1. Proteins & Enzymes

2. What are proteins? Large organic molecules Always contain nitrogen
Essential to the structure and function of living things
Made up of smaller units called ‘amino acids’
Amino Acid

3. Amino Acids
Join together to form long chains know as proteins or polypeptides
Order and number of amino acids in these chains determines the type of protein
20 identified amino acids in the human body

4. Sources of essential amino acids
Non-essential: can by synthesized from other amino acids in the body
Essential: cannot be manufactured by the body, must be present in food
Sources of essential amino acids

5. Transport Proteins Found in the membrane of cells
Control the movement of substances into and out of organelles and cells
Channel proteins, a type of transport protein, act like gates to allow large compounds (e.g. – glucose) to move across membranes

6. Structural Proteins
Link membranes, cytoplasm and the nucleus, allowing for communication
Structural protein, collagen, is found in the bones, cartilage, tendons, ligaments, connective tissue and skin of humans

7. Enzymes Enzymes are one of the most important groups of proteins
They speed up and control all chemical reactions within the body
Generally specific enzymes act as catalysts for specific reactions

8. Types of enzymes
Intracellular enzymes: occur inside cells, where they speed up and control metabolic reactions
Extracellular enzymes: produced by cells, but catalyze reactions outside the cell (e.g. – digestion)

9. 1. Enzymes generally work very rapidly
Properties of enzymes
1. Enzymes generally work very rapidly
One of the fastest enzymes is catalase
Converts hydrogen peroxide into oxygen and water
Accumulation of hydrogen peroxide can be toxic to the body

10. 2. Enzymes are not destroyed or altered by the reactions they catalyze
Properties of enzymes
2. Enzymes are not destroyed or altered by the reactions they catalyze
This means they can be used again
However, cannot be used forever, as there shape can be altered over time

11. Enzyme catalyses reaction
Properties of enzymes
3. Enzymes can work in either direction, as metabolic reactions are generally reversible
A + B
Substrate
C + D
Products
Enzyme catalyses reaction
The reaction will go in either direction until an equilibrium between the substrate and products is reached
NOTE: Substrate: substances that enter a reaction
Products: substances at the end of the reaction

12. Properties of enzymes
4. Enzymes are affected by temperature and have an optimal range at which they operate
Below optimal range, they do not function efficiently
Above this range, they are denatured – enzyme changes shape and can no longer function efficiently
Optimal range varies between organisms (mammals: 35-40*C)

13. 5. Enzymes are sensitive to pH
Properties of enzymes
5. Enzymes are sensitive to pH
Most intracellular enzymes function at their best around neutral (pH 7)
An excessively acidic (below pH 7) or basic (above pH 7) denatures the enzyme
However, digestive enzymes behave differently
‘Pepsin’ functions better in acidic environment
‘Trypsin’ functions better in a basic environments

14. 6. Enzymes are usually specific to particular reactions
Properties of enzymes
6. Enzymes are usually specific to particular reactions
Generally, one enzyme will only catalyze one type of reaction
Extracellular enzymes can work on a variety of substrates

15. Enzyme-substrate complex
enzyme + substrate(s)
When an enzyme controlled reaction takes place, the enzyme and substrate join briefly to form an enzyme-substrate complex
Substrate molecules then react together and the end product leaves the enzyme
enzyme-substrate complex
enzyme + end product(s)

16. Lock-and-key mechanism
Is thought that each enzyme has a precise place (‘active site’) to which its substrate molecules becomes attached
Recent research questions this theory

17. Induced-fit hypothesis
New theory suggests that when a substrate combines with an enzyme, the enzyme changes shape slightly to fit the substrate into the active site