Enzymes and Proteins Flashcards
what structures can be part of enzymes to help them work properly?
cofactors and coenzymes
what is the main function of enzymes?
increase the rate of spontaneous reactions
reduce activation energy for a reaction
speed up the time it takes to reach reaction equilibrium
in what ways do enzymes reduce the activation energy of a reaction?
decreasing entropy (create more order)
induced fit
desolvation
what is the active site of an enzyme complementary to and why?
it’s complementary to the transition state
if it was complementary to the substrate, it would be stable and not cause a reaction
what is Vmax?
it is the maximum reaction speed of an enzyme when it is saturated with substrate
what is Km in the context of enzymes and what do its values mean?
it’s the ratio of rate constant of breaking vs formation of an enzyme-substrate complex
high Km means poor affinity (unstable complex)
low Km means high affinity (stable complex)
how can Km be calculated from a V0 (initial velocity)/S (substrate) plot?
it’s calculated as half of Vmax
what is the basis of the Michaelis-Menten (M-M) equation?
that the first part of an enzyme/substrate reaction (E+S = ES) is reversible and faster than the second one (ES = E + S)
what are isoenzymes?
different enzymes that catalyse the same reaction
what are the mechanisms for multiple substrates to bind to an enzyme?
ternary complex formation (random or ordered)
no ternary complex (sequential, one substrate after the other)
ping pong reaction (simultaneous group transfers)
what is an allosteric enzyme?
an enzyme where substrate binding to one subunit will cause other subunits to have more affinity to substrate
what are three factors that can affect enzyme function?
temperature
pH
inhibitors
what are two ways allosteric enzymes can function, and what are they classed as?
allosteric enzymes = regulatory enzymes concerted model (all subunits bind at the same time) sequential model (one subunit+substrate triggers the others to open)
what are different types of enzyme inhibitors?
competitive (binds in place of substrate)
uncompetitive (binds to enzyme and changes its shape)
noncompetitive (binds after substrate to trap it)
what are possible ways for enzymes to be modulated?
allosteric enzymes (concerted or sequential) covalent modification (phosphorylation) proteolytic cleavage (eg prodrugs)
what can be used to study enzymes?
gel electrophoresis
what is the structure of an amino acid?
amino group
carboxylic acid group
R side chain (gives unique properties to protein)
what is primary amino acid structure and what bonds are present?
linear arrangement of polypeptides covalent bond (peptide bonds)
what is the secondary amino acid structure and what bonds are present?
spatial arrangement of linear polypeptides close to eachother alpha helix (HN-OC) hydrogen bonds, helical shape beta sheet (HN-OC) hydrogen bonds
what is the tertiary amino acid structure and what bonds are present?
spatial arrangement of linear polypeptides far away from eachother
bonded by: disulphide bridges, hydrogen bonds, ionic bonds, hydrophobic reactions, vd Waals forces
what is a quaternary amino acid structure?
arrangement of tertiary structures in subunits
what is protein denaturation and digestion, and what can cause them?
denaturation - loss of secondary and tertiary structure
causes: heat, pH, chemicals, solvents
digestion - loss of primary covalent bond
causes: enzymes that cleave strong peptide bonds
what is the effect of denaturation on a protein?
loss of shape
loss of function
less soluble/altered water solubility
how can proteins be classified in seven classes?
aliphatic aromatic sulphur-containing acids bases uncharged polar other
what are the different structural differences in proteins, and what functions can they have?
globular proteins - hemoglobin (enzymes, transporters, hormones, signalling)
fibrous proteins - collagen (ECM, tendons, connective tissue, bone)
membranous proteins - LDL receptor (cell-cell signalling, recognition, structure, transporters)
what is collagen composed of?
three polypeptides attached with hydrogen bonds
what are possible disorders caused by abnormalities in protein structure?
globular - sickle cell anaemia (Hb structure abnormal)
fibrous - scurvy, osteogenesis imperfecta (collagen weak)
membranous - familiar hypercholesterolaemia (LDL receptor mutation)
what are some of the molecules proteins can be attached to for different functional purposes?
lipids - lipoproteins (carry insoluble compounds)
metals - metalloproteins (metals often needed by enzymes to carry out function)
glucose - glycoprotein (variety of functions)
what is glycosylation and where does it occur?
addition of glucose molecule to protein
occurs in ER and Golgi complex
what is the result of amino acids joining together?
covalent bond (peptide bond) condensation (loss of one water molecule)
