MCDB 1: Cell Theory and Prokaryotes

Cell Theory

• cells are the fundamental units of life

• all living organisms are composed of cells

• all cells arise from preexisting cells

Life can be classified into three domains

• bacteria (prokaryote)

• archaea (prokeryote)

• eukarya - plants, animals, etc.

Differences between bacteria and archaea

• peptidoglycan is PRESENT in the cell wall of BACTERIA and ABSENT in ARCHAEA

• BACTERIA has ONE kind of RNA polymerase and ARCHAEA has SEVERAL KINDS like us

Prokaryotes

• single-celled organisms

• no membrane-bound organelles

• no mitochondria!

• no separation between nucleus and cytosol

Peptidogylcan

supports bacterial shape outside the membrane

Bacterial Cell Wall

peptidoglycan and plasma membrane

To make peptidoglycan layer,

prokaryotes go through the process of hydrolysis synthesis

Gram+

• have the peptidoglycan on the outside

• absorb the purple dye (dye binds to peptidoglycan)

Gram-

• peptidoglycan is in between an inner and outer membrane and bound to the outer membrane with lipoproteins

• doesn’t absorb purple due

Bacterial Morphologies

• cocci (round)

• bacilli (rod)

• spiral

• strept - chain

True of False: Gram+ bacterial cell walls contain fewer peptidoglycan than Gram- bacterial cell walls

true

Antibiotics

chemicals that inhibit bacterial growth and survival by disrupting essential cell functions; used as medicine to treat bacterial infections

• specifically harms bacteria and NOT eukaryotes

Penicillin

inhibits transpeptidase (enzyme that helps make cell walls)

• targets cell wall synthesis

All known antibiotics target one of 4 essential pathways

1. cell-wall synthesis or membrane function (works best on Gram+ bacteria)

2. DNA replication / RNA transcription

3. translation (protein synthesis)

4. metabolism

Flagella

a hair-like appendage that protrudes from certain cells to provide motility

Motor Proteins

can be activated to cause conformational changes and movement

Rotor-like protein complex that spins…

• counterclockwise: forward

• clockwise: tumbling

Flagellar rotation is work and to do work, cells require…

cellular respiration!

• they have no mitochondria, so it gets ATP from glycolysis and fermentation

Pili and fimbriae

collectively allow adherence and transfer in bacteria

The reason why cells can’t be that big is because…

there is a limit on diffusion, which is how nutrients, oxygen, and certain waste products move through cells, limited by surface area to volume ratio

Metabolic requirements

set upper limits for cell size

The plasma membrane is a selective barrier that…

allows sufficient passage of oxygen, nutrients, and waste through the surface of every cell