C1.2 Cell respiration

What are nucleotides?

Nucleotides are the subunits of RNA and DNA, consisting of a nitrogen-containing base, a five-carbon sugar, and one or more phosphate groups.

Why is ATP considered a nucleotide?

ATP is a nucleotide because it consists of the base adenine, the five-carbon sugar ribose, and three phosphate groups.

Why is ATP described as the energy currency of the cell?

ATP is used for temporary energy storage and energy transfer within cells.

What makes ATP suitable for its role in energy transfer?

ATP is water-soluble, stable at neutral pH, and cannot pass freely through membranes.

What happens during ATP hydrolysis?

The third phosphate group of ATP is removed, forming ADP, phosphate, and releasing energy.

How much energy is released by ATP hydrolysis?

A relatively small amount of energy is released, sufficient for many cellular processes.

What are the three main types of cellular activities requiring ATP?

Synthesizing macromolecules, active transport, and movement.

Why is ATP needed for synthesizing macromolecules?

ATP provides the energy needed to link monomers into polymers during anabolic reactions.

How does ATP contribute to active transport?

ATP causes reversible changes in the conformation of pump proteins to move ions or particles against concentration gradients.

Why is ATP required for cellular movements?

ATP provides energy for moving components like chromosomes and vesicles and for changing cell shapes during processes like cytokinesis.

Why does ATP release energy when converted to ADP?

ATP contains more chemical potential energy than ADP, so energy is released during the conversion.

What is the role of phosphorylation in cellular processes?

Phosphate groups from ATP can attach to molecules, releasing energy for conformational or chemical changes.

What processes regenerate ATP from ADP and phosphate?

Cell respiration, photosynthesis, and chemosynthesis regenerate ATP.

Why is ATP continually regenerated in cells?

The quantity of ATP in a cell is small, and processes requiring energy stop without constant regeneration.

What happens to cells without ATP?

Cells degrade within minutes, leading to irreparable damage and cell death.

What happens to excess energy during ATP-ADP interconversion?

Some energy is transformed into heat.

What is cell respiration?

A process where carbon compounds are oxidized to release energy for producing ATP.

What are common respiratory substrates?

Glucose and fatty acids are the main substrates.

How do oxygen and carbon dioxide move during respiration?

They move independently across the plasma membrane by simple diffusion.

Why are gas exchange and cell respiration interdependent?

Gas exchange supplies oxygen and removes CO2, while respiration creates concentration gradients for diffusion.

What are the two types of cell respiration?

Aerobic (using oxygen) and anaerobic (not using oxygen).

Why is anaerobic respiration used in muscles?

It supplies ATP rapidly during high-power muscle contractions.

What is a waste product of anaerobic respiration in muscles?

Lactate (lactic acid).

What limits anaerobic respiration in humans?

The body's tolerance to lactate concentration limits anaerobic respiration.

What is oxygen debt?

The oxygen needed to break down lactate after anaerobic respiration.

What happens during oxidation and reduction?

Oxidation is the loss of electrons, and reduction is the gain of electrons.

What is NAD and its role in respiration?

NAD is an electron carrier that accepts and loses electrons reversibly during respiration.

What happens when NAD+ is reduced?

NAD+ accepts two electrons and one proton, becoming NADH.

What is glycolysis?

A metabolic pathway that converts glucose into two molecules of pyruvate.

What is the net yield of ATP in glycolysis?

Two ATP molecules per glucose.

What is the role of NAD in glycolysis?

NAD is reduced to NADH, carrying electrons for further reactions.

How is NAD regenerated in anaerobic respiration?

Hydrogen from NADH is transferred to pyruvate, forming lactate or ethanol.

What is lactic fermentation?

A process where pyruvate is converted to lactate to regenerate NAD for glycolysis.

How does lactic fermentation preserve food?

Lactic acid lowers pH, preventing bacterial or fungal decomposition.

What is ethanol fermentation?

A process where pyruvate is converted to ethanol and carbon dioxide to regenerate NAD.

Which organism performs ethanol fermentation?

Yeast, a facultative anaerobe.

What are the uses of ethanol fermentation?

Baking (creating bubbles in dough) and brewing.

What is yeast?

A unicellular fungus that respires aerobically or anaerobically.

What are the stages of glycolysis?

Phosphorylation, lysis, oxidation, and ATP formation.

What happens in the phosphorylation stage of glycolysis?

ATP adds phosphate groups to glucose, forming fructose-1,6-bisphosphate.

What is the lysis stage of glycolysis?

Fructose-1,6-bisphosphate splits into two triose phosphate molecules.

What happens during oxidation in glycolysis?

Triose phosphate is oxidized, forming bisphosphoglycerate and reduced NAD.

What is the final stage of glycolysis?

ATP is formed by transferring phosphate groups from bisphosphoglycerate to ADP.

What is the overall outcome of glycolysis per glucose molecule?

Two pyruvates, two NADH, and a net gain of two ATPs are produced.

Why is glycolysis useful in anaerobic conditions?

It produces ATP without requiring oxygen.

What is required for glycolysis to continue?

Replenishment of glucose, ADP, and NAD.

What happens if glucose runs out in glycolysis?

Glycolysis stops unless glucose is transported or stored.

How does NAD regeneration allow glycolysis to continue?

Regeneration ensures NAD is available for the next round of glycolysis.

What is the role of decarboxylation in ethanol fermentation?

Pyruvate is converted to ethanal by removing carbon dioxide.

What happens to ethanal during ethanol fermentation?

It is reduced to ethanol by NADH.

What are examples of foods made by lactic fermentation?

Yogurt, kimchi, sauerkraut, and silage.

What is a facultative anaerobe?

An organism that can respire aerobically or anaerobically.

How does anaerobic respiration maximize muscle power?

It provides rapid ATP production for short bursts of activity.

What limits the duration of anaerobic respiration?

Accumulation of lactate restricts prolonged use.

What is the Benedict’s test?

A test for certain sugars that involves a reduction reaction with copper ions.

What happens to copper ions in the Benedict’s test?

Copper ions are reduced to copper atoms, forming a red or orange precipitate.

What does yeast produce during anaerobic respiration in dough?

Carbon dioxide and ethanol

Why does dough swell or "rise"?

Carbon dioxide forms bubbles within the dough.

What happens to ethanol in dough during baking?

It evaporates.

What is the aim of fermentation when brewing wine or beer?

To produce ethanol rather than carbon dioxide.

What type of sugar source is used to make wine?

Grape juice with a naturally high sugar concentration.

What is the primary ingredient in beer production?

Barley grains mixed with water.

What enzyme is needed to convert starch into sugar during beer production?

Amylase.

Why does anaerobic respiration occur during brewing?

Diffusion of oxygen into the liquid in the tank is limited.

What happens when the ethanol concentration reaches about 15% during brewing?

Ethanol fermentation stops because it becomes toxic to the yeast.

What is bioethanol used for?

As a renewable energy source and fuel for vehicles.

What are common feedstocks for bioethanol production?

Sugarcane and corn (maize).

How is ethanol purified in bioethanol production?

By distillation.

What molecule is oxidized in aerobic respiration for higher ATP yield?

Pyruvate.

What process links glycolysis to the Krebs cycle?

The link reaction.

What does decarboxylation in the link reaction do?

Removes carbon dioxide from pyruvate to form a two-carbon molecule.

What molecule accepts electrons during the link reaction?

NAD, converting it to reduced NAD.

What molecule is formed when the acetyl group binds to coenzyme A?

Acetyl coenzyme A.

Where does the link reaction occur?

In the matrix of the mitochondrion.

What molecule combines with acetyl groups in the Krebs cycle?

Oxaloacetate.

What is the six-carbon molecule produced in the Krebs cycle?

Citrate.

How many decarboxylation reactions occur per turn of the Krebs cycle?

Two.

What are the byproducts of decarboxylation in the Krebs cycle?

Carbon dioxide.

What are the carriers of electrons in the Krebs cycle?

NAD and FAD.

How many ATP molecules are produced directly per turn of the Krebs cycle?

One.

What is the purpose of the electron transport chain (ETC)?

To generate and maintain a proton gradient across the inner mitochondrial membrane.

Where does the ETC occur?

In the inner mitochondrial membrane.

What molecule donates electrons to the first carrier in the ETC?

Reduced NAD.

What is the energy released by electron transfer in the ETC used for?

Pumping protons across the inner mitochondrial membrane.

How many protons are pumped per pair of electrons from reduced NAD in the ETC?

Ten.

How many protons are pumped per pair of electrons from reduced FAD in the ETC?

Six.

What gradient is created by the ETC?

A proton gradient.

What is the enzyme that synthesizes ATP using the proton gradient?

ATP synthase.

What is the process of coupling the proton gradient to ATP synthesis called?

Chemiosmosis.

Where are the active sites for ATP production located on ATP synthase?

In the globular part projecting into the matrix.

What is the role of the rotor in ATP synthase?

It rotates, transferring energy to synthesize ATP.

How many β subunits does ATP synthase have?

Three.

How many ATP molecules are produced per full rotation of ATP synthase?

Three.

How many protons are needed to cause one full rotation of ATP synthase?

Ten.

What is the ATP yield per reduced NAD?

2.5 ATP.

What is the ATP yield per reduced FAD?

1.5 ATP.

What is the terminal electron acceptor in the ETC?

Molecular oxygen.

What happens to oxygen after accepting electrons in the ETC?

It combines with hydrogen ions to form water.

What happens if oxygen is unavailable for aerobic respiration?

The ETC stops functioning, and reduced NAD accumulates.

How many ATP molecules are produced per glucose molecule in anaerobic respiration?

Two.