1.5.1 structure of DNA

Question 1

what is the basic function of DNA in all living cells

Answer 1

holds genetic information which codes for polypeptides

Question 2

what is the basic function of RNA in all living cells

Answer 2

transfers genetic information from DNA to ribosomes

Question 3

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

Answer 3

RNA and proteins

Question 4

what is the structure of a DNA nucleotide

Answer 4

• phosphate group
• pentose ( deoxyribose )
• nitrogen containing organic base ( adenine, thymine, guanine or cytosine )

Question 5

what is the structure of an RNA nucleotide

Answer 5

• phosphate group
• pentose ( ribose )
• nitrogen containing organic base ( adenine, uracil, guanine or cytosine )

Question 6

what are the differences between a DNA nucleotide and an RNA nucleotide

Answer 6

• DNA nucleotides pentose sugar is deoxyribose whereas in RNA it is ribose
• DNA nucleotides base can be thymine whereas in RNA it can be uracil

Question 7

describe how nucleotides join together to form polynucleotides

Answer 7

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

Question 8

why did many scientists initially doubt that DNA carried the genetic code

Answer 8

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

Question 9

describe the structure of DNA

Answer 9

• polymer of nucleotides ( polynucleotides )
• each nucleotide is formed from deoxyribose, a phosphate group and a nitrogen containing organic base
• phosphodiester bonds join adjacent nucleotides
• 2 polynucleotide chains are held together by hydrogen bonds between specific complementary base pairs ( adenine/thymine and cytosine/guanine )
• double helix

Question 10

describe the structure of mRNA

Answer 10

• polymer of nucleotides ( polynucleotide )
• each nucleotide is formed from ribose, a phosphate group and a nitrogen containing organic base
• bases are uracil, adenine, cytosine and guanine
• phosphodiester bonds join adjacent nucleotides
• single helix

Question 11

compare and contrast the structure of DNA and mRNA

Answer 11

• DNA pentose sugar is deoxyribose whereas RNA is ribose
• DNA has the base thymine whereas RNA has base uracil
• DNA is doubled stranded/double helix whereas RNA is single stranded/single helix
• DNA is long ( has many nucleotides ) whereas RNA is shorter ( fewer nucleotides )
• DNA has hydrogen bonds/base pairing whereas RNA doesnt

Question 12

how does the structure of DNA relate to its function

Answer 12

• two strands means both can act as a template in semi conservative replication
• hydrogen bonds between bases are weak meaning strands can be separated for replication
• complementary base pairing means accurate replication
• many hydrogen bonds between bases means stable/strong molecule
• double helix with sugar phosphate backbone protects the bases and hydrogen bonds
• long molecule means stores lots of genetic information which codes for polypeptides
• double helix is coiled so compact

Question 13

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

Answer 13

• % of adenine in strand 1 = % of thymine in strand 2 ( and vice versa )
• % of guanine in strand 1 = % of cytosine in strand 2 ( and vice versa )
• this is because of complementary base pairing between 2 strands