save my exams enzymes Flashcards
Enzymes
biological catalysts
they speed up the rate of chemical reactions without being used up or changed
globular proteins
be intracellular or extracellular
intracellular
are produced and function inside the cell
Extracellular enzymes
secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)
denaturation
Extremes of heat or pH can change the shape of the active site, preventing substrate binding
specificity of an enzyme
result of the complementary nature between the shape of the active site on the enzyme and its substrate
shape of the active site (and therefore the specificity of the enzyme) is determined by the complex tertiary structure
how enzymes 3d shape is formed
Proteins are formed from chains of amino acids held together by peptide bonds
The order of amino acids determines the shape of an enzyme
If the order is altered, the resulting three-dimensional shape changes
Enzyme reactions can either be
catabolic or anabolic
Catabolic
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
cellular respiration and hydrolysis
Anabolic reactions
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
protein synthesis and photosynthesis
Activation energy
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
why enzymes lower activation energy
provide an alternative energy pathway
lock-and-key hypothesis
Enzymes are globular proteins
This means their shape
is determined by the complex tertiary structure of the protein that makes up the enzyme and is therefore highly specific
induced-fit hypothesis
the enzyme and substrate interact with each other
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
This ensures an ideal binding arrangement between the enzyme and substrate is achieved
This maximises the ability of the enzyme to catalyse the reaction
low temp and enzymes
Lower temperatures either prevent reactions from proceeding or slow them down:
Molecules move relatively slow
Lower frequency of successful collisions between substrate molecules and active site of enzyme
Less frequent enzyme-substrate complex formation
Substrate and enzyme collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)
high temp
Molecules move more quickly
Higher frequency successful collisions between substrate molecules and active site of enzyme
More frequent enzyme-substrate complex formation
Substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken
enzyme begins to denature
-Bonds holding the enzyme molecule in its precise shape start to break
-tertiary structure of the protein to change
-permanently damages the active site, preventing the substrate from binding
-Denaturation has occurred if the substrate can no longer bind
ph and enzymes
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
This alters the shape of the active site, which means enzyme-substrate complexes form less easily
Eventually, enzyme-substrate complexes can no longer form at all
At this point, complete denaturation of the enzyme has occurred
Enzyme concentration on ph
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
initial rate of reaction increases linearly with enzyme concentration
when Enzyme conc becomes a limiting factor
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
substrate conc
greater the substrate concentration, the higher the rate of reaction:
number of substrate molecules increases, the likelihood of enzyme-substrate complex formation increases
all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate
any substrate molecules that are added have nowhere to bind in order to form an enzyme-substrate complex
Enzyme Inhibitors
two types of reversible inhibitors
An enzyme’s activity can be reduced or stopped, temporarily, by a reversible inhibito
two types of reversible inhibitors
Competitive inhibitors
Non-competitive inhibitors
Competitive inhibitor
have a similar shape to that of the substrate molecules and 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 and therefore prevents the substrate from binding to it
the inhibitor changes the conformation of enzymes after binding so that substrate cannot bind to enzymes
the results inna decrease of Xmas
depends on inhibitor concentration
