1.4 (biological molecules) Flashcards
enzymes
enzymes are biological
catalysts
enzymes are catalysts because they
speed up the rate of chemical reactions without being used up or changed
critical to the enzymes function is the active site where the what binds
substrate
metabolic pathways are controlled by
enzymes in a biochemical cascade of reactions
enzymes can be what referring to whether they are active inside or outside the cell
- intracellular
- extracellular
intracellular enzymes are
- produced and function
- inside the cell
extracellular enzymes are
- secreted by cells
- catalyse reactions outside cells (eg. digestive enzymes in the gut)
hydrogen peroxide is produced as a by- product of many metabolic reactions, it is harmful to cells, catalase does what
- converts hydrogen peroxide into water and oxygen
- preventing any damage to cells or tissues
- intracellular
digestion is usually carried out by extracellular enzymes, this is because
- macromolecules being digested
- too large to enter the cell
amylase is involved in carbohydrate digestion it
hydrolyses starch into simple sugars
amylase is secreted by
- the salivary glands and the pancreas
- for digestion of starch in the mouth and small intestine
enzymes have an active site where specific substrates bind forming an
enzyme-substrate complex
the active site of an enzyme has a specific shape to fit a
specific substrate
extremes of heat or pH can change the shape of the
- active site
- preventing substrate binding
extremes of heat or pH can change the shape of the active site, preventing substrate binding, this is called
denaturation
the specificity of an enzyme is a result of the
- complementary nature
- between the shape of the active site on the enzyme and its substrates
the shape of the active site (and therefore the specificity of the enzyme) is determined by the complex what structure of the protein that makes up the enzyme
tertiary
proteins are formed from
chains of amino acids held together by peptide bonds
the order of amino acids determines the what of an enzyme
shape
the enzyme-substrate complex is only formed
temporarily
the enzyme-substrate complex is only formed temporarily, before the enzyme
catalyses the reaction and the product(s) are released
enzyme reactions can either be
catabolic or anabolic
catabolic reactions involve the
breakdown of complex molecules into simpler products
catabolic reactions involve the breakdown of complex molecules into simpler products, which happens when
a single substrate is drawn into the active site and broken apart into two or more distinct molecules
catabolic reaction diagram
examples of catabolic reactions include
- cellular respiration
- hydrolysis reactions
anabolic reactions involve the
building of more complex molecules from simpler ones
anabolic reactions involve the building of more complex molecules from simpler ones by
- drawing two or more substrates into the active site
- forming bonds between them
- and releasing a single product
anabolic reaction diagram
examples of anabolic reactions include
protein synthesis and photosynthesis
enzymes work by lowering the
activation energy of a reaction
for a reaction to proceed there must be enough
activation energy
activation energy is the
- amount of energy needed by the substrate to become just unstable enough for a reaction to occur - and for products to be formed
enzymes speed up chemical reactions because they influence
the stability of bonds in the reactants
the destabilisation of bonds in the substrate makes it more
reactive
enzymes work by lowering the activation energy of a reaction and in doing so they provide
an alternative energy pathway
exothermic activation energy diagram
enzymes are globular proteins, this means their shape (as well as the shape of the active site of an enzyme) is determined by the complex
tertiary structure of the protein that makes up the enzyme and is therefore highly specific
in the induced fit hypothesis the enzyme and its active site (and sometimes the substrate) can
change shape slightly as the substrate molecule enters the enzyme
the enzyme and its active site can change shape slightly as the substrate molecule enters the enzyme, these changes in shape are known as
conformational changes
conformational changes ensures an
ideal binding arrangement between the enzyme and substrate is achieved
conformational changes maximises
the ability of the enzyme to catalyse the reaction
what are the four actors affecting enzymes
- temperature
- pH
- enzyme concentration
- substrate concentration
enzymes have a specific optimum temperature, the temperature at which
they catalyse a reaction at the maximum rate
lower temperatures either prevent reactions from proceeding or slow them down as molecules move
relatively slow
molecules moving slow in a reaction means
- lower frequency of successful collisions between substrate molecules and active site of enzyme
- less frequent enzyme-substrate complex formation
lower temperatures in reactions mean that substrate and enzyme collide with less
- energy
- making it less likely for bonds to be formed or broken (stopping the reaction from occurring)
higher temperatures speed up reactions as molecules move
more quickly
molecules moving fast in a reaction means
- higher frequency successful collisions between substrate molecules and active site of enzyme
- more frequent enzyme-substrate complex formation
higher temperatures in reactions mean that substrate and enzyme collide with more
- energy
- making it more likely for bonds to be formed or broken (allowing the reaction to occur)
however, as temperatures continue to increase, the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to
denature
during denaturation the bonds
(eg. hydrogen bonds) holding the enzyme molecule in its precise shape start to break
breaking of bonds during denaturation causes the
tertiary structure of the protein (ie. the enzyme) to change
the tertiary structure of the protein changing permanently damages the
- active site, preventing the substrate from binding
- denaturation has occurred if the substrate can no longer bind
high temperatures causes the hydrogen bonds between amino acids to break, changing the
conformation of the enzyme
hydrogen and ionic bonds hold the
tertiary structure of the protein together
below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH- ions (alkaline solutions) can cause these bonds to
break
pH can cause these bonds to break which alters the shape of the
- active site
- which means enzyme-substrate complexes form less easily
when investigating the effect of pH on the rate of an enzyme-catalysed reaction, you can use buffer solutions to measure the rate of reaction at different pH values
- buffer solutions each have a specific pH
- buffer solutions maintain this specific pH, even if the reaction taking place would otherwise cause the pH of the reaction mixture to change
- a measured volume of the buffer solution is added to the reaction mixture
- this same volume (of each buffer solution being used) should be added for each pH value that is being investigated
the higher the enzyme concentration in a reaction mixture, the greater the number of
- active sites available - and the greater the likelihood of enzyme-substrate complex formation
if the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a
limiting factor
the effect of enzyme concentration on the rate of an enzyme-catalysed reaction graph
the greater the substrate concentration, the higher the
rate of reaction
as the number of substrate molecules increases, the likelihood of
enzyme-substrate complex formation increases
if the enzyme concentration remains fixed but the amount of substrate is increased past a certain point, however, all available active sites eventually become
- saturated
- any further increase in substrate concentration will not increase the reaction rate
when the active sites of the enzymes are all full, any substrate molecules that are added have nowhere to
bind in order to form an enzyme-substrate complex
the effect of substrate concentration on the rate of an enzyme-catalysed reaction graph
an enzymes activity can be reduced or stopped temporarily by a
reversible inhibitor
two types of reversible inhibitors are
- competitive
- non competitive
competitive inhibitors have a similar shape to that of the
- substrate molecules
- therefore compete with the substrate for the active site
non-competitive inhibitors bind to the enzyme at an
- alternative site
- which alters the shape of the active site
- therefore prevents the substrate from binding to it
competitve inhibition diagram
non competitve inhibition diagram
reversible inhibitors can act as regulators in
metabolic pathways
metabolic reactions must be very
- tightly controlled
- and balanced
- so that no single enzyme can ‘run wild’ and continuously and uncontrollably generate more and more of a particular product
metabolic reactions can be controlled by using the
the end-product of a particular sequence of metabolic reactions as a non-competitive, reversible inhibitor
as the enzyme converts substrate to product, the process is itself slowed down as the
- end-product of the reaction chain binds to an alternative site on the original enzyme
- changing the shape of the active site
- and preventing the formation of further enzyme-substrate complexes
the end-product can then detach from the enzyme and be used elsewhere, allowing
the active site to reform and the enzyme to return to an active state
this means that as product levels fall, the enzyme begins
catalysing the reaction once again, in a continuous feedback loop
end product inhibition diagram
for competitive inhibitors, countering the increase in inhibitor concentration by increasing the substrate concentration can
increase the rate of reaction once more (more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes
for non-competitive inhibitors, increasing the substrate concentration cannot
increase the rate of reaction once more, as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form
the effect of inhibitor concentration on the rate of an enzyme-catalysed reaction graph
