Download Basis of Cell Structure and Function

2-Basis of Cell Structure and
Function
Taft College
Human Physiology
Basis of Cell Structure and
Function
• Last time we spoke of the cell as the basic unit of
function.
• For the next couple of weeks we will continue to talk
about things at the cellular level- cells and their qualities.
• We spoke last time about characteristics of living cells or
what living cells do:
•
Intake, metabolism (anabolism and catabolism),
output (elimination of wastes), reproduction, movement,
growth, responsiveness.
• Although each of your 100 trillion cells exhibit each of
these characteristics that does not mean that all of your
cells are exactly the same.
Basis of Cell Structure and Function
• In multicellular organisms we tend to see a division of
labor, or specialization, amongst the cells.
That is, the different cells within the body perform different
jobs for functions.
• Due to the differences in function of the cells we are can
see great diversity in cell:
• 1. Size
• 2. Shape Of Cells
• Cell Size
• Cells vary in size from the smallest bacteria (1 micrometer)
to the largest cell, an ostrich egg.
• There are certain limits that are placed on cell size.
Cells cannot be infinitely larger or infinitely small.
There are Limits to Cell Size
• Cells can’t be infinitely small
• They must be at least large enough to contain
macromolecules (proteins and nucleic acids –
DNA) that are necessary to sustain life.
• Cells can’t be infinitely large
• 1. Cells must be small enough for the nucleus
to control cellular activities.
The largest cells in your body “cheat” in this
respect by being multinucleated.
• 2. Cells must be small enough for efficient
movement of nutrients into the cell and
movements of wastes out of the cell.
Cell Shape is Related to Cell
Function
• The cells that line blood vessels and alveoli are
shaped very flat and thin. The thin shape of cells
(simple squamous epithelium) allows for
passage of materials (O2, CO2) through the cell.
• Cells that absorb things typically have microvilli.
Microvilli increase surface area for absorption to
occur. Microvilli increase the amount of
absorptive area significantly without increasing
the amount of cytoplasm.
• Biconcave shape of an RBC creates maximum
surface area for the rapid diffusion of oxygen
and carbon-dioxide throughout the cell.
How do things move in and out of
cells?
• Things may move through cell membranes
by Passive Processes
• Passive Processes do not require
energy use by the cell and include:
• 1- Diffusion
• 2- Osmosis
• 3- Bulk Flow
• 4- Facilitated Diffusion
How do things move in and out of cells?
•
•
•
•
Things may move through cell
membranes by Active Processes
Active Processes do require energy
use by the cell and include:
1- Active Transport
2- Vesicular Transport
A. Endocytosis
1. Pinocytosis
2. Phagocytosis
3. Receptor mediated endocytosis
B. Exocytosis
Passive Processes
• 1. Diffusion
• Diffusion is the movement of molecules
from an area of high concentration of
those molecules to an area of low
concentration of those molecules
• Molecules move from [High] to [Low]
Diffusion
The movement of the
molecules is caused by the
kinetic energy of the
molecules.
Kinetic energy = energy of
movement
Example: Dye crystal in water.
Dye will first be concentrated
around the crystal. Slowly the
dye moves away from the
concentrated source until the
molecules become equally
distributed in the container at
which time they are said to be
in dynamic equilibrium.
Dynamic Equilibrium
• If molecules reach equal distribution or
concentration of molecules throughout a
container, they are said to be in dynamic
equilibrium.
• In dynamic equilibrium, do the molecules stop
moving?
• No – the molecules still have kinetic energy and
continue to move in random motion
• In dynamic equilibrium, there is no net
movement of molecules.
Rate of diffusion is influenced by:
• 1. Temperature
• The greater the temperature, the greater
the rate of diffusion.
• Why?
• Increased temperature increases the
kinetic energy (energy of motion) of the
molecules causing them to move faster.
Rate of diffusion is influenced by:
• 2. Concentration gradient (difference)
• The greater the concentration difference,
the greater the rate of diffusion
• Why?
• Molecules follow the path of least
resistance
• It easier for molecules to move from higher
concentration to lower concentration as
there are fewer molecules to run in to.
B
A
C
Rate of diffusion is influenced by:
• 3. Size of the diffusing molecule
• The greater the size of the molecule, the
slower the rate of diffusion.
• Why?
• The larger the molecule, the greater it’s
chances of running into other things which
slows it down.
(Golf ball vs Basketball?)
Passive Processes
• 2. Osmosis
• Osmosis is the movement of water molecules
from an area of high concentration of those
molecules to an area of low concentration of
those molecules through a semi-permeable
(selectively permeable) membrane.
• Water molecules move from [High] to [Low]
through semi-permeable membrane.
• Osmosis is a specialized type of diffusion.
ChemTerms - Review
• What is a solution?
• A solution is a mixture of a solute (solid)
and a solvent (dissolving liquid).
• Example Tea + water = solution
solute + solvent
Osmosis
Understanding Osmosis
• It’s your first day on the job in a blood lab
• Your boss has asked you to wash the red
blood cells in a blood sample –
• How do you do it?
• Distilled water?
• What would happen if you used distilled
water?
ChemTerms – Review
and Osmosis
• What is tonicity?
• Tonicity = solute(solid) concentration
• Understanding this term will help us make
sense of some other important terms.
ChemTerms – Review
and Osmosis
• Isotonic Solution
• =same solute concentration (and same
water concentration) as the cell
• = 0.9% NaCl in the RBC
• In a clinical setting, isotonic saline has the
same solute concentration as the contents
of an RBC = 0.9% NaCl.
ChemTerms – Review
and Osmosis
• Hypotonic Solution
• =lower solute concentration (and higher
water concentration) than the cell
• = any solution less than 0.9% salt.
• Exposing RBC’s to a hypotonic solution
(like distilled water) will cause them to
swell and burst = hemolysis
ChemTerms – Review
and Osmosis
• Hypertonic Solution
• =higher solute concentration (and lower
water concentration) than the cell
• = any solution greater than 0.9% salt.
• Exposing RBC’s to a hypertonic solution
will cause them to lose water and shrink =
Crenation
Understanding Osmosis
Understanding Osmosis
Passive Processes
• 3. Bulk Flow
• Bulk Flow is the movement in the same
direction, of large numbers of molecules
due to gravity or pressure.
• Example outside of the body?
• Water in river
• Example in the body?
• Blood in blood stream, air in respiratory
passages
Passive Processes
• Bulk Flow of materials through a
permeable membrane is called Filtration.
• Ex. – passage of materials through
capillary walls due to blood pressure.
• The nephrons in the kidney are
responsible for (non-selective ) filtration.
Passive Processes
• 4. Facilitated diffusion
• Facilitated diffusion is diffusion of a substance with the
help of special transporter proteins in the cell membrane.
• Transporter proteins are helpful when substances are
too lipid insoluble to diffuse through the plasma
membrane.
• Ex. Glucose is moved across the cell membrane by
transporter proteins. Insulin serves to speed up the
rate of facilitated diffusion of glucose by increasing
the number of transporter proteins to move sugar into
the body cells where it is needed.
Active Processes
• Active processes require energy
expenditure (ATP) by the cell.
• 1. Active Transport
• 2. Vesicular Transport
• Next Time!