Notes on: Water, carbohydrates, lipids, proteins, tests, colorimetry, chromatography, and biosensors.
These notes are written for each OCR A specification point however, can be used for all exam boards as the content is the same.
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(a) how hydrogen bonding occurs between water molecules, and relate this, and other properties of water, to
the roles of water for living organisms.
Hydrogen bonding is a type of electrostatic attraction
between two polar groups. Water molecules are made from
one oxygen atom that is covalently bonded to two hydrogen
atoms. The hydrogen atoms have a slight positive charge
whereas, the oxygen atom has a slightly negative charge.
This is because oxygen has more protons so it attracts more
electrons. The partial negative charge on the O of one
molecule can form a hydrogen bond with the partial positive
charge on the hydrogens of other molecules.
Properties obtained by water-
1. Thermal Stability- Water has a high specific heat capacity so a lot of energy is needed to heat it. Therefore, our
body maintains a constant temperature so it is an ideal transport medium (makes up blood). There is also
temperature stability in oceans/lakes.
2. Ice is less dense than water. This means that it can float so living things can survive below the ice. Also allows
polar bears to live as they live on floating ice packs.
3. Cohesion- Water molecules stick together which creates high surface tension. This means that small organisms
can walk on it. This also allows water to be pulled up a straw. It also allows water to be transported up the xylem.
4. Water is a good solvent. It can dissolve polar substances as it is polar.
5. Water is used in a wide range of reactions in the human body such as condensation and hydrolysis.
6. Adhesion Attraction between two different molecules. It is a strong attraction for water and other molecules
bearing positive or negative charges. It enables water to "climb up" a tube which is known as capillary action.
7. Water is transparent so allows underwater photosynthesis.
(b) the concept of monomers and polymers and the importance of condensation and hydrolysis reactions in a
range of biological molecules
Monomers are individual molecules that can bond to other identical monomers to form a string of such molecules called
a polymer.
Condensation Reaction- A reaction in which two molecules join together and release a water molecule
Hydrolysis Reaction- A reaction in which two molecules split and use up a water molecule to do so
(c) the chemical elements that make up biological molecules
C, H and O for carbohydrates
C, H and O for lipids
C, H, O, N and S for proteins
C, H, O, N and P for nucleic acids.
(d) the ring structure and properties of glucose as an example of a hexose monosaccharide and the structure
of ribose as an example of a pentose monosaccharide
Monosaccharides come in many different forms, ranging from three to
six carbon atoms. They all: are soluble in water, are sweet tasting and
form crystals. They are grouped according to the number of Carbon
atoms, being called triose, tetrose, pentose or hexose sugars, the
most common being hexose sugars. Pentose and hexose sugars tend
to form ring structures. One carbohydrate molecule is known as a
monosaccharide. (The formula is CnH2n0n). Hexose
monosaccharides (C6H1206) include Glucose, Fructose and
Galactose. These are known as structural isomers. They are different
forms of the same molecule.
Alpha and Beta Glucose:
, (e) the synthesis and breakdown of a disaccharide and polysaccharide by the formation and breakage of
glycosidic bonds. To include the disaccharides sucrose, lactose and maltose.
Disaccharide – Two monosaccharide units joined by a covalent bond Polysaccharides- Many monosaccharide units
joined together by covalent bonds
Glucose + Glucose ----> Maltose Broken down by the enzyme Maltase
Glucose + Fructose ----> Sucrose Broken down by the enzyme Sucrase
Glucose + Galactose ----> Lactose Broken down by the enzyme Lactase
(f) the structure of starch (amylose and amylopectin), glycogen and cellulose molecules
(g) how the structures and properties of glucose, starch, glycogen and cellulose molecules relate to their
functions in living organisms
Cells get energy from glucose. Plants store glucose as starch. Starch is a
mixture of two polysaccharides: Amylose and Amylopectin.
Amylose: A long, unbranched chain of alpha glucose. The angles of the glycosidic bonds give it a coiled helical
structure. This makes it compact so it is good for storage because you can fit more in a small space.
Amylopectin: A long, branched chain of alpha glucose. The side branches allow the enzyme to get in the glycosidic
bonds quickly, so glucose can be released rapidly.
Starch is insoluble in water. This means that water cannot enter the cell via osmosis. This makes it good for storage.
Glycogen: Animals store excess glucose as glycogen. It has a similar structure to Amylopectin, but has more branches.
It is also more compact.
Cellulose: (A major cell wall component) Made of long, unbranched chains of Beta glucose. They do a 180 degrees
turn at every monomer. The bonds are straight so the chains are straight. They are connected by hydrogen bonds.
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