2. proteins and enzymes fact test Flashcards
what are the structural roles of proteins
it’s the main component of body tissues like muscle, skin and hair
what are proteins also known as
polypeptides
what are the catalytic roles of proteins
all enzymes are proteins, catalysing many biochemical reactions
what are the signalling roles of proteins
many hormones and receptors are proteins
what are the immunological roles of proteins
all antibodies are proteins
what are the monomers from which proteins are made called
amino acids
what does the general structure of an amino acid consist of
central carbon
hydrogen
R group (variable)
amino group
carboxyl group
what is a polypeptide
long chain of amino acids joined together by peptide bonds
what is the name of the bond which joins amino acids together
peptide bond
what is the order of amino acids determined by
the order of bases in the gene that code for the polypeptide
what does peptide bond formation involve
removal of water in a condensation reaction
how is a dipeptide formed
by a condensation reaction between 2 peptides (amino acids)
what is the primary structure of a protein
sequence of amino acids
what is the secondary protein structure
local folding of the polypeptide chain into alpha helixes or beta pleated sheets (caused by hydrogen bonding)
what is the tertiary protein structure
3D folding pattern of a protein due to side chain (R group) interactions
are usually globular
what is the quaternary protein structure
protein consisting of more than one amino acid chain
what are bonds in a protein dependent on
interaction between R groups
what are disulfide bonds / bridges and which structure are they present in
a strong S=S double bond formed between sulfur atoms
present in tertiary structure
what are ionic bonds and which structure are they present in
some R groups carry a positive or negative charge so an ionic bond can form between 2 oppositely charged R groups
present in tertiary structure
which structure are hydrogen bonds present in
secondary and tertiary
what other bond is present in the tertiary structure but is not on the spec
hydrophobic/hydrophilic interactions
what does the biuret test for
the presence of peptide bonds
how do you carry out the biuret test
ensure sample is in solution
add biuret reagent
stays blue if no peptide bonds present
turns purple if peptide bonds are present
what are enzymes and what are they used for
they are biological catalysts meaning they are used in metabolic reactions to increase the rate of reaction
it lowers activation energy of the reaction it catalyses
what is the active site and what does it do
the small part of an enzyme which is involved in catalysis, it may consist of just a few amino acids
what do amino acids which aren’t part of the active site do
maintain the precise tertiary structure of the enzyme and active site
what is an enzyme-substrate complex and how is it formed
substrate binds to the active site of an enzyme forming and enzyme-substrate complex
what is the lock and key model
substrate will only fit active site of one particular enzyme
the shape of the substrate is complementary to that of the active site and it fits exactly
what is the induced fit model
- shape of enzyme and active site are not complementary
- enzyme is flexible and can mold around substrate
- enzyme changes shape slightly to fit the profile of the substrate (like a glove fitting a hand)
- as it changes shape, it puts pressure on the substrate molecule
- this distorts a particular bond in the substrate molecule and lowers the activation energy needed to break the bond
why is the induced fit model better than the lock and key model
it is a better explanation as it explains how other molecules can affect enzyme activity and how activation energy is lowered
how do you calculate pH
-log10 [H+]
what does the graph of the effect of temperature on enzyme activity look like
as temperature increases, rate of reaction increases gradually
the rate peaks at (give value)
above the optimum, the rate decreases steeply to 0
explain why the graph of the effect of temperature on enzyme activity looks the way it does
- at low temperatures, enzyme and substrate have less kinetic energy so there are few successful collisions between substrate and active site meaning fewer enzyme-substrate complexes (ESC) formed and less product produced
- as temperature increases, enzyme and substrate gain kinetic energy, increasing number of collisions between substrate and active site, more ESC formed and increasing rate of reaction
- peak indicates optimum temperature
- beyond optimum temperature, hydrogen bonds maintaining the tertiary structure of the enzyme are broken, this changes shape of active site, denaturing the enzyme, meaning fewer/no ESC formed, reducing rate of reaction
what does the graph of the effect of pH on enzyme activity look like
rate peaks at particular pH
above or below this pH, rate steeply decreases
explain why the graph of the effect of pH on enzyme activity looks the way it does
- peak represents optimum pH
- changing the pH changes the concentration of H+ ions
- change in pH can affect changes in the active site meaning substrate can no longer bind to active site to form ESC
- a larger change in pH can cause ionic and hydrogen bonds in tertiary structure of enzymes to break. this can cause the tertiary structure to change, leading to a change in shape of the active site, meaning fewer/no ESC can form
what does the graph of the effect of substrate concentration on enzyme activity look like
as substrate concentration increases, rate of reaction increases until it reaches a plateau
no further increase in substrate concentration increases the rate
explain why the graph of the effect of substrate concentration on enzyme activity looks the way it does
- at a low concentration, not all active sites are occupied by substrates therefore fewer ESC formed
- when the graph levels off, all active sites are occupied and enzyme is working at maximum rate
- beyond this point, enzyme concentration is limiting factor
what does the graph of the effect of enzyme concentration on enzyme activity look like
as enzyme concentration increases, rate of reaction increases until it reaches a plateau
no further increase in enzyme concentration increases the rate
explain why the graph of the effect of enzyme concentration on enzyme activity looks the way it does
- at low enzyme concentration, there is excess substrate and the umber of available active sites (enzyme concentration) is limiting the rate
- when graph levels off, all substrates are bound to active sites
- beyond this point, enzyme molecules are in excess and the concentration of substrate is limiting the rate
what are competitive inhibitors and what do they do
have a similar shape to substrate but not the same
occupies active site so fewer ESC form
inhibition can be overcome by increasing substrate concentration
substrate and competitor compete for active site of the enzyme
what are non-competitive enzymes and what do they do
permanently binds to the enzyme at a site away from the active site called the allosteric site
this causes active site to change shape preventing ESC from forming
inhibition cannot be overcome by increasing substrate concentration
what is end product inhibition
- allows control over metabolic pathways, so we don’t get too much or too little of a substance in cells
- enzymes are part of a pathway, where the product of one enzyme is the substrate for the next
- the end product can act as an inhibitor of an enzyme earlier on in the pathway
- too much product leads to more inhibition which means product level decreases
- too little product leads to less inhibition which means product level increases
