why are prokaryotes important? -...

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Why are Prokaryotes important?

▪ Date: October 17, 2013 ▪ Catalyst: ▪ 1. Describe the big bang theory. ▪ 2. How did the first life on Earth form? ▪ 3. What was the first form of genetic storage? ▪ 4. What were the first vesicles made of lipids and

proteins called?


Concept 24.1: Conditions on early Earth made the origin of life possible

▪ Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into macromolecules 3. Packaging of molecules into protocells, membrane-

bound droplets that maintain a consistent internal chemistry

4. Origin of self-replicating molecules


Abiotic Synthesis of Macromolecules

▪ RNA monomers have been produced spontaneously from simple molecules

▪ Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

▪ RNA was first genetic material ▪ Vesicles with RNA capable of replication would have

been protocells ▪ RNA could have provided the template for DNA


Figure 24.6

3 µ

m(a) Spherical (b) Rod-shaped (c) Spiral

1 µ

m

1 µ

m


Cell-Surface Structures

▪ A key feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment


Figure 24.7

Peptido- glycan layer

Cell wall

Gram-negative bacteria

10 µm

Gram-positive bacteria

(b) Gram-negative bacteria

(a) Gram-positive bacteria

Plasma membrane

Plasma membrane

Peptidoglycan layer

Cell wall

Outer membrane

Carbohydrate portion of lipopolysaccharide


Figure 24.7a

Peptido- glycan layer

Cell wall

(a) Gram-positive bacteria

Plasma membrane


Figure 24.7b

(b) Gram-negative bacteria

Plasma membrane

Peptidoglycan layer

Cell wall

Outer membrane

Carbohydrate portion of lipopolysaccharide


Internal Organization and DNA

▪ Prokaryotic cells usually lack complex compartmentalization ▪ Phototrophs obtain energy from light ▪ Chemotrophs obtain energy from chemicals ▪ Autotrophs require CO2 as a carbon source ▪ Heterotrophs require an organic nutrient to make

organic compounds


▪ Prokaryotes have considerable genetic variation ▪ Three factors contribute to this genetic diversity ▪ Rapid reproduction ▪ Mutation ▪ Genetic recombination

Prokaryote Characteristics


Rapid Reproduction and Mutation

▪ Prokaryotes reproduce by binary fission, and offspring cells are generally identical

▪ Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population

▪ High diversity from mutations allows for rapid evolution


Prokaryote Diversity

▪ Prokaryotes have diverse structural and metabolic adaptations

▪ Prokaryotes inhabit every environment known to support life


Bacteria

▪ Bacteria include the vast majority of prokaryotes familiar to most people

▪ Diverse nutritional types are scattered among the major groups of bacteria

Video: Tubeworms

24_19Tubeworms_SV.mpg









▪ Some archaea live in extreme environments and are called extremophiles

▪ Extreme halophiles live in highly saline environments ▪ Extreme thermophiles thrive in very hot

environments

Video: Cyanobacteria (Oscillatoria)

24_20Oscillatoria_SV.mpg









Figure 24.20


Ecological Interactions

▪ Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont

▪ Prokaryotes often form symbiotic relationships with larger organisms


Impact on Humans

▪ Intestines are home to about 500–1,000 species of bacteria

▪ Many of these are mutualists and break down food that is undigested by our intestines


Figure 23.14

Ancestral mammal

ANCESTRAL CYNODONT

Time (millions of years ago)250 200 150 100 50 0

Eutherians (5,010 species)

Marsupials (324 species)

Monotremes (5 species)


Concept 25.1: Eukaryotes arose by endosymbiosis more than 1.8 billion years ago

▪ Early eukaryotes were unicellular ▪ Eukaryotic cells have organelles and are structurally

more complex than prokaryotic cells ▪ A well-developed cytoskeleton enables eukaryotic

cells to have asymmetrical forms and to change shape



Endosymbiosis in Eukaryotic Evolution

▪ DNA sequence data indicate that eukaryotes are “combination” organisms

▪ Endosymbiosis, a symbiotic relationship in which one organism lives inside the body or cell of another organism



Endosymbiosis Reading and Discussion

Read the following passage on endosymbiotic theory with your group. As you read, come up with questions about eukaryotes vs prokaryotes, and how endosymbiosis occurred. Once you are done reading, discuss with your group.


Origin of Mitochondria and Plastids

▪ Endosymbiont theory proposes that mitochondria and plastids were formerly small prokaryotes that began living within larger cells

▪ An endosymbiont is a cell that lives within a host cell ▪ Prokaryote ancestors probably entered the host cell

as undigested prey or internal parasites



▪ The relationship between endosymbiont and host cells was mutually beneficial

▪ In the process of becoming more interdependent, the host and endosymbionts would have become a single organism



Figure 25.3

CytoplasmDNA

Nucleus

Engulfing of aerobic bacterium

Engulfing of photosynthetic bacterium

MitochondrionMito-

chondrion

Plastid

Plasma membrane

Endoplasmic reticulum

Nuclear envelope

Ancestral prokaryote

Ancestral heterotrophic eukaryote

Ancestral photosynthetic eukaryote


Red Light

▪ What is the difference between a prokaryote and a eukaryote?

▪ Are prokaryotes simple? Why or why not? ▪ Are bacteria always harmful? ▪ Describe how mitochondria and chloroplasts became

part of the eukaryote cell structure.

why are prokaryotes important? -...

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