Molecular basis Flashcards
Even tho the disc of —— by —- and —– by —- were almost at the same time, but that the —-acts as the genetic material took long to be —– and –
Nuclein- Meischer
Principle of inheritance- Mendel
DNA, discovered and proven
By —, the quest for determining the —— had reached the molecular level
1926
mechanism of genetic inheritance
previous dic by —,— and —- and numerous other scientists had narrowed the search to chromosomes located in —–
but, the q of what —– the genetic material had not been answered
Mendel, Sutton, Morgan
nucleus of MOST cells
molecule was actually
In —-, Frederick — in a series of exps with —– (bac responsible for —) witnessed miraculous — in the bac.
During the course of his exp, a living organism (bac) had —-
1928, Griffith
Streptococcus pneumoniae
pneumonia
transformation
changed in physical form
when streptococcus pneumoniae (—-) bacteria are grown on —-, some produce —- colonies (S) while others produce — colonies (R)
pneumococcus
culture plate
smooth, shiny
rough
S strain bac have a —– coat while R strain do not
mucous (polysaccharide)
Mice infected with S strain (—) — from pneumonia but mice infected with R strain —- pneumonia
virulent- die from
do not develop
Griffith was able to kill bac by
heating them
heat killed —- did not kill the mice, but a mixture of heat killed —- and —- killed the mice
moreover, griffith recovered —- from the dead mice
S strain
S strain and live R
living S bac
Griffith concluded that
R strain bac had somehow been transformed by the heat killed S strain bac
Some —– transferred from heat killed s strain had enabled r strain to —-
This must be due to the tranfer of —-. however the — nature of —- was not defined from his exp
transforming principle
synthesise a smooth polysaccharide coat and become virulent
genetic material
biochemical nature, genetic material
Prior to the work of —-, —-, —- (—–) the genetic material was thought to be —-
The worked to determine —— in griffiths exp
Oswald avery, Maclyn Mccarty, Colin Macleod
(1933-44)
protein
biochemical nature of transforming principle
They purified —- (—) from the heat killed S cells to see which ones could transform live R cells into S cells
biochemicals (proteins, dna, rna)
avery, mc cleoid, mc carty disc that — alone from s bac caused r bac to be transformed
dna
They also discovered that protein-digesting enzymes (—-) and
RNA-digesting enzymes (—-) did not affect —–, so the transforming substance was not a protein or RNA.
proteases, RNases
transformation
Digestion with DNase
did —- suggesting that the DNA caused the transformation.
inhibit transformation,
—- concluded that DNA is the hereditary material, but
not all biologists were convinced.
Mc cleois, mc carty, avery
At the time of Mendel, the nature of those ‘—–’ regulating the pattern of inheritance was not clear. Over the next —-, the nature of the —–
was investigated culminating in the realisation that DNA – deoxyribonucleic acid – is the genetic material, —-
factors, hundred years
putative genetic material
at least for the majority of organisms.
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two types of —- found in —-.
nucleic acids, living
systems
DNA acts as the —- in MOST of the organisms.
genetic material
RNA though it also acts as a genetic material in —-, mostly functions as a —-.
some viruses- messenger
RNA has additional roles as well. It functions as —, —- and in some cases as a — molecule.
adapter, structural, catalytic
The determination of complete nucleotide sequence of —- genome during—- has set in a new era of —-.
human
last decade, genomics
_____ is the most abundant genetic material
DNA
DNA is a — polymer of —.
long
deoxyribonucleotides
The length of DNA is usually defined as —- (or a —–) present in it.
number of nucleotides
pair of nucleotide referred
to as base pairs
—– is the characteristic of an organism.
No of Nts or bp
bacteriophage known as φ ×174 has —-
Bacteriophage lambda has —-, Escherichia coli has ———-
HAPLOID content of human DNA is
5386 nucleotides,
48502 base pairs (bp)
4.6 × 106 bp,
3.3 × 109 bp.
A nucleotide has three components – —-, —, —-.
a nitrogenous base, a pentose sugar and a phosphate group
Pentose sugar is
(ribose in case of RNA, and deoxyribose for DNA),
There are two types of nitrogenous bases – —-, —–
Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine).
—- is common for both DNA and RNA and —- is present in
DNA.
Cytosine, Thymine
—- is present in RNA at the place of Thymine.
Uracil
A nitrogenous base is linked to the —- of —- pentose sugar through a —
linkage to form a —-, such as adenosine or deoxyadenosine,
guanosine or deoxyguanosine, cytidine or deoxycytidine and —- or —–
OH , 1’ C
N-glycosidic, nucleoside
uridine or deoxythymidine.
When a phosphate group is linked to OH of—of a nucleoside through — linkage, a corresponding nucleotide (or deoxynucleotide depending upon the type of sugar present) is formed.
5’ C , phosphoester
Two nucleotides are linked through —- linkage to form a dinucleotide.
More nucleotides can be joined in such a manner to form a polynucleotide chain.
3’-5’ phosphodiester
A polymer thus formed has at one end a free —- at 5’ -end of sugar, which is referred to as 5’-end of
polynucleotide chain.
phosphate moiety
Similarly, at the other end of the polymer the sugar has a free —- of 3’C group which is referred to as 3’ -end of the polynucleotide chain.
OH
The backbone of a polynucleotide chain is formed due to —-.
sugar and phosphates
The nitrogenous bases linked to sugar moiety project from —
the backbone
In RNA, every nucleotide residue has an additional —- present
at — -position in the ribose.
–OH group, 2
Also, in —- the uracil is found at the place of thymine
RNA
5-methyl —, another chemical name for —
uracil, thymine
DNA as an — substance present in nucleus was first identified by
—- in —-. He named it as ‘—-’
acidic
Friedrich Meischer in 1869
Nuclein
However, due to —- in — such a long polymer intact, the elucidation
of structure of DNA remained — for a very long period of time.
technical limitation, isolating
elusive
It was only in — that —- Watson and — Crick based on the — data produced by —, proposed a — but —- Double Helix model for the — of DNA.
1953, James Watson and Francis Crick, X-ray diffraction
Maurice Wilkins and Rosalind Franklin
very simple but famous, structure
One of the hallmarks of Double helix proposition was — between
the —-.
However, this proposition was
also based on the observation of — that for a —, the ratios between Adenine and Thymine and Guanine and Cytosine are — and —
base pairing, two strands of polynucleotide chains
Erwin Chargaff, double stranded
DNA
constant and equals one.
The —- confers a very unique property to the polynucleotide
chains.
base pairing
They are said to be — to each other, and therefore if the sequence of bases in one strand is known then the sequence in other
strand can be predicted.
complementary
Also, if each strand from a DNA (let us call it as a —) acts as a — for synthesis of a new strand, the two
double stranded DNA (let us call them as —-) thus, produced
would be identical to the parental DNA molecule.
Because of this, the —- of the structure of DNA became very clear.
parental DNA, template
daughter DNA
genetic implications
The salient features of the Double-helix structure of DNA are as follows:
(i) It is made of —–, where the — is constituted by sugar-phosphate, and the bases —-
two polynucleotide chains
backbone, project inside.
(ii) The two chains have —- polarity. It means, if one chain has the polarity 5’à3’, the other has 3’à5’.
anti-parallel
(iii) The bases in two strands are paired through —- forming base pairs (bp).
hydrogen bond (H-bonds)
Adenine forms —- hydrogen
bonds with Thymine from opposite strand and vice-versa.
two
Similarly, Guanine is bonded with Cytosine with —- H-bonds.
three
As a result, always a — come opposite to —-. This generates approximately —- between the two
strands of the helix
purine comes opposite to a pyrimidine
uniform distance
(iv) The two chains are coiled in a —-fashion.
right-handed
The pitch of the helix is — (a nanometre is one billionth of a
metre, that is 10-9 m) and there are roughly —- in each turn.
3.4 nm, 10 bp
Consequently, the distance
between a bp in a helix is
approximately —-
0.34 nm.
(v) The —– in double helix. This, in addition to — confers
—-of the helical structure
The plane of one base pair stacks over the other
H-bonds, stability
The proposition of a —- for DNA and its — became revolutionary.
double helix structure
simplicity in explaining the genetic implication
Very soon, —- proposed the —- which states that the GENETIC
INFORMATION flows from DNA–>RNA—–>Protein.
Francis Crick, Central dogma in molecular biology,
In some — the flow of information is in reverse direction, that is, from —
Process ==
viruses, RNA to DNA
reverse transcription
Taken the distance between two consecutive base pairs as —, if the length of DNA double helix in a typical —- cell is calculated (simply
by multiplying the —- by —–, that is, ), it comes out to be approximately
—-.
0.34 nm , mammalian
total number of bp with distance
between two consecutive bp:
6.6 × 109 bp × 0.34 × 10-9m/bp
2.2 metres
A length of DNA that is far greater than the dimension of a typical nucleus (approximately —).
How is such a long polymer packaged in a cell?
10–6 m
In prokaryotes, such as,—- though they do not have a —-, the DNA is — throughout the cell.
E. coli, defined nucleus
not scattered
DNA (being —- charged)
is held with some —- (that have — charges) in a region termed as ‘—’, in pro
negatively, proteins
positive
nucleoid
The DNA in nucleoid is organised in — held by —-
large loops, proteins
In eukaryotes, this — of DNA much more complex.
organisation
In eu- There is a set of positively charged, —proteins called —–
basic
histones
A protein acquires charge
depending upon the abundance of —–
amino acids residues with charged side chains.
Histones are rich in the basic amino acid residues—, —–
Both the amino acid residues carry positive charges in their—-
lysine and arginine.
side chains.
Histones are organised to form
a unit of —- called —–
eight molecules
histone octamer.
The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called —-
nucleosome
A typical nucleosome contains— of DNA helix.
200 bp
Nucleosomes constitute the repeating unit of a structure in nucleus called —
chromatin
Chromation are —– bodies seen in nucleus.
threadlike stained (coloured)
The nucleosomes in chromatin are seen as —- structure when viewed under—-
‘beads-on-string’
electron microscope (EM)
The beads-on-string structure in chromatin is packaged to form
—- that are further coiled and condensed at —- of cell division to form —-.
chromatin fibers, metaphase stage
chromosomes
The packaging of chromatin at higher level requires additional set of — that collectively are referred to as —–
proteins, Non-histone Chromosomal (NHC) proteins
In a typical nucleus, some
region of chromatin are loosely packed (and stains —-) and are referred to as — .
light, euchromatin
The chromatin that is more densely packed and stains
— are called as —-.
dark, Heterochromatin
Euchromatin is said to be —- chromatin, whereas heterochromatin is —-.
transcriptionally active
inactive
The unequivocal proof that DNA is the genetic material came from the
experiments of —- (—).
Alfred Hershey and Martha Chase (1952)
Alfred Hershey and Martha Chase worked with viruses that infect bacteria called —–.
bacteriophages
The bacteriophage attaches to the bacteria and its — then enters the bacterial cell.
genetic material
The bacterial cell treats the —- as if it was its own and subsequently manufactures —-
viral genetic material
more virus particles.
Hershey and Chase worked to discover whether it was —- from the viruses that entered the bacteria.
protein or DNA
They grew some viruses on a medium that contained radioactive
phosphorus (—) and some others on medium that contained radioactive sulfur (—).
P 32
S 35
Viruses grown in the presence of radioactive phosphorus contained
radioactive —- but not radioactive — because DNA contains phosphorus but protein does not.
DNA,protein
Similarly, viruses grown on radioactive — contained radioactive protein but not radioactive DNA because
DNA does not contain sulfur
sulfur
Radioactive phages were allowed to attach to —-
E. coli bacteria.
Then, as the infection proceeded, the —- were removed from the bacteria by — them in a blender.
viral coats, agitating
The virus particles were separated from the bacteria by —-
spinning them in a centrifuge.
Bacteria which was infected with viruses that had —- were radioactive, indicating that DNA was the material that passed from
the virus to the bacteria.
radioactive DNA
Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicates that—-.
proteins did not enter the bacteria from the viruses
DNA is therefore the genetic material that is passed from — to —-
virus to bacteria
Radioactive S 35 is detected in
Supernatant
From the foregoing discussion, it is clear that the debate between proteins versus DNA as the genetic material was — resolved from Hershey-Chase experiment.
unequivocally
It became an established fact that it is — that acts as genetic material. However, it subsequently became clear that in some —, is the genetic material
DNA
viruses, RNA
RNA is the genetic material for
Tobacco Mosaic viruses, QB bacteriophage
Answer to some of the questions such as, why DNA is the — genetic material, whereas RNA performs
— functions of —- has to be found from the differences between chemical structures of the two nucleic acid molecules.-
predominant , dynamic
messenger and adapter
chemical structures
A molecule that can act as a genetic material must fulfill the following
criteria:
(i) It should be able to generate —-
(ii) It should be stable —-
(iii) It should provide the scope for — that are required for evolution.
(iv) It should be able to express itself in the form of—-
its replica (Replication).
chemically and structurally.
slow changes (mutation)
‘Mendelian
Characters’.
If one examines each requirement one by one, because of rule of —-, both the nucleic acids (DNA and RNA) have the ability to direct their duplications.
base
pairing and complementarity
The other molecules in the living
system, such as — fail to fulfill first criteria itself (–).
proteins- duplication
The genetic material should be stable enough not to change with
—, — or —-.
different stages of life cycle, age or change in physiological of the org
Stability as one of the properties of genetic material was very
evident in —-
Griffith’s ‘transforming principle’
In Griffiths exp- heat, which killed
the — , at least did not destroy —
This now can easily be explained in light of the DNA that the two strands being —if separated by heating come together, when —- are provided.
bacteria, some of the properties of genetic material.
complementary , appropriate conditions
Further, —– present at every nucleotide in RNA is a — group and makes RNA — and —
2’-OH group, reactive
labile and easily degradable
RNA is also now known to be —, hence reactive.
catalytic
Therefore, DNA — is less reactive and —- more stable when compared to RNA.
chemically, structurally
Therefore, among the two nucleic acids, the DNA is a —-
better genetic material.
In fact, the presence of thymine at the place of uracil also confers
— to DNA.
(Detailed discussion about this requires understanding of the process of —– in DNA)
additional stability
repair
Both DNA and RNA are able to mutate. In fact, RNA being —-,
mutate at a — rate.
unstable, faster
Consequently, viruses having —genome and having —- mutate and evolve faster.
RNA, shorter life span
RNA can directly code for the —-, hence can easily express the characters.
synthesis of proteins
DNA, however, is dependent on RNA for —-.
synthesis of proteins
The —- has evolved around RNA.
protein synthesising machinery
The above discussion indicate that both RNA and DNA can function as genetic material, but DNA being more stable is preferred for—-. For the —-, RNA is better
storage of genetic information
transmission of genetic information
From foregoing discussion, an immediate question becomes evident – which is the first genetic material?
RNA was the first genetic material.
There is now enough evidence to
suggest that essential life processes (such as —, —, —–, etc.), evolved around RNA.
metabolism, translation,
splicing
RNA used to act as a — and —-
genetic material as well as a catalyst
There are some important — in living systems that are catalysed by RNA catalysts and not by protein
enzymes.
biochemical reactions
But, RNA being a catalyst was reactive and hence —-.
Therefore, DNA has evolved from RNA with —- that make it more stable.
unstable, chemical modifications
DNA being double stranded and having —- further resists changes by evolving a process of —-.
complementary strand
repair
