Biological molecules Flashcards
Monomers and polymers
A monomer is a small, single molecule, many of which can be joined together to form a polymer
A polymer is a large molecule made up of many similar or identical monomers joined together
Monosaccharides and the resulting disaccharides
Monosaccharides are the monomers from which larger carbohydrates are made e.g. glucose, fructose and galactose
Glucose + glucose = maltose
Glucose + fructose = sucrose
Glucose + galactose = lactose
A condensation reaction between 2 monosaccharides forms a glycosidic bond
Isomers of glucose: alpha and beta glucose
C6H12O6
Isomers have the same molecular formula but differently arranged atoms
Difference in structures between alpha and beta glucose is that the OH group is below C1 on a-glucose but above C1 in B-glucose
Triglycerides what do they do
Triglycerides are energy-storage molecules
Triglycerides how are they formed
Formed by the condensation of 1 molecule of glycerol and 3 fatty acids.
The condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond
Triglycerides properties related to structure
They have a high ratio of C-H bonds to C atoms in the hydrocarbon tail so they release more energy than the same mass of carbohydrates.
They are insoluble in water (clump together as droplets) so no effect on the water potential of the cell.
Phospholipids what are they
1 molecule of glycerol, 2 fatty acids, a phosphate-containing group.
Phosphate head, fatty acid tails
Phospholipids properties related to structure
Phosphate heads are polar/hydrophilic so they are attracted to water. Orients to the aqueous environment either side of the membrane
Fatty acid tails are non-polar/hydrophobic so they are repelled by water. Orients to the interior of the membrane so that it repels polar/charged molecules.
Phospholipids what do they do
Forms bilayer in the cell membrane, allowing diffusion of non-polar/small molecules
Saturated fatty acids
No C=C bonds in hydrocarbon chain; all carbons fully saturated with hydrogen
Unsaturated fatty acids
One or more C=C double bonds in hydrocarbon chain
Emulsion test for lipids
1.) add ethanol and shake (to dissolve lipids)
2.) add water
3.) positive test: milky/cloudy white emulsion
Condensation reaction
Joins 2 molecules together
Eliminates a water molecule
Forms a chemical bond
Hydrolysis reaction
Separates 2 molecules
Requires addition of a water molecule
Breaks a chemical bond
Glycogen structure and function
Energy store in animal cells
Polysaccharide of α-glucose with C1-C4 and C1-C6 glycosidic bonds, so it is branched
Glycogen structure related to function
Branched; can be rapidly hydrolysed to release glucose for respiration to provide energy
Large polysaccharide molecule, cannot leave cell
Insoluble in water; water potential of cell is not affected, therefore there is no osmotic effect.
Polymer of glucose so easily hydrolysed
Glucose (polymer) so provides respiratory substrate for energy (release);
Starch structure and function
Energy store in plant cells
Polysaccharide of α-glucose. Mixture of amylose and amylopectin.
Amylose has C1-C4 glycosidic bonds so it is unbranched, whereas amylopectin has C1-C4 and C1-C6 glycosidic bonds so it is branched
Structure of starch related to its function (amylose)
Helical; compact for storage in the cell
Large polysaccharide molecule; cannot leave the cell
Insoluble in water, does not affect the water potential of the cell so there is no osmotic effect
Cellulose function
Provides strength and structural support to plant cell walls
Cellulose structure related to function
Every other beta-glucose molecule is inverted in a long, straight unbranched chain
Many hydrogen bonds link parallel strands to form microfibrils (strong fibres)
Hydrogen bonds are strong in high numbers, provide strength and structural support.
Benedicts test for reducing sugars
Add Benedicts reagent (blue due to copper (ii) sulfate) to the sample
Heat in a water bath
Positive = red precipitate (copper (ii) sulfate reduced to copper (i) oxide)
Benedicts test for non-reducing sugars
Add a few drops of dilute hydrochloric acid (hydrolyse sugar into its constituent reducing sugars)
Heat in a water bath
Neutralise with sodium bicarbonate
Add Benedicts solution and reheat
Positive = red precipitate
How a bond forms between amino acids
A condensation reaction between 2 amino acids forms a peptide bond
Protein primary structure
Sequence of amino acids in a polypeptide chain
Protein secondary structure
Hydrogen bonding between amino acids (between carbonyl O of one and amino H of another)
Causes polypeptide chain to fold into repeating pattern eg alpha helix
Protein tertiary structure
Overall 3D structure of a polypeptide held together by interactions between amino acid side chains:
Ionic bonds/disulfide bridges/hydrogen bonds
Quaternary structure of proteins
Some proteins are made of 2+ polypeptide chains
Held together by more hydrogen, ionic and disulfide bonds
eg haemoglobin
Test for proteins
Add Biurets solution: sodium hydroxide + copper (ii) sulfate
Positive = purple
Detects presence of peptide bonds
Enzymes what do they do
Lowers the activation energy of the reaction it catalyses -> speeds up rate of reaction
Lock and key model
Old, outdated
Active site is a fixed shape, it is complementary to one substrate
After a successful collision, an enzyme-substrate complex forms leading to a reaction
Induced fit model
Recent, accepted
Before reaction, active site is not completely complementary to the substrate
Active site shape changes as substrate binds and enzyme-substrate complex forms.
This stresses/distorts bonds in substrate leading to a reaction
Specificity of enzymes
Enzymes have a specific shaped tertiary structure and active site.
Active site is complementary to a specific substrate
Only this substrate can bind to the active site, inducing fit and forming an enzyme-substrate complex.
Concentration effect on enzyme-controlled reactions
Increasing concentration of enzymes/substrate -> rate of reaction increases.
More enzymes/substrates, more available active sites, more successful enzyme-substrate collisions.
Plateaus due to enzyme/substrate limiting factor.
Temperature effect on enzyme-controlled reactions
Increasing temperature up to optimum -> rate of reaction increases
Increase in kinetic energy, more successful enzyme-substrate complexes.
Increase temperature above optimum: rate of reaction decreases as enzymes are denatured - their tertiary structure and active sites change shape and hydrogen/ionic bonds break.
pH effect on enzyme-controlled reactions
pH above/below optimum pH -> rate of reaction decreases
Enzymes are denatured - their tertiary structure and active sites change shape and hydrogen/ionic bonds break.
Complementary substrate can no longer bind to active site
Fewer collisions
Competitive inhibitors
Decrease rate of reaction
Similar shape to substrate so competes for active site so substrates can’t bind.
Fewer enzyme/substrate complexes
Increasing substrate concentration reduces effect of inhibitor
Non-competitive inhibitors
Decrease rate of reaction
Binds to site away from the active site so that the enzymes tertiary structure changes shape so substrate cannot bind to the active site anymore
Fewer enzyme/substrate complexes
Increasing substrate concentration has no effect on the rate of reaction as there is permanent change on the active site.
