Chapter 6 Cellular Respiration

What is the net yield at the end of glycolysis?

One glucose molecule molecule will: - yield 2 pyruvates - yield 2 NADH - produce 4 ATPs but the total yield is 2 since 2 ATPs are used

Obligate anaerobes:

- are poisoned by oxygen, requiring anaerobic conditions, and - live in stagnant ponds and deep soils.

What are the main events or results of glycolysis?

- a single molecule of glucose is enzymatically cut in half through a series of steps, - two molecules of pyruvate are produced, - two molecules of NAD+ are reduced to two molecules to NADH, and - a net of two molecules of ATP is produced.

What is the end result of cellular respiration?

- glucose is broken down to carbon dioxide and water and - the cell captures some of the released energy to make ATP.

Stage 3: Oxidative phosphorylation

- involves electrons carried by NADH and FADH2, - shuttles these electrons to the electron transport chain embedded in the inner mitochondrial membrane, - involves chemiosmosis, and - generates ATP through oxidative phosphorylation associated with chemiosmosis.

The citric acid cycle:

- is also called the Krebs cycle - completes the oxidation pf organic molecules, and - generates many NADH and FADH2 molecules.

Is cellular respiration an exergonic or endergonic process?

Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to form ATP.

How are the electrons from glucose eventually transferred to oxygen?

Electrons acceptors are organic molecules that can take the electrons from glucose and transfer them to oxygen at the end of respiration.

How does cellular respiration slowly break up organic molecules?

Energy is: - gradually released in small amounts, - captured by a biological system, and - stored in ATP.

How is the movement of electrons to or from molecules classified/

The movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction: - the loss of electrons from one sunstance is called oxidation, - the addition of electrons to another substance is called reduction, - a molecule is oxidized when it loses one or mole electrons, and - reduced when it gains one or mole electrons.

Food molecules provide raw materials for biosynthesis:

cells use intermediates from cellular respiration for the biosynthesis of other organic molecules. Metabolic pathways are often regulated by feedback inhibition in which an accumulation of product suppresses the process that produces the product.

What are key events in the citric acid cycle?

during the citric acid cycle: - the two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate, - citrate is degraded back to the four-carbon compount -two CO2 are released, and - 1 ATP, 3NADH, and 1 FADH2 are produced.

How is ATP made during glycolysis?

ATP is formed in glycolysis by substrate-level phosphorylation during which: - an enzyme transfers a phosphate group from a substrate molecule to ADP and - ATP is formed.

Where does cellular respiration occur?

Cellular respiration takes place in the mitochondria of eukaryotic cells.

Respiration, as it relates to breathing, and cellular respiration are not the same.

- Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO2. - Cellular Respiration is the aerobic (oxygen binding) harvesting energy from food molecules by cells.

What is the net yield of oxidative phosphorylation?

- a total of 6 NADH and 2FADH2 yield a theoretical total of 32 ATP - 2 NADH made in glycolysis require 2 ATP to be used to transport them into the mitochondria - a net of 4 ATP were produced in glycolysis and the citric cycle - the net theoretical yield is 34 ATP is never acheived because leaky mitochondrial membranes result in lower yields of ATP so usually ~32 ATPs are made at the end of cellular respiration

Glycolysis is the universal energy-harvesting process of life. The role of glycolysis in fermentation and respiration dates back to:

- life long before oxygen was present, - when only prokaryotes inhabited the earth, - about 3.5 billion years ago. The ancient history of glycolysis is supported by its: -occurence in all the domains of life and - location within the cell, using pathways that do not involve any membrane-bounded organelles.

Stage 1: Glycolysis

- occurs in the cytoplasm - begins cellular respiration, and - breaks down glucose into two molecules of a three-carbon compound called pyruvate.

Why is oxygen a good acceptor of electrons?

- oxygen has a strong tendency to attract electrons. - an electron loses potential energy when it "falls" to oxygen.

What is the energy yield in cellular respiration?

- produces 32 ATP molecules from each glucose molecule and - captures only about 34% of the energy originally stored in glucose.

Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation:

- takes advantage of glycolysis, - produces two ATP molecules per glucose, and - reduces NAD+ to NADH. The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+

Stage 2: The citric acid cycle

- takes place in the mitochondria, - oxidizes pyruvate to a two-carbon compound, and - supplies the third stage with electrons

There are other electron "carrier" molecules that function like NAD+

- they from a staircase where the electrons pass from one to the next down the staircase. - these electrons carriers collectively are called the electron transport chain. - as electrons are transported down the chain, ATP is generated.

How is ATP made during oxidative phosphorylation?

-Electrons from NADH and FADH2 are transferred as H+ which travel down the electron transport chain to O2. -Each NADH will theoretically yield a total of ~3 ATP while each FADH2 will yield ~2 ATP - Oxygen picks up H+ to form water. - Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space. - In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.

What is the net yield at the end of the citric acid cycle?

-Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose. Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is: - 2ATP, - 6 NADH, and - 2 FADH2 - 4 CO2 molecules

What are the stages of cellular respiration?

-Stage 1: Glycolysis -Stage 2: Pyruvate oxidation and citric cycle -Stage 3: Oxidative phosphorylation

Although glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated usuing

-carbohydrates, -fats, and -proteins.

Fats make excellent cellular fuel because they:

-contain many hydrogen atoms and thus many energy-rich electrons and -yield more then than twice as much ATP per gram than a gram of carbohydrate or protein.

Facultative anaerobes:

-include yeasts and many bacteria, and -can make ATP by fermentation of oxidative phosphorylation.

What is the end result in photosynthesis?

-some of the energy in sunlight is captured by chloroplasts, - atoms of carbon dioxide and water are rearranged, and - glucose and oxygen are produced.

Three categories of cellular poisons obstruct the process of oxidative phosphorylation. These poisons:

1. block the electron transport chain (rotenone, cyanide, and carbon monoxide) 2. inhibit ATP synthase (anitbiotic oligomycin) 3. make the membrane leaky to hydrogen ions (called uncouplers, examples include dinitrophenol)

What happens in the case of glucose being metabolized?

Glucose will: - lose its hydrogen atoms and - becomes oxidized to CO2. During the same process oxygen, - gains hydrogen atoms and - becomes reduced to H2O.

How is lactate removed?

Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.

What is an example of an electron acceptor in respiration?

NAD+ - is an important enzyme in oxidizing glucose, - accepts electrons, and - becomes reduced to NADH.

Can other foods be used as energy sources?

Other foods (organic molecules) such as lipids can olse be used as a source of energy.

What are key features of oxidative phosphorylation?

Oxidative Phosphorylation: - occurs in the mitochondrial inner membrane - involves electron transport and chemiosmosis, and - requires an adequate supply of oxygen. - will produce the majority of ATP.

What occurs in pyruvate oxidation?

Pyruvate does not enter the citric acid cycle, but undergoes some chemical grooming in which, - a carboxyl group is removed and given off as CO2, - the two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH. - coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, and - acetyl CoA enters the citric acid cycle.

The human body uses energy from ATP for all its activities.

The average human needs about 2,200 kcal of energy per day. - about 75% of these calories are used to maintain a healthy body. - the remaining 25% is used to power physical activities.

Where does alcohol fermentation occur?

The baking and winemaking industries have used alcohol fermentation for thousands of years. In this process yeasts (single-celled fungi) -oxidize NADH back to NAD+ and -convert pyruvate to CO2 and ethanol.

What is the final organic molecule made at the end of glycolysis?

The compounds that form between the initial reactant, glucose, and the final product, pyruvate, are called intermediates.

What are some uses of lactate fermentation?

The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt. Other types of microbial fermentation turn: - soybeans into soy sauce and - cabbage into sauerkraut.

Cells tap energy from electrons "falling" from organic fuels to oxygen.

The energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules.

What happens to the pyruvate made in glycolysis?

The pyruvate formed in glycolysis is transported from the cytoplasm into a mitochondrion where: - the citric acid cycle and - oxidative phosphorylation will occur.

What are the key steps in glycolysis?

The steps of glycolysis can be grouped into two main phases. In step 1-4, the energy investment phase, -energy is consumed as two ATP molecules are used to energize a glucose molecule, glucose is then split into two small 3-carbon molecules (pyruvate) that are now primed to release energy. In step 5-9, the energy payoff, - two NADH molecules are produced for each initial glucose molecule and - 4 ATP molecules are generated.

What are the final products of cellular respiration?

The total yield is about 32 ATP molecules per glucose molecule. This is about 34% of the potential energy of a glucose molecule. In addition, water and CO2 are produced.

How do cells extract and transfer the energy from chemical bonds?

When the carbon-hydrogen bonds of glucose are broken, electrons are transferred to oxygen.

Where does lactate fermentation occur?

Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which: - NADH is oxidized to NAD+ and -pyruvate is reduced to lactate.

What is the net yield at the end of pyruvate oxidation?

two pyruvates: - yield 2 CO2 molecules (carbon removed from pyruvate) - yield two acetyl CoA molecules - yield 2 NADH molecules