Proteins and Enzymes Flashcards
(18 cards)
monomers of proteins are=
amino acids
dipeptide
formed when two amino acids join together
polypeptide
more than two amino acids.
proteins made up of-
one of more polypeptides
primary structure of proteins
sequence of amino acids in a polypeptide chain.
secondary structure of proteins
The polypeptide chain doesn’t remain flat and straight. Hydrogen bonds form between the amino acids in the chain. this makes it automatically foil into an alpha helix of beta pleated sheet.
tertiary structure of proteins
the coiled or folded chain of amino acids is often coiled and folded further. more bonds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds.
Disulphide bridges also form whenevertwo molecules of cysteine come close together.
quaternary structure of proteins
Some proteins are made of several different polypeptide chains held together by bonds. the quaternary structure is the way these polypeptide chains are assembled together. For proteins made fro more than one polypeptide chain (eg haemoglobin, insulin, collagen) the quaternary structure is the proteins final 3d structure.
Enzymes shape
Usually roughly spherical in shape due to tight folding of polypeptide chains. They’re soluble and often have roles in metabolism e.g. some enzymes break down large food molecules and other enzymes help to synthesis large molecules.
Antibodies shape
Made up of two light(short) polypeptide chains and two heavy (long) polypeptide chains bonded together.
Antibodies have variable regions- the amino acid sequences in these regions vary greatly.
Biuret test for proteins
The test solution needs to be alkaline, so first add a few drops off sodium hydroxide solution. The add some copper sulfate solution.
If protein is present, solution turns purple. If no protein- solutions remains blue.
enzyme-substrate complexes lower the activation energy because:
-If two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily
-If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily.
How temp affects enzyme activity
The rate of the enzyme controlled reaction increases when temperature is increased. More heat means more kinetic energy, so molecules move faster. This makes the substrate molecules more likely to collide with enzymes active sites. The energy of these collisions also increases meaning collision is more likely to result in a reaction.
If temp gets too high, the reaction stops. The rise in temp makes the enzymes molecules vibrate more. If the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzyme in shape. Active side changes shape and enzyme and substrate no longe fit together. Enzyme then denatured and can no longer act as a catalyst.
How pH affects enzyme activity
All enzymes have an optimum pH value. Above and bekow this optimum pH, the H+ and OH- ions found in acids and alkalis can disrupt the ionic bonds and H bonds that hold the enzymes tertiary structure in place. The enzyme becomes denatured and active site changes shape.
How substrate concentration affects enzyme activity
the higher the conc=faster reaction
more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be occupied.
This is only true until a ‘saturation’ point. After that there are so many substrate molecules that the enzymes active sites all occupied and adding more would make no difference.
How enzyme concentration affects enzyme activity
The more enzyme molecules that there are in a solution, the more likely that substrate molecules willl collide with one and then form an enzyme-substrate complex. Increasing concentration of enzyme increases rate of reaction.
But, if the amount of substrate is limited, there comes a point where there’s more than enough enzymes to deal with available substrate, adding further enzymes would then have no further effect.
Competitive inhibitors
Have a similar shape to that of substrate molecules.
They compete with substrate molecules to bind to the active site of the enzyme, but no reaction takes place. Instead they block the active site so no substrate molecules can fit inside.
Non-competitive inhibitors
Non competitive inhibitor molecules bind to the enzyme away from its active site. This causes the active site to change shape so substrate molecules can no longer bind to it.
They don’t compete because they are a different shape and inc conc of substrate makes no difference- enzyme activity still inhibited.
