lipids, proteins and enzymes Flashcards
(23 cards)
name two groups of lipids
triglycerides and phospholipids
describe the structure of a fatty acid (RCOOH)
variable R-group - hydrocarbon chain (saturated or unsaturated)
describe the difference between saturated and unsaturated fatty acids
saturated- no double carbon bonds in hydrocarbon chain, all carbons are fully saturated with hydrogen
unsaturated- one or more double carbon bond in hydrocarbon chain (creating bend)
describe how triglycerides form
-1 glycerol and 3 fatty acids
-condensation reaction
-removing 3 water molecules
-forming 3 ester bonds
explain how the properties of triglycerides are related to their structure
function= energy storage
- high ratio of C-H bonds to carbon atoms in hydrocarbon chain- so used in respiration to release more energy than same mass of carbohydrates
-hydrophobic/non-polar fatty acids so insoluble in water- no effect on water potential of the cell
describe the difference between the structure of triglycerides and phospholipids
one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
describe how the properties of phospholipids relate to their structure
function= to form a bilayer in cell membrane, allowing diffusion of lipid-soluble or very small substances and restricting the movement of water-soluble or larger substances
-phosphate heads are hydrophilic- attracted to water either side of the membrane
-fatty acid tails are hydrophobic- repelled by water so point away from water
describe the tests for lipids
-add ethanol, shake (to dissolve lipids), then add water
-positive result= milky white emulsion
draw general structure of an amino acid
COOH= carboxyl group
R= variable group
H2N= amine group
how many amino acids are common in all organisms and how do they vary
the 20 amino acids that are common in all organisms differ only in their side group (R)
describe how amino acids join together
-condensation reaction
-removing a water molecule
-between carboxyl group of one amine of another
-forming a peptide bond
what are dipeptides
2 amino acids joined together
what are polypeptides
many amino acids joined together
describe primary structure of protein
sequence of amino acids in a polypeptide chain, joined by peptide bonds
describe the secondary structure of a protein
-folding of polypeptide chain e.g. alpha helix/beta pleated sheets
-due to hydrogen bonding between amino acids
-between NH and C=O
describe the tertiary structure of a protein
-3D folding of a polypeptide chain
-due to interactions between amino acid R groups
-forming hydrogen bonds, ionic bonds and disulfide bridges
describe the quaternary structure of a protein
-more than one polypeptide chain
-formed by interactions between polypeptides
describe the test for proteins
-add biuret reagent
-positive result=lilac colour
-indicates presence of peptide bonds
-negative stays blue
how do enzymes act as biological catalysts
-each enzyme lowers activation energy of the reaction it catalyses
-to speed up the rate of reaction
describe the induced-fit model of enzyme action
- substrate binds to (not completely complemntary) active site of enzyme
- causes active site to change shape so it is complementary to substrate
- forms an enzyme-substrate complex
- causing bonds in substrate to bend/distort, lowering the activation energy
describe how models of enzyme activation energy have changed over time
-initially lock and key model- active site a fixed shape, complementary to substrate
-now induced fit model
explain the specificity of enzymes
-specific tertiary structure determines the shape of the active site- this is dependent on the sequence of amino acids (primary structure)
-active site is complementary to a specific substrate
-only this substrate can bind to active site, inducing fit and forming an enzyme
