1.5 Nucleic acids are important information-carrying molecules

Question 1

Describe basic functions of DNA and RNA in all living cells

Answer 1

DNA : holds genetic info which codes for polypeptides

RNA : transfers genetic info from DNA to ribosomes

Question 2

Name the two types of molecule from which a ribosome is made

Answer 2

RNA and proteins

Question 3

Draw and label a DNA nucleotide and RNA nucleotide

Answer 3

DNA nucleotide : deoxyribose
- phosphate group ( circle in top left corner )
- pentose ( pentagon in centre)
- nitrogen-containing organic base ( rectangle in right , adenine etc…)

RNA nucleotide : ribose
- same phosphate group and pentose
- nitrogen-containing organic base incl adenine URACIL, guanine or cytosine

Question 4

Describe the difference between a DNA nucleotide and RNA nucleotide

Answer 4

DNA nucleotide :
- pentose sugar is deoxyriboes
- base can be thymine

RNA nucleotide :
- pentose sugar is ribose
- base can be uracil

Question 5

Describe how nucleotide join together to form polynucleotides

Answer 5

• condensation reaction, removing water molecules
• between phosphate group of one nucleotide and deoxyribose/ribose of another
• forming phosphodiester bonds

Question 6

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

Answer 6

• the relative simplicity of DNA - chemically simple molecule with few components

Question 7

Describe the structure of DNA

Answer 7

+ Polymer of nucleotides (polynucleotide)
● Each nucleotide formed from
deoxyribose, a phosphate group and a
nitrogen-containing organic base
● Phosphodiester bonds join adjacent
nucleotides
● 2 polynucleotide chains held together by
hydrogen bonds
● Between specific complementary base
pairs - adenine / thymine and
cytosine / guanine
● Double helix

Question 8

Describe the structure of (messenger ) RNA

Answer 8

● Polymer of nucleotides (polynucleotide)
● Each nucleotide formed from ribose, a phosphate
group and a nitrogen-containing organic base
● Bases - uracil, adenine, cytosine, guanine
● Phosphodiester bonds join adjacent nucleotides
● Single helix

Question 9

Compare and contrast the structure of DNA and (messenger) RNA

Answer 9

DNA
- pentose sugar is deoxyribose
- has base thymine
- double helix
- long
- has hydro bonds

RNA
- pentose sugar is ribose
- has base uracil
-single stranded
-shorter
- doesnt have hydro bonds

Question 10

Suggest how the structure of DNA relates to its function

Answer 10

● Two strands → both can act as templates for semi-conservative replication
● Hydrogen bonds between bases are weak → strands can be separated for replication
● Complementary base pairing → accurate replication
● Many hydrogen bonds between bases → stable / strong molecule
● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
● Long molecule → store lots of genetic information
● Double helix (coiled) → compact

Question 11

Suggest how you can use incomplete information about the frequency of
bases on DNA strands to find the frequency of other bases

Answer 11

1. % of adenine in strand 1 = % of thymine in strand 2 (and vice versa)
2. % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa)
   Because of specific complementary base pairing between 2 strands