Enzymes

1
Enzymes

• Proteins that catalyze specific reactions
• Contain active site or pocket which modifies a
  molecule called the substrate into a product
• Returns to ready-form and is not used-up by the
  reaction
• Tend to perform only a single, specific reaction
  and not multiple reactions

2
Active Sites and Inhibition

• The active site possesses a 3D structure which
  allows it to bind substrate
• Molecules that have a similar structure to the
  substrate may also bind the active site and
  prevent reaction-competitive inhibitor
• Other molecules may bind elsewhere on the enzyme
  and change the conformation of the active
  site-noncompetitive inhibitor

3
Enzyme interactions

• Enzymes often have active state and inactive
  state and require an interaction with another
  molecule to become active-activator
• Cooperative interactions-the interaction of a
  enzyme with one substrate increases the rate of
  binding to additional substrate molecules

4
Regulation

• Feedback inhibition is very common
• The presence of high levels of a molecule will
  inhibit the pathway that synthesizes that
  molecule
• Like a thermostat

5
Overview of Cells

• Eukaryotic
• Protist, fungi, plant and animal cells
• Some have cell walls
• Possess membrane-bound organelles
• Biochemical reactions take place in specialized
  compartments
• Much larger than bacteria

• Prokaryotic
• All bacteria
• Most have cell wall
• No membrane-bound organelles
• Biochemical reactions take place in cytoplasm or
  cell membrane
• Typically very small

6
Prokaryotic Cell
7
Animal Cells

• Surrounded by plasma membrane
• Allows certain molecules in or out of the cell
• Does not have a cell wall

8
Plant Cells

• Have plasma membrane and cell wall
• Cell wall gives support
• Has chloroplasts (contain chlorophyll) sand large
  vacuole

9
Why Small Cells?

• Cells obtain nutrients (gases, water other
  molecules) from the environment through the cell
  membrane
• High surface areavolume ratios maximizes the
  amount of cell/environment interaction
• Large cells would starve

10
Cell Membrane

• Lipid bilayer
• Integral proteins float in fluid
• Hydrophobic region of proteins reside in fatty
  acid layer of membrane
• Hydrophilic regions are on cytoplasmic and
  extracellular surfaces
• Membrane fluidity may be altered by adjusting
  fatty acid chains

11
Membranes are complex
12
Roles of Membranes

• Gatekeeper of cell
• Determines what goes in or out of cell
• Compartmentalization
• Every membrane-bound organelle is isolated
• Transport
• Actively move molecules into cell
• Signal transduction
• Environmental conditions trigger genetic and
  biochemical changes in cell via receptors
• Cell-cell communication and interaction

13
Diffusion

• Starts with a gradient
• System will eventually reach equilibrium (even
  distribution)
• Happens passively without selective barriers
• Many small molecules diffuse through cell membrane

14
Osmosis

• Requires a gradient and a selectively permeable
  membrane
• Water will move to area of greater solvent
  concentration

15
Facilitated diffusion

• Some structure helps molecules across the
  membrane
• Often act as a revolving door or tunnel

16
Active Transport

• Cell expends energy to move molecule or atom
  inside
• Often forms gradients to accomplish this

17
Entry into Cell Summarized

• Diffusion and Facilitated diffusion are passive
  transport because no energy is required
• Facilitated diffusion and active transport can be
  very selective processes

18
Membrane Pumps

• Can be used to remove unwanted molecule from
  cytoplasm (like sump pump)
• Can also be used to form a gradient across the
  membrane which can drive other transports
  (protomotor force)