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Biochem (2016) > Lab Exam > Flashcards

Lab Exam Flashcards

1
Q

What does the Beer-Lambert law state?

A

Light absorption is proportional to the number of molecules of absorbing substance through which the light passes

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2
Q

What is the Beer-Lambert equation?

A

A = Elc

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3
Q

If wavelength and path length are unchanged, how can absorbance be changed?

A

A change in concentration

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4
Q

Does absorbance have units?

A

NO

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5
Q

Does ONPG in solution absorb light?

A

Nope

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6
Q

What happens when ONPG is mixed with lactase?

A

Lactase catalyzes the hydrolysis of ONPG into ONP and galactose

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7
Q

How do you find the new concentration of a substance that is diluted in another substance?

A

Original [ ] / (final volume/original volume of what is diluted)

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8
Q

What is the value of Kw at 25 C?

A

10^-14 M^2

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9
Q

____ allows a buffer solution to maintain a near constant pH

A

The presence of both the weak acid and its conjugate base

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10
Q

What will the pH of a solution be if HA and A are in equal concentrations?

A

pH will equal pKa

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11
Q

Define buffer capacity

A

How much acid/base a buffer can be subjected to before the pH of the buffer changes dramatically

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12
Q

If 2 buffers have equal volumes and pHs, which will have a greater buffer capacity?

A

The one with a higher concentration

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13
Q

Why is Bradford assay popular?

A

It is very rapid and can detect very small quantities of protein

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14
Q

What is the Bradford assay based upon?

A

The binding of CBB to the protein under acidic conditions

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15
Q

What occurs when protein is added to the Bradford reagent?

A

The small amount of the free blue form can bind to the protein

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16
Q

What types of interactions occur in a Bradford assay?

A
  • Ionic interactions with the side chains of basic residues

- Hydrophobic interactions with aromatic residues

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17
Q

Bradford assays can be monitored at ____ nm

A

595

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18
Q

What does a high Kf value mean?

A

A protein has a high affinity for its ligand

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19
Q

What is the Bradford assay graph equation?

A

Pt/Y = 1/nKf [1/1-Y] + Lt/n

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20
Q

How can you determine n?

A

Lt / y-intercept

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21
Q

How can you determine Kf?

A

1 / (n)(slope)

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22
Q

When are catalytic rate and substrate concentration almost proportional?

A

At low substrate concentration

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23
Q

What is Vmax?

A

The catalytic rate when the enzyme is saturated with substrate

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24
Q

What is the Michaelis-Menten rate equation?

A

Vo = Vmax[S] / Km + [S]

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25
Q

What is Km?

A

The substrate concentration that generates an initial rate equal to 1/2 of the maximum rate

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26
Q

Is Km dependent on enzyme concentration?

A

Nope

27
Q

How are the y-values determined for a Lineweaver-Burk plot?

A

1/Vo

28
Q

How are the x-values determined for a Lineweaver-Burk plot?

A

1/[S]

29
Q

How is the slope determined for a Lineweaver-Burk plot?

A

Km/Vmax

30
Q

How is the y-intercept determined for a Lineweaver-Burk plot?

A

1/Vmax

31
Q

How is the x-intercept determined for a Lineweaver-Burk plot?

A

-1/Km

32
Q

4-nitroaniline strongly absorbs light at ___ nm

A

410

33
Q

What does beta-galactosidase do?

A

Catalyzes the hydrolysis of lactose into glucose and galactose

34
Q

Why was ONPG used for the assays with E. coli and A. oryzae?

A
  • ONPG is an artificial substrate of A. oryzae and E. coli

- Its chromophore (ONP) strongly absorbs light at 420 nm, while the natural substrate lactose doesn’t absorb light well

35
Q

How is Kcat determined?

A

Vmax/Etotal

36
Q

Irreversible inhibitors form ______ with an enzyme

A

Stable covalent bonds

37
Q

Reversible inhibitors form ____ with an enzyme

A

Fleeting associations

38
Q

Why are simple sugars easily detected?

A

Their anomeric carbons are free to reduce oxidizing agents

39
Q

How can the amount of reducing sugars in a sample be quantified?

A

By measuring how much oxidizing agent is reduced

40
Q

What happens to DNS when it is reduced?

A

It undergoes a colour change

41
Q

How can you find concentration of reducing sugar?

A

Using the trendline equation, solve for x

42
Q

How can you find total mass of reducing sugar?

A

Multiply the concentration of reducing sugar by supernatant volume and dilution factor

43
Q

How can you find average reducing sugar %?

A

Mass of reducing sugar/sample mass * 100%

44
Q

How can you find average % starch content?

A

Dry mass of starch/sample mass * 100%

45
Q

What is transcription?

A

Conversion of DNA to RNA

46
Q

What is translation?

A

Conversion of RNA to an amino acid sequence

47
Q

What happens once DNA starts melting?

A

It becomes progressively easier to separate more of the DNA

48
Q

What is Tm?

A

The midpoint of the transition between the double and single-stranded forms

49
Q

DNA strongly absorbs light at ___ nm

A

260

50
Q

Single-stranded DNA absorbs _____ more light than double-stranded DNA because ______

A
  • 40%

- Decrease in base-base interactions

51
Q

What is standard redox potential?

A

A measure of a species affinity for electrons

52
Q

What does a high Eo value mean?

A

Higher affinity, so the compound can be more easily reduced

53
Q

A substance with a ___ Eo will give electrons to a substance with a ____ Eo

A

Low, high

54
Q

What is Eo proportional to?

A

The standard free energy of the reaction

55
Q

How does the mitochondrial electron transport chain transfer electrons?

A

From NADH and FADH2 through a sequence of redox reactions to oxygen, which acts as the final electron acceptor

56
Q

Does cytochrome c exist in an oxidized or reduced form?

A

Both (2+ or 3+)

57
Q

What is Eo’?

A

The standard reduction potential at pH = 7.0

58
Q

When is delta G = 0?

A

When the E value for one redox pair equals the E value for the other pair

59
Q

How can you find fraction reduced?

A

A(sample) - A(fully oxidized) / A(fully reduced) - A (fully oxidized)

60
Q

How can you find fraction oxidized?

A

1 - fraction reduced

61
Q

What are the first steps of the calculations for making a buffer?

A
  • Rearrange Henderson-Hasselbalch to solve for ratio of log [A-][HA]
  • Plug in pH and pKa values
  • Rearrange so [A] is by itself
  • Plug value for [A] into [A] + [HA}
  • Solve for [HA] then subtract that value from concentration of buffer to get [HA] and [A]
62
Q

For a competitive inhibitor, what will change?

A

Km but not Vmax

63
Q

For a non-competitive inhibitor, what will change?

A

Vmax but not Km

64
Q

For a uncompetitive inhibitor, what will change?

A

Km and Vmax

Biochem (2016) (8 decks)

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