Enzymes Flashcards
What is a chemical reaction?
Converting substrate into product
by breaking old bonds
forming new ones
What is activation energy?
Energy required to be put into the substrate in order to start it off
What is the transition state?
Point of maximum energy
have intermediate between substrate and product
How can the rate of a reaction be increased?
Increase temperature
Increase concentration
How does increasing temperature increase rate of reaction?
Molecules have more energy
more molecules with activation energy
How does increasing concentration increase rate of reaction?
More collisions between molecules
What are enzymes?
Biological catalysts
What do catalysts do?
Increase the rate of reaction
How do enzymes increase the rate of reaction?
Lower activation energy
Facilitate formation of transition state
How do enzymes lower the activation energy of chemical reactions?
Bring substrate molecules closer to each other
more likely to collide
Weaken the bonds in substrates
so less energy is required to break them
What is the active site of an enzyme?
Point where substrate binds
where the chemical reaction occurs
How much space of the enzyme does the active site take up?
Small amount
What is the function of the rest of the enzyme, other than the active site?
Act as a scaffold to form the active site
How are the amino acids that form the active site related to each other?
Active site is formed by amino acids at different points in the primary sequence
they come together by folding of the protein
What structure do most active sites form? Why?
Form clefts or crevices
to exclude water
How does the active site relate to the subtrate?
Active site has complementary shape to substrate
What is the lock and key hypothesis?
Substrate has completely complementary shape to active site
substrate fits into active site perfectly
What is the induced fit hypothesis?
Substrate has somewhat complementary shape to active site
binding of substrate to active site induces conformational change in active site
so that they fit together properly
How do substrates bind to active sites of enzymes? Why?
By multiple non-covalent bonds
binding must be weak
What are some examples of bonds that form between the substrate and active site?
Hydrogen bonds
Van der waals
Hydrophobic interactions
What shape would a graph of y axis-product against x axis-time look like? Describe the shape
Rectangular hyperbola
- steep
- flatter
- completely flat
What does the gradient of a graph of y axis-product against x axis-time measure?
Measures the rate of reaction
Why does a graph of y axis-product against x axis-time take a hyperbolic shape?
Initially, lots of substrate molecules so have high rate of reaction
Then fewer substrate molecules, reduced rate of reaction
Then no substrate molecules, reaction stops
Why does more substrate molecules means an increased rate of reaction?
More likely to collide with each other
form more product
What is another term for rate of reaction? What is its symbol?
Reaction velocity, V
What is V0?
The reaction velocity at time 0s
How does temperature affect the rate of an enzyme-controlled reaction?
Initially, as temperature increases so does rate of reaction
but after optimum temperature, it decreases
What is the optimum temperature?
Temperature that gives maximum enzyme activity and maximum rate of reaction
Why does the rate of an enzyme-controlled reaction decrease after the optimum temperature?
Enzyme denatures with high temperatures
What is enzyme denaturation?
Bonds in enzyme tertiary structure break
enzyme loses its tertiary structure
active site loses its 3D shape
What are the consequences of the active site losing its shape?
Substrate can no longer bind
reaction stops
How does pH affect the rate of an enzyme-controlled reaction?
Below or above optimum pH, rate of reaction decreases
Why does the rate of an enzyme-controlled reaction decrease above or below the optimum pH?
Enzymes denatures
What is the shape of a graph of y axis-reaction velocity against x axis-substrate concentration?
Rectangular hyperbola
How does low or high pH cause enzyme denaturation?
Affects ionisation state on amino acids
affects electrostatic interactions in tertiary structure
What is Vmax?
The maximum reaction velocity
How is Vmax drawn on a graph?
Horizontal line above end point of graph
What is happening with enzyme and substrate molecules at Vmax?
Enzyme active sites are saturated with substrate
cannot bind any more
What is the Michaelis Menten model?
E + S E-S —–> P
What is E-S?
Enzyme-substrate complex
is the intermediate between substrate and product
What does the Michaeles Menten equation predict?
That the graph of y axis-reaction velocity against x axis-substrate concentration will be rectangular hyperbola
What is Km?
Substrate concentration that gives half of Vmax
What do Km values measure?
Affinity of enzyme for its substrate
What does a low Km value mean? Why?
Enzyme has high affinitiy for substrate
because require lower concentration to reach Vmax/2
What does a high Km value mean? Why?
Enzyme has low affinity for substrate
because require higher concentration to reach Vmax/2
What do rates generally measure?
Amount per unit time
How is enzyme activity measured?
Amount of enzyme that produces 1micromole of product per minute under standardised conditions
How is measure of enzyme activity standardised?
Per litre
Per gram of tissue
How does the rate of an enzyme-controlled reaction relate to enzyme concentration?
Rate of enzyme-controlled reaction is proportional to enzyme concentration
How does enzyme concentration affect rate of reaction and enzyme activity?
Rate of reaction changes with enzyme concentration
Enzyme activity is not affected by enzyme concentration
What is the Lineweaver-Burk plot?
Converting the rectangular hyperbola of y axis-reaction velocity against x axis-substrate concentration into a linear graph
What are the x- and y-axes of the Lineweaver-burk plot?
x-axis is 1/substrate concentration
y-axis is 1/reaction velocity
What is the advantage of the Lineweaver-burk plot over the rectangular hyperbola?
Can more easily measure Km and Vmax
How is Km measured from a Lineweaver-burk plot?
x-intercept is -1/Km
How is Vmax measured from a Lineweaver-burk plot?
y-intercept is 1/Vmax
What is the gradient of the Lineweaver-burk plot?
Km/Vmax
