Biological Molecules

Transcription

1 SIM Tuition Biological Molecules I won t lie. This is probably the most boring topic you have ever done in any science. It s pretty much as simple as this: learn the material deal with it. Enjoy don t say I didn t warn you. Revision from GSE and earlier ells contain many small molecules such as: - water (approximately 80% of the mass of a typical cell) - inorganic ions (e.g. sodium and calcium essential for cell function) - large molecules (e.g. carbohydrates, lipids and proteins made up of lots o small molecules) arbohydrates, lipids and proteins found in living organisms are described as organic because the contain carbon. Many of these organic molecules are very large in size and so are called macromolecules. ften the smaller molecules that make up the macromolecule are identical (or similar) to each other and so are described as monomers. Monomers join together to form polymers. Right, so let s see how much you remember with a childish, yet still useful, fill in the gaps! Starch, protein and lipids are all large molecules. Starch is made up of many molecules and proteins are made up of. A lipid consists of a molecule of and three. Now just to add a little variety into the mixture Which of the molecules in the above short paragraph is: 1. a monomer (1) 2. a polymer (2) 3. a macromolecule (3) K that was so easy, if you didn t get 100% you should be worrying. But don t worry too much, we have a year to work on these basic principles. ondensation and ydrolysis reactions - two monomers can be joined together by a condensation reaction. As you may have guessed from the name, in this process, water is formed. (And if you didn t guess never mind maybe next time) o the water molecule comes from a hydrogen on one monomer and a hydroxyl group () on the other - the remaining monomers now remain as residues - joining many monomers together by condensation reactions form polymers - polymers can be broken back into monomers by a hydrolysis reaction. o In this reaction, water is added Page 1

2 SIM Tuition General example of condensation and hydrolysis condensation linked with the removal of a molecule of water hydrolysis broken down with the addition of a molecule of water As you can see, the monomers get joined together by condensation to form a polymer. The diagram shows two monomers joining together. When a large number of monomers are joined like this, we get a polymer. A polymer can be broken down into its monomers by hyrolysis. arbohydrates - have the general formula: x 2y y - Monosaccharides are monomers, but different monosaccharides contain different numbers of carbon atoms (e.g. pentose has 5, hexose has 6 etc.) - Disaccharides are composed of two monosaccharides - Polysaccharides are large molecules containing many monosaccharides Type of arbohydrate Disaccharide Examples Sucrose Maltose Molecular composition Glucose + Fructose Glucose + Glucose Biological importance The form in which sugars are transported in plants Formed from digestion of starch Triose ( ) Pentose ( ) exose ( ) Polysaccharides Lactose Glucose + Galactose arbohydrate found in milk Intermediate product in the Triose biochemical pathways of respiration and photosynthesis Ribose Deoxyribose Sugars found in nucleic acids Glucose Fructose Energy source in respiration Found in sweet tasting fruits Starch Glucose arbohydrate storage in plants Glycogen Glucose arbohydrate storage in animals ellulose Glucose omponent of cell walls Page 2

3 SIM Tuition Glucose As you can see from the table, glucose is really important as it makes up a lot of the other carbohydrates. - Glucose is a monosaccharide - It is a hexose sugar (contains 6 carbon atoms) - The molecular formula is: Diagram showing the structural formula of an α-glucose molecule. A simplified version of the diagram on the left. This is all you need to know for the exam! ther hexose sugars have the same molecular formula but their arrangements differ slightly. Two α-glucose molecules can be joined by a condensation reaction to form maltose. The bond forms between carbon 1 of one α-glucose and carbon 4 of the other. This forms a glycosidic bond. Two α-glucose condensation 2 Maltose Glycosidic bond Reducing sugars - these consist of monosaccharides and disaccharides (except sucrose) - as we know from GSE o these can be tested by: Which gives an precipitate on heating - sucrose is a disaccharide in which glucose is joined to fructose by a glycosidic bond. It has the formula: Page 3

4 SIM Tuition Some structures you may need to know 2 2 Deoxyribose Ribose 2 2 α-glucose β-glucose Really, there are only two structures to learn here. - The only difference between deoxyribose and ribose is the / - The only difference between the α- and β-glucose is the positioning of the and Polysaccharides Starch - a mixture of amylose and amylopectin o amylose and amylopectin are both polymers of α-glucose molecules o they contain a variable number of α-glucose linked by condensation So why is it that the starch in different plants vary? - different numbers of α-glucose molecules - composition of starch (amount of amylose and amylopectin varies) Amylose is mainly a linear structure with 1,4 links (i.e. the carbon atoms that bond are arbon numbers 1 and 4). It often forms a spiral (held together by hydrogen bonds). Amylopectin is highly branched. The linear structure is 1,4 and the branches are formed by 1,6 links. Starch is efficient as a storage molecule. It is used as a way to store excess glucose. - amylose and amylopectin are compact molecules. A lot of starch can be stored in a small space - starch is easily hydrolysed into glucose when needed for respiration - starch is insoluble. Therefore, it is more likely to remain in one place and less likely to affect the water potential of the cell in which it is stored. This reduces water movements (in large quantities) into the cell. Page 4

5 SIM Tuition Glycogen - insoluble for easy storage - main storage compound in animal cells - stored in liver (to be released into blood for widespread use) and muscles (for use in muscles only) - can be easily hydrolysed into glucose when needed for respiration - similar structure to amylopectin but even more branched o as with amylopectin, 1,4 bond is straight. 1,6 link causes branch ellulose - structural polysaccharide - vital component of plant cell walls - composed of β-glucose monomers linked by 1,4 glycosidic bonds o BUT as it is β-glucose, the molecules have to be inverted every other molecule adjacent cellulose molecules bond with hydrogen bonds forming microfibrils. - microfibrils are held together in fibres - these fibres form a mesh in the cell wall - this gives a high tensile strength ensuring strength for the cell wall Unit 1.1 Molecules arbohydrates SYLLABUS EKLIST understand that hexoses and pentoses are monosaccharides and have a role as monomers; recall the structure and understand the roles of the monosaccharides _ and _ glucose, ribose and deoxyribose; understand the roles of fructose and galactose; understand that disaccharides and polysaccharides are composed of monomers joined by glycosidic bonds; understand that condensation and hydrolysis reactions are involved in the synthesis and degradation of disaccharides and polysaccharides; know the monomers of and understand the roles of the disaccharides sucrose, maltose and lactose; recall the structure and understand the roles of the polysaccharides starch (amylose and amylopectin), cellulose and glycogen; relate structure to function of these polysaccharides. Page 5