Enzymes + proteins Flashcards
(25 cards)
3 principles of enzymatic catalysis
enzymes are catalysts
cannot alter equilibrium of a reaction
accelerate chemical reactions
What is Km?
substrate concentration at which the velocity is half the maximum velocity
measure for stability of enzyme-substrate complex
large Km = (~10-3 M) = low substrate-enzyme affinity
small Km = (~10-5 M) = high substrate-enzyme affinity
What are co-enzymes?
helper molecules that play an essential role in enzyme-catalysed reactions
co-enzyme as co-substrate = co-enzyme reversibly bound to enzyme
co-enzyme as prosthetic group = co-enzyme covalently linked with enzyme
Types of co-enzymes
energy-transferring coenzymes (eg. ATP transfers phosphate groups)
electron and oxygen transferring coenzymes (eg. NADH transfers electrons)
group-transferring coenzymes (eg. lipoic acid transfers acyl groups)
What is irreversible inhibition?
when enzyme reacts with irreversible inhibitor, enzyme will die
eg. penicillin
What is reversible inhibition?
competitive or non-competitive inhibition
Describe competitive inhibition
enzyme can bind to substrate or competitive inhibitor (but not both at same time)
can overcome competitive inhibition by increasing substrate concentration
eg. sulfonamides
Describe non-competitive inhibition
enzyme or enzyme-substrate complex can bind to non-competitive inhibitor (bind to different parts of enzyme)
cannot be overcome by increasing substrate concentration
enzyme usually only partially inhibited
eg. calcium channel blockers
What is the definition of enzyme activity?
determined by amount of substrate converted per unit time under defined conditions (25 degrees celsius, optimal pH, substrate saturation)
What are proteins?
polypeptides
How many amino acids can be found in proteins?
20
Describe the structure of an amino acid
basic amino group (NH3+) hydrogen atom side chain (variable) acidic carboxyl group (COO-) Central carbon atom
Describe translation (synthesis of proteins)
Initiation = ribosome and initiation factors assemble at start codon (AUG) Elongation = amino acids on tRNA bind to mRNA to deliver next amino acid to be joined to the growing polypeptide chain Termination = any of stop codon (UAA, UAG or UGA) occur on mRNA
What is a codon?
sequence of 3 amino acids that code for a specific amino acid
What does degenerate mean?
more than one codon can specify a specific amino acid (some exceptions)
Describe a peptide bond
chemical bond between 2 amino acids when a carboxyl group of one amino acid reacts with the amino acid group of another amino acid and a water molecule is released
peptide bond = planar, rigid + cannot rotate (double bond character)
What is the primary structure of a protein?
sequence of amino acids
always written from amino end/N-terminus –> carboxyl end/C-terminus
What is the secondary structure of a protein?
certain common/repeating structures
alpha helix
beta pleated sheet
Describe alpha helix structure
rod-like structure
polypeptide chain coiled tightly
stabilised by hydrogen bonds
right-handed (clockwise) coiled
Describe beta pleated sheet structure
zigzag structure
stabilised by hydrogen bonds
polypeptide chain runs in same direction = parallel beta pleated sheet
polypeptide chain runs in opposite direction = antiparallel beta pleated sheet
What is the tertiary structure of a protein?
overall folding of backbone (3D structure)
stabilised by: ionic bonds, hydrogen bonds, disulfide bridges, hydrophobic interactions
What is the quaternary structure of a protein?
only if more than one polypeptide chain
identical and/or different polypeptide chains = subunits
prosthetic groups may be present (non amino acid group part of conjugated proteins)
What are the 4 protein types?
globular = compact spheres (haemoglobin, albumin) fibrous = filamentous molecule (collagen, keratin) soluble = dissolve in water (haemoglobin, immunoglobulins) membrane = associated with membranes (glucose transporter)
What is serum protein electrophoresis?
examines specific proteins in blood
serum proteins separated based on size and charge
separated into 5 major fractions (albumin, alpha 1, alpha 2, beta 1, beta 2, gamma)
diseases can be indicated by changes in serum proteins
