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Enzymes:

Previously you have learned about DNA and that DNA carries ‘codes’ which in turn via the process of protein synthesis (transcription and translation) make proteins… Well Enzymes are proteins… and now you need to know about the structure and function of these biological catalysts!

So what you have to know: -

• Enzymes as biological catalysts

• Enzymes catalyse chemical reactions – e.g DNA replication, Protein Synthesis, Digestion. 

• Factors affecting enzyme action

• Enzymes are highly specific for their substrate

• Lock-and-key hypothesis

• Enzymes can be denatured

• Enzyme technology

• Enzymes in food production

[practical work you should do in school/college should cover: -

Factors that affect enzyme activity…

Investigate the use of immobilised lactase / Enzymes in food production]

Ok.

Previously you learned about how proteins are made… (transcription and translation)… 

So, what are Proteins? 

Protein - comes from the Greek word “proteios” meaning 1st place! (because - Proteins account for more than 50% of the dry weight of cells – and are VITAL in almost everything organisms do (especially when considering that ENZYMES are proteins!)

PROTEINS 

Proteins are Organic molecules Containing

Carbon, Hydrogen, Oxygen and Nitrogen

Proteins have many vital functions including…

• Structural support

• Storage

• Signalling

• Defense

• Transport

• Movement

Additionally as ENZYMES proteins regulate metabolism by regulating chemical reactions in the cell.

Humans have tens of thousands of different proteins… each with a different, specific structure & function. e.g. 

Globular proteins: like ENZYMES, ANTIBODIES and HORMONES

Fibrous proteins: like Keratin and Collagen.

[images]

So, Proteins have a variety of functions:

Enzymes: usually globular, due to tight folding and coiling of polypeptide chains. They are often soluble and are important in metabolism… (e.g. enzymes hydrolyse (breakdown) large food molecules (digestive enzymes) whilst others help make (synthesise) large molecules.

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Enzymes as biological catalysts

• Enzymes catalyse chemical reactions

• Enzymes are highly specific for their substrate

• Lock-and-key hypothesis

So, Enzymes are proteins. 

They are very important substances because they control the chemical reactions that happen in our bodies… 

Enzymes are known as biological catalysts - substances which speed up reactions but which do not get used up themselves. 

[image of enzyme and substrate]

Enzyme names usually end in the letters ‘ase’ for example: -

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Amylase, protease and lipase.

Enzymes are specific  for what they will catalyse and Enzymes Are Reusable:

• DNA /  RNA polymerase

• Sucrase

• Lactase

• Maltase

Enzymes act as “Biological Catalysts” - they speed up chemical reactions.

How does an enzyme actually catalyses a chemical reaction?

Enzymes catalyse a chemical reaction by combining with a reactant and speeding up the reaction. 

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The reactant is called the substrate. 

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The enzyme has a specific indentation called an active site, which helps it to recognise that substrate.

Just like a key only fits into a specific lock, each enzyme has its own specific substrate. Once the reaction is complete and the required product has been produced, the enzyme releases itself and moves on to the next reaction.

[video - enzymes basics]

[image of lock and key ESC]

[image of activation energy graph]

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There are two main types of enzymes: -

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1) Those that break down large molecules into smaller ones. 

These are very important in digestion, why?

They are required to break down large food molecules into smaller ones that can be used by our cells.

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2) Those that build up large molecules from small ones. These are very important for growth and repair. 

Enzyme specificity (enzymes are very specific).

[PDF task… Use the diagram to help you to explain why each enzyme will only catalyse one particular reaction… Enzymes are specific to one particular type of reaction, in this case it will only be able to bind/attach to substrate A, which fits into the active site of the enzyme].

Factors affecting enzyme action

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Enzymes can be denatured

Many factors affect how well enzymes function: you need to know 3 of them…

1) Temperature

2) pH

3) Substrate Concentration

1. Temperature

Most enzymes function best at normal Body temperature: 37°C

High temperatures will usually result in an enzymes denaturation

Most enzymes like near neutral pH (6 to 8)

Denaturation is defined as a permanent change in the tertiary (3-Dimensional) structure of a protein

When an enzyme is denatured it is no longer able to function.

[image / video of graph]

As temperature increases the rate of reaction increases up to a maximum (usually around 40°C). After this point the rate of reaction will decrease.

Q. Why do you think that the reaction goes faster as the temperature increases? (think about what happens to molecules as they warm up) 

A. The molecules involved in the reaction will have more kinetic energy as the temperature increases, so they will move about more, collide more. 

So the enzyme and substrate molecules are more likely to collide or combine with each other (and therefore react)

High temperatures will result in enzyme denaturation.

Enzymes are proteins. At high temperatures these proteins start to unravel. This changes the shape of the active site and as a result the substrate can no longer fit into it. 

When this happens the enzyme is said to be ‘denatured’. Once an enzyme is denatured it will not work.

[image of enzyme denaturation - graph explained]

2. The Effect of pH

Enzymes in the human body will work at an optimum within narrow pH ranges. pH changes beyond an enzymes optimum will result in the enzymes denaturation.

How does pH affect enzyme activity?

An enzymes catalytic activity is affected by how acidic or alkaline its environment is. 

The majority of enzymes work best in neutral conditions. However, some prefer acidic and others prefer alkaline conditions. 

[image of pH - enzymes]

Similar to temperature, the active site of an enzyme can be changed by conditions that are either too acidic or too alkaline. 

Q. Explain how pH could reduce the rate of a chemical reaction.

A. If the active site of the enzyme is changed (i.e. it is denatured) then the substrate can no longer bond/attach to the active site of the enzyme. Therefore no reaction can take place and no product produced.

3) Substrate Concentration

The more enzyme in a solution, the greater the chance that an enzyme substrate complex will form, and the greater the rate of reaction up to a maximum when all active sites are fully occupied.

[images of substrate concentration / graphs explained]

The more substrate in the solution the greater the chance of a substrate molecule finding an active site, and the faster the rate of reaction up to a maximum when all active sites are fully used.

Enzymes lower Activation energy.

Enzymes lower the activation energy for a reaction [image / video of activation energy]

Enzyme technology & Enzymes in food production

Enzymes use in sweet manufacturing…

Q. How do you get the runny centre inside a cream egg?

A. Enzymes!

To make soft centres in chocolates many manufactures add an enzyme called invertase (sucrase) which catalyses the reaction to break the sugar sucrose down.

Many Confectionary sweets are made using enzymes – specifically and enzyme called Invertase (sucrase). Invertase is produced by yeast and we can utilise this enzyme.

Invertase / sucrase breaks down sucrose into the monosaccharides  glucose and fructose.

Enzymes used in making Vegetarian Cheese

Enzymes in cheese making. Cheese is made when the enzyme chymosin. 

Chymosin acts upon milk – specifically the enzyme catalyses reactions that cause proteins in the milk (called curds) to coagulate and separate from the liquid (whey).

Chymosin was originally obtained from calves stomach tissues. However now, the enzyme is made using genetically modified bacteria. The process is more efficient and the product (Chymosin) contains less impurities and acts more predictably.

Enzymes using in Biological washing powders

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[images]

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Biological washing powders contain enzymes, for example:

Proteases – break down proteins into amino acids

Lipases – break down fats into glycerol and fatty acids

Carbohydrases (e.g. amylase) – break down sugars (polysaccharides, e.g. starch) into monosaccharides (e.g. glucose)

Because biological washing powders contain enzymes (biological catalysts) they work best at “optimal temperatures”.

Which means they are most effective at lower temperatures, e.g around 30OC. 

This has many other benefits:

• Less energy is used (heating water / production of carbon emissions)

• Dyes in fabrics are less likely to ‘run’ out of fabrics

• Clothes are less likely to shrink in the wash

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Enzymes are super important… and you will learn more about enzymes when you learn about The digestive system – e.g. Enzymes that break down carbohydrates (Carbohydrases) like the enzyme amylase which is found in the saliva in the mouth).