Module 2: Foundations In Biology Enzymes Flashcards
What is an enzyme
Biological catalyst
Globular protein that catalyse reactions at a cellular level and whole organism level affecting structure and function of an organism
How many polypeptide chains does an enzyme have??
1
Why can an enzyme not form a quaternary structure??
Because it only has one polypeptide chain
What structure do enzymes have??
Tertiary structure
What is the polypeptide chain in enzymes made of??
Amino acids joined by peptide bonds
Intercellular enzyme action
Action within a cell
Can be fixed within membranes (e.g. chloroplast)
Action of DNA Polymerase
Acts within nucleus for DNA replication before cell division
Action of catalase
Breaks down hydrogen peroxide
A waste product of metabolism which is very toxic and needs to be rapidly broken down within cells into o2 and water
Extra cellular enzyme function
Enzyme action outside of a cell
Function of amylase
Digests starch into maltose which is then digested into glucose in the duodenum by Maltase
Catabolic enzymes
Breaking down polymers
Example of catabolic enzyme
Proteins are digested into amino acids
Anabolic enzymes
Build up reactions
Example of an anabolic reaction
Starch is synthesised from alpha helix
Why are enzymes specific for a substrate??
due to their active site
Which has a specific shape
Is complementary to the substrate
What is the active site??
Particular area of enzyme molecule
Composed of small number of amino acids within the polypeptide
What is the effect of enzymes on activation energy??
Enzymes lower the activation energy required for a reaction to occur
Lock and key hypothesis
Theory of enzyme action in which the enzymes active site is complimentary to the substrate molecule
Induced fit hypothesis
Theory of enzyme action in which the enzyme’s active site changes shape to fit the substrate molecule more closely as it binds to it
What happens to the activity of enzymes as temperature increases
Activity of enzyme increases due to the enzyme and substrate having more kinetic energy
This increases the chances of successful collisions which helps to form more enzyme substrate complexes
What is the optimum temperature for enzymes
37-40 degrees
What is the optimum temperature definition
The temperature at which the highest rate of enzyme activity occurs
What is the optimum temperature of bacteria in thermal vents??
Around 70 degrees
What is the optimum temperature of organisms living in the arctic
5 degrees
What are physiological adaptations
Processes that take place within the body of the organism
What are anatomical adaptions??
Physical features internal or external
What are behavioural adaptations??
The way an organism acts
In a hot environment how is the structure of an enzyme adapted??
They have more bonds in their tertiary structure
What is the effect of a 10 degree rise in temperature
Doubles the rate of reaction
Up to the optimum what is the general value of Q10
2
What is the effect on the bonds when heat is applied above the optimum temperature to the enzymes?
Heat makes molecules vibrate as they have more kinetic energy
Puts strain on weak hydrogen bonds and ionic bonds and these bonds may break
What happens when the bonds break in the tertiary structure of the enzymes
Tertiary structure eventually lost
Active site changes and no longer complimentary to the substrate
This is known as denaturing and activity of the enzyme is lost
What happens to Q10 above the optimum temperature?
Above the optimum temperature Q10 does not apply
Why is the rate of reaction slower when the temperature is below the optimum rate of reaction
Fewer collisions and fewer enzyme substrate complexes formed
Do enzymes denature at low temperatures??
Enzymes don’t denature at low temperatures they are just less active
What is the effect of low pH on enzymes??
Lots of H+ ions present
Positive charge can interfere with the hydrogen bonds and ionic bonds between the R groups of amino acids
This can change the active site which causes the denaturing of the enzymes
What happens if the pH changes the charge on the amino acids at the active site
The properties of the active site change and the substrate can no longer bind
What is the typical optimum pH of an intracellular enzyme??
6.5
What happens to rate of reaction as the substrate concentration rises?
Rate of reaction increases because there are more substrate molecules to react
Free active sites so more collisions occur and more enzyme substrate complexes form
What happens as the active sites become occupied
The enzyme is saturated and the rate plateaus
Rate of reaction remains the same (known as V max)
What happens to the rate of reaction as the enzyme concentration increases??
Rate of reaction increases as there are more active sites available
More reactions occur between the substrate and the enzyme forming more enzyme substrate complexes
What is an inhibitor
Any substance that slows down or stops and enzyme catalysed reaction by affecting the enzyme in some way
What are the two types of inhibitors
Competitive inhibitors and non competitive inhibitors
What is the shape of a competitive inhibitor
Has a similar shape to that of the substrate molecule
How does the shape of the competitive inhibitor affect the action of the substrate
Similar shape so they occupy the active sites
They form enzyme-inhibitor complexes
Prevents the substrate from entering the active site to form an enzyme substrate complex
Why do enzyme-inhibitor complexes not lead to the formation of products
Because the inhibitor is not identical to the substrate
The part of their shape that binds to the active site is similar
What does the level of inhibition by a competitive inhibitor depend on?
The concentrations of inhibitors and substrates
What happens to the level of inhibition with competitive inhibitors when the number of substrate molecules is increased
Level of inhibition decreases because a substrate molecule is more likely to collide with the active site than an inhibitor molecule
Tempering effect of competitive inhibitors
Do not bind permanently to the active site
Bind for a short period of time and then leave
Removal of the inhibitor from the reaction mixture leaves the enzyme molecule unaffected
Why is antifreeze toxic??
Contains ethylene glycol
In the the body this is broken down by alcohol dehydrogenase to oxalic acid which is extremely toxic
Why is a person given alcohol intoxication when they have antifreeze poisoning??
Ethanol is a competitive inhibitor to alcohol dehydrogenase
Ethylene glycol is not broken down into oxalic acid
So therefore there is no toxicity and death
Action of non-competitive inhibitors
Do not compete with substrate molecules for a place in the active site
Where do non competitive inhibitors bind to??
Molecules attach to the enzyme molecule in a region away from the active site
What effect does the attachment of non competitive inhibitors have on enzymes
Changes the tertiary structure of the enzyme molecule leading to the shape of the active site changing
After the non competitive inhibitors have attached to the enzyme what is the effect of the active site and collisions??
Active site is no longer complimentary to the substrate
Enzyme substrate complex cannot form and the reaction rate decreases
What is the effect of non competitive inhibitors on the v MAX
VMax = lower
What does the level of inhibition of non competitive inhibitors depend on??
Number of inhibitor molecules present
Effect of cyanide poisoning??
Affects the heart and intercostal muscles
No heart contraction or ventilation
What is the effect of penicillin
Inhibits cell wall formation
What is the effect of aspirin
Inhibits cyclooxygenase which affects vasoconstriction
Examples of non competitive inhibitors
Aspirin and penicillin
What is a cofactors??
A substance not made of amino acids
Required by an enzyme to function
Can be permanently bound to the enzyme or have a temporary part but help the esc to form
What is a coenzyme??
A cofactor that is an organic molecule for an enzyme
Can donate or accept hydrogen ions or chemical groups
What is a prosthetic group??
Permanent part of an enzyme, tightly bound
Contribute to the tertiary structure of the enzyme and vital to functioning
What is an apoenzyme??
An inactive form of an enzyme
What is an actifactor??
Something which binds to a apoenzyme and activates them
How to calculate rate from a time graph
Find the gradient
Y/x
How is a glycosidic bond broken in the digestion of a disaccharide??
Hydrolysis
What is the sugar that forms from the digestion of a disaccharide
Beta glucose
Why are different enzymes involved in each stage of the digestion process?
All enzymes are specific
Substrates are different shapes
Active site and substrate are complimentary so that the substrate will fit
Which two factors should be controlled when investigating the effect of pH on the activity of an enzyme
Temperature
Concentration of substrate or enzyme
