Structure of Prokaryotic & Eukaryotic Cells

Review of Prokaryotic & Eukaryotic Cells

• Nucleus vs nucleoid • DNA : circular vs linear, presence of

histones• Membranous organelles• Cell wall-peptidoglycan• Cell division: binary vs mitosis• Ribosomes: 70S vs 80S• Cytoskeleton

Shape

• Cocci– Diplococci– Streptococci– Tetrads– Sarcinae– Staphylococci

Bacillus

• Coccobacilli

• Diplobacilli

• Streptobacilli

Spiral

• Vibrio-curved rods

• Spirilla-helical & rigid

• Spirochetes-helical & flexible

• Other shapes• Pleomorphic

Glycocalyx

• Glycolipids or glycoproteins

• Surrounds cell

• Capsule or slime layer

• Capsule more organized & attached to wall

• Advantages of capsule

Slime Layer(Biofilm)

• Surrounds cell

• Loosely organized & not attached

• Tangled mass of fibers-dextran

• Attachment to surfaces -S. mutans

• Shields bacteria from immune defense & antibiotics

Glycocalyx -Eukaryotes

• Animal cells have one

• Made of carbohydrates

• No do not have a cell wall

• Surround plasma membrane

• Stabilizes PM

Flagella

• Movement– Spins like propeller– Clockwise or counter clockwise

• Chemotaxis- movement toward or away

Arrangements

• Monotrichous: one at end

• Amphitrichous: both ends

• Lophotrichous: tuft at end or ends

• Peritrichous: around the cell

Structure

• Composition-protein subunits: flagellin (H protein) E. coli H7– Chains twisted together with hollow core– Helical shaped– Filament, hook, basal body– Hook– Basal body:

Flagella

• Basal body

• Classified by flagella protein

Axial Filament

• Spirochetes– Treponema pallidum-syphilis– Borrelia burgdorferi-Lyme disease

• Bundle of fibrials within a sheath

• Corkscrew motion

Movement Eukaryotes

• Flagella & cilia

– 9+2 arrangement of microtubules

– Cilia in Paramecium & respiratory cells

Prokaryote Fimbriae & Pili

• Made of pilin: string of subunits

• Function: attachment

• Few to hundreds• Fimbrae

• Pili-longer & fewer

• Not in eukaryotes

Cell Wall

• Function

• Basis of Gram stain

Composition

• Peptidoglycan– Repeating subunits of disaccharides

• N-acetyl glucosamine (NAG) • N-acetyl muramic acid (NAM)• Linked alternately in rows

– Attached by polypeptides• Tetrapeptide side chains link NAM subunits• Cross bridge of amino acids link tetrapeptides

– Forms lattice

Peptidoglycan

• Confers shape & prevents lysis• Cell growth

– Autolysins break cross linkages in peptidoglycan

– Transpeptidases seal breaks– Penicillin inactivates these enzymes

• Existing cells– Treat with lysozyme-tears, saliva etc.– Destroys linkages between carbohydrates

Gram Positive Cell Wall

• Thick layers: 40-80% of dry wt, up to 30 layers

• Contains teichoic acid– Alcohol and phosphate– Negative charge

– Cell growth-prevents lysis– Antigenic properties

Gram Negative Cell Wall

• Few layers of peptidoglycan- 10%

• Outer membrane: bilayer

• Periplasm

LPS

• Strong negative charge

• Barrier to some antibiotics

• Outer membrane-endotoxin– O polysaccharides– Lipid-lipid A

Gram Stain

• Differential stain dev by Hans Gram 1880s– Classifies bacteria into 2 groups– Based upon cell wall composition– Gram variable stain unevenly

– Gram non reactive do not stain or stain poorly

Comparison

• Gram positives

Gram Negatives

• ETOH disrupts outer layer

• CV-I complex is washed out of thin peptidoglycan layer

• Counterstain

Atypical Cell Walls

• Streptococci

• Mycobacteria

• Mycoplasma– PM unique with sterols protect from lysis

Mycoplasma

• Lack a cell wall so pleomorphic• Classified with gram positives• Smallest genome of any bacteria

• Droplet spread-use regular mask• Why can’t you use penicillin?

     

Cell wall of Eukaryotes

• Simpler than prokaryotes

• Algae & plants

• Fungi

• Yeasts

• Protozoa

• Animals

Plasma Membrane

• Thin, fluid structure inside cell wall-viscous

• Proteins

• Phospholipids-2 layers

Functions of Membrane

• Selective permeability

• Passive transport:

• Active transport:

• Enzymes break down nutrients

• Infoldings

Plasma Membrane of Eukaryotes

• Phospholipids and proteins

• Carbohydrates and sterols-cholesterol

• More rigid than prokaryotic PM

• Endocytosis

• Exocytosis

Cytoplasm of Prokaryotes

• 80% water, thick, solutes

• Increase in osmotic pressure on membrane– Rigid cell wall prevents lysis

• Contains DNA

• Ribosomes

• Inclusion bodies

Cytoplasm of Eukaryotes

• Cytosol-fluid portion

• Cytoskelton– Microfilaments: – Microtubules:

– Intermediate filaments:

• Cytoplasmic streaming

Ribosomes

• 2 subunits of protein and rRNA

• 70s ribosomes

• Polyribosomes-chains

• Protein synthesis

• Eukayotes-80s

Inclusions

• Polysaccharide granules

• Sulfur granules

• Reserve deposits-volutin (phosphates)

Endospores

• Unique to bacteria: Clostridium & Bacillus

• Sporulation-formation of spores

Germination

• Triggered by damage to coat

• Enzymes break down endospore

• Water enters & metabolism begins

• Not a reproductive structure

Nuclear Area of Bacteria

• Single, ds DNA chromosome

• Attached to PM at some point

• Nucleoid area, not a nucleus

• Plasmids

Nucleus

• Largest structure in cell

– Nucleoli

• DNA associated with proteins -histones

Organelles in Eukaryotes

• Unique to eukaryotes

• Membranous structures– Endoplasmic reticulum

• Smooth & rough

– Golgi complex– Lysosomes– Mitochondria– Cloroplasts

ER

• Flattened membranous sacs• Rough ER-ribosomes attached

• Smooth ER- no ribosomes

• Free ribosomes- proteins don’t need processing

Golgi Complex

• Stacks of membranous sacs

• Receive transport vesicles from ER

• Modify molecules to form glycoproteins, glycolipids lipoproteins

• Transported in secretory vesicles to PM or to outside cell

Lysosomes

• Formed from Golgi– Contain digestive enzymes: proteases &

nucleases– Break down old parts of cell– Breaks down pathogens

Mitochondria

• Double membrane

• Generation of ATP

Chloroplasts

• Thylakoids-flattened membranous sacs

• Contain DNA 70s ribosomes

• Stroma thick fluid in center- Calvin cycle

• Generation of ATP & sugars