5.1 Energy Transformation and Metabolism

Question 1

What is cellular metabolism?

Answer 1

sum of all the chemical reaction that occur in a cell

Question 2

What is a significant part of cellular metabolism?

Answer 2

involves the breaking down and the building up of molecules

Question 3

What is catabolism?

Answer 3

the breaking down of molecules

Question 4

What is anabolism?

Answer 4

the building up (synthesis) of molecules

Question 5

What are reactants in a chemical reaction?

Answer 5

substances that participate in a reaction

Question 6

What are products in a chemical reaction?

Answer 6

substances that form as a result of a reaction

Question 7

How do you know if a reaction will proceed in the indicated direction?

Answer 7

using the concept of entropy, it is possible to state that a reaction will occur if it increases the entropy of the universe

HOWEVER, in cell biology, we d o not usually wish to consider the entire universe; we simply want to consider a particular reaction

therefore, cell biologists use the concept of free energy instead of entropy

Question 8

What is free energy (△G)?

Answer 8

amount of energy available, that is, energy that is “free” to do work after a chemical reaction has occurred

Question 9

How is the change in free energy after a reaction occurs calculated?

Answer 9

by subtracting the free energy content of the reactants from that of the products

Question 10

What does a negative result when calculating the change in free energy after a reaction mean?

Answer 10

that products have less free energy than the reactants, and the reaction will go forwards

Question 11

What is an exergonic reaction?

Answer 11

spontaneous and release energy

Question 12

What is an endergonic reaction?

Answer 12

requires an input of energy to occur

Question 13

Which reactions in the body are endergonic?

Answer 13

protein synthesis, nerve impulse conduction, muscle contraction

Question 14

What are endergonic reactions in the body (protein synthesis, nerve impulse conduction, muscle contraction) driven by?

Answer 14

the energy released by exergonic reactions

Question 15

What is ATP?

Answer 15

adenosine triphosphate

the common energy currency of cells, unstable and has high stored energy

Question 16

What happens when cells require energy?

Answer 16

they “spend” ATP

the more active the organism, the greater demand for ATP

Question 17

What is ATP constantly being generated from?

Answer 17

ADP (adenosine diphosphate) and a molecule of inorganic phosphate

Question 18

Why is a cell assured of a supply of ATP?

Answer 18

because glucose breakdown during cellular respiration provides the energy for the buildup of ATP in mitochondria

Question 19

How much free energy of glucose is transformed to ATP?

Answer 19

only 39%, the rest is lost as heat

Question 20

What are the biological advantages to the use of ATP as an energy carrier in living systems? (4)

Answer 20

• common universal energy currency because it can be used in many different types of reactions
• when ATP is converted to energy, ADP and inorganic phosphate, the amount of energy released is sufficient for a particular biological function, and little energy is wasted
• ATP breakdown can be coupled to endergonic reactions in a way that minimizes energy loss

Question 21

Describe an endergonic reaction.

Answer 21

creation of ATP from ADP and inorganic phosphate requires input of energy from other sources

ie. cellular respiration

Question 22

Describe an exergonic reaction.

Answer 22

hydrolysis of ATP releases previously stored energy, allowing the change in free energy to do work and drive other processes

ie. protein synthesis, nerve conduction, muscle contraction

Question 23

Describe the ATP cycle.

Answer 23

• in cells, ATP carries energy between exergonic reactions and endergonic reactions
• when a phosphate group is removed by hydrolysis, ATP releases the appropriate amount of energy for most metabolic reactions

Question 24

What is ADP?

Answer 24

more stable than ATP