Inorganic ions like iron, calcium, magnesium and phosphate are key components of molecules in living things.   Role of ions in living organisms Calcium Ca2+ Calcium phosphate is an important structural component of bones and teeth. Calcium ions are important in the transmission of nervous impulses and in the contraction of muscles. Magnesium Mg2+ Ions are central to photosynthesis in plants because they are a constituent of chlorophyll. Some enzymes which catalyse the breakdown of ATP have these ions at their active sites. Iron Fe2+ Iron is a component of haemoglobin, which circulates oxygen around the body. Haemoglobin has iron ions at its core to bind it to the oxygen. Phosphate PO43- Used for making nucleotides With calcium it makes calcium phosphate that gives bones their strength.

Water is important because it is a major component of cells. It's molecules have an imbalance of charge (dipolar) and this generates hydrogen bonding between them.   Water is a polar solvent: Oxygen in water has a negative charge and hydrogen bears a relative positive charge. Ions such as those found in sodium chloride (NaCl) can bind respectively to the oxygen side or to the hydrogen side Thus, the salt is soluble and dissolves. Non-polar molecules like lipids do not dissolve in water and tend to be pushed together by it. This is important in hydrophobic interactions in protein structure and in membrane structure. Due to it's ability to dissolve so many molecules, water is an important transport medium in animals and plants. Thermal properties Water molecules are attracted to one another by hydrogen bonds, restricting the movement of the molecules. A relatively large amount of energy is required to increase the temperature of water. Due to their high water content, bodies of organisms are also slow to change temperature which makes maintaining a stable body temperature easier. Water has a large latent heat of vaporisation. This means it can produce a cooling effect when it evaporates without needing much of it, thus risking excessive water loss. Density and freezing properties Waters solid form is less dense than it's liquid form. Below 4°c the density of water starts to decrease, so ice floats on water and insulates the water below it. High surface tension and cohesion Water molecules tend to stick together. When you have long water columns e.g. transport cells in plants, it's a continuous stream that's difficult to break. This property is cohesion. It's also the reason behind water's tight surface against air, called surface tension, Surface tension enables small organisms e.g. pond skaters to exploit water as a habitat.

Monosaccharides:   The smallest units (monomers) of carbohydrates are simple sugars and include trioses, pentoses and hexoses, named due to the number of carbon atoms present- they are monosaccharides. Monosaccharides are soluble in water, are sweet tasting and form crystals. The most common monosaccharide are hexose sugars Pentose and hexose sugars tend to form ring structures. General formula: (CH2O)n where n is a number between 3 and 9. They are classified according to the number of carbon atoms. The monosaccharides you will have to know fall into these categories: C = 3 = triose C = 4 = tetrose C = 5 = pentose C = 6 = hexose Trioses: (e.g. glyceraldehydes), intermediates in respiration and photosynthesis. Tetroses: rare. Pentoses: (e.g. ribose, ribulose), used in the synthesis of nucleic acids (RNA and DNA), co-enzymes (NAD, NADP, FAD) and ATP. Hexoses: (e.g. glucose, fructose), used as a source of energy in respiration and as building blocks for larger molecules. All but one carbon atom have an alcohol (OH) group attached. The remaining carbon atom has an aldehyde or ketone group attached.   When Glucose forms a ring structure, it can do so in two different ways: If the OH at C1 is below the plane of the ring, it is called an α Glucose. If the OH at C1 is above the plane of the ring, it is called β Glucose. This difference in structure leads to a difference in properties.

Disaccharides and glycosidic bonds These are formed when two monosaccharides are condensed together: One monosaccharide loses an H atom from carbon atom number 1 and the other loses an OH group from carbon 4 to form the bond. This condensation reaction involves the loss of water and the formation of an 1,4-glycosidic bond. Depending on the monosaccharides used, this can be an α-1,4-glycosidic bond or a β-1,4-glycosidic bond. The reverse of this reaction is called a hydrolysis reaction and requires one water molecule to supply the H and OH to the sugars formed. Examples of Disaccharides Sucrose: glucose + fructose, used in many plants for transporting food reserves, often from the leaves to other parts of the plant. Lactose: glucose + galactose, the sugar found in the milk of mammals. Maltose: glucose + glucose, the first product of starch digestion and is further broken down to glucose before absorption in the human gut.     Biochemical tests All monosaccharides and some disaccharides including maltose and lactose are reducing sugars. These can be tested fo, by adding Benedict's reagent to the sugar and heating in a water bath. If a reducing sugar is present, the solution turns green, then yellow and finally produces a brick red precipitate. Non-reducing sugars can also be tested for using Benedict's reagent but first require addition of an acid and heating to hydrolyse (break apart) the sugar. The acid must then be neutralised using an alkali like sodium hydroxide before carrying out the test as described above.

Polysaccharides are large complex polymers. They are formed from very large numbers of monosaccharide units, which are their monomers, linked by glycosidic bonds. Starch: This is the main store of glucose for plants. Grains are found in high concentrations in seeds and storage organs. Insoluble therefore good for storage as it has no osmatic effect. The helix is compact. The branches mean that the compound can easily hydrolysed to release the glucose monomers. Starch is made of a-glucose molecules bonded together in 2 different ways, forming the 2 polymers, amylose and amylopectin: Amylose a polymer of glucoses joined by α-1,4-glycosidic bonds. Forms a helix with 6 glucose molecules per turn and about 300 per helix. # Amylopectin a polymer of glucoses joined by α-1,4-glycosidic bonds but with branches of α-1,6-glycosidic bonds. This causes the molecule to be branched rather than helical. Biochemical testing for the presence of starch Iodine solution or potassium iodide solution can be used to test for the presence of starch. A positive result changes the solution from an orange-brown to a blue-black colour. Glycogen: Main storage polysaccharide in animals and fungi, it is our mammalian energy storage e.g. in the liver and muscles. Similar to amylopectin but with many more branches which are also shorter. The number and length of the branches means that it is extremely compact. Cellulose: It is the main structural constituent of plant cell walls Structure made up of adjacent chains of long, unbranched polymers of glucose joined by β-1,4-glycosidic bonds. These straight chains laid next to one another form hydrogen bonds which strengthen them into larger sub-units called microfibrils. Microfibrils are what cellulose is made of, and what gives plant cell walls their great strength. Freely permeable, spaces between the fibres. Chitin: Found in the exoskeleton of insects and in fungal cell walls. Resembles cellulose, with long chains of β-1,4-linked monomers, but has groups derived from amino acids added, to form a heteropolysaccharide. Strong, waterproof, leightweight.

Cell membranes are made of phospholipids, which are made of lipids. Lipids are made up of the elements carbon, hydrogen and oxygen but in different proportions to carbohydrates. The most common type of lipid is the triglyceride. Lipids can exist as fats, oils and waxes. Fats and oils are very similar in structure (triglycerides). At room temperature, fats are solids and oils are liquids. Fats are of animal origin, while oils tend to be found in plants. Waxes have a different structure (esters of fatty acids with long chain alcohols) and can be found in both animals and plants. Triglycerides: These are made up of 3 fatty acid chains attached to a glycerol molecule. Fatty acids are chains of carbon atoms, the terminal one having an OOH group attached making a carboxylic group (COOH). The length of the chain is usually between 14 and 22 carbons long (most commonly 16-18). Three of these chains become attached to a glycerol molecule which has 3 OH groups attached to its 3 carbons. This is called a condensation reaction: 3 water molecules are formed from 3 OH groups from the fatty acids chains. 3 H atoms from the glycerol. The bond between the fatty acid chain and the glycerol is called an ester linkage.   In the fatty acid chains, the carbon atoms may have single bonds between them making the lipid saturated. These are usually solid at room temperature and are called fats. If one or more bonds between the carbon atoms are double bonds, the lipid is unsaturated. These are usually liquid at room temperature and are called oils.

Functions of lipids Storage - lipids are non-polar and so are insoluble in water. High-energy store - they have a high proportion of H atoms relative to O atoms and so yield more energy than the same mass of carbohydrate. Production of metabolic water - some water is produced as a final result of respiration. Thermal insulation - fat conducts heat very slowly so having a layer under the skin keeps metabolic heat in. Electrical insulation - the myelin sheath around axons prevents ion leakage. Waterproofing - waxy cuticles are useful, for example, to prevent excess evaporation from the surface of a leaf. Hormone production - steroid hormones. Oestrogen requires lipids for its formation, as do other substances such as plant growth hormones. Buoyancy - as lipids float on water, they can have a role in maintaining buoyancy in organisms. Phospholipids A phosphate-base group replaces one fatty acid chain. Phospholipids have a hydrophilic (water loving) head, and hydrophobic (water repelling) tails. This results in the formation of a phospholipid bilayer (double layer), which forms the basis for the plasma membrane. These membranes are what separate cells in the body, and enable the transfer of different chemicals between cells and with their environment. Most chemicals in cells are water soluble so lipid membranes act as good barriers that can control the movement of different substances between cells. Only certain small molecules would be able to cross the membrane freely. Other compounds would require carriers or special channels to enable them to overcome the repelling effect between the membrane and their particular chemical state e.g. chemical charge, size, etc. Lipids in health Lipids are central to cell function and health. However, a diet high in certain types of fat has been previously associated with cardiovascular disease. Saturated fats were thought to contribute to disease by increasing low-density lipoproteins (LDL) in the blood, while unsaturated fats could counteract this effect by increasing the high-density lipoproteins (HDL) in the blood.

The functions of proteins are extremely varied but are all made up of amino acid subunits. Proteins are polymers made of monomers called amino acids. The chains of amino acids are called polypeptides. The shape of a protein is determined by the specific sequence of amino acids in the chain Amino acids have the same basic structure. Attached to a central carbon atom are: An amino group: -NH2, at the end of one molecule. A carboxyl group, -COOH, at the other end of the molecule. A hydrogen atom. The R group, different in each amino acid. - At pH7 (pH of a cell), it gains a H and becomes positively charged. - The carboxyl group is acidic and at this pH it loses a H, becoming negatively charged - So at pH7, an amino acid has a both positive and negative charge. Formation of a peptide bond: The amino group of one amino acid reacts with the carboxyl group of another with the elimination of water. The bond formed from this condensation reaction is a peptide bond, and the resulting compound is a dipeptide. Protein Structure: The shape of the protein is held together by H bonds between some of the R groups and ionic bonds between positively and negatively charged side chains. The protein may be reinforced by strong covalent bonds called disulphide bridges which form between two amino acids with sulphur groups on their side chains. Primary structure: The order of amino acids in a polypeptide chain (up to 20 amino acids). The primary structure is determined by the base sequence on one strand of DNA molecule. Secondary structure: The shape polypeptide chains form as a result of hydrogen bonding between the =O on -CO groups, and the -H on -NH groups in the peptide bonds along the chain. Causes the long polypeptide chain to be twisted into a 3D shape. The spiral shape is the a-helix. Another arrangement is the B-pleated sheet. Tertiary structure: The tertiary structure of proteins is their 3D shape which is highly folded and has a unique structure and this structure gives proteins their specific function. The shape is maintained by: Hydrogen bonds Ionic bonds Disulphide bonds Hydrophobic interactions These bonds are important in giving globular proteins, e.g. enzymes, their shape. For example, if insulin was misfolded, it would cease to function properly.   This unique structure gives proteins their specific function. For example, if insulin was misfolded, it would cease to function properly. The origin of misfolding is likely to be in the primary structure, due to a mutation. If the gene responsible for coding the amino acid sequence for insulin was mutated, then the insulin's primary structure would be different, leading to a different secondary & tertiary structure, and ultimately, a lack of proper function.

The roles of proteins depend on their molecular shape. Fibrous proteins: Fibrous proteins are made of long, thin molecules arranged to form fibres. Their shape make them insoluble in water, so they have structural functions. Polypeptides are in parallel chains or sheets, with many cross-linkages forming long fibres. Fibrous proteins are tough and strong. Collagen is another fibrous protein, consisting of three polypeptide chains coiled round each other in a triple helix. The 3 chains are linked by hydrogen bonds, making it very stable. We are largely held together by collagen as it is found in bones, cartilage, tendons and ligaments. Globular proteins: Globular proteins are compact and folded into spherical molecules. They are soluble in water and have many functions, including enzymes, antibodies, plasma proteins and hormones. Folds are highly specific and a particular protein will always be folded in the same way. If the structure is disrupted, the protein ceases to function properly and is said to be denatured. A globular protein based mostly on an α-helix is haemoglobin. A globular protein based mostly on a β-pleated sheet is the immunoglobulin antibody molecule. Functions of proteins Virtually all enzymes are proteins. Structural: e.g. collagen and elastin in connective tissue, keratin in skin, hair and nails. Contractile proteins: actin and myosin in muscles allow contraction and therefore movement. Hormones: many hormones have a protein structure (e.g. insulin, glucagon, growth hormone). Transport: for example, haemoglobin facilitates the transport of oxygen around the body, a type of albumin in the blood transports fatty acids. Transport into and out of cells: carrier and channel proteins in the cell membrane regulate movement across it. Defence: immunoglobulins (antibodies) protect the body against foreign invaders; fibrinogen in the blood is vital for the clotting process. Biochemical test: The reagent used to test for proteins is called biuret reagent. It can be used as two separate solutions of copper sulphate and potassium or sodium hydroxide or as a ready-made biuret solution. In either case, a purple colour indicates a positive result.