chapter 4: functional anatomy of prokaryotic and eukaryotic cells

Chapter 4:

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Prokaryote Eukaryote

• One circular chromosome, not in a membrane

• No histones

• No membrane-bound organelles

• Complex cell walls (peptidoglycan in bacteria)

• Binary fission

• Paired chromosomes, in nuclear membrane

• Histones bound to DNA

• Membrane-bound organelles

• Simpler cell walls (polysaccharide)

• Mitosis

Pre-nucleus True nucleus

Prokaryotic Cells: Morphology• Average size: 0.2 -2.0 µm in diameter

2.0-8.0 µm in length

• Basic shapes/morphologies:

Coccus (spherical) Bacillus* (rod-shaped) Spiral

Coccobacillus

Pairs: diplo- diplococci diplobacilli

Chains: strepto- streptococci streptobacilli

Clusters: staphylo-staphylococci

Prokaryotic cells: Arrangements

Prokaryotic cells:Structures external to the cell wall

• Capsule: Glycocalyx firmly attached to the cell wall

• Sticky outer coat

• Polysaccharide and/or polypeptide composition

• Aids in attachment of cell to a substrate

• Helps prevent dehydration

• Impairs phagocytosis (host defense mechanism)

Prokaryotic cell structures: Glycocalyx

Figure 4.6a

http://lecturer.ukdw.ac.id/dhira/BacterialStructure/SurfaceStructs.html

• Cellular propellers

• Three basic parts

• Filament: Made of chains of flagellin protein

• Hook

• Basal body: anchor to the cell wall and membrane

• Rotation in the basal body propels the cell

Figure 4.8

Prokaryotic cell structures: Flagella

Figure 4.7

( flagella at both poles)

(tuft from one pole) (flagella distributed over the entire cell)

Flagella ArrangementProkaryotic cell structures: Flagella

Figure 4.9

Taxis: movement toward or away from a stimulus-chemotaxis-phototaxis


Motility


Motile E. coli with flourescently-labelled flagella from the Roland Institute at Harvard

• Axial filaments= endoflagella

• Spirochete movement

• Anchored at one end of a cell

• Contained within an outer sheath

• Rotation causes cell to move

• Spiral/corkscrew motion

Figure 4.10a

Prokaryotic cell structures: Axial Filaments

• Composed of protein pilin

• Fimbriae allow attachment to surfaces/other cells

• Few to hundreds per cell

• Pili are used to transfer DNA from one cell to another

• Longer, 1-2 per cell

Figure 4.11

Prokaryotic cell structures: Fimbriae and Pili

Prokaryotic cells:The cell wall

• Main functions of the cell wall

• Prevents osmotic lysis

• Helps maintain cell shape

• Point of anchorage for flagella

• Contains peptidoglycan (in bacteria)

Prokaryotic cell structures: Cell Wall

Macromolecular network:

• Polymer of a repeating disaccharide unit (backbone)

• Backbones linked by polypeptides

Prokaryotic cell structures: Cell WallPeptidoglycan (or murein)

Figure 4.13a

Prokaryotic cell structures: Gram-positive Cell Walls

Gram-positive cell wall

• Thick PG layer; rigid structure

• Teichoic acids:

• Lipoteichoic acid links PG to plasma membrane

• Wall teichoic acid links PG sheets

• Polysaccharides & teichoic acids are cellular antigens

Figure 4.13b, c

Gram-negative cell wall

Prokaryotic cell structures: Gram-negative Cell Walls

• Thin PG layer

• Surrounded by an outer membrane

• Protection from phagocytes, some antibiotics

• Periplasm (contains PG, degradative enzymes, toxins)

• Lipopolysaccharide (LPS)

• O polysaccharide antigen

• Lipid A is called endotoxin

• Porins (proteins) form channels through membrane

• Thick peptidoglycan

• Teichoic acids

• Thin peptidoglycan

• No teichoic acids

• Outer membrane

• Lipopolysaccharide

• Porins

Gram-positive cell

walls

Gram-negative cell

walls

Prokaryotic cell structures: Cell Walls

Gram stain mechanism• Step 1: Crystal violet (primary stain)

• Enters the cytoplasm (stains) both cell types

• Step 2: Iodine (mordant)

• Forms crystals with crystal violet (CV-I complexes) that are too large to diffuse across the cell wall

• Step 3: Alcohol wash (decolorizer)

• Gm +: dehydrates PG, making it more impermeable

• Gm -: dissolves outer membrane and pokes small holes in thin PG through which CV-I can escape

• Step 4: Safranin (counterstain)

• Contrasting color to crystal violet

• Mycoplasma

• Smallest known bacteria

• Lack cell walls

• Sterols in plasma membrane protect from lysis

• Acid-fast cells (Mycobacterium and Nocardia genera)

• Mycolic acid (waxy lipid) layer outside of PG resists typical dye uptake

• Archaea

• Wall-less, or

• Walls of pseudomurein (altered polysaccharide and polypeptide composition vs. PG)


Atypical Cell Walls

• Lysozyme attacks disaccharide bonds in peptidoglycan

• Penicillin inhibits peptide cross-bridge formation in peptidoglycan

• Bacteria with weakened cell walls are very susceptible to osmotic lysis


Damage to Cell Walls

Prokaryotic cells:Structures internal to the cell wall

• Phospholipid bilayer

• Proteins

• Fluid Mosaic Model• Membrane is as viscous as olive oil

• Proteins move to function

• Phospholipids rotate and move laterally

Figure 4.14b

Prokaryotic cell structures:Plasma Membrane

Main function: selective barrier• Selective permeability allows passage of

select molecules

• Small molecules (H2O, O2, CO2, some sugars)

• Lipid-soluble molecules (nonpolar organic)



• Passive processes do not require energy (ATP)—involves movement down a concentration gradient

• Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration

• Facilitated diffusion: Solute combines with a transporter protein to move down its gradient

• Osmosis: Diffusion of water down its gradient

• Diffusion continues until the solute is evenly distributed (state of equilibrium)

Movement across membranes:Passive Processes


• Osmosis: Movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration

• Water moving down its concentration gradient

Figure 4.18

Osmotic lysis Plasmolysis

Figure 4.18c-e


[sol]solution = [sol]cell [sol]solution > [sol]cell[sol]solution < [sol]cell

Isotonic solution

[sol]cell = concentration of solute inside the cell

Hypotonic solution* Hypertonic solution

Three types of osmotic solutions:


• Active transport of substances requires a transporter protein and ATP

• Solute movement up/against its concentrationgradient

• Important when nutrients are scarce

Movement across membranes:Active Transport Processes

• Cytoplasm: substance inside plasma membrane

• 80% water, contains mainly proteins, carbohydrates, lipids, inorganic ions and low-molecular weight compounds

• Chromosomal DNA: single circular string of double-stranded DNA attached to the plasma membrane

• Located in the “nucleoid” area of the cell

• Plasmids: small, circular, extrachromosomal DNA

• Genes encoded typically not required for survival under normal conditions

Prokaryotic cell structures:Other Internal Structures

• Ribosomes: machinery for protein synthesis (translation)

• Tens of thousands of ribosomes per cell


Complete 70S ribosome


Type:

• Metachromatic granules (volutin)

• Polysaccharide granules

• Lipid inclusions

• Sulfur granules

• Carboxysomes

• Gas vacuoles

• Magnetosomes

Contents:

•Phosphate reserves (for ATP generation)

•Energy reserves

•Energy reserves

•Energy reserves

•Ribulose 1,5-diphosphate carboxylase for CO2 fixation

•Protein covered cylinders

•Iron oxide (destroys H2O2)

Inclusions: Reserve deposits


Endospores• Specialized resting cells (metabolically inactive)

• Resistant to desiccation, heat, chemicals

• Can remain dormant for thousands of years

• Bacillus, Clostridium genera only (Gram-positive)

• Sporulation: Endospore formation

• Triggered by deficiency of a key nutrient

• Germination: Return to vegetative state

• Triggered by physical/chemical

damage to endospore’s coat

http://qlab.com.au

www.textbookofbacteriology.net

Stained pus from a mixed anaerobic infection

Functional Anatomy of Eukaryotic Cells

Figure 4.22

• Contain cytoplasm, enclosed by plasma membrane

• Move in a wavelike motion

Figure 4.23

Functional Anatomy of Eukaryotic Cells: Flagella and Cilia

Functional Anatomy of Eukaryotic Cells: Flagella and Cilia

Figure 4.23a, b

• Cell walls

• Plants, algae, fungi

• Polysaccharide; simpler than prokaryotic cell walls

• Glycocalyx

• Carbohydrates extending from animal plasma membrane

• Anchored to cell membrane

• Strengthens surface, aids in attachment

Functional Anatomy of Eukaryotic Cells: Cell Walls and Glycocalyx

Functional Anatomy of Eukaryotic Cells: Plasma Membrane

Similar to prokaryotic PM structure and function:

• Phospholipid bilayer

• Peripheral proteins

• Integral proteins

EXCEPT, they contain

• Sterols (complex lipids, help strengthen membrane)

• Site for endocytosis (phagocytosis and pinocytosis)

• Selective permeability

• Passive transport processes

• Active transport processes

• Cytoplasm Substance inside plasma membrane and outside

nucleus

• Cytoskeleton Microfilaments, intermediate

filaments, microtubules

• Contains organelles Specialized functions(nucleus, ER, Golgi

complex, mitochondria, lysosomes, ribosomes)

Functional Anatomy of Eukaryotic Cells: Cytoplasm

• Larger, denser than prokaryotic

• Eukaryotic ribosomes: 80S Prokaryotic ribosomes: 70S

• Membrane-bound pool (attached to ER)

• Free pool (in cytoplasm)

Functional Anatomy of Eukaryotic Cells: Ribosomes

Functional Anatomy of Eukaryotic Cells: Nucleus

• Storage for almost whole cell’s genetic information

• Enclosed by nuclear envelope

• Proteins bound to DNA (histones and nonhistones)

Figure 4.24

Functional Anatomy of Eukaryotic Cells: Mitochondrion

• Contains DNA and ribosomes (70S)

• Double membrane

• Inner membrane folds: cristae

• Portion inside of inner membrane: matrix

• Proteins involved in respiration and ATP production in cristae and matrix

• Chloroplasts: enzymes for light-gathering necessary for photosynthesis

Figure 4.27

Endosymbiotic Theory• Theory on evolution of eukaryotic cells’ organelles

• Prokaryotes: 3.5-4 byo

• Eukaryotes: ~2.5 byo

• Mitochondria and chloroplasts share properties with prokaryotes

• Reproduce independently of cell

• Size/shape

• Circular DNA

• Their ribosomes are 70S

chapter 4: functional anatomy of prokaryotic and eukaryotic cells

Documents

cell figure

cell wall slide

attachment of cell

cell pili

cell wall peptidoglycan

gramnegative cell walls

cell shape point of

flagella motility slide