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AS Biology > F212 Enzymes > Flashcards

F212 Enzymes Flashcards

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0
Q

What are enzymes?

A

Globular proteins with a specific tertiary structure

Catalyse metabolic reactions in living organisms

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1
Q

What do organisms use enzymes for?

A

To catalyse metabolic reactions

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2
Q

Endothermic animals

A

Animals that are able to maintain their internal body temperature independent of the environment
This allows enzymes to function at near optimum temperature inside the organism

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3
Q

Heterotrophs

A

Organisms that obtain nutrients by consuming other organisms

They break down the bodies of these organisms to extract the nutrient molecules they need for growth and energy

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4
Q

Digestion

A

The breaking down of larger molecules into their subunits

This requires the breaking of bonds e.g. glycosidic, peptide and ester bonds

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5
Q

Digestion

Enzyme Secretion

A

Some organisms secrete enzymes outside of themselves in to the food source
The enzymes digest the molecules into their monomers which the organism can take in and use

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6
Q

Digestion

Internal Digestive System

A

As food taken in by the organism passes through the digestive system various enzymes are mixed with it to digest the nutrients it contains
Many enzymes is digestive systems are extra cellular

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7
Q

Extracellular Enzymes

A

Enzymes that are released from the cells that make them

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8
Q

Intracellular Enzymes

A

Enzymes whose actions take place inside of cells

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9
Q

Enzymes and Protection

A

Enzymes that catalyse reactions to break down molecules are useful tools in protecting an organism
Many organisms use enzymes as a defence mechanism e.g. phagocytes take in and digest bacteria using lysosomal enzymes

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10
Q

Covalently Bonded Molecules…

A

…are too stable to just assemble or break down

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11
Q

Maltose

A

Two glucose molecules joined together by a glycosidic bond

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12
Q

Splitting Maltose

A

To split maltose in a hydrolysis reaction in to two glucose molecules the glycosidic bond has to be broken and a water molecules needs to be split

To make this reaction happen in a test tube maltose can be boiled in acid providing the right conditions for molecules of maltose and water to collide with enough energy to achieve hydrolysis

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13
Q

Activation Energy

A

The energy required for a reaction to take place

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14
Q

How do Enzymes Reduce the Activation Energy?

A

By holding the substrate molecule in a certain way that allows the reaction to proceed more easily

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16
Q

Catalysts and Metabolic Reactions

A

Boiling in acid gives molecules a great deal of extra energy
However cells would not survive boiling in acid so need catalysts to drive the metabolic reactions
Without catalysts metabolic reactions could not occur fats enough to sustain life

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17
Q

Active Sites

A

An enzyme has a specifically shaped active site

The active site of the enzyme is the complementary shape substrate molecule(s) involved in the reaction

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18
Q

Lock and Key Model

A

The substrate, key, fits in to the active site, lock, of the enzyme
The substrate is then held in place so that the reaction can take place

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19
Q

The Induced Fit Hypothesis

A

As the substrate molecule collides with the active site, the enzyme changes shape slightly
This makes the actives site fit more closely around the substrate
The substrate is also held in place by the oppositely charged groups that make up the substrate and the active site
The change in enzyme shape also puts strain on the substrate molecule, destabilising it allowing the reaction to occur more easily
This produces a product which is a different shape from the substrate
The product(s) no longer fits into the active site so move away
The enzyme is now able to catalyse the same reaction with another substrate molecule

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20
Q

Enzyme-Substrate Complex

A

The intermediate structure formed when a substrate molecule binds to an enzyme molecule

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21
Q

Enzyme-Product Complex

A

The intermediate structure in which product molecules are bound to the enzyme molecule

22
Q

Heat and Kinetic Energy

A

The molecules in a gas or liquid move around continually
If a gas or liquid is heated the kinetic of the molecules is increased meaning they collide more frequently and with more force

23
Q

Enzymes and Collisions

A

An enzyme can only catalase a reaction if the substrate collides with the active site
Random movements lead to these collisions
Heating the enzyme and substrate increases the kinetic energy therefore increasing the number of collisions and therefore the rate of reaction

24
Q

Heat and Vibration

A

Applying heat to molecules not only makes them move faster but also causes them to vibrate
These vibrations out strain on the bonds holding the molecule together
In large molecules like enzymes these vibrations can break weaker bonds e.g. hydrogen and ionic bonds
These bonds hold together the tertiary structure of the enzyme (protein) and maintain the shape of the active site

25
Q

Heat, Vibration and Denaturation

A

As heat is increased more bonds are broken
The tertiary structure is held less and less in the shape of the working active site
This causes the rate of reaction to decrease
If enough bonds are vp broken the whole tertiary structure will unravel and the enzyme will stop working
This process, denaturation, is irreversible

26
Q

Effect of Increasing Temperature

A

At first increasing temperature will increase the reaction rate at first
But as the temperature increases further the rate of reaction decreases

27
Q

What bonds would you expect to find holding together the tertiary structure of a heat resistant enzyme?

A

Disulphide binds because they aren’t broken down by Heat, only reducing agents

28
Q

Optimum Temperature

A

The temperature that gives the maximum rate of reaction is the enzymes optimum temperature

It is a ball prance between energy and vibrations

Optimum temperature varies between enzymes depending on the environment that they have to function in

30
Q

What is pH?

A

A measure of hydrogen ion H+ concentration between pH1 and pH14
pH7 = neutral

pH7 < alkaline - high H+ concentration

pH7 > acid (proton donor) - low H+ concentration

31
Q

pH and Bonds

A

A hydrogen ion carries a positive charge so will be attracted to negatively charged molecules and parts of molecules and will repel positively charged molecules

32
Q

Pepsin

A

Protein digesting enzyme
Optimum pH - pH 2
Ideal for working in the stomach which contains hydrochloric acid

33
Q

Trypsin

A

Protein digesting enzyme
Optimum pH - pH 7
Ideal for working in the small intestine

34
Q

Effect of pH

A

Because of their charge hydrogen ions can interfere with hydrogen bonds and ionic bonds that hold the tertiary structure of the enzyme in place
Changes in pH cause changes in the shape of the active site and therefore effect the rate of the reaction

35
Q

Optimum pH

A

Enzymes only function in a fairly narrow pH range
Outside of this range the concentration of the hydrogen ions disrupts the shape of the active site denaturing the enzyme
Optimum pH varies depending on the location that the enzyme has adapted to work best in

38
Q

Increasing Substrate Concentration

A

As the concentration of the substrate increases collisions between enzyme and substrate occur more often increasing the rate of reaction

As the concentration is increased the rate of reaction will reach a maximum where all of the active sites are full and further increasing the substrate concentration will have no effect

39
Q

Increasing Enzyme Concentration

A

As the enzyme concentration increases more active sites become available
More enzyme-substrate complexes form and therefore kore products p ,increasing the rate of reaction
As enzyme concentration increases further a maximum rate is reached where all substrate molecules are in an active site and further increasing the enzyme concentration will have no effect

40
Q

Initial Reaction Rate

A

In an experimental situation where enzyme and substrate are mixed together the rate of the enzyme controlled reaction will be at its highest when they are first mixed
As the reaction proceeds product molecules are formed an increase in number
At the same time substrate molecules are used up and decrease in number
So frequency of collisions decreases
The highest reaction rate or initial reaction rate gives the maximum possible rate of reaction for an enzyme under a particular experimental situation

41
Q

Enzyme and Substrate Concentration in Cells

A

Enzyme concentrations in cells are usually fairly low

Partly because enzymes, being catalysts, work over and over again

42
Q

Advantages of an Internal Digestive System Compared With Secreting Enzymes

A

The enzymes produced are not lost to the outside environment

The internal environment can be regulated to provide optimum conditions for the enzyme

43
Q

Competitive Inhibitors

A

Molecules of a similar shape to the substrate
Occupy the active site forming an enzyme-inhibitor complex
This slows down the rate of reaction because less enzyme-substrate complexes are formed
Most competitive inhibitors do not bind permanently, the removal of the inhibitor leaves the enzyme unaffected

44
Q

Non-Competitive Inhibitors

A

Molecules do not compete with substrate molecules for the active site they instead attach elsewhere on the enzyme
This attachment distorts the tertiary structure of the enzyme leading to a change in shape of the active site
The denaturing of the enzymes reduces the rate of the reaction

45
Q

Cofactor

Definition

A

Any substance that must be present to ensure an enzyme controlled reaction can take place at the appropriate rate
Can be an inorganic ion or a coenzyme

46
Q

Coenzyme

Definition

A

Small organic non-protein molecules that bind briefly to the active site just before or at the same time as the substrate
They are essential for enzyme activity
Often take part in the reaction in that they are changed in some way by the enzyme but are recycled to take part again
Often used to carry chemical groups between enzymes to link reactions together in sequence

47
Q

Prosthetic Group

Definition

A

A coenzyme that is a permanent part of an enzyme

They contribute to the final 3D shape of the enzyme and other properties including charge

48
Q

Cofactors - Inorganic

Definition

A

In some reactions the presence of certain ions can increase reaction rate
The ions may combine with either the substrate or the enzyme to affect charge distribution making it easier for the enzyme-substrate complex to form

49
Q

Poisons

How they work

A

Many poisonous substances have an effect by inhibiting or over activating enzymes

50
Q

Poisons

Potassium Cyanide

A

Non competitive inhibitor
Effects vital respiratory enzymes in the mitochondria meaning that ATP cannot be made
This causes the organism to respire anaerobically
Build up of lactic acid in the blood
Death

51
Q

Poisons

Ethylene Glycol

A

Found in antifreeze
Broken down in the liver by an enzyme called alcohol dehydrogenase
The break down product oxalic acid is very toxic
Treated with the drug, fomepizole, which is a strong inhibitor of alcohol dehydrogenase
Ethanol can also inhibit break down, as a competitive inhibitor it is metabolised in preference to ethylene glycol

52
Q

Medicines

Viruses

A

Infections caused by viruses are treated using chemicals that act as competitive inhibitors for protease enzymes
They prevent the virus from replicating by inhibiting the activity of protease enzymes which viruses need to build new virus coats

53
Q

Medicines

Antibiotics

A

Can kill or inhibit the growth of microorganisms
Penicillin is an inhibitor of a bacterial enzyme that forms cross links in bacterial cell walls to stop the bacteria from reproducing

54
Q

Medicines

Cystic Fibrosis

A

Doctors prescribe digestive enzymes as the normal passage of produced digestive enzymes in the pancreas to the gut is blocked

AS Biology (15 decks)

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