Lecture 3: Bioenergetics and Homeostasis - Exam 3 Flashcards

1
Q

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

A

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).

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2
Q

What is a way to measure disorder in a system?

A

Entropy

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3
Q

In order to prevent entropy, what is required?

A

Work (energy input)

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4
Q

What is entropy?

A

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

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5
Q

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

A

Favored

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6
Q

What is Gibbs free energy (G)?

A

Amount of free energy available for work.

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7
Q

Free energy change (deltaG) = ?

A

deltaG = Gproduct - Gprecursor

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8
Q

Free energy change (deltaG) is the..?

A

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

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9
Q

What is the Cell’s goal?

A

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.

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10
Q

What are the two categories of biological reactions?

A

Catabolism and Anabolism

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11
Q

What are the two ways that cells can generate ATP?

A
  1. Substrate level phosphorylation
  2. Oxidative phosphorylation
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12
Q

What is substrate level phosphorylation? What is Oxidative phosphorylation?

A

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.

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13
Q

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

A

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

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14
Q

Describe the generation of electrical and chemical gradients.

A

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

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15
Q

What creates both electrical and chemical gradient?

A

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)

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16
Q

H+ pumping requires…?

A

Energy (from respiration, ATP hydrolysis, photosynthesis)

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17
Q

T or F. lipid membranes are permeable to ions.

A

False. Impermeable to ions

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18
Q

When is proton motive force created?

A

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

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19
Q

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

A

Conserved in the proton gradient that has been established.

20
Q

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

A

Electrical energy and chemical energy

21
Q

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

A

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

22
Q

What is electrical energy?

A

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

23
Q

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

A

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

24
Q

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

A

The energy required to translocate the proton to the outside.

25
Q

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

A

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

26
Q

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

A

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.

27
Q

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

A

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

28
Q

Remember the pH formula?

A

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

29
Q

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

A

In the concentration gradient

30
Q

Describe the utilization of PMF.

A

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+ )

31
Q

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

A

100

32
Q

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

A

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

33
Q

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

A

Break ; Make
Reversible

34
Q

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

A

ATP Synthase

35
Q

Describe proton flow in ATP Synthase.

A

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.

36
Q

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

A

-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

36
Q

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

A

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

36
Q

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

A

3

37
Q

What is a Bacteriorhodopsin? Who has it?

A

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.*

38
Q

What is a retinal?

A

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

39
Q

What is pH homeostasis?

A

Many enzymes function at neutral pH.

40
Q

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

A

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

41
Q

How is the regulation of cytoplasmic pH controlled?

A

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

42
Q

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

A

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

43
Q

How does an acidic and alkaline environment affect PMF?

A

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)