LECTURE 10 Flashcards
why are ROS a danger for bacteria?
can hydrolyse DNA and RNA, which causes great damage
how are those ROS formed?
which is the most dangerous ROS?
the OH. radical
(hydroxyl radical)
what are protective enzymes of obligate and facultative anaerobes?
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
what are the different enzymes contents of different bacteria depending on their oxygen needs?
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
what are microaerophiles?
need only a little bit of oxygen, but not too much
how does the anaerobic jar work?
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
what are conditions like for bacteria in a liquid medium?
all cells are in the same condition, liquid medium so it’s equally distributed
what are the different conditions faced by bacteria on a petri dish based on their placement?
- 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
what are two ways to measure how many bacteria you have?
- turbidity using a spectrophotometer (ew trauma)
- serial dilutions and then multiplying
what is the formula to find the population number at the end of a time period, starting from one cell?
what is the formula to find the population number at the end of a time period, starting from more than one cell?
what is a gene?
DNA segment that codes for a protein, rRNA or tRNA
what is the genome?
complete DNA sequence present in a cell or a virus
what is the genotype?
the specific set of genes of an organism
what is the phenotype?
observable characteristics
sets of genes in eukaryote vs prokaryote
prokaryotes: haploid
eukaryotes: diploid
what did griffith’s transformation experiment show?
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
what did oswald t. avery et al show?
people used to believe proteins carried genetic information
this experiment showed that it was DNA
if you did not add DNA to the mix, the R colonies would not be turned into S colonies
things they had added: polysaccharides, protein, RNA, protease, RNAase
what is the hershey chase experiment?
took the T2 bacteriophage
in one they labelled the protein cap with radioactive sulfur, and in the other labelled DNA with radioactive phosphate
what is the central dogma?
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
what are the two reactions that DNA can undergo?
replication and gene expression
reminders on nucleic acids
what is the strength of a DNA base pair H-bond relative to a covalent bond?
5% of the strength of a covalent bond
needs to be easy to open
what are the dimensions of the DNA double helix?
one turn is 3.4nm (about 10 base pairs)
the width of DNA is 2.0nm
how is the DNA organised in eukaryotic cells?
- inside the nucleus
- genome of 10^9 bp
- numerous linear chromosomes
- highly compacted and organised (chromatin)
- associated with small proteins (histones)
- generally no plasmids
how is the DNA organised in prokaryotic cells?
- no nucleus, anchored to cell membrane
- genome of 10^6 bp
- one circular chromosomes
- only supercoiled
- associated with small basic proteins (nonhistone)
- contain plasmids
how is eukaryotic DNA packaged?
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
how many times is the DNA condensed in humans?
human genome is 1.8meters long but the cell nucleus is 6 micrometers in diameter
DNA is condensed 10,000 fold
how many times is the DNA condensed in bacteria?
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
