MICR 200B Lab Quiz #1

Question 1

What reagents are added to LB medium for bacteriophage lambda cultivation?

Answer 1

Magnesium and maltose.

Question 2

What does LB stand for in LB medium?

Answer 2

Lysogeny broth.

Question 3

What type of medium is LB?

Answer 3

Supportive (general purpose).

Question 4

What is the advantage of selective media?

Answer 4

They can increase the relative numbers of a particular microorganism that would otherwise be present in very low numbers compared to the total number of bacteria.

Question 5

Why is the ability to generate solid media important?

Answer 5

It is the most effective way to isolate different microorganisms from each other.

Question 6

What concentration of agar is used to solidify liquid media?

Answer 6

1.5%.

Question 7

Why is agar a good solidifying agent?

Answer 7

• Indigestible by most microorganisms
• After melting, remains molten until ~45 °C
• After solidifying, won’t melt again until ~100 °C

Question 8

What concentration of agar is used to make phage overlay media?

Answer 8

0.7%.

Question 9

What concentration of agar is used to make semi-solid motility media (“sloppy”)?

Answer 9

0.3%.

Question 10

When is filtration typically used to sterilize culture medium?

Answer 10

For media supplements that would be destroyed by the high heat of an autoclave.

Question 11

Which destroys endospores: sterilization, disinfection, or sanitization?

Answer 11

Sterilization only.

Question 12

Define wild-type.

Answer 12

An organism or virus with the most common phenotype or genotype of its species (found in nature).

Question 13

Define mutant strain.

Answer 13

A strain of an organism or virus that manifests new or different characteristics (compared to the wild-type of its species) as a result of changes to its DNA.

Question 14

Define mutation.

Answer 14

Any change in the genetic information of a bacterium that makes it different from the most prevalent form, either in terms of a particular strain or a particular gene.

Question 15

Define spontaneous mutation.

Answer 15

A mutation occurring in the absence of any outside stimulus.

Question 16

Define induced mutation.

Answer 16

A mutation occurring as a result of a chemical or physical mutagen.

Question 17

Define conditional mutation.

Answer 17

A mutation creating changes in proteins that are only observable as changes in phenotype under specific conditions (e.g. change in temperature or growth medium).

Question 18

Define auxotroph.

Answer 18

A biochemical mutant with a mutation in an anabolic pathway such that it can no longer synthesize a certain nutrient.

Question 19

Define prototroph.

Answer 19

A microorganism that can synthesize the same nutrients as most members of its species and can grow on minimal media.

Question 20

Define substrate utilization mutant.

Answer 20

A mutant that has lost the ability to catabolize a particular substrate.

Question 21

Define resistance mutant.

Answer 21

A mutant that has gained the ability to grow in the presence of an antimicrobial compound, toxin, or pathogen that would otherwise be harmful to wild-type cells.