proteins 3.14 Flashcards
what is a chain of amino acids called
a polypeptide chain
what is the structure of an amino acid
carbon (C) attached to an amine (NH3), a carboxyl (COOH), and an R group (varient)
how many different R groups/amino acids are there
20
what bonds are in a polypeptide
peptide bonds
where do the peptide bonds form
between N in amine group and C in carboxyl group
what type of reaction forms a dipeptide
condensation
what does a condensation reaction produce
H20
what is the primary structure
sequence of amino acids in a polypeptide chain
what can a change in the polypeptide amino sequence cause
may cause a change in the protein shape and may stop it from carrying out its function
what is the secondary structure
either an alpha helix or a beta pleated sheet
how does the secondary structure form
H of the amine group has overall positive charge
O of the carboxyl group has overall negative charge
hydrogen bonds can form between these 2 groups
causes the chain to be twisted into a 3D shape
what bonds form the tertiary structure
hydrogen bonds
ionic bonds
disulphide bridges
where do the tertiary structure bond forms
only between the R groups
what is the relative strength of hydrogen bonds
weak
what is the relative strength of disulphide bridges
very strong
what are the features of ionic bonds (2)
strong and vulnerable to pH
what is the purpose of the 3D tertiary structure
makes each protein distinctive and allows it to recognise and be recognised by other molecules.
what feature defines a protein having a quaternary structure
protein has more than one polypeptide chain
what are the 2 molecular shapes of proteins
fibrous or globular
fibrous vs globular stability
fibrous stable
globular not stable
fibrous vs globular bonds
fibrous mainly H bonds
globular many types of bonds
fibrous vs globular shape
fibrous long and linear
globular coiled with depressions
fibrous vs globular sequence
fibrous regular sequence
globular irregular sequence
fibrous vs globular function
fibrous structural function
globular metabollic function
fibrous vs globular solubility
fibrous insoluble
globular soluble
what is biuret solution made of
sodium hydroxide and copper (II) sulphate solution
what colour is biuret solution originally
blue
what colour is biuret solution in the presence of protein
purple
what type of protein is an enzyme (2)
globular
tertiary structure
how is an enzyme substrate complex held together
weak non covalent interactions (H, ionic, hydrophobic)
how do enzymes lower the activation energy of a reaction (2)
put stress on the bonds within a molecule
hold molecules closer together
what is the lock and key model
each substrate will only fit the active site of one particular enzyme
what is the induced fit model
suggests the active site is flexible, the substrate doesn’t only have to fit the active site, it also has to make the active site change in the right way.
how does increasing temperature affect enzyme action
increasing temperature means more heat energy so more kinetic energy for enzyme and substrate.
move faster so more collisions.
more ES complexes formed.
rate of reaction is increased.
how does too high temperature affect enzyme action
too high temperature means more kinetic energy.
enzyme molecules vibrate more, H bonds in tertiary structure break.
changes shape of enzyme.
active site changes shape so substrate cannot fit.
how does optimum pH affect enzyme action
solution of optimum pH has H ions, does not disrupt ionic bonding.
no change in shape of enzyme, no change in active site, ES complexes formed, rate of reaction is maximum.
how does pH being too high or low affect enzyme action
ionic bonds in tertiary structure break, changes shape of enzyme, ES complexes not formed, rate is reduced.
how does substrate concentration affect enzyme action
substrate concentration increasing means more chance of enzymes and substrates colliding.
more ES complexes formed.
increases rate of reaction.
why is substrate concentration limiting
eventually all enzyme active sites are occupied, enzymes are working at maximum turnover rate.
how does increasing enzyme concentration affect enzyme action
more enzymes so more active sites
more ES complexes formed
more products formed
what are the two types of enzyme inhibitors
competitive and non competitive
where do competitive inhibitors bind
the active site
limitation of competitive inhibitors
when the inhibitor leaves the active site, substrates can then bind
where do non competitive inhibitors bind
to the allosteric site
what do non competitive inhibitors do
attach to allosteric site
changes shape of the active site so further substrate molecules cannot enter and form ES complexes
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3 marks)
Substrate binds to the active site
Active site changes shape so it is complementary to substrate
Reduces activation energy
A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how. (3 marks)
inhibitor similar shape to substrate
binds to active site
Prevents/reduces enzyme-substrate complex forming
