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Macromolecules: large molecules, such as lipids, proteins, complex carbohydrates and nucleic acids, that are made by the cell.

Synthesis of biomacromolecules • Autotroph – an organism that makes its own food from light energy or chemical energy without eating. • Chemotroph – an organism that synthesis food through chemical processes other than photosynthesis. • Heterotroph – organisms that consume other organisms as food. They are not able to make organic molecules from simple inorganic compounds.

Making a polymer • Biomacromolecules are built up by linking monomers to form long chains called polymers. This is known as polymerisation.

– Monomer – a small molecule that acts as a building block for macromolecules. – Polymer – large molecules built up from linking smaller molecules together by the process of polymerisation.

• Condensation polymerisation: Monomers link together when the hydroxyl (-OH) group of one monomer reacts with the hydrogen atom of another monomer, forming a water molecule.




+ H2 O

Carbohydrates • Carbohydrates – organic compound consisting of a chain of carbon atoms to which hydrogen and oxygen are attached in a 2:1 ratio. • Carbohydrates can be classified as – Monosaccharides (one sugar) – disaccharides (two sugars) – polysaccharides (many sugars) depending on the linkage of monomers. Glycoproteins – a combination of carbohydrate and protein molecules.

• Cellulose is a polysaccharide that is the most abundant organic compound found in nature. It is only found in plants. • Humans lack the enzyme required to break cellulose down.

Lipids • Lipids – a general term for fats, oils and waxes; they are insoluble in water (hydrophobic) and largely made up of molecules containing carbon, hydrogen, oxygen and, at times, phosphorous and nitrogen. • In cells, lipids have three important functions: – Energy storage – they have twice the amount of energy as carbohydrates – Structural component of membranes – Specific biological functions, such as transmission of chemical signals both within and between cells.

The structure of lipids • Hydrophilic (water loving) head • Hydrophobic (water hating) tail

• Lipids can have hydrophobic and hydrophilic regions (amphipathic)

- Triglycerides • Triglyceride – a simple neutral lipid formed by linking the alcohol glycerol with three fatty acids; these lipids are stored in special cells in the adipose tissue of animals. • Triglycerides can be – – Saturated: when all the bonds between carbon and hydrogen atoms are single bonds. (solid at room temp). – Unsaturated: when one or more double or triple bonds exist between carbon atoms within the molecule. (liquid at room temp)

Lipids in the membranes of cells • Phospholipids – lipid molecules that contain a phosphorus; each molecule has a hydrophilic and hydrophobic end; forms the bilayer of the plasma membrane. • Glycolipids – lipid molecule with an attached short chain carbohydrate; its role is to provide energy or to serve in cell membranes as a marker for cellular recognition. • Cholesterol – a lipid steroid that is essential in the structure of animal cell membranes. It is the starting point for synthesis of all the steroid hormones, e.g. testosterone and oestrogen.

PROTEINS • Protein – a macromolecule built up of amino acid monomers; proteins have specific structural and functional roles in living things and are produced from the information encoded in an organism’s genetic material. • Virtually everything a cell is or does depends on the proteins it contains. • Proteome – the structure and properties of all the proteins produced by an organism’s genetic material. • The diversity of proteins can be explained by the way their subunits, the 20 amino acids are sequenced in various combinations.

- Amino acids • Amino acids – a small molecule that is the monomer for proteins; 20 different amino acids make up proteins and all have the same functional groups (NH2 and COOH). They differ in the number and types of atoms that make up the R group of the molecule. (these can be polar or non-polar)

From amino acids to proteins 1. PRIMARY STRUCTURE DNA determines the sequence of amino acids in the polypeptide. Amino acids bond together in the process of condensation polymerisation and each bond formed is called a peptide bond. 2. SECONDARY STRUCTURE Alpha helices or beta sheets are formed due to hydrogen bonding between the amino acids. 3. TERTIARY STRUCTURE Hydrophilic R groups attract each other as do hydrophobic R groups. Polypeptide becomes coiled folded or twisted into the functional shape. Disulfide bridges can form (s-s). A change in one amino acid will alter this shape and it may not function properly. 4. QUATERNARY STRUCTURE Two or more polypeptides bonding together. E.g. haemoglobin.

• Proteins can lose their functional shape if they are exposed to high temperatures, strong salty solutions or very acidic or alkaline conditions. These conditions can denature or change the shape of the protein molecules. • Sometimes if the change is small the protein can return to its functional shape. However if the change is major, it cannot.

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