Prokaryotes vs. Eukaryotes

• Growth (increase in size)• Reproduction• Responsiveness• _Metabolism___

Process of Life

• _Metabolism___Both prokaryotes and eukaryotes undergo these processes

• Simple structure• No nucleus• Small; ~1.0 µm in

diameter• One circular

chromosome, not in a membrane

• No histones

Prokaryote Eukaryote

• Complex Structure• Nucleus• Larger; 10-100 µm in diameter• Paired_ chromosomes, in

nuclear membrane• Histones• No histones

• No _membrane___bound organelles

• Peptidoglycan cell walls

• Binary fission • Comprised of bacteria

and archaea

• Histones• Organelles• Polysaccharide cell walls• Mitotic spindle__• Comprised of algae, protozoa,

fungi, animals, and plants

Comparing Prokaryotes and Eukaryotes

Figure 3.2ab

Comparing Prokaryotes and Eukaryotes

Figure 3.2ab

Prokaryotes

• Average size: 0.2 -1.0 µm × 2 - 8 µm• Basic shapes:

Arrangements

• Glycocalyx• Flagella

External Structures of Prokaryotic Cells

• Fimbriae and Pili

• Gelatinous, sticky substance surrounding the outside of the cell

• Composed of polysaccharides, polypeptides, or both

• Two types

Glycocalyx

• Two types– Slime Layer– Capsule

Slime Layer

• Loosely attached to cell surface

• Thinner• Water soluble• Water soluble• Protects cells from

drying out• Sticky layer that allows

prokaryotes to attach to surfaces

Capsule

• Composed of organized repeating units of organic chemicals

• Thicker• Firmly attached to cell

surfacesurface• Protects cells from drying

out• May prevent bacteria from

being recognized and destroyed by host

Flagella• Responsible for

movement• Long, whiplike

structures that extend beyond surface of cell

• Composed of filament, hook, and basal body• Flagellin protein (filament) arranged in chains

and forms helix around hollow core• Base of filament inserts into hook• Basal body anchors filament and hook to cell

Flagella Structure

• Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings

• Filament capable of _rotating_ 360º

• Rotate flagella to run or tumble• Move toward or away from stimuli (taxis)

– Move toward food (+)– Move away from harmful chemicals (-)

Motile Cells

– Move away from harmful chemicals (-)

• Flagella proteins are H antigens (e.g., E. coli O157:H7)

• Not all bacteria are motile– Only those with a flagellum

• _Cocci_ do not have flagella

Motile Cells

Figure 4.9

Arrangements of Flagella

Monotrichous

Figure 3.6

Lophotrichous

Arrangements of Flagella

Amphitrichous

Figure 3.6

Peritrichous

Axial Filaments

• Endoflagella = flagellum covered in a sheath

• In spirochetes• In spirochetes• Anchored at one end

of a cell• Rotation causes cell

to move

Figure 4.10a

• Nonmotile extensions• Fimbriae

– Sticky, proteinaceous, bristlelike projections– Used by bacteria to adhere to one another, to

hosts, and to substances in environment

Fimbriae and Pili

hosts, and to substances in environment– May be hundreds per cell and are shorter than

flagella– Serve an important function in biofilms

Fimbriae Versus Flagella

Figure 3.9

• Long hollow tubules composed of pilin• Longer than fimbriae but shorter than flagella• Bacteria typically only have one or two per

cell

Pili

• Join two bacterial cells and mediate the transfer of DNA from one cell to another (conjugation)

• Also known as conjugation pili or sex pili

Pilus Versus Fimbriae

Figure 3.10

• Provides structure and shape• Protects cell from osmotic forces• Assists some cells in attaching to other cells

or in eluding antimicrobial drugs

Prokaryotic Cell Walls

• Animal cells do not have cell walls– target cell wall of bacteria with antibiotics

• Bacteria and archaea have different cell wall chemistry

• Most have cell wall composed of peptidoglycan_; a few lack a cell wall entirely

• Peptidoglycan composed of sugars, NAG and NAM

Bacterial Cell Walls

NAM• Chains of NAG and NAM attached to other

chains by tetrapeptide crossbridges– Bridges may be covalently bonded to one another– Bridges may be held together by short connecting

chains of amino acids

• Polymer of disaccharideN-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)

Peptidoglycan

• Linked by _____________

Figure 4.13a

Structure of Peptidoglycan

• Gram-Positive Cell Walls– Relatively thick layer of peptidoglycan– Contains unique polysaccharides called teichoic

acids

Bacterial Cell Walls

acids• Some covalently linked to lipids, forming lipoteichoic

acids that anchor _peptidoglycan_ to cell membrane

– Retains crystal violet dye in Gram staining procedure; appear purple

– Acid-fast bacteria contain up to 60% mycolic acid; helps cells survive dessication

Bacterial Cell Walls – Gram positive

Figure 3.13a

• Gram-Negative Cell Walls– Have only a thin layer of peptidoglycan– Have a bilayer membrane composed of

phospholipids, channel proteins _(porins)_, and lipopolysaccharide (LPS)

Bacterial cell walls

lipopolysaccharide (LPS) – May be impediment to the treatment of disease– Following Gram staining procedure, cells appear

pink

Bacterial Cell WallsGram Negative

Figure 3.13b

• Union of lipid with sugar• Also known as endotoxin• Lipid portion known as lipid A

– Released from dead cells when cell wall disintegrates

LPS

wall disintegrates– May trigger fever, vasodilation,

inflammation, shock, and blood clotting– Can be released when antimicrobial

drugs kill bacteria

Periplasmic Space• Between outer membrane and cell membrane

– Contains peptidoglycan and periplasm– Contains water, nutrients, and substances secreted

by the cell, such as digestive enzymes and proteins involved in transport

• Do not have peptidoglycan• Cell walls contain variety of specialized

polysaccharides and proteins• Gram-positive archaea stain purple

Archael Cell Walls

• Gram-positive archaea stain purple • Gram-negative archaea stain pink

• Phospholipid bilayer - composed of lipids and associated proteins

• Proteins act as – recognition proteins, enzymes, receptors,

Prokaryotic Cytoplasmic Membrane

– recognition proteins, enzymes, receptors, carriers, or channels

– Integral proteins – Peripheral proteins – Glycoproteins

• Fluid mosaic model describes current understanding of membrane structure

Phospholipid Bilayer of Cytoplasmic Membrane

Figure 3.14

Cytoplasmic Membrane Function

• Controls passage of substances into and out of the cell; selectively permeable

• Functions in energy production• Harvests light energy in photosynthetic

prokaryotesprokaryotes

• Naturally impermeable to most substances• Proteins allow substances to cross

membrane• Occurs by passive or active processes

Control of Substances Across Cytoplasmic Membrane

• Occurs by passive or active processes• Maintains a concentration gradient and

electrical gradient; collectively known as electrochemical gradient– Chemicals concentrated on one side of the

membrane or the other– Voltage exists across the membrane

• Diffusion• Facilitated Diffusion • Osmosis

– Isotonic solution

Passive Processes of Transport

– Isotonic solution – Hypertonic solution – Hypotonic solution

• Active Transport • Group Translocation

Movement Across Membranes• Simple diffusion: Movement of a solute from an

area of high concentration to an area of low concentration.

Movement Across MembranesFacilitated diffusion: Solute combines with a transporter protein in the membrane.

Figure 4.17

Movement Across Membranes

• Osmosis– Movement of water

across a selectively permeable membrane from an area of high water concentration to an area concentration to an area of lower water concentration.

Figure 4.18a

Figure 4.18c-e

Effects of Solutions on Organisms –Osmotic Pressure

Figure 3.18

Movement Across Membranes• Active transport of substances requires a

transporter protein and ATP.• Group translocation of substances requires

a transporter protein and PEP.– Substance chemically modified during transport

• Cytoplasm is the substance inside the plasma membrane– Cytosol is the liquid portion

Cytoplasm of Prokaryotes

Figure 4.6a, b

• Nuclear area (nucleoid)

Nuclear Area

Figure 4.6a, b

Ribosomes

Figure 4.6a

Ribosomes

Figure 4.19

Differ slightly in size from Eukaryotic ribosomal subunits

Streptomycin & gentamycin attach to 30S subunitErythromycin & Chloramphenicol attach to 50S subunit

• Metachromatic granules (volutin)

• Polysaccharide granules• Lipid inclusions

Inclusions

•Phosphate reserves

•Energy reserves•Energy reserves•Energy reserves

• Sulfur granules• Carboxysomes

• Gas vacuoles• Magnetosomes

•Energy reserves

•Ribulose 1,5-diphosphate carboxylase for CO2 fixation

•Protein covered cylinders•Iron oxide (destroys H2O2)

Eukaryotic Cells

• Glycocalyx• Flagella• Cilia

External Structures of Eukaryotic Cells

• Cilia

• Not as organized as prokaryotic capsules• Helps anchor animal cells adhere to each

other• Strengthens cell surface• Provides protection against dehydration

Glycocalyx

• Provides protection against dehydration• Function in cell-to-cell recognition and

communication

• Shaft composed of tubulin arranged from microtubules

• “9 + 2” arrangement of microtubules• Filaments anchored to cell by basal body; no hook• Basal body has “9 + 0” arrangement of

Flagella

• Basal body has “9 + 0” arrangement of microtubules

• Originate inside the cell (not extensions outside the cell)

• May be single or multiple• Generally found at one pole of cell• Do not rotate, but undulate rhythmically

Eukaryotic Flagella and Cilia

Figure 3.23

Flagella & Cilia

Eukaryotic Flagella and Cilia

Figure 3.23

• Shorter and more numerous than flagella

• Composed of tubulin in “9 + 2” and “9 + 0” arrangements

Cilia

0” arrangements• Coordinated beating propels cells

through their environment• Also used to move substances past the

surface of the cell

Eukaryotic Flagella and Cilia

Figure 3.23

• Fungi, algae, and plants have cell walls but no glycocalyx

• Composed of various polysaccharides– Cellulose found in plant cell walls– Fungal cell walls composed of cellulose, chitin,

Eukaryotic Cell Walls

– Fungal cell walls composed of cellulose, chitin, and/or glucomannan

– Algal cell walls composed of cellulose, agar, carrageenan, silicates, algin, calcium carbonate, or combination of these

What is not present in a eukaryotic cell wall?

• All eukaryotic cells have cell membrane• Fluid mosaic of phospholipids and proteins• Contains steroid lipids to help maintain

fluidity• Controls movement into and out of cell

Eukaryotic Cell Membranes

• Controls movement into and out of cell– Use diffusion, facilitated diffusion, osmosis, and

active transport– Endocytosis

• Phagocytosis if solid substance • Pinocytosis if liquid substance

– Exocytosis enables substances to be exported from cell

Phagocytosis

• Ribosomes• Cytoskeleton

Cytoplasm of Eukaryotes –Nonmembranous Organelles

• Centrioles and Centrosome

Ribosomes

• Eukaryotic cells have two types of ribosomes• 80S

– Composed of 60S and 40S subunits– Membrane-bound Attached to ER– Free In cytoplasm

• 70S– In chloroplasts and mitochondria

• Extensive • Functions

– Provides basic shape – Anchor organelles– Cytoplasmic streaming and movement of

organelles

Cytoskeleton

organelles– Cell contraction– Movement during endocytosis – Amoeboid action (pseudopodia)

• Made up of microtubules, microfilaments, and intermediate filaments

• Centrioles play a role in mitosis, cytokinesis, and in formation of flagella and cilia

• Centrioles composed of “9 + 0” arrangement of microtubules

• Centrosome – region of cytoplasm where

Centrioles and Centrosome

• Centrosome – region of cytoplasm where centrioles are found

• Nucleus• Endoplasmic Reticulum• Golgi Body• Lysosomes, Peroxisomes, Vacuoles, and

Cytoplasm of Eukaryotes –Membranous Organelles

• Lysosomes, Peroxisomes, Vacuoles, and Vesicles

• Mitochondria• Chloroplasts

• Often largest organelle in cell• Contains most of the cell’s DNA• Semi-liquid portion called nucleoplasm• One or more nucleoli

Nucleus

– RNA synthesized

• Chromatin – DNA associated with histones• Double membrane bound

– two phospholipid bilayers – nuclear envelope

• Nuclear envelope contains nuclear pores

Nucleus

• Continuous with the nuclear envelope• Netlike arrangement of hollow tubules• Functions

– Protein modification– As transport system

Endoplasmic Reticulum

– As transport system

• Two forms– Smooth endoplasmic reticulum (SER) – plays

role in lipid synthesis– Rough endoplasmic reticulum (RER) –

ribosomes attached to its outer surface; protein modification

Rough and Smooth Endoplasmic Reticulum

Figure 3.32

Golgi Body

• Receives, processes, and packages large molecules for export from cell

• Protein modification and traffickingtrafficking

• Composed of flattened hollow sacs surrounded by phospholipid bilayer

Lysosomes, Peroxisomes, Vacuoles, and Vesicles

• Vacuoles – store chemicals within cells– Vesicles –

transport chemicals within cellscells

• Lysosomes -contain catabolic enzymes

• Peroxisomes -contain enzymes that degrade poisonous wastes

Mitochondria

• Powerhouse of the cell– Produce most of cell’s

ATP

• Double membrane boundbound

• Interior matrix contains– 70S ribosomes – circular molecule of

DNA

Chloroplasts• Used by algae and

plants for photosynthesis

• Double membrane boundbound

• Contain – 70S ribosomes– DNA

• Simple structure• No nucleus• Small; ~1.0 µm in

diameter• One circular

chromosome, not in a

Prokaryote Eukaryote

• Complex Structure• Nucleus• Larger; 10-100 µm in

diameter• Paired chromosomes, in

nuclear membranechromosome, not in a membrane

• No histones• No membrane bound

organelles• Peptidoglycan cell walls• Binary fission • Comprised of bacteria

and archaea

nuclear membrane• Histones• Organelles• Polysaccharide cell walls• Mitotic spindle• Comprised of algae,

protozoa, fungi, animals, and plants

• Eukaryotes formed from phagocytosis of small aerobic prokaryotes– lost ability to exist independently– Retained portion of DNA, ribosomes, and

cytoplasmic membranes

Endosymbiotic Theory

cytoplasmic membranes– Larger cell became dependent on for aerobic

ATP production– Aerobic prokaryotes evolved into mitochondria– Similar scenario for origin of chloroplasts

• Not universally accepted

Endosymbiotic Theory

Figure 10.2

Prokaryotic membranes