It transfers genetic information from DNA to the ribosomes.

What three components make up a nucleotide?

A pentose sugar, a nitrogen-containing organic base and a phosphate group.

Which sugar and bases are in DNA?

Deoxyribose; adenine, cytosine, guanine and thymine.

Which sugar and bases are in RNA?

Ribose; adenine, cytosine, guanine and uracil.

What forms a phosphodiester bond?

A condensation reaction between the phosphate group of one nucleotide and the pentose of another, releasing water.

What holds the two strands of DNA together?

Hydrogen bonds between complementary base pairs.

Which bases pair, and with how many hydrogen bonds?

A with T (two); C with G (three).

If a DNA sample is 30 % adenine, what percentage is guanine?

20 %, as T is also 30 %, leaving 40 % for C and G.

How does an RNA molecule differ in size and strands from DNA?

It is a relatively short polynucleotide chain, usually single-stranded.

Why did many scientists doubt that DNA carried the genetic code?

It seemed relatively simple, with only four bases, compared with the greater variety of proteins.

Structure of DNA and RNAAQA A-Level Biology: Flashcards

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What does DNA do in all living cells?

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What does DNA do in all living cells?: It holds the genetic information.
What does RNA do?: It transfers genetic information from DNA to the ribosomes.
What are ribosomes made from?: RNA and protein.
What three components make up a nucleotide?: A pentose sugar, a nitrogen-containing organic base and a phosphate group.
Which sugar and bases are in DNA?: Deoxyribose; adenine, cytosine, guanine and thymine.
Which sugar and bases are in RNA?: Ribose; adenine, cytosine, guanine and uracil.
What forms a phosphodiester bond?: A condensation reaction between the phosphate group of one nucleotide and the pentose of another, releasing water.
How many phosphodiester bonds are in a strand of 20 nucleotides?
What holds the two strands of DNA together?: Hydrogen bonds between complementary base pairs.
Which bases pair, and with how many hydrogen bonds?: A with T (two); C with G (three).
If a DNA sample is 30 % adenine, what percentage is guanine?: 20 %, as T is also 30 %, leaving 40 % for C and G.
How does an RNA molecule differ in size and strands from DNA?: It is a relatively short polynucleotide chain, usually single-stranded.
Why did many scientists doubt that DNA carried the genetic code?: It seemed relatively simple, with only four bases, compared with the greater variety of proteins.

Exam questions on Structure of DNA and RNA

Analysis of a sample of double-stranded DNA from a bacterium showed that 22 % of its bases were guanine.
Explain why the percentage of adenine in the sample is equal to the percentage of thymine.2 marks
In a eukaryotic cell, DNA is held in the nucleus. A gene is copied into a molecule of messenger RNA (mRNA), which then moves to the ribosomes in the cytoplasm.
Explain how the structure of mRNA makes it suitable for carrying genetic information from the nucleus to the ribosomes.2 marks
In the early twentieth century many scientists doubted that DNA carried the genetic code. A synthetic double-stranded DNA fragment, 10 base pairs long, contains 3 adenine-thymine base pairs and 7 cytosine-guanine base pairs.
Suggest why many scientists doubted that DNA carried the genetic code.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).