enzymes Flashcards
(36 cards)
what are proteins and polypeptides
polymers of amino acids joined
together by peptide bonds
what are the 4 groups of amino acids
Non-polar – hydrophobic
Polar – uncharged
Acidic – negatively charged at physiological pH
Basic – positively charged at physiological pH
what do the R groups determine
the properties, structure and functions, and overall charge of protein
what r groups are found of surface of protein and inside protein
polar and hydrophilic - surface
hydrophobic - inside
what are the interactions between the R groups
disulfide bonds
hydrogen bonds
salt bridge
hydrophobic interaction
what is the hierarchy of protein structure
primary - linear sequence (order) of amino acid residues, joined by peptide bonds
secondary - the localised conformation of the polypeptide backbone e.g. α helix or β sheet
tertiary - the 3-dimensional structure of an entire polypeptide, including all its side chains
quaternary - the spatial arrangement of polypeptide
chains in a protein with multiple subunits
what are enzymes
catalysts, mostly proteins that can increase the rate of a reaction by a factor of up to 10^20
what can each enzyme molecule convert
many substrate molecules into product per second
what are the 6 major classes of enzymes
- Oxidoreductases – catalyse REDOX reactions e.g. lactate dehydrogenase
- Transferases – transfer functional groups e.g. aminotransferases
- Hydrolases – cleaves molecules by addition of water e.g. trypsin
- Lyases – adds (or removes) atoms or functional groups to a carbon carbon
double bond (C=C) e.g. decarboxylases - Isomerases – move functional groups e.g. triose phosphate isomerase
- Ligases – join 2 molecules together using ATP for energy e.g. DNA Ligase
what does the catalytic activity of many enzymes depend on
the presence of small molecules called cofactors
what are the 2 groups of cofactors
metal ions
organic molecules
what do cofactors do
change during course of reaction but are regenerated
what are prosthetic groups
tightly bound coenzymes
what are some examples of cofactors
metal ions - zinc, copper, iron
involved in redox reactions, stabilise transition states
coenzymes - vitamins,
involved in redox reactions - act as reducing or oxidising reaction
do enzymes affect the equilibrium position of reaction
NO
what is the transition state of the enzyme action graph
reaction intermediate species which has the greatest free energy
how do enzymes affect the course of a reaction
they specifically bind and stabilise the transition state and reduce the activation energy by providing alternative pathways but doesn’t affect delta G
Ea definition
- activation energy - energy required to start the reaction
Transition state meaning
intermediate stage in the reaction
delta G
Gibbs free energy - energy change for reaction
what 2 ways can enzymes attach to substrate
lock and key - active site of unbound enzyme is complementary to shape of substrate
induced fit model - binding of substrate induces a conformational change in enzyme, results in complementary fit
what is substrate specificity determined by
size, structure, charge, polarity, hydrophobicity of site
what holds the substrate and the enzyme together
multiple weak attractions usually electrostatic interactions - h bonds, van der waals
how does temperature and Ph affect enzyme activity
temperature - above optimum temp, they may lose tertiary
structure due to breakage of
non-covalent bonds
pH - ionisation states change affecting 3D structure and chemistry of amino acid R chains
