Molecular Basis of Inheritance Test - 21

Chromosome 1 has 2968 genes, while chromosome Y has 231 genes.

It was only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rasalind Franklin, proposed a very simple but famous double helix model for the structure of DNA. Erwin Chargaff observed that for a double-stranded DNA, the ratios between adenine and thymine and guanine and cytosine are constant and equals one. On the other bond Matthew Meselson and Franklin Stahl in 1958 performed experiments on E.coli to prove that DNA replication is semi-conservative. But had no contribution it the development of double helix model.

The enzyme called DNA polymerase progressively adds deoxyribonucleotides to the free 3'-end of the growing polynucleotide chain so, that replication of the 3'-5' strand of the DNA molecule is continuous (growth of the new strand in 5'\(\longrightarrow\)3'direction). So, to prevent polymerization of nucleotides 3'OH group in deoxyribose should be replaced/removed.

DNA polymerase adds deoxyribose nucleotides to the free 3'-end of the growing polynucleotide chain so, that replication of the 3'\(\longrightarrow\) 5' strand of the DNA molecule is continuous (growth of the new strand in 5'\(\longrightarrow\) 3'direction). Since, DNA dependent DNA polymerase catalyses polymerization only in one direction (5\(\longrightarrow\)3'), discontinuous synthesis of DNA occurs in the other strand.

RNA polymerasefacilitatesinitiation,elongation and terminationduring transcription.

Transcription is the first step of gene expression. In this process, a particular segment of DNA is copied into mRNA. Thus, it controls gene expression.

Regulatory proteins affecttheability of RNA to recognize initiationsites. Regulatory proteins have both negative (repressor) and positive (activator) role.

Chromosome 1 was the last completed chromosome, sequenced two decades after the beginning of the human Genome Project(hGP). It is the designation for the largest human chromosome.  

rRNA, mRNA and tRNA are major classes of RNAs that are involved in gene expression. rRNAs bind protein molecules and give rise to ribosomes. mRNA carries coded information for translation into polypeptide formation.rRNA is called soluble or adaptor RNA and carries amino acids to mRNA during protein synthesis.

Chargaff’s rules states that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases. This means that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. This pattern is found in both strands of the DNA. In this case, percentage of adenine is not equal to that of guanine and same holds true for cytosine and thymine. Hence, it is a single stranded DNA.