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OCR Biology AS H020 > Enzymes > Flashcards

Flashcards in Enzymes Deck (40):

What are anabolic reactions?

Building up (synthesis)


What are catabolic reactions?

Breaking down (digestion)


What is metabolism?

The sum of all the different reactions and pathways in an organism.


Explain the term Vmax...

Enzymes can only increase the rate if reaction up to a certain point, maximum initial velocity/rate of the enzyme controlled reaction.


What is collision theory?

For a reaction to happen, molecules need to collide with enough energy and the right orientation, when high temperatures and pressures are applied the speed of the molecules will increase hence the number of successful collisions and the overall rate of reaction.


Why are enzymes described as specific?

They only catalyse one reaction.


Define activation energy...

The minimum amount of energy required for a reaction to take place, enzymes reduce this by forming an enzyme-substrate complex.


Explain lock and key hypothesis.

The substrate fits into the active site (tertiary structure) as it has a complementary shape. An enzyme-substrate complex is formed. The substrate(s) react forming an enzyme-product complex. The R groups interact with the substrate forming temporary binds, putting strain on existing bonds. The product is released and the enzyme remains unchanged.


Describe induced fit hypothesis...

The active site changes shape slightly as the substrate enters (it has a complementary shape). The initial reactions are weak but they induce changes in the enzymes tertiary structure weakening bonds and lowering the activation energy.


What are intracellular enzymes?

Enzymes that act within cells


Give an example of an intracellular enzyme...

Catalayse breaks down hydrogen peroxide (H2O2) a toxic by product of many metabolic reactions into H2O and O2 which prevents dangerous accumulation.


What are extracellular enzymes?

Enzymes that work outside of cells, commonly breaking down polymers.


Explain how starch is broken down by extracellular enzymes...

Amylase (salivary glands and pancreas) breaks starhpch down into maltose. Maltase (small intestine) breaks maltose down into glucose.


Explain how proteins are broken down by extracellular enzymes...

Trypsin (protease) breaks down proteins into peptides by hydrolysis, pancreas/small intestine.


Explain how increasing the temperature changes the rate if reaction...

As the temperature increases the molecules have more kinetic energy hence they move faster and collide more frequently with the enzyme forming more enzyme-substrate complexes increasing the rate if reaction.


What happens at high temperatures to enzymes...

A high temperatures enzymes denature as the binds holding their tertiary structure together vibrate more until they break changing the shape of the active site so the enzyme no longer has a complementary shape to the substrate.


What is Q10/temperature coefficient?

How much the rate of reaction changes with a 10 degrees change in temperature.


What is the usual Q10 of an enzyme controlled reaction?



Explain how a changing pH effects the rate of reaction...

Above and below optimum pH, H+ and OH- ions interact with bonds in the tertiary structure changing it hence the active site is no longer complementary, so the enzyme has been denatured, the enzyme can become renatured...


How does substrate concentration change the rate of reaction?

The number of substrate particles in a given area increases meaning a higher collision rate as more active sites are being used so more enzyme-substrate complexes are formed increasing the rate of reaction until the enzyme concentration becomes a limiting factor as Vmax has been reached.


What's are cofactors?

Small inorganic molecules or ions that help the substrate and active site bind together.


Give an example of a cofactor...

Cl- ions in amylase.


What are coenzymes?

A type of cofactor that is organic, they are changed during a reaction but are recycled during reactions.


What are prosthetic groups?

Tightly bound cofactors that form a permanent part of the enzyme.


Give an example of a prosthetic group...

Zn+ ions are part of carbonic anhydrase which catalyses the production of carbonic acid from CO2 and H2O.


What is precursor activation?

Enzymes can be synthesised as precursor inactive enzymes so they do not cause damage within cells producing them or tissues where they are released. These enzymes need a tertiary shape change to be activated.


How can a tertiary shape change be achieved to a precursor enzyme?

Addition of a cofactor or a pH/temp change.


When a precursor enzymes is changed by the addition of a coenzyme it goes from a _____ to a _____ .

Apoenzyme, holoenzyme.


What are precursor enzymes called if to be activated they have to go through a pH or temperature change?

Zymogens or proenzymes.


What are inhibitors?

Enzymes that prevent enzymes from carrying out catalysis.


What are the two types of inhibition...

Competitive and non-competitive.


Describe competitive inhibition...

A molecule has a similar shape to a substrate so it can fit into the active site of its enzyme. This blocks the active site preventing catalysis. The enzyme has been inhibited.


What is an example of competitive inhibition?

Aspirin permanently binds to the active site, the COX enzyme catalyses chemicals that cause fever and pain.


What is the allorsteric site?

A site where an non-competitive inhibitor can bind other than the active site.


Describe non-competitive inhibition...

The inhibitor binds to the allorsteric site, this induces a tertiary shape change so the active site is no longer complementary so the enzyme has been inhibited.


What is an example of non-competitive inhibition?

Proton pump inhibitors. Long term indigestion, stops the enzyme system secreting H+ ions into the stomach.


What is end product inhibition?

Using a product made at the end of a metabolic pathway to inhibit an enzyme that acts earlier on.


What is the purpose of end product inhibition?

It regulates the pathway so the amount of end product can be controlled. This type of inhibition is reversible so when the concentration of the end product falls, more end product will be made.


Give an example of end product inhibition...

Phosphodructokinase is involved in the pathway of breaking down glucose to form ATP, ATP competitively inhibits the production of phosphofructokinase.


What are enzymes?

Biological catalysts , globular proteins that interact with substrate molecules reducing the activation energy and increasing the rate of reaction.