Proteins & Enzymes Flashcards
what are proteins? (3)
- usually very large molecules
- each organism makes its own unique proteins; it is these proteins that give the organism their characteristics and allow key functions to occur
- the shape of every protein molecule is highly specific
AMINO ACIDS: structure
- nitrogen, hydrogen, oxygen and carbon
- some also contain sulphur
draw the structure of an amino acid
state six examples of different proteins within the body
haemoglobin
transports oxygen
antibodies
defend the body against infection
enzymes
biological catalysts
actin and myosin
involved in muscular contraction
keratin
found in hair and nails
collagen
found in tendons
how many different types of amino acids are there?
20
what is the only thing that is different in each amino acid?
the R group (they’re all a different size)
explain how a dipeptide is formed (3)
- two amino acids join together via a condensation reaction to form a dipeptide
- a H2O molecule is removed and a peptide bond is formed
- the hydroxyl group (OH) from the carboxyl group of one amino acid reacts with a hydrogen from the amine group on the second amino acid
“many (hundreds) of amino acids can be joined together through many condensation reactions to form a __________”
polypeptide
how many levels of organisation are there in proteins?
four
primary structure (2)
- the number AND sequence/order of amino acids in a polypeptide chain
- because there are 20 different amino acids, there is almost a limitless number of possible sequences they can be combined in
secondary structure (4)
- linked amino acids all have -NH and -C=O groups on either side of the polypeptide chain
- the -NH group has an overall positive charge and the -C=O has an overall negative charge; a hydrogen bond forms between H and O
- weak hydrogen bonds form between these groups throughout the polypeptide
- this causes the polypeptide chain to coil into alpha helices or fold into beta-pleated sheets
tertiary structure (4)
- further folding of the secondary structure into a specific, complex 3D shape
- the R groups determine how the polypeptide chain folds into its specific 3D shape
- the structure is held together by bonds and interactions between the R groups
specific tertiary structure = specific shape = necessary for them to carry out their function
what are the three bonds that can be found in the tertiary structure of a protein? (2) (3) (3)
HYDROGEN - weak; easily broken with increasing temperature
IONIC - stronger than hydrogen; form between oppositely charged R groups; broken by changes in pH
DISULPHIDE BRIDGES - covalent bonds; form between sulphur atoms; extremely strong
quaternary structure (2)
- only occurs when the protein has more than one polypeptide chain
- some large proteins form these complex molecules
e.g. haemoglobin, keratin
what are enzymes?
proteins that act as biological catalysts
what do enzymes do? (2)
- they increase the rate of reaction without being used up (the active site is always free to be used again)
- they do this by lowering the activation energy needed for a chemical reaction
in order to lower activation energy…
enzymes put pressure on the bonds in the substrate and bend them during the formation of enzyme-substrate complexes
this allows reactions that would normally need high temperatures to work at a lower temperature
ENZYMES: structure (2)
they have a specific tertiary structure, which gives them a specific 3D shape
has an active site that is complementary to only one substrate
- this allows the enzyme and substrate to bind together
describe the induced fit model (5)
- active site is initially not complementary to the substrate
- substrate enters the active site and induces a change in shape
- enzyme substrate complex forms
- bonds in the substrate are stressed; activation energy is lowered
- when the products leave the active site, the enzyme returns to its previous shape
list the four factors affecting enzyme controlled reactions
- TEMPERATURE
- pH
- SUBSTRATE CONCENTRATION
- ENZYME CONCENTRATION
describe the effect of temperature on enzyme controlled reactions (2)
what happens when optimum temperature is reached? (2)
- as temperature increases, the enzymes and substrates have more kinetic energy
- therefore they are more likely to collide successfully and form enzyme substrate complexes
- when optimum temperature is reached, the hydrogen bonds and ionic bonds within the R groups are broken
- the enzyme is denatured
describe the effect of pH on enzyme controlled reactions (2)
- if the pH is changed, the H+ ions can break the hydrogen and ionic bonds
- this causes the enzyme to be denatured
what does it mean for an enzyme to be denatured?
there’s a permanent change to its tertiary structure
describe the effect of substrate concentration on enzyme controlled reactions (4)
as the substrate concentration increases, the rate of reaction increases and then levels off
- the initial rate of reaction is slow when there is a low substrate conc. ; this is because not all of the active sites of the enzyme are saturated
> the substrate is a limiting factor
when the rate of reaction levels off, there is a very high concentration of substrate
- there is no further increase in rate of reaction since all the active sites have been filled
> the enzyme conc. is now the limiting factor
describe the effect of enzyme concentration on enzyme controlled reactions (4)
in a fixed concentration of substrate, the rate of reaction increases and then levels off as enzyme concentration increases
- when there is a low enzyme concentration, the rate of reaction is low ; this is because all of the active sites of the enzymes are saturated
> the enzyme concentration is a limiting factor
when the rate of reaction levels off, there is a very high concentration of enzyme
- there is no further increase in the rate of reaction since there isn’t enough substrate to fill the active sites
what is an inhibitor?
a substance that decreases the rate of reaction
list the two types of inhibitor
- COMPETITIVE
- NON-COMPETITIVE
describe what a competitive inhibitor does? (3)
- have a similar shape to the substrate
- they bind to the active site of an enzyme to block it from the substrate
- prevent enzyme substrate complexes from forming
how could some products still be formed even though a competitive inhibitor is being used? (2)
- because not all active sites are being occupied by the inhibitor
- sometimes the inhibitor can be knocked out by the substrate
describe what a non-competitive inhibitor does? (3)
- binds to the allosteric site, which is in a different location on the enzyme to the active site
- changes the shape of the active site so that it is no longer complementary to the substrate
- fewer enzyme substrate complexes are formed
what is the name of the test that is used for proteins?
the biuret test
describe how to carry out the biuret test (2)
- place a small volume of sample into a test tube
- add an equal volume of biuret’s solution
what colour change will occur if a protein is present?
and if a protein isn’t present?
a purple/violet colour change
colour stays blue
