A Level Biology: Lesson 24.
Nucleic Acids: Nucleotides & Polynucleotides
Task 1. Check Where this Lesson fits into your Exam Specification!
Task 2. Watch the Revision Notes Lesson in Full.
00:40 Learning Outcomes
01:12 Nucleotides are the monomers of DNA and RNA
01:34 The Pentose Sugar
02:10 The Nitrogenous Bases
03:05 Purines and Pyrimidines
03:44 The Phosphate Group
03:58 Nucleotide Structure
04:48 Condensation Reactions Build Polynucleotides
06:09 Compare DNA and RNA
Download, Print out & complete the accompanying Interactive Worksheet.
A-Level Biology Lesson 24. "Nucleic Acids: Nucleotides & Polynucleotides" Summary.
Nucleotides are the monomers (mononucleotides) that make up Polynucleotides such as DNA and RNA.
Each Nucleotide is composed of 3 parts.
The Pentose Sugar
The Nitrogenous base (either Adenine, Thymine (DNA), Cytosine, Guanine or Uracil (RNA)
The Phosphate Group (ion)
Notice Carbon number 2 of these Pentose Sugars.
Ribose, has an OH group at Carbon 2.
Deoxyribose, has a Hydrogen at Carbon 2.
The Nitrogenous Bases are either Purines or Pyrimidines.
Purines (A and G) have “2 Rings”
Pyrimidines (C, T and U) have only “1 ring”
The basic structure of a nucleotide:
Nucleotides join to one another via Condensation Reactions.
An OH group - located on the Phosphate group, attached to Carbon number 5 of the Pentose Sugar, undergoes a condensation reaction with the OH group attached to Carbon Number 3 of the Pentose Sugar. This condensation reaction results in the removal of a water [H2O] molecule and the formation of a phosphodiester bond between the nucleotides. Many of these condensation reactions take place to form the Sugar-Phosphate Backbone of polynucleotides.
You also have to be able to compare and contrast DNA and RNA… These are useful points from this lesson to include in your answers…
DNA has the Pentose Sugar “Deoxyribose” and is made up of the Nitrogenous bases, Adenine, Thymine, Cytosine and Guanine.
RNA has the Pentose Sugar “Ribose” and is made up of the Nitrogenous bases, Adenine, Uracil, Cytosine and Guanine.
Check Your Spec!
Specification Reference: - 126.96.36.199 Structure of DNA and RNA. Both DNA and RNA are polymers of nucleotides. Each nucleotide is formed from a pentose, a nitrogen-containing organic base and a phosphate group: -
• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.
• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.
• A condensation reaction between two nucleotides forms a phosphodiester bond.
Specification Reference: -6 Nucleic acids and protein synthesis. 6.1 Structure and replication of
DNAa) describe the structure of nucleotides.
★ Edexcel (Biology A – Salters-Nuffield)
Specification Reference: -Topic 2: Genes and Health. 2.5 i) Know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base, including thymine, uracil, cytosine, adenine or guanine) and the structures of DNA and RNA (polynucleotides composed of mononucleotides linked through condensation reactions).
★ Edexcel (Biology B)
Specification Reference: - Topic 1: Biological Molecules. 1.1 Carbohydrates ii) Know the structure of the pentose ribose (and deoxyribose).1.4 DNA and protein synthesis i) Know the structure of DNA, including the structure of the nucleotides (purines and pyrimidines), the sugar-phosphate backbone and phosphodiester bonds.
★ OCR (Biology A)
Specification Reference: - Module 2: Foundations in biology –
2.1.2 Biological molecules. (d) the ring structure of ribose as an example of a pentose monosaccharide. 2.1.3 Nucleotides and nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made. To include the differences between RNA and DNA nucleotides, the identification of the purines and pyrimidines and the type of pentose sugar. (b) the synthesis and breakdown of polynucleotides by the formation and breakage of phosphodiester bonds.
★ OCR (Biology B)
Specification Reference: - 2.1.4 Nucleic acids. (a) the structure of a nucleotide as the monomer from which nucleic acids are made - To include the differences between RNA and DNA nucleotides, the identification of the purines and pyrimidinesthe type of pentose sugar and the formation of phosphodiester bonds (the sugar-phosphate backbone).
Specification Reference: -
Basic Biochemistry and Cell Organisation (1). (c) the structure, properties and functions of carbohydrates: pentose sugars Ribose and Deoxyribose).
Basic Biochemistry and Cell Organisation (5). Nucleic acids and their functions, (a) the structure of nucleotides (pentose sugar, phosphate, organic base). (e) the structure of nucleic acids: DNA bases: purines and pyrimidines. (f) the similarities and differences in the structure of RNA and DNA.