Lecture 3: Bioenergetics and Homeostasis - Exam 3

Question 1

What is the second law of thermodynamics? How do cells overcome it?

Answer 1

The 2nd Law of Thermodynamics states that closed systems spontaneously move toward equilibrium over time, or that nature moves from order to disorder in an isolated system.
In order to overcome this, ALL life MUST import energy to move toward order, or “negative entropy”
(Like releasing the energy trapped in macromolecules (food) or in sunlight to increase order).

Question 2

What is a way to measure disorder in a system?

Answer 2

Entropy

Question 3

In order to prevent entropy, what is required?

Answer 3

Work (energy input)

Question 4

What is entropy?

Answer 4

Measure of chaos or disorder.
The larger the value of S, the greater the chaos.
Favored reactions: deltaS > 0

Question 5

Reactions that cause chaos are _______ (favored/not favored) over biosynthetic reactions.

Answer 5

Favored

Question 6

What is Gibbs free energy (G)?

Answer 6

Amount of free energy available for work.

Question 7

Free energy change (deltaG) = ?

Answer 7

deltaG = Gproduct - Gprecursor

Question 8

Free energy change (deltaG) is the..?

Answer 8

Measurement of how much energy is released or required to do work.
- The more negative the deltaG, the more energy released = favored

Question 9

What is the Cell’s goal?

Answer 9

Harness the -deltaG released from breakdown (catabolic) reactions to drive biosynthetic (anabolic) reactions.
-Energy is stored as ATP or NAD(P)H or as PMF.

Question 10

What are the two categories of biological reactions?

Answer 10

Catabolism and Anabolism

Question 11

What are the two ways that cells can generate ATP?

Answer 11

1. Substrate level phosphorylation
2. Oxidative phosphorylation

Question 12

What is substrate level phosphorylation? What is Oxidative phosphorylation?

Answer 12

Substrate level: The formation of ATP by breaking down sugars, like glucose, into smaller molecular weight phosphorylated intermediated which in turn are used to synthesize ATP from ADP. Example: Glycolysis
Oxidative: Energy to synthesize ATP from ADP + Pi is derived from membrane potential = proton motor force (PMF)
- Electron transport dependent phosphorylation.

Question 13

Who proposed the chemiosmotic theory? What does it say, in a nutshell?

Answer 13

Dr. Peter Mitchell
It states: the coupling between energy-yielding reactions and energy requiring reactions in the membrane is via ion currents.

Question 14

Describe the generation of electrical and chemical gradients.

Answer 14

Electrons from oxidation reactions transferred successfully among membrane-associated e- carriers in the electron transport chain result in protons (H+) being pumped across membrane during
the e- transport

Question 15

What creates both electrical and chemical gradient?

Answer 15

H+ on the outside and OH- on the inside of the cell.
(electrical b/c protons carry a charge and chemical b/c of the difference in internal and external concentration creates a concentration gradient)

Question 16

H+ pumping requires…?

Answer 16

Energy (from respiration, ATP hydrolysis, photosynthesis)

Question 17

T or F. lipid membranes are permeable to ions.

Answer 17

False. Impermeable to ions

Question 18

When is proton motive force created?

Answer 18

A proton motive force is created when an exergonic reaction is coupled to the movement of protons across the cytoplasmic membrane.

Question 19

When bacteria translocate protons across the membrane to the outside surface, energy is…?

Answer 19

Conserved in the proton gradient that has been established.

Question 20

The energy in the proton gradient is what kind of energy?

Answer 20

Electrical energy and chemical energy

Question 21

PMF: The proton potential is due to a combination of?

Answer 21

membrane potential outside positive, and a change in pH, outside acid.

Question 22

What is electrical energy?

Answer 22

A positive charge has been moved to one side of the membrane, resulting in a charge separation and therefore a membrane potential .
-Outside = positive (A proton (H+) has been pumped out of the cell membrane
-Inside = negative

Question 23

PMF: When the proton moves back into the cell toward the negatively charged membrane surface, the membrane potential is…?

Answer 23

Dissipated (the stored energy is given up, energy is released) allowing work to be done.

Question 24

PMF: The amount of energy dissipated when the proton moves into the cell is equal to?

Answer 24

The energy required to translocate the proton to the outside.

Question 25

PMF: What is chemical energy (pH gradient, deltapH)?

Answer 25

Energy is require to move the proton across its concentration gradient.

Question 26

PMF: In order to generate a pH gradient, what must be conserved?

Answer 26

In order to generate a pH gradient, electrical neutrality must be conserved, so each proton must be pumped out with an anion, or there must be an ion exchanged via antiport.

Question 27

PMF: Since the external proton concentration is higher, what is necessary?

Answer 27

Energy is necessary to pump H+ across the membrane to the outside.

Question 28

Remember the pH formula?

Answer 28

pH = log10(1/[H+]) so,
higher H+ = lower pH (more acidic)

Question 29

PMF: The energy needed to pump H+ across the membrane to the outside is conserved where?

Answer 29

In the concentration gradient

Question 30

Describe the utilization of PMF.

Answer 30

Intake of H+ = release of stored energy (towards negative and
lower [H+] b/c H+ has been pumped out of the cytoplasm, the
cytoplasm has a more negative charge, and a more basic pH).
This Energy can be used for work (e.g., ATP Synthase, Flagellar
Rotation, etc.)
- A concentration gradient is possible for any ion (not just H+ )

Question 31

The membrane potential from a small number of protons moving across the cell membrane can be more than _____ mV!

Answer 31

100

Question 32

Once established, the energy from PMF can be used…?

Answer 32

To energize flow of other ions, or for ATP synthesis, flagellar rotation, solute transport, etc.

Question 33

ATP Synthase can either ____ ATP (ATPase) or _____ ATP (Synthase). It is _______!

Answer 33

Break ; Make
Reversible

Question 34

What is the MAJOR energy source for establishing delta p in fermenting bacteria?

Answer 34

ATP Synthase

Question 35

Describe proton flow in ATP Synthase.

Answer 35

H+ transverses the membrane at the interface of a and c polypeptides of the F0 rotor.
-Protons flow through the F0 rotor, driving a rotation that converts PMF into mechanical energy
-The F1 “coupling factor” is located on the inner surface of the membrane and is responsible for the catalytic parts of the enzyme.

Question 36

Describe the conformational changes at the catalytic sites due to rotation.

Answer 36

-When three H+ have entered the rotor, this causes the y (gamma) rod to turn, resulting in conformational change at the catalytic sites in the F1 (stator) subunit.
-The conformational change catalyzes the phosphate bond formation between ADP + Pi
- There are three conformational states of the Beta subunits
- Loose (ADP + Pi substrate binds loosely), Tight (tight substrate binding, the active catalytic site), Open (very low affinity for substrate),
- ATP is made spontaneously at site T
- ATP is released upon conformational change to an open catalytic site

Question 36

The F1 subunit is made of ___ different proteins. What specifically contains a catalytic site for ATP synthesis/hydrolysis?

Answer 36

5 ;
Each of the Beta polypeptides contain a catalytic site for ATP synthesis/hydrolysis.

Question 36

How many protons are required of the generation of one molecule of ATP?

Answer 36

3

Question 37

What is a Bacteriorhodopsin? Who has it?

Answer 37

It is an integral membrane protein usually found in two-dimensional crystalline patches known as “purple membrane,” which can occupy up to nearly 50% of the surface area of the archaeal cell. Halophilic Archaea have a unique light-powered proton pump, the bacteriorhodopsin.*

Question 38

What is a retinal?

Answer 38

Bacteriorhodopsin has 7 membrane helices that surround a chromophore called retinal. Retinal absorbs a photon from light, resulting in isomerization.
-This isomerization is the key event in proton pumping by bacteriorhodopsin.
Retinal isomerization results in a shift in protein configuration, allowing a proton to be pumped out.
-For every photon absorbed, 1 H+ is pumped from the cytoplasm across the membrane.
The proton gradient generated drives ATP synthesis by typical F1F0 ATP Synthase

Question 39

What is pH homeostasis?

Answer 39

Many enzymes function at neutral pH.

Question 40

No matter the environment, internal pH of the cytosol needs to be?

Answer 40

Maintained near neutral pH (1-2 pH units from 7).
-Acidophiles and alkaliphiles must, to some degree, neutralize the extreme pH
-Most enzymes have a narrow range pH

Question 41

How is the regulation of cytoplasmic pH controlled?

Answer 41

To a large extent, by controlling the flow of protons across the cell membrane.

Question 42

Remember, that PMF = what kind of gradient?
The proton potential is due to what?

Answer 42

Both electrical and pH gradient.
The proton potential is due to a combination of membrane potential, outside positive, and deltapH, outside acid.

Question 43

How does an acidic and alkaline environment affect PMF?

Answer 43

Acidophiles in pH 2 environment - has deltapH of 5.
-Internal more basic
-Requires an inverted membrane potential (small membrane potential, inside positive at low external pH)
-Inverted membrane potential maintained by higher K+ influx than proton efflux.
Alkaliphiles inn pH 11 environment - has deltapH of 2.5 if intracellular = 8.5
-internal more acidic
-to maintain pH homeostasis, they must always be brining protons into the cell.
-Na+/H+ antiporters
Alkaliphiles must use Na+ gradient for solute transport.
Solute transport driven by the sodium potential rather than the proton potential (which is low because of the inverted delta pH)