Transcript Cellular Functioning

Cellular Functioning
Chapter 5
CELLULAR MEMBRANES
Plasma Membrane’s Role
• Physical isolation
– Ions & nutrient in, wastes & secretions out
– Allows a concentration gradient to develop
• Regulates exchange with environment
– Maintains homeostasis
– Selective permeability
• Polarity (hydrophobic vs. hydrophilic)
• Charge (charged vs. uncharged)
• Size (large vs. small)
• Genes not necessary to arrange
– Structure and function similar in all life
The Fluid Mosaic Model
• Integral proteins
– Channels
– Carriers
• Peripheral proteins
• Cell – cell recognition
• Phospholipid bilayer
– Hydrophilic heads
– Hydrophobic tails
• Fluidity
– Cholesterol
– Temperature
Types of Transport
Passive
• Energy not required
• Movement ‘down’ a
concentration gradient
• Maintains dynamic
equilibrium
• Specific types
– Diffusion
– Osmosis
Active
• Energy required
• Movement against a
concentration gradient
• Maintains disequilibrium
Reviewing Terms
• Solute
• Solvent
• Solution
• Concentration
Simple Diffusion
• Movement of MOLECULES ‘down’ their concentration
gradient
– Small, nonpolar molecules
• E.g. O2 in and CO2 out of red blood cells
– Each substance is independent
• Continues until equilibrium = no NET movement
Facilitated Diffusion
• Integral proteins move MOLECULES ‘down’ their
concentration gradient
– Large, polar molecules
• E.g sugars, AA’s, ions, and water
– Are specific to substances
• Channels can open or close; carriers change shape
• Rate increases with an increase in protein number
Osmosis
• Movement of WATER ‘down’ its concentration
gradient
– Water binds to solute in solution
– More solute = less free water = less water available to move
• Depends on TOTAL solute concentration and
permeability
water
molecules
glucose
molecules
Tonicity
• Ability of a solution to cause a cell to gain or lose water
– Depends on [solutes] that can’t cross PM relative to that in the cell
• Hypotonic solutions have a ___?__ [solute] than the cell
– Water moves ____?______
• Animal = lyse
• Plant = turgor pressure (central vacuole)
• Hypertonic solutions have a ___?__ [solute] than the cell
– Water moves ____?______
• Animal = crenation
• Plant = plasmolysis
• Isotonic solutions have ___?__ [solute] as the cell
– Water shows no NET movement
• Plant = flaccid
Active Transport
• Movement of molecules against their concentration
gradient
• ATP is energy source
• Maintains disequilibrium
Applying These Concepts
• Diffusion overview
• Practice problem
– “Cell” is impermeable to sucrose
•
•
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Movement of solutes?
Movement of water?
Solution type?
Resulting ‘cell’ shape?
Bulk Transport
• Exocytosis removes ‘stuff’
from inside the cell
– Golgi apparatus to PM
• Endocytosis brings ‘stuff’ into
the cell
– PM pinches in to form vesicles
• Phagocytosis
• Pinocytosis
• Receptor-mediated
ENERGY REACTIONS
Energy
• Capacity to cause change or rearrange matter
– Kinetic energy: energy of movement or objects in motion
• Heat: random movement of particles associated with KE
– Potential energy: stored energy as a result of structure or
location
• Chemical energy: PE available for release to do work
• Cells transform chemical energy into usable energy
Chemical Reactions
• Exergonic releases energy
– Reactants have more PE than products
– Cellular respiration converts stored energy to usable energy
• Endergonic needs a net input of energy
– Products have greater PE than reactants
– Photosynthesis converts energy-poor reactants to energy rich sugars
• Degree of energy change is equal to the differences in PE
The Importance of ATP
• Powers all cellular work
• ATP + H2O
ADP + phosphate + E release
– Reversible because phosphate can rejoin ADP
– Process of phosphorylation, phosphate binds to a
molecule to energize it
The Role of Enzymes
• Proteins that increase the rate of reaction w/o being
consumed
– Generally end in ‘-ase’ and are named for substrates
– Lower the EA barrier
• Energy of activation (EA) is the energy needed to be
overcome to start a reaction
• Net change of energy is the same with or without
Enzymatic Reactions
• 3D shape determines
reactivity
• Synthetic or degradative
• Enzyme activity factors
– Temperature and pH denature
– Buffers help regulate
– Concentrations
Enzyme Inhibitors
• Competitive
– Resembles substrate and competes for binding
– Increasing [substrate] can compensate
• Noncompetitive
– Binds elsewhere than at active site
– Causes conformational change so substrate can’t bind
• Facilitates feedback inhibition which prevents
overproduction of a substance by the cell