Molecular Basis Of Inheritance Flashcards
DNA basics
- RNA in?
- length of DNA
- e.coli n bacteriophage
- structure of DNA
DNA genetic material most organisms. RNA it also act some viruses, mostly messenger adapter, structural some cases catalytic molecule. length of DNA no. of nucleotides. ex, a bacteriophage known as φ ×174 has 5386 nucleotides, Bacteriophage lambda has 48502 base pairs (bp), Escherichia coli has 4.6 × 106 bp, and haploid content of human DNA is 3.3 × 109 bp.
STRUCTURE-nb, pentose sugar,phosphate group. n b - Purines (A n G), and Pyrimidines (Cyto, Uracil and Thymi) Uracil is present in RNA instead Thymine
DNA linkage
- N.B with pentose?
- phosphate to 5’-OH ?
- 2 nucleisides are linked through?
- backbone in a polynucleotide chain is formed due to?
n.b is linked to pentose sugar through a N-glycosidic linkage to form nucleoside.phosphate group linked to 5’ -OH of a nucleoside through phosphoester linkage, a corresponding nucleotide is formed.
Two nucleotides are linked through 3’-5’ phosphodiester linkage to form a dinucleotide.n. A polymer thus formed has at one end a free phosphate moiety at 5’ -end of ribose sugar, which is 5’-end of polynucleotide chain. Similarly, at the other end of the polymer the ribose has a free 3’ -OH group which is referred to as 3’-end of the polynucleotide chain.
The backbone in a polynucleotide chain is formed due to sugar and phosphates. The nitrogenous bases linked to sugar moiety project from the backbone
RNA structure
In RNA, every nucleotide residue has an additional –OH group present
at 2’ -position in the ribose. Also, in RNA the uracil is found at the place of
thymine (5-methyl uracil, another chemical name for thymine).
DNA research
- DNA acidic or basic ?why?
- 1st identified by?
- then who did gave proper n why?
- what was the hallmark of thier proposition?
- this proposition was also based on ?
DNA ;acidic substance ;nucleus ;phosphate group
- first identified ;Friedrich Meischer in 1869.named ‘Nuclein’.
-but due to technical limitation in isolating a long polymer intact, the elucidation of structure of DNA remained elusive for a very long period of time. It was
only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, Double Helix model
-. One of the hallmarks of their proposition was base pairing between the two strands of polynucleotide chains. However, this proposition was
also based on the observation of Erwin Chargaff that for a double strandedDNA, the ratios btw A and T n G and C are constant and equals one
The salient features of the Double-helix structure of DNA are :- 1) 2) 3) 4) 5)
(i) It is made of two polynucleotide chains, the backbone is sugar-phosphate, and the bases project inside.
(ii) The two chains have anti-parallel polarity.
(iii) The bases in two strands are paired through (H-bonds) forming base pairs (bp). A;2H-bonds
with T from opposite strand and vice-versa. G is bonded C w 3 H-bonds.purine comes opposite to a pyrimidine. This generates approx uniform distance between the two strands .
(iv) The two chains are coiled in a right-handed fashion. The pitch is 3.4 nm ( 10-9 m) and there are roughly 10 bp in each.Consequently, the distance btw a bp in a helix is approx equal to 0.34 nm.
(v) The plane of one base pair stacks over the other in double helix. This,in addition to H-bonds,
stability of the helical structure
HOW DOES GENETIC INFORMATION FLOWS AND WHO PROPOSED THIS THEORY?
-in some viruses?
Very soon, Francis Crick proposed the Central dogma in molecular biology, which states that the genetic
information flows from DNA-RNA-Protein.
PACKAGING OF DNA -In prokaryotes -length of typical mammalian cell=? -length of e.coli? -in pro,is the DNA scattered throughout the cell? -do they have defined nucleus? -DNA -charge? -protein charge? -term? how is DNA organised in nucleoid?
-distance btw 2 consecutive bps 0.34 nm,length of DNA typical mammalian cell is by multiplying total no. of bp w/ distance btw 2 consecutive bp, i.e, 6.6 × 109 bp ×0.34 × 10-9m/bp), it approx is 2.2 m. it is far greater than the typical nucleus (approximately 10–6 m).
-If the length of E. coli DNA is 1.36 mm, can you
calculate the number of base pairs in E.coli?
-In prokaryotes, such as, E. coli, they don’t have a defined nucleus, the DNA is not scattered throughout the cell. DNA ( -ive charged) is held with some proteins ( +ive charges) in a region termed as ‘nucleoid’.
-The DNA in nucleoid is organised in large loops held by proteins.
PACKAGING OF DNA
- In eukaryotes(1)
- histone?residues?unit of how many molecules?term?
- what is nucleosome?
- a typical nucleus contains how many bp of DNA helix
- cromatin?
- nucleosomes in chromatin ____ structure .viewed under a _______ microscope
-In eukaryotes, much more complex. set of +ve charged, basic proteins ; histones. A protein gets charge depending on amino acids with charged side chains. Histones rich basic amino acid residues lysines and arginines. Both carry+ve charges on side chains.
- Histones are organised ; a unit of eight molecules ; histone octamer. The -ve charged DNA is wrapped around the +ve charged histone octamer to form
nucleosome. A typical nucleosome contains 200 bp of
DNA helix.
-Nucleosomes ; repeating unit of a structure in nucleus ; chromatin, thread-like stained (coloured) bodies seen in nucleus. The nucleosomes in chromatin are seen as ‘beads-on-string’ structure viewed electron microscope (EM) .
PACKAGING OF DNA
- in eukaryotes (2)
- the beads on sting are further coiled to?to form?at what phase?
- packaging of chromatin at higher level requires?
- euchoromatin?
- Heterochromatin?
- which is active and which in inactive/
The beads-on-string structure in chromatin is packaged to form chromatin fibers that are further coiled and condensed at m stage to form chromosomes. The packaging of chromatin at higher level requires additional set of proteins that collectively are referred to as Non-histone Chromosomal (NHC) proteins. In a typical nucleus, some region of chromatin are loosely packed (and stains light) and are referred to as euchromatin. The chromatin that is more densely packed and stains dark are called as Heterochromatin. Euchromatin is transcriptionally active chromatin, heterochromatin is inactive
THE SEARCH FOR GENETIC MATERIAL
- discovery of nuclein?
- By 1926, the quest for mechanism for genetic inheritance reached?
- who r the other scientists?
discovery of nuclein by Meischer; principles of inheritance- Mendel; almost same time, but DNA as a genetic material ;long to discover n prove. By 1926, the quest for mechanism for genetic inheritance reached molecular level. Previous discoveries by Gregor Mendel, Walter Sutton, Thomas Hunt Morgan and other narrowed the search to the chromosomes located in the nucleus of most cells. But what molecule was actually the genetic material, had not been answered.
Transforming Principle
-
In 1928, Frederick Griffith, experiments w/ Streptococcus pneumoniae (bacterium for pneumonia), witnessed a miraculous transformation in the bacteria. a living organism (bacteria) had changed in physical form. When Streptococcus pneumoniae (pneumococcus) bacteria grown on culture plate, some produce smooth shiny colonies (S) others produce rough colonies (R).because the S strain bacteria have a mucous (polysaccharide) coat, while R strain does not.
s strain—–) inject into mice—–) mice die(pneumonia)
R strain—–) inject into mice—–)mice alive
Transforming Principle
Griffith was able to kill bacteria by heating them.
S strain—–)inject into mice——)mice alive
(heat killed)
S strain
(heat killed)
+ —–)inject into mice—)mice die
R strain
(live)
he recovered living S bacteria from the dead mice. He concluded that the R strain bacteria had somehow been transformed by the heat-killed S strain bacteria. Some ‘transforming principle’, transferred from the heat-killed S strain, had enabled the R strain to synthesise a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material, the biochemical nature of genetic material not defined from experiments.
Biochemical Characterisation of Transforming Principle
Prior to the work of Oswald Avery, Colin MacLeod and Maclyn McCarty
(1933-44), the genetic material was thought to be a protein. They worked
to determine the biochemical nature of ‘transforming principle’ in Griffith’s
experiment.
They purified biochemicals (proteins, DNA, RNA, etc.) from the
heat-killed S cells to see which ones could transform live R cells into
S cells. They discovered that DNA alone from S bacteria caused R bacteria
to become transformed.
They also discovered that protein-digesting enzymes (proteases) and
RNA-digesting enzymes (RNases) did not affect transformation, so the
transforming substance was not a protein or RNA. Digestion with DNase
did inhibit transformation, suggesting that the DNA caused the
transformation. They concluded that DNA is the hereditary material, but
not all biologists were convinced.
Can you think of any difference between DNAs and DNase?
