MCBL Lab Lecture 5

What can UV light do?

260-265nm can be lethal since it’s the maximal absorption for DNA.

UV causes the formation of pyrimidine (C or T) dimers, leading to DNA replication errors. (Overexposure to sun)

What does Heat do?

Heat & water disrupts hydrogen bonds, denaturing macromolecules such as DNA & proteins.

Strategies to reduce heat damage

1. Heat shock esponse

2. Heat stability can be conferred by structural changes in macromolecules

3. Specific compounds can stabilize proteins.

What is Disc Diffusion Test (Antibiotic Efficacy)

Disks with specific drugs/antibiotics are placed on agar plates inoculated w/test microbes.

Traditional methods of identification.

Gram status, morphology, and physiological properties.

Bacterial Growth Curve

Four Phases

• Lag Phase

• Exponential Phase

• Stationary Phase

• Death Phase

Lag Phase

Period after inoculation & before exponential growth where cells do not immediately divide

Factors affecting Lag phase

Age of Culture

Growth Substrates

Environmental Changes

Log/exponential phase

Period characterizied by cell doubling across the cell population.

Equation for Log phase

Stationary Phase

Cells are live but death rate > production rate

Many cells stop growing

Subsrate limitation & waste accumulation

Cells are smaller

Death Phase

Loss of viable cells due to accumulation of toxins & byproducts of metabolism & absence of new nutrients.

Decline in cell #s highly variable & not predictable by any relationships

Accompanied by cell lysis.