LECTURE 10

Question 1

why are ROS a danger for bacteria?

Answer 1

can hydrolyse DNA and RNA, which causes great damage

Question 2

how are those ROS formed?

Answer 2

Question 3

which is the most dangerous ROS?

Answer 3

the OH. radical
(hydroxyl radical)

Question 4

what are protective enzymes of obligate and facultative anaerobes?

Answer 4

superoxide dismutase (SOD) can deal with the superoxide radical by transforming it to oxygen and hydrogen peroxide

catalase hydrolyses hydrogen peroxide to water and oxygen

peroxidase takes hydrogen peroxide and NADH to make water and NAD+

there is no enzyme to protect from OH., so the bacteria want to deal with superoxide before it turns into the hydroxyl radical, bc after that it’s too late

Question 5

what are the different enzymes contents of different bacteria depending on their oxygen needs?

Answer 5

obligate aerobes: SOD and catalase
facultative anaerobes: SOD and catalase
aerotolerant anaerobe: SOD but no catalase
strict anaerobe: no SOD and no catalase
microaerophile: SOD and low levels of catalase

Question 6

what are microaerophiles?

Answer 6

need only a little bit of oxygen, but not too much

Question 7

how does the anaerobic jar work?

Answer 7

there is a gas generator envelope inside which supplies carbon dioxide and hydrogen
above there is a catalyst chamber with palladium pellets, which will catalyse the reaction of turning hydrogen and oxygen into water
this removes all the oxygen in the anaerobic jar
of course there are seals and lids and screws to keep it anaerobic
inside the anaerobic indicator strip, made of methylene blue, becomes colorless in the absence of oxygen

Question 8

what are conditions like for bacteria in a liquid medium?

Answer 8

all cells are in the same condition, liquid medium so it’s equally distributed

Question 9

what are the different conditions faced by bacteria on a petri dish based on their placement?

Answer 9

• cells in the center are in the stationary or death phase
• cells on the edge are actively growing (exponential phase)
• cells at the surface are in aerobic conditions
• cells under the surface are in anaerobic conditions

Question 10

what are two ways to measure how many bacteria you have?

Answer 10

• turbidity using a spectrophotometer (ew trauma)
• serial dilutions and then multiplying

Question 11

what is the formula to find the population number at the end of a time period, starting from one cell?

Answer 11

Question 12

what is the formula to find the population number at the end of a time period, starting from more than one cell?

Answer 12

Question 13

what is a gene?

Answer 13

DNA segment that codes for a protein, rRNA or tRNA

Question 14

what is the genome?

Answer 14

complete DNA sequence present in a cell or a virus

Question 15

what is the genotype?

Answer 15

the specific set of genes of an organism

Question 16

what is the phenotype?

Answer 16

observable characteristics

Question 17

sets of genes in eukaryote vs prokaryote

Answer 17

prokaryotes: haploid
eukaryotes: diploid

Question 18

what did griffith’s transformation experiment show?

Answer 18

two strains of streptococcus pneumoniae: smooth, pathogenic strain (has a capsule)
rough, non pathogenic, does not have a capsule
the capsule is the virulence factor
if you heat kill the S strain and put it into a mouse, the mouse survives because the cells are dead
if you add heat killed S strain and live R strain, the mouse will die
nonvirulent bacteria can be transformed to be pathogenic

Question 19

what did oswald t. avery et al show?

Answer 19

people used to believe proteins carried genetic information
this experiment showed that it was DNA

Question 20

if you did not add DNA to the mix, the R colonies would not be turned into S colonies

Answer 20

things they had added: polysaccharides, protein, RNA, protease, RNAase

Question 21

what is the hershey chase experiment?

Answer 21

took the T2 bacteriophage
in one they labelled the protein cap with radioactive sulfur, and in the other labelled DNA with radioactive phosphate

Question 22

what is the central dogma?

Answer 22

DNA carries genetic information
replication of DNA is needed for cell division
transcription creates single stranded copy of RNA from RNA
messenger RNA is used as a template for protein synthesis

Question 23

what are the two reactions that DNA can undergo?

Answer 23

replication and gene expression

Question 24

reminders on nucleic acids

Answer 24

Question 25

what is the strength of a DNA base pair H-bond relative to a covalent bond?

Answer 25

5% of the strength of a covalent bond
needs to be easy to open

Question 26

what are the dimensions of the DNA double helix?

Answer 26

one turn is 3.4nm (about 10 base pairs)
the width of DNA is 2.0nm

Question 27

how is the DNA organised in eukaryotic cells?

Answer 27

1. inside the nucleus
2. genome of 10^9 bp
3. numerous linear chromosomes
4. highly compacted and organised (chromatin)
5. associated with small proteins (histones)
6. generally no plasmids

Question 28

how is the DNA organised in prokaryotic cells?

Answer 28

1. no nucleus, anchored to cell membrane
2. genome of 10^6 bp
3. one circular chromosomes
4. only supercoiled
5. associated with small basic proteins (nonhistone)
6. contain plasmids

Question 29

how is eukaryotic DNA packaged?

Answer 29

nucleosome: (7mm) histone octamer and 146 base pairs of DNA
histone H1 binds to the linker region (14-100bp) and promotes the chromatin structure
DNA can be seen as a string of beads

Question 30

how many times is the DNA condensed in humans?

Answer 30

human genome is 1.8meters long but the cell nucleus is 6 micrometers in diameter
DNA is condensed 10,000 fold

Question 31

how many times is the DNA condensed in bacteria?

Answer 31

the bacterial chromosome is 1,000 times longer than the cell
10 times less condensed than the human
makes sense because bacterial cells divide a lot more, DNA needs to be more readily available