosphorylation utilizes electron transport while SLP uses enzymes

The Inner Mitochondrial Membrane is impermeable to most small molecules and contains ____.

ATP Synthase

Complex I

NADH Dehydrogenase transfers electrons from...

- NADH --> CoQ

- Pumps 4 H+ out of the Mitochondrial Matrix into the Intermembrane Space per 2 e-

Complex II

Succinate Dehydrogenase

- Succinate + UQ --> Fumarate + UQH2

Complex III

UQ-Cytochrome C Reductase

- Accepts e- from Ubiquinol, passing it to Cytochrome C via the Q Cycle

- Pumps 4 H+ out of the Mitochondrial Matrix into the Intermembrane Space

Ubiquinone

Lipid-soluble coenzyme that transfers e- from Complex II to Complex III in the ETC

Cytochrome C

Water-soluble enzyme that transfers electrons from Complex III to Complex IV in the ETC

Complex IV

Cytochrome C Oxidase

- 4H+ + O2 + 4e- --> 2H2O

- Pumps 2 H+ out of the Mitochondrial Matrix into the Intermembrane Space

Oxygen is the ____ of e- in the ETC.

terminal acceptor

All of the proteins in Mitochondrial ETC Complexes have ____.

Fe-Sulfur Centers

Aid in e- transport

What role does H+ within the Intermembrane Space of Mitochondria play?

It travels down a concentration gradient into the Mitochondrial Matrix through ATP Synthase. This process drives the production of the majority of ATP in metabolism.

Uncouplers

Compounds that prevent ATP synthesis by shuttling H+ ions across the Mitochondrial membrane, dissipating the proton gradient

What are the 2 subunits of ATP Synthase?

- F0

- F1

F0

Transmembrane pore of ATP Synthase that mediates H+ transport

What 2 carriers are vital for ATP production in the ETC?

- Adenine Nucleotide Translocase

- Phosphate Translocase

Adenine Nucleotide Translocase

Antiporter that carries ADP into and ATP out of the Mitochondrial Matrix to support ATP synthesis

Phosphate Translocase

Symporter that transfers H+ and Phosphate groups into the Mitochondrial Matrix to combine with ADP

How much ATP is made through one ETC cycle?

4 ATP

- 2.5 from electrons entering as NADH

- 1.5 from electrons entering as Succinate

____ ATP per Glucose is made if the Glycerophosphate Shuttle is used.

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____ ATP per Glucose is made if the Malate-Aspartate Shuttle is used.

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Uncoupling of mitochondrial electron transport and oxidative phosphorylation ____.

halts all mitochondrial metabolism, but allows continued O2 consumption