Nucleotides (OCR A-level Biology)

This detailed lesson describes the structure of a nucleotide and a phosphorylated nucleotide and explains how polynucleotides are synthesised and broken down. The engaging PowerPoint has been designed to cover points [a], [b] and [c] of module 2.1.3 as detailed in the OCR A-level Biology A specification and links are made throughout to earlier topics such as biological molecules.

Students were introduced to the term monomer and nucleotide in the previous module, so the start of the lesson challenges them to recognise this latter term when only the letters U, C and T are shown. This has been designed to initiate conversations about why only these letters were used so that the nitrogenous bases can be discussed later in greater detail. Moving forwards, students will learn that a nucleotide is the monomer to a polynucleotide and that deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two examples of this type of polymer. The main part of the lesson has been filled with various tasks that explore the structural similarities and structural differences between DNA and RNA. This begins by describing the structure of a nucleotide as a phosphate group, a pentose sugar and a nitrogenous base. Time is taken to consider the details of each of these three components which includes the role of the phosphate group in the formation of a phosphodiester bond between adjacent nucleotides on the strand. At this point students are challenged on their understanding of condensation reactions and have to identify how the hydroxyl group associated with carbon 3 is involved along with the hydroxyl group of the phosphoric acid molecule. A number of quiz rounds are used during this lesson, as a way to introduce key terms in a fun and memorable way. One of these rounds introduces adenine and guanine as the purine bases and thymine, cytosine and uracil as the pyrimidine bases and the students are shown that their differing ring structures can be used to distinguish between them. The remainder of the lesson focuses on ADP and ATP as phosphorylated nucleotides and links are made to the hydrolysis of this molecule for energy driven reactions in cells such as active transport