Typed lecture notes covering chapter 3 of Microbiology: An Evolving Science, the textbook used in the "General Microbiology" course (BioM122) at UCI. Aligns with lecture 3.
Cell Structure and Function (ch. 3, lec. 3)
Tuesday, October 6, 2020 8:36 PM
Cell membrane
• Prokaryotic cells do not have organelles enclosed in membranes, instead organized in distinct
locations.
• Cell membrane: selectively permeable barrier that separates cellular components from external
environment.
○ Membranes have equal volumes of phospholipids (glycerol w/ ester links to 2 fatty acids and a
phosphoryl head group) and proteins.
○ Leaflets: 2 layers of phospholipids in the bilayer.
• Phospholipids vary by phosphoryl head groups and fatty acid side chains. Ex. Cardiolipin: double
phospholipid linked by a glycerol. Its conc INCs under cell stress; localizes to cell poles (binds to
certain environmental stress proteins/like protein that transfers osmo-protectants).
○ Fatty acid chains may be saturated, unsaturated, or polyunsaturated.
• Membranes also include planar molecules that fill gaps b/w hydrocarbon chains.
○ In eukaryotes, reinforcing agents are sterols (ie cholesterol).
○ In bacteria, agents are hopanoids.
• Archaea have the most extreme variations in phospholipid side chains.
○ Ether links b/w glycerol and fatty acids are diethers or tetraethers. Hydrocarbon chains are
branched terpenoids (can cyclize to form cyclopentane).
○ Live in harsh environments. -> Need diversity in their membrane structure to survive in
extremes.
○ *Archaea have ETHER linkages while bacteria have ester.
Membrane proteins
• Phospholipid membranes have hydrophilic heads on outside and hydrophobic fatty acids facing
inside of cell.
○ Membrane proteins are able to float inside said structures and transport thru the membrane.
○ They also have hydrophilic and hydrophobic regions, allowing them to be inserted into the cell
membrane.
• Membrane proteins serve many functions: structural support, detection of environmental signals,
secretion of virulence factors and communication signals, ion transport and energy storage.
Cell wall
• Confers shape and rigidity; helps withstand turgor pressure.
• Cell wall is a single molecule. The sacculus, bacterial cell wall, consists of a single interlinked
molecule.
• Most bacterial walls are made of peptidoglycan (murein)-- long polymers of repeating
disaccharides bound to a 4-6 amino acid peptide. Peptides can form cross-bridges connecting
parallel glycan strands (b/w 3rd and 4th aa).
• Peptidoglycan forms a helical strand. -> proteins up to 50kDa can pass through!
• Peptidoglycan is unique to bacteria. -> Enzymes responsible for its biosynthesis make great targets
for antibiotics. Ex. Penicillin inhibits the transpeptidase that cross-links the peptides.
3.3: The Envelope and Cytoskeleton
• For many prokaryotic species, the cell envelope includes at least one layer of support (ie cell wall).
• Envelope composition defines whether a bacteria is: (assume all components are in cell wall)
○ Gram positive: thick cell wall. Ex Firmicutes
• Teichoic acids: anchor cell wall to plasma membrane. -> Protect cell from harmful
substances, important for ion uptake, help their pathogens bind to host tissue. Made of
phosphate, glycerol, and a side chain (R). Covalently linked to peptidoglycans.
• Periplasmic space: narrow space b/w cell wall and plasma membrane; contains structural
proteins/exoenzymes.
○ Gram negative: thin, yet strong cell wall. Ex. Proteobacteria
• Lipopolysaccharides (LPS): Lipid A component is an inflammatory endotoxin -> induces
inflammation. Contributes to negative charge on bacterial surface (core polysaccharide
contains charged sugars/phosphate), stabilize outer membrane structure, creates a
permeability layer, protects pathogenic bacteria from host defenses. Contains a repeating
unit (elicits immune response), outer and inner core, and lipid A.
• Braun's lipoprotein: connects murein w/ outer membrane, most abundant.
• Porin proteins: assure permeability. Tube-shaped, water-filled channels.
• Large periplasmic space w/ hydrolytic enzymes/transport proteins.
○ Mycobacteria: complex, multilayered cell wall. Ex. Actinobacteria
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller PrinceAlixD. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.49. You're not tied to anything after your purchase.
