Exam 3 A

Question 1

What is metabolism ?

Answer 1

is the sum of the chemical reactions in an organism.

Question 2

what is catabolism?

Answer 2

is the energy-releasing processes.-provides the building block and energy for anabolism/ fueling reactions energy-conserving reactions provide ready source of reducing power (electrons) generate precursors for biosynthesis

• fueling reactions
• energy-conserving reactions
• provide ready source of reducing power (electrons)
• generate precursors for biosynthesis

Question 3

Anabolism

Answer 3

is the energy-using processes.

• the synthesis of complex organic molecules from simpler ones
• requires energy from fueling reactions

Question 4

What is a metabolic pathway ?

Answer 4

• A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell.
• Metabolic pathways are determined by enzymes.
• Enzymes are encoded by genes.

Question 5

What is the collision theory?

Answer 5

• The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide.
• Activation energy is needed to disrupt electronic configurations.
• Reaction rate is the frequency of collisions with enough energy to bring about a reaction.
• Reaction rate can be increased by enzymes or by increasing temperature or pressure.

Question 6

Enzymes

Answer 6

• carry out reactions at physiological conditions so they proceed in a timely manner
• enzymes speed up the rate at which a reaction proceeds toward its final equilibrium

Question 7

The Mechanism of Enzyme Reactions

Answer 7

a typical exergonic reaction

A + B ® AB‡ ® C + D

transition-state complex –

resembles both the substrates and the products

Question 8

Enzymes lower activation energy

Answer 8

• activation energy – energy required to form transition-state complex
• enzyme speeds up reaction by lowering Ea

Question 9

How Enzymes Lower Ea

Answer 9

•by increasing concentrations of substrates at active site of enzyme
•by orienting substrates properly with respect to each other in order to form the transition-state complex
•two models for enzyme-substrate interaction
–lock and key and induced fit

Question 10

Enzymes usually tur over how many molecules per second

Answer 10

•The turnover number is generally 1-10,000 molecules per second.

Question 11

Structure and Classification of Enzymes

Answer 11

•protein catalysts
–have great specificity for the reaction catalyzed and the molecules acted on
•catalyst
–substance that increases the rate of a reaction without being permanently altered
•substrates
–reacting molecules
•products
–substances formed by reaction

Question 12

Structure and Classification of Enzymes

Answer 12

• some enzymes are composed solely of one or more polypeptides
• some enzymes are composed of one or more polypeptides and nonprotein components

Question 13

Structure and Classification of Enzymes

Answer 13

•apoenzyme
–protein component of an enzyme
•cofactor
–nonprotein component of an enzyme
•prosthetic group – firmly attached
•coenzyme – loosely attached
•holoenzyme = apoenzyme + cofactor

Question 14

Enzyme strcuture

Answer 14

.

Question 15

Important Coenzymes

Answer 15

• NAD+
• NADP+
• FAD
• Coenzyme A

Question 16

Coenzymes as Carriers

Answer 16

•often act as carriers, transporting substances around the cell

Question 17

Environmental Effects on Enzyme Activity

Answer 17

•enzyme activity is significantly impacted by
–substrate concentration
–pH
–temperature

Question 18

Effect of [substrate]
Michaelis-Menton Kinetics

Answer 18

• rate increases as [substrate] increases
• no further increase occurs after all enzyme molecules are saturated with substrate

Question 19

Effect of pH and Temperature

Answer 19

•each enzyme has specific pH and temperature optima
•denaturation
–loss of enzyme’s structure and activity when temperature and pH rise too much above optima

Question 20

Factors Influencing Enzyme Activity

Answer 20

•Enzymes can be denatured by temperature and pH

Question 21

Factors Influencing Enzyme Activity

Answer 21

enzyme activity increases at the reaches ph 7 then goes down

Question 22

Enzyme Inhibition

Answer 22

•competitive inhibitor
–directly competes with binding of substrate to active site
•noncompetitive inhibitor
–binds enzyme at site other than active site
–changes enzyme’s shape so that it becomes less active

Question 23

Ribozymes

Answer 23

•Thomas Cech and Sidney Altman discovered that some RNA molecules also can catalyze reactions
•examples
–catalyze peptide bond formation
–self-splicing
–involved in self-replication

Question 24

Regulation of Metabolism

Answer 24

• important for conservation of energy and materials
• maintenance of metabolic balance despite changes in environment

Question 25

Metabolic Regulation

Answer 25

•three major mechanisms
–metabolic channeling
–regulation of the synthesis of a particular enzyme (transcriptional and translational)
–direct stimulation or inhibition of the activity of a critical enzyme
•post-translational

Question 26

Metabolic Channeling

Answer 26

•differential localization of enzymes and metabolites
•compartmentation
–differential distribution of enzymes and metabolites among separate cell structures or organelles
–can generate marked variations in metabolite concentrations

Question 27

Post-Translational Regulation of Enzyme Activity

Answer 27

•two important reversible control measures
–allosteric regulation
–covalent modification

Question 28

Allosteric Regulation

Answer 28

•most regulatory enzymes
•activity altered by small molecule
–allosteric effector
•binds non-covalently at regulatory site
•changes shape of enzyme and alters activity of catalytic site
•positive effector increases enzyme activity
•negative effector inhibits the enzyme

Question 29

Allosteric Regulation

Answer 29

Question 30

Covalent Modification of Enzymes

Answer 30

•reversible on and off switch
•addition or removal of a chemical group (phosphate, methyl, adenyl)
•advantages of this method
–respond to more stimuli in varied and sophisticated ways
–regulation of enzymes that catalyze covalent modification adds second level

Question 31

Covalent Modification
Glutamine Synthetase

Answer 31

Attach Images

Question 32

Feedback Inhibition

Answer 32

•also called end-product inhibition
•inhibition of one or more critical enzymes in a pathway regulates entire pathway
–pacemaker enzyme
•catalyzes the slowest or rate-limiting reaction in the pathway

Question 33

Feedback inhibition

Answer 33

•each end product regulates its own branch of the pathway
•each end product regulates the initial pacemaker enzyme
•isoenzymes
–different enzymes that catalyze same reaction

Question 34

Factors Influencing Enzyme Activity

Answer 34

•Feedback inhibition

This is a mechanism to shut down the enzymes.

Substrate binds in the Active, the end product the product shuts down the , by the end product

If many products it can shut down the enzyme in the allosteric which causes a change in the shape which does not allow the substate to attach to the active site.

Question 35

What is the significance of the fact that regulatory enzyme are often located at a branch point of metabolic pathway

Answer 35

•Branch point of the metabolic point,
•
•It is a enegergy conserve meechanism to save as much energy as possible, usually the branch site is the point where it is the slowest- rate determining, if we can shut those off then we are going to shut down everything else

Question 36

Name three ways metabolic pathways may be regulated

Answer 36

• Feedback inhibition
• Metabolic channeling-same location in a cell
• Synthesis of an enzyme