Biol 212- Campbell Chap. 27: Prokaryotes

Front 1

characteristic of prokaryotes:

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- small (1-5 micrometer diameters)

- many shapes:
---> spheres (cocci)
---> rods (bacilli)
---> sprials... etc.

- cell wall

Front 2

What is the most important feature of prokaryotic cell?

Back 2

CELL WALL
- maintains cell shape

- provides physical protection

- prevents cell from bursting in a hypotonic environment.

Front 3

what do cell walls of prokaryotes contain?

Back 3

peptidoglycan

Front 4

define peptidoglycan:

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a network of modified sugar polymers crosslinked by short polypeptides (enclosed the entire bacterium and anchors other molecules that extend from its surface)

Front 5

What happens to prokaryotes in a hypertonic environment?

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most prokaryotes lose water and shrink away from their wall (plasmolyze), like other walled cells. Severe water loss inhibits the reproduction of prokaryotes, which explains why salt can be used to preserve certain foods, such as pork and fish.

Front 6

Gram Stain:

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develped by the 19th cent. danish physician Hans Christian Gram

- gram-positive:
bacteria have simpler walls with a relatively large amount of peptidoglycan

- gram-negative:
bacteria have less peptidoglycan and are structurally more complex with an outer membrane that contains lipoplysacchrides.

Front 7

Why is gram staining a particularly valuable ID tool in medicine?

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- gram-negative species are generally more threatening than gram-positive species.

- lipopolysaccharides on walls of gram-negative generally more toxic and outer membrane helps protect bacteria against body's defenses.
-----> more commonly resistant to antibiotics because of outer membrane impeding drug entry.

Front 8

define capsule:

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- a sticky layer of polysacchrides or protein.

- enables prokaryotes to adhere to their substrate or to other individuals in a colony.

- can also shield for protection.

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flagella:

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a structure that enables prokaryotes to move.

- maybe scattered over the entire cell surface or concentrated at one or both ends of the cell.

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taxis:

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movement toward or away from stimulus.

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nucleoid region:

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- where prokaryotic chromosome is located

- is a part of the cytoplasm that appears lighter than the surrounding cytoplasm in electron micrographs.

Front 12

plasmids:

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small rights of DNA in prokaryotic cells. most consisting of only a few genes.
---> provides resistance to antibiotics
---> direct the metabolism of rarely encountered nutrients.

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endospores:

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resistant cells
- occurs when an essential nutrient is lacking in the environment.
--> the original cell produces a copy of its chromosome and surrounds it with a tough wall (forming endospore)
-------> water is removed
-------> metabolism comes to a hault.

Front 14

What are the four major modes of nutrition?

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1. photoautotrophs
2. chemoautotrophs
3. photoheterotrophs
4. chemoheterotrophs

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photoautotrophs:

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are photosynthetic organisms that capture lgiht energy and use it to derive the synthesis of organic compounds from carbon dioxide.

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Chemoautotrophs:

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also need only carbondioxide as a carbon source. However, instead of using light for energy, they oxidize inorganic substances, such hydrogen sulfide, ammonia, or ferrous ions.

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Photoheterotrophs:

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use light for energy but must obtain their carbon in organic form.

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Chemoheterotrophs:

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must consume organic molecules for both energy and carbon.

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Obligate aerobes:

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use oxygen for cellular respiration. cannot grow without it.

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faculative anaerobes:

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use oxygen if it is present but can also grow by fermentation in an anerobic environment.

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obligate anaerobes:

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- poisoned by oxygen

- some live exclusively by fermentation

- some extract chemical energy by anaerobic respiration.

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Biofilms:

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- surface-coating colonies

- cells in a colony secrete signaling molecules that recruit nearby cells, causing colony to grown

- cells produce proteins that adhere the cells to the substrate and to one another

- channels allow nutrients to reach cells in the interior and wastes to be expelled.

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What are two important lessons learned over time from prokaryotes?

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1. the genetic diversity of prokaryotes is immense.

2. the apparent significance of horizontal gene transfer in the evolution of prokaryotes.

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Extremophiles:

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organisms that live in environments so extreme that few other organisms can survive there.

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extreme thermophiles:

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thrive in very hot environments

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extreme halophiles:

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live in highly saline environments.

Front 27

Methanogens:

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- have a unique way to obtain energy
-----> use carbon dioxide to oxidize hydrogen, releasing methane as a waste product.

- are poisoned by oxygen.

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decomposers:

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Break down corpses, dead vegetation, waste products... therefore unlocking supplies of carbon, nitrogen, and other elements.

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symbiois:

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an ecological relationship between organisms of different species that are in direct contact.

"living together"

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Mutualsim:

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both symbiotic organisms benefit.

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commensalism:

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one organism benefits while neither harming nor helping the other in any significant way.

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parasitism:

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one organism "parasite" benefits at the expense of the host.