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| Chapter 1Evolution of the Cell | 1 All life forms on Earth are believed to be derived from simple primordial cells that incorporated nucleic acids as the basis of a system of self-replicating molecules. |
| 2 Variation in nucleic acids provided the variation in organisms upon which natural selection could act. | 3 The formation of cells provided stable environments for metabolism. 4 The universal genetic code uses a set of 20 amino acids to form proteins and is found in all life forms. |
| 5 The increase in size of eukaryotic cells was possible because of the development of intracellular compartments and transport systems. | 6 A major evolutionary step occurred with the emergence of multicellular organisms, cell differentiation and specialization into organ systems. This evolutionary development necessitated intercellular signalling and transport systems. |
| Figure 1.9 A segment of the human genome from the centre of the major histocompatibility complex on chromosome 6. This segment is 8 × 10 5base pairs in length and contains a large number of different genes (indicated by coloured boxes), which are expressed in different tissues. | |
| Each gene contains many separate exons separated by large introns, so that only a small proportion of the region shown (< 5%) actually encodes protein. | Expanded below are the genes for lymphotoxin (LTB) and one form of TNF. Each of these genes includes four exons (indicated by coloured boxes), and are transcribed into RNA before being spliced to remove the non-coding regions |
| The region between the two genes contains several regulatory elements (not individually identified), which control whether the gene will be transcribed or not. | Learning outcomes for Chapter 1 When you have studied this chapter, you should be able to: 1.1 Define and use each of the terms printed in bold in the text. 1.2 Describe some of the properties of living systems and relate these to the biological molecules, cellular subsystems, and biological processes that underlie them. |
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