PROKARYOTESBY: BECKS

Overview of the chapter

Prokaryotes are microscopic. They have a biomass that is ten times larger than all eukaryotes. Thinkof this; The amount of prokaryotes on ahandful of soil is greater than the numberof people who have ever lived. In thischapter, prokaryotes are classified intotwo domains: Bacteria and Archaea.

Prokaryotes live almost everywhere! Including hot geysers!

Ch 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success.

Cell Surface Structures

One of the most important features of prokaryotes is their cell wall. It maintains shape, provides protection, and prevents the cell from bursting in a hypotonic environment, an environment where the solute concentration is higher on the inside.

Most Prokaryotes lose water and shrink away from their cell wall, which means to plasmolyze, like other walled cells.

Severe water loss activates the reproduction of prokaryotes.

The 3 most common shapes (:

1 m 2 m 5 m (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

Eukaryotes Prokaryotes

•Have chromosomes located in a membrane-enclosed organelle called the nucleus.•Has membrane bound organelles in the cytoplasm.•Cell walls made of cellulose or chitin.

•The DNA is concentrated in a region called the nucleoid, but there is no membrane that separates it from the rest of the cell.•Lacks organelles in cytoplasm.•Cell walls made of peptidoglycan.

*Peptidoglycan- a network of modified-sugar polymers cross-linked by short polypeptides

The Gram StainUsing a technique called the Gram stain,

developed by Hans Christian Gram, scientists can classify many bacterial species into two groups based on their differences in cell wall composition.

Gram-Positive bacteria have simple walls and a large amount of peptidoglycan.

Gram-Negative bacteria have less peptidoglycan and are more complex and contain lipopolysaccharides, which are carbohydrates bonded to lipids.

(a) Gram-positive. Gram-positive bacteria have

a cell wall with a large amount of peptidoglycan

that traps the violet dye in the cytoplasm. The

alcohol rinse does not remove the violet dye,

which masks the added red dye.

(b) Gram-negative. Gram-negative bacteria have less

peptidoglycan, and it is located in a layer between the

plasma membrane and an outer membrane. The

violet dye is easily rinsed from the cytoplasm, and the

cell appears pink or red after the red dye is added.

Peptidoglycan

layer Cell wall

Plasma membrane

Protein

Gram-

positive

bacteria

20 m

Outer

membrane

Peptidoglycan

layer

Plasma membrane

Cell wall

Lipopolysaccharide

Protein

Gram-

negative

bacteria

Applications

Gram Staining is a valuable tool in medicine.

Among disease causing bacteria, gram-negative bacteria are often more threatening than gram-positive species.

Some drugs destroy species of bacteria without affecting human cells.

Capsule, Fimbriae, and PiliThe cell wall of most prokaryotes

is covered by a capsule, a sticky layer of polysaccharide or protein.

Capsules shield the cell from attacks of the hosts immune system, and they enable prokaryotes to stick to their substrate or to other individuals in a colony.

• Some prokaryotes stick to their substrate or to another because of hair like appendages called fimbrae and pili.

200 nm

Capsule

200 nm

Fimbriae

MotilityAbout half of all prokaryotes are

capable of directional movement.Some species can move at speeds

up to 50 times their body length per second!

VROOM!

•Flagella is the main structure that helps the prokaryotes to move.•In a heterogeneous environment, many prokaryotes exhibit taxis, movement toward or away from a stimulus. (site that influences activity)

Flagellum

Filament

Hook Cell wall

Plasma membrane

Basal apparatus

50 nm

Internal and Genomic organizationProkaryotic cells are simpler than

eukaryotic cells. In their internal structure and genomic organization.

Prokaryotic cells lack complex compartmentalization. ( the ability of a cell to make cellular compartments such as membranes)

The typical prokaryotic genome is a ring of DNA that isn’t surrounded by a membrane.

There is a nucleoid region which is lighter than the surrounding cytoplasm.

Some species also have smaller rings of DNA called plasmids.

Reproduction and AdaptationProkaryotes reproduce quickly by binary

fission. Many form endospores, which can remain

viable in harsh conditions for centuries.Rapid reproduction and horizontal gene

transfer facilitate the evolution of prokaryotes in changing environments.

Endospore

0.3 m

Concept 27.2: a great diversity of nutritional and metabolic adaptations have evolved in prokaryotes.

Examples of all four models of nutrition-photoautotrophy,

chemoautotrophy, photoheterotrophy, and

chemoheterotrophy- are all found among prokaryotes!

Metabolic Relationships to Oxygen

Obligate aerobes require O2 , Obligate anaerobes are poisoned

by O2 ,

Faculative anaerobes can survive with or without O2

Anaerobic respiration-substances other than O2, accept electrons at the “downhill” end of electron transport chains.

Nitrogen Metabolism

Prokaryotes can metabolize a large variety of nitrogenous compounds.

Some can turn atmospheric nitrogen into ammonia in a process called nitrogen fixation, which is the assimilation or “fixing” of nitrogen by prokaryotes.

Metabolic cooperationCooperation between prokaryotes

allows them to use environmental resources they could not use as individual cells.

Prokaryotes depend on the metabolic activities of other prokaryotes.

In Anabaena, photosynthetic cells and nitrogen fixing cells exchange their metabolic products.

Biofilms are surface-coating colonies, which may include different species.

A Biofilm

1

m

Molecular SystematicsLeading to a phylogenetic

classification of prokaryotes.Allows systematists to identify

new clades, or a group of organisms.

Concept 27.3 Molecular systematics is illuminating prokaryotic phylogeny

Domain Bacteria Domain

Archaea

Domain

Eukarya

A

lph

a

B

eta

G

am

ma

Ep

silo

n

D

elt

a

Proteobacteria

C

hl a

myd

ias

S

pir

och

ete

s

C

yan

ob

act

eri

a

G

ram

-posi

tive

b

act

eri

a

Kora

rch

aeote

s

Eu

ryarc

haeote

s

C

ren

arc

haeote

s

N

an

oarc

haeote

s

Eu

kary

ote

s

Universal ancestor

BacteriaWhen we think of bacteria we

think of it as only being harmful and disease causing.

They cause strep throat and other diseases.

Some “beneficial” species are used to make Swiss cheese.

Bad Bacteria Good Bacteria

ArchaeaShare some traits with bacteria.Some are different though…Extremophiles- love extreme

conditionsExtreme thermophiles- thrive in hot

environmentsExtreme halophiles- live in highly

saline (salty) environments.Methanogens obtain energy by using

carbon dioxide to oxidize hydrogen, and releases methane as waste.

ProteobacteriaA clade, or group of Gram-negative

bacteria.It includes photoautotrophs,

chemoautotrophs, and heterotrophs.

There are 5 subgroups : alpha, beta, gamma, delta, and epsilon.

They each do their own things, such as producing nitrate, or sulfur as wastes.

Rhizobium (arrows) inside a

root cell of a legume (TEM)

Nitrosomonas (colorized TEM)

Chromatium; the small

globules are sulfur wastes (LM)

Fruiting bodies of

Chondromyces crocatus,

a myxobacterium (SEM)

Bdellovibrio bacteriophorus

Attacking a larger bacterium

(colorized TEM)

Helicobacter pylori (colorized TEM).

Chlamydias

Parasites that can only survive in animal cells.

Lack peptidoglycan.

Peptidoglycan- a network of modified-sugar polymers cross-linked by short polypeptides

Spirochetes•Like living flagellum•Some are free-living, but some are parasites.•Cause syphilis

Gram positive bacteriaForm chains of cellsCause tuberculosis and leprosyLack cell walls.They are very tiny cells

CyanobacteriaThe only prokaryotes that use

photosynthesis.Abundant in water or wherever

there is food, like freshwater.They also have cells that do

nitrogen fixation, the process that converts nitrogen into other molecules

If humans disappeared tomorrow, life on Earth for other species would go on. Prokaryotes are so important on Earth that if they disappeared, any other life surviving is impossible.

Concept 27.4 Prokaryotes play crucial roles in the biospere

Chemical Recycling

Ecosystems depend on recycling of chemical elements between the living and nonliving parts of the environment, and prokaryotes have a major job in this process.

Example: Chemoheterotrophic prokaryotes function as decomposers, they break down dead corpses, waste products, and dead vegetation.

Symbiotic RelationshipsSymbosis- an ecological relationship between

organisms of different species that live together.Host- larger organismSymbiont- smaller organismMutualism- both symbiotic organisms benefit.Parasitism- one organism, the parasite, benefits

from the host.

The best known prokaryotes are those that cause diseases in humans. But, these only are a small part of prokaryotes. Some have good interactions with humans.

Concept 27.5 Prokaryotes have both harmful and beneficial impacts on humans.

Pathogenic prokaryotes

Cause half of all human diseases!Like lyme disease and

tuberculosisExotoxins are proteins secreted

by prokaryotes.Endotoxins are

lipopolysaccharide components of the outer membrane of gram-negative bacteria.

5 µm

Prokaryotes in research and technologyExperiments using prokaryotes

have led to important advances in DNA technology

Prokaryotes are the principal agents in bioremediation the use of organisms to remove pollutants from the environment

Prokaryotes also…Are good in miningMaking new medicines and

antibioticsSynthesizing vitaminsGenetic engineering!

The End