Why are Prokaryotes important?

Transcription

1 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?

2 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, membranebound droplets that maintain a consistent internal chemistry 4. Origin of self-replicating molecules

3 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

4 Figure µm 1 µm 3 µm (a) Spherical (b) Rod-shaped (c) Spiral

5 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

6 Figure 24.7 (a) Gram-positive bacteria (b) Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Cell wall Peptidoglycan layer Plasma membrane Cell wall Outer membrane Peptidoglycan layer Plasma membrane Gram-positive bacteria Gram-negative bacteria 10 µm

7 Figure 24.7a (a) Gram-positive bacteria Cell wall Peptidoglycan layer Plasma membrane

8 Figure 24.7b (b) Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Outer Cell membrane wall Peptidoglycan layer Plasma membrane

9 Internal Organization and DNA Prokaryotic cells usually lack complex compartmentalization Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals Autotrophs require CO 2 as a carbon source Heterotrophs require an organic nutrient to make organic compounds

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

11 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

12 Prokaryote Diversity Prokaryotes have diverse structural and metabolic adaptations Prokaryotes inhabit every environment known to support life

13 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

14 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)

15 Figure 24.20

16 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

17 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

18 Figure Ancestral mammal ANCESTRAL CYNODONT Monotremes (5 species) Marsupials (324 species) Time (millions of years ago) Eutherians (5,010 species)

19 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

20 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

21 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.

22 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

23 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

24 Figure 25.3 Cytoplasm DNA Ancestral prokaryote Plasma membrane Endoplasmic reticulum Nuclear envelope Nucleus Engulfing of aerobic bacterium Engulfing of photosynthetic bacterium Ancestral heterotrophic eukaryote Mitochondrion Mitochondrion Plastid Ancestral photosynthetic eukaryote

25 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.