2.1 Structure of RNA and DNA

Question 1

Describe the basic function of DNA and RNA in all living cells

Answer 1

DNA: Holds genetic information which codes for polypeptides (proteins)

RNA: Transfers genetic information from DNA to ribosomes

Question 2

Name the types of molecules from which a ribosome is made

Answer 2

RNA and Proteins

Question 3

What is the monomer that makes up DNA

Answer 3

A nucleotide

Question 4

What are the 4 nitrogenous bases in DNA

Answer 4

Guanine
Cytosine
Adenine
Thymine

Question 5

Describe how nucleotides join together to form polynucleotides (3)

Answer 5

• Condensation reactions, removing water molecules
  ● Between phosphate group of one nucleotide and deoxyribose / ribose of another
  ● Forming phosphodiester bonds

Question 6

How is the polynucelotide held together

Answer 6

Strong covalent bonds called phosphodiester bonds

Question 7

How are the DNA polymer pairs joined together

Answer 7

Hydrogen bonds between the Nitrogenous bases

This is how the double helix strcutre is created as the two chains twist

Question 8

What is the only condition through which hydrogen bonds form in polynucelotides

Answer 8

They can only form between complimentary base pairs
Cytosine—Guanine 3
Adenosine–Thymine 2
Guanine—Cytosine 3
Thymine–Adenine 2

Number of ‘-‘ represent the number of h bond bwteen the bases

Question 9

What is RNA (3)

Answer 9

*A polymer of a nucleotide formed of a:
- Ribose
-Nitrogenous base
- Phosphate group
*Relatively short
*Single Stranded

Question 10

Name the 4 nitrogenous bases in RNA

Answer 10

Adenine
Uracil
Guanine
Cytosine

Question 11

What are the differences between the DNA and RNA monomers

Answer 11

• DNA contains the base Thymine whereas RNA has Uracil instead of Thymine
• DNA contains the pentose suagr deoxyribose whilst RNA contains Ribose

Question 12

What are the two differences between the polymers of DNA and RNA

Length

Answer 12

• DNA is much longer as it contains 23,000 genes whereas RNA is shorter as it only contains 1
• DNA is double stranded whilst RNA is single stranded

Question 13

Which Nitrogenous bases are Purine

Answer 13

Adenine and Guanine
They both have two rings
Guanine has a double bond to O

Question 14

Which Nitrogenous bases are pyrimidine

Answer 14

Thymine Cytosine and Uracil
Has one ring

Question 15

Why can Adenine and Cytosine not bond

Answer 15

Adenine would form 2 hydrogen bonds whereas Cytosine would form 3 hydrogen bonds

Question 16

What is the differnece between Deoxyribose and Ribose

Answer 16

Deoxyribose chemical formula-C5 H10 O4
Ribose has the same but one more oxygen
Strcture of Deoxyribose is more stable so it has a sotrnger covalent bonds as the C3 bond will be bonded directly oto the phosphate group

Question 17

How are polynucleotides formed

Answer 17

When DNA contains a second antiparallel chain that runs in the opposite direction

E.g. 5’ prime and 3’ prime end

Question 18

Why is DNA stable

Answer 18

• The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
• Hydrogen bonds link the organic base pairs forming bridges

Question 19

Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases (3)

Answer 19

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