Notes 10/12

Notes from class

September 12, 2009

a. Hydrostatic pressure/atmospheric pressure
b. Oxygen
i. 20% of atmosphere on earth
ii. Toxic – Why is it toxic?
1. Inhibits growth of many kinds of bacteria
2. Antioxidant – any chemical that ‘soaks up’ free electrons
a. This helps prevent damage to DNA proteins caused by electrons bouncing around and breaking DNA strands/altering protein strands
3. Oxygen is very electronegative – attractive to electrons
a. So cell in environment with lots of oxygen is also in presence of a lot of electrons, electrons bounce around, break DNA, proteins
iii. Anaerobes
1. Strict vs. facultative
2. Strict
a. Cannot live in the presence of ANY oxygen
b. Ex. C. difficile
c. Environment where they can live:
i. Bottom of ocean possibly
ii. Deep in the soil
iii. Intestines
iv. Vagina
3. Facultative
a. Can live with or without oxygen
b. Ex. E. Coli
iv. Aerobes
1. Require oxygen to grow – same way we require oxygen to breathe, so our cells can divide
2. Electrons are going to the oxygen (terminal electron acceptor)
3. Environment cells – ours and all bacterial cells that live in normal oxygen must have mechanisms for fixing DNA and protein damage caused by electrons, oxygen
4. Use aerobic respiration as primary means for generating ATP – why require oxygen
a. Use identical ATP-generating mechanism (with oxygen as terminal electron acceptor) as our mitochondria do
b. Most skin normal flora are aerobes
i. Staph
ii. Additional bonus back up staph
Based on scientific findings, was it always the case that oxygen made up 20% of the atmosphere?
v. Other atmospheric requirements
1. Microaerophiles
a. Must have ~5% oxygen to grow, but die with more oxygen than that
b. If there’s more oxygen they can’t deal with the damage done by DNA
2. Capnophiles
a. Must have some amount of oxygen to grow and have 5-10% of Carbon dioxide to grow
i. Lungs is a good environment for these
ii. Almost all pneumonia-causing bacteria

Why does oxygen inhibit the growth of many kinds of bacteria? Why do other kinds of bacteria (and your mitochondria) need oxygen?

c. Temperature
i. Why do cells die when they are burnt?
1. Denatures proteins
ii. Psychrophiles
1. Grow best ~-5-10 degrees Celsius
a. Very cold
2. Lots unsaturated fats in membrane
a. Unsaturated fat: olive oil
3. Little G & C, lots A & T in DNA
a. Only a double bond so it is easier to break A & T bonds
iii. Mesophiles
1. Grow best ~20-35 degrees Celsius
a. All bacteria that live on/in human bodies pretty much have to be mesophiles
iv. Thermophiles & hyperthermophiles
1. Thermophiles
a. Live best ~60 degrees Celsius
i. Hot enough to give you a nasty burn
b. Lots of saturated fat membrane
i. Saturated fat: butter
c. Lots of G & C, little A & T in DNA
i. Takes more energy to break up G & C bonds because it’s a triple bond
ii. DNA double helix is more stable at high temperatures
2. Hyperthermophiles
a. Live best ~> 100 degrees Celsius
i. Boiling point at sea level
d. Environments of pH
i. Internal pH of ~7, no matter what sort of alkalophiles or acidophiles environments that they live in
ii. Acidophiles
1. Live best at low pH (1-3)
2. Virtually 100% of stomach ulcers are caused by H. pylori
a. Is happily in people’s stomachs because of the pH level
iii. Alkalophiles
1. Live best at high pH (10+)
Toxic Shock Syndrome – What is the relationship between having an aerobic environment or anaerobic environment in causation of TSS

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