Chapter 3
Cells Physiology
•Membrane Transport
-Passive
-Active
•Cell Cycle
•Protein Synthesis
Cellular Physiology:
Membrane Transport
 Membrane Transport – movement of
substance into and out of the cell
 Transport is by two basic methods
 Passive transport
 No energy is required
 Active transport
 The cell must provide metabolic energy
Solutions and Transport
 Solution – homogeneous mixture of two
or more components
 Solvent – dissolving medium
 Solutes – components in smaller quantities
within a solution
• Intracellular fluid –
nucleoplasm and
cytosol
• Extracellular fluid –
fluid on the exterior
of the cell
• Interstitial fluid –
only the fluid that
surrounds the cells
Selective Permeability
 The plasma membrane allows some
materials to pass while excluding others
 This permeability includes movement into
and out of the cell
Passive Processes
•
What determines whether or not a substance can
passively permeate a membrane?
1. Lipid solubility of substance
2. Channels of appropriate size
3. Carrier proteins
PLAY
Animation: Membrane Permeability
Passive Transport Processes
 Diffusion
 Particles tend to distribute themselves evenly
within a solution (reach equilibrium)
 Movement is
from high
concentration
to low
concentration,
or down a
concentration
gradient
Figure 3.8
Passive Transport Processes
 Types of diffusion
 Simple diffusion
(Dialysis)
 Unassisted process
 Solutes are lipid-soluble materials or
small enough to pass through membrane
pores
Passive Transport Processes Diffusion
• Nonpolar lipidsoluble
(hydrophobic)
substances diffuse
directly through the
phospholipid
bilayer
PLAY
Animation: Diffusion
(a) Simple diffusion of fat-soluble molecules
directly through the phospholipid bilayer
Extracellular fluid
Lipidsoluble
solutes
Cytoplasm
(a) Simple diffusion of fat-soluble molecules
directly through the phospholipid bilayer
Figure 3.7a
Passive Transport Processes
• Facilitated diffusion
• Substances require
a protein carrier for
passive transport.
• Still moves with
the concetration
gradient.
Diffusion through the Plasma
Membrane
Figure 3.9
PhysioEx Lab
• Simple Diffusion
• Facilitated Diffusion
Passive Transport Processes
 Types of diffusion
 Osmosis – simple diffusion of water across
a semipermeable membrane
Passive Processes: Osmosis
• Water diffuses through plasma membranes:
• Through the lipid bilayer
• Through protein channels
Water
molecules
Lipid
billayer
Aquaporin
(d) Osmosis, diffusion of a solvent such as
water through a specific channel protein
(aquaporin) or through the lipid bilayer
Figure 3.7d
Passive Processes: Osmosis
• Water concentration is determined indirectly by
solute concentration because solute particles
displace water molecules
• Osmolarity: The measure of total concentration
of solute particles
• When solutions of different osmolarity are
separated by a membrane, osmosis occurs until
equilibrium is reached
(a)
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions. Fluid volume remains the same in both compartments.
Left
compartment:
Solution with
lower osmolarity
Right
compartment:
Solution with
greater osmolarity
Both solutions have the
same osmolarity: volume
unchanged
H2O
Solute
Membrane
Solute
molecules
(sugar)
Figure 3.8a
(b)
Membrane permeable to water, impermeable to solutes
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
Left
compartment
Right
compartment
Both solutions have identical
osmolarity, but volume of the
solution on the right is greater
because only water is
free to move
H2O
Membrane
Solute
molecules
(sugar)
Figure 3.8b
Importance of Osmosis
• When osmosis occurs, water enters or leaves a
cell
• Change in cell volume disrupts cell function
PLAY
Animation: Osmosis
PhysioEx Lab
• Osmosis
• Get Laptops ready to go.
Tonicity
• Tonicity: The ability of a solution to cause a cell
to shrink or swell
• Isotonic: A solution with the same solute
concentration as that of the cytosol
• Hypertonic: A solution having greater solute
concentration than that of the cytosol
• Hypotonic: A solution having lesser solute
concentration than that of the cytosol
(a)
Isotonic solutions
Cells retain their normal size and
shape in isotonic solutions (same
solute/water concentration as inside
cells; water moves in and out).
(b)
Hypertonic solutions
Cells lose water by osmosis and
shrink in a hypertonic solution
(contains a higher concentration
of solutes than are present inside
the cells).
(c)
Hypotonic solutions
Cells take on water by osmosis until
they become bloated and burst (lyse)
in a hypotonic solution (contains a
lower concentration of solutes than
are present in cells).
Figure 3.9
Passive Transport Processes
 Filtration
 Water and solutes are
forced through a
membrane by fluid, or
hydrostatic pressure
 A pressure gradient must
exist
 Solute-containing fluid is
pushed from a high
pressure area to a lower
pressure area
Active Transport Processes
 Transport substances that are unable to pass
by diffusion
 They may be too large
 They may not be able to dissolve in the fat core
of the membrane
 They may have to move against a
concentration gradient
 Two common forms of active transport
 Solute pumping
 Bulk transport
Active Transport Processes
 Solute pumping
 Amino acids, some sugars and ions are
transported by solute pumps
 ATP energizes protein carriers, and in most
cases, moves substances against
concentration gradients
Active Transport Processes
Figure 3.10
Active Transport Processes
 Bulk transport
 Exocytosis
 Moves materials out of the cell
 Material is carried in a membranous vesicle
 Vesicle migrates to plasma membrane
 Vesicle combines with plasma membrane
 Material is emptied to the outside
Active Transport Processes
Figure 3.11
Active Transport Processes
 Bulk transport
 Endocytosis
 Extracellular substances are engulfed by
being enclosed in a membranous vesicle
 Types of endocytosis
 Phagocytosis – cell eating
 Pinocytosis – cell drinking
Active Transport Processes
Figure 3.12
Passive Membrane Transport – Review
Process
Energy Source
Example
Simple diffusion
Kinetic energy
Movement of O2 through membrane
Facilitated diffusion
Kinetic energy
Movement of glucose into cells
Osmosis
Kinetic energy
Movement of H2O in & out of cells
Filtration
Hydrostatic pressure
Formation of kidney filtrate
Active Membrane Transport – Review
Process
Energy Source
Example
Active transport of solutes
ATP
Movement of ions across
membranes
Exocytosis
ATP
Neurotransmitter secretion
Endocytosis
ATP
White blood cell phagocytosis
Pinocytosis
ATP
Absorption by intestinal cells
Osmosis Lab
Osmosis Lab
• Complete the lab calculations, graph and
questions at home. Formal report due
Wednesday, 9/26
Cell Life Cycle
 Cells have two major periods
 Interphase
 Cell grows
 Cell carries on metabolic processes
 Cell division
 Cell replicates itself
 Function is to produce more cells for
growth and repair processes
Events of Cell Division
 Mitosis
 Division of the nucleus
 Results in the formation of two daughter
nuclei
 Cytokinesis
 Division of the cytoplasm
 Begins when mitosis is near completion
 Results in the formation of two daughter
cells
Preparations for DNA Replication
 Interphase
 No cell division occurs
 The cell carries out normal metabolic
activity and growth
DNA Replication
 Genetic material
duplicated and
readies a cell for
division into two cells
 Occurs toward the
end of interphase
 DNA uncoils and
each side serves
as a template
Figure 3.13
Stages of Mitosis
• Prophase
• Mitosis begins here
• First part of cell division
• Centrioles migrate to the
poles
Stages of Mitosis
 Metaphase
 Spindle from centrioles
are attached to
chromosomes at the
centromeres that are
aligned in the center of
the cell
• The chromatids
appear to
repell each other,
taking the shape of
an X.
Stages of Mitosis
 Anaphase
 Daughter
chromosomes are
pulled toward the
poles
 The cell begins to
elongate
• Anaphase
• The separated sister
chromatids (daughter
chromosomes) appear to be
pulled apart by the centromeres.
• Telophase
• Daughter nuclei begin
forming
• A cleavage furrow (for
cell division) begins to
form
• Telophase
• When the daughter
chromosomes reach
the end
of the spindle.
• new nucleus forms.
Cytokinesis
• plasma membrane constricts
(cleavage furrow) and the
cytoplasm divides,
called cytokinesis.
• The two resulting cells are
called daughter cells.
Stages of Mitosis
Figure 3.14; 1
Stages of Mitosis
Figure 3.14; 2
Online Mitosis Lab
Protein Synthesis
 Gene – DNA segment that carries a
blueprint for building one protein
 Proteins have many functions
 Building materials for cells
 Act as enzymes (biological catalysts)
 RNA is essential for protein synthesis
Role of RNA
 Messenger RNA (mRNA)
 Carries the instructions for building a protein
from the nucleus to the ribosome
 Has 3 base codons
 Transfer RNA (tRNA)
 Transfers appropriate amino acids to the
ribosome for building the protein
 Has 3 base anticodons
 Ribosomal RNA (rRNA)
 Helps form the ribosomes where proteins are
built
Transcription and Translation
 Transcription
More
 Transfer of information from DNA’s base
sequence to the complimentary base
sequence of mRNA. In the nucleus
 Translation
Translation
 Base sequence of nucleic acid is translated
to an amino acid sequence outside the
nucleus
 Amino acids are the building blocks of
proteins
Protein Synthesis
Figure 3.15