Friday, April 4, 2008


RNA is structurally similar to DNA!

Both nucleic acids are sugar-phosphate polymers and both have nitrogen bases attached to the sugars of the backbone- but there are several important differences.

  • They differ in composition:
  1. The sugar in RNA is ribose, not the deoxyribose in DNA (as we previously learned).
  2. The base uracil is present in RNA instead of thymine.
  • They also differ in size and structure:
  1. RNA molecules are smaller (shorter) than DNA molecules,
  2. RNA is single-stranded, not double-stranded like DNA.
  • Another difference between RNA and DNA is in function. DNA has only one function-STORING GENETIC INFORMATION in its sequence of nucleotide bases. But there are three main kinds of ribonucleic acid, each of which has a specific job to do.

  1. Ribosomal RNAs-exist outside the nucleus in the cytoplasm of a cell in structures called ribosomes. Ribosomes are small, granular structures where protein synthesis takes place. Each ribosome is a complex consisting of about 60% ribosomal RNA (rRNA) and 40% protein.
  2. Messenger RNAs-are the nucleic acids that "record" information from DNA in the cell nucleus and carry it to the ribosomes and are known as messenger RNAs (mRNA).
  3. Transfer RNAs-The function of transfer RNAs (tRNA) is to deliver amino acids one by one to protein chains growing at ribosomes.

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