molecular basis of inheritance Flashcards
(22 cards)
haploid number of base pairs in human DNA
3.3 * 10^9 bp
lenght of a pitch
3.4 nm
no of base pairs in one pitch
roughly 10
stability of DNA
1) The 2’-OH group present in every nucleotide of the RNA polymer is a reactive group and makes RNA labile and easily degradable hence, RNA is reactive.
2) Double stranded structure of DNA makes it chemically less reactive and structurally more stable when compared to RNA. DNA being double stranded and having complementary strand further resists changes by evolving a process of repair
3) Thymine confers additional stability to DNA. DNA repair mechanisms exist. RNA contains uracil, which is a reactive group, in place of thymine making RNA less stable.
4) Both DNA and RNA mutate, Viruses containing RNA genome and having shorter life span, mutate and evolve faster whereas DNA mutates very slowly.
5) RNA is catalytic in nature, so it is reactive and unstable.
how are DNA organised in nucleoid prokaryotic cells
The DNA in nucleoid is organised in large loops held by positively charged proteins.
define nucleosome
Negatvely charged DNA is wrapped around positively charged around the positively charged histone octamer to form a structure called nucleosome.
how many bp of DNA helix in nucleosome
200 bp
criteria that genetic matieral must follow
1) it should be able to generate its replica
2) it should be stable chemically and structurally.
3) It should provide the scope for slow changes (mutation) that are required for evolution.
4) It should be able to express itself in the form of Mendelian Characters
5) It should be able to store information for characters
experiment to prove semiconservative DNA replication
1) Meselson and Stahl grew E.coli in a medium containing 15NH4Cl (N15 is the heavier isotope) as the only nitrogen source for many generations. The result was that N15 was incorporated into newly synthesised DNA. This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in Caesium chloride density gradient.
2) They transferred these cells into a medium with normal 14NH4Cl and took samples at various time intervals as the cells multiplied.
3) The DNA was extracted from the culture after 20 mins had a hyrbid or intermediate density and DNA extracted from the culture after another generation (after 40 mins), was composed of equal amounts of the hybrid DNA and light DNA.
what proteins required for chromatin packaging
chromatin packaging at higher levels require additional set of proteins called “non-histamine chromosomal proteins”
types of chromatin
1) euchromatin: transciptionally active, light stain, loosely packed
2) heterochromatin: inactive, densely packed, dark stain
what year and who did transforming princple?
1928, frederick griffith
conclusions of transforming principle
some ‘transforming principle’, transferred from the heat-killed S strain, had enable R strain to synthesiss a smooth polysaccharide coat and become virulent. This must be due to the transfer of genetic material.
who is behind biochemical characterisation of transforming principle
avery, macleod, mcCarty
results of biochemical characterisation of TP
1) DNA alone from S bacteria caused R bacteria to be transformed -> mice died (DNA from heat killed S + R + mice= dead)
2) Protein digesting enzymes (protease) and RNA digesting enzymes (RNAase) did not affect transformation so the transforming substance was not a protein or RNA. Digestion with DNAase did inhibit transformation, suggesting that DNA caused the transformation.
=> DNA is the hereditary material
UNEQUIVOCAL PROOF THAT DNA IS THE GENETIC MATERIAL PROVIDED BY WHO?
hershey and chase experiment
what is hersshey and chase experiment
grew some bacteriophages on a medium with radioactive sulphur and thus the bacteriophages had radioactive proteins and grew others on a medium with radioactive phosphorus and thus the bacteriophages had radioactive DNA.
1) Infection: radioactive phages were allowed to attach to the E.coli bacteria.
2) Blending: Viral coats were removed from the bacteria by agitating them in a blender.
3) Centrifugation: viral particles were seperated from bacteria by spinning them in a centrifuge
results of hershey and chase experiment?
1) Bacteria which was infected by radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria. (No radioactivity detected in the supernatant).
2) Bacteria which was infected by viruses with radioactive proteins were not radioactive which indicates that proteins did not enter the bacteria from the viruses. (Radioactrive sulphur detected in the supernatant)
experimental proof for semiconservativity of DNA`BY WHO?
meselson and stahl
why only one dna strand is copied for transcription into RNA?
1) If both strandss act as template, they would code for rna molecule with different sequences (complementary, but not identical) which in turn, if they code for proteins, the sequences of amino acids in the proteins would be different. Thus, one segment of DNA would code for 2 different proteins which complicates the genetic information transfer machinery.
2) 2 RNA molecules are simultaneously produced which are complemntary to each other, hence forming a double stranded RNA which would prevent RNA from being translated into a protein and the exercise of transcription would become a futile one.
types of cistron
polycistronic: multiple cistrons or structural genes with a common promotor and terminator present in prokaryotes and bacteria
monocistronic: (both eukaryotes and prokaryotes)ONE cistron within a promotor and terminator having interrupted coding sequences, the coding or expressed sequences called exons-which occur in processed or mature RNA- being interrupted by intervening sequences called introns that do not appear in mature or processed RNA i,e,. split gene arrangement.
steps of transcription
