Question

for the uracil:
1. Describe chemical characteristics, classification and biological molecule in which it is found
2. Identify each of the parts that make it up and graph nitrogenous base, nucleoside and nucleotide.

Answer 1

1.

• Uracil is a nitrogenous base present in RNA.
• RNA is ribonucleic acids.

Chemical characteristics:

• The structural monomeric units of RNA are nucleotides.

• There are 3 basic components of nucleotides:

  1: Pentose sugar- It is 5-carbon sugar.

  RNA has Ribose as pentose sugar. Its structure has OH group attached to the second carbon atom (called 2 prime or 2’). Thus, RNA is designated as Ribonucleic acid (for ribose).

  2. Nitrogenous base- The ringed structure base is attached to the 1’ carbon of the pentose sugar. Nitrogenous bases may be of two types:

  a) Purines- Adenine (represented as A) and Guanine (represented as G).

  b) Pyrimidine- Uracil (U) and Cytosine (C).

  The combined structure of pentose sugar with nitrogenous bases are called nucleosides.

  3. Phosphate groups: The 5’ carbon atom of pentose, may bond with phosphate group (which may be mono phosphate, bi phosphate or triphosphate).

  Combination of nucleosides (pentose+ nitrogenous base) + phosphate forms a nucleotide.

Structure:

• Nucleotides form covalent bond to attach to each other and form a chain or strand of nucleic acid.
• Covalent linkage between nucleotides are formed by, 3’ carbon atom of one nucleotide with phosphate group (attached to the 5’ carbon) of another nucleotide. The primary structure of nucleic acids are thus formed.
• These linkages are called phosphodiester bonds. The strands thus formed, will exhibit polarity, as one end will have 3' and the other end will be 5’, due to presence of nitrogen or oxygen groups of nucleotides.
• Thus, RNA may be described as polymers of nucleotides (if few nucleotide the called oligonucleitide, if larger number of nucleotides bond it is called polynucleotide).
• The phosphodiester linkages forms the backbone of nucleic acids and render them with a negative charge.
• RNA molecules with a single strand may further twist around itself to form a stable structure.
• RNA may form base pairing, during its folding or forming hybrid with DNA.
• Where the Adenine pairs to uracil (A=U) by two hydrogen bonds.

Classification:

1. mRNA: . Messenger RNA or m RNA carries the genetic code received from the DNA, in 5’to 3 ‘direction reading frame. It is generated by transcription form DNA.

2. tRNA: Transfer RNA carry anti-codon and corresponding amino acids. During translation, tRNA carries amino acid to the ribosome, by matching anti-codons to codons in mRNA.

3. rRNA: Ribosomal RNA are components of ribosomes. rRNA (in larger subunit)-28s, 5.3s, 5s, rRNA (in larger subunit)- 23s and 5s.

4.

RNAi or RNA interference has an ability of gene silencing, by inhibiting expression of genes. The two major forms included in RNA interference are:Micro RNA or miRNA, Small interfering RNA or siRNA.