Chapter 4: Functional Anatomy of Prokaryotic and Eukaryotic Cells

prokaryote

one circular chromosome, not in a membrane, no histones, no organelles, divides by binary fission, examples include bacteria & archaea

eukaryote

paired chromosomes in nuclear membrane, histones, organelles, polysaccharide cell walls when present, divides by mitosis/meiosis

most bacteria are

monomorphic (single shape)

pleomorphic

many shapes

bacillus

rod shaped bacteria

coccus

spherical shaped bacteria

bacterial shapes

bacillus, coccus, spiral, star, rectangular, and can be long filaments

pairs

diplococci, diplobacilli

clusters

staphylococci

chains/chainlike patterns

streptococci, streptobacilli

divide in planes of 2 and remain in groups of 4

tetrad

divide in planes of 3 and remain in cubelike groups of eight

sarcinae

arrangements of bacteria

single (one), diplo (pair), tetrad (four, square), sarcina (eight, cube), staphylo arrangement (cluster), and strepto- arrangement (sheets, chains)

the plasma membrane

a phospholipid bilayer that encloses the cytoplasm, peripheral proteins, integral and transmembrane proteins; this regulates what can enter and exit the cell

size range for the diameter of most bacteria

0.2µm to 2.0µm

peripheral proteins

proteins on the membrane surface

integral proteins

proteins that are permanently attached to a biological membrane; play critical roles in movement of molecules across them and the transduction of energy and signals

transmembrane proteins

often function as channels or receptors, allowing specific substances to pass across the membrane

integral and transmembrane proteins

penetrate the membrane

fluid mosaic model

a way of describing the dynamic arrangement of proteins and phospholipids in a cell membrane, where components can move laterally within the layer

components of the fluid mosaic model

membrane is as viscous as olive oil, proteins move freely for various functions, phospholipids rotate and move laterally, self-sealing

phospholipids

consists of a hydrophilic head and two hydrophobic tails (one saturated and unsaturated), forming a bilayer in cell membranes

selective permeability

a characteristic of the plasma membrane; it allows the passage of certain molecules while restricting others

functions of the plasma membrane

selective permeability, contain enzymes for ATP production (ATPase), some membranes have chromatophores

causes of leakage of cell contents

damage to the membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics

chromatophores

present in some membranes; photosynthetic pigments on foldings

movement processes across the cell membrane

active and passive

passive process

substances move from high to low concentration; no energy expended

active processes

substances move from low to high concentration; energy expended

examples of passive processes

simple diffusion, facilitated diffusion, osmosis, osmotic pressure, isotonic solution, hypotonic solution, hypertonic solution

simple diffusion

movement of a solute from an area of high concentration to low concentration; continues until molecules reach equilibrium

facilitated diffusion

solute combines with a transporter protein in the membrane; transports ions and larger molecules across a membranes with the concentration gradient

osmosis

the movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration; happens through lipid layer & uses aquaporins (water channels) in the process

osmotic pressure

the pressure needed to stop the movement of water across the membrane

isotonic solution

solute concentrations equal inside and outside of cell; water at equilibrium

hypotonic solution

solute concentration is lower outside than inside the cell; water moves into the cell and will eventually cause it to burst

hypertonic solution

solute concentration is higher outside of cell than inside; water moves out of the cell eventually causing it to shrink

examples of active processes

active transport & group translocation

active transport

requires a transporter protein and ATP; goes against the gradient

group translocation

requires a transporter protein and phosphoenolpyruvic acid (PEP); substance is altered as it crosses the membrane

the cell wall

prevents osmotic lysis and protects the cell membrane, made of peptidoglycan (in bacteria), can contribute to pathogenicity

osmotic lysis

the bursting or rupturing of cell membrane due to osmotic movement of water into the cell when the cell is in a hypotonic environment

peptidoglycan

polymer of a repeating disaccharide in rows: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM); rows are linked by polypeptides (usually 4 × 6)

gram-postive cell walls

contains a thick, multilayered peptidoglycan layer, teichoic acids, and lacks an outermembrane

teichoic acids

a polysaccharide found in gram-positive cell walls; consists of lipoteichoic acid and wall teichooc acid; carries a negative charge and regulates the movement of cations

lipoteichoic acid

links cell wall to plasma membrane; found in gram-postive cell walls

wall teichoic acid

covalently bound to/links the peptidoglycan; found in gram-postive cell walls

provides antigenic specificity

polysaccharides and terichoic acids

gram-negative cell walls

has periplasm between the outer membrane and the plasma membrane contains peptidoglycan; outer membrane made of polysaccharides, lipoproteins, and phospholipids; protects from phagocytes and antibiotics; made of lipopolysaccharide (LPS); contains porins

lipopolysaccharide (LPS)

large, complex molecule that contains lipids and carbohydrates and consists of three components: (1) lipid A, (2) a core polysaccharide, and (3) and O polysaccharide

lipid A

the lipid portion of the LPS and is embedded in the top layer of the outer membrane; is also an endotoxin

core polysaccharide

is attached to lipid A and contains unusual sugars; role is structural, as it provides stability

O polysaccharide

extends outward from the core polysaccharide and is composed of sugar molecules; functions as an antigen

porins

proteins that form channels through membranes; permits the passage of molecules

gram-postive cell wall characteristics

2 rings in basal body of flagella, produce exotoxins, high susceptibility to penicillin, & are disrupted by lysozymes

gram-negative cell wall characteristics

4 rings in basal body of flagella, produce endotoxins and exotoxins, low susceptibility to penicillin, & have an outer membrane

atypical cell wall examples

acid-fast cell walls, mycoplasmas, archaea

acid-fast cell walls

like gram-postitive cell walls, have waxy lipid (mycolic acid) bound to pepitdoglycan; found in Mycobacterium & Norcardia; can be stained with carbolfuchsin

mycoplasma

bacteria with no cell wall; sterols in plasma membrane

archaea

lack cell walls or have walls of pseudomurein (lack NAM and D-amino acids)

damage to the cell wall can be caused by

lysozymes or certain antibiotics (like penicillin)

lysozyme

hydrolyzes bonds in pepitidoglycan in gram-positive bacteria, leading to cell lysis

penicillin

an antibiotic that inhibits peptide bridges in peptidoglycan

protoplast

a wall-less gram-positive cell

spheroplast

a well-less gram-negative cell

protoplasts and spheroplasts

are susceptible to osmotic lysis

L forms

are wall-less cells that swell into irregular shapes

glycocalyx

the general term used for substances that surround cells, it is a viscous (sticky), gelatinous polymer that is external to the cell wall and composed of polysaccharide, polypeptide, or both; many prokaryotes secrete this on their surface

types of glycocalyx

capsule & slime layer

capsule

neatly organized and firmly attached to the cell wall

slime layer

unorganized and loosely attached to the cell wall

capsules prevent

phagocytosis or facilitate adherence

extracellular polymeric substance (EPS)

a glycocalyx that helps cells in a biofilm attach to their target environment and to each other

flagella

filamentous appendages external of the cell, propel bacteria, & made of protein flagellin

3 parts of flagella

filament, hook, basal body

filament

long, outermost region of flagella

hook

attaches to the filament

basal body

consists of rod and pairs of rings; anchors flagellum to the cell wall and membrane

arrangements of bacterial flagella

peritrichous or polar (includes monotrichous, lophotrichous, & amphitrichous)

peritrichous

distributed over the entire cell

monotrichous & polar

a single flagellum at one pole

lophotrichous & polar

a tuft of flagella coming from one pole; multiple flagella arising from the same point in the cell

amphitrichous & polar

flagella at both poles of the cell

flagella allows bacteria

to move toward or away from stimuli (taxis); examples include chemotaxis, phototaxis

flagella rotations

they “run” counterclockwise or “tumble” clockwise

flagella proteins

are H antigens and distinguish among serovars (e.g., Escherichia coli O157:H7)

motility

the ability to move

fimbriae

hairlike appendages that allow for attachment to surfaces

pili

involved in motility (gliding & twitching)

conjugation pili

involved in DNA transfer from one cell to another

axial filaments or endoflagella

found in spirochetes, anchored at one end of a cell where the rotation causes the cell to move like a corkscrew

cytplasm

the substance inside the plasma membrane; 80% water plus proteins, carbohydrates, lipids, & ions; contains cytoskeleton

the nucleoid

region in a prokaryotic cell that contains genetic information

bacterial chromosome

circular thread of DNA that contains the cell’s genetic information

plasmids

extrachromosomal genetic elements carry non-crucial genes (e.g., antibiotic resistance, production of toxins)

ribosomes

sites of protein synthesis; made of protein and ribosomal RNA

70S (prokaryotic) ribosomal unit consists of

50S & 30S subunits

80S (eukaryotic) ribosomal unit consists of

60S & 40S subunits

average length of bacterial cells

1-10 μm

average size of eukaryotes

10-100 μm