Cellular Respiration Overview

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Questions and Answers

During glycolysis, what is the primary molecule that is produced?

Oxygen

Acetyl-CoA

Fatty acids

ATP (correct)

NADH is produced during glycolysis and through the Krebs Cycle.

True

What molecule combines with pyruvate in the mitochondrial matrix during pyruvate oxidation?

CoA

The end product of the Krebs Cycle is _____, which is then used to regenerate the cycle.

oxaloacetate Signup and view all the answers

Match the energy carrier with its function:

NADH = Electron carrier in oxidative phosphorylation FADH2 = Provides electrons for the electron transport chain ATP = Main energy currency of the cell CoA = Carrier of acetyl group for metabolic reactions Signup and view all the answers

Which process directly produces ATP in the Krebs Cycle?

Substrate-level phosphorylation Signup and view all the answers

The Krebs Cycle occurs in the cytoplasm of eukaryotic cells.

False Signup and view all the answers

Name the two 3-carbon molecules produced from glucose during glycolysis.

Pyruvate Signup and view all the answers

Which of the following terms refers to the breakdown of glucose during cellular respiration?

Glycolysis Signup and view all the answers

The Krebs Cycle produces ATP directly.

False Signup and view all the answers

What is the primary purpose of the Electron Transport Chain in cellular respiration?

To produce ATP by harnessing energy from electrons. Signup and view all the answers

In the redox reaction of NAD, it gets reduced to form ______.

NADH Signup and view all the answers

Match the following energy carriers with their reduced forms:

NAD = NADH FAD = FADH2 NADP = NADPH Coenzyme A = Acetyl CoA Signup and view all the answers

Which of the following describes exergonic reactions?

Energy is released Signup and view all the answers

Oxidative phosphorylation occurs in the mitochondria.

True Signup and view all the answers

What is the main product formed during glycolysis?

Pyruvate Signup and view all the answers

In cellular respiration, the energy produced from glucose is harnessed into ______.

ATP Signup and view all the answers

How many ATP molecules are produced from the glycolysis process?

2 Signup and view all the answers

FADH2 generates more ATP than NADH during the electron transport chain.

False Signup and view all the answers

What is the primary function of the electron transport chain?

To transport electrons and create an electrochemical gradient for ATP synthesis. Signup and view all the answers

The final acceptor of electrons in the electron transport chain is __________.

oxygen Signup and view all the answers

Match the following terms with their corresponding descriptions:

ATP = Energy currency of the cell NADH = Carriers electrons and generates 3 ATP FADH2 = Carriers electrons and generates 2 ATP Oxidative Phosphorylation = Process of ATP synthesis using a proton gradient Signup and view all the answers

What is the total possible ATP yield from one glucose molecule during aerobic respiration?

36 to 38 Signup and view all the answers

Electrochemical gradients are not important for ATP production.

False Signup and view all the answers

Which enzyme catalyzes step 3 of glycolysis?

Phosphofructokinase Signup and view all the answers

Study Notes

Reduced Molecules

When a molecule accepts electrons, its overall positive charge decreases.

Oxidative Phosphorylation

ATP is formed indirectly.
Uses redox reactions.
Involves NADH and FADH2.
The molecules harvest energy, which is transferred to ATP by the end of cellular respiration.

Glycolysis

A glucose molecule is broken down into two pyruvate molecules.
Occurs in the cytoplasm.
Is anaerobic, meaning it doesn't require oxygen.

Key Points of Glycolysis

Two ATP molecules are used to phosphorylate substrate molecules.
A six-carbon compound (Fructose 1,6 biphosphate) turns into Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde 3-phosphate (G3P).
DHAP turns into G3P.
Inorganic phosphate is added to G3P, while NAD+ is reduced to form NADH.
ADP is converted to ATP by substrate-level phosphorylation.
The three-carbon substrate molecules are rearranged, and water is removed.
ADP is converted to ATP by substrate-level phosphorylation.
There are two GAP, or G3P molecules per glucose.

Glycolysis: Balance Sheet

Two ATP ~P bonds are expended.
Four ~P bonds of ATP are produced.
The net production of ~P bonds of ATP per glucose is two.

Overall Glycolysis Equation

Glucose + 2 ADP + 2 Pi + 2 NAD+ → 2 Pyruvate + 2 ATP + 2 (NADH + H+)

Mitochondrion Anatomy

A mitochondrion is a double-membrane-bound organelle.
The outer membrane is smooth.
The inner membrane is folded into cristae.
The space between the membranes is called the intermembrane space.
The space inside the inner membrane is called the matrix.

Pyruvate Oxidation

Occurs in the matrix of the mitochondria.
Two pyruvate + 2 NAD+ + 2 CoA → 2 acetylCoA + 2 NADH + 2H+ +2CO2
Acetyl CoA then enters the Krebs cycle.

Krebs Cycle

Occurs in the matrix of the mitochondria.
Many enzymes, coenzymes, and other molecules exist in an organized pattern on the inner membrane.

Krebs Cycle Steps

Acetyl-CoA delivers two carbons from glucose.
It reacts with oxaloacetate to produce citrate (6C).
Citrate undergoes five reactions to produce succinate.
Two oxidative reactions make CO2 while NAD+ is reduced to form NADH with each CO2 being produced.
ATP is produced by substrate-level phosphorylation.
A phosphate group is added to the molecule guanosine triphosphate (GTP).
The phosphate group is then transferred to ADP.
Steps 7 to 9 are oxidation reactions, where NAD+ and FAD are reduced.
The final product is oxaloacetate.

Krebs Cycle Summary

The entire glucose molecule is consumed by the end of the Krebs cycle.
6C is converted to 6 CO2.
The following energy is harnessed:
- 4 ATP (2 Glycolysis, 2 Krebs)
- 12 reduced coenzymes:
  - 2 NADH (Glycolysis)
  - 2 NADH (Pyruvate Oxidation stage)
  - 6 NADH (Krebs)
  - 2FADH2 (Krebs)

Electron Transport Chain

Occurs on the inner membrane of the mitochondria.
Transports electrons from NADH and FADH2 through a series of redox reactions, which release free energy.
The energy is used to pump protons (H+) into the inner membrane space of the mitochondria, creating an electrochemical gradient.
The gradient is a source of free energy, which is used to create ATP.

The Importance of Oxygen

Oxygen is the final acceptor of electrons that pass through the ETC.
Its high electronegativity pulls the electrons through the ETC.
Electrons "fall" through each enzyme complex like a skydiver.
This energy pumps H+ ions into the inner membrane space.
The H+ ions then "fall" back into the matrix and make ATP.

Chemiosmosis

Protons move through a proton channel in ATP synthase to produce ATP.
This process is called oxidative phosphorylation.
The electrochemical gradient must be maintained (by eating!) or ATP production stops.

What Happens to NADH From Glycolysis?

Electrons are delivered to NAD+
NADH passes electrons to FAD to make FADH2.

NADH vs FADH2

NADH pumps three H+ ions across the membrane, generating three ATP molecules.
FADH2 enters the ETC at Q, therefore only pumping two H+ ions across and making two ATP molecules.
Two electrons through each hydrogen pump create one ATP.

Aerobic Respiration Efficiency

Aerobic respiration can produce between 36 and 38 ATP per glucose.
However, efficiency is reduced by:
- Proton leak through the intermembrane without passing through ATP synthase.
- Some protons are used to transport pyruvate generated from glycolysis from the cytoplasm into the mitochondria.
- Some energy is used to transport ATP out of the mitochondria for use in the cytoplasm.

Metabolic Rate

An organism's metabolic rate is the amount of energy consumed at a given time, and a measure of the overall rate of cellular respiration reactions.

Control Mechanisms

Phosphofructokinase (which catalyzes step 3 of glycolysis) controls cellular respiration.

First Law of Thermodynamics

The total amount of energy in the universe is constant.
Energy cannot be created or destroyed, but it can be converted from one form to another.
Activation energy is the amount of energy required to break chemical bonds.

Second Law of Thermodynamics

The universe favors entropy. Entropy is a measure of randomness or chaos.

Endergonic Reactions

Energy of the products is more than the reactants.
Photosynthesis is an example of an endergonic reaction.
Light energy is converted into stored chemical energy, such as glucose, which contains 2870kJ per molecule.

Exergonic Reactions

Energy of the products is less than the reactants.
Free energy is released.
Cellular respiration is an example of an exergonic reaction.
The energy from glucose is released and harnessed into ATP at a controlled rate.