2.3.1 Nucleotides & Phosphodiester Bonds

Question 1

Nucleotides

Answer 1

DNA and RNA are nucleic acids
- polymers that are made up of many repeating units (monomers) called nucleotides
Each nucleotide is formed from:
- a pentose sugar (a sugar with 5 carbon atoms)
- a nitrogen-containing organic base
- a phosphate group

Question 2

DNA Nucleotides

Answer 2

The components of a DNA nucleotide are:
- a deoxyribose sugar with hydrogen at the 2’ position
- a phosphate group
- one of 4 nitrogenous bases:
- adenine (A)
- cytosine (C)
- guanine (G)
- thymine (T)

Question 3

RNA Nucleotides

Answer 3

The components of an RNA nucleotide are:
- a ribose sugar with a hydroxyl (OH)b group at the 2’ position
- a phosphate group
- one of 4 nitrogenous bases:
- adenine (A)
- cytosine (C)
- guanine (G)
- uracil (U)
The presence of the 2’ hydroxyl group makes RNA more susceptible to hydrolysis
- this is why DNA is the storage molecule and RNA is the transport molecule with a shorter molecule lifespan

Question 4

Purines & Pyrimidines

Answer 4

The nitrogenous base molecules that are found in the nucleotides of DNA (A,T,C,G) and RNA (A,U,C,G) occur in 2 structural forms:
- purines
- pyrimidines
The based adenine and guanine are purines
- they have a double ring structure
The based cytosine, thymine and uracil are pyrimidines
- they have a single ring structure

Question 5

Nucleotide Structure Summary

Answer 5

DNA
Pentose Sugar = Deoxyribose
Bases = Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
Number of Strands = double-stranded (double-helix)
RNA
Pentose Sugar = Ribose
Bases = Adenine (A), Uracil (U), Cytosine (C), Guanine (G)
Number of Strands = single-stranded

Question 6

Phosphodiester Bond

Answer 6

DNA and RNA are polymers (polynucleotides), meaning thatc they are made up of many nucleotides joined together in long chains
Separate nucleotides are joined together via condensation reactions
- these condensation reactions occur between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide
A condensation reaction reaction between two nucleotides forms a phosphodiester bond
- it is called a phosphoDIester bond because it consists of a phosphate group and two ester bonds
The chain of alternating phosphate groups and pentose sugars produced as a result of many phosphodiester bonds is known as the sugar-phosphate backbone (of the DNA or RNA molecule)
As the synthesis of polynucleotides requires the formation of phosphodiester bonds, the same is true for the reverse process:
- the breakdown of polynucleotides requires the breakage of phosphodiester bond