Structure of DNA and RNA 2.6

DNA is the long molecules which makes up the genetic material in all cells. It is made from smaller units called nucleotides and in this topic a knowledge of the structure of nucleotides of DNA and RNA is required, as is a simple understanding of the structure of the double stranded, double helix, DNA.

Key words

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Clean sweep - quick revision through the whole topic

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Revision summary list for 2.6 strcture of DNA and RNA

  • DNA and RNA are polymers each made of nucleotides.
  • A DNA nucleotide is made from phosphate, deoxyribose (pentose sugar), and nucleotide bases (T, A,G,C)
  • RNA nucleotides are made from phosphate, ribose (pentose sugar) and nucleotide bases (U, A, G, C)
  • Base pairing is "complementary"
  • DNA is a double helix made of two strands of nucleotides linked by hydrogen bonding RNA is a single strand of nucleotides.
  • Students should be able to draw simple diagrams of DNA and RNA nucleotides - using simple shapes (not chemical symbols). Two antiparallel strands of DNA showing base pairing, A 'ladder' structure is enough, and details of purines / pyrimidines are not required

Revision mind map

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Review questions

This is a self marking quiz containing questions covering the topic outlined above.
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To which carbons of deoxyribose is the phosphate groups bonded in DNA?

The nucleotide base is bonded to carbon 1

Carbons 3 and 5 form the sugar -phosphate bond by binding to phosphate.


Which of the following are found in DNA but not in RNA

Thymine and deoxyribose are found only in DNA and not in RNA


Where do hydrogen bonds form in molecules of DNA?

Diagrams of DNA often show dotted lines between the nucleotide base pairs representing the hydrogen bonds that hold the DNA strands of the double helix together.


Which bases pair with T and G in DNA structure?

C always pairs with G and vice versa.

A always pairs with T, and vice versa.


In what ways is RNA the same as DNA?

RNA and DNA share the same phosphate, the bases A,C and G.
Both can form hydrogen bonds in the same way, but as RNA is single stranded the hydrogen bonding is different from DNA, depending on the type of RNA.


Which of the following is a correct drawing of an DNA nucleotide?

The deoxyribose connects the phosphate to the thymine correctly in diag A

In C and D the phosphate connects to the base, which is incorrect.


What is the difference between a ribose and a deoxyribose sugar molecule?

Both ribose and deoxyribose are pentose sugars with 5 carbon atoms in each.

Deoxyribose has one oxygen less than ribose, making one fewer -OH groups. The -OH becomes -H


In biology polymers are quite common types of molecules. Which of the following molecules are polymers?

Polymer is the chemical name for a long molecule made from repeated subunits called monomers.

These include, polysaccharides, polypeptides, and polymers of nucleotides, DNA and RNA.

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