Cellular Respiration: Pyruvate Oxidation and the Krebs Cycle Flashcards

General Sequence of Events:
    * Glycolysis: The initial process producing pyruvate.
    * Pyruvate Oxidation: Pyruvate from glycolysis is oxidized into an acetyl group that feeds into the subsequent cycle.
    * Citric Acid Cycle (Krebs Cycle): A 2-carbon (2-C) acetyl group combines with a 4-carbon (4-C) oxaloacetate to produce the 6-carbon (6-C) compound citrate.
    * Secondary Reactions: Two decarboxylations and oxidation reactions produce $NADH$ , $CO_2$ , and a new 4-carbon molecule.
    * Regeneration: Two additional oxidations generate another $NADH$ and an $FADH_2$ , effectively regenerating the original 4-carbon oxaloacetate to restart the cycle.
    * Downstream Processes: The products move into the Electron Transport Chain and Chemiosmosis to generate $ATP$ .

Aerobic Conditions: Pyruvate Oxidation and the Krebs Cycle occur strictly in the mitochondria under aerobic conditions where Oxygen ( $O_2$ ) is present.
Redox Reactions: Cells utilize oxidation and reduction reactions, collectively termed "Redox Reactions," to release and transfer energy from food molecules.
Energy Transfer Destinations: Redox reactions transfer energy from food molecules to:
    * $ADP$ to produce $ATP$ (an energy-rich molecule).
    * $GDP$ to produce $GTP$ (an energy-rich molecule).
    * $FAD$ to produce $FADH_2$ (an energy-rich molecule used to make $ATP$ in the mitochondria).
    * $NAD^+$ to produce $NADH$ (an energy-rich molecule used to make $ATP$ in the mitochondria).
Pyruvate Oxidation Summary: Occurs in the mitochondrion matrix; catabolizes pyruvate from glycolysis to produce energy-rich Acetyl CoA, $NADH$ , and one Carbon Dioxide ( $CO_2$ ) molecule as a catabolic waste product.
Krebs Cycle Summary: Occurs in the mitochondrion matrix; releases energy from Acetyl CoA to produce energy-rich $FADH_2$ , $GTP$ , and $NADH$ molecules, along with two $CO_2$ molecules as waste products.
ATP Generation Mechanism: Energy-rich $FADH_2$ and $NADH$ molecules supply (donate) energy-rich electrons ( $e^-$ ) to the Electron Transport Chain (ETC) to energize $ATP$ Synthase for $ATP$ production.

Oxidation Definition: The loss of one or more electrons ( $e^-$ ) and/or Hydrogen atoms ( $H$ ) from a substance. This process reduces the substance's energy content.
Reduction Definition: The gain of one or more electrons ( $e^-$ ) and/or Hydrogen atoms ( $H$ ) by a substance. This process increases the substance's energy content.
Functional Application: Cells use the reduced, energy-rich form of cellular molecules to energize endergonic reactions and produce additional $ATP$ molecules.
Macromolecule Conversion: Polymeric food molecules are converted into smaller monomers during these metabolic processes to facilitate energy extraction.

Matrix: The site where Pyruvate Oxidation and the Krebs Cycle occur.
Inner Membrane: The location of the Electron Transport Chain (ETC).
Aerobic Requirement: Most $ATP$ is synthesized within the mitochondrion under aerobic conditions (the presence of Oxygen).

Location and Prerequisites: Occurs in the mitochondrion matrix specifically when Oxygen ( $O_2$ ) is available.
Produced Energy-Rich Molecules:
* Acetyl Coenzyme A (Acetyl CoA): Will be further catabolized by the Krebs cycle to produce $FADH_2$ , $GTP$ , and $NADH$ .
* NADH: Utilized downstream for $ATP$ production.
Waste Management: Generates one Carbon Dioxide ( $CO_2$ ) molecule as a waste product.
    * $CO_2$ molecules diffuse out of the mitochondrion and the cell.
    * They enter the bloodstream for delivery to the lungs.
    * They exit the body via exhalation to prevent toxic $CO_2$ accumulation.
Cofactor Precurors (B Vitamins): Pyruvate oxidation requires four specific B vitamins acting as precursors to essential coenzymes:
    * Vitamin B1 (Thiamine): Precursor to make Thiamine Pyrophosphate ( $TPP$ ).
    * Vitamin B2 (Riboflavin): Precursor to make $FAD$ .
    * Vitamin B3 (Niacin): Precursor to make $NAD^+$ .
    * Vitamin B4 (Pantothenic Acid): Precursor to make Coenzyme A ( $CoA$ ).

Sequence: Consists of eight enzymatic reactions occurring in the mitochondrion matrix.
Function: Releases energy from energy-rich Acetyl CoA molecules produced by pyruvate oxidation.
Chemical Equation:
* $ACETYL CoA + 3 NAD^+ + FAD + GDP \rightarrow 3 NADH + FADH_2 + GTP + 2 CO_2$
Waste Products: Two Carbon Dioxide ( $CO_2$ ) molecules are produced from Acetyl CoA as metabolic waste and are removed via exhalation.
Theoretical ATP Yields:
    * $1 NADH$ molecule $\approx$ $2.5 - 3 ATP$ molecules.
    * $1 FADH_2$ molecule $\approx$ $1.5 - 2 ATP$ molecules.
    * Nucleoside-Diphosphate Kinase: An enzyme that converts $1 GTP$ into $1 ATP$ .

Substrate Exchange: Anabolic and catabolic processes in the cell exchange molecules constantly.
Biosynthesis: Cells use substrates from Glycolysis and the Krebs Cycle to synthesize:
    * Amino acids
    * Carbohydrates
    * Lipids
    * Nucleotides
Classification: The Krebs Cycle is considered "Amphibolic" because it is involved in both catabolism (breaking down Acetyl CoA) and anabolism (providing precursors for synthesis).

Which reactions do cells use to transfer energy from one molecule to another?
The Krebs Cycle and Pyruvate Oxidation reactions occur in which organelle?
Why does each human cell contain multiple mitochondria?
Why does each mitochondrion contain multiple copies of each Pyruvate Oxidation enzyme and each Krebs Cycle enzyme?
Are some B vitamins cofactors for Pyruvate Oxidation & Krebs Cycle enzymes?
Which two types of energy-rich molecules does Pyruvate Oxidation produce?
Which energy-rich product of Glycolysis is the substrate for Pyruvate Oxidation?
Which waste product molecule is generated during Pyruvate Oxidation?
Which three types of energy-rich molecules does the Krebs Cycle produce?
Which catabolic process produces the Acetyl CoA molecules that enter the Krebs Cycle?
Is the energy stored in $FADH_2$ and $NADH$ molecules used to make $ATP$ in mitochondria when $O_2$ is available?
Are some $GTP$ molecules converted to $ATP$ molecules?
How do the $CO_2$ molecules produced as waste products during Pyruvate Oxidation and the Krebs Cycle exit your body?
Do the Glycolysis, Pyruvate Oxidation, and the Krebs Cycle redox reactions transfer the energy in food molecules to $NAD^+$ to make $NADH$ ?
The Krebs Cycle transfers some energy in food molecules to $FAD$ to make which energy-rich molecule?
The Krebs Cycle transfers some energy in food molecules to $GDP$ to make which energy-rich molecule?