the oldest life forms on planet...

1

Prokaryotesthe oldest life forms

on planet Earth

1

I. Bacteria Are OmnipresentA. Appeared apx. 3.5 billion ybpB. The only life forms on earth for 1.5 billion yrs.C. Found in all habitats - dominating the biosphereD. Approximately 5,000 species identified

1. however 400K - 4 million species are likely to existE. Small percentage cause diseaseF. Some are decomposers

1. key organisms in life sustaining chemical rxn’sG. Many form symbiotic relationships with other

prokaryotes and eukaryotes1. bacteria in mammalian intestines produce critical vitamins

2

2

A. Cell Shape1. cocci: spherical (most common)2. bacilli: rod shaped3. spirilla and spirochetes : spiral helices (smallest)

B. Size1. most have diameters of 1-5 µm

(vs. eukaryotes @ 10 -100 µm)

II. Morphological Diversity Of Prokaryotes

3

Fig. 27.2

4

3

III. Structure, Function, and ReproductionA. Living organisms are made of either prokaryotic or eukaryotic cells.

1. prokaryotes = all bacteria; eukaryotes = all non-bacterial cells/organisms

2. structural differences distinguish the two typesB. Prokaryotic Structural Overview

1. no true nucleus (lack nuclear membrane)2. genetic material in nucleoid region3. no membrane-bound organelles4. most are unicellular

a. some aggregates/colonies feature division of labor via specialized cells5. cell wall present in nearly all prokaryotes

a. provides physical protection - particularly in hypotonic and hypertonic conditions. b. constructed of a special polymer of modified sugars, cross-linked with short polypeptidesc. pathogenic issues: either an external/outer membrane -or- a sticky polysaccharide layer

external to the cell wall can confer pathogeniety and/or resistance to host defenses

5

C. Functional Overview1. bacteria function in 2 of 4 different metabolic pathways (their way of obtaining carbon and energy)

a. phototrophic - use light energy like plantsb. chemotrophic - obtain energy from chemicalsc. autotrophic - need only use CO2 as their carbon sourced. heterotrophic - use organic molecules as a source of carbon

2. heterotrophs are assumed to be the very first prokaryotesa. the first metabolic pathway is assumed to be glycolysis - the extraction of energy

from organic molecules to generate ATP anaerobically = absence of O2

D. Reproductive Overview1. reproduction occurs asexually via binary fission2. fastest: every 20 minutes; typical: every 1-3 hours3. although meiosis does not happen, individuals can combine genes

a. transformation: “naked” DNA is absorbed from the environmentb. conjunction: direct transfer of DNA from one cell to anotherc. transduction: transfer of DNA via viral infection

4. when under stress certain bacteria can produce an endospore: a protein based capsulecontaining the individual’s genome - suspended until adequate conditions return

6

4

A. Eukaryotic Structural Overview

1. true nucleus (membrane-bound nucleus) 2. genetic material in nucleus

3. contain membrane-bound organelles

Prokaryotic Cell Fig. 6.5Eukaryotic/Animal Cell Fig. 6.8

IV. Eukaryotic Structural Overview

7

The End

8