Biomolecules Test - 43

Retrovirus has RNA as genetic material RNA. Retroviridae is a family of enveloped viruses that replicate in a host cell through the process of reverse transcription. The RNA present in the retrovirus is a single-stranded positive sense with a DNA intermediate. It acts as an obligate parasite and targets a host cell.

In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine. Uracil could be considered a demethylated form of thymine. Each nucleotide in RNA contains a ribose sugar, with carbons numbered 1' through 5'. A base is attached to the 1' position, in general, adenine (A), cytosine (C), guanine (G), or uracil (U). Adenine and guanine are purines, cytosine and uracil are pyrimidines.

Transcription is when RNA is made from DNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One notable difference, however, is that eukaryotic RNA polymerase associates with mRNA-processing enzymes during transcription so that processing can proceed quickly after the start of transcription. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language. The two can be converted back and forth from DNA to RNA by the action of the correct enzymes. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript. As opposed to DNA replication, transcription results in an RNA complement that includes the nucleotide uracil (U) in all instances where thymine (T) would have occurred in a DNA complement. So, if If the base sequence in DNA is 5' AAAA 3' then the bases sequence in m-RNA is 3' UUUU 5'. 

The nucleotides form the structural backbone of the DNA. The two nucleotide units are held together by phosphodiester bonds. The phosphodiester bonds are formed by linkage of 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA and ribose in RNA. 

The unit of nucleic acid is nucleotide. Nucleotides are organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar - ribose or deoxyribose, and at least one phosphate group. Thus, a nucleoside plus a phosphate group yields a nucleotide.

A sequence of three nucleotides in messenger RNA makes a codon for an amino acid. A codon is a sequence of three adjacent nucleotides constituting the genetic code that determines the insertion of a specific amino acid in a polypeptide chain during protein synthesis or the signal to stop protein synthesis. A codon is defined by the initial nucleotide from which translation starts.

Both the strands of DNA are not copied during transcription because if both strands act as a template, they would code for RNA with different sequence the two RNA molecules, if produced simultaneously would be complementary to each other, hence would form a double stranded RNA. Transcription is when RNA is made from DNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One difference, however, is that eukaryotic RNA polymerase associates with mRNA processing enzymes during transcription so that processing can proceed quickly after the start of transcription.

Enzymes are biological catalysts which speed up the biological reactions. All metabolic reactions in a cell are catalyzed by enzymes. Almost all enzymes are proteins. There are some nucleic acids that behave like enzymes. These are called ribozymes. Ribozymes are molecules of ribonucleic acid with catalytic activity.

Horns, nails and hairs are derivatives of skin in mammals. The keratins are found in the hair (including wool), horns, nails, claws and hooves of mammals. The harder keratins are found in nails and in the scales and claws of reptiles, their shells (Testudines, such as tortoise, turtle, terrapin), and in the feathers, beaks, claws of birds and quills of porcupines.