2.1 Structure of RNA and DNA

Question 1

What are the three components that make up a nucleotide?

Answer 1

• a pentose sugar
• a phosphate group
• a nitrogen-containing organic base; cytosine, thymine, uracil, adenine or guanine

Question 2

How is a nucleotide formed?

Answer 2

the pentose sugar, organic base and phosphate group are joined by condensation reactions to form a single nucleotide.

Question 3

How is a nucleic acid formed from a single nucleotide?

Answer 3

• Two mononucleotides undergo a condensation reaction between the deoxyribose sugar of one nucleotide and the phosphate group of another
• this forms a phosphodiester bond
• the new structure is called a dinucleotide. these can undergo the same reaction again to form a nucleic acid.

Question 4

Describe the structure of ribonucleic acid.

Answer 4

• a polymer made up of nucleotides
• a single, short polynucleotide chain
• the pentose sugar is always ribose
• the organic bases are adenine, cytosine, guanine and uracil.
• one type transfers genetic information from DNA to ribosomes.
• another type is involved in protein synthesis

Question 5

Describe the structure of deoxyribose nucleic acid.

Answer 5

• pentose sugaris deoxyribose
• organic bases are adenine, thymine, cytosine, guanine
• made up of two very long chains of nucleotides joined by hydrogen bonds formed between the bases.

Question 6

What are the complimentary bases?

Answer 6

• Adenine and thymine

- Guanine and cytosine

Question 7

Why is DNA stable?

Answer 7

• phosphodiester backbone protects the more chemically reactive organic bases within the double helix
• Hydrogen bonds link the organic bases forming bridges between the upright phosphodiesters. there are three hydrogen bonds between cytosine and guanine so the more C-G bonds present, the more stable the molecule

Question 8

What is the function of DNA?

Answer 8

• to pass genetic information between cells and between generations
• The vast number of base pairs within an organism means that there is an almost infinite variety of sequences of bases along the length of a DNA molecule.

Question 9

How is a DNA molecule adapted to carry out its function?

Answer 9

• it is a very stable structure which rarely mutates between generations
• Its 2 separate strands are joined by only H bonds which allow them to separate during replication and protein synthesis.
• It is a v large molecule so carries lots of genetic information
• the organic bases, and therefore the genetic information, is within the cylinder of the phosphate-sugar backbone so is protected from outside chemical and physical forces
• Base pairings lead to DNA being able to replicate and transfer info to RNA