Molecular basis of inheritance Flashcards
The length of the DNA is equal to
the number of nucleotides present in it
A nucleotide consists of
A nitrogenous base, phosphate group, and a pentose sugar
The nitrogenous bases are
Purines and Pyrimidines
Purines and Pyrimidines are
Purines - Adenine and Guanine
Pyrimidine - Cytosine, Thymine, Uracil
DNA as an acidic substance (Nuclien) was first identified by
Friederich Meishcer
Who proposed the Double Helix
James Watson and Francis Crick, 1953
(based on the X-rays by Maurice Wilkins and Rosalind Franklin)
What are the salient features of the Double helix structure
(i) It is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside.
(ii) The two chains have antiparallel polarity
(iii) The bases of the two strands are paired through hydrogen bonds forming base pairs.
(iv) The two chains are coiled in a right-handed fashion.
(v) The plane of one base pair stacks over the other in a double helix.
Packaging of DNA Helix in eukaryotes
There is a set of positively charged, basic proteins called histones. A protein acquires a charge depending upon the abundance of amino acid residues with charged side chains. Histones are rich in the basic amino acid residues lysine and arginine. Both amino acid residues carry positive charges in their side chains. They are organized to form a unit of eight molecules called histone octamer. The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called a nucleosome. [There’s more but I’m lazy]
In a typical nucleus, some regions of chromatin are loosely packed and are referred to as
Euchromatin
The densely packed chromatin that stains dark are called as
Heterochromatin
What is the Transforming principle
In 1928, Frederick Griffith, in a series of experiments noticed that when Streptococcus pneumoniae is grown on a culture plate some produce smooth shiny colonies while others produce rough colonies. This is because the S strain bacteria have a mucous coat, while the R strain does not. Mice infected with the S strain die from a pneumonia infection but the mice infected with the R strain are not infected. Griffith observed that heat-killed S strain bacteria did not kill the mice. When he injected a mix of heat-killed S strain bacteria and live R bacteria, the mice died. the S strain had enabled the R strain to develop a smooth polysaccharide coat and became virulent. This is due to the transfer of genetic material.
How did they prove DNA was the genetic material (transforming principle)
Oswald Avery, Colin MacLeod, and Maclyn McCarty purified biochemicals from the heat-killed S cells to see which ones could transform live R cells into S cells. DNA alone from S bacteria caused the R strain to transform. They noticed the protein-digesting enzymes and RNA-digesting enzymes did not affect transformation.
