I. Introduction to Prokaryotes

A. Background B. Cellular Organization C. Cell Wall D. Motility E. Reproduction

Background

• First appeared about 4 billion years ago

• Prokaryotes shaped Earth’s Chemistry

• Heterotrophs -> photosynthetic autotrophs -> aerobes 

• Abundant and ubiquitous 

Cellular Organization

• Small cell size

  • Helps with rapid replication

• Lower structural compartmentalization 

  • Not divided into membrane bound components 

  • Most biochemical reactions take place in cytosol 

• No membrane bound organelles 

Prokaryotes have

1. Ribosomes (synthesize proteins, free floating)

2. Nucleoid- single haploid chromosome

3. Cytosol (primary space for metabolic pathways, enzymes coexist here)

4. Cell membrane 

5. Enzymes for respiration and photosynthesis 

6. Plasmids (extra DNA found in prokaryotes, code for genes not needed for basic survival can be expressed at random times ex. Antibiotic resistance)

Cell Wall

Found in all prokaryotes

Cell Wall Functions

1. Protection

2. Maintain cell shape

3. Prevents bursting in hypotonic solution 

Cell Wall part

peptidoglycan

• Carbohydrate polymer (tetra peptide: specialized sugar that are held together by peptide chains (needed for sturdiness) )

• Only found in domain bacteria

• In archaea made of protein or polysaccharide, same function but composition different 

• Eukarya like plants made of cellulose, chitin in fungi

Motility

50% of Prokaryotes are motile

Taxis

• movement (not random but with goal in specific environment)

  • Positive taxis- moves toward stimulus (ex. Toward light for photosynthesis)

  • Negative taxis- moves away from stimulus 

Flagella

• Common motility structures, found in all 3 domains

• Similar function, but arose independently in different domains

• Convergent evolution -> analogous structures

Flagella function

• Pumped across plasma membrane by ETC

• Similar to chemiosmosis

• As H+ pumped out gradient forms and H+ protons move back into bacteria, the flagellar motor spins allowing movement, H+ diffuses through motor

• ATP indirectly involved with e- carriers so gradient forms

Binary fission