Download Cells Part 1 Powerpoint

Cells Part 1: Cell Membranes
By the end of this class you should understand:
• The three major parts of all cells
• The structure and function of a cell membrane
• The distinction between a cell membrane and
cell wall
• The nature of diffusion and osmosis
• The three types of membrane transport
• Bulk transport and ionic transport in cells
Parts of a Cell
• There are two major types
of cells
– Prokaryotic cell
– Eukaryotic cell
• All cells have three parts:
– Cell membrane
– Genetic information
– Cytoplasm
Prokaryotic Cells
• Prokaryotic cells are cells
without a nucleus
– All genetic info is bundled
but not separated from
cytoplasm
• All known prokaryotes
are single-celled bacteria
– Prokaryotic cells are tiny!
Eukaryotic Cells
• If every cell was a
company:
– Prokaryotic cells are a 1man startup in a garage
– Eukaryotic cells are a large
corporation
• Eukaryotic cells have
organelles which each
perform separate jobs
• Genetic info stored in
nucleus
Eukaryotes
• Some eukaryotes are single
celled organisms
– One eukaryotic cell performs
all functions of life
• Some eukaryotes are
multicellular
– The different cells specialize
in different tasks
– Each cell is still individually
alive!
Key Parts of Eukaryotic Cells
• Nucleus
– Stores genetic information
• Cytoplasm
– Composed of a liquid called
cytosol
– Filled with various organelles
• Cell Membrane
– Often referred to as plasma
membrane
Cell Membrane
• The cell membrane is a
flexible, selectively
permeable (or
semipermeable) barrier
• Boundary of cell, visible
under microscope only as
border of cell
• NOT the same as a cell wall
– Cell wall is rigid
Cell Membrane Structure
• The cell membrane is
composed of phospholipids
– Hydrophilic head,
hydrophobic tail
• The nonpolar tails orient
themselves into a
hydrophobic zone
surrounding the cell
– Essentially a thin bubble of
oil
Cell Membrane Structure
Cell Membrane Proteins
• Proteins are
macromolecules
constructed from many
linked amino acids
• Some amino acids are
hydrophobic and so mix
with the inside of the cell
membrane
• These proteins sit inside
the cell membrane
Membrane Protein Functions
• Cell membrane proteins
serve many vital
functions:
– Markers
– Receptors
– Channels
• Transporting things in
and out of cells is a key
function of life!
Selective Permeability
• Some things can move
through cell membranes
– Water
– Lipids
• Many things cannot
– Ions
– Proteins
– Sugars
– Most other things
Diffusion
• Diffusion is the random
movement of particles
• Diffusion results in
particles, on the average,
moving from an area of
high concentration to an
area of low concentration
– Referred to as moving
down the concentration
gradient
Diffusion of Water
• If there is more sugar or
salt inside a cell than
outside, then there is less
water
• Water moves on average
towards where there is
less water
• This diffusion of water is
called osmosis
Osmosis in Animals and Plants
Relative Concentration of Solutes
• Sugars and salts dissolved in water (solutes)
may be more or less concentrated in cytosol
than outside the cell
– More concentrated = hypertonic
– Less concentrated = hypotonic
– Equally concentrated = isotonic
Consequences of Hydration
• Animal cells subjected to
excessively dilute water
swell up and may burst
(lyse)
– Plant cells are protected
from lysis by their cell walls
• Management of an
animal’s water, sugar and
salt levels is vital to life!
What about Transport of Solutes?
• Solutes may move in three ways through cell
membranes:
• Passive transport: membrane is permeable
– Example: CO2
• Facilitated diffusion: membrane is impermeable but
protein channels permit movement
– Example: potassium ions
• Active transport: energy must be expended to move
solute against concentration gradient
– Example: Sugars
Three Types of Transport
Active Transport of Ions
• Actively moving charged
particles to one side of the cell
can create an electrical gradient
– Similar to a concentration
gradient
– The outside of the cell may be
positive or negative relative to the
inside
• This is how neurons send
signals!
Bulk Transport
• Cells may also absorb or
release materials using
vesicles
– A vesicle is a small
membrane-bound organelle
within the cell
• Absorption: Endocytosis
• Excretion: Exocytosis
Vesicular Transport
See you Wednesday!