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Cellular Biology > Transport: More Power! > Flashcards

Transport: More Power! Flashcards

Lecture 19

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1
Q

What is chemiosmotic coupling?

A

when the transport of ions releases free energy, allowing ATP to be synthesized

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2
Q

Describe the structure of the mitochondria

A

Shaped like a kidney bean
Outer membrane and an inner membrane with intermembrane space between.
Invaginations of the inner membrane form cristae

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3
Q

What is the inner mitochondrial membrane made of?

A

Inner membrane is made of 80% protein and cardiolipin.

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4
Q

What is cardiolipin? Classify it.

A

a major lipid component of the inner mitochondrial membrane
a phosphoglyceride (2 acyl chains and an amide, phosphate on the third carbon)
a dilipid (2 lipids attached to one another)
a phospholipid
provides a conical shape at sites of membrane curvature

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5
Q

Why is the inner mitochondrial membrane so impermeable to ions?

A

Because cardiolipin, one of the major components, has 4 hydrocarbon chains and is extremely hydrophobic. It is especially impermeable to protons.

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6
Q

What is the mitochondrial matrix?

A

everything within the inner mitochondrial membrane

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7
Q

Why does the mitochondria have its own DNA?

A

It likely evolved from a bacteria that formed a symbiotic relationship inside an ancient archaeal cell.

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8
Q

Does the mitochondrial genome encode all proteins required for the mitochondria’s structure?

A

No. Over 1000 of the genes required are encoded in the nucleus, synthesized in the cytosol, and imported into the mitochondria. However, the mitochondrial genome encodes 13 of its own genes.

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9
Q

Why have the 13 genes encoded in the mitochondrial genome remained in the genome instead of in the nucleus over evolutionary time?

A

They are very hydrophobic proteins, which would be difficult to import across the hydrophobic inner mitochondrial membrane (due to its high amount of cardiolipin).

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10
Q

How are new mitochondria created?

A

via fission; existing mitochondria divides in half using proteins just like a bacteria would

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11
Q

Where are mitochondria positioned within a cell?

A

close to the nucleus, where the majority of protein synthesis (and other energetic processes) is occurring, requiring ATP

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12
Q

Describe the structure of a sperm cell.

A

Sperm head has DNA.
Long tail in spiral pattern.
Midpiece largely made of mitochondria at the base of the head.

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13
Q

Why is there mitochondria in the midpiece of the sperm cell?

A

The molecular motors use lots of ATP along the length of the tail

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14
Q

Describe the process of chemiosmotic coupling (3+ steps).

A
  1. Pyruvate is imported into the mitochondria, combined with CoA to form acetyl coA
  2. Acetyl CoA enters the Krebs cycle.
  3. CO2 leaves the mitochondria and NAD and FAD are reduced (receive protons).
  4. NADH and FADH2 are used by the electron transport chain.
  5. Electrons can be used or combined with O and H to form water. As NADH and FADH2 are oxidized, the proton gradient is established and protons are released in the intermembrane space, creating a proton-motive force.
  6. F0F1 synthase phosphorylates ADP to form ATP.
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15
Q

What is the end product of glycolysis and what is it used for in chemiosmotic coupling?

A

Pyruvate is used to combine with CoA to create Acetyl CoA, which then enters the Krebs cycle.

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16
Q

Describe the structure of the electron transport chain.

A

Comprised of four large prrotein complexes associated with the inner mitochondria membrane.

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17
Q

Which way are protons released when the electron carriers are oxidized and CO2 is released?

A

A gradient is established across the inner membrane, creating high H+ concentration in the intermembrane space and low H+ concentration in the mitochondrial matrix.

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18
Q

During chemiosmotic coupling, describe the proton concentrations across the mitochondrial membranes.

A

Low concentration in the mitochondrial matrix; high concentration in the intermembrane space

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19
Q

How are reduced coenyzmes created for chemiosmotic coupling?

A

Acetyl CoA is formed and enters the citric acid cycle.

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20
Q

What pumps protons from the mitochondrial matrix into the intermembrane space?

A

The oxidation of coenzymes (NADH and FADH2)

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21
Q

What is the proton-motive force? What creates it?

A

The proton-motive force is a combination of the membrane potential and the concentration gradient established between the mitochondrial matrix and the intermembrane space by proton movement. It is created by the oxidation of coenzymes NADH and FADH2, which pumps protons into the intermembrane space.

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22
Q

Describe the concentration gradient that creates the proton-motive force.

A

Going down the concentration gradient, protons would be headed into the mitochondrial matrix from the intermembrane space.

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23
Q

Describe the membrane potential that creates the proton-motive force.

A

Positive charges line up at the intermembrane side of the inner membrane and negative forces line up at the mitochondrial matrix end of the inner membrane.

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24
Q

What 3 steps are required for ATP synthesis in the mitochondria?

A
  1. Acetyl CoA enters the Krebs cycle, producing reduced coenzymes and CO2.
  2. Oxidation of coenzymes pumps protons into the intermembrane space
  3. F0F1 synthase phosphorylates ADP to form ATP
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25
Q

What class of pump is the F0F1 pump?

A

F-class

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26
Q

What does the F0F1 pump do?

A

Moves protons from high to low concentration, from the intermembrane space to the mitochondrial matrix

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27
Q

How does the F0F1 pump pump protons into the mitochondrial matrix without a passageway?

A

Protons interact with polypeptides and are exchanged between amino acids. Protons trade off between amino acids until a proton gets close enough to be allowed into the mitochondrial matrix

28
Q

What kind of experiments demonstrated what was needed to produce ATP?

A

The inner membrane was isolated and in vitro reconstitution experiments were used to demonstrate the mechanism of the F0F1 pump.

29
Q

What experiment showed that F0F1 pumps were relevant to ATP synthesis?

A

A liposome (artificial membrane of a vesicle) was embedded with bacteriorhodopsin and an F0F1 pump and was placed in a solution with ADP and 4 inorganic phosphates. Light was turned on and the bacteriorhodopsin moved protons into the lumen of the liposome, creating a high lumenal concentration. The F0F1 pump transferred protons out of the lumen, while ADP and Pi were converted into ATP.
The detection of ATP indicated that protons were successfully moved from high to low concentration by the pump.

30
Q

Why was bacteriorhodopsin used experimentally to show that F0F1 was moving protons?

A

Bacteriorhodopsin is a protein that moves protons across a membrane if light shines on it.

31
Q

What is the diameter of the F1 subunit of the F0F1 pump?

A

100 nm

32
Q

What does the F0 subunit of the F0F1 pump do?

A

rotates, transferring the protons from the intermembrane space into the mitochondrial matrix

33
Q

What does the F1 subunit of the F0F1 pump do?

A

rotates, producing ATP

34
Q

What must happen before the F1 subunit is activated?

A

The gamma polypeptide (shaft) of the F0 subunit must rotate.

35
Q

Describe the experiment that proved the gamma subunit was rotating in the F0F1 pump.

A

The F1 subunit was isolated and placed upside down on a black slide with a gamma subunit. A fluorescently labeled actin filament was attached to the gamma subunit.
ATP was added, causing the gamma shaft to rotate, which was indicated by the actin filament spinning.

36
Q

What is the difference between F0F1 pump rotation in vitro and in vivo?

A

In vitro, during the experiment, ATP allowed the gamma subunit to rotate.
However, in vivo, ADP and Pi are used to produce ATP (ATP is not needed to cause the pump to rotate).

37
Q

Describe the structure of the F1 subunit of the F0F1 pump.

A

The F1 consists of a rotating gamma subunit stalk and 3 alternating alpha and beta subunits (lollypop shape).

38
Q

Why wouldn’t ATP form if you put ADP and Pi in a test tube? Why can ATP be produced by F0F1 pump?

A

The formation of high energy bonds in standardized conditions is energetically unfavorable.
Protons moving across the inner membrane, providing free energy that rotates pump’s gamma subunit. After, the binding pocket undergoes a conformational change that makes ATP synthesis exergonic.

39
Q

Describe the binding change model for ATP synthesis.

A
  1. ADP and Pi enter one of the alpha-beta binding sites.
  2. After a rotation of the gamma subunit, they become locked into the structure.
  3. After another rotation, the binding site enters a tight position.
  4. A reaction occurs at the binding site (without another rotation).
  5. After another rotation, the ATP produced in step 4 is released.
40
Q

What drives the exchange of ATP and ADP?

A

the proton-motive force

41
Q

Where is ATP formed?

A

in the mitochondrial matrix

42
Q

How does the ATP enter the intermembrane space?

A

Via the co-transport of ADP from the intermembrane space.

43
Q

Which direction does the proton motor force move ATP and ADP?

A

ADP is moved into and ATP is moved out of the mitochondrial matrix.

44
Q

Why does the ATP leave the mitochondrial matrix?

A

ATP is highly charged; it is energetically favorable for it to leave the matrix, enter the intermembrane space, and exit the outer membrane.
This is necessary because ATP must be used to energize other processes.

45
Q

What is oxidative phosphorylation?

A

Formation of ATP by coupling the exergonic oxidation of reduced coenzymes to the phosphorylation of ADP

46
Q

How does a bacterium generate ATP?

A

Proton pumps (or sometimes sodium pumps) run in reverse, synthesizing ATP (enzyme reactions can go in both directions; it depends on conditions).

47
Q

Why is oxygen useful as a final electron acceptor during cellular respiration?

A

With oxygen available as the terminal electron acceptor, pyruvate can be oxidized completely to CO2 instead of being used to accept electrons from NADH. This yields much more ATP than glycolysis alone.

48
Q

What happens during glycolysis?

A

Glucose is oxidated to pyruvate. Pyruvate is later combined with CoA to make acetyl CoA.

49
Q

How wide are mitochondria across?

A

0.5-1.0 micrometers

50
Q

How thick are the inner and outer membranes of the mitochondria?

A

about 7 nm thick

51
Q

Where is the F0 subunit located in the mitochondria? The F1 subunit?

A

The F0 subunit is embedded in the inner membrane. The F1 subunit is inside the mitochondrial matrix.

52
Q

Can electrons flow without possibility of ATP synthesis under normal conditions?

A

No. Electron transport and ATP synthesis are coupled under normal conditions.

53
Q

Describe respiratory control as it regards to ATP synthesis>

A

It is favorable to transport electrons and synthesize ATP when ADP concentrations are high (and ATP concentrations are low). The concentration of ADP controls the rate at which cellular respiration occurs; this keeps ATP synthesis related to the energy needs of a cell.

54
Q

Why does oxidative phosphorylation require a membrane-enclosed compartment?

A

Otherwise, the proton gradient that drives ATP synthesis could not be maintained.

55
Q

What happens to the protein gradient if ATP synthesis is uncoupled from electron transport?

A

The protons diffuse evenly across the membrane, destroying the gradient.

56
Q

Which typically has a higher pH, the intermembrane space or the mitochondrial matrix during respiration?

A

The matrix, due to the increased concentration of protons.

57
Q

For reconstitution experiments of the mitochondrial ATP-synthesizing system, what are the capabilities of intact mitochondria? Can they undergo electron transport? ATP synthesis?

A

Yes, both electron transport and ATP synthesis.

58
Q

For reconstitution experiments of the mitochondrial ATP-synthesizing system, what are the capabilities of submitochondrial particles? Can they undergo electron transport? ATP synthesis? ATPase activity (ATP hydrolysis)?

A

Yes, both electron transport and ATP synthesis. ATP is not used, it is synthesized.

59
Q

For reconstitution experiments of the mitochondrial ATP-synthesizing system, what are the capabilities of disassociated particles (separated from F1 subunit)? Can they undergo electron transport? ATP synthesis? ATPase activity (ATP hydrolysis)?

A

Yes, electron transport. No ATP synthesis. However, there is ATPase activity. ATP is hydrolyzed instead of synthesized.

60
Q

For reconstitution experiments of the mitochondrial ATP-synthesizing system, what are the capabilities of membranous factions (F1 subunits completely removed)? Can they undergo electron transport? ATP synthesis? ATPase activity (ATP hydrolysis)?

A

Yes, electron transport. No ATP synthesis and no ATPase activity (due to the complete removal of the F1 subunit). The functions were uncoupled.

61
Q

For reconstitution experiments of the mitochondrial ATP-synthesizing system, what are the capabilities of a soluble fraction with F1 particles (no membrane)? Can they undergo electron transport? ATP synthesis? ATPase activity (ATP hydrolysis)?

A

No electron transport and no ATP synthesis. However, ATPase activity occurs. ATP is used to rotate the F1 particles.

62
Q

For reconstitution experiments of the mitochondrial ATP-synthesizing system, what are the capabilities of reconstituted particles? Can they undergo electron transport? ATP synthesis? ATPase activity (ATP hydrolysis)?

A

Yes, electron transport and ATP synthesis occur. There is no ATPase activity (no ATP hydrolysis).

63
Q

Can the intact F0F1 complex run in reverse, hydrolyzing ATP instead of synthesizing?

A

Yes. In anaerobic bacteria, which produce ATP by fermentation, the ATP synthase works in reverse: it uses ATP to generate a proton gradient, which the bacterium uses for ion transport and for moving its swimming appendage (flagellum).

64
Q

Why does the gamma F1 subunit have to rotate?

A

to transmit the energy from the proton gradient at the F0 subunit to the F1 subunit (to synthesize ATP)

65
Q

Do each of the beta subunits of F1 make ATP at the same time?

A

Each undergo the same sequence of events and progress with each gamma rotation, but the sequences are temporally staggered.

Cellular Biology (23 decks)

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