Chapter 9

Which of the following is a correct description of the events of cellular respiration and the sequence of events in cellular respiration?

-oxidation of glucose to pyruvate -oxidation of pyruvate -oxidation of acetyl coA -oxidative phosphorylation

What is the total production of ATP, NADH, and FADH2 in the citric acid cycle from one molecule of glucose?

2 ATP, 6 NADH, 2 FADH+

During the energy payoff phase of glycolysis, __________.

During the energy payoff phase of glycolysis, both NADH and ATP are produced. The word glycolysis means "sugar splitting," and that is exactly what happens during this pathway. Glucose, a six-carbon sugar, is split into two three-carbon sugars. These smaller sugars are then oxidized and their remaining atoms rearranged to form two molecules of pyruvate. (Pyruvate is the ionized form of pyruvic acid.) Glycolysis can be divided into two phases: the energy investment phase and the energy payoff phase. During the energy investment phase, the cell actually "spends" ATP by phosphorylating glucose. Glucose is then split into two three-carbon molecules. The investment is repaid with interest during the energy payoff phase, when ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by the release of electrons during the oxidation of glucose. The net energy yield from glycolysis, per glucose molecule, is two ATP plus two NADH.

Fermentation by itself produces no ATP but keeps glycolysis going, which produces a small amount of ATP. How does fermentation do this?

Fermentation oxidizes NADH to NAD+, which facilitates the production of ATP in glycolysis. Fermentation is a way of harvesting chemical energy without using either oxygen or any electron transport chain—in other words, without cellular respiration. As an alternative to respiratory oxidation of organic nutrients, fermentation is an extension of glycolysis that allows continuous generation of ATP by the substrate-level phosphorylation of glycolysis. For this to occur, there must be a sufficient supply of NAD+ to accept electrons during the oxidation step of glycolysis. Fermentation consists of glycolysis plus reactions that regenerate NAD+ by transferring electrons from NADH to pyruvate or derivatives of pyruvate. The NAD+ can then be reused to oxidize sugar by glycolysis, which nets two molecules of ATP by substrate-level phosphorylation.

Most of the ATP in cellular respiration is produced by the process of chemiosmosis. How does this process produce ATP?

H+ flows acroos mitochondrila membrane thorugh enxyme ATP synthase

What is the role of oxygen in the electron transport chain?

It is reduced to form water

In preparing pyruvate to enter the citric acid cycle, which of the following steps occurs?

It's oxidized, and the resulting electrons reduce an NAD+ to an NADH, a carbon atom is released in carbon dioxide, and a coenzyme A binds to a two-carbon fragment.

Which statement correctly describes the difference between alcohol fermentation and lactic acid fermentation?

Lactic acid fermentation produces lactate, and alcohol fermentation produces ethanol.

Most of the electrons removed from glucose by cellular respiration are used for which of the following processes?

Most of the electrons removed from glucose by cellular respiration are used for reducing NAD+ to NADH in glycolysis and the citric acid cycle AND producing a proton gradient for ATP synthesis in the mitochondria. The full name for NAD+, nicotinamide adenine dinucleotide, describes its structure: The molecule consists of two nucleotides joined together at their phosphate groups. (Nicotinamide is a nitrogenous base, although not one that is present in DNA or RNA.) The enzymatic transfer of 2 electrons and 1 proton (H+) from an organic molecule in food to NAD+ reduces the NAD+ to NADH; the second proton (H+) is released. Most of the electrons removed from food are transferred initially to NAD+. Glucose and other organic fuels are broken down in a series of steps, each one catalyzed by an enzyme. At key steps, electrons are stripped from the glucose. Each electron travels with a proton—thus, as a hydrogen atom. The hydrogen atoms are not transferred directly to oxygen, but instead are usually passed first to an electron carrier, a coenzyme called NAD+. NAD+ is well suited as an electron carrier because it can cycle easily between oxidized (NAD+) and reduced (NADH) states. As an electron acceptor, NAD+ functions as an oxidizing agent during respiration.

After completion of the citric acid cycle, most of the usable energy from the original glucose molecule is in the form of __________.

NADH

In what molecule(s) is the majority of the chemical energy from pyruvate transferred during the citric acid cycle?

NADH & FADH2

During the energy payoff phase of glycolysis, __________.

NADH and ATP are produced

The ATP synthase in a human cell obtains energy for synthesizing ATP directly from which of the following processes?

The flow of H+ across the inner mitochondrial membrane through the ATP synthase enzyme

Which of the following pairs of pathways and their location in the cell is incorrectly matched?

The following pair of a pathway and its location in the cell is incorrectly matched: citric acid cycle: cytosol. The citric acid cycle does not occur in the cytosol. The citric acid cycle functions as a metabolic furnace that oxidizes organic fuel derived from pyruvate. Pyruvate is broken down to three CO2 molecules, including the molecule of CO2 released during the conversion of pyruvate to acetyl CoA. The cycle generates one ATP per turn by substrate-level phosphorylation, but most of the chemical energy is transferred to NAD+ and a related electron carrier, the coenzyme FAD (flavin adenine dinucleotide, which is derived from riboflavin, a B vitamin), during the redox reactions. The total yield per glucose from the citric acid cycle is six NADH molecules, two FADH2 molecules, and the equivalent of two ATP molecules. This pathway occurs in the matrix of the mitochondrion. Glycolysis occurs in the cytosol. The electron transport chain occurs on the cristae of the mitochondrion. Oxidative phosphorylation occurs in the mitochondrion.

During aerobic respiration, molecular oxygen (O2) is used for which of the following purposes?

at the end of the electron transport chain to accept electrons and form H20

Most of the NADH that delivers electrons to the electron transport chain comes from which of the following processes?

citric acid cycle

Which part of the catabolism of glucose by cellular respiration requires molecular oxygen (O2) and produces CO2?

combination of electron transport and citric acid cycle

Fermentation is essentially glycolysis plus an extra step in which pyruvate is reduced to form lactate or alcohol and carbon dioxide. This last step __________.

enables cell to recycle reduced NADH to NAD+

The function of cellular respiration is to __________.

extract usable energy from glucose

Cells must regulate their metabolic pathways so that they do not waste resources. What is the most common mechanism that regulates cellular respiration in most cells?

feedback inhibition go glycolysis

During the energy investment phase of glycolysis, __________.

glucose is phosphyrlated and split into 2 3 carbon molecules

In the overall process of glycolysis and cellular respiration, __________ is oxidized and __________ is reduced.

glucose, oxygen

Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule?

glycolosis

In which process is glucose oxidized to form two molecules of pyruvate?

glycolosis (Glycolysis is the process during which glucose is oxidized to form two molecules of pyruvate. The word glycolysis means "sugar splitting," and that is exactly what happens during this pathway. Glucose, a six-carbon sugar, is split into two three-carbon sugars. These smaller sugars are then oxidized and their remaining atoms rearranged to form two molecules of pyruvate.)

All of the processes involved in cellular respiration produce ATP. Which of the following processes produces the most ATP?

oxidative phosprylation

The energy from the electrons in NADH and FADH2 fuel what process in the electron transport chain?

the pumping of H+ across mitochondria

Muscle tissues make lactate from pyruvate to do which of the following?

to regenerate NAD+

A small amount of ATP is made in glycolysis by which of the following processes?

transfer of phosphate group from fragment of glucose to ADP by substrate level phosrylation