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ENZYMES. What can you recall from IGCSE?. Define the following terms:. Reactions that build up molecules. Reactions that break down molecules. Anabolic reactions: Catabolic reactions: Metabolism: Catalyst: Metabolic pathway: Specificity: Substrate: Product:.

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define the following terms
Define the following terms:

Reactions that build up molecules

Reactions that break down molecules

  • Anabolic reactions:
  • Catabolic reactions:
  • Metabolism:
  • Catalyst:
  • Metabolic pathway:
  • Specificity:
  • Substrate:
  • Product:

Combination of anabolic and catabolic reactions

A substance that speeds up reactions without changing the produced substances

Sequence of enzyme controlled reactions

Only able to catalyse specific reactions

The molecule(s) the enzyme works on

Molecule(s) produced by enzymes

naming enzymes
Naming enzymes:

Work inside cells eg.DNA polymerase

  • Intracellular enzymes
  • Extracellular enzymes
  • Recommended names
  • Systematic name
  • Classification number

Secreted by cells and work outside cells eg. pepsin, amylase

Short name, often ending in ‘ase’ eg. creatine kinase

Describes the type of reaction being catalysed eg.

ATP:creatine phosphotransferase


timeline of enzyme discovery

1946: Sumner finally awarded Nobel prize

Timeline of enzyme discovery


Breakdown of starch to sugar by malt


Name enzyme coined to describe chemicals in yeast that ferment sugars


Eduard Buchner extracted enzyme from yeast and showed it could work outside cells


Otto Rohm exyracted pancreatic proteases to supply enzymes for tanning


James B Sumner produced first pure crystalline enzyme (urease)

and showed enzymes were proteins


Protein nature of enzymes finally established when digestive enzymes

crystallised by John H Northrop

enzymes lower the activation energy of a reaction
Enzymes lower the activation energy of a reaction

Activation energy

of uncatalysed reactions

Initial energy state

of substrates

Activation energy

of enzyme catalysed


Energy levels of molecules

Final energy state of products

Progress of reaction (time)

enzymes lower activation energy by forming an enzyme substrate complex

Substrate + Enzyme

Enzyme/substrate complex

Enzyme/product complex

Product + Enzyme

Enzymes lower activation energy by forming an enzyme/substrate complex

In anabolic reactions enzymes bring the substrate molecules together.

In catabolic reactions the enzyme active site affects the bonds in substrates so they are easier to break

lock and key hypothesis assumes the active site of an enzyme is rigid in its shape
Lock-and-key hypothesis assumes the active site of an enzyme is rigid in its shape

How ever crystallographic studies indicate proteins are flexible.


The Induced-fit hypothesis suggests the active site is flexible and only assumes its catalytic conformation after the substrate molecules bind to the site.

When the product leaves the enzyme the active site reverts to its inactive state.

enzymes are globular proteins
Enzymes are globular proteins
  • Active site has a specific shape due to tertiary structure of protein.
  • A change in shape of the protein affects shape of active site and the function of the enzyme.

Click to link to jmol interactive representation courtesy of University of Arizona

characteristics of enzymes
Characteristics of enzymes
  • Only change the rate of reaction. They do not change the equilibrium or end products.
  • Specific to one particular reaction
  • Present in very small amounts due to high molecular activity:Turnover number = number of substrate molecules transformed per minute by one enzyme molecule

Catalase turnover number = 6 x106/min

how would you measure the effect of an enzyme
How would you measure the effect of an enzyme?
  • Compare uncatalysed rate with catalysed.
  • Enzymes can increase rate by a factor of between 108 to 1026
characteristics of enzymes14
Characteristics of enzymes
  • Rate of enzyme action is dependent on number of substrate molecules present

Vmax = maximum rate of reaction

Vmax approached as all active sites become filled

Rate of Reaction (M)

Some active sites free at lower substrate concentrations

Substrate concentration

why do scientists measure the initial rate of reaction of enzyme catalysed reactions
Why do scientists measure the initial rate of reaction of enzyme-catalysed reactions?

Initial rate of reaction

They measure rate at start of reaction before any factors, eg. substrate concentration, have had time to change.

Rate of Reaction (M)

Independent variable

rate of enzyme catalysed reactions are affected by temperature
Rate of enzyme –catalysed reactions are affected by temperature.

Temperature coefficient Q10:

rate of reaction at (x + 10) oC

Q10 = -----------------------------------------

rate of reaction at x oC

Q10 for between 0 - 40 oC is 2

enzymes denature at 60 o c
Enzymes denature at 60oC

Optimum temperature

Enzyme denaturing and losing catalytic abilities

Rate doubles every 10oC

Rate of reaction


Some thermophilic bacteria have enzymes with optimum

temperatures of 85oC

ph affects the formation of hydrogen bonds and sulphur bridges in proteins and so affects shape
pH affects the formation of hydrogen bonds and sulphur bridges in proteins and so affects shape.




Rate of Reaction (M)







enzymes in medicine
Enzymes in medicine

Glucose oxidase + peroxidase + blue dye on dipsticks to detect glucose in urine:

Glucose oxidase


Hydrogen peroxide


Dye: Blue---Green---Brown

Dye changes according to amount of glucose

Enzyme-linked immunosorbent assays (ELISAs) detect antibodies to infections.

now answer the exam questions
Now answer the exam questions
  • The first question you will complete and then swap with your partner. You will then mark each others work using the provided mark-scheme. You must agree each others marking.
  • The second question you will complete and mark your own and then I will mark it and see if I agree with your marking.
  • The third question you will complete and I will mark it. You will then check my marking and we will agree a score.
  • The total score for all three questions will be recorded.