Lab Exam

Question 1

What does the Beer-Lambert law state?

Answer 1

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

Question 2

What is the Beer-Lambert equation?

Answer 2

A = Elc

Question 3

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

Answer 3

A change in concentration

Question 4

Does absorbance have units?

Answer 4

NO

Question 5

Does ONPG in solution absorb light?

Answer 5

Nope

Question 6

What happens when ONPG is mixed with lactase?

Answer 6

Lactase catalyzes the hydrolysis of ONPG into ONP and galactose

Question 7

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

Answer 7

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

Question 8

What is the value of Kw at 25 C?

Answer 8

10^-14 M^2

Question 9

____ allows a buffer solution to maintain a near constant pH

Answer 9

The presence of both the weak acid and its conjugate base

Question 10

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

Answer 10

pH will equal pKa

Question 11

Define buffer capacity

Answer 11

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

Question 12

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

Answer 12

The one with a higher concentration

Question 13

Why is Bradford assay popular?

Answer 13

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

Question 14

What is the Bradford assay based upon?

Answer 14

The binding of CBB to the protein under acidic conditions

Question 15

What occurs when protein is added to the Bradford reagent?

Answer 15

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

Question 16

What types of interactions occur in a Bradford assay?

Answer 16

• Ionic interactions with the side chains of basic residues

- Hydrophobic interactions with aromatic residues

Question 17

Bradford assays can be monitored at ____ nm

Answer 17

595

Question 18

What does a high Kf value mean?

Answer 18

A protein has a high affinity for its ligand

Question 19

What is the Bradford assay graph equation?

Answer 19

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

Question 20

How can you determine n?

Answer 20

Lt / y-intercept

Question 21

How can you determine Kf?

Answer 21

1 / (n)(slope)

Question 22

When are catalytic rate and substrate concentration almost proportional?

Answer 22

At low substrate concentration

Question 23

What is Vmax?

Answer 23

The catalytic rate when the enzyme is saturated with substrate

Question 24

What is the Michaelis-Menten rate equation?

Answer 24

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

Question 25

What is Km?

Answer 25

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

Question 26

Is Km dependent on enzyme concentration?

Answer 26

Nope

Question 27

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

Answer 27

1/Vo

Question 28

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

Answer 28

1/[S]

Question 29

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

Answer 29

Km/Vmax

Question 30

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

Answer 30

1/Vmax

Question 31

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

Answer 31

-1/Km

Question 32

4-nitroaniline strongly absorbs light at ___ nm

Answer 32

410

Question 33

What does beta-galactosidase do?

Answer 33

Catalyzes the hydrolysis of lactose into glucose and galactose

Question 34

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

Answer 34

- 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

Question 35

How is Kcat determined?

Answer 35

Vmax/Etotal

Question 36

Irreversible inhibitors form ______ with an enzyme

Answer 36

Stable covalent bonds

Question 37

Reversible inhibitors form ____ with an enzyme

Answer 37

Fleeting associations

Question 38

Why are simple sugars easily detected?

Answer 38

Their anomeric carbons are free to reduce oxidizing agents

Question 39

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

Answer 39

By measuring how much oxidizing agent is reduced

Question 40

What happens to DNS when it is reduced?

Answer 40

It undergoes a colour change

Question 41

How can you find concentration of reducing sugar?

Answer 41

Using the trendline equation, solve for x

Question 42

How can you find total mass of reducing sugar?

Answer 42

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

Question 43

How can you find average reducing sugar %?

Answer 43

Mass of reducing sugar/sample mass * 100%

Question 44

How can you find average % starch content?

Answer 44

Dry mass of starch/sample mass * 100%

Question 45

What is transcription?

Answer 45

Conversion of DNA to RNA

Question 46

What is translation?

Answer 46

Conversion of RNA to an amino acid sequence

Question 47

What happens once DNA starts melting?

Answer 47

It becomes progressively easier to separate more of the DNA

Question 48

What is Tm?

Answer 48

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

Question 49

DNA strongly absorbs light at ___ nm

Answer 49

260

Question 50

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

Answer 50

- 40% | - Decrease in base-base interactions

Question 51

What is standard redox potential?

Answer 51

A measure of a species affinity for electrons

Question 52

What does a high Eo value mean?

Answer 52

Higher affinity, so the compound can be more easily reduced

Question 53

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

Answer 53

Low, high

Question 54

What is Eo proportional to?

Answer 54

The standard free energy of the reaction

Question 55

How does the mitochondrial electron transport chain transfer electrons?

Answer 55

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

Question 56

Does cytochrome c exist in an oxidized or reduced form?

Answer 56

Both (2+ or 3+)

Question 57

What is Eo'?

Answer 57

The standard reduction potential at pH = 7.0

Question 58

When is delta G = 0?

Answer 58

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

Question 59

How can you find fraction reduced?

Answer 59

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

Question 60

How can you find fraction oxidized?

Answer 60

1 - fraction reduced

Question 61

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

Answer 61

- 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]

Question 62

For a competitive inhibitor, what will change?

Answer 62

Km but not Vmax

Question 63

For a non-competitive inhibitor, what will change?

Answer 63

Vmax but not Km

Question 64

For a uncompetitive inhibitor, what will change?

Answer 64

Km and Vmax