Enzymes as proteins

Reflections and Exam tips

Proteins

Proteins are organic compounds containing the elements Carbon, Hydrogen, Oxygen and Nitrogen. They are similar to carbohydrates in that they share Carbon, Hydrogen and Oxygen but have additional Nitrogen.

Proteins are made up of small units called amino acids, these are joined together by ribosomes during protein synthesis.

Proteins and DNA

Proteins are made from instructions from DNA. DNA consists of 4 bases, the instructions are copied from the Nucleus and translated into proteins in the cytoplasm.

Uses of proteins in living things

• Enzymes - see next section
• Hormones e.g. insulin- sugar control, produced in the pancreas
• Antibodies- for immunity ('Y' shaped proteins that bind to microbes)
• Structural proteins (building material) e.g. collagen-for tendons; keratin- for outer layer of skin, nails and hair

Enzymes

Enzymes are proteins which speed up chemical reactions inside living things. They are biological catalysts.

How do they work?

• The substance that they work on is called a substrate.
• The enzyme has a specific place called an active site.
• The active site has a shape which fits the substrate like a lock and a key.
• The enzyme and the substrate bind together to form an enzyme-substrate complex.
• The enzyme catalyses the substrate then they seperate into the enzyme and the products.

Enzyme + Substrate —› enzyme-substrate complex —› Enzyme + product

Naming enzymes

Enzymes are either named using family names or specific names.

Family names

Enzyme family names derive from the substrate that the enzyme catalyses, just add ...ase at the end.

• Carbohydrates-Carbohydrase (breakdown carbohydrates)
• Proteins- Protease (breakdown proteins into amino acids)
• Lipids- Lipase (breakdown fats/lipids into fatty acids and glycerol)
• Isomerase- Changes one molecule/isomer into another

Specific names of enzymes

Each enzyme acts on one specific chemical/substrate hence they have more specific names.

• Amylase- breaks down starch to glucose
• Pepsin- a protease
• Renin- also a protease

Factors affecting rates of enzyme reactions

Enzymes are made up of proteins, (so they are a bit fragile), they are affected by anything which affects their movement or changes the shape of the active site.

1. Temperature

As the temperature increases, the kinetic energy of the enzyme and substrate molecules increases, this means that the rate of the reaction also increases as chances of active sites and substrates joining up (colliding) increase.

The temperature at which the enzyme works best is called the optimum temperature. Above the optimum temperatur,e too much vibrations of the atoms within the enzyme breaks the bonds holding the active site together. The substrate cannot fit anymore and the reaction stops.

We say the enzyms has been denatured.

Most enzymes have an optimum temperature of around 40°C.

2. pH

pH is how acidic or alkaline the surroundings are. Each enzyme acts within a very narrow pH range, a change in pH disrupts the bonds which hold the active site. the anzyme is denatured.

You can easily tell the optimum pH of an enzyme by checking where it works in the body. As a guide these are the pHs around the body:

Mouth = around pH7 (+-1)

Stomach =around pH2

Small intestine = around pH 7.5 (can be slightly more alkaline to pH8)

Blood = around 7.4

3. Substrate concentration

As the substrate concentration is increased, the rate of reaction increases up to a maximum point where it does not increase anymore. This is because at this point all active sites are occupied, new substrate has to wait for free active sites.

Industrial and domestic uses of enzymes

Why use enzymes?

• Enzymes work very fast
• They work at low temperatures- so reduce the need for heating up water- less fossil fuels burned, less global warming, money saved
• They work at low concentrations
• Enzymes can be recycled
• *But enzymes are very expensive.

Biological washing powders

Enzymes used in washing powders include:

• Proteases- to digest protein stains
• Lipases- remove fat stains
• Carbohydrases- remove starch stains

Advantages of using enzymes in washing powders are:

• They work at low temperatures, 30°C, so it means:
• Less energy spent heating up water, which means:
• Less carbon dioxide produced, less global warming

But as noted earlier, enzymes are expensive.

Making fruit juice- pectinases

These digest the pectins, carbohydrates that form cell walls in fruits like oranges and apples, opening up cells and releasing more juice.

Isomerases- for making slimming foods

• Isomers are compounds which have the same formula but a different structure, for example both glucose and fructose have the formula C6H12O6, but the atoms are arranged differently.
• Isomerases are used to convert glucose into fructose, fructose is twice as sweet as glucose, so you use less of it in sweetening tea therefore take less calories.

Proteases- For making baby foods

• Babies produce less proteases (mainly renin, which digests milk protein)
• Proteases are used to pre-digest other proteins added to baby foods so that babies can just absorb the amino acids.