Biology-Cell Respiration

Describe the structure of ATP.

ATP is a nucleotide composed of adenine, ribose and three phosphates.

Outline properties of ATP that make it a suitable source of energy.

There are high energy bonds between the three phosphates. The bond between the last two phosphates is unstable, and when broken releases energy which can be used as activation energy for metabolic chemical reactions.

List the 4 examples of cellular processes we talked about in class that require use of ATP.

Active transport across membranes

Anabolism

Movement of the whole cell

Movement of components within the cell such as chromosomes during mitosis and meiosis

Describe the ATP-ADP cycle, including the relative amount of energy (is energy required or not) and the roles of hydrolysis and phosphorylation.

The hydrolysis of ATP to ADP (Adenosine diphosphate) and an inorganic phosphate (Pi) releases energy that is used as activation energy for metabolic reactions. The regeneration of ATP from ADP and Pi by condensation reactions require energy. Cellular respiration provides the energy for the regeneration of ATP.

Define cellular respiration.

Cell respiration is the controlled release of ATP energy from organic compounds (food) within cells.

Distinguish between cellular respiration and gas exchange.

Gas exchange is the exchange of carbon dioxide and oxygen in living cells and tissues. Gas exchange happens in the alveoli of the lungs and respiring tissues in humans. The gasses move by diffusion. Respiration is the controlled release of ATP energy from organic compounds (food) within cells.

List reasons why cellular respiration must be continuously performed by all cells.

ATP can not be stored for later use.

ATP can not be transferred from cell to cell.

When ATP is used in cells, heat energy is released. This heat energy can not be reused and will be lost to the environment.

Identify factors that affect the rate of cellular respiration.

Factors that affect the rate of respiration of insects or seeds include:

Temperature (if using insects, ensure that the insects are not exposed to temperatures outside of their normal range)

Mass of respiring organisms

Factors that affect the rate of respiration of yeast include:

Temperature

Mass of yeast

pH of suspension

Type of substrate (food source)

Substrate concentration

Chemical inhibitors of enzymes

List common substrates of cellular respiration. ​

Glucose and fatty acids are the principal substrates that cells use for respiration, however they can use other organic molecules. Organic molecules are compounds which contain carbon, but not oxides or carbonates.

Compare and contrast anaerobic fermentation and aerobic respiration.​

Aerobic and anaerobic respiration are vital metabolic processes in humans. Both occur within cells, utilizing glucose as the initial substrate and enzymatic reactions to catalyze pathways for ATP production. Aerobic respiration requires oxygen and yields a high net gain of 36 ATP molecules, with carbon dioxide and water as waste products. It primarily occurs in mitochondria. In contrast, anaerobic respiration operates without oxygen, resulting in a low net gain of 2 ATP molecules and producing lactate as a waste product. It takes place in the cytoplasm, bypassing mitochondria.

List three approaches for determining the rate of cellular respiration.

Measuring volume of gas produced by yeast (there are several methods)

Measuring the change in oxygen concentration using oxygen probes.

Measuring the change in carbon dioxide concentration using carbon dioxide probes.

State the equation for calculating the rate of respiration.

Rate of Reaction = Change in Reactant or Product/Time

Changes that can be measured include:

Decrease in oxygen

Increase in carbon dioxide

Outline oxidation and reduction reactions in terms of movement of hydrogen and electrons.

Oxidation

addition of oxygen

removal of hydrogen

loss of electrons

Reduction

loss of oxygen

addition of hydrogen

gain of electrons

State the name of the electron carrier molecules used in cellular respiration.

NAD (Nicotinamide adenine dinucleotide) is an electron carrier that is reduced during many stages in aerobic respiration.

Define "electron carrier."

An electron carrier is a small organic molecule involved in the transfer or shuttling of electrons from one molecule to another. NAD removes two electrons and hydrogen from substrates at various stages of respiration.

Outline the formation of reduced NAD during glycolysis.

When NAD gains electrons and hydrogen from a substrate, it forms reduced NAD. The substrate which has lost electrons and hydrogen to NAD is oxidized. Reduced NAD carries electrons and hydrogen to the electron transport chain, where Reduced NAD becomes oxidized and returns to NAD.

State the location of the glycolysis reaction in a cell.

Glycolysis converts glucose to pyruvate in the cytoplasm of the cell.

What is the first step in glycolysis?

Phosphorylation of Glucose: Two ATP molecules are hydrolyzed. The two phosphates, produced by the hydrolysis of ATP, bond to glucose, forming an unstable 6-carbon compound (Hexose bisphosphate).

What happens during the lysis phase of glycolysis?

Lysis: The unstable 6-carbon compound breaks apart to form two 3-carbon compounds (Triose phosphates).

How is NAD involved in glycolysis?

Reduction of NAD: NAD is converted to reduced NAD as it takes electrons and hydrogen from the 3-carbon compound. The 3-carbon compound is oxidized. Two molecules of reduced NAD are produced, one from each 3-carbon compound.

What is the final step in glycolysis that produces ATP?

Formation of ATP: As each 3-carbon compound is converted to glucose, two ATP are produced.

State why NAD+ must be regenerated in anaerobic respiration.

Glycolysis requires a constant supply of NAD. NADH carries electrons to the electron transport chain in aerobic respiration. However, in anaerobic respiration, there is no oxygen to accept the electrons from NADH. Therefore, the cell must regenerate NAD+ from NADH to keep glycolysis going.

Compare anaerobic respiration in yeasts and humans.

Similarities of anaerobic respiration in humans and yeast include:

Oxygen is not available

Occurs in the cytoplasm of the cell

The first substrate is glucose

Glycolysis is the first stage and produces:

A net gain of 2 ATP

2 pyruvates

2 reduced NAD molecules

Regenerates NAD from reduced NAD, which allows glycolysis to continue

Outline the process of regenerating NAD+ and the production of lactate in humans during anaerobic respiration.

Pyruvate is converted to lactate by oxidizing reduced NAD (NADH) to NAD. The NAD generated by anaerobic respiration can be used in glycolysis. Anaerobic respiration produces a net gain of 2 ATP molecules, regenerates NAD, and produces the waste product lactate in humans.

State the condition in which humans would perform anaerobic respiration.

If oxygen is not present in human cells, then anaerobic respiration is used to regenerate NAD.

Outline the process of regenerating NAD+ and production of ethanol in yeast during anaerobic respiration.

Anaerobic respiration occurs in the cytoplasm of yeast cells when there is not sufficient oxygen for aerobic respiration. Anaerobic respiration begins with the glycolysis of glucose, which produces a net gain of 2 ATP, 2 pyruvate and 2 reduced NAD molecules. Pyruvate is converted to ethanol and carbon dioxide, which regenerates NAD. The regeneration of NAD allows glycolysis to continue.

Outline how anaerobic respiration in yeast is used in brewing and baking.

Carbon dioxide produced by yeast during anaerobic respiration causes bread dough to rise. Yeast produces ethanol in the brewing process.

Summarize the reactants and products of the link reaction.

Reactants: Two pyruvate

Products: Two CO2, Two NADH, Two Acetyl-Coa

State the location that the link reaction occurs.

Pyruvate from glycolysis enters the matrix of a mitochondrion.

Outline the link reaction with references to decarboxylation, oxidation and binding of CoA.

The link reaction involving pyruvate includes:

Decarboxylation of pyruvate: Pyruvate loses carbon dioxide, which is released as a waste product of respiration, to produce 2-carbon acetyl group

Reduction of NAD: Pyruvate is oxidized, as it loses electrons and hydrogen. NAD is reduced, as it gains electrons and hydrogen.

Formation of acetyl coenzyme A: The acetyl group combines with coenzyme A to form acetyl coenzyme A.

The acetyl group is transferred to the Krebs cycle by coenzyme A.

State the location that the Krebs cycle occurs.

The Krebs cycle occurs in the mitochondrial matrix.

Outline the events of the Krebs cycle.

Oxaloacetate, a 4-carbon compound, combines with an acetyl group from acetyl coenzyme A to form citrate, a 6-carbon compound. Citrate is converted back to oxaloacetate through a series of 2 decarboxylations and 4 oxidation reactions.

Events that occur during the Krebs cycle include:

Two decarboxylations: Citrate loses carbon dioxide to form a 5-carbon compound. A 5-carbon compound loses carbon dioxide to form a 4-carbon compound.

Four Oxidation reactions: Citrate is converted back to oxaloacetate through a series of enzyme-catalyzed reactions. Three intermediate compounds lose electrons and hydrogen to NAD to form reduced NAD.

One carbon compound is oxidized, and loses electrons and hydrogen to the electron carrier FAD, producing reduced FAD.

The oxidation reactions are dehydrogenation reactions, as compounds lose hydrogen to NAD and FAD.

Production of ATP: Each turn of the Krebs cycle provides enough energy to convert ADP and a phosphate to ATP, through a condensation reaction.

State where the reduced NAD and reduced FAD produced in the Krebs cycle carry electrons.

Reduced NAD and reduced FAD bring electrons to the electron transport chain.

List the net products of one turn of the Krebs cycle.

1 ATP

1 FADH2

3 NADH

2 CO2

The reduced NAD from glycolysis, the link reaction and the Krebs cycle carries electrons to the electron transport chain. State the specific part of the mitochondria these are carried to.

The inner mitochondrial membrane.

List the reactions that generated the reduced NAD (NADH) and reduced FAD (FADH2) used in the electron transport chain.

Reduced NAD (NADH): Glycolysis, the link reaction, Krebs cycle

Reduced FAD (FADH2): Krebs cycle

Describe how the movement of electrons through the electron transport chain is used to generate a proton gradient in the intermembrane space.

Electron transport chains are present in the inner mitochondrial membrane. Electrons are passed along the electron transport chain through a series of oxidation-reduction reactions. The movement of electrons provides the energy for the active transport of protons (H+) from the mitochondrial matrix into the intermembrane space. This creates a high concentration of protons in the intermembrane space.

Define chemiosmosis.

Chemiosmosis is the generation of ATP using kinetic energy as protons move through ATP synthase.

Describe the structure ATP synthase.

The ATP synthase enzyme is composed of two components. The F0 is a transmembrane channel that facilitates enhanced diffusion of protons across the mitochondrial membrane. The second part, F1, is a peripheral membrane protein complex evident towards the matrix.

Outline the formation of ATP by ATP synthesis, with reference to movement of protons and phosphorylation of ADP.

The protons that accumulate in the intermembrane space are used to produce ATP. The charged protons cannot pass through mitochondrial membranes. The inner mitochondrial membrane contains ATP synthase, which includes a protein channel.

Protons (H+) pass through ATP Synthase from the high concentration in the intermembrane space to the low concentration in the matrix. This is an example of facilitated diffusion. The protons moving through ATP synthase provide the energy to convert ADP and phosphate to ATP.

Compare the total amount of ATP made from anaerobic and aerobic

espiration. ​

Anaerobic: 2 ATP

Aerobic: 30-34 ATP

State that oxygen is the final electron acceptor in the electron transport chain.

Aerobic respiration of glucose occurs when oxygen is available as a final electron acceptor.

Explain why aerobic respiration will stop if oxygen is not present.

Oxygen accepts the electrons from the electron transport chain, and protons (H+) from the matrix to produce water. If oxygen is not present, the electron transport chain does not function.

Compare the use of carbohydrates and lipids as respiratory substrates in aerobic and anaerobic respiration.

Lipids and carbohydrates can be respired. Fatty acids and carbohydrates, such as glucose, can be used to produce acetyl coenzyme A, which enters the Krebs cycle. Glycolysis and anaerobic respiration only occur with the respiration of carbohydrates, and not with lipids.

Explain the greater energy yield of lipids compared to carbohydrates when used as respiratory substrates.

Lipids produce a much higher yield of ATP, as lipids have less oxygen and more oxidizable hydrogen and carbon (more 2-carbon acetyl groups can be formed). CARBS = 17 kJ per gram vs LIPIDS = 37 kJ per gram.

Outline the process by which lipids can be a substrate for respiration.

Triglycerides can also be respired, but do not go through the process of glycolysis. Triglycerides are hydrolyzed to fatty acids and glycerol. Fatty acids enter the mitochondrion, and are converted to multiple acetyl coenzyme A molecules. The acetyl coenzyme A molecules produced from fatty acids can enter the Krebs cycle.