Chapter 6 Exam 1 BIO 260

Define metabolism and describe the difference between anabolism and catabolism.

Metabolism = all chemical reactions in a cell that sustain life

• Catabolism

  • Breaks molecules down

  • ATP is MADE

  • Process of breaking bonds or oxidizing organic compounds

  • Example: glucose → CO₂ + energy

• Anabolism

  • Builds molecules

  • ATP is USED

  • Example: amino acids → proteins

Define enzymes and their characteristics. 

• Enzymes are proteins that lower the activation energy of a reaction.

• Help facilitate the breakdown of organic compounds slowly to help make ATP

• Interact with substrates and generate a product as a result of that interaction. (Enzyme is unchanged by interaction)

• Characteristics:

  • Highly specific (one enzyme = one reaction)

  • Reusable

  • Work best at optimal temperature and pH

  • Can be denatured if conditions are extreme

Factors that influence enzyme activity

• Temperature

  • Too low = slow reaction

  • Too high = enzyme denatures (loses structure)

• pH

  • Each enzyme has an optimal pH

  • Extreme pH changes shape → loss of function

• Substrate concentration

  • More substrate → faster reaction until saturation

• Inhibitors

  • Block enzyme activity (competitive or noncompetitive)

What are cofactors?  What are coenzymes?

• Cofactors

  • Help facilitate the binding of the substrate to the enzyme.

  • Inorganic helpers (metal ions like magnesium, zinc)

• Coenzymes

  • Coenzymes are a special kind of organic cofactor that act as loosely bound carriers of molecules or carry electrons.

  • Organic molecules (often vitamins)

  • Example: NAD⁺, FAD

Competitive and noncompetitive enzyme inhibition. Example of each.

Competitive inhibition

• Inhibitor binds active site

• Competes with substrate

• Example: E. Coli infection, Sulfa based antibiotics inhibiting PABA (needed for folic acid).

Noncompetitive inhibition

• Inhibitor binds to other site (allosteric site)

• Changes enzyme shape

• Example: heavy metals (Hg²⁺, Pb²⁺)

Glycolysis

Glycolysis What it is

• A 10-step pathway in the cytoplasm

• Breaks 1 glucose (6C) into 2 pyruvate (3C each)

Energy outcome

• Net gain:

  • 2 ATP by substrate-level phosphorylation

  • 2 NADH + 2H⁺

  • 6 different precursor metabolites

Key idea

• Does NOT require oxygen

• Happens in all cells (universal pathway)

Fermentation

• Occurs without oxygen

• The incomplete breakdown of glucose with an organic compound serving as the final electron acceptor

• The ONLY metabolic pathway that is operating is glycolysis

• What it is

  • Anaerobic process that occurs after glycolysis

  • Purpose: regenerate NAD⁺ so glycolysis can continue

  Key idea

  • No electron transport chain

  • ATP comes ONLY from glycolysis

  Energy yield

  • 2 ATP per glucose (very low)

  Types

  • Lactic acid fermentation

  • Alcohol fermentation

  • Mixed acid fermentation

Tricarboxylic Acid (TCA) Cycle / Krebs Cycle

• Energy carrier production

• What it is

  • Cyclical pathway in cytoplasm (prokaryotes) or mitochondria (eukaryotes)

  • Uses acetyl-CoA (from pyruvate)

  Purpose

  • Fully oxidizes carbon → CO₂

  • Loads energy onto electron carriers

  Per glucose (2 turns of cycle):

  • 2 ATP by substrate-level phosphorylation

  • 6 NADH + 6 H⁺

  • 2 FADH₂

  • Two different precursor metabolites

Electron Transport Chain (ETC)

• What it is

  • A series of membrane proteins in the cytoplasmic membrane

  • Transfers electrons from NADH/FADH₂ to a final acceptor

  Main function

  • Uses released energy to pump H⁺ (protons) out of the cell

  Result

  • Creates an electrochemical gradient (proton motive force)

  Key idea

  The ETC does NOT directly make ATP—it builds a gradient that powers ATP synthesis.

• Input: NADH/FADH₂ + O₂ (or other acceptor)

• Output: ATP + water (aerobic)

Oxidative phosphorylation

What it is

• ATP production driven by the proton motive force

• Occurs via ATP synthase

Key idea

• Requires:

  • Electron Transport Chain (ETC)

  • Oxygen (or alternative electron acceptor in anaerobic respiration)

Major ATP source in respiration

• Produces the majority of ATP in aerobic respiration

Substrate-level phosphorylation

Direct transfer of phosphate to ADP → ATP (no Electron Transport Chain required)

The process of making ATP within the metabolic pathways. ATP is made when a phosphate group is transferred from an organic compound to ADP to make ATP.

Proton Motive Force Fuels:

Form of energy generated as an electron transport chain moves protons across a membrane to create a chemiosmotic gradient.

PMF Powers:

• Synthesis of ATP (cell's energy currency)

• Flagellar rotation (movement)

• Active transport systems

Aerobic respiration vs fermentation

Aerobic respiration

• Uses oxygen

• Final electron acceptor: O₂

• High ATP yield (~30+ ATP)

Fermentation

• No oxygen

• Final electron acceptor: organic molecule

• Low ATP yield (2 ATP from glycolysis only)

What is the final end product from fermentation of glucose by E. coli? By lactic acid bacteria? By Saccharomyces?

• E. coli → mixed acids

• Lactic acid bacteria → lactic acid

• Saccharomyces (yeast) → ethanol + CO₂

What is the difference between aerobic respiration and anaerobic respiration?  Do they differ in the amount of energy (ATP) produced?  What is the final electron acceptor in each pathway?

Aerobic respiration

• Final electron acceptor: O₂

• High ATP yield

Anaerobic respiration

• Final electron acceptor: inorganic molecules other than oxygen

  • nitrate (NO₃⁻), sulfate (SO₄²⁻), etc.

• ATP yield: less than aerobic but more than fermentation

What is unique with the Pentose Phosphate Pathway?

Unique features:

• Does NOT produce ATP directly

• Produces:

  • NADPH (used for biosynthesis)

  • Ribose-5-phosphate (for DNA/RNA synthesis)

Main importance:

• Provides building blocks for anabolism

• Helps with reducing power (NADPH) for biosynthesis

Oxidation–Reduction (Redox) reactions

Oxidation

• Loss of electrons (or hydrogen)

• Often = loss of energy

Reduction

• Gain of electrons (or hydrogen)

Key rule (VERY testable):

• LEO GER

  • Lose Electrons = Oxidation

  • Gain Electrons = Reduction

In metabolism

• Glucose is oxidized

• Oxygen (or other acceptor) is reduced

Anaerobic respiration

What it is

• Uses an electron transport chain, but NOT oxygen

• Occurs when oxygen is absent

Final electron acceptors

• Inorganic molecules such as:

  • Nitrate (NO₃⁻)

  • Sulfate (SO₄²⁻)

  • Carbon dioxide (CO₂)

ATP yield

• Less than aerobic respiration

• More than fermentation

Substrate-level phosphorylation

What it is

• Direct transfer of a phosphate group (from organic compound) to ADP → ATP

• Does NOT require ETC or oxygen

Where it occurs

• Glycolysis

• TCA cycle

Key idea

• Fast but low yield compared to oxidative phosphorylation

Energy flow pathway:

Cells extract energy by breaking glucose down step-by-step, storing electrons in NADH/FADH₂, and using the electron transport chain to build a proton gradient that drives ATP production.

• Glycolysis → small ATP + NADH

• TCA cycle → electron carriers

• ETC → proton gradient

• ATP synthase → major ATP production

• Fermentation → low ATP only (no ETC)

Chemoorganotroph

Energy (ATP) from degrading organic compounds through a series of oxidation reduction reactions.

Photophosphorylation

Seen in photosynthetic bacteria. Make ATP by trapping light energy.

Aerobic Respiration

respiration the pathways operating are glycolysis AND the tricarboxylic acid cycle AND the electron transport chain.

What it is

1. Complete breakdown of glucose using oxygen

Includes:

1. Glycolysis

2. TCA cycle

3. Electron transport chain

Final electron acceptor

Oxygen (O₂) → forms water (H₂O)

ATP yield

High (~30–38 ATP depending on organism)

Precursor Metabolites

Metabolic intermediates that link catabolic and anabolic pathways because they can either be broken down to generate ATP or used to make the subunits of macromolecules.