Cellular Respiration Overall Reaction

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

Three Major Goals of Cellular Respiration

Harvest electrons, create proton gradient, make ATP

Four Stages of Cellular Respiration

Glycolysis → Pyruvate Oxidation → Krebs Cycle → Oxidative Phosphorylation

Glycolysis Location

Cytoplasm

Glycolysis Inputs

Glucose, 2 ATP, 2 NAD+

Glycolysis Outputs

2 Pyruvate, 2 NADH, 2 ATP net

Why does Hexokinase phosphorylate glucose?

Traps glucose inside the cell

Why is PFK-1 important?

Committed step and major regulatory point of glycolysis

What activates PFK-1?

AMP and ADP

What inhibits PFK-1?

ATP and citrate

Why does ATP inhibit PFK-1?

Signals the cell has sufficient energy

Why does citrate inhibit PFK-1?

Signals the Krebs cycle has enough fuel

Why does glycolysis require NAD+?

NAD+ accepts electrons during oxidation reactions

What happens if NAD+ is unavailable?

Glycolysis stops

NAD+

Oxidized electron carrier

NADH

Reduced electron carrier carrying high-energy electrons

Primary role of NADH

Deliver electrons to the ETC

OIL RIG

Oxidation Is Loss, Reduction Is Gain

Oxidation

Loss of electrons

Reduction

Gain of electrons

Reducing Agent

Donates electrons and becomes oxidized

Oxidizing Agent

Accepts electrons and becomes reduced

Fermentation Main Purpose

Regenerate NAD+

Does fermentation primarily make ATP?

No, it regenerates NAD+

Lactic Acid Fermentation

Pyruvate → Lactate + NAD+

Alcohol Fermentation

Pyruvate → Ethanol + CO2 + NAD+

Similarity between lactic and alcohol fermentation

Both regenerate NAD+ and allow glycolysis to continue

Pyruvate Oxidation Location

Mitochondrial matrix

Pyruvate Oxidation Inputs

Pyruvate, NAD+, CoA

Pyruvate Oxidation Outputs

Acetyl-CoA, NADH, CO2

Why is pyruvate oxidation important?

Links glycolysis to the Krebs cycle

Krebs Cycle Location

Mitochondrial matrix

Main Purpose of Krebs Cycle

Produce NADH and FADH2 for the ETC

First Step of Krebs Cycle

Acetyl-CoA combines with oxaloacetate to form citrate

Acetyl-CoA Carbon Count

2 carbons

Oxaloacetate Carbon Count

4 carbons

Citrate Carbon Count

6 carbons

Isocitrate Carbon Count

6 carbons

Alpha-Ketoglutarate Carbon Count

5 carbons

Succinyl-CoA Carbon Count

4 carbons

Succinate Carbon Count

4 carbons

Fumarate Carbon Count

4 carbons

Malate Carbon Count

4 carbons

Products of One Krebs Cycle Turn

3 NADH, 1 FADH2, 1 ATP, 2 CO2

Products of Krebs Cycle per Glucose

6 NADH, 2 FADH2, 2 ATP, 4 CO2

Where is most CO2 released?

Pyruvate oxidation and Krebs cycle

What is deamination?

Removal of amino group from amino acids

Why is deamination useful?

Allows amino acids to enter energy metabolism

Beta Oxidation Purpose

Break fatty acids into acetyl-CoA

Beta Oxidation Location

Mitochondrial matrix

Products of Beta Oxidation

Acetyl-CoA, NADH, FADH2

Why do fats yield more ATP than glucose?

They generate large amounts of NADH, FADH2, and acetyl-CoA

What can feed the Krebs cycle besides glucose?

Fatty acids and amino acids

Ketoacidosis Cause

Excess acetyl-CoA converted into ketone bodies

Electron Transport Chain Location

Inner mitochondrial membrane

Main Purpose of ETC

Create a proton gradient

ETC Electron Donors

NADH and FADH2

Terminal Electron Acceptor

Oxygen

What does terminal electron acceptor mean?

Final molecule that receives electrons

What happens if oxygen disappears?

ETC stops

What happens to NADH if oxygen disappears?

NADH accumulates

What happens to NAD+ if oxygen disappears?

NAD+ becomes depleted

What happens to glycolysis when NAD+ runs out?

Glycolysis stops unless fermentation occurs

Water Formation in ETC

Oxygen accepts electrons and protons to form water

Reduction Potential

Tendency of a molecule to accept electrons

Direction of Electron Flow

From lower reduction potential to higher reduction potential

Proton Gradient Definition

Accumulation of H+ across a membrane

Proton-Motive Force

Stored energy in the proton gradient

What powers ATP synthase?

Movement of H+ down its gradient

ATP Synthase Function

Converts ADP + Pi into ATP

Pump in Battery-Pump-Turbine Analogy

ETC complexes

Battery in Battery-Pump-Turbine Analogy

Proton gradient

Turbine in Battery-Pump-Turbine Analogy

ATP synthase

Substrate-Level Phosphorylation

Direct formation of ATP from metabolic intermediates

Where does substrate-level phosphorylation occur?

Glycolysis and Krebs cycle

Oxidative Phosphorylation

ATP production driven by ETC and proton gradient

Where is most ATP produced?

Oxidative phosphorylation

Catabolic Pathway

Breaks molecules down and releases energy

Anabolic Pathway

Builds molecules and requires energy

Gluconeogenesis Definition

Production of glucose from non-carbohydrate sources

Gluconeogenesis Location

Primarily liver

Major Sources for Gluconeogenesis

Lactate, glycerol, amino acids

Purpose of Gluconeogenesis

Maintain blood glucose levels

Gibbs Free Energy (ΔG)

Energy available to do work

Negative ΔG

Spontaneous reaction

Positive ΔG

Nonspontaneous reaction

ΔG = 0

Reaction at equilibrium

Activation Energy (Ea)

Energy required to start a reaction

Difference Between Ea and ΔG

Ea is the barrier; ΔG is the overall energy change

What do enzymes do?

Lower activation energy

Do enzymes change ΔG?

No

Do enzymes change equilibrium?

No

Competitive Inhibition

Inhibitor competes for active site

Can competitive inhibition be overcome?

Yes, with more substrate

Noncompetitive Inhibition

Inhibitor binds elsewhere and changes enzyme shape

Can noncompetitive inhibition be overcome?

No

Allosteric Regulation

Regulation through binding at a site other than the active site

First Law of Thermodynamics

Energy cannot be created or destroyed

Second Law of Thermodynamics

Entropy tends to increase

Light Reactions Location

Thylakoid membrane

Calvin Cycle Location

Stroma

Inputs of Light Reactions

Light and water

Outputs of Light Reactions

ATP, NADPH, O2

Inputs of Calvin Cycle

CO2, ATP, NADPH

Outputs of Calvin Cycle

G3P

Purpose of Light Reactions

Convert light energy into ATP and NADPH

Purpose of Calvin Cycle

Use ATP and NADPH to fix carbon into sugars

Chlorophyll

Main pigment that absorbs light energy

Best Light for Photosynthesis

Blue and red light

Worst Light for Photosynthesis

Green light

Photosystem II Reaction Center

P680

Photosystem I Reaction Center

P700

Role of Water in Photosystem II

Provides replacement electrons

What happens if water cannot be split?

Electron flow stops

Linear Electron Flow Products

ATP, NADPH, O2

Cyclic Electron Flow Products

ATP only

Purpose of Cyclic Electron Flow

Generate extra ATP without producing NADPH

What regulates cyclic electron flow?

ATP demand exceeding NADPH demand

NADPH

Main reducing agent for biosynthesis

Difference Between NADH and NADPH

NADPH has an extra phosphate group

Main Function of NADH

ATP production

Main Function of NADPH

Anabolic reactions and carbon fixation

Carbon Fixation

Conversion of atmospheric CO2 into organic molecules

RuBP

5-carbon CO2 acceptor

RuBisCO

Enzyme that fixes CO2 to RuBP

Three Phases of Calvin Cycle

Fixation, Reduction, Regeneration

Which Calvin Cycle Phase Uses ATP and NADPH?

Reduction

Which Calvin Cycle Phase Uses ATP?

Regeneration

Product Removed from Calvin Cycle

G3P

Photorespiration

RuBisCO binds O2 instead of CO2

Why is photorespiration bad?

Wastes ATP and carbon while producing no sugar

C3 Plants

Most photorespiration

C4 Plants

Reduce photorespiration through spatial separation

CAM Plants

Reduce photorespiration through temporal separation

When do CAM plants open stomata?

At night

Highest Water Efficiency

CAM plants

What connects glycolysis and Krebs cycle?

Pyruvate oxidation

What connects Krebs cycle and ETC?

NADH and FADH2

What connects light reactions and Calvin cycle?

ATP and NADPH

Why is oxygen indirectly required for glycolysis?

It allows NAD+ regeneration through the ETC

Why is Krebs cycle dependent on ETC?

ETC regenerates NAD+ and FAD needed by Krebs cycle