Metabolism & Free Energy

Question 1

Metabolism

Answer 1

All the chemical reactions occurring in an

organism

Question 2

Metabolic Pathways

Answer 2

a molecule is altered through a series of steps resulting in a specific product
-Catalyzed by enzymes

Question 3

Catabolic Pathways

Answer 3

release energy by breaking down molecules (exergonic)

Question 4

Anabolic Pathways

Answer 4

consume energy to build complicated molecules from simpler ones (endergonic)

Question 5

Energy

Answer 5

the capacity to cause change

Question 6

Types of Energy

Answer 6

kinetic, heat (thermal), potential, chemical

Question 7

Kinetic Energy

Answer 7

energy due to motion

-molecules move due to kinetic energy (ie passive transport)

Question 8

Heat (thermal) energy

Answer 8

affects the speed of molecular movement

-type of kinetic energy

Question 9

Potential Energy

Answer 9

based on position/location in surroundings

-stored energy

Question 10

Chemical Energy

Answer 10

potential energy stored in chemical bonds

Question 11

1st Law of Thermodynamics

Answer 11

Energy of the universe is constant so it can be transferred or transformed but not created or destroyed

Question 12

2nd Law of Thermodynamics

Answer 12

Every energy transformation leads to increased entropy

Question 13

Free Energy: definition

Answer 13

The portion of energy within a system that is free to do work (symbolized by G)

Question 14

Free Energy: equation

Answer 14

ΔG = ΔH – TΔS

Question 15

If ΔG is a negative value…

Answer 15

the process is spontaneous and exergonic & decreases the system’s free energy
– The final state of energy is less likely to change & is
more stable

Question 16

If ΔG is a positive value…

Answer 16

the process requires energy input (endergonic) & increases the system’s free energy

Question 17

Exergonic Reactions

Answer 17

Release energy (ΔG is negative)
– Spontaneous (this doesn’t indicate the required time)
– Ex: Cellular Respiration

Question 18

Endergonic Reactions

Answer 18

Absorbs energy (Δ G is positive)
– Nonspontaneous
– Ex: Photosynthesis

Question 19

Types of Cellular Work

Answer 19

mechanical, transport, chemical

Question 20

Mechanical Work

Answer 20

– Beating cilia
– Contracting muscles
– Moving chromosomes (by spindle fibers during mitosis/meiosis)

Question 21

Transport Work

Answer 21

Pumping substances across the cell membrane

and up the concentration gradient

Question 22

Chemical Work

Answer 22

– Pushing endergonic reactions

– Creating polymers

Question 23

To manage energy resources, cells use

Answer 23

energy coupling

Question 24

Energy Coupling

Answer 24

Exergonic processes drive endergonic ones
– ATP is responsible for most coupling in cells and
acts as the immediate power source for work

Question 25

How does ATP release energy?

Answer 25

The bonds between the phosphate groups are broken by hydrolysis creating an inorganic phosphate (Pi), ADP, and a release of energy
– The energy released from ATP is greater than most other molecules due to the high negative charge on the phosphate tail

Question 26

ATP & Energy Coupling

Answer 26

When ATP is hydrolyzed the free phosphate will be used to phosphorylate other molecules through use of an enzyme
• The phosphorylated molecule is less stable & more reactive & this change allows it to perform work
• This ties together an endergonic reaction with an exergonic one
– Used in cellular work

Question 27

Regeneration of ATP

Answer 27

ATP is a renewable resource…just add a phosphate group to ADP
– Requires energy from exergonic reactions in the cell
– Creating and breaking down ATP is known as the ATP Cycle
– performed during cellular respiration

Question 28

Enzyme

Answer 28

Catalytic proteins that speed up reactions without being consumed
– Without these many metabolic pathways would
be stuck for years (ex. sucrose hydrolyzed into
fructose and glucose)

Question 29

How do you recognize an enzyme?

Answer 29

• It will usually end with –ase
• Conveniently, its name will usually indicated
its substrate

Question 30

Activation Energy

Answer 30

Energy input required to start a metabolic process or chemical reaction (EA)
• Determines the rate of reaction
– Many EA are very high & transition states are rarely reached without assistance
– EA is directly proportional to the difficulty of breaking
apart bonds in the substrate

Question 31

Enzyme Action Curves

Answer 31

Enzymes lower EA, allowing molecules to absorb enough energy to transition at moderate temperatures & reasonable time frames
• They do NOT change the overall reaction (ΔG)

Question 32

Why isn’t heat used to speed up chemical reactions?

Answer 32

• Heat would increase the rate of all chemical reactions, wasting energy
• Proteins within cells can be denatured
• Enzymes are specific, reusable, and energy-efficient

Question 33

Enzymes-Substrate Interaction

Answer 33

While the enzyme and substrate are joined the
catalytic action converts the substrate to the
product(s)

Question 34

Enzyme specificity:

Answer 34

Each enzyme only catalyzes a specific substrate

Question 35

Active Site

Answer 35

the region of the enzyme that binds to the

substrate is the active site

Question 36

Induced fit

Answer 36

means active sites are not rigid but change shape slightly once chemical interactions occurs with the substrate to ensure a snug fit
(ie handshake)

Question 37

substrate

Answer 37

The molecule an enzyme will act upon

Question 38

How do enzymes lower activation energy?

Answer 38

1. Acting as a template for substrate orientation
2. Stressing the substrate by bending critical bonds
3. Providing a favorable mini environment, such as
   a pH pocket
4. Participating directly in the catalytic reaction by
   providing temporary covalent bonding

Question 39

point of saturation

Answer 39

A point of saturation can be reached by
enzymes & the only way to speed up creation
of the product is to create more enzymes

Question 40

temperature

Answer 40

– Reaction rates increase with higher temperatures because substrates collide with active sites more frequently (greater kinetic/heat energy)
– Only works to a point because too high of a temperature will cause enzyme denaturation

Question 41

pH

Answer 41

There are optimal pH range because too acidic an environment will cause denaturation
– Example: Pepsin works at pH 2 because functions in
our stomach & trypsin works at pH 12 works in the alkaline environment of the small intestine

Question 42

Cofactors

Answer 42

Non protein that all function in various ways to increase enzymatic productivity
– Inorganic cofactors examples are Cu, Fe, Zn
– Organic cofactors (coenzymes) such as vitamins

Question 43

Inhibitors

Answer 43

Chemicals that selectively inhibit the actions of enzymes
– Are reversible if bond with a weak bond, but can be irreversible if covalently bonded
Many inhibitors are naturally occurring in the cell

Question 44

Competitive Inhibitors

Answer 44

Resemble the normal substrate & compete for admission into active site
ex. penicillin

Question 45

Noncompetitive Inhibitors

Answer 45

Molecules that bind to a portion of the enzyme away
from the active site (allosteric site)
– Cause the enzyme to change shape & the active site becomes unreceptive
– Ex. DDT

Question 46

Feedback Inhibition:

Answer 46

A metabolic pathway is switched off by its end product
• Product inhibits an enzyme in its own pathway by noncompetitive inhibition
– Prevents unnecessary waste from excess products

Question 47

enthalpy

Answer 47

total energy (H) or a system
in a spontaneous reaction, enthalpy decreases

Question 48

entropy

Answer 48

(S)
the measure of the disorder/randomness of a system
in spontaneous reactions, entropy increases

Question 49

how does ΔG decrease?

Answer 49

decrease in enthalpy (H) or increase in entropy (S) and/or temperature