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

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

Cell wall

Capsule

Flagella

Bacterialchromosome

(a) A typical rod-shaped bacterium

(b) A thin section through the bacterium Bacillus coagulans (TEM)

0.5 µm

Animal Cells

Surrounded by plasma membrane Allows certain molecules in or out of the cell Does not have a cell wall

ENDOPLASMIC RETICULUM (ER)

Smooth ERRough ERFlagellum

Centrosome

CYTOSKELETON:

Microfilaments

Intermediatefilaments

Microtubules

Microvilli

Peroxisome

MitochondrionLysosome

Golgiapparatus

Ribosomes

Plasma membrane

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

Plant Cells

Have plasma membrane and cell wall Cell wall gives support Has chloroplasts (contain chlorophyll) and large vacuole

Fig. 6-9b

NUCLEUS

Nuclear envelopeNucleolus

Chromatin

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Ribosomes

Central vacuole

Microfilaments

Intermediate filaments

Microtubules

CYTO-SKELETON

Chloroplast

PlasmodesmataWall of adjacent cell

Cell wall

Plasma membrane

Peroxisome

Mitochondrion

Golgiapparatus

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 MembraneClip

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

Fig. 7-3

Phospholipidbilayer

Hydrophobic regionsof protein

Hydrophilicregions of protein

Membranes are complex

Membranes are embedded with:Integral proteinsPeripheral proteinsGlycoproteinsProteoglycansCarbohydrates

Membranes are connected to cytoskeleton on the Cytoplasmic surface

Fig. 7-7

Fibers ofextracellularmatrix (ECM)

Glyco-protein

Microfilamentsof cytoskeleton

Cholesterol

Peripheralproteins

Integralprotein

CYTOPLASMIC SIDEOF MEMBRANE

GlycolipidEXTRACELLULARSIDE OFMEMBRANE

Carbohydrate

Roles of Membranes Gatekeeper of cell

Determines what goes in or out of cell

Compartmentalization Every membrane-bound organelle is isolated

Transport Actively move molecules into cell

Signal transduction Environmental conditions trigger genetic and

biochemical changes in cell via receptors

Cell-cell communication and interaction

Diffusion Starts with a gradient System will eventually reach equilibrium (even

distribution) Happens passively without selective barriers Many small molecules diffuse through cell

membrane

Fig. 7-11Molecules of dye Membrane (cross section)

WATER

Net diffusion Net diffusion Equilibrium

(a) Diffusion of one solute

Net diffusion

Net diffusion

Net diffusion

Net diffusion

Equilibrium

Equilibrium

(b) Diffusion of two solutes

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

Lowerconcentrationof solute (sugar)

Fig. 7-12

H2O

Higher concentrationof sugar

Selectivelypermeablemembrane

Same concentrationof sugar

Osmosis

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

(a) A channel protein

Solute CYTOPLASM

Solute Carrier protein

(b) A carrier protein

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

Diffusion Facilitated diffusion

Active transport

ATP