1. WORK

2. Cell Metabolism and ATP
ATP is the energy molecule of the cell.
Billions are used and reassembled every second!!
Endergonic Rxn – Requires energy
(ie. Photosynthesis)
Exgergonic Rxn – releases energy
(ie.Cellular Respiration)
Glucose = 1 dollar
ATP = 1 penny

3. Our “Key” to Biochemical Reactions
Enzymes
Our “Key” to Biochemical Reactions

4. ENZYMES Proteins that accelerate chemical reactions
Almost all processes in the cell need enzymes in order to occur – Cellular Respiration, Photosynthesis, food digestion etc.
Are extremely selective – very specific to certain reactions

5. ENZYMES
For Example:
Lysozyme digests bacterial cell walls, and is found in human tears, egg-white, etc

6. ENZYMES
Enzymes are known to catalyze about 4,000 reactions in the human body
Named according to the reaction they catalyze … “ase” is added to the name of the substrate
Ex: Lactase breaks down lactose

7. HOW ENZYMES WORK:
By providing a lower activation energy for a reaction and dramatically accelerating its rate
For example… (Do not copy)
the reaction catalysed by orotidine-phosphate decarboxylase will consume half of its substrate in 78 million years if no enzyme is present. However, when the decarboxylase is added, the same process takes just 25 milliseconds

8. HOW ENZYMES WORK: Enzyme SUBSTRATE PRODUCT(S) Eg: Sucrase
Sucrose + Water Glucose + Fructose
Enzymes help a reaction to occur …
without being directly involved!!!

10. Check these out! http://www.yellowtang.org/animations/enzymes.swf

11. Enzymes lower the activation energy of a reaction
of uncatalysed reactions
Initial energy state
of substrates
Activation energy
of enzyme catalysed
reaction
Energy levels of molecules
Final energy state of products
Progress of reaction (time)

12. Enzymes lower activation energy by forming an enzyme/substrate complex
Substrate + Enzyme
Enzyme/substrate complex
Enzyme/product complex
Product + Enzyme

13. 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

14. HOW ENZYMES WORK:
“Lock and Key” Model:

15. HOW ENZYMES WORK:

16. Lock-and-key hypothesis assumes the active site of an enzyme is rigid in its shape
How ever crystallographic studies indicate proteins are flexible.

17. 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.

18. Enzyme Reaction Rates

19. Rates 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

20. Temperature -Enzymes denature at 60oC
Optimum temperature
Enzyme denaturing and losing catalytic abilities
Rate doubles every 10oC
Rate of reaction
Temperature
Some thermophilic bacteria have enzymes with optimum
temperatures of 85oC

21. pH - affects the formation of hydrogen bonds and sulphur bridges in proteins and so affects shape.
trypsin
cholinesterase
pepsin
Rate of Reaction (M) 2 4 6 8 10 pH

22. In Summary... Work at optimal concentrations, temp. & pH
If it is too hot, an enzyme can become DENATURED… and will no longer function properly

23. Define the following terms:
Anabolic reactions:
Catabolic reactions:
Metabolism:
Catalyst:
Metabolic pathway:
Specificity:
Substrate:
Product:
Reactions that build up molecules
Reactions that break down molecules
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

24. Competitive Inhibitors
A molecule similar in shape to the substrate bonds with the enzyme’s active site and inhibit its function.
Can be reversible or irreversible
Poisons: cyanide and arsenic bind to key enzymes in this manner…death may result!

25. Non-Competitive Inhibitors
Attach to a binding site on the enzyme other than the active site...causing the shape to change.
The enzyme loses affinity for substrate

27. Allosteric Regulation
Inhibits or stimulates enzyme activity
Enzyme can be turned on or off...therefore cellular reactions are controlled through feedback.

28. The switch: Allosteric inhibition
Allosteric means “other site”
Active site E
Allosteric site

29. Switching off These enzymes have two receptor sites
One site fits the substrate like other enzymes
The other site fits an inhibitor molecule
Inhibitor molecule
Substrate
cannot fit into the active site
Inhibitor fits into allosteric site

30. The allosteric site the enzyme “on-off” switch
Active site E
Allosteric site empty E
Conformational change
Substrate
fits into the active site
Inhibitor molecule is present
Substrate
cannot fit into the active site
The inhibitor molecule is absent
Inhibitor fits into allosteric site

31. Negative Feedback Inhibition

32. This example demonstrates how an end product can inhibit the first step in its production.
Isoleucine binds to the allosteric site of threonine deaminase and prevents threonine from binding to the active site because the shape of the active site is altered.
When the level of isoleucine drops in the cell’s cytoplasm, the isoleucine is removed from the allosteric site on the enzyme, the active site resumes the activated shape and the pathway is “cut back on” and isoleucine begins to be produced.

33. Example!

34. The End!!!