AQA A Level Biology复习笔记1.5.4 The Structure of RNA

The Structure of RNA

 

  • Like DNA, the nucleic acid RNA (ribonucleic acid) is a polynucleotide – it is made up of many nucleotides linked together in a chain
  • Like DNA, RNA nucleotides contain the nitrogenous bases adenine (A), guanine (G) and cytosine (C)
  • Unlike DNA, RNA nucleotides never contain the nitrogenous base thymine (T) – in place of this they contain the nitrogenous base uracil (U)
  • Unlike DNA, RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose)

Comparison-between-RNA-nucleotide-and-DNA-nucleotide

An RNA nucleotide compared with a DNA nucleotide

 

  • Unlike DNA, RNA molecules are only made up of one polynucleotide strand (they are single-stranded)
  • RNA polynucleotide chains are relatively short compared to DNA
  • Each RNA polynucleotide strand is made up of alternating ribose sugars and phosphate groups linked together, with the nitrogenous bases of each nucleotide projecting out sideways from the single-stranded RNA molecule
  • The sugar-phosphate bonds (between different nucleotides in the same strand) are covalent bonds known as phosphodiester bonds
    • These bonds form what is known as the sugar-phosphate backbone of the RNA polynucleotide strand
    • The phosphodiester bonds link the 5-carbon of one ribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-carbon of the ribose sugar molecule of the next nucleotide in the strand

     

  • An example of an RNA molecule is messenger RNA (mRNA), which is the transcript copy of a gene that encodes a specific polypeptide. Two other examples are transfer RNA (tRNA) and ribosomal RNA (rRNA)

 

mRNA-as-an-example-of-RNA-structure

Messenger RNA (mRNA) provides a good example of the structure of RNA

 

转载自savemyexams

更多Alevel课程
翰林国际教育资讯二维码