Download Overview of Cells

Overview of Cells
Prokaryotic

All bacteria
Most have cell wall

No membrane-bound

organelles
Biochemical reactions take
place in cytoplasm or cell 
membrane
Typically very small

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Eukaryotic
Protist, fungi, plant and
animal cells
Some have cell walls
Possess membrane-bound
organelles
Biochemical reactions
take place in specialized
compartments
Much larger than bacteria

Prokaryotic Cell
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
(a) A typical
rod-shaped
bacterium
Flagella
(b) A thin section
through the
bacterium
Bacillus
coagulans (TEM)
Animal Cells

Surrounded by plasma membrane


Allows certain molecules in or out of the cell
Does not have a cell wall
Nuclear
envelope
ENDOPLASMIC RETICULUM (ER)
Flagellum
Rough ER
NUCLEUS
Nucleolus
Smooth ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Microtubules
Ribosomes
Microvilli
Golgi
apparatus
Peroxisome
Mitochondrion
Lysosome
Plant Cells

Have plasma membrane and cell wall
Cell wall gives support
 Has chloroplasts (contain chlorophyll) and large vacuole

Fig. 6-9b
NUCLEUS
Nuclear envelope
Nucleolus
Chromatin
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
Mitochondrion
Peroxisome
Chloroplast
Plasma
membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
CYTOSKELETON
Why Small Cells?


Cells obtain nutrients
(gases, water other
molecules) from the
environment through the
cell membrane
High surface
area:volume ratios
maximizes the amount
of cell/environment
interaction

Large cells would
starve
Cell Membrane


Lipid bilayer
Integral proteins “float” in fluid
Hydrophobic region of proteins reside in fatty acid layer of
membrane
 Hydrophilic regions are on cytoplasmic and extracellular
surfaces


Membrane fluidity may be altered by adjusting fatty acid chains
Clip
Fig. 7-3
Phospholipid
bilayer
Hydrophobic regions
of protein
Hydrophilic
regions of protein
Membranes are complex
Membranes are embedded with:
Integral proteins
Peripheral proteins
Glycoproteins
Proteoglycans
Carbohydrates
Membranes are connected to cytoskeleton on the
Cytoplasmic surface
Fig. 7-7
Fibers of
extracellular
matrix (ECM)
Glycoprotein
Carbohydrate
Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Cholesterol
Microfilaments
of cytoskeleton
Peripheral
proteins
Integral
protein
CYTOPLASMIC SIDE
OF MEMBRANE
Roles of Membranes

Gatekeeper of cell

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Compartmentalization


Actively move molecules into cell
Signal transduction


Every membrane-bound organelle is isolated
Transport


Determines what goes in or out of cell
Environmental conditions trigger genetic and
biochemical changes in cell via receptors
Cell-cell communication and interaction
Diffusion

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
Starts with a gradient
System will eventually reach equilibrium (even
distribution)
Happens passively without selective barriers
Many small molecules diffuse through cell
membrane
Fig. 7-11
Molecules of dye
Membrane (cross section)
WATER
Net diffusion
Net diffusion
Equilibrium
(a) Diffusion of one solute
Net diffusion
Net diffusion
(b) Diffusion of two solutes
Net diffusion
Net diffusion
Equilibrium
Equilibrium
Osmosis

Requires a gradient and a selectively permeable membrane
Solute is unable to pass through membrane to reach equilibrium
 Water will move to area of greater solvent concentration until
equilibrium is reached

Fig. 7-12
Lower
concentration
of solute (sugar)
Higher
concentration
of sugar
H2O
Selectively
permeable
membrane
Osmosis
Same concentration
of sugar
Facilitated diffusion


An integral protein helps molecules across the
membrane
Often act as a revolving door (carrier) or tunnel
(channel)
Fig. 7-15
EXTRACELLULAR
FLUID
Channel protein
Solute
CYTOPLASM
(a) A channel protein
Carrier protein
(b) A carrier protein
Solute
Active Transport

Cell expends energy to move molecule or atom inside

Often forms gradients to accomplish this
Entry into Cell Summarized

Diffusion and Facilitated diffusion are passive
transport because no energy is required

Facilitated diffusion and active transport can be
very selective processes
Membrane Pumps


Can be used to remove unwanted molecule from
cytoplasm (like sump pump)
Can also be used to form a gradient across the
membrane which can drive other transports
(protomotor force)
Fig. 7-17
Passive transport
Active transport
ATP
Diffusion
Facilitated diffusion