Enzymes

Question 0

What is activation energy

Answer 0

Around of energy that must be supplied for a reaction to proceed. Enzymes lower this because the active site is specific for its substrate

Question 1

Describe enzymes

Answer 1

Globular proteins with specific tertiary structure. Generally soluble in water. Act as catalysts and are specific. Catalyse metabolic reactions in living organisms. Can be intracellular or extra cellular

Question 2

Describe the lock and key model

Answer 2

Enzymes have specifically shaped active site for their substrate. In this model they both stay the same shape

Question 3

Describe the induced fit hypothes

Answer 3

As a substrate molecule collides with an enzymes active site, the enzyme molecule changes shape slightly. This creates an enzyme substrate complex. The Chang in enzyme shape destabilises the substrate which means the reaction occurs more easily and the product is formed. The product is a different shape so it doesn’t fit into the active site and moves away

Question 4

Describe the effect of ph on enzyme activity

Answer 4

All enzymes have an optimum ph value. Above and below this the ions (h+ in acids OH- in alkalis) disrupt the ionic and hydrogen bonds that hold the enzymes tertiary structure together. This makes the active site change shape and so the enzyme is denatured

Question 5

Describe the effect of temperature on enzyme activity

Answer 5

Rise in temperature makes the enzymes molecules vibrate more. If temp goes above a certain level this vibration breaks some of the bonds that hold the enzyme in shape. The tertiary structure is disrupted so the Clive site changes shape so no more enzyme substrate complexes can form. Enzyme is denatured, it cannot function as a catalyst

Question 6

Describe how enzyme concentration affects rate of reaction

Answer 6

More enzyme molecule there are in a solution the more likely a substrate molecule is to collide with one and form an enzyme substrate complex. So increasing Cocentrtiom of enzymes increases rate of reaction. If amount of substrate is limited, there is a plateu where an increase in enzyme concentration has no further effect as not nough substrate molecules to occupy all active sites

Question 7

Describe how substrate concentration affects rate of reaction

Answer 7

Higher the substrate centralism the faster the reaction. More substrate molecules mean collisions more likely so more active sites used and more e s complexes formed. Only applies up until saturation point where plates as all active sites occupied so increasing substrate concentration has no further effect

Question 8

How can you measure reaction rate

Answer 8

How fast product is made, eg carbon dioxide in a gas cylinder. Measure disappearance of substrate. Can time how long it takes for all substrate to be used by regularly sampling the solution

Question 9

What do you need to say when talking about measuring reaction rate

Answer 9

Method, apparatus, dv, variations of if, what controlling, state need to repeat, need a control with no iv influence

Question 10

Describe competitive inhibitors

Answer 10

Have a similar shape to the substrate molecules so compete with substrate to bind to active site but no reaction takes place to they block the active site and so no substrate molecules can fit so no es completed form. How much enzyme inhibited depends on relative concentrations of inhibitor and substrate

Question 11

Describe non competitive inhibition

Answer 11

Bind to enzymes away from its active site. Causes active site to change shape so substrate molecules can no longer bind so no es complexes form and no product made. Different shape so don’t directly complete with substrate. Can be permanent or non permanent inhibition

Question 12

Describe cofactors

Answer 12

Some Enzymes will only work if another non protein substance is bound to them, thee substances ar called cofactors. Some are inorganic molecules and they work by helping the enzyme and the substrate to bind together. They don’t directly participate in th rectioms do aren’t used up or changed

Question 13

Describe coenzymes

Answer 13

Organic cofactors. They participate in reaction and ar changed by it. Often act as carriers, moving chemical groups between different enzymes. Continually recycled by the process.

Question 14

Describe metabolic poisons, cyanide and arsenic

Answer 14

Interfere with metabolic reactions, they are enzyme inhibitors. Cyanide is an irreversible inhibitor of cytochrome c oxidase which is an enzyme that catalyses respiration reactions. Cells that can’t respire die. Arsenic inhibits pyruvate dehydrogenase which also catalyses respiration reactions

Question 15

Describe medicinal drugs in terms of inhibiting enzyme activity

Answer 15

Eg antiviral drugs such as reverse transcriptase inhibitors inhibit reverse Transcriptsse which catalyses the replication of viral DNA so this prevents virus from replicating. Some antibiotics eg penicillin inhibits enzyme transpeptidase which catalyses the formation of proteins in bacterial cell walls. This weakens the cell all and prevents bacterium from regulating its osmotic pressure, so the cell bursts and the bacterium is destroyed