DNA Structure & Function

Question 1

Describe the structure of DNA.

Answer 1

1. DNA is a polymer of nucleotides (a polynucleotide).
2. Each nucleotide is made up a deoxyribose sugar, a phosphate group and a nitrogenous base.
3. Nucleotides are joined together by condensation reactions to form a polynucleotide strand, phosphodiester bonds form between nucleotides.
4. DNA is made up of two polynucleotide strands held together by weak hydrogen bonds formed between complementary base pairs.
5. Adenine pairs with Thymine and Cytosine pairs with Guanine.
6. DNA structure forms a double helix, with one strand being a coding strand and one being a template strand.

Question 2

Why do base sequences differ between different species?

Answer 2

They form different proteins.

Question 3

Describe how to calculate base percentages.

Answer 3

1. Copy the number of bases on strand 1 with the complementary base on strand 2
2. Ensure the number of bases on each strand adds up to 100

Question 4

Relate each structure of DNA to its function.

Answer 4

1. Sugar-phosphate backbone
   —> gives strength
2. DNA mlcules are coiled
   —> compact shape
3. Double helix
   —> protects the bases, more stable
4. Weak hydrogen bonds
   —> easily broken down
5. Many hydrogen bonds
   —> strong and stable
6. Only certain bases joined
   —> DNA copied accurately
7. Bases occur in sequence on each strand
   —> provides code for protein synthesis
8. DNA molecules can be very long/ large
   —> large amounts of ‘information’ can be stored