4 - Enzymes 🍽 Flashcards
Enzymes are…
biological catalysts
What type of proteins are enzymes?
Globular
What causes enzymes to react at faster rates?
Interacting with substrate molecules
What is an anabolic reaction?
Building up thinhs
What is a catabolic reaction?
Breaking down reactions
What do enzymes catalyse in food?
Digestion
Define metabolism
The sun of all of the different reactions and reaction pathways happening in a cell or an organism
What is the certain point called that enzymes can increase the rate of reactions up to?
Vmax (max initial velocity)
The specificity of an enzyme
Each enzyme catalyses one biochemical reaction
What is the activation energy?
The energy needed to be supplied for most reactions to start
How do enzymes help reduce the activation energy needed?
Enzymes help the molecules collide successfully
What is the active site?
An area within the 3Y of the enzyme with a shape complementary to the specific substrate
When the substrate is bound to the active site, what is formed?
Enzyme-substrate complex
When the substrates react, the products are formed in…
An enzyme-product complex
How is the substrate held?
In such a way that the right atom-groups are close enough to react
How are temporary bonds formed in an enzyme / substrate?
The R-groups within the active site of the enzyme will interact with the substrate
How do temporary bonds help a reaction along?
By putting strain on the bonds within the substrate
What is the induced-fit hypothesis?
The active site of the enzyme changed shape slightly as the substrate enters
What is the initial intereaction between enzyme/substrate in induced-fit?
Weak initial interaction
How do the weak interactions rapidly change in induced-fit?
Induces changes in the enzymes 3Y that strengthen the binding, putting strain on the substrate molecule
How does putting strain on the substrate effect the reaction in induced-fit?
This weakens a particular bond(s) in the substrate, therefore lowering the activation energy
What does catalase do?
Breaks down hydrogen peroxide into water and oxygen quickly, preventing its accumulation
Where is catalase found?
In both plant and animal tissues
What is the purpose of most
extracellular enzymes?
Released from cells to break down large nutrients into smaller molecules that can enter the cell-surface membrane
What type of organisms need extracellular enzymes?
Both single-celled and multi-cellular to make use of polymers for nutrition
Where do single felled organisms release their extracellular enzymes?
Directly into their surroundings
How are extracellular organisms used in multicellular organisms?
Nutrients are taken in by food, but need to be digested into smaller molecules to be absorbed into the bloodstream
Digestion of starch
What does amylase do?
Starch polymers are partially broken down into maltose (disaccharide)
Digestion of Starch
Where is amylase produced?
By the salivary glands and the pancreas
Digestion of Starch
Where is amylase released?
In saliva in the mouth or in pancreatic juice into the small intestine
Digestion of starch
How is maltose then broken down into glucose (monosaccharide)?
By maltase found in the small intestine
Digestion of starch
Why are amylase and maltase needed to turn starch into glucose?
It’s small enough to be absorbed by the cells lining the digestive system and then into bloodstream
Digestion of proteins
What is trypsin?
A protease
Digestion of proteins
What are proteases?
A type of enzymes that catalyses the digestion of proteins into smaller peptides, which can then be broken down further into amino acids
Digestion of proteins
Where is trypsin produced and found?
Produced in the pancreas and released with the pancreatic juice into the small intestine
Why is it important reactions don’t happen too fast?
Leads to a build up of excess products
What controls the different steps in reaction enzymes?
Different enzymes
What regulates the rate and quantity of product formation?
Controlling the activity of enzymes at crucial points
What activates enzymes?
Cofactors
What inactivates enzymes?
Inhibitors
What are inhibitors?
Molecules that prevent enzymes from carrying out their normal function of catalysis
What are the two types of inhibitors?
Competitive and non-competitive
Competitive inhibition
Step 1 = a molecule or part of a molecule that has a similar…
shape to the substrate of an enzyme can fit into that active sit of the enzyme
Competitive Inhibition
Step 2 = this blocks the substrate from entering…
the active site, preventing the enzyme from catalysing the reaction
Competitive Inhibition
Step 3 = the enzyme cannot carry out…
it’s function and is said to be inhibited
Competitive Inhibition
Step 4 = what is the non-substrate molecule that binds to the active site?
A type of inhibitor
Competitive Inhibition
Step 4 = substrate and inhibitor molecules present in a solution will compete…
to bind to the active sites of the enzymes catalysing the reaction
Competitive Inhibition
Step 5 = this will reduce the number of…
substrate molecules binding to the active sites in a given time and slows down the rate of reaction
Competitive Inhibition
How do most competitive inhibitors bind to the active site?
Temporarily so their effect is reversible
Competition Inhibition
What does the degree of inhibition depend on?
Relative concentrations of substrate, inhibitor and enzyme
Competitive Inhibition
What is an exception to the temporary binding to the active site?
Aspirin
Competitive Inhibition
What is their effect of rate of reaction?
Reduces
Competitive Inhibition
What is their effect on the Vmax?
Doesn’t change it of the enzyme it inhibits
Competitive Inhibition
What inhibitor of an enzyme is used in the synthesis of cholesterol?
Statins
What can high blood cholesterol levels cause?
Heart disease
Competitive Inhibition
What active site does aspirin irreversibly inhibit?
COX enzymes, preventing the synthesis of prostaglandins and thromboxane = the chemicals responsible for producing pain and fever
Non-competitive Inhibition
Step 1 = the inhibitor binds to the enzyme at…
a location other than the active site - this location is called the allosteric site
Non-competitive Inhibition
Step 2 = the binding of the inhibitor causes…
3Y of the enzyme to change, meaning the active site changes shape
Non-competitive Inhibition
Step 3 = this results in the active site no longer having a…
complementary shape to the substrate so it is unable to bind to the enzyme
Non-competitive Inhibition
Step 4 = the enzyme cannot carry out its…
function and is said to be inhibited
Why is it called non-competitive inhibition?
The inhibitor doesn’t compete with the substrate for the active site
Non-competitive Inhibition
What does increasing the concentration of inhibitor do to rate?
Decrease it as more active sites are unavailable
Organophosphates are used as what?
Insecticide or herbicides
What do organophosphates do?
Irreversibly inhibit the enzyme acetyl cholinesterase
What does acetyl cholinesterase do?
Necessary for nerve impulse transmission
What does the absence of acetyl cholinesterase do?
Leads to muscle cramps, paralysis and even death if accidentally inhested
What is used to treat long term indigestion?
Proton pump inhibitors (PPIs)
What do PPIs do?
Irreversibly block an enzyme system responsible for secreting hydrogen ions into the stomach
What are PPIs effective at?
Reducing the production of excess acid, which can lead to stomach ulcers
Define end-product inhibition
The term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
What does end-product inhibition serve as?
A negative feedback control mechanism for reactions so excess products are not made and resources aren’t wasted
What is end-product inhibition:
Competitive or non-competitive?
Non-competitive
What is respiration?
A metabolic pathway resulting in the production of ATP
How is glucose broken down in respiration?
- addition of two phosphate groups to glucose
- addition of second group results in intial breakdown
What enzyme catalyses the addition of a phosphate group to break down glucose?
Phosphofructokinase (PFK)
This enzyme is inhibited by ATP
What happens when ATP levels are high?
More ATP binds to PFK, preventing the addition of the second phosphate to glucose so it isn’t broken down and ATP isn’t produced at the same raye
What happens as ATP is used up?
Less ATP binds to PFK and the enzyme catalyses the addition of the second phosphate to glucose, resuming respiration and the production of ATP
Define a cofactor
A non-protein component or metallic ion that is required for an enzymes activity as a catalyst
Cofactors can be considered what?
“Helper molecules” that assist in biochemical transformations
Cofactor = Zn++
Enzyme/protein = ?
- Carbonic anhydrase
- alcohol dehydrogenase
Cofactor = Fe++ or Fe+++
Enzyme/protein = ?
- cytochromes
- haemoglobin
- ferredoxin
Cofactor = Cu++ or Cu+
Enzyme/protein = ?
Cytochrome oxidase
Cofactor = K+ or Mg++
Enzyme/protein = ?
Pyruvate phosphokinase
What is vitamin B3 used to synthesise?
NAD and NADP
What does NAD do?
A coenzyme responsible for transfer of hydrogen atoms between molecules involved in respiration
What do NADP do?
Similar as NAD but in photosynthesis
What does vitamin B5 synthesis?
Coenzyme A
What does coenzyme A do?
Breakdown fatty acids and carbohydrates in respiration
What are prosthetic groups?
Cofactors as they are required got certain enzymes to carry out their catalytic function
How do prosthetic groups add to the structure of proteins?
Tightly bound and form a permanent feature
What are inactive enzymes called?
Inactive precursor enzymes
What do inactive precursor enzymes tend to do?
Cause damage within cell producing them or to tissues once released
How are precursor enzymes activated?
Undergo a change in shape (3Y) particularly to the active site
What must be added to activate a precursor enzyme?
A cofactor
Define an apoenzyme
An inactive precursor enzyme without its non-protein part (cofactor)
Define a holoenzyme
The active enzyme with its cofactor added
Cofactor =
Non-protein part is a metal ion
Coenzyme =
A small organic molecule
What external influences can result in a change in 3Y and activate a precursor enzyme?
Changes in conditions such as pH or temperature
What type of precursor enzymes are produced when they are activated by external conditions?
Zymogens or proenzymes
What happens when inactive pepsinogen is released into the stomach to digest proteins?
The acid pH brings about the transformation into the active enzyme pepsin
This adaption protects the body tissues against the digestive action of pepsin
Factors Affecting Enzyme Activity
Increase in temperature = increased frequency of…
…successful collisions between substrate and enzyme = increased rate of reaction
Factors Affecting Enzyme Activity
Define the temperature coefficient
A measure of how much the rate of a reaction increases with a 10°C temperature increase
Factors Affecting Enzyme Activity
What is the symbol for the temperature coefficient?
Q10
Factors Affecting Enzyme Activity
What is the Q10 for enzyme-controlled reactions?
2 as the rate of reaction doubled with a 10°C temp increase
Factors Affecting Enzyme Activity
What happens do the bonds holding proteins together at a higher temp?
They vibrate more = bonds break = change in precise 3Y = denature
Factors Affecting Enzyme Activity
What happens when an enzyme denatures?
The enzyme is no longer complementary to the substrate
Factors Affecting Enzyme Activity
Define the optimum temperature
The temp at which the enzyme has the highest rate of activity
Factors Affecting Enzyme Activity
What is the optimum temp in humans?
40°C
Factors Affecting Enzyme Activity
What is thermophilic enzymes optimum temp?
70°C
Factors Affecting Enzyme Activity
What is psychrophillic enzymes optimum temp?
Below 5°C
Factors Affecting Enzyme Activity
What happens to rate with enzymes that have denatured below optimum temp?
decrease is rate as they haven’t denatured but are just less active
Factors Affecting Enzyme Activity
Enzymes adapted to cold will have what properties?
- more flexible
- less stable
- smaller temp changes will denature then
Factors Affecting Enzyme Activity
Define the optimum pH
The active site will only be at the right shape at a certain hydrogen ions concentration
Factors Affecting Enzyme Activity
If the pH changed and denatured enzyme, but then changed back, what will happen?
The enzyme will go back to the correct shape = renaturation
Factors Affecting Enzyme Activity
What happens if pH is changed significantly?
Structure of the enzyme will be irreversibly altered
Factors Affecting Enzyme Activity
pH hydrogen ions interact with what, and what causes a change in this interaction?
Polar and charged R-groups
- changing the conc of H+ ions will change the degree of the interactive
Factors Affecting Enzyme Activity
A low pH means lots of H+ ions =
The less the R-groups are able to interact with each other = bonds break = enzyme changes shape
(Same with high pH)
Factors Affecting Enzyme Activity
Which factor is rarely limiting?
Substrate and enzyme concentration
Factors Affecting Enzyme Activity
What happens when there is an increased number of substrate particles?
Higher collision rates with the active site of enzymes = increasing rate
Factors Affecting Enzyme Activity
How can you increase the available active sites?
Increase the enzyme concentration
Factors Affecting Enzyme Activity
What is the Vmax?
The rate of reaction is at its maximun
Factors Affecting Enzyme Activity
What causes a Vmax?
All active sites are occupied by substrate particles and no more enzyme-substrate complexes can be formed until products are released from the active sites
Factors Affecting Enzyme Activity
Is the rate of reaction directly proportional to enzyme conc?
Yes
