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Cell Structure and
Function
What color are cells in the body?
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clear
Functions of the Cell
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Basic unit of life
Protection and support
Movement
Communication
Cell metabolism and energy release
Inheritance
Cell Characteristics
• Plasma (cell) Membrane
– Outer cell boundary
• Cytoplasm
– Composed of cytoplasmic organelles
• ER, ribosomes, centrioles, mitochondria, Golgi
complex, lysosomes and vacuoles
• Organelles
– Specialized structures that perform specific
functions
Plasma Membrane
• Intracellular versus extracellular
• Selectively permeable
• Fluid-mosaic model: regulate the passage of nutrients and
waste
• Composed of proteins and lipids
Nucleus
• DNA dispersed throughout; controls and integrates the
function of the entire cell
• Consists of :
– Nuclear envelope: Separates nucleus from cytoplasm and regulates
movement of materials in and out
– Chromatin: Condenses to form chromosomes during cell division
– Nucleolus: Assembly site of large and small ribosomal units where
rRNA is manufactured
Cytoplasm
• Cellular material outside
nucleus but inside plasma
membrane
• Cytosol: Fluid portion
• Cytoskeleton: Supports
the cell
– Microtubules
– Microfilaments
– Intermediate filaments
• Cytoplasmic inclusions
Organelles
• Small specialized structures for particular
functions
• Most have membranes that separates the
interior of organelles from cytoplasm
• Related to specific structure and function of
the cell
Ribosomes
• Sites of protein synthesis
• Composed of a large and
small subunit
• Types
– Free
– Attached to endoplasmic
reticulum
• Found in both eukaryotes
and prokaryotes
Endoplasmic Reticulum
• Extension of outer nuclear
membrane
• Types
– Rough
• Attached ribosomes
• Proteins produced and modified
for secretion and for internal use
– Smooth
• No attached ribosomes
• Manufacture lipids
• Cisternae: Interior spaces isolated
from rest of cytoplasm
• Transports nutrients to the nucleus
and provides some cell structure
Golgi Apparatus
• Modification,
packaging, distribution
of proteins and lipids
for secretion or
internal use produced
by ER
• Flattened membrane
sacs stacked on each
other
Function of Golgi Apparatus
Mitochondria
• Provide energy for cell
• Major site of ATP
synthesis
• Membranes
– Crista: Infoldings of
inner membrane
– Matrix: Substance
located in space
formed by inner
membrane
Centrioles
• In specialized zone
near nucleus:
Centrosome
• Each unit consists of
microtubules
• Before cell division,
centrioles divide,
move to ends of cell
and become spindle
fibers in eukaryotic
cells
Cilia
• Appendages projecting
from cell surfaces
• Capable of movement
• Moves materials over
the cell surface
Flagella
• Similar to cilia but
longer
• Usually only one
exists per cell
• Move the cell itself in
wavelike fashion
• Example: Sperm cell
Microvilli
• Extension of plasma
membrane
• Increase the cell
surface
• Normally many on
each cell
• One tenth to one
twentieth size of cilia
• Do not move
Prokaryotes
• Simple cells which lack a membrane bound
nucleus
• Initial or primitive cell type found on earth
• Less complex than eukaryotes
– Have no organelles (microtubules or centrioles)
– Examples include bacteria
• Division is by binary fission
Eukaryotes
• Evolved from prokaryotes; they have a true
nucleus
• Structurally and biochemically more complex
– Examples include protozoa, fungi, algae, plant
and animal cells
• Golgi apparatus is the structure in eukaryotic
cells which secretes substances
Viruses
• Acellular: neither prokaryotic or eukaryotic
• Contain nucleic acid and either RNA or DNA
but not both
• Depend on the energy of the host cell
• Has protective coat which makes them hard
to control; antibiotics have no effect
• Bacteriophage: virus which invades bacteria
• Examples of viral diseases: measles,
chickenpox, mumps, mono, hepatitis, AIDs
Overview of Cell Metabolism
Movement through the Plasma
Membrane
• Four different modes
– Directly through the plasma membrane
• Small, uncharged, hydrophobic molecules
• Osmosis
– Membrane channels
• Rapid movement of water, charged small molecules
– Carrier molecules
• Large polar molecules that are not lipid soluble
• Glucose
– Vesicles
• Large non-lipid soluble molecules, small pieces of matter,
whole cells
• Small sac surrounded by membrane
Movement through the Plasma
Membrane
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Diffusion
Osmosis
Filtration
Mediated transport mechanisms
– Facilitated diffusion
– Active transport
– Secondary active transport
Diffusion
• Movement of solutes from an area of higher
concentration to lower concentration in solution
• Only applies to small, hydrophobic, uncharged
molecules
• Factors that influence rate of diffusion
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Temperature of solution
Distance
Size of diffusing molecules
Concentration or density gradient
• Difference between two points
– Viscosity
• How easily a liquid flows
Osmosis
• Diffusion of water (solvent) across a selectively
permeable membrane (water most abundant compound in
cell)
• Important because large volume changes caused by
water movement disrupt normal cell function
• Cell shrinkage or swelling
– Isotonic: equal concentration on both sides
• cell neither shrinks nor swells
– Hypertonic: Less water/more solute than other side
• cell shrinks (crenation)
– Hypotonic: More water/less solute than other side
• cell swells (lysis)
Osmosis
• Osmotic pressure – force required to prevent
the movement of water a solution by osmosis
across a selectively permeable membrane
• The greater the concentration of the solution
(the more hypertonic the solution) the greater
the osmotic pressure
• The greater the osmotic pressure the greater
the tendency for water to move into the
solution
Osmosis
Filtration
• Works like a sieve
• Depends on pressure difference on either side of
partition
• Moves from side of greater pressure to lower
– Example: In kidneys in urine formation
Osmosis