Enzymes Flashcards
graph showing how enzymes lower activation energy on page 2 (21 cards)
describe metabolism
to stay alive, cells must perform many biochemical reactions to break down larger molecules into smaller molecules and build up smaller molecules into larger molecules
describe what type of proteins enzymes are
globular proteins with a specific tertiary structure, held by hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interactions
what do enzymes act as and what does this mean?
act as biological catalysts
means they speed up rate of metabolic reactions by lowering the activation energy (energy required for a reaction to begin)
where can enzymes work?
inside cells (intracellular) - in solution, membrane-bound
outside cells (extracellular) i.e. they are secreted
(enzyme are synthesised in living cells)
what two ways can enzymes catalyse metabolic reactions?
and give examples
anabolic reactions e.g. condensation, photosynthesis
catabolic reaction e.g. hydrolysis, respiration
what part of the enzyme is functional?
the active site
what happens when a substrate meets with the active site and enzyme?
(diagram on page 3)
a substrate complex forms
the reaction takes place then the products are released from the active site
the enzyme is then free to catalyse another reaction
what are the two main models for enzyme action?
lock and key model
induced fit model
describe the lock and key model
the substrate molecule fits into the active site of the enzyme molecule like a key fitting into a lock as they are complementary shapes
this forms the enzyme substrate complex
the product is then formed and as it no longer fits into the active site it is released
this model explains why enzymes are very specific i.e. each enzyme will only catalyse one reaction
describe the induced fit model
(diagram on page 4)
the substrate and the active site of the enzyme are not complementary shapes
when a substrate molecule binds to the active site, the active site changes shape and fits itself around the substrate
this places a strain on the substrate molecule and distorts a particular bond, lowering the activation energy required to break the bond
the products are formed and leave the active site which then returns to its original shape
describe the enzyme lysozyme and where it is present
helps to kill bacteria by catalysing the hydrolysis of sugars in the peptidoglycan cell walls
the cell walls are weakened, the bacteria absorb water by osmosis and burst
lysozyme is present in many secretions such as tears, saliva, human milk and is also found inside lysosomes
give three properties of enzymes
specific due to the sequence of amino acids that make up the active site
fast-acting with a very high turnover number
this means they can convert many molecules of substrate per unit time e.g. catalase, the enzyme that hydrolyses hydrogen peroxide has a turnover number of 40 million molecules per second
soluble, as hydrophilic R groups are found on the outside of the molecule
describe the process of formation of a product for an enzyme controlled reaction on the graph on page 5
the curve is steepest initially as there is a large concentration of substrate molecules, so they are more likely to successfully collide with an active site and form the product
initially the enzyme concentration is the limiting factor
as the reaction proceeds there is a decreasing concentration of substrate so less chance of successful collisions; now substrate concentration is the limiting factor
the graph eventually levels off as all of the substrate has been converted to product and no further product is formed
describe the graph on page 6 showing the mass of substrate over time for an enzyme controlled reaction
substrate concentration is at maximum level at the start of the reaction
there is a rapid fall in the concentration of substrate, substrate molecules bind to enzyme active sites and are converted into product
substrate concentration is very low
all the substrate has been converted into product
what factors affect enzyme-controlled reactions?
temperature
pH
substrate concentration
enzyme concentration
inhibitors (competitive/non-competitive)
describe the effect of temperature on rate of reaction
at low temperatures the rate of reaction is low because the enzyme and substrate molecules have low kinetic energy
increasing the temperature up to the optimum increases rate of reaction because the kinetic energy of the enzyme and substrate molecules increases, increasing the chance of successful collisions and more enzyme-substrate complexes are formed
optimum temperature; the rate of reaction is at its highest
above the optimum rate of reaction decreases because the molecules have more kinetic energy and the increasing vibrations begins to break hydrogen bonds, changing the tertiary structure of the enzyme which alters the shape of the active site so it is no longer complementary to the substrate and this lowers the rate of reaction as enzyme-substrate complexes cannot form
at very high temperatures the rate of reaction falls to zero because the enzymes are denatured and this is when the active site is permanently distorted by irreversible breaking of hydrogen bonds, this prevents the substrate from binding as it is no longer complementary to the active site
describe the effect of pH on enzymes
most enzymes have an optimum pH at which the rate of reaction is at its maximum
enzymes can only work within a narrow range of pH values
small deviations from the optimum pH can cause reversible changes in enzyme structure resulting in inactivation i.e. pH can affect the charge which can repel substrates with the same charge
extremes of pH can permanently denature an enzyme
what happens to enzymes which are in extreme pH conditions?
(diagrams on page 9)
an extreme change in pH may alter the electrostatic charge on the side chains of the amino acids
if the active site has too many H+ ions or OH- ions , the active site and substrate may both have the same charge and the enzyme will repel the substrate
what can be added to enzyme-controlled reactions to maintain a constant pH?
buffers
describe the effect of the substrate concentration on enzymes
(diagram on page 10)
at a fixed enzyme concentration, the rate of reaction will increase as substrate concentration increases
at low substrate concentration, the substrate concentration is the limiting factor - the enzyme molecules only have a few substrate molecules to collide with
as more substrate is added, there are more successful collisions and more enzyme active sites become occupied, until the rate of reaction reaches a maximum and substrate molecules are in excess - the enzyme concentration becomes the limiting factor
how can the rate of digestion be determine?
by using a colorimeter
as DNA is digested, it absorbs more light at a wavelength of 260nm
