DNA as genetic material Flashcards
what are the Mendelian laws of inheritance
-Segregation: genes come in pairs, and individuals only pass on one of these to their offspring
-Independent assortment: different genes are passed on separately from each other – inheritance of one does not depend on that of another
-Dominance: an individual with two alleles of a gene will express the dominant form
what’s the information needed to translate genetic material into physical characteristics
-Replication of information
-Storage of information
-Expression of information
-Variation by mutation
what did Walter Sutton and Theodor Boveri do
-asked the questions where is the genetic material carried
-quality of microscopes improved in the lead up to their investigation
what were Sutton’s observations in grasshoppers and Boveri’s observations in Ascaris worms
-Observed chromosomes in these species because their chromosomes are large and few in number, and therefore easy to see.
-Grouping in pairs and subsequent separation; reduction in chromosome number in gametes.
-Destruction of chromosomes stopped normal development of embryos
-Noticed that their observations were consistent with Mendel’s laws of heredity.
-Suggested that different combinations of chromosomes could cause variation
Sutton-Boveri chromosome theory of inheritance: a physical basis for Mendel’s independent assortment
-Chromosomes are required for embryonic development.
-Chromosomes carry Mendel’s “factors” (Sutton used the term gene).
-Chromosomes are linear structures with genes along them- need chromosomes to inherit genetic diseases
what’s the transforming principle: using streptococcus pneumoniae
-Streptococcus pneumoniae can cause pneumonia in humans and in mice.
-Only some strains cause infection and illness – Streptococcus can live in the nasal passages without causing disease- doesn’t always cause pneumonia due to different strains
-S strain - Smooth bacteria – polysaccharide coats – pathogenic- causes illness
-R strain – Rough bacteria – no polysaccharide coats – not pathogenic- doesn’t cause illness
-The polysaccharide coat forms a capsule that protects some strains from the host immune system.
results of the experiment of streptococcus strains and which causes infection and illness
-Inoculation with dead S bacteria + live R bacteria establishes infection. Bacteria taken from infected mice do have a polysaccharide capsule.
-Therefore, the R cells have undergone a “transformation”.
Some sort of hereditary material has passed from the S bacteria to the R bacteria, changing the genotype.
how was the streptococcus strain experiment handled
-kill S strain by heating them to high temperatures- heat killed
-this heat killed strain meant the bacteria was opened and left with molecules jumbled up in the cell which destroys al function- this is called extract and this extract doesn’t kill the mouse
-inject s bacteria into mice together with live R strain- individually these strains don’t cause infections but together they do as the smooth extract has effected the rough extract
what are the candidates for the transforming principle
-Protein- a popular choice because these are complex and abundant molecules
-DNA - many thought it was too simple because it only has 4 bases
-Polysaccharide
-Lipids
-RNA
Which molecules are responsible for the transformation that Griffith observed?
-Systematically destroyed each component of the S strain extract using enzymes that specifically digest each type of molecule
-before combining with live R bacteria to test for transformation.
for the bacteria to be virulent in the transformation complex what’s required
-the DNA encoding for the enzymes to make the polysaccharide coat – but not the polysaccharides themselves
-this is for the mouse to live rather than dying from s strain
what does small pieces of DNA from the dead smooth cells being taken up and integrated into the genome of the rough cells entail of
-Lots of different pieces of DNA from the S cell extract, are being taken up by different individual R cells.
-Only the few cells that take up the gene coding for the polysaccharide capsule will become virulent.
-Other bacteria that have integrated different genes will not be virulent.
what did Alfred Hershey and Martha chase investigate
-which component of a bacteriophage is injected into bacteria
-What they knew:
The basics of the bacteriophage life cycle,
The basics of the chemical composition of DNA and proteins
what’s a bacteriophage
-A category of viruses
-All viruses require a host cell to reproduce. We can think of them as parasites.
-Host cell for bacteriophage is a bacterium.
what’s the bacteriophage T2 life cycle
-DNA genome; destruction of the host cell’s chromosome- so only contains viral genome
-Transcription and translation of viral genes and replication of the viral genome
-Assembly of new virus particles from DNA + protein subunits
what’s the outline of the experiment for bacteriophage genetic material testing
-Label bacteriophage DNA or protein with a radioactive isotope
-Infect unlabelled bacteria with radioactive phage
-Separate phage ghosts from infected bacteria
-Test bacteria and phage ghosts for radioactivity
-they knew DNA contained phosphate and that protein contained sulphur
what occurs in the first stage of bacteriophage genetic material testing: Label bacteriophage components with radioactivity
-32P and 35S are unstable isotopes of those elements. Can be detected by Geiger counter
-Growing bacteriophage in media containing 32P will yield phage containing radioactively labelled DNA
-Growing bacteriophage in media containing 35S will yield phage containing radioactively labelled protein
what occurs in the second stage of bacteriophage genetic material testing: Let the phage infect unlabelled bacteria
-They knew that only the genetic material entered the infected cell – the rest of the virus remained attached to the outside of the bacterial host.
what occurs in the third stage of bacteriophage genetic material testing: Disrupt in a blender
-To make “phage ghosts” fall off the bacteria. bacteria themselves remain intact.
what occurs in the fourth stage of bacteriophage genetic material testing: Centrifuge to separate phage and bacteria
-Separate by their weight (bacteria are heavier).
-So pellet contains bacteria (including the phage genetic material)
-Supernatant contains phage ghosts.
-Test both fractions for radioactivity with a Geiger counter.
what occurs in the fifth stage of bacteriophage genetic material testing: Are the bacteria or the phage labelled?
Where would you expect to retrieve the radiolabel :
= if the DNA were the infectious material
= if the protein were the infectious material.
-Remember, genetic material should end up inside the bacteria
bacteriophage: if the protein were genetic material
-for isotope 32P:
=phage component labelled - DNA
=phage ghost- label
=bacteria- no label
-for isotope 35S:
=phage component labelled- protein
=phage ghost- no label
=bacteria- label
bacteriophage: if DNA were the genetic material
-for isotope 32P:
=phage component labelled- DNA
=phage ghost- no label
=bacteria- label
-for isotope 35S:
=phage component labelled- protein
=phage ghost- label
=bacteria- no label
results of bacteriophage experiment
-it is the DNA that is being injected and directing the formation of new phage
