C1.1: Enzymes And Metabolism Flashcards
(36 cards)
What is a catalyst?
A substance that increases the rate of a chemical reaction without
itself undergoing any permanent chemical change
Important because most chemical reaction -> occur slowly/not spontaneously
-> need catalyst for sufficient concentration of product molecules
What are enzymes?
Globular proteins that act as biological catalyst in cells and allows chemical reactions to occur at a suitable rate in the conditions found in living organisms
-> use enzyme because cannot change temp/pressure/pH because cell is sensitive
Reactants collide at correct angle + speed -> product molecule
-> normally change if this occurring small
-> enzyme ensure orientation correct
Reusable -> small number to catalyze reaction
Without enzyme -> rate of reaction too slow to sustain life
Cell control enzymes produced -> cell can control reactions occurring
What is metabolism?
What is a metabolic pathway?
Metabolism: the complete network of interdependent and interacting enzymes catalyzed reactions
- many stages -> each stage separate enzyme
Metabolic pathway: a series of interlinked metabolic reactions
What is enzyme-substrate specificity?
Enzyme-substrate specificity:
Shape (for protein 3D structure) and chemical properties of enzyme active site + substrate => complementary
-> due to specificity thousands of enzymes needed
—> usually one reaction, others multiple
-> allow control of metabolism
Active site bind to substrate (specificity) -> enzyme-substrate complex -> lower energy needed for reaction -> reaction lead to change in chemical structure of substrate -> product formed -> detach
What is anabolism?
Monomers -> macromolecules (condensation)
Endergonic -> require input of energy (store energy in end product)
Eg:
Protein synthesis on ribosomes
Glycogen formation in muscle and liver
Photosynthesis in chloroplast
What is catabolism?
Macromolecules -> small molecules (hydrolysis)
Exergonic -> output of energy (free energy released for cellular processes or as heat)
Eg:
Hydrolysis of macromolecule in digestion
- amylase and maltase -> catalyze hydrolysis of large molecules
Oxidation of substrates in respiration
What is the lock and key theory?
1894 - Hermann Fischer
Shape of active site -> precise and maintained by 3D/tertiary structure of enzyme (specificity)
Substrate fits exactly into active site like LOCK AND KEY
-> held in place by various bonds => enzyme-substrate complex
What is the induced fit theory?
1958 - Daniel Koshland
Enzyme + substrate interact:
Enzyme active site (and sometimes substrate) can change shape SLIGHTLY as substrate enters enzyme
=> CONFORMATIONAL CHANGES
Allows ideal binding arrangement
Maximizes catalysis ability
Forces distorted enzyme -> glove-hand fit
-> once reaction complete back to original shape
What are are cofactors?
Some enzymes -> additional non-protein substance before they can catalyze reaction
Activators:
Inorganic groups
Permanently bound to enzyme
Type of prosthetic group
Eg: iron, zinc, copper
Coenzymes:
Organic molecules
Bind temporarily
Transfer necessary chemical group for reaction
Eg: vitamin C, ATP
How does molecular motion affect the rate of reaction?
All molecules have some motion
All chemical reactions need:
Reactant molecules to collide
Molecules colliding to have enough energy to break existing bonds and form new one
=> change one or both -> change in rate
More KE -> faster movement -> more likely yo collide + have enough energy -> more enzyme-substrate complexes
What are immobilized enzymes? What is the advantage of using them?
Immobilized enzymes are enzymes embedded in membranes/matrix or attached to an inert substance
ADVANTAGES:
No contamination: no enzyme in product -> no need to filter product
Reusable: immobilized enzymes can be reused many times -> efficient and cost-effective
Tolerance: immobilized enzymes have greater temp and pH tolerance
Concentration: substrate can be exposed to higher enzyme concentrations -> increase rate
Control: conditions can be carefully controlled (optimum conditions)
What is denaturation?
Structural change in a protein that results in the loss of its biological properties
-> change in tertiary structure and folding
-> change in shape of active site
Result of high temp or extreme pH
-> bonds holding 3D structure broken (not peptide bonds) (3D shape changes) -> permanently change of active site -> substrate cannot bind -> no reaction
=> enzyme becomes insoluble -> form precipitate
How do different factors affect rate of reaction?
TEMPERATURE:
Optimum temp: most collisions, for humans 35-40°C
Above optimum: increased energy level -> disrupt bond in enzyme and between E+S ->denaturation
Below optimum: molecules move slower -> decreased collision between E+S
pH:
Change -> disrupt bonds/3D shape between charge AA -> denature protein
Optimum: humans 6-8 (depends on location)
SUBSTRATE CONCENTRATION:
+ substrate = + rate
-> more frequent collisions
Eventually -> level off
-> all active sites occupied -> enzyme saturated
-> max rate
ENZYME CONCENTRATION:
+ enzyme = + rate
-> more frequent collisions
Eventually -> level off
-> substrate = limiting factor
-> some enzymes cannot find substrate
Explain an experiment investigating the effect of temperature of pH on catalase activity
Rate of procure of formation used:
Hydrogen peroxide -> common but toxic byproduct of metabolism -> needs to be broken down quick
Catalase (from potatoes) -> enzyme that breaks down H2O2 -> water + oxygen
H2O2 + catalase -> volume of oxygen generated measured
If measure affect of temp:
Conical flask with potatoes in water bath (water level in bath higher than H2O2 in flask)
If measure affect of pH:
Change pH of potato flask
NEUTRASE-MILK EXPERIMENT WORKS TOO!
Explain an experiment investigating the effect of substrate concentration on amylase activity
Rate of substrate disappearance used
Amylase: digestive enzyme that hydrolyzes starch -> maltose + glucose
-> optimum pH 7, temp 37°C
Amylase + starch combined -> tested for starch at regular intervals
-> take sample and add iodine solution
-> blue-black color -> starch
-> yellow-brown color -> no starch
Time taken from starch to be broken down measured
Investigation done under different starch concentrations
- can be acted to measure affect of pH, temp, enzyme concentration
Explain an experiment investigating the effect of starch concentration on amylase using colorimetry
Colorimeter: measure light absorbance or light transmission through a substance
- can be used when color change -> color breaks down -> transmission of light increase/light absorption decrease
STEPS:
Colorimeter calibration: weak iodine solution used to calibrate the colorimeter
Preparation of starch solution of known concentration
-> range of concentration by dilution
After calibration switch on red filter (maximize percentage of trans/absorb)
Sometimes reagent or indicator used to produce the colors detected by the colorimeter, sometimes solution absorb light waves
Calibration graph plotted:
- starch concentration x axis
- percentage absorbance or percentage transmission y axis
How would you interpret a graph on the effects of temperature on the rate of enzyme activity?
Enzymes -> optimum temp -> temp where they catalyze a reaction at max rate
Lower temp -> prevent reaction from proceeding or slow them down
- less KE -> slower -> less collisions -> less enzyme substrate complex formation
-> also collide with less energy -> less likely bonds formed/broken
Higher temp -> speed up reaction
- more KE -> quicker -> more collisions -> more enzyme substrate complex formation
-> collide with more energy -> more likely bond formed/broken
=> increased temp: rate of enzyme reaction drop sharply -> enzyme denature
How would you interpret a graph on the effects of pH on the rate of enzyme activity?
pH -> hydrogen ion concentration in a solution, logarithmic scale
Low -> acidic, high H+
High -> alkaline, low H+
Extreme pH -> alter H bonding in enzyme structure -> irreversible denaturation
- all enzymes optimum pH
How would you interpret a graph on the effects of substrate concentration on the rate of enzyme activity?
More substrate molecules -> increase frequency of collisions with enzyme active site
Active sites blocked by substrates when reaction taking place
-> more active sites occupied -> fewer available to catalyze other substrate
Substrate concentration increase -> slower rise in rate - active sites become saturated -> level off
-> increase in substrate concentration will not increase rate
-> if this happens one way to increase rate -> more enzymes/active sites
How can you measure the rate of reaction in enzyme catalyzed reactions?
Can be determined by measuring the rate of disappearance of substrate/product accumulation:
Rate = change in amount of reactant or product/time
Can be determined based on the time measured:
Rate = 1/time taken (with unit s⁻¹)
- less time -> higher rate
Rate of reaction usually change during reaction as substrate concentration decrease
- graph starts straight line -> plateaus
- steeper line = faster reaction
How can the rate of reaction be determined from a graph?
Gradient at a point = rate of reaction at that time
Draw tangent:
Place ruler on point/time wanted -> extend line as far as needed
Once tangent drawn:
Calculate gradient
Unit: cm³ sec⁻¹(this means volume per sec)
What is activation energy?
The amount of energy needed by the substrate to become unstable enough for a reaction to occur and for new products to be formed
How do enzymes affect activation energy?
All reactions -> energy changes
For reaction to proceed -> need enough activation energy
Enzyme speed up reaction by lowering stability of bonds in the substrate -> lower the activation energy need to catalyze
- Energy released/absorbed unchanged
= rate of reaction quicker
What are extracellular and intracellular enzymes?
Extracellular:
Enzymes produced inside the cell -> packaged in vesicle -> secreted
- catalyze outside of the cell
- eg: chemical digestion in the gut
Intracellular:
Produced and function within the cell
- eg: glycolysis/Krebs cycle
