Chapter 2: biological molecules Flashcards
reagent used for reducing sugars
Benedict’s reagent
reducing sugars test
- Benedict’s reagent contains copper ions
- when heated with reducing sugars, the copper ions are reduced to copper compounds
- the colour changes from blue to brown
- this test can be used for a range of concentrations of sugars
reagent used for non-reducing sugars
Benedict’s reagent, following acid hydrolysis
non-reducing sugars test
- sucrose is a commonly occurring non-reducing sugar
- when heated with dilute acid, sucrose is hydrolysed into its constituent monosaccarides, glucose and fructose, which are both reducing sugars
- excess acid is then neutralised by the addition of sodium hydrogen carbonate and the mixture is then tested with Benedict’s reagent. This will show the production of reducing sugars
reagent used for starch
iodine in potassium iodide solution
starch test
iodine solution turns from brown to blue black in the presence of starch
proteins reagent
biuret reagent
‘macromolecule’ definition
a large biological molecule
‘monomer’ definition
a simple molecule which is used as a basic building block for the synthesis of a polymer
‘polymer’ definition
a giant molecule made from many similar repeating subunits joined together in a chain
monosaccharides function
- source of energy in respiration
- building blocks for larger molecules
monosaccharide definition
a molecule consisting of a single sugar unit with the general formula (CH20)n
‘disaccharide’ definition
a sugar molecule consisting of two monosaccharides joined together vy a glycosidic bond
‘polysaccharide’ definition
a polymer whose subunits are monosaccharides joined together by glycosidic bonds
what is starch made up of?
a mixture of amylose and amylopectin
what is the storage carbohydrate in animal cells?
glycogen
why are hydrogen bonds strong?
they are individually weak but collectively they provide enormous strength
describe the characteristics of cellulose fibres:
- very high tensile strength so that they can withstand the high pressures caused by osmosis
- freely permeable, allowing water and solutes to reach or leave the cell surface membrane
what chemical group do fatty acids contain?
-COOH
acid + alcohol produces what chemical?
an ester
what is the bond between an acid and an alcohol called?
an ester bond
what are the most common lipids?
triglycerides
describe the solubility of triglycerides
insoluble in water but soluble in certain organic solvents
describe the roles of triglycerides
- energy reserves
- insulator against loss of heat
- metabolic source of water
describe the unusual property of phospholipids
- one end is soluble in water
- one of the three fatty acid molecules is replaced by a phosphate group, which is polar
describe the phosphate group in a phospholipid in one word
hydrophilic (water-loving)
describe three functions of proteins
- enzymes
- some hormones (eg insulin)
- antibodies
describe the general structure of all amino acids
- central carbon atom
- bonded to an amine group NH2
- and a carboxylic acid group, COOH
how do amino acids differ from each other?
by the R group
when two amino acids join together, they form a…
peptide bond
what is a polypeptide?
a molecule made up of many amino acids linked together by peptide bonds
where are polypeptides formed?
in the ribosomes
‘primary structure’ definition
the sequence of amino acids in a polypeptide or protein
‘secondary structure’ definition
the structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids
‘tertiary structure’ definition
the compact structure of a protein molecule resulting from the dimensional coiling of the already-folded chain of amino acids
hydrogen bonds form between…
strongly polar groups eg -NH-, -CO- and -OH groups
disulfide bonds form between…
cysteine molecules
disulfide bonds are…
strong covalent bonds
ionic bonds form between…
- ionised amine (NH3+) groups
- ionised carboxylic acis (COO-) groups
how are disulfide bonds broken?
by reducing agents
how are ionic bonds broken?
by pH changes
weak hydrophobic interactions occur between…
non-polar R groups
what structure does haemoglobin have?
a quaternary structure
describe the structure of haemoglobin
- four polypeptide chains
- each chain is a protein called a globin
- two chains are alpha-globin, two are beta-globin
- each chain contains a haem group (a prosthetic group)
- each haem group contains an iron atoms
- one 02 molecule can bind with each iron atom
describe the structure of collagen
- three polypeptide chains wound round each other
- every third amino acid in each polypeptide is glycine
- covalent bonds form between the R groups of amino acids lying next to each other
- these cross links form fibrils
- they form fibres
water as a solvent
- water molecules are attracted to the ions and polar molecules
- they collect around and separate them
the high specific heat capacity of water
- the amount of heat required to raise its temperature by a given amount
- hydrogen bonds need to be broken to allow free movement
high latent heat of vaporisation of water
- a measure of the heat energy needed to vaporise a liquid, changing it from a liquid to a gas
- it means that living organisms can use evaporation as a cooling system
high surface tension and cohesion of water
- the molecules tend to stick together
- water can move through long, unbroken columns through the vascular tissue in plants
- the surface of water is a habitat for small organisms
