Oxford Handbook of Medical Sciences 2/e

Book Preface

General principles: overview

There are four major chemical components to biological life—carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).
• O, C, and H form the bulk of the dry mass—65%, 18%, and 9% respectively of the human body (e.g. carbohydrates, simple lipids, hydrocarbons)
• N represents 4% and is an essential part of life (nucleotides, amino acids, amino sugars, complex lipids)
• They are supplemented by phosphorus (P) in the form of phosphate (PO4
3– ) and by small amounts of sulphur (S) in the amino acids methionine and cysteine, and in thioester bonds
• There are also a number of essential trace elements (e.g. Mn, Zn, Co, Cu, I, Cr, Se, Mo) that are essential co-factors for enzymes. Note that all biological molecules (biomolecules) must obey the basic rules of chemistry! One important such example for C atoms is stereochemistry:
• Three-dimensional (3D) structures in biomolecules are often key to their function
• Carbon atoms can have four different groups attached to them (i.e. be tetrahedral)
• Under these conditions, the C atom is said to be chiral—it has two mirror-image forms (D- and L-) that cannot be superimposed (see Fig. 1.1)
• Nature has favoured certain stereoisomers:
• For example, naturally occurring mammalian amino acids are always in the L-form, whereas carbohydrates are always in the D-form
• The stereoisomers of therapeutic compounds may have very different effects
° For example, one stereoisomer of the drug thalidomide (which is a racemic mix), used briefl y in the late 1950s to relieve symptoms of morning sickness in pregnancy, caused developmental defects in approximately 12 000 babies.

Biomolecules
Roughly speaking, biomolecules can be divided up into two groups: small and large (macromolecules).
• Small: relative molecular mass (Mr) <1000 (mostly under 400)
• Intermediates of metabolic pathways (metabolites), and/or
• Components of larger molecules
• Macromolecules: Mr >1000, up to millions
• Usually comprise of small biomolecule building blocks, for example:
° Proteins (made up of amino acids)
° Polysaccharides (sugars)
° DNA, RNA (nucleotides, themselves sugars, bases, and
phosphate)
• Macromolecules can contain more than one type of building block; for example, glycoproteins (amino acids and sugars). How are larger biomolecules formed from small ones? When smaller molecules are to be combined into larger ones, often the smaller molecules are activated in some way before the joining reaction takes place. This is because fi rstly, often the activation will allow an otherwise energetically unfavourable reaction to take place and, secondly, it may well infl uence the reaction that takes place to ensure that the correct product is formed.

Contents
Contributors x
Abbreviations xi
1 Cellular structure and function 1
2 Cellular metabolism 95
3 Molecular and medical genetics 183
4 Nerve and muscle 211
5 Musculoskeletal system 267
6 Respiratory and cardiovascular systems 353
7 Urinary system 473
8 Digestive system 511
9 Endocrine organs 587
10 Reproduction and development 621
11 Neuroanatomy and neurophysiology 683
12 Infection and immunity 797
13 Growth of tissues and organs 867
14 Medicine and society 885
15 Techniques of medical sciences 895
Index 941