Unit 2 - Enzymes Flashcards
What does a substrate need to have in order to bind with an active site
Complementary shape
Opposite charges to the active site
How does change in pH alter the rate of the reaction
Electric charges of both the enzyme and substrate are neutralised by the presence of either positive or negative ions so no enzyme-substrate complex is formed
Allosteric enzyme regulation
An inhibitor can bind to the allosteric site and usually inhibits the activity
However Cyclic AMP can bind to the inhibitor and remove it so the enzyme can be active again
Competitive inhibition
Competitive inhibitors compete with the substrate to bind with the active site
Has sim shape to part of/all of substrate
A competitive inhibitor occupies the active site only temporarily and so the reaction is reversible
Doe not change Vmax
Non-competitive inhibition
Non competitive inhibitors binds with the enzyme at allosteric site. Inactivates the enzyme by altering shape (changes 3’ structure)
Can be irreversible
Why are heavy metals (e.g. lead and arsenic) poisonous
They have such strong affinities for - SH (sulfhydryl) groups and destroy catalytic activity
How is enzyme inhibition exploited to control disease
Penicillin and other drugs inhibit enzymes that certain diseases use in order to survive
2 types of enzymes
Intracellular (catalase, converts H2O2 into O2 and H2O)
Extracellular (digestive enzymes)
Properties of enzymes
Complementary active site to shape of substrate
High turnover no.
Ability to reduce activation energy
Left unchanged after reaction
What are enzymes affected by
Temperature
pH
Enzyme conc.
Substrate conc.
Lock and key hypothesis
Shape of active site caused by sequence of amino acids (specific tertiary structure - 3D)
Induced fit hypothesis
Explains how activation energy is reduced
Active site is not perfectly complementary but when substrate moves into active site, interferes with the bonds holding active site together
Induces changes in 3’ structure to strengthen binding and weaken bonds in substrate
Active site alters to give perfect fit. Changed shape of active site —> bonds in substrate easier to make or break (reduces activation energy)
Enzyme controlled reaction
Enzyme + substrate (E + S) —> enzyme substrate complex (ESC) —> enzyme product complex (EPC) —> Enzyme and product (E + P)
Effects of pH on enzymes
Enzymes fully denatures before pH 3 and after pH 11
Enzymes start to denature after pH 7
Hydrogen ions that cause acidity affect interaction between polar and charged R groups and alter tertiary structure
Co-enzymes
Small, organic, non protein molecules that bind to active site for short time
Take part in reaction and is recycled
Can carry chemical groups
Example of co-enzymes
FAD
NAD
Co-enzyme A
Vitamin B3 - helps break down carbs and fat
Prosthetic groups
Co-enzyme that is a permanent part of an enzyme molecule (inorganic ion)
Found in conjugated protein molecules e.g. haemoglobin (Fe^2+)
Contribute to final 3D shape and charge
Example of prosthetic groups
Carbonic anhydrase contains a zinc based prosthetic group, helps catalyse CO2 and H2O to make carbonic acids (found in rbc)
Co-factors
Presence of certain ions increase reaction rate
Ions combined with an enzyme or substrate
Binding helps form an ESC more easily, affects shape and charge
e.g. Cl- helps form active site to amylase
How are hydrogen bonds formed
The slight -ve charge on the oxygen atom attracts the slight +ve charge on a hydrogen atom forming a strong bond
Which enzyme group can catalyse oxidation reactions
Dehydrogenases
What is the approximate temperature coefficient (Q10) of an enzyme controlled reaction
2
The rate of reaction typically doubles w/ a 10 degrees C increase
Does not apply to denatured enzymes
Which enzyme catalyses the breakdown of triglycerides into glycerol and 3 fatty acids
Hydrolase
Which type of enzyme catalysed the conversion of a dipeptide into two separate amino acids
Hydrolase
End product inhibition
Where the product made stops the enzyme from making further products and binding to more substrates
Measuring the rate of an enzyme-controlled reaction
Measure how fast the product appears and use this for comparison
Catalase catalyses H2O2 –> H2 + O2
Variables for reaction of breakdown of H2O2
IV -Temp (use water baths)
DV - vol of O2. produced
CV - pH (use same type of buffer), vol and conc of H2O2 and catalase (from celery)
Precursors (apoenzymes)
Enzymes that are inactive because we don’t want the metabolic process to occur
Requires cofactors to be activated (holoenzyme)
Vmax
Maximum initial velocity/ rate of enzyme controlled reaction
Digestion of starch
Starch + amylose –> maltose
Occurs in mouth (saliva) and small intestine (pancreatic juice)
Maltose + maltase –> glucose (absorbed directly into bloodstream)
Occurs in small intestine
Digestion of proteins
Trypsin catalyses breakdown of proteins into smaller peptides in small intestine - release w/ pancreatic juices
AA absorbed by cells lining digestive system and then absorbed into the bloodstream
pH of enzymes in small intestine
8 Trypsin Lipase Amylase Maltase
How to increase Vmax
Add more enzyme
Increase temp
End product inhibition
Example of -ve feedback
Prevents waste of resources to make excess products
Example of non competitive reversible inhibition
Precursors (Zymogens)
Require action of another enzyme to bring about change in 3’ structure
