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Chapter 15: The First Single
Cells
20
Biology
Undergraduate 2
02/20/2006

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Term
What are the The Simplest Organisms?
Definition
The fossil record indicates that prokaryotes appeared 2.5 billion years ago

Eukaryotes, on the other hand, appeared only 1.5 billion years ago

Today prokaryotes are the simplest and most abundant form of life on earth

Prokaryotes occupy a very important place in the web of life in earth

Term
What is the The Structure of a Prokaryote?
Definition
Prokaryotes are small, simply organized, single cells that lack a nucleus

Prokaryotes include the bacteria and archaebacteria

They come in three main shapes Rod-shaped (bacilli) Spherical (cocci) Spirally coiled (spirilli)

Term
What is the cell membrane encased in?
Definition
The cell membrane of prokaryotes is encased in a cell wall

Bacterial cell walls are composed of peptidoglycan Network of polysaccharides linked together by peptide cross-links

Term
What do Archaebacterial cell walls lack ?
Definition
peptidoglycan
They are made of proteins, sugars or both.
Term
What two groups can Bacteria can be divided into?
Definition
Gram-positive Have a thick peptidoglycan layer Lack outer membrane

Gram-negative Have a thin peptidoglycan layer Have an outer membrane containing lipopolysaccharide

The name refers to a differential stain developed by Hans Christian Gram

Gram-positive cells retain the primary crystal violet stain

Gram-negative cells don’t and are stained by a safranin (red) counterstain

Term
The structure of bacteria cell walls (diagram).
Definition
[image]
Term
What are a list of things that bactera may have?
Definition
Many bacteria have capsules A gelatinous layer found external to the cell wall

Many bacteria possess threadlike flagella Long external appendages used for locomotion

Some bacteria also possess pili Short external appendages used for attachment

In harsh conditions, a few bacteria can form endospores Highly-resistant structures that may germinate into active bacteria when conditions improve

Term
How does bacteria reporoduce?
Definition
Binary Fission
Term
What are Plasmids?
Definition
Plasmids are (typically) circular double-stranded DNA molecules that are separate from the chromosomal DNA

Plasmids often contain genes that confer a selective advantage to the bacterium harboring them, e.g., the ability to make the bacterium antibiotic resistant.

Term
Diagram with plasmids
Definition
[image]
Term
What are pili?
Definition
Bacteria such as Neisseria gonorrhoeae use pili to adhere to the mucous membranes of the urethra and thus resist the flushing action of the urine.
Term
What are Sex Pili ?
Definition
F (conjugation, sex) pili F pili are long pili found in low numbers and used to attach one bacteria to a another, typically of the same species.

F pili are involve in the transfer of plasmids from one bacteria to the other, a process called conjugation.

Term
Sex Pili conjugation
Definition
[image]
Term
What is a bacteria conjugation?
Definition
The undirectional transfer of plasmid DNA following cell-to-cell contact.
Term
Comparing Prokaryotes to Eukaryotes
Definition
Prokaryotes differ from eukaryotes in many respects

They have very little internal organization They are unicellular and much smaller They possess a single chromosome They are far more metabolically diverse (different means of obtaining energy)

Term
Prokaryotic Metabolism
Definition
Prokaryotes have evolved many more ways than eukaryotes to acquire carbon and energy

Acquisition of Carbon Autotrophs = Use CO2 as their only carbon source Heterotrophs = Use preformed organic compounds as carbon sources

Acquisition of Energy Phototrophs = Use light as energy source Chemotrophs = Use chemicals as energy source

Term
Prokaryotic Metabolism (2)
Definition
Based on carbon and energy sources, prokaryotes can be divided into four categories

1. Photoautotrophs Use the energy of sunlight to build organic molecules from CO2 Cyanobacteria

2. Chemoautotrophs Obtain energy by oxidizing inorganic substances Nitrifiers oxidize ammonia or nitrite

Term
Prokaryotic Metabolism (2)
Definition
Based on carbon and energy sources, prokaryotes can be divided into four categories

3. Photoheterotrophs Use light as energy and pre-formed organic molecules as carbon sources Purple nonsulfur bacteria

4. Chemoheterotrophs Use organic molecules as carbon and energy sources Decomposers and most pathogens

Term
Importance of Prokaryotes
Definition
Prokaryotes were largely responsible for creating the properties of the atmosphere and soil found on Earth

They are the principal decomposers

They are the only organisms capable of fixing nitrogen, thus making it available for others

They cause major diseases in plants and animals, including humans

Term
Prokaryotic Engineering
Definition
Prokaryotes are instrumental in genetic engineering
Nonpolluting insect control agents
Removing environmental pollutants
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