Ch. 3 Cell structure and function

Prokaryotic cells

small ~ 1 micrometer in diameter

bacteria and archaea

-lack a nucleus

have cell wall

lack a nucleus

free floating ribosomes

circular chromosome

morphology

coccus = round

bascillus = rod

strepto- = chain arrangement

staph- = cluster arrangement

External structures of prokaryotic cells: Glycocalyces

-gelatinous, sticky subtances surrounding the cell

-protection from dyring

2 types:

1. Capsules: composed of polysaccharides, polypeptides or both, firmly attached to surface of bacterium, may prevent bacteria from being recognized and destroyed by host

2. Slime layer: loosely attached to cell, water soluble, sticky layer allows prokaryotes to attach to surfaces

External structures of prokaryotic cells: Flagella

responsible for movement— like propeller

made up of flagellin protein

have long structures that extend beyond cell surface

are NOT present on all prokaryotes

structure= filament, hook, and basal body

Monotrichous, amphitrichous, lophotrichous, perticichous

Gram positive vs gram negative flagella

gram positive: 2 rings attached— one attached to plasma membrane and one embedded in thick peptidoglycan wall

gram negative: has 4 rings — across outer membrane, peptidoglycan layer, the periplasmic layer, and plasma membrane

Flagella function

propels bacterium through environment

bacteria move in response to stimuli

Runs (counterclockwise rotation) = forward motion; happens more frequently when closer to target cell

Tumbles (clockwise rotation)= re-orients cells to get closer to target ; happens more frequently when further away from target cell

Spirochetes— axial filaments

internal flagella found only in spirochetes

extends end to end of bacterium between the outer membrane and cell membran

movement= rotation

important human pathogens bc they penetrate tissues

external structures of prokaryotic cells— Fimbriae

NOT flagellum

sticky, bristle-like projections

used for attachment (surfaces, cells)

shorter than flagella

hundreds per cell

serve an important function in biofilms

biofilms “slime matters”

organized layered systems of bacteria and other microbes attached to a surface

2/3 infections are biofilsm

plaque formation is a type of biofilm

have different antibiotic sensitivies

external structures of prokarytic cells— pilli

composed of pilin protein

known as conjuntion pili : donor —> recipient using pilin = transfer of genetic material

longer than fimbriae/ shorter than flagella typically only 1-2 per cell

mediate conjucation: important in the transfer of DNA between bacterial cells

External factors in prokaryotic cells— overview

Glycocalyces: capsules and slime layer

Flagella

Fimbriae

Pili

prokaryotic cell walls

provide structure and shape

bacteria and archaea have different cell wall chemistry

protect from osmotic forces

target for many antibiotics

prokaryotic cell wall— bacterial

composed of peptidoglycan

alternation linked NAG and NAM

NAG and NAM attached to other chains by tetrapeptide crossbridges

gram positive bacterial cell walls

structurally simple; contain thick layer of peptidoglycan

-peptidoglycan layer is anchored into cell membrane by teichoic acid

Gram negative bacterial cell wall

more complex; contain thin layer of peptidoglycan and outer membrane containing lipopolysaccharides (LPS)

peptidoglycan is sandwiched between inner membrane and outer membrane

prokaryotic cell walls

a few bacteria lack cell walls

often mistaken for viruses due to small size and lack of cell wall

Ex: Mycoplasma , infections by mycoplasma cannot be treated by antibiotics bc they lack peptidoglycan cell wall which is what antibiotics target

archaeal cell walls

do not have peptidoglycan

contains variety of specialized polysaccharides and proteins — psuedopeptidoglycan

Prokaryotic cytoplasmic membranes- structure

phospholipid bilayer—> fluid mosaic; composed of lipids and associated proteins

approximately ½ composed of proteins

prokaryotic cytoplasmic membranes— function

energy storage

harvest light energy in photosynthetic prokaryotes

Control movement of molecules in and out of cell

-selectively permeable

-passive or active processes

-maintain concentration and electrical gradient

membrane transport mechanisms

diffusion : natural movement of molecules from high —> low; small nonpolar molecules

facilitated diffusion: molecules than can cross easily but use pores or protein channels

osmosis: diffusion of water across membrane

• isotonic solutions

• hypertonic solutions

• hypotonic solutions

osmosis regulation in cells without a wall

Isotonic: cells are at equilibrium w/ outside fluids: molecules coming in= molecules going out

Hypertonic solution: more molecules outside than internally; movement of water = out of the cell to try and dilute the excess molecules on the outside

caused cell to shrivel = crenation

Hypotonic solution: more molecules on the inside of cell so water moves into cell to try and dilute the molecules

causes cell to swell and burst= lysis

osmosis regulation in cells with a cell wall

isotonic solution: at equilibrium molecules going in= molecules going out

hypertonic solution: more molecules on outside of cell so water moves out of cell

causes cell to shrink/ shrivel= plasmolysis

hypotonic solution: more molecules on inside of solution so water moves in

causes cell to swell but it won’t burst bc of the cell wall

active transport

low —> high concentration or really large molecules

utilize permease proteins and expends cellular ATP

cytoplasm of prokaryotes

cytosol= liquid portion of cytoplasm

inclusions= reserve deposits of storage/chemcials

nucleoid region: space when chromosome is anchored onto— condensed area of DNA within prok. cell

Ribosomes: sites of protein synthesis; simultaneous transcription and translation

70s complete ribosome belongs to prokaryotic cell

cytoplasm of prokaryotes

endospores— unique structures produced by some bacteria

defense strategy against unfavorable conditions — called sporulation when this process occurs