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Module 1 ­ Biological Molecules
· 2.1.1 ­ Biological molecules
(a)
describe how hydrogen bonding occurs between water molecules, and relate this, and other properties of water, to the roles of water in
living organisms (HSW1);
(b)describe, with the aid of diagrams, the structure of an amino acid;
(c)describe, with the aid of diagrams, the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and
polypeptides;
(d)explain, with the aid of diagrams, the term primary structure;
(e)explain, with the aid of diagrams, the term secondary structure with reference to hydrogen bonding;
(f)explain, with the aid of diagrams, the term tertiary structure, with reference to hydrophobic and hydrophilic interactions, disulfide
bonds and ionic interactions;
(g)explain, with the aid of diagrams, the term quaternary structure, with reference to the structure of haemoglobin;
(h)describe, with the aid of diagrams, the structure of a collagen molecule;
(i)compare the structure and function of haemoglobin (as an example of a globular protein) and collagen (as an example of a fibrous
protein);
(j)describe, with the aid of diagrams, the molecular structure of alpha-glucose as an example of a monosaccharide carbohydrate;
(k)state the structural difference between alpha-and beta-glucose;
(l)describe, with the aid of diagrams, the formation and breakage of glycosidic bonds in the synthesis and hydrolysis of a disaccharide
(maltose) and a polysaccharide (amylose);
(m)compare and contrast the structure and functions of starch (amylose) and cellulose;
(n)describe, with the aid of diagrams, the structure of glycogen;
(o)explain how the structures of glucose, starch (amylose), glycogen and cellulose molecules relate to their functions in living organisms;
(p)compare, with the aid of diagrams, the structure of a triglyceride and a phospholipid;
(q)explain how the structures of triglyceride, phospholipid and cholesterol molecules relate to their functions in living organisms;
(r)describe how to carry out chemical tests to identify the presence of the following
molecules: protein (biuret test), reducing and non-reducing sugars (Benedict's test), starch (iodine solution) and lipids (emulsion test);
(s)describe how the concentration of glucose in a solution may be determined using colorimetry…read more

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Describe how hydrogen bonding occurs between water molecules, and relate
this, and other properties of water, to the roles of water in living organisms
Property of water Importance Examples Hydrogen bonds
Solvent Metabolic processes in all organisms rely on 70-95% of cytoplasm is water. If the solute is slightly charged or ionic, they
chemicals being able to react together in Dissolved chemicals take part in processes will interact with water molecules.
solution such as respiration and photosynthesis in The water molecules will cluster around the
living organisms. charged parts, keeping solute molecules
apart
Liquid The movement of materials around Blood in animals and the vascular tissue in Water remains liquid over a range of
organisms, both in cells and on a large scale plants use water as a liquid transport temperature range and can act as a solvent
in multicellular organisms requires a liquid medium for many chemicals
transport medium
Cohesion Water molecules stick to each other creating Transport of water in the xylem relies on A drop of water on the waxy surface of the
surface tension at the water surface. water molecules sticking to each other as leaf looks almost spherical ­ it hardly wets
Cohesion also makes long, thin water they are pulled up the xylem in the the leaf at all.
columns very strong and difficult to break transpiration stream. This is because hydrogen bonds pull the
Some small organisms make use of surface water in at the surface.
tension to `walk on water'. This is cohesion, which also results in surface
tension
Freezing Water freezes, forming ice on the surface. Organisms such as polar bears live in an Water is unusual because its solid form is
Water beneath the surface becomes environment of floating ice packs. less dense than its liquid form.
insulated and less likely to freeze Lakes tend not to freeze completely, so As water cools, its density increases until the
aquatic organisms are not killed as temperature drops to 4 degrees, the density
temperatures fall increases again, so ice floats on water
Thermal stability Large bodies of water have fairly constant Oceans provide a relatively stable The hydrogen bonds in liquid water restrict
temperatures. environment in terms of temperature. the movement of the water molecules, so a
Evaporation of water can cool surfaces by Many land-based organisms use evaporation relatively large amount of water is needed to
removing heat as a cooling mechanism, e.g. In panting or increase the temperature of water.
sweating
The evaporation of water uses a relatively
large amount of energy, so water
evaporating from the surface `removes' heat
energy from the surface
Metabolic Water takes part as a reactant in some Water molecule are used in hydrolysis
chemical processes. reactions and in the process of
photosynthesis.…read more

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Describe with the aid of diagrams, the
structure of an amino acid
H2N ­ CHR - COOH…read more

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Describe, with the aid of diagrams, the
formation and breakage of peptide
bonds in the synthesis and hydrolysis
Synthesis:
· A condensation reaction occurs between the
hydroxide group of an acid group of one amino
acid and the bottom hydrogen of another.
1) A water molecule is released
2) A new covalent bond is formed (peptide bond)
3) A larger molecule (dipeptide) is formed by the
bonding of smaller molecules.
Hydrolysis:
1) A water molecule is used
2) A covalent bond (peptide bond) is broken
3) Smaller molecules (amino acids) are formed by
the splitting of a larger molecule.…read more

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Explain, with the aid of diagrams, the
term primary structure
· Primary structure: A
sequence of amino
acids…read more

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