cell structure combined: introduction to cell structure , domain bacteria, domain archaea, domain eukarya

characteristics of all cells

-cell membrane

-cytoplasm

-ribosomes

-enzymes

-RNA

-DNA

two prokaryote domains

bacteria and archaea

major cell morphologies

-coccus (spherical or ovoid)

-bacillus (rod/cylindrical)

-spirillum (spiral)

diplococci

pairs of cocci

streptococci

chains of cocci

staphylococci

grape-like clusters of cocci

cocci tetrads

4 cocci in a square

sarcinae cocci

cubic configuration of 8 cocci all perpendicular to each other

diplobacilli

pairs of bacilli

streptobacilli

chains of bacilli

palisade bacilli

several parallel cells along a long axis

coccobacilli

very short rods

vibrios

resemble rods, comma shaped

spirilla

rigid helices

spirochetes

flexible helices

mycelium

network of long, filamentous cells

pleomorphic

variable shapes

archaea

unique shapes (branched flat square)

prokaryote size

0.2 um-700um diameter

eukaryote size

10 um-200 um

surface to volume ratio

as volume increases the SA:V ratio decreases

advantages to being small

- higher surface to volume ratio

- nutrients and waste can be transferred into and out of the cell more easily

- higher metabolic rate

- supports faster growth rate, faster evolution

cell membrane functions for all domains

-requirement for all organisms

-separates cytoplasm from environment

-regular transport

-energy metabolism (prokaryotes)

-protein attachment

-receptors

fluid mosaic model of membrane structure

membrane somewhat fluid, somewhat solid (liquid crystal)

basic structure: lipid bilayer with floating proteins

phospolipid bilayer

double layer of phospholipids that have a hydrophilic head and two hydrophobic tails

peripheral proteins

-loosely connected to membrane proteins on cytoplasmic side

integral proteins

-amphipathic

-embedded withing membrane

-project outward or inward

transmembrane proteins

completely cross membrane

membrane strengthening agents

sterols and hopanoids

sterols

-rigid lips that strengthen and stabilize membranes

-all eukaryotes

hopanoids

-structurally similar to sterols

-present in membranes of many Bacteria

membrane fluidity

temperature dependent

too cold: solidification (gelling)- due to vanderwaals forces

too hot: thermal lysis (cell death)

how to maintain correct membrane fluidity

-adjust fatty acid composition

cold: more unsaturated fatty acids which minimize van der Waals forces

hot: more saturated fatty acids which maximize van der Waals forces

-adjust ratio of sterols, hopanoids, or other lipids

transport

how a molecule gets across a membrane

depends on size, shape, charge of molecule

passive transport

transport which does not require cellular energy

simple diffusion

Movement of molecules from high to low concentration

Non polar molecules, water

facilitated diffusion

transport which requires a transport protein

ex: ions and polar molecules

osmosis

diffusion of water across a membrane

active transport

transport which requires the cell to expend energy

always protein mediated

moves molecules against concentration gradient

uniporters

transport one types of molecules in one direction across the membrane

symporters

function as co-transporters of 2 or more molecules in the same direction

antiporters

transport a molecule across the membrane while simultaneously transporting another molecule in the opposite direction

cell net charge

negative

receptor-mediated transport system

ligand binds specific protein receptors on cell surface

-show saturation effect

-highly specific (lock and key)

group translocation

simultaneous transport and chemical modification of transported substance (only prokaryotes)

osmotic lysis

pressure from water entering cell causes a rupture of the cell membrane and death of the cell

tonicity

solute concentration of a solution

isotonic

solute concentration on both sides of membrane are equal

hypertonic

higher solute concentration therefore, lower water concentration

(cells want to be this!!)

hypotonic

means lower solute concentration therefore, higher water concentration

hypertonic environment on the outside of the cell

-solute concentration higher on outside

-water LEAVES cell

-plasmolysis occurs

hypotonic environment on the outside of the cell

-solute concentration lower on outside

-water ENTERS cell & cell swells

-cell wall protects from lysis

water moves towards...

higher solute concentration

plasmolysis

cell shrinks and cell membrane pulls away from wall

cells without cell walls

-genus mycoplasma

-cell membrane is stronger (more sterols)

-stays slightly hypertonic

gram positive

-stain purple

-thick layer of peptidoglycan

gram negative

-stain pink

-thin layer of peptidoglycan and outer membrane

peptidoglycan

the structural polysaccharide in cell walls of bacteria

peptidoglycan structure

-mesh-like

-identical subunits

-strands are composed of structural polysaccharides with amino acids

peptidoglycan subunits

-disaccharide of two alternating modified sugars joined by beta glycosidic bonds

peptidoglycan strands

-helical shape

-crosslinked by covalent bonds

-in gram positive, there is an inter-bridge of additional amino acids

-in gram negative, crosslinks are directly between amino acids

gram positive cell wall

-90% peptidoglycan

-contain teichoic acids

-layer of proteins on surface

-lipoteichoic acid

-mycolic acid

teichoic acids

negatively charged

functions: protection from environment binding to host cell storage of PO4

lipoteichoic acids

anchors wall to membrane

mycolic acids

found in acid fast bacteria ex. mycobacterium

periplasmic space of gram positive bacteria

-lies between cell membrane and cell wall

-smaller than gram negative

-secretes enzymes called exoenzymes

exoenzymes

produced by enzymes in periplasmic space of gram positive bacteria

aid in degradation of large nutrients

gram negative cell walls

-more complex

-5-10% peptidoglycan

-thin layer of peptidoglycan surrounded by an outer membrane

-no teichoic acid

-periplasmic space much larger

lipopolysaccharide (LPS)

3 parts: lipid A, core polysaccharide, O side chain

importance of LPS

-contributes to negative charge

-protection from viruses

-act as endotoxin

periplasmic space of gram negative bacteria

-may constitute 20-40% of cell volume

-many enzymes present in periplasm (hydrolytic enzymes, transport proteins, and other proteins)

glycocalyx

polysaccharide rich material exterior to cell wall which as a capsule and slime layer

glycocalyx functions

-attachment to solid surfaces

-protection

S-layer

-regularly structured layers of protein or glycoprotein that self-assemble

-in gram negative -> adheres to outer membrane

-in gram positive -> associated with peptidoglycan

s-layer functions

-protect from ion and pH fluctuations, osmotic stress, and enzymes

capsule layer

a glycocalyx that is highly organized, tightly attached to cell wall

slime layer

a glycocalyx that is unorganized and loosely attached to the cell wall

bacteria

single-celled organisms that lack a nucleus prokaryotes

bacteria cell size

0.2 um - > 700 um

what are the major cell shapes?

cocci, bacilli, spirillum

external structures beyond the cell envelop

fimbriae, pili, and flagella

functions of external structures

protection, attachment to surfaces, horizontal gene transfer, cell movement

fimbriae

short, thin, hairlike appendages made of protein (up to 1,000 per cell)

-mediate attachment to surfaces

-some are required for motility, DNA uptake

sex pili

similar to fimbriae but longer, thicker, and less numerous (1-10 per cell)

-gene transfer between bacteria

flagella

threadlike locomotor appendages extending outwards from the plasma membrane and cell wall

3 parts: filament, hook, basal body

functions of flagella

-motility and swarming behavior

-attachment to surfaces

patterns of flagella distribution

monotrichous, polar flagellum, amphitrichous, lophotrichous, peritrichous

monotrichous flagella

one flagellum

polar flagellum

flagellum at end of cell

amphitrichous flagella

flagella at both ends of the cell

lophotrichous flagella

cluster of flagella at one or both ends

peritrichous flagella

spread over entire surface

structure/ parts of flagella

filament, hook, basal body

filament

extends from cell surface to the tip

hollow, rigid cylinder composed of flagellin

some bacteria have a sheath

hook

links filament to basal body

made of protein

basal body

series of rings that drive flagellar motor

flagellar, spirochete, twitching, gliding

types of motility

Taxis

directed cell movement in response to stimuli such as chemicals, temperature, light, oxygen, osmotic pressure, and gravity

Chemotaxis

movement toward a chemical attractant (positive) or away from a chemical repellent (negative)

flagellar motility

-flagella rotate like a propeller, reaching speeds up to 1100 revolutions per second

-structure: rotor and stator

-function: proton motive force drives protons through channels, generating torque that powers rotation