Enzymes

What is a catalyst? (-)

A substance that speeds up a chemical reaction without being changed in the process

What enzyme does pineapple have that makes us feel discomfort when eating it (-)

Bromelain, an enzyme that digests proteins (e.g. epidermal tissue in mouth)

What makes up enzymes?

Proteins

What makes up proteins?

(from peptides) → (ultimately) Amino acids

What are enzymes?

Proteins that speed up biochemical reactions that remains unchanged at the end of reactions.

What are active sites?

Specific sites which binds to specific substances and where the chemical reaction is catalysed

What are the characteristics of Enzymes? And why?

Sensitive to temperature and pH changes. (they need an optimum temperature and pH to work efficienty)

Not affected by the reactions they catalyse, needed in small amounts. The same number of enzyme molecule can process a large number of substrate molecules

Highly specific (lock and key hypothesis)

What is the lock and key hypothesis?

Lock → enzyme molecule

Key → substrate molecule

Substrate molecule binds to active site of the enzyme to form an enzyme-substrate complex. After the enzyme catalyses the reaction, the products move away from the active site, allowing other substrate molecules bind to the active sites.

What change are enzymes more sensitive to?

pH changes

What if enzymes are exposed to high temperatures and extreme pH levels?

It will denature and inactivate the enzymes

What is denaturation

Change in three-dimensional structure of an enzyme or any other soluble protein caused by heat or chemicals such as acids/alkalis

What is the factors affecting enzyme activities?

Temperature

pH

Substrate concentration

Define the meaning of optimum temperature for catalysing biochemical reactions?

Temperature at which the enzyme catalyses a reaction at the maximum rate

What is the optimum temperature for most enzymes to catalyse a reaction the maximum rate?

37°C (in humans)

Explain why the rate of reaction for most enzymes increases till optimum temperature but decreases from then on?

As the temperature increases, the substrate and enzyme molecules collide more frequently, increasing the chances of the substrate molecules coming into contact with the active site of the enzyme to form a enzyme-substrate complex. (Thus the enzyme catalyses the reaction at a higher rate and doubles for every 10°C increase in temp. until optimum temp is reached)

As it increases above 37°C (the optimum temperature), it causes the rate of reaction to decrease sharply, as the enzymes become denatured, causing the active site on the enzyme to change and substrate molecules can no longer fit into the active site. (hence less enzyme-substrate complex formations)

Is denaturation reversible?

It may be irreversible

Why does pH affect enzyme activity?

Enzyme activity is affected by the acidity or alkalinity of the solutions they act in. A slight change in pH can affect enzyme-catalysed reactions as each enzyme functions optimally at a particular pH.

At very high or low pH values, ionic bonds within the enzyme can be disrupted and this changes the shape active site. The substrate molecule is then unable to ind to the enzyme and the reaction cannot be catalysed by the enzyme

Why does substrate concentration affect enzyme activitiy?

The rate of an enzyme catalysed reaction increases in direct proportion to the substrate concentration until a maximum value

It then remains constant as the enzyme molecules are saturated (e.g. substrate molecules have occupied all the active sites of the enzyme molecules)

What are some commercial uses of enzymes

Food processing

Textile industry

Detergents

Food processing applications

Protease → tenderises meat

Lactase → converts lactose crystallises (gritty) to glucose and galactose to make it smoother

Cellulase → cataylses the break-down of cellulose and the removal of seed coats from cereal grains

Cellulase catalyses the extraction of agar from seaweed

Textile industry

Amylase removes starch that is used as stiffeners from fabrics

Cellulase softens cotton fabrics in biopolishing

Detergents

Protease and amylase help digest protein and starch stains in clothes (respectively)

What are the two types of reactions?

Anabolic reactions

Catabolic reactions

What are anabolic reactions?

Chemical reactions in which simpler substances combine to form more complex substances. (requires energy)

What are catabolic reactions?

Chemical reactions that result in the breakdown of more complex organic molecules into simpler substances. (energy released)

What is the function of enzyme inhibitors?

Enzyme inhibitors interfere with enzyme catalysed reactions

e.g. cyanide, cadmium, mercury, lead, arsenic, carbon monoxide

What are the two types of inhibitors?

Competitive and non-competitive inhibitors

What does competitive inhibitors do to the enzyme?

Binds to active site of enzymes, causing substrate to be unable to bind to active sites of the enzymes

What does non-competitive inhibitors do to the enzyme?

Binds to other parts of the enzyme, changing the shape of the enzyme (and its active site), causing substrate to be unable to bind to the enzyme

What are some of the digestive enzymes produced in the body, and the enzymes that synthesize DNA from deoxyribonucleotides

Lipases → fat

Amylase → starch into glucose

Maltase → maltose into glucose

Trypsin → protein, digest it into polypeptides

Lactase → lactose into glucose and galactose

DNA polermerase → synthesize DNA