C1.1: Enzymes and Metabolism Flashcards
Define Catalyst
A substance that increases the rate of chemical reactions but is not used up in the reaction
What is the active site
- Sequence of amino acids responsible for the catalytic activity of enzymes
State the role of enzymes in the chemical reactions on which life is based.
Enzymes catalyse metabolic reactions by binding onto a substrate at the active site
What do enzymes do to chemical reactions
Enzymes speed up chemical reactions without being altered, so can be reused.
Define metabolism.
The complex network of interacting chemical reactions that occurs in living organisms
Define specificity in relation to enzyme structure and function.
Each enzyme catalyses one specific reaction or a specific group of reactions - because of enzyme specificity, living organisms have to make large numbers of different enzymes
What allows for specific binding to occur between active site and the substrate
- Similarity in chemical and physical properties between active site and the substrate
Outline how control of metabolism is regulated by enzymes.
An enzyme can catalyse a specific reaction to take place thus, cells can control the rate of metabolic reactions by producing more or less of the enzyme
Contrast anabolic and catabolic reactions.
Catabolic reactions: breakdown of complex molecules into simpler molecules and includes the hydrolysis of macromolecules into monomers
- Releases Energy
Anabolic reactions: Synthesis of complex molecules from simpler moleculesand includes the condensation reaction of monomers into macromolecules
- Consumes Energy
List three examples of anabolic processes.
- Protein synthesis by ribosomes (translation)
- DNA synthesis (replication)
- Synthesis of complex carbs including starch, cellulose and glycogen
List three examples of catabolic processes.
- Digestion of food (happens in mouth, stomach and small intestine)
- Cell respiration (glucose/lipids are oxidised to CO2 and H2O)
- Digestion of complex carbon compounds (decomposers)
Outline properties of globular proteins.
- Enzymes are globular proteins
- Contain a 3d structure and chemical properties that allow them to function as catalysts
Explain the relationship between enzyme structure and enzyme specificity, including the structure and function of the active site.
- Amino acids form the active site
- Substrates must bind to the active site for a reaction to be catalysed - the shape and chemical properties of the active site & substrate match one another.
- When the substrate is bound to the active site, it is converted into products as bonds in the substrate are broken
Outline the stages of enzyme catalysis of a chemical reaction.
- A substrate approaches the active site (the substrates direction of movement is random)
- shape and properties of the substrate and active site are complementary resulting in enzyme-substrate specificity
- Active site undergoes a conformational change to optimally interact with the substrate (induced fit occurs)
- This conformational change weakens the chemical bonds within the substrate which lowers the activation energy
- Substrate converts into product and thus, products disassociate from the active site and the enzyme’s active site returns to its original state
Describe the induced fit model of enzyme binding.
- Substrate binds to active site hence, forming an enzyme-susbtrate complex which triggers a conformational change in the enzyme
- When the substrate and enzyme fit tightly together, there is a weakening of bonds within the molecules of the substrate thus, lowering the activation energy.
- Bonds in the substrates are broken and enzyme-product complex forms where the substrate converts to product
- When the enzyme-catalysed reaction is completed, the products disassociate from the enzyme
- Enzyme’s active site goes back to original shape
Explain the role of random collisions in the binding of the substrate with the enzyme active site.
- The random collisions occur usually in a watery environment (cytoplasm)
- The collisions allow the substrate to bind to the active site on the enzyme so that the reaction can occur
- Active site and substrate should collide in the correct orientation and with enough energy for the reaction to start
Compare enzyme and substrate movement involved in reactions that occur in the cytoplasm, with large substrates and with immobilized enzymes.
- Substrates may be immobilised
- In this case, the enzyme has to move in relation to the substrate
- Enzymes can be immobilised by being embedded in membranes
- In this case, the enzyme can’t move and the substrate has to move
Discuss variation in specificity of different enzymes.
- Enzymes exhibit specificity due to the matching chemical and physical properties between the substrate and the active site
- Certain enzymes are capable of binding to a single substrate exclusively whereas others can bind to a range of similar substrates
Define denaturation.
Irreversible change to an enzyme which changes the shape of its active site hence, it can no longer function
Outline the causes and effects of denaturation on enzyme structure and function.
Causes:
- Extreme pH, heat and the presence of heavy metals
Effects:
- Destroys the tertiary or quaternary structure of a protein or if the temperature or pH is extreme, the secondary structure of a protein can be altered too
Explain the effects of temperature on enzyme structure and function
Low temp:
- Molecules tend to move slowly hence, collisions between substrate and enzyme molecules are not frequent, reduces rate of reaction
Higher temp:
- Molecules move faster hence, collisions between substrate and enzyme molecules are more frequent, rate of reaction increases
If the temperature gets too high (higher than the optimal which is 37*C), enzyme denatures
Outline the equipment used to set up a study into the effect of temperature on amylase activity up to the point of getting results
- Measuring cylinder used to measure equal volumes of substrate
- 5 different water baths at a range of at least 5 different range of temperatures
- Control substrate concentration and pH by ensuring they stay the same
- Amylase and starch is mixed in each water bath for at least 5 mins
- Test for starch by adding drops of iodine and if positive, iodine turns blue-black
Identify the manipulated (independent), responding (dependent) and controlled variation in experiments of enzyme catalyzed reactions.
Manipulated variation:
- Factors that can change; Temp, pH or substrate conc.
Responding variation:
- Measurable factor; Time, mass or volume (quantitative data)
Controlled variation
- Factors that may alter the responding variation; if temp is manipulated variable, mass is responding variable then pH, substrate conc and enzyme conc. must be controlled and stay the same
Define quantitative data
Information that can be measured and recorded with numbers
State the unit for enzyme reaction rate.
s^-1
Define what the reaction rate is
A quantitative measurement of the speed at which the product is produced or the substrate is consumed
- Quantity of the produced product / change in time
- Quantity of consumed reactants / change in time
State two methods for determining the rate of enzyme reaction rates.
- Allow reaction to happen for fixed time and measure amount of substrate used up or product formed. Time should be short so substrate conc. remains high
- Start with known amount of substrate and allow the reaction to continue until all substrate has been converted to products. Measure time taken for the reaction to go to completion.
Describe at least three investigative techniques for measuring the activity of an example enzyme.
Example enzyme: Catalase (converts hydrogen peroxide to water and oxygen gas which bubbles out the solution)
- Time to float an enzyme saturated filter disc
- H2O displacement in by formation of O2 gas
- O2 gas bubble volume
- Change in pressure due to O2 gas
- Change in O2 levels with sensor
All these methods measure amount of O2 formed in a set amount of time.
Define activation energy
The minimum amount of energy required to reach the transition state in which the bonds of the substrate are broken
What is activation energy used for
The activation energy is used to break or weaken bonds in the substrate.
Explain the role of enzymes in lowering the activation energy of a reaction.
- Activation energy required to reach transition state is lowered by enzymes in the catalysed reaction due to binding of the substrate to the active site which weakens bonds in the substrate
- Thus, this increases the rate of reaction
Interpret graphs showing the effect of lowering the activation energy by enzymes.
Substrates are at the higher base
Products are at the lower base
- Curved line with peak is drawn from substrates to products to show without enzyme and curved line has a smaller peak with enzyme
Compare the location of synthesis of enzymes used within and outside of a cell
Intracellular enzyme-catalysed reactions:
- Metabolic reactions that take place inside the cell
- Catalysed by enzymes produced by free ribosomes
Extracellular enzyme-catalysed reactions:
- Metabolic reactions that take place outside the cell
- Catalysed by enzymes produced by bound ribosomes + ribosomes secreted outside the cell by exocytosis