$$ \text { Give any six features of the human genome. } $$
Salient features of human genome
(i) The human genome contains 3164.7 million nucleotide bases.
(ii) The average gene consists of 30000 the largest know human gene being dystrophin at 2.4 Million bases.
(iii) The total number of genes is estimated to be 30000 and $99.9 \%$ nucleotide bases are exactly the same in all people.
(iv) The functions are unknown for over $50 \%$ of the discovered genes.
(v) Less than $2 \%$ of the genome codes for proteins.
(vi) The human genome contains large repeated sequences.
(vii) The repeated sequence is thought to have no direct coding functions but they throw light on chromosome structures, dynamics and evolution.
viii) Chromosome I has most genes (2968) and the Y has the fewest genes (231).
(ix) Scientists have identified about 1.4 million locations where single base DNA sequence differences called SNPs or Single Nucleotide Polymorphisms occur in humans.
During DNA replication, why is it that the entire molecule does not open in one go? Explain replication fork. What are the two functions that the monomers (dNTPs) play?
While replicating, the entire DNA molecule to keep the whole molecule stabilised does not open in one go because it would be highly expens energetically. Actually unwiding creates tension in the molecule as uncoiled parts.
Actually, unwinding creates tension in the molecule as uncoiled parts start forming super coils due to the interaction of exposed nucleotides.
Instead, helicase enzyme acts on the double strand at ori site (origin of replication) and a small stretch is unzipped. Immediately, it is held and stabilised by single strand binding proteins.
Slowly with the help of enzymes, exposed strands are copied as a point of unwinding moves and ahead in both directions.
It gives an appearance of Y-shaped structure which is called replication fork.
The two functions that the monomer units of NTPs play are
(i) They pair up with exposed nucleotides of the template strand and make phosphodiester linkages and release a pyrophosphate.
(ii) Hydrolysis of this pyrophosphate by enzyme pyrophosphatase releases energy that will facilitate making hydrogen bonds between free nucleotides and bases of the template strand.
Retroviruses do no follow central dogma. Comment.
Retroviruses do not follow central dogma of biology (DNA $\rightarrow$ RNA $\rightarrow$ Protein) because their genetic material is not DNA. Instead they have RNA that is converted to DNA by the enzyme reverse transcriptase.
In an experiment, DNA is treated with the compound which tends to place itself amongst the stacks of nitrogenous base pairs. As a result of this, the distance between two consecutive base increases. From $0.34-0.44 \mathrm{~nm}$ calculate the length of DNA double helix (which has $2 \times 10^9 \mathrm{bp}$ ) in the presence of saturating of this compound.
$$ \text { The length of DNA double helix }=2 \times 10^9 \times 0.44 \times 10^{-9} / \mathrm{bp} . $$
What would happen if histones were to be mutated and made rich in acidic amino acids such as aspartic acid and glutamic acid in place of basic amino acids such as lysine and arginine?
If histones were mutated and made rich in acidic amino acids. They will not be able to serve the purpose of keeping the DNA coiled around them. This is because DNA is negatively charged molecule and histones are positively charged because of basic amino acids.
So, they are attracted to each other. If histones become negatively charged, instead of binding, they will rather repel DNA. The packaging of DNA in eukaryotes would not happen. Consequently, the chromatin fibre would not be formed.