Biological Molecules

Question 1

Condensation reaction

Answer 1

• Monomers are joined together
producing a larger molecule forming a
bond.
• A molecule of water is used in this
process

Question 2

Hydrolysis reaction

Answer 2

• Polymers and dimers are split a part
breaking bonds
• A water molecule is formed in this
process

Question 3

Disaccharides

Answer 3

• glucose + glucose → maltose (malt sugar)
• glucose + galactose → lactose (milk sugar)
• glucose + fructose → sucrose (table sugar)

Question 4

Starch in plants

Answer 4

• Alpha glucose monomers
• Polysaccharide
• Has 1-4 glycosidic bonds
• Amylose is helical
• Amylopectin is branched and has additional 1-6 glycosidic bonds
• Insoluble so doesn’t effect water potential
• Branched so accessible for respiration

Question 5

Glycogen in animals

Answer 5

• Alpha glucose monomers
• Polysaccharide
• Has 1-4 glycosidic bonds
• Is branched and has many additional 1-6 glycosidic bonds
• Highly branched so accessible for
respiration

Question 6

Cellulose in plants

Answer 6

• Beta-glucose monomers
• Polysaccharide
• Has 1-4 glycosidic bonds
with alternating molecules being rotated
by 180 degrees
• Straight, unbranched
chains
• Straight chains ideal for cell wall, have crosslinks for stability

Question 7

Test for reducing sugars

Answer 7

• Add Benedict’s reagent
• Boil in a waterbath
• Brick red colour indicates a
reducing sugar

Question 8

Test for non reducing sugars

Answer 8

• Carry out benedict’s test and see a negative result
• Boil in a water bath with hydrochloric acid
• Neutralise the acid with sodium
hydrogen carbonate
• Carry out Benedict’s test – a brick red
result indicates a reducing sugar.

Question 9

Iodine test- starch

Answer 9

• Add iodine to food sample
• Blue/Black indicates starch is present

Question 10

Amino acids and peptide bonds

Answer 10

• Amino acids contain C, O, H
and N
• They have a carboxyl group and an amine group
• They also have an R group which can change the properties of the amino acid
• There are 20 amino acids
• They react in a condensation reaction and are joined by a peptide bond
• A polymer of amino acids is called a polypeptide

Question 11

Protein structure

Answer 11

• Proteins have a primary structure that is formed by a sequence of
many amino acids that are joined by peptide bonds in a condensation
reaction
• The primary structure folds into a secondary structure of either alpha
helix or beta pleated sheets and these are held together by hydrogen
bonds
• The secondary structure further folds into a tertiary 3D structure that
is held together by hydrogen bonds, ionic bonds and disulphide bonds
• Some proteins e.g. antibodies may form a quaternary structure of
more than one polypeptide chain(some of these may have prosthetic
groups e.g. haem)

Question 12

Biuret test for proteins

Answer 12

• Add Biurets reagent to sample (copper sulphate and sodium
hydroxide)
• Mix and heat
• Lilac colour indicates protein is present

Question 13

Triglycerides

Answer 13

• Condensation of one glycerol and
three fatty acids forming and
ester bond
• Fatty acids have an R group that
can be saturated(C-C) or
unsaturated (C=C)
• Triglycerides are non-polar
• Insoluble
• Can’t form a bilayer

Question 14

Phospholipids

Answer 14

• Condensation reaction forming
ester bonds
• One glycerol and two fatty acids
• One fatty acid is replaced by a
phosphate group
• The phosphate group is polar
• The fatty acids are non-polar
• Insoluble
• Used in the phospholipid bilayer

Question 15

Emulsion test for lipids

Answer 15

• Mix sample with ethanol and shake
• Add water
• If lipid is present a milky white emulsion will be seen

Question 16

Enzyme induced fit

Answer 16

• Enzyme active site is complementary to the substrate
• When substrate binds the enzyme changes shape slightly
• This stresses the bonds in the substrate
• Reducing the activation energy for the reaction
• The reaction occurs quicker

Question 17

Competitive inhibition

Answer 17

• Binds to active site
• Blocks active site so substrate
can’t bind
• Fewer enzyme-substrate
complexes form

Question 18

Non competitive inhibition

Answer 18

• Binds to allosteric site
• Changes tertiary structure
• Enzyme is no longer
complementary to substrate
• Fewer enzyme-substrate
complexes form

Question 19

DNA structure

Answer 19

• DNA is made of a polymer of nucleotides/polynucleotide
• It is two molecules that are antiparallel to each other coiled into a double
helix.
• Each nucleotide is made of deoxyribose, a phosphate group and a
nitrogenous base that can either be adenine, cytosine, thymine or guanine
• The adjacent nucleotides are joined to each other between the sugar and
phosphate groups in a condensation reaction forming a phosphodiester
bond
• Complementary base pairing holds the two strands together due to
hydrogen bonds forming between A - T and C - G.

Question 20

DNA replication

Answer 20

• DNA helicase breaks the hydrogen bonds causing the strands to
separate
• Both strands act as a template
• Free nucleotides complementary base pair to the template A-T and G-C
• DNA polymerase joins adjacent nucleotides together forming a
phosphodiester bond
• Hydrogen bonds form between the old strand and the newly synthesised strand
• DNA replication is semi-conservative replication

Question 21

ATP structure

Answer 21

• ATP has a nucleotide structure
• It is a ribose sugar with adenine base and three phosphates groups
attached to it
• These phosphate groups can be hydrolysed to remove one phosphate
• This hydrolysis can be used to release energy for chemical reactions,
but can also be used in phosphorylation which can make substrates
more reactive
• ATP can be resynthesised by ATP synthase during respiration and
photosynthesis

Question 22

Water

Answer 22

• It is a metabolite in hydrolysis/condensation reactions
• A solvent so metablic reactions can occur
• High specific heat capacity to buffer changes in temperature
• High latent heat of vaporisation providing a cooling effect
• Cohesion between molecules forms a continuous column of water in the xylem and surface tension for organisms to move on bodies of water

Question 23

Inorganic ions

Answer 23

• Inorganic ions are dissolved in bodily fluids and cytoplasm
• They typically have a specific role
• H+ For Chemiosmosis and Oxidative phosphorylation and maintaining pH
• Fe2+ Haemoglobin
• Na+ Co-transport, depolarisation, sodium potassium pump in action potentials
• K+ For sodium potassium pump
• Ca2+ For NMJ, synaptic transmission and sliding filament
• PO4
3- For phospholipid bilayer, DNA, RNA and ATP
• NO3
- For N-cycle and Nitrogen containing compounds e.g. amino acids, DNA, ATP
etc