#7.2 Biological molecules - Syllabus 2016
2.1 Testing for biological molecules2.2 Carbohydrates and lipids2.3 Proteins and water This section introduces carbohydrates, proteins and lipids: organic molecules that are important in cells. Nucleic acids are covered in a separate section. Biological molecules are based on the versatile element carbon. This section explains how macromolecules, which have a great diversity of function in organisms, are assembled from smaller organic molecules such as glucose, amino acids, glycerol and fatty acids. Life as we know it would not be possible without water. Understanding the properties of this extraordinary molecule is an essential part of any study of biological molecules. The emphasis in this section is on the relationship between molecular structures and their functions. Some of these ideas are continued in other sections, for example, the functions of haemoglobin in gas transport in Transport of mammals, phospholipids in membranes in Cell membranes and transport and antibodies in Immunity.
Candidates should be able to:
2.1 Testing for biological molecules
Tests for biological molecules can be used in a variety of contexts, such as identifying the contents of mixtures of molecules and following the activity of digestive enzymes.
a) carry out tests for reducing sugars and non-reducing sugars, the iodine in potassium iodide solution test for starch, the emulsion test for lipids and the biuret test for proteins to identify the contents of solutions
b) carry out a semi-quantitative Benedict?s test on a reducing sugar using dilution, standardising the test and using the results (colour standards or time to first colour change) to estimate the concentration
2.2 Carbohydrates and lipids
Carbohydrates and lipids have important roles in the provision and storage of energy and for a variety of other functions such as providing barriers around cells: the phospholipid bilayer of all cell membranes and the cellulose cell walls of plant cells.
a) describe the ring forms of ?-glucose and ?-glucose
b) define the terms monomer, polymer, macromolecule, monosaccharide, disaccharide and polysaccharide
c) describe the formation of a glycosidic bond by condensation, with reference both to polysaccharides and to disaccharides, including sucrose
d) describe the breakage of glycosidic bonds in polysaccharides and disaccharides by hydrolysis, with reference to the non-reducing sugar test
e) describe the molecular structure of polysaccharides including starch (amylose and amylopectin), glycogen and cellulose and relate these structures to their functions in living organisms
f) describe the molecular structure of a triglyceride with reference to the formation of ester bonds and relate the structure of triglycerides to their functions in living organisms
g) describe the structure of a phospholipid and relate the structure of phospholipids to their functions in living organisms
2.3 Proteins and water
An understanding of protein structure and how it is related to function is central to many aspects of biology, such as enzymes, antibodies and muscle contraction.
Globular and fibrous proteins play important roles in biological processes such as the transport of gases and providing support for tissues.
Water is a special molecule with extraordinary properties that make life possible on this planet 150 million kilometres from the Sun.
a) describe the structure of an amino acid and the formation and breakage of a peptide bond
b) explain the meaning of the terms primary structure, secondary structure, tertiary structure and quaternary structure of proteins and describe the types of bonding (hydrogen, ionic, disulfide and hydrophobic interactions) that hold these molecules in shape
c) describe the molecular structure of haemoglobin as an example of a globular protein, and of collagen as an example of a fibrous protein and relate these structures to their functions (The importance of iron in the haemoglobin molecule should be emphasised. A haemoglobin molecule is composed of two alpha (?) chains and two beta (?) chains, although when describing the chains the terms ?-globin and ?-globin may
be used. There should be a distinction between collagen molecules and collagen fibres)
d) explain how hydrogen bonding occurs between water molecules and relate the properties of water to its roles in living organisms (limited to solvent action, specific heat capacity and latent heat of vapourisation)
- #16 Summary Of Biological Molecules
From small to large 1. The larger biological molecules are made from smaller molecules. Polysaccharides are made from monosaccharides, proteins from amino acids, nucleic acids from nucleotides, lipids from fatty acids and glycerol. 2. Polysaccharides,...
- #14. Globular And Fibrous Proteins - Haemoglobin And Collagen
Globular and Fibrous are 2 main types of proteins with a 3D structure. 1. Haemoglobin, a globular protein Composed of 2 ? + 2 ? polypeptide chains + 1 inorganic prosthetic haem group. Hb's function: carry O2 from...
- #10.tests For Carbohydrates
Tests for Reducing sugars, Non-reducing sugar and Starch. 1. Reducing sugar (Benedict's test) All monosaccharides and most disaccharides (except sucrose) will reduce blue CuSO4(II), producing a precipitate of red Cu2O(I).Benedict?s...
- #9. Carbohydrates - Polysaccharides
Molecules contain hundreds/thousands of monosaccharides linked into long chains. Molecules are enormous --> the majority do not dissolve in water --> good for storing energy (starch and glycogen) or for forming strong structures (cellulose)....
- #8. Carbohydrates - Monosaccharides, Disaccharides
Carbohydrates: - Sugar polymers - Molecules contain C, H, O atoms - H atoms are twice as many as C or O atoms (C6H12O6) Monosaccharides The simplest carbohydrates They are sugar: C = 3 = triose C = 4 = tetrose C = 5...