Chapter 10 Assignment

Metabolic pathways can be regulated in three major ways. Select the correct methods of metabolic pathway regulation from the choices below.

-Post-translational regulation of enzyme activity -Regulation of protein expression -Separate distribution of enzymes and metabolites in the cell

Review your knowledge of how enzyme activity is affected by substrate concentration by selecting the correct statements concerning enzyme activity at low substrate concentrations.

-contact between enzyme and substrate is rare -enzyme makes product slowly

Arrange the following electron acceptors in the proper order in which they participate in the electron transport chain.1 = Cytochrome c 2 = Oxygen 3 = Cytochrome c oxidase

132

The most commonly used form of cellular energy is the nucleoside triphosphate

ATP

ATP has a high phosphate transfer potential because it readily donates a phosphoryl group to other molecules. From your understanding of substrate-level phosphorylation, compare ATP's phosphate transfer potential to other molecules by choosing the correct statement below.

ATP has a higher phosphate transfer potential than glucose 6-phosphate and lower than phosphoenolpyruvate (PEP).

In living organisms, ATP is the most commonly used practical form of energy. Review your knowledge of the structure of ATP by analyzing its components.

ATP is composed of adenine and the pentose sugar ribose and three phosphates.

ATP is formed by exergonic reactions and then used to drive endergonic reactions creating the cell's energy cycle. Classify the labels below to demonstrate understanding of the cell's energy cycle.

ATP used: Chemical, Mechanical, and Transport Work ATP formed: aerobic respiration, phototrophy, fermentation

Check all of the answers that apply to positive and negative effector molecules.

Allosteric effectors bind to the regulatory site of an enzyme Positive effectors increase enzyme activity. Negative effectors decrease enzyme activity.

Choose the answer that does not apply to metabolic channeling.

Bacterial cells, having no nucleus or organelles, are not capable of metabolic channeling. (Transport of metabolites and coenzymes can be regulated between cell compartments. Enzymes and metabolites are differentially distributed among organelles according to the needs of the cell. Compartmentation allows similar metabolic pathways to run simultaneously but under separate regulatory mechanisms.)

From the following statements about biochemical pathways, pick the most descriptive true statement.

Biochemical pathways are very well organized and structured and they convert an initial substrate, via a series of steps, into an end product.

During cellular respiration, cells obtain energy from food molecules such as glucose by using which of the following reactions?

Cells obtain energy from glucose by using oxidation-reduction reactions.

Drag the descriptions to their corresponding class in order to examine the various types of work performed in a biological cell.

Chemical Work: Anabolism, Synthesis of macromolecules Transport Work: uptake of nutrients, maintaining ion balances Mechanical work: cell motility, cell division, movement of chromosomes

Which equation correctly represents the mechanism of enzyme function (Substrate = S, Product = P, Enzyme = E)?

E + S → E-S → E-P → E + P

Cells must perform three types of work in order to survive and multiply. Match the correct type of work to the statements below.

Energy for flagella movement and cell division is due to mechanical work Correct. Energy for nutrient acquisition and waste removal involves transport work Correct. Synthesis of a complex compound from two simpler compounds is an example of chemical work Correct.

Consider the biochemical pathway: A - E1 → B - E2 → C and select the correct statement(s) for enzyme 1.

Enzyme 1 can utilize only A as substrate.

Check all of the true statements concerning enzymes and ribozymes.

Enzymes are made of protein. Ribozymes are made of RNA. Enzymes demonstrate Michaelis-Menten kinetics. Ribozymes demonstrate Michaelis-Menten kinetics.

In the conjugate redox pair Fe3+ + e− → Fe2+

Fe2+ is the reducing agent while Fe3+ is the oxidizing agent In the conjugate redox pair Fe3+ + e− → Fe2+, Fe2+ is the electron donor and is thus the reducing agent.

Nucleoside triphosphates other than ATP also provide energy for metabolism. Match the metabolic process with the nucleoside triphosphate which provides the energy for the process from the choices below.

GTP Correctsupplies some of the energy used during protein synthesis. CTP Correctis used for energy during lipid synthesis. UTP Correctis used for the synthesis of peptidoglycan. ATP is not the only energy currency, other nucleoside triphosphates have major roles in metabolism. Guanosine 5'-triphosphate (GTP) supplies some of the energy used during protein synthesis. Cytidine 5'-triphosphate (CTP) is used during lipid synthesis, and uridine 5'-triphosphate (UTP) is used for the synthesis of peptidoglycan and other polysaccharides.

Demonstrate understanding of noncompetitive enzyme inhibitors by selecting correct characteristics of noncompetitive inhibitors below.

Includes heavy metals such as mercury binding alters enzyme shape Binds to the enzyme at a site different from the active site Noncompetitive inhibitors affect enzyme activity by binding to the enzyme at some location other than the active site.This alters the enzyme's shape, rendering it inactive or less active. These inhibitors are called noncompetitive because they do not directly compete with the substrate.

Which of the following is not a metabolic characteristic common to all organisms?

Microbes evolved to provide humans with chemical energy in the form of ATP. Microbes did not evolve to provide humans with ATP. All organisms metabolize for their own reproduction and survival of the species.

Which of the following chemical equations best describes the reduction of the coenzyme NAD+?

NAD+ +2H+ +2e- → NADH + H+

The electrons that are transferred through the electron transport system were initially transferred from _

NADH and FADH2

Consider the biochemical pathway: A - E1 → B - E2 → C. If enzyme 2 is inactive, which of the following compounds will accumulate?

Only compound B will accumulate

Ribozymes are important molecules that were discovered in the 1980s. Select the most complete true statement below concerning ribozymes.

Ribozymes are RNA molecules that catalyze reactions and have Michaelis-Menten Kinetics.

Consider allosteric enzymes and their regulatory activities when completing the sentences below.

The allosteric effector binds to the regulatory Correctsite. Binding of the allosteric effector to the enzyme causes a conformational change in the catalytic Correctsite. Changes in allosteric enzyme activity results from changes in enzyme affinity for its substrate Correct. Allosteric enzymes that bind a positive Correctallosteric effector increase enzyme activity.

Describe metabolic processes by completing each sentence with the correct term below.

The total of all chemical reactions in a cell is referred as metabolism Correct. Biosynthetic reactions that build new organic molecules are part of anabolism Correct. In contrast, the breakdown of organic molecules is part of catabolism Correct. The latter generate energy Correctthat can be captured. This energy is in the form of electrons that supply reducing power Correct.

To understand how enzymes work, complete the following statements.

To bring reacting molecules A and B together in the correct way to reach the transition state, activation energy Correctis required. The transition-state complex can then resolve to yield the products Correct. Enzymes accelerate reactions by lowering Correctthe activation energy. In the presence of an enzyme, equilibrium Correctis reached more rapidly due to the decrease in activation energy.

Which nucleotide triphosphate supplies the energy required for the synthesis of the complex bacterial cell wall polymer, peptidoglycan?

Uridine 5'- triphosphate UTP provides energy for the synthesis of peptidoglycan.

Consider the biochemical pathway used to synthesize the amino acid proline. A high concentration of proline will most likely lead to __________.

a decrease in proline production

ATP has a lower phosphate transfer potential than phosphoenolpyruvate but a higher transfer potential than glucose-6-phosphate. This means that _________.

a phosphate group can be readily removed from phosphoenolpyruvate and transferred to ADP during glycolysis

The difference between a prosthetic group and a coenzyme is that

a prosthetic group is firmly attached to the aopenzyme, whereas a coenzyme is loosely bound

Glutamine synthetase is an enzyme involved in nitrogen assimilation in E. coli. Regulation is mediated by the addition of a(n) _________ group to each of the 12 enzyme subunits.

adenylyl An adenylyl group in the form of adenylic acid binds to glutamine synthetase.

The activity of an allosteric enzyme is altered by a small molecule known as an _________ _________.

allosteric effector

posttranslational control

allosteric effector binds to regulatory site AMP binds to glutamine synthethase

During feedback inhibition, the inhibitor binds to the _

allosteric site of the enzyme being inhibited

In an electron tower, the electron donors with the most negative reduction potentials

are at the top and include glucose and NADH

In metabolic channeling, enzymes and metabolites are differentially distributed among separate cell structures or organelles and this different distribution is called

compartmentation

An inhibitor that directly competes with the substrate at an enzyme's catalytic site and prevents the enzyme from forming product is called a _________ inhibitor.

competitive A competitive inhibitor directly competes with the substrate at an enzyme's catalytic site and prevents the enzyme from forming product.

ATP is formed by exergonic reactions and then used to drive endergonic reactions so ATP is considered a link or _________ _________ between these reactions.

coupling agent

Allosteric regulation involves the action of an effector molecule that binds to the active site of an enzyme. By contrast, covalent modification involves the binding of a chemical group to the regulatory site of an enzyme, which changes the conformation of the active site. (T/F)

false Allosteric regulation involves the binding of a positive or negative effector molecule to the regulatory site of an enzyme which changes the conformation of the active site. By contrast, covalent modification involves the covalent binding of a particular chemical group to the enzyme.

The energy released from catabolic reactions is used to hydrolyze ATP into ADP and orthophosphate within the cell. (T/F)

false The energy released from catabolic reactions within the cell is used to synthesize ATP by either substrate-level or oxidative phosphorylation.

in a branching metabolic pathway, when an end product is in excess, the end product inhibits the _________ enzyme on the branch leading to its formation.

first

The amount of energy in a system (or cell) available to do useful work at constant temperature and pressure is ΔG or the change in _________ _________.

free energy The change in free energy (ΔG) is the amount of energy in a system (or cell) available to do useful work at constant temperature and pressure.

Because the reduction potential of the CO2/glucose conjugate redox pair is more negative than the Fe3+/Fe2+ conjugate redox pair, electrons flow _________.

from glucose, the donor, to the acceptor Fe3+

In an electron transport chain, the first electron carrier

has the most negative E'o and each successive carrier is slightly less negative

A complete enzyme, which consists of protein called the apoenzyme and a nonprotein part called a cofactor, is called a

holoenzyme

The electron transport chain in bacterial and archaeal cells is located in the plasma membrane, whereas eukaryotic electron transport chains take place in the _________ _________ membrane.

inner mitochondrial The electron transport chain in bacterial and archaeal cells is located in the plasma membrane, whereas eukaryotic electron transport chains take place in the inner mitochondrial membrane.

Metabolic channelling

localization of metabolites compartmentation

Regulatory enzymes can be switched on and off by reversible covalent modification, usually through the addition and removal of a particular chemical group such as a(n) _________ group.

methyl Regulatory enzymes can be switched on and off by reversible covalent modification. Usually this occurs through the addition and removal of a particular chemical group, typically a phosphoryl, methyl, or adenylyl group.

Pick the most complete answer below for regulation of a multibranched pathway. Regulation of a multibranched pathway can be due to feedback inhibition

of the initial enzyme, the branchpoint enzyme, and by the presence of isoenzymes

Enzymes lower the energy of activation required for a biochemical reaction to take place. They achieve this by

orienting the substrates such that they require less energy to reach the transition state

Enzymes act as catalysts and are made up of _________.

proteins

Allosteric enzymes have two separate binding sites: the catalytic site, which binds substrate, and the _________ site, which binds the allosteric effector.

regulatory Allosteric enzymes have two important sites: the catalytic site and the regulatory site. Substrate binds to the catalytic site; an allosteric effector binds to the regulatory site.

Peptide bond formation during protein synthesis is catalyzed by RNA molecules called

ribozymes

Some RNA molecules are able to catalyze a reaction that cuts out a fragment of their own nucleic acid molecule then joins the loose ends back together again. This describes the action of

ribozymes

regulation of gene expression

rna synthesis is downregulated translation is upregulated

Enzymes speed up cellular reactions by providing an active site for reacting molecules that are known as _________.

substrates

Enzyme activity is changed not only by substrate concentration but also by alterations in pH and _________.

temperature

In feedback inhibition, the inhibitor of the biochemical pathway is typically

the final product of the biochemical pathway In the process known as feedback inhibition, the end product of the pathway often inhibits a regulatory enzyme of the pathway.

It is feasible that a regulatory enzyme can be both allosteric and covalently modified. Having both levels of regulation allows for the allosteric effectors to exert varying effects depending on the nature and number of the covalently bound chemical groups (T/F)

true

The discovery of ribozymes was vital to our understanding of the origins of life since it provided an explanation for the evolution of coding and catalytic molecules. (T/F)

true