Midterm 2

Question 1

Metabolism

Answer 1

All of the chemical reactions happening in a cell
(anabolism and catabolism)
All organisms undergo both catabolic and anabolic processes

Microbial metabolisms have a huge impact on humans
can get energy from light, organic or inorganic molecules, etc

Question 2

Catabolism

Answer 2

Breakdown of materials
Starts with Large substrates - substrates comes from anabolism which uses small products from catabolism
In the process of breaking them down, energy is harvested, small products are produced
(small products produced factor into anabolism as they are built up into large macromolecules that are eventually broken down in catabolism)

Question 3

What is the chemical, transport, and mechanical components of metabolism

Answer 3

● Chemical work
○ Building biomolecules
● Transport work
○ Moving things in and out of a cell
● Mechanical work
○ Division
○ Motility
● Can convert energy into different forms (like three processes above)
○ But we cannot destroy energy
● Metabolism affects nearly all aspects of microbes

Question 4

What are the two different energy sources
(metabolism)

Answer 4

1. Chemical - chemotrophs
2. Light - Phototrophs

Question 5

What are the two different electron sources?
(Metabolism)

Answer 5

1. Organic - organic trophs
2. Inorganic - Lithotrophs

Question 6

Electrons can come from carbons, which groups of carbons do different types of organisms get their electrons from?

Answer 6

Autotrophs - carbon dioxide
Heterotrophs - other

break down or build up small building blocks, Need ATP and electrons

Question 7

Free Energy
What is it?

Answer 7

This is the energy available to do work
Free energy, G, drives reactions

Question 8

Free Energy
What is the standard?

Answer 8

Delta G naught is the standard free energy
Standard Conditions: pH 7.0, 1 atm pressure, 25 degree Celsius (298K), 1 M concentration of all reactants and products
+△G naught = the rxn is endergonic, not spontaneous
-△G naught = rxn is exergonic, spontaneous
△G=0 the system is in equilibrium

Standards let us compare certain things, therefore we use the same conditions for different reactions
Free energy tells us whether or not the reaction will proceed
Can compare reactions under standard conditions: values do not change, standard must be determines experimentally (real-world values)
Standard biochemical energy conditions includes pH 7 compared to normal standard
conditions
● Not going to have 1M in normal conditions

Standard value is important because it is experimentally determined and does not alter
○ Lets us compare different reactions under the same conditions ● Delta G (△G) is the actual cellular conditions
○ Includes the right concentrations
● Does not give us any information about reaction rates
● Tells us if a reaction will occur

Question 9

if △G naught is positive

Answer 9

the reaction if endergonic and is therefore not spontaneous
endergonic is unfavourable

Question 10

If △G naught is negative

Answer 10

the reaction is exergonic and therefore spontaneous
exergonic is favourable

Question 11

If △G = 0

Answer 11

the system is in equilibrium

Question 12

△G versus △G naught

Answer 12

△G, the free energy change describes whether a reaction will be spontaneous in the actual cellular conditions
(will it be spontaneous or require an input of energy)
General reaction: A + B ↔ C + D
△G = △Go’ + RT ln [C][D]/[A][B]
R = gas constant = 8.31 x 10^(-3)kJ/Kmol
T = 298K
Standard values do not change for a particular reaction - add modifiers to the equation to show what is actually happening in a cell
negative free energy is spontaneous
This equation takes into account the actual concentrations
cell does not usually have 1M of reactant and products

Question 13

△G reaction equation + constants

Answer 13

General reaction: A + B ↔ C + D
△G = △Go’ + RT ln [C][D]/[A][B]
R = gas constant = 8.31 x 10^(-3)kJ/Kmol
T = 298K

Question 14

Spontaneity of Reactions
What shows us this?

Answer 14

Exergonic reaction (negative △G → spontaneous)
- forward reaction is favourable

Endergonic reaction (positive △G → cannot occur spontaneously)
- not spontaneous

Question 15

Does △G rely on the reaction path?

Answer 15

○ Depends only on G (free energy) of reactants and products
○ △G provides no info on rate of reaction
○ Does not tell us how many steps
○ Delta G (△G) has no effect on the reaction rate
○ Even if something is very exergonic, it can be very slow in the cell

Question 16

Can we tabulate the free energy of common substances?

Answer 16

Yes tabulated in table 3.3
● If organisms uses one of these substances as a food source, we can see how much energy they may have for work
○ E.g. glucose has a more negative free energy than acetate
■ More work can be done (more available energy)

Question 17

Discuss Gibbs free energy at equilibrium
concentration of products?
equations?
Constants?

Answer 17

At equilibrium, △G is zero (△G = 0)
the concentration of all reactants and products are unchanging
○ The reaction is not being driven in one direction or the other
○ Rate of the forward reaction is the same as the rate of the reverse reaction
△G’ can be determined experimentally (that’s how we determine all these values)
G°’ = -RT lnK’eq
○ Can only be used at equilibrium
○ G°’ = -2.303 RT log10K’eq
Equilibrium constant is:
○ Above 1 - favours products
○ Below 1 - favours reactants
K’eq = [C][D]/[A][B]
○ This is the equilibrium constant
○ Tells us if there are more products or reactants at equilibrium (i.e. what side is
more favoured)
○ It is a constant, it does not change
○ Lets us see if our reaction is favorable or not
■ Linked to the standard free energy
○ Determined experimentally
○ When that reaction goes to completion, it tells us the ratio of products to
reactants

Question 18

Equations and constants for Gibbs free energy at equilibrium

Answer 18

G°’ = -RT lnK’eq
○ Can only be used at equilibrium
○ G°’ = -2.303 RT log10K’eq
Equilibrium constant is:
○ Above 1 - favours products
○ Below 1 - favours reactants
K’eq = [C][D]/[A][B]
○ This is the equilibrium constant
(review example p. 14 in section 2)

Question 19

What are the commonalities of metabolism?
(4)

Answer 19

1. ATP conserves energy from exergonic reactions, and this energy can be used to drive endergonic reactions
2. Metabolic reactions are organized in pathways and cycles
3. Metabolic reactions are catalyzed by enzymes or ribozymes
4. Oxidation-reduction reactions are important for energy conservation