paper 1: Proteins and Enzymes Flashcards
what is the definition of an amino acid
the monomers from which proteins are made
what is the definition of a dipeptide
two amino acids joined together by condensation
what is the definition of a polypeptide
many amino acids formed together by condensation
what is the definition of a peptide bond
forms during a condensation reaction between the amine group of one amino acid and the carboxyl group of another amino acid
define the primary structure of a protein
the sequence of amino acids in a polypeptide chain. it determines the rest of the structure
define the secondary structure of a protein
the folding of the polypeptide chain into an alpha helix or beta plated sheet because of hydrogen bonding between NH group of one amino acid and the C=O group of another
define the tertiary structure of a protein
the foldingof he polypeptide chain into a specific 3D shape held together by hydrogen bonds, ionic bonds and disulfide bridges between R groups of different amino acids
define the quaternary structure of a protein
the arrangement of more than one polypeptide chain
define an alpha helix
polypeptide chain is wound round to form a helix and is held together by many hydrogen bonds making it a very stable and strong structure
define a beta pleated sheet
the poltpeptide chain zig-zags back and forth forming a sheet of antiparallel strands held together by many hydrogen bonds
what is the Biuret Test
- the test for proteins
- add biuret solution to sample
- there will be a colour change from blue to lilac if protein is present
define an enzyme
biological catalysts that speed up the rate of reaction by decreasing the activation energy needed for a chemical reaction
define activation energy
the minimum amount of energy required for a chemical reaction to occur
define the active site of an enzyme
the region of an enzyme with a specific 3D tertiary structure that is complimentary to a specific substrate molecule
define enzyme-substrate complex
forms when a specific substrate binds to the active site of an enzyme
define complimentary
fits into
explain how enzymes are highly specific
- enzyme combines with only one specific substrate
- as enzyme has specific tertiary structure and so the active site has a specific shape which is only complementary to one type of substrate
- substrate binds to active site to form an enzyme substrate complex
what is the basic structure of an amino acid
draw a diagram showing the condensation of 2 amino acids:
describe the induced fit hypothesis
- before the reaction the active site is not fully complimentary to the substrate.
- when substrate binds, this causes the tertiary structure of the enzyme to change which causes the active site to change shape so that it becomes complimentary to the substrate.
- an enzyme substrate complex forms which causes the bonds in the substrate to bend so that they break more easily which reduces activation energy
how do enzymes lower the activation energy
the shape of the active site alters as substrate binds to it. This stresses the bonds which cause them to break more easily.
draw the graph representing the effect of temperature on enzyme activity
describe and explain the effect of temperature on enzyme activity
- initially the rate of enzyme action increases as temperature increases because the substrate and enzymes are given more kinetic energy so there are more likely to be more successful collisions which form more enzyme-substrate complexes
- beyond the optimum temperature, rate of enzyme action decreases because the enzymes denature as hydrogen bonds break, changing the 3D tertiary structure of the active site so it is no longer complimentary to the substrate. no enzyme-substrate complexes can form
why is the rate of enzyme action slow at 0 degrees but not 0?
the enzyme and substrate molecules have some kinetic energy so some enzyme-substrate complexes can still form.
draw a graph to show the effect of pH on enzyme action
describe and explain the effects of pH on enzyme action
below or above the optimum pH the rate of reaction decreases because the enzyme hydrogen bonds break changing the 3D tertiary structure of the active site so it is no longer complimentary complimentary to the substrate therefor less enzyme-substrate complexes form
why does pH effect the rate of enzyme action
the change in pH changes the amount of hydrogen ions present
draw a graph showing the effect of substrate concentration on enzyme action
describe and explain the effects of substrate concentration on the rate of enzyme action
initially the rate of enzyme action increases as the concentration increases because more enzyme-substrate complexes form. the concentration is the limiting factor
the rate of reaction plateaus as at a high substrate concentration there are no free active sites and the maximum number of enzyme-substrate complexes are formed. the enzyme is now the limiting factor.
draw a graph showing the effect of enzyme concentration on the rate of enzyme action
describe and explain the effects of enzyme concentration on the rate of enzyme action
initially the rate of enzyme action increases as the concentration increases because more enzyme-substrate complexes form. the enzyme is the limiting factor
the rate of reaction plateaus as at a high substrate concentration there are no more substrates free to bind to the active sites and the maximum number of enzyme-substrate complexes are formed. the substrate is now the limiting factor.
what is a competitive inhibitor
they are substances similar in shape to the real substrate. they enter into the enzymes active site and prevent the substrate from binding but are not permanently bound.
explain how the competitive inhibitor reduces the rate of reaction of an enzyme
- the inhibitor is a similar shape to the substrate
- the competitive inhibitor enters the active site of the enzyme
- the specific substrates cannot bind the the complimentary active sites
- therefore reducing the number of enzyme-substrate complexes forming
draw a graph showing the effect of a competitive inhibitor on enzyme action
explain why a maximum rate of reaction can still be reached with a high concentration in the presence of a competitive inhibitor
- competitive inhibitors only temporarily bind so the substrate will be able to bind
- the high concentration of substrate means there is a higher chance of the substrate binding to the enzyme active site instead of the inhibitor.
what is a non-competitive inhibitor
- these bind to the enzyme not at the active site
- they change the 3D tertiary structure and shape of the active site
- the substrate cannot bind
- enzyme substrate complexes cannot form
draw a graph showing the effect of a non-competitive inhibitor on the rate of enzyme action
explain why by adding more substrate you cannot reduce the effect of the non-competitive inhibitor
- the enzyme active site has been changed permanently, reducing the concentration of functioning enzymes
- you cannot reach the maximum number of enzyme-substrate complexes as without the imhibitor.
how are protiens denatured
- when hydrogen bonds in protein break, the tertiary structure changes and the protien become non-funcional
