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Why do we need RNA molecule for coding?

Why do we need RNA molecule for coding?. Nucleus membrane has small pores which let small molecules through to the cytoplasm. Double helix DNA molecule is too big to move through the pores. Amino acids and ribosome occur only outside the nucleus in the cytoplasm of the cell.

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Why do we need RNA molecule for coding?

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  1. Why do we need RNA molecule for coding? Nucleus membrane has small pores which let small molecules through to the cytoplasm. Double helix DNA molecule is too big to move through the pores. Amino acids and ribosome occur only outside the nucleus in the cytoplasm of the cell. Have to use small molecules with the same codes as the DNA to form the correct protein in the ribosome. This small molecule is RNA. Study the next slide.

  2. Diagrammatical presentation of some parts of a cell (Not drawn to scale) DNA Nucleus Nucleus membrane Pore in nucleus membrane Ribosome – ‘protein fabric’ Amino acids

  3. Coding for proteins in the cytoplasm by a single strand molecule, called RNA • The RNA molecule is a polymer, a long molecule that is made up of many monomers called nucleotides. • Three types of RNA are messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA). • All RNA molecules are formed from a DNA template in the nucleus. Will discuss the detail under protein synthesis.

  4. Forming and movement of mRNA From the DNA template a mRNA is formed in the nucleus Single strand mRNA moves through the pores in the nucleus membrane into the cytoplasm of a cell

  5. Coding for proteins by mRNA • Because mRNA has a single strand structure it can move through the small pores of the nucleus membrane into the cytoplasm of the cell. • It is the nitrogenous bases that is responsible for the coding of the proteins. • Threeconsecutive (next to each other) bases in mRNA are called a codon. • These three bases (codon) represent the code for a particular amino acid.

  6. Coding for Life – mRNA molecule Note: Single strand – No complementary bases Uraciel replaces Thymine U A simplified diagram of a part of a mRNA molecule.

  7. Three types of RNA molecules Messenger RNA (mRNA). Move from the nucleus to the ribosome in the cytoplasm. Carrying the genetic codes from DNA. Ribosomal RNAs (rRNA) combine with proteins to form a subunit of a ribosome. Transfer RNA (tRNS) is a single strand that is folded to form loops. At one of the looped ends it has three exposed bases, called anticodon. tRNA are used to transfer amino acids to the ribosome during protein synthesis.

  8. Diagrams to show the three types of RNA tRNA mRNA rRNA U Codon anticodon

  9. Comparison between DNA and RNA Differences Similarities Both have the same phosphate groups Sugar-phosphate bond joins the adjacent sugars of the nucleotides together

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