MICROM 410 Exam 1

What is a microbe?

a living organism that is too small to be seen with the naked eye

• Prokaryotes: bacteria and archaea

• Eukaryotes: algae, fungi, and protozoa

• Viruses are acellular and lack many hallmarks of living organisms

What are the defining features of a Eukaryote?

• Possess a membrane-bound nucleus

• Possess membrane-bound organelles

• Possess cytoskeletal elements such as microtubules and microfilaments

• Typically much larger than prokaryotes

What is the 16s rRNA gene?

• found in all cells (18S in eukaryotes)

• Performs the same function in all organisms, so selection pressures should be similar for all during evolution

• Not expected to be subject to horizontal gene transfer

• Both highly conserved and highly variable regions within the sequence

What are Conserved Regions of rRNA?

sequence divergence within conserved regions can be used to distinguish between distantly-related organisms

What are Variable Regions of rRNA?

sequence divergence within variable regions can be used to distinguish between different genera and/or species of organisms

What are Eukaryotic Signature Proteins?

Gene products found exclusively in Eukaryotes and entirely absent from Prokaryotes

• Cytoskeletal elements (actin, tubulin)

• Nuclear pore complex proteins

• Membrane sorting and trafficking proteins

Archea contain homologs of many of these genes

What are the characteristics of all living organisms?

Chromosome material: Double-stranded DNA

RNA transcription: Common ancestral RNA polymerase

Translation: Nearly universal genetic code; shared ancestral rRNAs and elongation factors

Protein: Common ancestral functional domains

Prokaryotes (+Archea): Genome Structure and Metabolic Diversity

Cell volume: very small (typically)

DNA chromosome: circular

DNA organization: Nucleoid

Gene organization: Multigene operons

Eukarya Genome Structure and Metabolic Diversity

Cell volume: large

DNA chromosome: linear

DNA organization: Nucleus with membrane

Gene organization: Single genes

Bacteria: Transcription and Translation

Intron splicing: introns are rare

RNA polymerase: Bacterial homologs

Transcription factors: Bacterial homologs

Ribosome sensitivity (antibiotics): Sensitive

Translation initiatior: Formylmethionine

Archea + Eurkarya: Transcription and Translation

Intron Splicing: Introns are common

RNA polymerase: Eurkaryotic homologs

Transcription factors: Eukaryotic homologs

Ribosome sensitivity: Resistant

Translation initiator: Methionine

Bacteria + Eukaryotes: Characteristics

Methanogenesis: No

Thermophilic growth: Up to 95C/80C

Photosynthesis: Many species

Light absorption by chlorophylls: Yes

Membrane lipids: Ester-linked fatty acids

Pathogens infection animals or plants: yes

Archaea: Characteristics

Methanogenesis: Yes

Thermophilic growth: Up to 120C

Photosynthesis: only haloarchaea

Light absorption by chlorophylls: No

Membrane lipids: Ether-linked isoprenoids

Pathogens infection animals or plants: None

What is the endosymbiotic theory?

Evidence for the symbiotic origins of mitochondria and plastids:

• Same size as bacteria

• Multiply autonomously by binary fission

• Have double membrane envelope structure

• Have bacteria-like (70S) ribosomes

• Contain circular DNA genomes

• Bacterial genes found in nuclear genome of Eukaryotic cells

• Mitochondria and plastids monophyletic with bacteria

How does an organism transition from endosymbiont to organelle?

• Reduced genome size with significant gene transfer to the host nucleus

• Significant loss of metabolic versatility

• High numbers of proteins imported from the host

• Horizontal gene transfer can confuse genetic inheritance

How is the bacterial cytosol organized?

• Genome highly condensed into the nucleoid

• Have a single, circular chromosome of double-stranded DNA

• High degree of internal organization and structure

• Invaginations of cytoplasmic membrane

What are subcellular structures in bacterial cytosol?

• Carboxysomes

• Gas vesicles

• Inclusion bodies

• Magnetosomes