biological molecules Flashcards
What is a polymer?
Molecule made of large number of monomers joined together
What are monomers?
single units that join to form polymers
What are the monomers in carbohydrates called?
Monosaccharides
(e.g. glucose, fructose, galactose)
Draw the skeletal structure for α-glucose
H on top
OH on bottom
Draw the skeletal structure for β-glucose
H OH
HO H
What is a condensation reaction?
Joining together of molecules with a chemical bond & the elimination of a water molecule (it’s released)
What type of bond is formed between the 2 monosaccharides as a molecule of water is released?
A glycosidic bond
What is formed when 2 monosaccharides join together?
A disaccharide
How is sucrose formed?
α-glucose molecule and fructose molecule
What is lactose formed from?
From glucose molecule & galactose molecule
What is maltose formed from?
2 α-glucose molecules
What is hydrolysis?
Breaking of the chemical bond between monomers using a water molecule
What are polysaccharides?
When more than 2 monosaccharides are joined together by condensation reactions
What is the purpose of starch?
Plants store excess glucose as starch
How are glycogen and starch produced?
the condensation of α-glucose.
what is the structure of starch?
long unbranched coiled or long branched chain
Describe glycogen’s structure
similar to starch but more side branches coming off it + shorter chains
features of starch and glycogen that make it a good storage molecule
insoluble in water so it doesn’t affect water potential
branched so makes molecule compact
polymer of α-glucose so provides glucose for respiration
large so cant cross cell membrane
highly branched also means more enzyme action
Describe the test for starch
- Add iodine solution to test sample
2.If starch present = sample changes from browny-orange to blue-black colour
Describe the structure of cellulose
Long, unbranched chains made up of β-glucose
Straight chains run parallel to each other in cell walls which allows hydrogen bonds to form cross-linkages between chains
formation of micro fibrils which then join together with hydrogen bonds to make fibrils
function of cellulose
used for cell walls bc it adds rigidity and structural support
Describe Benedict’s test for reducing sugars
Add Benedict’s reagent (blue) to sample & heat it in water bath that’s been brought to a boil (for 5 mins)
Test’s positive is orange/red precipitate
Higher the concentration of reducing sugar, further the colour change goes
What’s a more accurate way of comparing the amount of reducing sugar in different solutions (than colour change)?
Filter solution & weigh precipitate
Describe the test for non-reducing sugars
1.Boil (new test sample) with dilute hydrochloric acid (in water bath)
- neutralise it with 5cm3 sodium hydrogencarbonate
3.Carry out Benedict’s test as you would for a reducing sugar
If test’s positive = orange/red precipitate
If test’s negative = solution remains blue = no sugar present
In the test for non-reducing sugars, why is dilute hydrochloric acid added?
To hydrolyse, break down, the non-reducing sugar (disaccharide) into monosaccharides
Name 4 roles of lipids
Energy source-provide more than twice energy as carbs
Protection-stored around delicate organs
Insulation-slow conductors of heat
Waterproofing-insoluble in water
How are triglycerides are formed
condensation of one molecule of
glycerol and three molecules of fatty acid.
each fatty acid forms an ester bond with glycerol
how is the structure of triglycerides related to their properties?(4)
high ratio of energy-storing carbon-hydrogen bonds to carbon atoms so good source of energy
low mass to energy ratio so good storage as lots of energy stored in small volume
insoluble and large so doesn’t affect water potential
high ratio of hydrogen to oxygen atoms means water is released when oxidised
Describe the structure of a phospholipid
One molecule of glycerol with 2 fatty acids + a phosphate group attached to it
what are the two parts of a phospholipid?
hydrophilic head
hydrophobic tail
Describe how a phospholipid’s structure relates to its function(3)
Phospholipids make up the bilayer of cell membranes
Heads are hydrophilic & tails are hydrophobic which forms double layer with their heads facing out towards the water on either side
structure allows them to form glycolipids with carbohydrates which is important for cell recognition
Describe the emulsion test for lipids
- add 2cm3 of sample to dry test tube
- add 5cm3 of ethanol
- shake and add 5cm3 water
- shake thoroughly to mix
if there is milky emulsion, lipid is present
what is the general structure of an amino acid?(4)
R group
central carbon
COOH group
amine group
what bond is formed in the condensation of 2 amino acids?
peptide bond
What is the primary structure in proteins?
Sequence of amino acids in polypeptide chain
What is the secondary structure in proteins?
Hydrogen bonds form between amino acids in chain making it coil into alpha helix or fold into beta pleated sheet
What is the tertiary structure in proteins?
Further folding of whole polypeptide chain to create 3d structure
formation of:
Hydrogen bonds
Ionic bonds
Disulfide bonds
What is the quaternary structure in proteins?
Arrangement of more than 1 polypeptide chain in a protein
Describe the biuret test for proteins
- add equal volumes of sodium hydroxide and sample into test tube
- add biuret solution
colour change from blue to purple indicates protein
what is an enzyme?
a globular protein that acts as a biological catalyst by lowering activation energy
what is the induced fit model?
the enzyme is flexible and moulds around the substrate. as it changes shape, this puts a strain on the substrate and lowers activation energy
what are competitive inhibitors?
an enzyme inhibitor that binds to the active site of the enzyme as it has a complementary shape to the tertiary structure of the active site.
what is a non competitive inhibitor?(2)
inhibitors that attach themselves to the enzyme at a binding site other than the active site
this alters the shape of the enzyme so that the substrates are no longer complementary and so can not bind
