Enzymes :). Flashcards
How do enzymes speed up chemical reactions?
By acting as a biology catalyst.
What parts of metabolic reactions do enzymes catalyse?
Both at cellular (respiration) and for organisms as a whole (digestion in mammals)
What can enzymes affect in organism?
The structure and the functions
Give of an example of how an enzyme can affect the structure in an organism?
Enzymes involved in the production of collagen an important protein in the connective tissues of animals
Give an example of how enzymes can affect function?
Respiration
Where can enzyme action happen?
Intercellular (within cell)
Extracellular (outside cells)
Give an intercellular enzyme example?
Catalase
Hydrogen peroxide is the toxic-by-product of several cellular reactions. If left can kill cells.
Catalase (enzyme) works inside cell catalyses breakdown of hydrogen peroxide into harmless oxygen and water
Give an enzyme extracellular example work where?
Amylase and trypsin both work outside cells in human digestive system.
Amylase is found where and what does it do?
Amylase found in saliva.
Secreted into mouth by cells in salivary glands, catalyses by hydrolysis of starch into maltose in the mouth.
What do trypsin do?
Produced by cells in pancreas and secreted into small intestine. Catalyst the hydrolysis of peptide bonds turning big polypeptides into smaller one. ( these can be broken down into amino acids by other enzymes)
What type of proteins are enzymes?
Gobular proteins
What do enzymes have?
An active site
Explain an active site
Has a specific shape Part of enzyme substrates molecules bind to.
How is the specific shape of the enzyme determined?
By the enzymes tertiary structure
What needs to happen for the enzyme to work?
The substrate has to fit into the active site (shape has to be complementary).
What happens if substrate shape doesn’t match?
Reaction won’t be catalysed.
So how many substrates work with?
Usually only one
Define activation energy.
The certain amount of energy needed to be supplied to the chemical before the reaction will start.
How is activation energy usually provided?
As heat
What do enzymes reduce?
The amount of activation energy needed making reactions happen at a lower temperature then without an enzyme. Speeding up rate of reaction.
What happens when a substance has bonded to an enzymes active site?
An enzyme-substrate is formed.
What lowers the activation energy?
The formation of enzyme-substrate complex
What are the two reasons for the formation of enzyme-substrate complex reducing the activation energy?
1) if substrate molecules need to be joined attaching to enzyme holds them closer reducing repulsion between molecules so can bond easier
2) if enzymes is catalysing a breakdown reaction fitting into active site puts strain on bonds in substrate. Strain means substrate molecule breaks up easier
What does enzymes being picky mean?
Only work with substrate fitting their active site
What did early scientists come up with?
Lock and key model
Explain lock and key model?
Substrate fits into enzyme in same way key fits into lock.
What did scientists soon realise?
Lock and key model didn’t give full story.
What actually is true about the lock and key model?
Enzyme and substrate do have to fit together in first place
What wrong with lock and key model?
Enzyme-substrate complex change shake slightly to complete the fit. This kicks the substrate even more tightly to enzyme.
What did scientists do to come up with induced fit model?
Modified old lock and key model
What does induced fit help to explain?
Why enzymes are so specific and only bond to one particular substrate
What else does induced fit mean the substrate have to do other than fit the active site in shape?
Make the active site change their in the right way
What does lock and key and induced fit show?
Widely accepted theory can change when new evidence comes along. Induced fit model widely accepted for now.
What do enzymes do?
They speed up chemical reactions
How much of an influence does temperature have on enzyme activity?
A big influence
What happens when the temperature increases to the enzyme-controlled reaction?
ILike any chemical reaction as temperature increases so does the rate of an enzyme- controlled reaction.
What does more heat mean for kinetic energy?
More heat means more kinetic energy so molecules move faster.
What does the fact the molecules moving faster mean for the enzyme?
The enzymes more likely to collide with the substrate molecules
What also happens as the energy of these collisions increases?
As energy of collisions increases each collusion is more likely to result in a reaction.
What happens if the temperature gets too hot?
The reaction stops.
What does a rise in temperature increase make the enzymes molecules do more?
Vibrate more
What happens if temperature goes above a certain level?
The vibration breaks some of the bonds that hole the enzymes in shape
What does breaking bonds holding the enzymes shape mean?
Active site changes shape
Enzyme and substrate no longer fit together
When the active site changes shape what happens?
Denaturing
No longer functions as catalyst
Does every enzyme have an optimum temperature?
Yes
Most human enzymes work around 37 degrees
Some enzymes (washing powder) around 60 degrees
What is Q10?
Temperature coefficient
What’s the temperature coefficient?
The value for a reactions that shows how much rate of reaction changed when temperature raised by 10 degrees
What before optimum is Q10 of 2 meaning?
The rate doubles when temperature raised by 10 degrees
What before optimum is Q10 of 3 meaning?
The rate trebles when temperature raised by 10 degrees
What do most enzyme-controlled reactions have a Q10 value of?
Around 2
What is the best pH for enzymes?
Their optimum pH value
Human enzyme optimum pH value
Around 7 but have few exceptions
Give an example of an exception in humans?
Pepsin works best at around 2
Useful because found in stomach
What can mess up bonds above or below pH?
H+ and OH- ions found in acids and alkalis can mess up ionic bonds and hydrogen bonds
What do these ionic and hydrogen bonds do in enzymes?
Hold enzymes tertiary structure in place Therefore denature ( changes shape)
When will some enzymes only work?
If there is another non-protein substance bound to them.
What are these non-polar substances called?
Cofactors
What are some inorganic molecules or ions?
Cofactors
How do inorganic molecules or ions work as cofactors?
By helping the enzyme and substrate to bind together.
What participation do inorganic molecules or ions cofactors have on the reaction?
Don’t directly participate in the reaction
Aren’t used up or changed in any way
Give an example of a inorganic molecule or ion cofactors?
Chloride ions (Cl-) are cofactors for the enzyme amylase
What are some organic molecules?
Cofactors
What are these organic molecules cofactors called?
Coenzymes
How do coenzymes participate in the reaction?
They do participate in the reaction and are changed by it
What do coenzymes act as?
Carriers, moving chemicals groups between different enzymes
Continuously recycled during this process
What are vitamins often good sources of?
Coenzymes
What if a cofactor is tightly bound to the enzyme?
Known as prosthetic group
Give an example of a prosthetic group?
Zinc ions (Zn2+) are a prosthetic group for carbonic anhydrase
What carbonic anhydrase?
Enzyme in erythrocytes which catalyses production of carbonic acid from water and carbon dioxide
What are these zinc ions?
A permanent part of the enzymes active site
What does enzyme concentration affect?
The rate of reaction
What does there being more enzyme molecules in a solution do?
The more likely a substrate molecule is to collide with one and form an enzyme-substrate complex.
What increasing the concentration of the enzyme do do the rate of reaction?
Increases it
What eventually happens if the amount of substrate is limited?
There comes a point when there’s more than enough enzyme molecules to deal with all available substrates so adding more enzymes has no effect.
What does substrate concentration affect?
The rate of reaction up to a point
What happens the high the substrate concentration?
The faster the reaction
Why does the higher concentration of substrate causes a faster reaction?
More substrate molecules mean a collision between substrate and enzyme is more likely and do more active sites will be used.
Up to when is the higher the substrate concentration the faster the reaction true?
Until a “saturation” point through.
What happens after the “saturation” point?
There are so many substrate molecules that the enzymes have about as much as they can cope with (all active sites are full), and adding more substrate makes no difference to the rate of reaction.
What happens to substrate concentration during a reaction?
It decreases with time
When wouldn’t the substrate concentration decrease over time?
More substrate is added to the reaction mixture
What happens to the rate of reaction over time if no other variables are changed?
The rate of reactions will decrease over time.
What is the initial rate of reaction?
The highest rate of reaction
How many ways of measuring the rate of an enzyme-controlled reaction?
Two
Name one way you can measure the rate of an enzyme-controlled reaction?
Measure how fast the product of the reaction appears.
How could you use the first method for the enzyme catalase?
Have an underside down measuring cylinder in water measuring the amount of oxygen produced per minute from the delivery tube connected to a test tube containing hydrogen peroxide solution and catalase enzyme
Name another way you can measure the rate of an enzyme-controlled reaction?
Measure the disappearance of the substrate rather than the appearance of the product and use this to compare the rate of reaction under certain conditions.
Give an example of when the second method might be used?
The enzyme amylase catalyses the breakdown of starch to maltose.
Give advantages for using the second method for the enzyme amylase catalyses the breakdown of starch to maltose?
Easier to detect starch using a solution of potassium iodide and iodine.
Can time how long it takes for starch to disappear by regular sampling the starch solution.
Can alter conditions of reaction and compare rates
How can you tell when starch has been used up?
Adding iodine to starch solution on spotting tile when iodine solution no longer turns blue-black starch has been broken down
What is an independent variable?
The thing you change
In this case temperature
What is the dependent variable?
The thing you measure
Volume of oxygen produced
What do you need to do to the other variables?
You need to control all the other variables that could affect the outcome of the investigation including: pH, enzyme concentration and substrate concentration
How do you do the experiment ( effect temperature on catalase activity)
Step 1?
Set up boiling tube containing same volume and concentration of hydrogen peroxide. To keep pH constant add equal volumes of buffer solution to each tube
How do you do the experiment ( effect temperature on catalase activity)
Step 2?
Set up apparatus to measure volume of oxygen produced from each boiling tube
E.g. Use delivery tube and upside firm nesting cylinder
How do you do the experiment ( effect temperature on catalase activity)
Step 3?
Put each boiling tube in water bath set to different temperature along with another tube containing catalase
How do you do the experiment ( effect temperature on catalase activity)
Step 4?
Use pipette to add same volume and concentration of catalase to each boiling tube
How do you do the experiment ( effect temperature on catalase activity)
Step 5?
Record how much oxygen is produced in first 60 seconds of this reaction using stop watch.
How do you do the experiment ( effect temperature on catalase activity)
Step 6?
Repeat experiment at each temperatures three times and use results to find mean volume of oxygen produced at each temperature.
How do you do the experiment ( effect temperature on catalase activity)
Step 7?
Calculate mean rate of reaction at each temperature by dividing volume of oxygen produced by time taken. Cm3/ seconds
How is it easy to alter this experiment?
To investigate effect of different variables on catalase activity
E.g. To investigate substrate concentration effects keep temperatures the same but prepare boiling tubes with different concentrations of hydrogen pesticide
To investigate pH effect add buffer with different pH to each
How can enzyme activity be prevented?
By enzyme inhibitors
What are enzyme inhibitors?
Molecules that bind to the enzyme that they inhibit.
What are the two types of enzyme inhibitors?
Competitive or non-competitive
What do competitive inhibitors have a similar shape to?
The substrate molecules
How do competitive inhibitors inhibit enzyme action?
Compete with substrate molecule to bind to active site but no reactive take place.
Instead they block the active site so no substrate molecules can fit in it
What does the amount of enzyme inhibited depend on?
The relative concentration of the inhibitors and the substrate
What happens if there is a high concentration the inhibitor?
It’ll take up nearly all active sites and hardly any of that substrate will get to the enzyme
What happens if there is a high concentration the substrate?
The substrate chances of getting to an active sure before the inhibitor increases so increasing concentration of substrate will increase rate of reaction up to a point.
How do non-competitive inhibitor molecules work?
Bind to enzyme away from active site known as allosteric site. Causes active site to chant shape so substrate molecules no longer bind to it. Don’t compete with substrate molecules to bind to active site as different shape
What will increasing concentration of substrate do it to reaction rate?
Nothing it will still inhibited.
How is whether an inhibitor is reversible or not determined?
The strength of bonds between enzyme and the inhibitor
If strong, covalent inhibitor can’t be moved so irreversible
If weaker hydrogen bonds or weak ionic bonds inhibitor can be removed inhibition is reversible
What are some drugs and metabolic poisons?
Enzyme inhibitors
Give two examples of medicinal drugs which are enzyme inhibitors?
Some antiviral drugs (drugs that stop virus like HIV)
Some antibodies
Give an example of an antiviral drug that is an enzyme inhibitor?
Reverse transcriptase inhibitors inhibit the enzyme reverse transcriptase which catalyses the replication of viral DNA (prevents virus from replicating).
Give an example of an antibiotic which is a enzyme inhibitor?
Penicillin inhibits the enzyme transpeptidase which catalyses the formation of proteins in bacterial cell walls. Weakens the cell wall and prevents the bacterium from regulating its osmotic pressure. As result cell hurts and bacterium killed.
What do metabolic poisons Interfere with?
Metabolic reactions (reactions in cells) causing damage, illness or death. Often enzyme inhibitors
Give three examples of metabolic poisons which are enzyme inhibitors?
Cyanide
Malonate
Arsenic
Describe cyanide?
Irreversible inhibitor of cytochrome c oxidase which catalyses respiration reactions
Cell die that can’t respire
Malonate describe?
Inhibits succinate dehydrogenase which also catalyses respiration reactions
Arsenic describe?
Inhibits actions of pyruvate dehydrogenase another enzyme that catalyses respiration reactions
What is a metabolic pathway?
A series of connected metabolic reactions
What are metabolic pathways regulated by?
End-product inhibition
In a metabolic pathway what is the product of the first reaction?
The substrate in the next and so on.
How is each of these different reactions catalysed?
By a different enzyme
How are most enzymes inhibited?
By the product of the reaction they catalyse (product inhibition)
What is end-product inhibition?
When the final product in a metabolic pathway inhibits an enzyme that acts earlier in in the pathway
What is end-product inhibition a good way of regulating controlling?
Regulating the pathway
Controlling the amount of end-product that gets made
Give an examples of end-product inhibition?
Phosphofructokinase is an enzyme involved in metabolic pathway breaks down glucose to make ATP
ATP inhibits action of phosphofructpkinase so high level of ATP prevents more ATP being made
What are both product and end-product inhibition?
Reversible
So when levels of product starts dropping level of inhibition will start falling and enzyme can start functioning again so more product can be made
What are enzyme sometimes made out of?
Inactive precursors in metabolic pathways preventing them causing damage to cells
What are some protease used for and made of?
Break down proteins
Synthesised as inactive precursors to stop damaging proteins in cell in which they are made
What does part of the precursor molecule do?
Inhibit it’s action as an enzyme
What happens when precursor molecule is removed from enzyme?
The enzyme become active
