1. Proteins - Many proteins are enzymes Flashcards
Define an enzyme
Enzymes are biological catalysts that speed up chemical reactions without being used up or changed.
How did scientists discover the induced fit model of enzyme action?
They noticed that other molecules could bind to enzymes, which then affected the enzyme’s activity.
This led to the conclusion that the enzyme shape must be changing.
What is a substrate?
The substance on which an enzyme acts
Why are enzymes essential to organisms?
They allow essential chemical reactions to occur rapidly at low temperatures e.g. 37°C.
Enzymes that catalyse chemical reactions outside of cells are called…
extracellular enzymes
Which 3 conditions must be satisfied for a chemical reaction to take place?
- The substrates must collide with sufficient energy to alter the arrangement of their atoms
- The energy of the products must be lower than the substrates.
- The activation energy needs must be met.
The functional part of an enzyme is called the…
active site
Describe the lock and key model of enzyme action
- Substrate will only fit one active site like a key and a lock
- Explains specificity of enzymes
- If this was correct, enzymes would have rigid structure however we know that it is flexible as other molecules can bind to the enzyme altering active site
Which have a higher energy level: substrates or products?
substrates
The specific 3D shaped active site of an enzyme is determined by..
Unique primary structure
Enzymes that catalyse reactions inside of cells are called…
intracellular enzymes
When a substrate binds to the active site we call the resulting structure an…
enzyme-substrate complex
A substrate does not have the same shape as the active site it has a _____________ shape.
complementary
What does the following describe:
- A substrate is specific to an enzyme.
- A substrate binds to the active site of an enzyme.
- This lowers the activation energy.
- Product is released from enzyme.
The lock and key model of enzyme action
Hormones are proteins that have a binding site so that they can switch on or off bodily processes. Are they enzymes?
No - many proteins have binding sites or receptor sites. These are not active sites.
Which type of biological molecule are enzymes?
Proteins
Which structural type of protein are enzymes?
Globular proteins
What do we call the initial energy required for a chemical reaction to take place?
Activation energy
How does a substrate temporarily bind to an enzyme active site?
The substrate temporarily forms bonds with certain amino acids in the active site.
What does the following describe:
- Substrate approaches active site
- Enzyme changes shape and forms functional active site.
- Enzyme moulds to substrate
- Change in shape puts a strain on bonds of substrate, lowering activation energy.
- Product is released from enzyme.
The induced fit model of enzyme action
What is the name of the currently accepted model of enzyme action?
The induced fit model of enzyme action
Why are enzymes still effective even in small amounts?
Because they are not used up or changed so can be used again and again.
Describe the induced fit model of enzyme action
- Substrate approaches active site
- active site not complementary/will fit substrate
- active sitechanges shape and forms functional active site - as substrate binds
- Enzyme moulds to substrate
- Change in shape puts a strain on bonds of substrate, lowering activation energy.
Why does formation of enzyme substrate complex increase rate of reaction?
Reduces activation energy
due to the bending/weakening of bonds
For an enzyme to work it must:
come into contact with its substrate.
have an active site which complements the substrate.
How can the progress of an enzyme controlled reaction be measured? (2 methods)
measure the amount of product produced over time.
measure substrate disappearance over time..
Explain the initial rate of reaction shown in the graph
Lots of substrate, no product.
Easy for substrate molecules to come into contact with enzyme.
All enzyme active sites filled with substrate so product rapidly produced.
Explain the rate of reaction shown in the graph after 1 minute
Less substrate now so less product being produced.
More difficult for substrate to come into contact with active sites of enzyme
The graph eventually flattens because there is no substrate left to act on.
Explain the initial drop in starch shown in the graph below
Lots of substrate, no product to get in way
Easy for substrate molecules to come into contact with enzyme.
All enzyme active sites filled with substrate so substrate rapidly reduced.
Explain the drop in starch shown in the graph below after 3 minutes
Less substrate now and more product to get in the way.
More difficult for substrate to come into contact with active sites of enzyme
The graph eventually flattens because there is no substrate left to act on.
How would you calculate the rate of reaction at the red point?
Draw a straight line against the point (a tangent line)
The rate of reaction is equal to the gradient of this line.
Gradient = change in Y / change in X
Explain the the change in reaction rate between 0-40 Degrees Celsiusshown in the graph below
Higher temp, more kinetic energy given to enzymes and substrate
More successful collisions between enzymes and substrate
This is shown by the rising curve which reaches its peak at 40 DegC
Explain the the change in reaction rate after 40 Degrees Celsiusshown in the graph below
Hydrogen bonds in enzyme start to break due to high temp.
The enzyme and its active site begin to change chape, substrate fits less easily and reaction slows.
Enzyme eventually changes shape so much, it denatures. Enzyme can no longer bind to substrate so reaction ends.
Many of the enzymes in the body have an optimum temperature of 40°C. Why has the body evolved to have a temperature of 37°C?
Body needs to use more energy to maintain 40°C
Other, non-enzyme, proteins in the body may denature at 40°C
During illness body temperature would increase above 40°C.This might denature the enzymes.
Why do birds have a body temperature of 40°C?
They have a high metabolic rate in order to release the energy required for flight.
How can we calculate the gradient of a line on a line graph?
Gradient = Change in Y/Change in X
Draw a Tangent on the graph to show the rate of reaction at a specific point. Label the change in X “a” and change in Y “B”
How can we calculate the rate of enzyme reaction at a specific point on a graph that shows the “amount of product formed” OR “substrate used”up the Yaxis and “time” along the X axis.
Draw a tangent at this point and calculate its gradient.
Gradient = Change in Y/Change in X
A solution with a high H+ ion concentration is an…
acid
A solution with a high OH- concentration is an…
alkali
What is the equaiton for calculating the pH of a solution?
pH = -log10[H+]
What happens at pH’s that are outside of an enzymes optimum pH range?
The enzyme will denature
Explain why an enzyme denatures at pH’s outside of its optimum range.
Change in pH alters the amino acid charges in the active site so substrates can no longer bind.
The change in pH can cause the ionic and hydrogen bonds holding the teriary structure to break. This changes the shape of the active site.
Why are enzymes denatured faster at 60 degrees compared to 40 degrees?
More kinetic energy
bonds (ionic/hydrogen) between amino acids broken faster
Temperature effect on enzymes
The rate initially increases as the molecules gain kinetic energy - more ES complexes are formed and more have the activation energyHydrogen bonds and ionic interactions in the tertiary structure begin to break - enzyme is denatured - active site no longer complimentary to substrate
pHeffect on enzymes
- A small change in pH can alter the charges on the R groups of the amino acids, means that substrate will no longer bind to form ES complexes
- Larger change will cause Hydrogen and ionic bonds to break disrupting the tertiary structure - enzyme is denatured
Substrate concentration effect on enzymes
If enzyme concentration is fixed - rate of reaction will plateau as the enzymes are saturated
If excess - the line will be constant and keep increasing
Competitive inhibitors
have a similar shape to substrateoccupy active sitecompete with substrateoften temporary
Non Competitive Inhibitors
Not a similar shape to substrateBinds at allostearic siteAlters shape of active siteOften permanentDoesn’t compete with substrate
enzymes are globular proteins therefore have specific primary structure aka sequence of amino acids. The active site(the active site have an specifi ctertiary structure The active site forms a small depression within the much larger enzyme molecule, a subtrate fits in active site of enzyme This fits neatly into this depression and forms an enzyme-substrate complex.
Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction.
- Attaches to the enzyme at a site other than the active site;
Accept ‘attaches to allosteric/inhibitor site’ - Changes (shape of) the active site
OR
Changes tertiary structure (of enzyme); - (So active site and substrate) no longer complementary so less/no substrate can fit/bind;
Draw an antibody
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