Bioenergetics & Enzymes Unit 4

Question 1

Define metabolism.

Answer 1

Consists of all the chemical reactions by which organisms transform matter & energy

Question 2

What two(2) metabolic pathways are there?

Answer 2

Catabolic pathways, and Anabolic pathways

Question 3

Define catabolic pathways.

Answer 3

The release of energy by breaking down complex molecules into simpler molecules (cellular respiration)

Question 4

Define anabolic pathways.

Answer 4

The consumption of energy by using simple molecules to build more complex molecules (photosynthesis)

Question 5

What is free energy?

Answer 5

Any available energy to do work

Question 6

What is work?

Answer 6

Any change in motion or position, other than the change of random motions of particles (heat)

Question 7

What are the two(2) chemical reactions that have a characteristic ‘free energy change’?

Answer 7

Exergonic & endergonic

Question 8

Define Exergonic free energy change.

Answer 8

Reactions that release free energy, these occur spontaneously, w/o a source of free energy outside the system

Question 9

Define Endergonic free energy change.

Answer 9

Reactions that absorb free energy, but do not occur spontaneously. They must be coupled w/ a exergonic reaction, or process outside of the system

Question 10

What three(3) characteristics need to be known for a reaction?

Answer 10

Temperature, Heat released or absorbed, and the entropy change (increase or decrease of disorder)

Question 11

What are the two(2) different types of physical work in cells w/ definition?

Answer 11

Transport work, & mechanical work (both require a free energy source)

Question 12

What is an example of chemical work?

Answer 12

Linking glucose molecules together

Question 13

What is ATP?

Answer 13

(adenosine triphosphate, one of the four ribonucleotides) is used as one of the monomers in the synthesis of RNA, but also used as an energy carrier in cells, picking up energy from exergonic reactions and processes, and giving up some energy to endergonic reactions and processes to make them go.

Question 14

What type of reaction is the hydrolysis of ATP?

Answer 14

An exergonic reaction

Question 15

What does the hydrolysis reaction of ATP look like?

Answer 15

ATP + H2O–>ADP + Pi G’o= -30.5 kJ/mol

Question 16

Although the hydrolysis of ATP is exergonic, and therefore is a spontaneous reaction, the reaction has a high activation energy and will not happen without being catalysed by an enzyme. What is the name of this enzyme?

Answer 16

ATPases (speeds up reaction)

Question 17

What is the opposite reaction of ATP hydrolysis?

Answer 17

ATP synthesis

Question 18

What type of reaction is ATP synthesis?

Answer 18

Endergonic reaction

Question 19

What is the ATP cycle?

Answer 19

The linking of cellular exergonic and endergonic processes by ATP hydrolysis and ATP synthesis

Question 20

What kind of reaction can happen when an endergonic reaction is coupled w/ ATP hydrolysis?

Answer 20

An exergonic reaction

Question 21

What are enzymes, what do they do, and give an example.

Answer 21

Enzymes are proteins that catalyse biochemical reactions, increasing the reaction rate enormously. RNA molecules: ribozymes

Question 22

How do enzymes work to increase reaction time?

Answer 22

They lower the activation energy of the reaction

Question 23

Although enzymes do speed up reactions, what do they not affect?

Answer 23

The deltaG of reactions whether exergonic or endergonic

Question 24

Why are enzymes so important?

Answer 24

Cells can control what reactions happen and their rate by altering the identity and amount of the enzymes they produce

Question 25

Are enzymes selective of where they bind?

Answer 25

Yes, very, as they only bind with one or a few different substrates (active sites) where catalysis takes place

Question 26

What happens to the active site shape upon substrate binding w/ the enzyme?

Answer 26

It changes its shape, induced fit (conformational change)

Question 27

What happens to the enzyme and substrate post reaction?

Answer 27

They regenerate with no net change, further ready for more catalytic cycles

Question 28

What factors effect enzyme activity? (5)

Answer 28

Substrate concentration, pH, temperature, cofactors, & inhibitors/activators

Question 29

Are enzymes saturable? Explain why?

Answer 29

There are finite locations of active sites on an enzyme, they have a maximum rate of processing substrates

Question 30

Why is temperature so important to enzyme activity?

Answer 30

There is an optimal, to low and the reaction cannot happen or is slow. To high and the enzyme may not be able to react at all

Question 31

Why is pH important to enzyme activity?

Answer 31

There is an optimal pH, to low and its slow or doesn’t occur, to high and it also cannot take place

Question 32

What are enzyme cofactors?

Answer 32

Small non-proteinaceous molecules required by some enzymes for their catalytic activity (non-active alone)

Question 33

What are the molecules called that can turn down, or turn up enzyme activity?

Answer 33

Inhibitors & activators (competitive and non-competitive inhibitors for active site location)

Question 34

What is an allosteric enzyme?

Answer 34

An enzyme w/ four active sites

Question 35

Enzyme Info.

Answer 35

Enzymes act sequentially in regulated metabolic pathways. An example of a control circuit: the product of a pathway inhibits the first enzyme of the pathway (feedback inhibition).

Question 36

What are oxidation and reduction reactions?

Answer 36

Oxidation- the loss of electrons (either entire, or shares)

Reduction- the gain of electrons (either entire, or shares)

Question 37

How electrons often transferred?

Answer 37

Via H atoms (1 proton, 1 electron), least electronegative atom

Question 38

What compounds are common electron carriers?

Answer 38

NADH, NADPH, & FADH^2

Question 39

Why is electron transfer important in energy economy of the cell?

Answer 39

B/C electron transfer may absorb or release free energy during oxidation & reduction reactions

Question 40

What is the difference between energy transfer in the form of heat, and energy transfer in the form of work?

Answer 40

Energy transfer in the form of heat increases the random motion of particles such as molecules and atoms. Work, however, brings about any other kind of change, such as chemical work, transport work, and mechanical work.

Question 41

Thermodynamically speaking, how can ATP hydrolysis drive reactions that would not otherwise happen? How, in specific molecular terms, is this often done?

Answer 41

ATP hydrolysis is an exergonic process. When it is coupled with an endergonic process, the combined 􏰂G might be negative, and so the combined reaction would be thermodynamically favourable.

Question 42

Why do enzymes have saturation kinetics?

Answer 42

A given quantity of enzyme will have a finite number of active sites, each taking a certain amount of time to process substrates. When the substrate concentration reaches a high enough value that a new substrate molecule diffuses to the active site the moment the products from the previous catalytic cycle are ejected, further increases in substrate concentration will have no effect on the rate of reaction.

Question 43

a) Why does the rate of an enzyme-catalyzed reaction increase with increasing temperature up to the optimum temperature? b) Why does the rate of reaction fall when the optimum temperature is exceeded?

Answer 43

a) As the temperature rises, substrates diffuse into active sites more quickly, and the collisions of molecules are more violent; the activation
Bioenergetics and Enzymes - 10
energy is reached by a greater proportion of molecules at a given moment, so the reaction rate increases.
b) The enzyme denatures.

Question 44

What are the enzymes that catalyze ATP hydrolysis?

Answer 44

ATPases