Transcript Cells : The Living Units

Cells : The Living Units
Chapter 3
Cell Physiology
• Metabolism ( build to cell material, breakdown
substances, make ATP)
• Digest foods
• Dispose of wastes
• Grow
• Move
• Irritability
• Reproduce
Plasma Membrane
• Flexible, transparent and separates the cell
contents from the surrounding environment:
intracellular and extracellular fluids
• Fluid mosaic model:
– Two lipid layers arranged tail to tail
– Mainly phospholipids but also contains cholesterol 
give fluidity
Plasma Membrane Components
• The polar heads are hydrophilic:interact with water
and other polar molecules
• Nonpolar tails are hydrophobic: makes the plasma
membrane relatively impermeable to most water
soluble molecules
• Proteins: Responsible for the specialized functions (
enzymes, receptors, transporters, carriers)
Cell Membrane
Membrane proteins
• Integral and peripheral
membrane proteins
Membrane junctions: Desmososome
• Desmosomes: Mechanical couplings scattered like rivets along the sides of
abutting cells to prevent separation. Anchoring function
• Cytoplasmic surface of each plasma membrane is a plaque ( button)
Membrane junctions: Gap junctions
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Gap junctions, or nexus: Seen in heart and between embryonic cells: function mainly to
allow communication for chemical molecules.
Neighboring cells are connected by connexons: hollow cylinders composed of
transmembrane proteins
Membrane junctions: Tight Junctions
• Impermeable
• bind cells together, integral
proteins of adjacent cells fuse
together
The Plasma Membrane
• Selectively permeable: allows some
substances to pass through and keeps other
substances out
• Transport across the membrane
– Passive Transport
– Active Transport
Passive Transport Active Transport
• Substances are
transported without
the use of energy
• The cell provides ATP
that drives the
transport process
Diffusion and Filtration
• Diffusion:
Process whereby molecules scatter
themselves throughout the
available space by means of their
own kinetic energy. When
molecules move from an area of
greater concentration to an are of
lesser concentration they move
down the concentration gradient.
Simple
• What?
Facilitated
• What?
– Substances that are lipid
insoluble and too large to
pass through the pores
– Lipid soluble ( fats, fat-soluble
vitamins, O2,CO2) or small
enough to pass through the • How?
pores
– Protein carrier is used,
– Osmosis- Water is highly
(permease) transmembrane
polar and passes through the
integral protein
membrane pores
– Channels: proteins allow ions
(Aquaporins), as well as
or water through aqueous
through the bilayer by moving
channels
from gap to gap
Osmosis
• Osmosis is diffusion of water from am area of higher
concentration to a lower concentration across
plasma membranes
• Osmolarity: the total of all solute particles in a
solution
• When equal volumes of aqueous solutions of
different osmolarity are separated by a membrane
that is permeable to all molecules in a system, then
net diffusion of both water and solute occurs until
equilibrium is reached
Osmosis
• Animal cells lack cell walls
• Osmotic imbalance will cause these cells to swell or
shrink
• Tonicity: the ability of a solution to change
the shape or tone of a cell by altering their
internal water volume
• Isotonic: 0.9% saline or 5% glucose, same
concentrations of nonpenetrating solutes as those
found in the cells. Cells exposed to this solution
retain their normal shape
Osmosis
• Extracellular fluids and are
isotonic
• Hypertonic: Solutions with
higher concentrations of
nonpenetrating solutes than
as seen in cells. Causes the
cells to shrink or crenate when
immersed in this solution
• Hypotonic: Solutions that are
more dilute. Causes the cells
to swell and finally lyse or
burst
Filtration
• In the body filtration occurs because blood exerts
hydrostatic pressure
• Pressure gradient: Pushes the filtrate from highpressure areas to low pressure areas
• Kidneys
• Only blood cells and large proteins are held back- not
very selective process
Vesicular Transport
• Exocytosis
Move substances out of the cell. Secretion of hormones, mucus
and other cell products as well as the ejection of wastes
• Endocytosis
Includes all those ATP-requiring processes that take up or
engulf the extra cellular substances. Includes phagocytosis
and pinocytosis( cell drinking) which is a routine activity of
most cells. (cells lining the walls of the small intestine and
kidney tubules)
Phagocytosis & Pinocytosis
Active Transport
• Cells use its own supply of ATP to move
substances across the membrane
• Solute pumping( active transport): requires
protein carriers like facilitated diffusion but
here the cell uses ATP to energize its solute
pumps (proteins)
Cell Cytoplasm
• Cytosol
• Organelles
• Inclusion
– Dissolved
– Insoluble
Nonmembranous Organelles
• Ribosomes
– Free
– Fixed
– Protein synthesis
• Vaults
Nonmenbranous Organelles
Ribosomes are nonmembranous organelles
composed of RNA and protein
Cytoskeleton
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Strength
Support
Shape
Transport
Cell to cell links
Protein fibers
– Microfilaments
– Intermediate
– Microtubules
Cytoskeleton