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Biology AS CIE

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  1. 1-cell-structure
    10 主题
  2. 2-biological-molecules
    19 主题
  3. 3-enzymes
    13 主题
  4. 4-cell-membranes-and-transport
    16 主题
  5. 5-the-mitotic-cell-cycle
    8 主题
  6. 6-nucleic-acids-and-protein-synthesis
    9 主题
  7. 7-transport-in-plants
    11 主题
  8. 8-transport-in-mammals
    16 主题
  9. 9-gas-exchange
    6 主题
  10. 10-infectious-diseases
    6 主题
  11. 11-immunity
    10 主题
课 6, 主题 6
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6-1-structure-of-nucleic-acids-and-replication-of-dna AS the-structure-of-rna

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Exam code:9700

RNA structure

  • Like DNA:

    • The nucleic acid RNA (ribonucleic acid) is a polynucleotide

      • It is made up of many nucleotides linked together in a long chain

    • 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)

    • RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose)

    • RNA molecules are only made up of one polynucleotide strand (they are single-stranded)

  • Each RNA polynucleotide strand is made up of alternating ribose sugars and phosphate groups linked together

    • The nitrogenous bases of each nucleotide projecting out sideways from the single-stranded RNA molecule

Properties

DNA

RNA

Pentose sugar

Deoxyribose

Ribose

Bases

Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Adenine (A) Uracil (U) Cytosine (C) Guanine (G)

Number of strands

Double-stranded (double helix)

Single-stranded

Diagram showing DNA and RNA structures; DNA includes thymine, adenine, guanine, cytosine. RNA includes adenine, guanine, cytosine, uracil.
There is much overlap of the nucleotides found in DNA and RNA, the only difference is that RNA contains uracil (U) instead of thymine (T)
Diagram comparing RNA and DNA nucleotides, highlighting differences in the pentose sugar: ribose with OH for RNA and deoxyribose with H for DNA.
An RNA nucleotide compared with a DNA nucleotide
  • 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)

    • mRNA is the transcript copy of a gene that encodes a specific polypeptide

Illustration of mRNA structure showing sugar-phosphate backbone and nitrogenous bases: guanine, cytosine, adenine, uracil.
Messenger RNA (mRNA) provides a good example of the structure of RNA

Examiner Tips and Tricks

You need to know the difference between DNA and RNA molecules (bases, number of strands, pentose sugar present).

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