1. ENZYMES

2. Enzymes Enzymes are protein catalysts
A catalyst is a substance that speeds up a chemical reaction without being used up in the process
Rates of chemical reactions could be increased with the addition of heat, however heat may denature proteins
A catalyst can speed up the rate of chemical reactions at moderate temperature decreasing risk of denaturation

3. Enzymes
The substrate is the reactant that an enzyme acts on when it catalyzes a chemical reaction
Enzymes are very specific for the substrate to which they bind
Name of enzymes ally end in –ase (ex. lactase, polymerase, maltase, etc.)

4. How Do Enzymes Work?
In an enzyme-catalyzed reaction, the substrate binds to a very small portion of the enzyme
The location where the substrate binds is called the active site
The substrate must fit into a pocket or groove of the 3D structure of the protein
Once the substrate binds to the enzyme, the structure is called the enzyme/substrate complex

6. Induced-Fit Model
As the substrate enters the active site, its functional groups come close to the functional groups of a number of amino acids in the enzyme
This causes the enzyme to change shape slightly to accommodate the substrate
This slight change in shape causes the substrate to become “stressed” (distorting a particular bond) and, therefore, lowers the activation energy needed to break the bonds

8. When the bonds are broken the conformation of the substrate changes and the enzyme loses its affinity for the products releasing them back into the environment
The active site now becomes available for another substrate to attach
The recycling of enzyme molecules causes cells to catalyze many reactions with relatively small numbers of enzymes

10. Co-factors & Co-enzymes
Some enzymes require additional assistance to function
These co-factors and co-enzymes are not proteins
Co-factors:
Inorganic metal ions such as Zn2+ and Mn2+
They help draw out electrons from the substrate where bonds need to be broken

12. Co-enzymes Organic Shuttle molecules from one enzyme to another
Examples: NAD+ and FAD+
These usually get reduced to harvest energy
Act as electron carriers

13. Membrane Structure & Function
The “Fluid Mosaic Model”

14. Eukaryotic Cell Every eukaryotic cell has three main parts:
Plasma (cell) membrane: separates inside of cell from external environment
Nucleus: organelle that contains the cell’s DNA and is surrounded by a double membrane
Cytosol: gel-like fluid from the nucleus to the plasma membrane

16. Plasma membrane
Separates the protoplasm of a cell from the non-living environment
Living structure that regulates what enters and leaves the cell
Cells must always be in contact with their environment in order to survive (to obtain nutrients and to excrete waste)

17. Fluid Mosaic Model
Scientists have inferred that the cell membrane contains a mosaic of different components scattered throughout it (much like raisins in a slice of bread)
Proteins and lipids molecules can drift sideways in the bilayer, supporting the idea that the bilayer has a fluid consistency  fluid- mosaic membrane model

18. Most of the surface area of the cell membrane is made of phospholipids, but accounts for only 42% of the weight of the membrane.
The phosphoslipid is an amphipathic molecule – phosphate heads face the outside and inside, and fatty acid tails are in the middle.
The phosphate heads are hydrophilic (water loving) which are soluble in water
The fatty acid tails are hydrophobic (water hating) which are not soluble in water

19. Pg. 83 Fig 3a

20. Hydrophilic
Hydrophobic

21. Phospholipid Bilayer
Since there are two sets of phosphate heads and fatty acid tails (lipids) the membrane is called the phospholipid bilayer
The membrane is selectively permeable
Fat soluble substances and some other small, uncharged molecules can pass through
Cholesterol is a large molecule, and helps to stabilize the membrane.
At high temperatures: it helps maintain rigidity
At low temperatures: keeps the membrane fluid, flexible and functional – preventing cell death from a frozen membrane

22. assymmetrical
Pg. 82 Fig 2

23. Protein Molecules
Embedded within the lipid bilayer (peripheral or integral) and carry out a number of functions:
Attachment & Recognition
Most carry a special carbohydrate molecule and are known as glycoproteins: provide the cell with a unique identity
Basis for the function of white blood cells and for organ transplant rejection
Some attach to cytoskeleton filaments to help stabilize
Enzymatic activity
Some membranes proteins are enzymes
eg. those involved in respiration and photosynthesis

24. Protein Molecules Triggering signals Transport
Some act as receptor sites for hormones which allow cells to communicate with one another
Triggers cascade of events within the cell
eg. insulin  regulates blood sugar levels
eg. serotonin  insufficiency may result in depression
Transport
Gatekeepers: opening and closing paths (shape-shifting) through which materials might move
eg. sodium-potassium pump  nerve impulses
Channels: allow hydrophilic molecules and certain ions to move in/out
eg. Cl- channel (malfunctioned in CF patients)