enzymes Flashcards
what are enzymes
- enzymes are biological catalysts (Proteins that speed up a reaction by lowering activation energy without being used up itself in a metabolic reaction)
- Specific tertiary structure determines the shape of the active site which is complementary to its specific substrate.
- they form an enzyme substrate complex which lowers activation energy of metabolic reaction
Give one example of an intercellular and extracellular enzyme
catalyse intercellular
amylase and trypsin extracellular
how do ESCs reduce activation energy and speed up a reaction
- In a chemical reaction, a certain amount of energy is needed to be supplied to the chemicals before the reaction will start, this is called activation energy.
- enzymes reduce the amount of energy that is needed When enzyme substrate complexes are formed
- In an anabolic reaction, attaching to the enzyme holds them together, reducing repulsion so they bind more easily Hence speeding up reaction
- In a catabolic reaction, the bond between the active site and substrate puts a strain on the bonds in the substrate meaning the substrate molecule breaks up more easily Hence speeding up reaction
What is the lock and key model of Enzyme action
Suggest that the active site has a specific shape determined by tertiary structure so is only complementary to one type of substrate
what is the Induces fit model
The most recent theory that replaced the lock and key model, indicates that The shape of active site is not directly complementary to substrate but is flexible so when a substrate fits into the active site it changes slightly to fit it better
how does temperature affect enzyme activity
- Rate increases as temperature increases because there’s more kinetic energy,
- so molecules move faster making the substrates more likely to collide with the active sites and for ESCs
- until enzyme reaches optimum temp where rate is the highest.
- If kinetic energy goes any higher, The vibration caused by the high energy levels break some of the hydrogen bonds in its tertiary structure that hold the enzyme in shape
- therefore the active site changes shape and the enzyme and Substrate no longer fit together meaning that enzyme has denatured
how does PH affect enzyme activity
- enzymes have a narrow optimum PH where rate is highest.
- Outside the range, OH and H ions found in the acid and alkali can break the ionic and hydrogen bonds that hold the enzyme’s tertiary structure in place
- this makes the active site change shape/enzyme denature.
how does enzyme concentration affect enzyme activity
the more enzymes, the more likely a substrate is to collide and form an enzyme substrate complex so higher rate. but levels off when there is a limit of substrates
how does substrate concentration affect enzyme activity
the more substrate available, the more likely a substrate is to collide and form an enzyme substrate complex so higher rate. but levels off after saturation point when there is a limit of enzymes as they’re all occupied
What is the temperature coefficient Q10
Q2/Q1
catalase
Intercellular enzyme; catalyses decomposition of harmful hydrogen peroxide into water and oxygen
trypsin
Extracellular pancreatic enzyme; catalyses hydrolysis of peptide bonds in small intestine
amylase
A carbohydrase Extracellular enzyme; catalyses digestion of starch to Maltese in saliva and small intestine
How do competitive inhibitors work and how do we overcome their effect
They are a similar shape to the substrate and compete for the active site
increasing substrate concentration can overcome their effect
how do non-competitive inhibitors work?
binds to an allosteric site resulting in the active site changeing shape due to breaking of bond in the tertiary structure so ESCs can’t form and enzyme is not functional anymore. increasing substrate concentration can’t overcome the effect.
what is end product inhabitation
when the final product in a metabolic pathway (a series of metabolic reactions) inhibits an enzyme that acts earlier on in the pathway. This is to control the amount of end product made. When the level of product starts to fall, level of inhibition also drops allowing enzyme function again to produce more product.
What is product inhibitation
when enzymes are inhibited by the product of the reaction they catalyse. This is reversible
What is irreversible inhibitors and give an example of
inhibitor permanently binds to the enzyme due to strong covalent bond eg Cyanide binds to cytochrome C oxidase (enzyme that catalyses respiration reactions)
What is reversible inhibitation
inhibitor temporarily binds to enzyme due to weak hydrogen bonds or few ionic bonds. ESCs can form after inhibitor is released
What is metabolic poison and give examples
Substances that damage cells by Interfering with metabolic reactions. (Usually inhibitors) Cyanide (non-competitive, irreversible inhibitor) inhibits cytochrome c oxidase so cells can’t respire & die.
two other metabolic poisons
Malonate (competitive inhibitor) inhibits succinate dehydrogenase (catalyses respiration reactions)
Arsenic (non-competitive inhibitor) inhibits pyruvate dehydrogenase (catalyses respiration reactions)
How are medical drugs used as inhibitors
penicillin (non-competitive inhibitor of transpeptidase) stops the formation of peptidoglycan crosslinks in bacterial cell wall. This weakens the cell wall and prevents it from regulating its osmotic pressure. As a result, the cell bursts and the bacterium is killed.
What are inactive precursors in a metabolic pathway
- Sometimes enzymes are synthesised as inactive precursors to prevent them causing damage to own cells.
- Part of the precursor molecules inhibits its own action, once this part is removed (e.g. by chemical reaction), enzyme becomes active, ESCs form
- E.g. protease (which breakdown proteins) are synthesised as inactive precursors to prevent them from damaging proteins in the cell in which they are made.
What are the three types of cofactors
Cofactors are non-protein molecule that enable enzyme action and increase rate of reaction; Types are prosthetic groups, inorganic ions and organic coenzymes
