Transcript Diffusion and the Molecules of Life

Water Chemistry, Diffusion and Ions
• What is the aqueous
environment inside our
cells like?
• Importance of Diffusion
• Importance of Water
• pH
• Body Systems,
Homeostasis and
Feedback Mechanisms
Larry Frolich, Water Chemistry and Diffusion
Common Elements Composing the Human Body
Larry Frolich, Water Chemistry and Diffusion
Common Elements Composing the Human Body
Besides Water (H,O) and Molecules of Life (C,H,O,N),
dissolved ions are crucial to creating cellular aqueous
environment
Larry Frolich, Water Chemistry and Diffusion
The importance of Diffusion
• Diffusion is fast and effective across microscopic distance
• Virtually all living processes involve diffusion and/or osmosis
• Cell membranes control diffusion and allow for life chemical
reactions to take place
• Diffusion lets tissues do job and permits organ systems to
function
• Examples:
– Oxygen in circulatory
system
– Food in digestive
system
– Calcium in muscular
function
– Nerve impulses
Cell membranes and Diffusion
Larry Frolich, Molecules and Diffusion
The importance of water
•Water is the single most
abundant component of cells and
organisms. 75-85% of a cell is
water (10-20 in spores and dry
seeds)
•The polarity of water molecules
are caused by the angles that
hydrogen atom bond to the
oxygen atom (104.50), making the
oxygen atom electronegative (-).
This property accounts for the
cohesiveness, the temperaturestabilizing capacity and the
solvent properties of water.
Larry Frolich, Water Chemistry and Diffusion
Hydrogen bonding
between water
molecules
•Water molecules are cohesive -Hydrogen bonds form between the
hydrogen atoms and the oxygen atoms of
water molecules and are responsible for
its high boiling point, high specific heat,
and high heat of vaporization.
•Water has a high temperaturestabilizing capacity -- Specific heat is
the amount of heat a substance absorb
per gram to increase its temperature 10C.
The specific heat of water is 1.0 calorie
per gram.
•Water has a high heat of vaporization,
the amount of energy required to convert
one gram of a liquid into vapor.
•Water is an excellent solvent. A solvent
is a fluid in which another substance,
called the solute, can be dissolved.
•Hydrophobic: “water fearing”
•Hydrophilic: “water loving”
Larry Frolich, Water Chemistry and Diffusion
More properties of water originated
from its polarity
The solubilization of sodium chloride
because water molecules form spheres of
hydration
pH and lungs and kidneys
• Concentration of
free H+ ions is kept
very constant by
bicarbonate
buffering
• Kidneys and lungs
are crucial in
keeping this
balance
Larry Frolich, Water Chemistry and Diffusion
The importance of selectively permeable membranes
•Membranes are physical barriers of
cells and subcellular compartments
controlling material exchange
between the internal environment
and the extracellular environment
•A membrane is essentially a
hydrophobic permeability barrier
consisting of phospholipids,
glycolipids, and membrane proteins
Polar head
•Membranes contain amphipathic Nonpolar tail
molecules such as phosphatidyl
ethanolamine, an example of
phosphoglycerides, the major class
of membrane phospholipids in most
cells.
Larry Frolich, Water Chemistry and Diffusion
The properties of membranes
A membrane is a lipid bilayer with
proteins embedded in it. Each layer
is about 3-4 nm thick, with the
hydrophobic tails facing each other
in the middle.
•Functions of the associated proteins:
transport proteins; enzymes, receptors,
electron transport intermediates
(mitochondria), or chlorophyll-binding
proteins (chloroplast)
•Membranes are selectively permeable.
Larry Frolich, Water Chemistry and Diffusion
•Freely diffusing molecules: H2O, CO2 or MW <
100 Dalton
•However, ions like Na + and K+ are effectively
excluded (10 8 times less efficient). They need
either hydrophilic channels or carriers for their
crossing of the membrane
Ions and dissolved substances
move across cell membrane
• It is crucial to keep
the right
concentrations of
salts and other
dissolved
substances,
especially glucose,
inside the cell
• Diffusion and active
transport across cell
membrane are
involved
Larry Frolich, Water Chemistry and Diffusion
Larry Frolich, Water Chemistry and Diffusion
Body Systems
and Diffusion
Understand path through body of:
• Food/Nutrients (glucose)
• Oxygen
• Carbon Dioxide
• Nitrogen
Larry Frolich, Molecules and Diffusion
Homeostasis
“…the ability to
maintain relatively
constant internal
conditions even though
the outside world
changes
continuously…”
• Within cells
• Within body
Larry Frolich, Molecules and Diffusion
Feedback Mechanisms
• Negative Feedback Examples—more
common
– home heating system
– Glucose regulation in blood
Larry Frolich, Molecules and Diffusion
Feedback Mechanisms
• Negative Feedback Examples
– home heating system
– Glucose regulation in blood
• Positive Feedback Examples
– Fire-Starting
– Blood clotting
Larry Frolich, Molecules and Diffusion