BIOLOGY EXAM 3

Metabolism

The totality of an organism's chemical reactions.

metabolic pathways

catabolic & anabolic

catabolic

(breaking down molecules, releasing energy)

anabolic

(building molecules, consuming energy)

Kinetic Energy

Energy of motion

Potential Energy:

Stored energy due to location/structure.

Chemical Energy:

Type of potential energy stored in chemical bonds.

1st Law (Conservation):

Energy cannot be created or destroyed, only transferred/transformed.

2nd Law (Entropy):

Energy transfers increase entropy (disorder).

Free Energy (ΔG):

Determines if a reaction occurs spontaneously.

Exergonic reactions

(–ΔG, spontaneous, release energy).

Endergonic reactions

(+ΔG, non-spontaneous, consume energy).

ATP → ADP + Pi (phosphate) releases

7.3 kcal/mol energy

ATP Hydrolysis:

Breaking bond between phosphate groups releases energy (Exergonic).

Powers cell work (chemical, mechanical, transport).

Regeneration of ATP:

Endergonic process, energy derived from catabolic pathways (like cellular respiration).

Enzymes:

Proteins that speed up reactions by lowering activation energy (Ea).

Activation Energy (Ea):

Initial energy required to start a reaction.

Active Site:

Region of enzyme where substrate binds (induced fit model).

Factors Affecting Enzyme Activity:

Temperature, pH, substrate/enzyme concentration.

Enzyme Regulation

Cofactors & Coenzymes

Cofactors:

Inorganic (metal ions like zinc, iron).

Coenzymes:

• Organic molecules (NAD⁺, vitamins).

Competitive

Bind active site, competing with substrate.

Non-Competitive (Allosteric)

Bind to other site (not active site), changing enzyme shape/function.

Feedback Inhibition (Important):

• End product of metabolic pathway acts as inhibitor to enzyme in that pathway.

• Helps maintain homeostasis, prevents waste of resources.

Metabolic Pathways

• Pathways are enzyme-catalyzed reactions.

• Can involve both exergonic and endergonic steps, but total pathway is categorized based on overall energy change (ΔG).

Catabolic

Breakdown molecules

Exergonic (Releases energy)

Anabolic

Build complex molecules

Endergonic (Consumes energy)

Cellular Respiration

catabolic pathway

Photosynthesis

Anabolic pathway

7.3 kcal/mol

Energy released when ATP → ADP + Pi

686 kcal/mol

Energy released from oxidizing one molecule of glucose

How does feedback inhibition control metabolic pathways

The end product of a pathway inhibits an earlier enzyme, preventing excess production.

Which type of enzyme inhibitor binds to a location other than the active site?

Non-competitive (allosteric).

Cellular Respiration:

• A catabolic pathway that breaks down glucose and other molecules to produce ATP.

• Can be aerobic (uses oxygen) or anaerobic (without oxygen).

Redox Reactions:

Oxidation;Reduction

Oxidation

loss of electrons.

Reduction:

gain of electrons.Electron transfers release energy used to synthesize ATP.

Electron Carriers (Coenzymes):

NAD⁺ → NADH (primary carrier).FAD → FADH₂ (secondary carrier).

Stages of Cellular Respiration

1)Glycolysis

2)Pyruvate Oxidation (Transition Step)

3) Citric Acid Cycle (Krebs Cycle)

4) Oxidative Phosphorylation (Electron Transport Chain + Chemiosmosis)

Glycolysis

• Location: Cytoplasm

• Input: Glucose (6-carbon)

• Output: 2 Pyruvate (3-carbon each), 2 ATP (net), 2 NADH.

• No O₂ consumed, No CO₂ released here.

Pyruvate Oxidation (Transition Step)

• Location: Mitochondrial Matrix

• Input: 2 Pyruvate

• Output: 2 Acetyl-CoA (2-carbon each), 2 CO₂, 2 NADH

• No ATP produced directly here, No O₂ consumption yet.

Citric Acid Cycle (Krebs Cycle)

• Location: Mitochondrial Matrix

• Input: 2 Acetyl-CoA

• Output (for two turns):

  • 4 CO₂ (completing oxidation of original glucose)

  • 2 ATP

  • 6 NADH

  • 2 FADH₂

• No O₂ directly consumed here yet.

Oxidative Phosphorylation (Electron Transport Chain + Chemiosmosis)

• Location: Inner mitochondrial membrane (cristae)

• Input: Electrons from NADH and FADH₂

• Process:

  • Electrons move through ETC, releasing energy.

  • Energy pumps H⁺ ions across membrane, creating gradient.

  • ATP synthase uses H⁺ gradient (chemiosmosis) to produce ATP.

• Output:

  • Approximately 34 ATP

  • O₂ consumed (terminal electron acceptor), forming H₂O.

• Key numbers:

  • 1 NADH ≈ 3 ATP

  • 1 FADH₂ ≈ 2 ATP

1 glucose fully oxidized

36–38 ATP total

How much energy does 1 glucose release

686 kcal/mol energy released

Total Energy from 1 Glucose:

36–38 ATP × 7.3 kcal/mol per ATP ≈ ~277 kcal/mol

amount of energy captured and stored in ATP during aerobic cellular respiration compared to the total energy available in glucose.

Efficiency ≈ 40%

Anaerobic Pathways (Fermentation)

• Occurs in absence of oxygen.

• Glycolysis + additional reactions regenerate NAD⁺.

Alcoholic Fermentation (Yeasts, bacteria)

• Pyruvate → Ethanol + CO₂

• Only 2 ATP produced (from glycolysis)

Lactic Acid Fermentation (Muscle cells, some bacteria)

• Pyruvate → Lactic Acid

• Only 2 ATP produced (from glycolysis)

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Produced per glucose (aerobic)

36–38 ATP

Efficiency of aerobic respiration

40%

Where does glycolysis occur?

Cytoplasm

What is the net ATP yield in glycolysis?

2 ATP

What molecule is the final electron acceptor in aerobic respiration?

Oxygen (O₂)

Fermentation

anaerobic (without oxygen) energy production used by some cells when oxygen is unavailable.

Why do cells use fermentation?

To regenerate NAD⁺ so that glycolysis can continue making small amounts of ATP in the absence of oxygen.

Fermentation (Anaerobic Metabolism

• Occurs after glycolysis

• No oxygen required

• ATP produced: only 2 per glucose (from glycolysis)

• Main goal: Recycles NAD⁺

• Happens in cytoplasm

Lactic Acid Fermentation

organisms: Animal muscle cells, some bacteria

End Products: Lactic acid

Alcoholic Fermentation

End Products: Ethanol + CO₂

organisms: Yeast, some microbes

buildup causes muscle fatigue during intense exercise.

Lactic acid

produces alcohol and bubbles in bread.

Yeast fermentation

Does fermentation require oxygen?

No, fermentation occurs without oxygen.

Does aerobic respiration require oxygen?

Yes, aerobic respiration requires oxygen as the final electron acceptor.

How much ATP is produced during fermentation?

Only 2 ATP per glucose molecule (from glycolysis).

How much ATP is produced during aerobic respiration?
Back:

About 36–38 ATP per glucose molecule.

What is the final electron acceptor in fermentation?

An organic molecule (e.g., pyruvate in lactic acid fermentation or acetaldehyde in alcohol fermentation).

What is the final electron acceptor in aerobic respiration?

Oxygen (O₂)

What are the end products of lactic acid fermentation?

Lactic acid (in muscle cells and some bacteria)

What are the end products of alcoholic fermentation?

Ethanol + Carbon Dioxide (CO₂) (in yeast)

Where does fermentation occur in the cell?

In the cytoplasm

Where does aerobic respiration mainly occur?

In the mitochondria

What is the main function of the mitochondrion?

It is the site of aerobic respiration and produces the majority of the cell's ATP.

What is the main function of the mitochondrion

It is the site of aerobic respiration and produces the majority of the cell's ATP.

What are the main parts of the mitochondrion

Outer membrane

Inner membrane (folded into cristae)

Intermembrane space

Matrix

Where does the Krebs (Citric Acid) Cycle take place

In the mitochondrial matrix