Chapter 26

Early Earth and The Origin of Life

Early history of life

• Solar system - 12 billion years ago (bya)

• Earth - 4.5 – 6.2 bya• Life - 3.5 to 4.0 bya• Prokaryotes - 3.5 to 2.0 bya

stromatolites• Oxygen accumulation - 2.7 bya

photosynthetic cyanobacteria• Eukaryotic life - 2.1 bya• Muticelluar eukaryotes - 1.2 bya• Animal diversity - 543 mya• Land colonization - 500 mya

The Origin of Life• Spontaneous generation

vs. biogenesis (Pasteur)• The 4-stage Origin of life

Hypothesis:• 1- Abiotic synthesis of

organic monomers• 2- Polymer formation• 3- Origin of Self-

replicating molecules• 4- Molecule packaging

(“protobionts”)

Organic monomers/polymersynthesis• Oparin (Rus.)/Haldane (G.B.)

hypothesis (primitive earth): volcanic vapors (reducing atmosphere) with lightning & UV radiation enhances complex molecule formation (no O2)

• Miller/Urey experiment:

• water, hydrogen, methane, ammonia

• all 20 amino acids, nitrogen bases, & ATP formed

• Fox proteinoid formation (abiotic polypeptides) from organic monomers dripped on hot sand, clay or rock

• Oparin (coacervates) protobionts (aggregate macromolecules; abiotic) surrounded by a shell of H2O molecules coated by a protein membrane

Abiotic genetic replication• First genetic material• Abiotic production of

ribonucleotides• Ribozymes (RNA

catalysts)• RNA “cooperation”• Formation of short

polypeptides (replication enzyme?)

• RNA-DNA template?• Viruses?

The Major Lineages of Life

Whitaker System

Classification

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

Scientific Name: Genus species

3 DOMAIN SYSTEM

• Chapter 27

Prokaryotes and the Origins of Metabolic Diversity

Initially Archaea seem more similar to Eubacteria than to Eukaryotes.  Archae and Eubacteria are BOTH PROKARYOTIC organisms; they both have closed, circular DNA;

They both are transcription and translation linked; and they both usually reproduce via binary fission.

1.  They utilize different metabolic pathways. 

2. They also differ in number of ribosomal proteins and in the  size and shape of their ribosomal S unit. 

3. The Eubacteria genome is almost two times larger and they contain more plasmids than Archae. 

4. Archaea are similar to Eukaryotes in that they have several kinds of RNA polymerase, have a great number of histone-like proteins, have DNA in the form of nucleosomes, and contain introns.

However, there are several differences between Archae and Eubacteria.

Biochemical determination:Archaebacteria are distinguished by cell walls

with pseudopeptidoglycan or protein components, and cell membranes composed of branched hydrocarbons linked to glycerol molecules.

• Archaea are highly diverse organisms, both morphologically (form and structure) and physiologically (function). 

• The organisms' possible shapes include spherical, rod-shaped, spiral, lobed, plate-shaped, irregularly shaped, and pleomorphic. There are many different types of Archaea that live in extremely diverse environments. 

• Modern-day Archaebacteria are found in extreme environments, such as areas of intense heat or high salt concentration.

ALL ABOUT ARCHAEBACTERIA

EUBACTERIA

Within their domains, identification of microbes begins with their physical appearance, followed by biochemical and genetic tests.

EUBACTERIA

SHAPE is/was the most commonly used physical appearance for determination of species.

Pili

Made of the protein pilin and project from the cell surface. There are 2 types:

Sex or conjugation Pili for the transfer of extrachromosomal DNA between donor and recipient.

                             

 Attachment Pili or Fimbriae. There are many and are used for attachment to surfaces. Pili are virulence factors.

                               

Gram positive bacteria

Have an extra layer of peptidoglycan in their cell wall, and retain dye.

Gram negative bacteria

Have a thin layer of peptidoglycan in their cell wall. AND have lipopolysaccharides with protein channels in the cell membrane. This keeps dyes (along with antibiotics) out!

http://www.sirinet.net/~jgjohnso/monerans.html

A bacterial flagellum has 3 basic parts: a filament, a hook, and a basal body.

• 1) The filament is the rigid, helical structure that extends from the cell surface. It is composed of the protein flagellin arranged in helical chains so as to form a hollow core. During synthesis of the flagellar filament, flagellin molecules coming off of the ribosomes are thought to be transported through the hollow core of the filament where they attach to the growing tip of the filament causing it to lengthen.

• 2) The hook is a flexible coupling between the filament and the basal body

• 3) The basal body consists of a rod and a series of rings that anchor the flagellum to the cell wall and the cytoplasmic membrane. Unlike eukaryotic flagella, the bacterial flagellum has no internal fibrils and does not flex. Instead, the basal body acts as a molecular motor, enabling the flagellum to rotate and propell the bacterium through the surrounding fluid. In fact, the flagellar motor rotates very rapidly. (The motor of E. coli rotates 270 revolutions per second!)

EUKARYOTIC FLAGELLA

• Cell Locomotion via Cilia and FlagellaCilia and flagella, which extend from the plasma membrane, are composed of microtubules, coated with plasma membrane material. Eukaryotic cilia and flagella have an arrangement of microtubules, known as the 9 + 2 arrangement (9 pairs of microtubules (doublets) around the circumference plus 2 central microtubules). "Spokes" radiate from the microtubules towards the central microtubules to help maintain the structure of the cilium or flagellum.

• Each of the microtubule doublets have motor molecule "arms", the dynein arms, which can grip and pull an adjacent microtubule to generate the sliding motion. (The protein of this motor molecule is dynein.)

Prokaryote flagella function:• Flagella are the organelles of

locomotion for most of the bacteria that are capable of motility. Two proteins in the flagellar motor, called MotA and MotB, form a proton channel through the cytoplasmic membrane and rotation of the flagellum is driven by a proton gradient. This driving proton motive force (def) occurs as protons accumulating in the space between the cytoplasmic membrane and the cell wall as a result of the electron transport system travel through the channel back into the bacterium's cytoplasm.

Under environmental stress (lack of water, nutrients etc.) some vegetative cells produce endospores e.g. Clostridium and Bacillus. Spores can be dormant for many years. They can survive extreme heat, desiccation, radiation and toxic chemicals. However, when conditions become favorable they revert to a vegetative state. Spore germination is activated by heat in the presence of moistures but the endospore must degrade the layers around the spore.

ENDOSPORES

PROKARYOTIC CELL DIVISIONBinary Fission:

• cell elongates, duplicates its chromosome

Allocation of chromosomes to daughter cells depends on MESOSOME – an extension of the cell membrane

• It ensures the distribution of the "chromosomes" in a dividing cell.

• Upon attachment to the plasma membrane, the DNA replicates and reattaches at separate points.

•Continued growth, to about twice the size of the cell, gradually separates the chromosomes.

A diagram of the attachment of bacterial chromosomes, indicating the possible role of the mesosome.

BACTERIA

VIRUS

What is an antibiotic?

Chemical substances that INHIBIT the growth of bacteria or KILL it.

HOW:1. Prevent cell wall from forming properly

2. Prevent protein synthesis

3. Interfere with chromosome replication

4. Disrupt plasma / outer membrane

5. Interference with metabolism

Alexander Fleming discovers the first antibiotic (1928)

Sir Alexander Fleming discovers the drug penicillin, which counteracts harmful bacteria. Fleming makes the discovery by accidentally contaminating a bacteria culture with a "Penicillium notatum" mold.

He noticed that the non-toxic mold halts the bacteria's growth, and later conducts experiments to show penicillin's effectiveness in combating a wide spectrum of harmful bacteria

ZONE OF INHIBITION

What is antibiotic resistance?

The ability of a bacterial cell to resist the harmful effect of an antibiotic. This could be incorporated into the chromosome or plasmid.- System to prevent entry?- To destroy the antibiotic if into cell- To block action of antibiotic- A pump system to move antibiotic out

How is antibiotic resistance acquired?

• Consistent exposure to antibiotics– Long-term therapy– Farm animals

• Indiscriminate usage of antibiotics– For example for a cold/flu

• Non-therapeutic use– For animals to gain weight

Transfer of antibiotic resistance genes by conjugation

CAN BACTERIA BE GOOD FOR YOU?

• The majority is not only helpful but necessary!– Occupy and compete for limited nutrients

• Tough for bad bacteria to get a foothold

– Antibiotics kill both good AND bad bacteria • Thus, good are killed and some could become

antibiotic resistant. Since there’s no good bacteria to stop them -

– Bad strain increases in number

• Chapter 28

The Origins of Eukaryotic Diversity

Protists

• Ingestive (animal-like); protozoa

• Absorptive (fungus-like)

• Photosynthetic (plant-like); alga

The Endosymbionic Theory• Mitochondria and chloroplasts were formerly

from small prokaryotes living within larger cells (Margulis)

Protist Systematics & Phylogeny, I

• 1- Groups lacking mitochondria; early eukaryotic link; Giardia (human intestinal parasite; severe diarrhea); Trichomonas (human vaginal infection)

• 2- Euglenoids; autotrophic & heterotrophic flagellates; Trypanosoma (African sleeping sickness; tsetse fly)

Protist Systematics & Phylogeny, II• Alveolata: membrane-bound

cavities (alveoli) under cell surfaces; dinoflagellates (phytoplankton); Plasmodium (malaria); ciliates (Paramecium)

Protist Systematics & Phylogeny, III• Stamenophila: water molds/mildews and

heterokont (2 types of flagella) algae; numerous hair-like projections on the flagella; most molds are decomposers and mildews are parasites; algae include diatoms, golden, and brown forms

Protist Systematics & Phylogeny, IV

• Rhodophyta: red algae; no flagellated stages; phycobilin (red) pigment

• Chlorophyta: green algae; chloroplasts; gave rise to land plants; volvox, ulva

Protist Systematics & Phylogeny, V• Affinity uncertain:• Rhizopods: unicellular with

pseudopodia; amoebas• Actinopods: ‘ray foot’ (slender

pseudopodia; heliozoans, radiolarians

Protist Systematics & Phylogeny, VI

• Mycetozoa: slime molds (not true fungi); use pseudopodia for locomotion and feeding; plasmodial and cellular slime molds