3.1.4 │ PROTEINS Flashcards
what are amino acids
monomers from which proteins are made
describe the general structure of an amino acid
central carbon bonded to COOH (carboxyl group), R (variable group) and H₂N (amine group)
how many amino acids are common in all organisms? how do they vary?
20
differ only in their side R group
describe how proteins are formed
condensation reaction eliminating a water molecule between the carboxyl group of one amino acid and the amine group of another amino acid forming a peptide bond
how are dipeptides formed
condensation reaction between two amino acids forming a peptide bond and eliminating a water molecule
how are polypeptides formed
condensation reaction between many amino acids
describe the primary structure of a protein
sequence of amino acids in a polypeptide chain, joined by peptide bonds
describe the secondary structure of a protein
folding of polypeptide chain to formed either an alpha helix or beta pleated sheets
due to hydrogen bonding between amino acids
describe the tertiary structure of a protein
3D folding of polypeptide chain due to interactions between amino acid R groups forming hydrogen bonds, ionic bonds and disulphide bridges
describe the quaternary structure of protein
more than one polypeptide chain formed by interactions between polypeptides
describe the test for proteins
add biuret reagent (blue)
postive result = purple/lilac
how do enzymes act as biological catalysts
lowers activation energy of reaction to speed up rate
describe the induced-fit model of enzyme action
substrate binds to (not completely complementary) active site of enzyme
causing active site to change shape (slightly) so it is complementary to substrate
so enzyme-substrate complex forms
causing bonds in substrate to bend / distort, lowering activation energy
explain the specificity of enzymes
specific tertiary structure determines shape of active site
dependent on 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-substrate complex
describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions
as enzyme conc. increases, rate of reaction increases
enzyme conc. = limiting factor (excess substrate)
more enzymes so more available active sites
so more enzyme-substrate (E-S) complexes form
at a certain point, rate of reaction stops increasing / levels off
substrate conc. = limiting factor (all substrates in use)
describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions
as substrate conc. increases, rate of reaction increases
substrate conc. = limiting factor (too few enzyme molecules to occupy all active sites)
more E-S complexes form at a certain point, rate of reaction stops increasing / levels off
enzyme conc. = limiting factor
as all active sites saturated / occupied (at a given time)
describe and explain the effect of temperature on the rate of enzyme-controlled reactions
as temp. increases up to optimum, rate of reaction increases more kinetic energy so more E-S complexes form
as temp. increases above optimum, rate of reaction decreases enzymes denature- tertiary structure and active site change shape as hydrogen / ionic bonds break so active site no longer complementary so fewer E-S complexes form
Describe and explain the effect o
describe and explain the effect of pH on the rate of enzyme-controlled reactions
as pH increases / decreases above / below an optimum, rate of
reaction decreases
enzymes denature- tertiary structure and active site change shape
as hydrogen / ionic bonds break so active site no longer complementary so fewer E-S complexes form
describe and explain the effect of competitive inhibitors on the rate of enzyme-controlled reactions
as concentration of competitive inhibitor increases, rate of
reaction decreases similar shape to substrate competes for / binds to / blocks active site so substrates can’t bind and fewer E-S complexes form
increasing substrate conc. reduces effect of inhibitors (dependent on relative concentrations of substrate and inhibitor)
describe and explain the effect of non-competitive inhibitors on the rate of enzyme-controlled reactions
as concentration of non-competitive inhibitor increases, rate of
reaction decreases binds to site other than the active site (allosteric site)
changes enzyme tertiary structure / active site shape so active site no longer complementary to substrate so substrates can’t bind so fewer E-S complexes form
increasing substrate conc. has no effect on rate of reaction as
change to active site is permanent
what are competitive inhibitors
molecules with a similar shape to an enzymes substrate that binds to its active site preventing the formation of enzyme-substrate complexes
what are non-competitive inhibitors
molecules which bind to the allosteric enzyme on an enzymes substrate causing the shape of the active site to change preventing the formation of enzyme-substrate complexes
