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Lecture 3Prokaryotes & Eukaryotes

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Components of ALL cells

Plasma membrane = lipid bilayer that forms a physical barrier to all cells

Cytoplasm = the semisolid components within the cell (Cytosol = Fluid portion)

Chromosomes = DNA structure containing genes

Ribosomes = tiny structures of RNA/protein that synthesize new proteins using instructions from

the genes

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Prokaryotes v. Eukaryotes nucleoid versus a nucleus

Cell size - Prokaryotic cells are smaller (Most 0.2 - 5 µm) 1000 X magnification - Eukaryotic cells are larger (Most 10 - 100 µm) 200 to 500 X magnification

Membrane-bound organelles - Almost none in prokaryotes - Eukaryotic cells have many organelles of specialized form and function

- Complex cytoskeleton composed of various types of filaments

- Large ribosomes

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Distinguishing Features of Prokaryotes

• Nucleoid• No histones

• No numerous organelles• Cell walls

• Peptidoglycan• Binary fission• Pili or fimbriae• Single Circular Chromosome

• Some exceptions• Plasmids

• Smaller usually circular pieces of DNA

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The Prokaryotic Cell Wall

Many Types of Bacterial Cell Wallsbut Two Main Types…

1. Gram Positive

2. Gram Negative

Both contain peptidoglycan but differ on amount

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Hans Christian Gram (1853-1938)

Hans Christian Gram was a Danish doctor studying in Berlin who studied lung tissues of pneumonia victims. He noticed that different bacteria behaved differently when stained with a cationic dye and classified them as Gram positive (stained) or Gram negative (didn’t stain).

7Fig. 4.p097

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Gram Stain Slide Gram + have a thick layer of peptidoglycan

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Peptidoglycan• Macromolecule composed of a

repeating framework of long chains cross-linked by short peptide fragments– Unique to bacteria– Composed of 2 sugars: NAG &

NAM– Sugars alternate in the backbone– Rows linked by polypeptides

• Provides strong, flexible support to keep bacteria from bursting or collapsing because of changes in osmotic pressure

N-acetylglucosamine(NAG)

N-acetylmuramic acid(NAM)

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Be able to identify all the parts of a Gram + & - cell wall for the next exam.

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Fig. 4.16

Teichoic acids are found only in Gram-positive cell walls. They are negatively charged and their function is unknown.

Lipopolysaccharide and outer membrane are only found in Gram-negative cell walls.

Gram-positive versus Gram-negative Cell Walls

Thick – 20-80 nm Thin – 8-11 nm

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Eukaryotic Cell Wall• Many eukaryotes have a cell

wall composed of a carbohydrate

• Cell wall of algae & plants is made of cellulose• A carbohydrate chain

• Cell wall of fungi is made of chitin• A carbohydrate chain

• Cell wall of yeasts is made of glucan and mannan• A carbohydrate chain

• Animal cells have no cell wall • Elaborate extracellular matrices

• Collagen & glycoproteins

• No eukaryotic cell has

peptidoglycan in their cell wall

• Peptidoglycan is unique to bacteria

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Plant Cell Wall

Cellulose

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Fungal cellIllustration shows relationship between the cell membrane and cell wall.Glycocalyx is the outermost section.

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All Cells have a Membrane

Plasma membrane functions as a selective barrier

O2 & nutrients must enter the cell

Waste products must exit the cell

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• Two layers of phospholipids

• Main component of cell membranes

• Membrane has fluid properties

• Most phospholipids and some

proteins can drift through

membrane

– It’s FLUID & not static

Lipid Bilayer

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Fig. 2.18

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Fluid Mosaic Model• Membrane is a mosaic of

– Phospholipids– Glycolipids Carbohydrates– Sterols

• Eukaryotes

– Proteins

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Cell Membrane Pro v. Euk• Prokaryotes

– Lipid bilayer– Selectively permeable– Allows secretion– Site for metabolic rxns

• Respiration• Photosynthesis

– Nutrient processing– Synthesis of proteins

& other molecules

• Eukaryotes– Lipid bilayer– Selectively permeable – Endocytosis– Exocytosis– Sterols

• Cholesterol• Reinforces cell wall

– All organelles have a membrane very similar to the cell membrane

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• Cell membranes of both Prokaryotes and Eukaryotes perform • Diffusion, osmosis & active transport

• Endocytosis is unique to Eukaryotes

• Phagocytosis

• Uses pseudopods - surround and engulf

• Pinocytosis

• Cell drinking

• Plasma membrane folds in on itself

• Often times receptor mediated

• Exocytosis

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Cell Membranes Show Selective Permeability

O2, CO2, and other small, nonpolarmolecules; some H2O molecules

Glucose and other large, polar, water-soluble molecules, H+, Na+, K+, Ca++, Cl–, H2O

DiffusionOther Mechanisms

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Plasma Membrane• Passive Transport

– Diffusion

• Active Transport– Requires energy as ATP (adenosine triphosphate)

• Cell membrane proteins carry out many tasks– Highly specialized proteins

• Enzymes• Recognition and signaling• Energy Reactions (Prokaryotes)

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Osmosis • Diffusion of water molecules across a selectively

permeable membrane

water molecules protein molecules

semipermeable membranebetween two compartments

• Direction of net flow is determined by water concentration gradient

• Side with the most solute molecules has the lowest water concentration

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Biological Relevance of Osmosis

Cells can be in one of 3 conditions

Isotonic - solutes balanced

Hypotonic - more solute inside cell

Hypertonic - more solute outside cell

Good Situation!

Cell lysis = death Plasmolysis = death

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Animal Cell

[H2O] is greaterin the cell thanoutside

[H2O] is greateroutside the cellthan inside

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Plant CellHypertonic Isotonic Hypotonic

[H2O] is greaterin the cell thanoutside

[H2O] is greateroutside the cellthan inside

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Flagella & Cillia

Prokaryotic & Eukaryotic flagella are not similar in size or structure

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Prokaryotic Flagella• Long filamentous projections used to propel bacteria – 18-20 nm• Several types of flagella arrangements

Monotrichous – One flagellum usually at one pole (Polar)

Amphitrichous - tufts of flagella at both poles

Lophotrichous - two or more flagella at one pole

Petritrichous - flagella distributed over entire surface

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Parts of the Flagellum• Filament - main body of flagella, made of flagellin

• Hook - attaches flagella to basal body

• Basal body - attaches flagella to cell

• Movement is accomplished by rotating basal body

• ATP

• Results in rotation of filament

• Smooth running or tumbling

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Direction of Flagellar Rotation Important for Motility

• Counterclockwise rotation results in movement

• Clockwise results in tumbling

• Responds to chemo and phototaxis possible

• Attractants induce “running”

• Repellants induce “tumbling”

•This model is for Escherichia coli

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Axial Filaments• Spirochetes

• Endoflagella

• Bundle of fibrils

• Run length of organism

• Drives spirochete forward in a spiral motion

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• Flagella - long (~40 um), few• 10X larger (diameter) than Pro

flagella (~180-200 nm in width)

• Cilia – short (10 um long), many • Oars• Ciliated protozoa & animal cells

• Both used for motility

• Both have 9+2 microtubule structure• Hollow tubes that slide past one

another (made up of tubulin)

• Waves and whips• Doesn't rotate - different from

bacterial flagella• Pull & push

Eukaryotic Flagella and Cilia

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Motor ProteinDynein

ATP

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Prokaryotic Genome SizeBacteria Size (Mbp)Escherichia coli 4.64Bacillus subtilis 4.20Streptococcus pyrogenes 1.85Mycobacterium genitalium 0.58

Archaea Size (Mbp)Methanococcus jannaschii 1.66Sulfolobus solfactaricus 2.25Pyrococcus furiosus 1.75

Genome consists of usually one circular chromosome and plasmids (if present)

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Eukaryotic Genome SizeOrganism MbpHomo sapiens 3000Drosophilia melanogaster 165Plasmodium falciparum 23Saccharomyces cerevisiae 12.07

Eukaryotes also have Mitochondrial DNAChloroplast DNA

Genome usually consists of a number of linear chromosomes

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Glycocalyx, Capsule & SlimeGlycocalyxOutermost layer of cell that come into contact with environment

This term is used for both Eukaryotes and ProkaryotesSticky carbohydrates attached to proteins

Important in protection & adhesion

CapsuleRepeating units of polysaccharide, protein or both (a polymer)Adheres tightly, thick & gummyMostly a Prokaryotic term – interchangeable with glycocalyx

Slime LayerPolysaccharide, protein or both that is easily washed offMostly a Prokaryotic term

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Pili & Fibriae• Prok surface appendages

– Pilus is longer• Gram negative bacteria• Conjugation

– Fibria is shorter• Bristlelike• Stick to surfaces• Colonize host tissue

• Euk do not produce these structures

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Ribosomes – RNA and Protein

Prok Euk

All ribosomes are made up of two subunits

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• Prok Ribosomes• Smaller

– 70S• 50S & 30S

• Free ribosomes– Located in the cytosol

• Euk Ribosomes• Larger

– 80S• 60S & 40S

• Free ribosomes– Located suspended in the cytosol – Synthesize proteins that function

within the cytosol

• Bound ribosomes – Are attached to the outside of the

endoplasmic reticulum– Synthesize proteins that are

included into membranes or exported from the cell

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Organelles

• Membrane-bounded functional units• Compartmentalized tasks instead of a mixture• Allows for much more variety of functionality• Present in Euk• Absent in Prok

• Prok conduct the similar activities at the cell membrane

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A View of the Eukaryotic Cell

Much more complex - many levels of compartmentalization

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The Nucleus• Largest organelle - contains DNA

• Enclosed by double layered lipid envelope

• Pores allow transport of various cytoplasmic substances

• Contain nucleoli - sites of rRNA synthesis

• DNA organized by histones

• Further organized into chromatin - thread like

• Further condenses to chromosomes for replication

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The Endoplasmic Reticulum

• Extensive network of flattened cisterns continuous with the nuclear envelope

• Rough ER - studded with ribosomes

• Protein entry point

• Modifications made, lipids and carbohydrates attached

• Smooth ER - no ribosomes

• More enzymatic diversity

• Synthesize lipids, oils, phospholipids, steroids

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Be able to identify all structures listed in this illustration

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The Golgi Complex

• Receives all proteins transported from RER

• Mail station of the cell - all proteins sorted for transport

• Composed of cisterns - flattened membranous stacks• Many post-translational modifications made• Determines fate of protein

• Packaged into secretory vesicle

• Can be packaged into transport vesicle (transfer between stacks, transfer to storage vesicles)

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Lysosomes• Single membrane enclosed vesicles

• Contain many digestive enzymes

• Play important role in immune response

• White blood cells engulf bacteria• Phagosome fuses with lysosome• Digestive enzymes kill bacteria

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Central Vacuoles• Found in many mature plant cells

• Can occupy up to 90% of plant cell cytoplasm• Surrounded by a tonoplast that can• Selectably transport solutes • Functions

• Stockpiling proteins or inorganic ions• Storing pigments• Storing defensive compounds against herbivores

• Increase the surface to volume ratio for the whole

cell

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Mitochondria• Generates ATP• Double membrane - structure similar to plasma membrane• Inner membrane - complex folds (cristae), large surface area• Center is matrix

• Reactions occur on cristae - ATP generation

• Have own ribosomes

• Have some DNA

•Divide by binary fission

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Chloroplasts• Found in algae and green plants

• Membrane enclosed structure• Contains chlorophyll• Contains other enzymes required for photosynthesis

• Chlorophyll contained in flattened sacs - thylakoids

• Stacks of thylakoids make grana

• Have DNA

• Have ribosomes

• Divide by binary fission

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Peroxisomes - Degrade hydrogen peroxide (H2O2)

- Unavoidable by-product of oxygen respiration- Peroxisomes convert H2O2 to water

- Some break down fatty acids to smaller molecules that are transported to mitochondria for fuel

- Others detoxify alcohol and harmful compounds

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Cytoskeleton• Complex in Eukaryotes • Various-sized thin protein

“microfilaments” and microtubules

• Maintain cell shape• Used for cellular movement

– Cytoplasmic streaming– Pseuodpodia

• Support motor proteins– Move molecules in & out of the cell

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Cytoplasm• Everything inside plasma membrane and

outside nucleus• Fluid portion termed cytosol• Packed with enzymes, structural

proteins, ribosomes, tRNA, mRNA, DNA, pigments• Eukaryotes show cytoplasmic streaming• Prokaryotes do not show streaming

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Cell Divsion

• Eukaryotes undergo mitosis – consists of several steps involving a number of specific structures… is complex because a number of chromosomes must divide and thus be separated

• Prokaryotes do not… one circular chromosome… binary fission or “budding”

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Centrioles

• Near nucleus

• Organizing center for mitotic organizing apparatus

• 9 + 0 array organization

• Produces microtubules that separate chromosomes & chromatids

• Starting material for flagella & cilia

• Found in almost all Eukaryotes, never in prokaryotes