Structure of DNA & RNA

Question 1

What are the basic functions of DNA & RNA in all living cells?

Answer 1

• DNA - holds genetic info which codes for proteins
• RNA - transfers genetic info from DNA to ribosomes

Question 2

What are the 2 molecules ribosomes are made of?

Answer 2

RNA & proteins

Question 3

What are the 3 main components of a nucleotide?

Answer 3

• phosphate group
• pentose sugar
• nitrogenous base

Question 4

What are the differences between a DNA & RNA nucleotide?

Answer 4

• DNA’s pentose sugar is deoxyribose whilst RNA’s is ribose
• RNA has uracil as one of the bases whilst DNA has thymine

Question 5

How do nucleotides join together to form polynucleotides?

Answer 5

condensation reactions removing water molecules between phosphate group of 1 nucleotide & pentose sugar of another forming phosphodiester bonds

Question 6

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

Answer 6

Due to the simplicity of DNA which is a chemically simple molecule with a few components

Question 7

What is the structure of DNA?

Answer 7

• a polynucleotide made of a phosphate group, deoxyribose & nitrogenous base
• phosphodiester bonds join nucleotides
• 2 polynucleotide chains are held by H bonds
• complementary base pairs are adenine & thymine and guanine & cytosine
• double helix

Question 8

What is the structure of mRNA?

Answer 8

• polynucleotide made of a phosphate group, ribose & nitrogenous base
• bases are uracil, adenine, cytosine & guanine
• phosphodiester bonds joining nucleotides
  -single helix

Question 9

What are the structural differences between DNA & mRNA?

Answer 9

• DNA is longer than mRNA since it has more nucleotides
• DNA has H bonds/base pairing whilst mRNA doesn’t

Question 10

How does the structure of DNA relate to its functions?

Answer 10

• 2 strands act as a template for semi-conservative replication
• H bonds between bases are weak allowing strands to be separated for replication
• complementary base pairing allows accurate replication
• double helix with sugar-phosphate background protects bases
• long molecule stores a lot of genetic info
• double helix allows it to be compact

Question 11

How can you use incomplete info about the frequency of bases of DNA to find the frequency of other bases?

Answer 11

• % of A in strand 1 = % of T in strand 2 (and vice versa)
• % of G in strand 1 = % of C in strand 2 (and vice versa)