Microbiology ( lecture 3)

why cytoplasmic membrane proteins might be more abundant in

prokaryotes than eukaryotes?

• Prokaryotes pack more proteins into their cytoplasmic membrane because they completely lack internal membrane - bound organelles ( The outer membrane has to do all the work (ATP generation)

Summarize the common chemical characteristics of all cytoplasmic membranes. How

are the cytoplasmic membranes of Bacteria and Archaea similar and different to each

other?

• All cell membranes share an amphipathic Lopid framework that forms a selective barrier( Vacteria and Archea use completely different chemical connections

• Commo characteristic (What all membrane share)

→ Hydrophilic heads face outside ( amphipathic lipids) ( water loving)

→ Hydrophobic tails face inside ( water fearing)

→ Fluid mosaic : ipids and proteins drift around laterally

→ Selective permeability : block large or charged molecules , less small ones pass

• How Bacteria and Archaea differ

→ Bacteria features:

→ Chemical bond: uses Ester link (weak)

→ Hydrocarbon tails: Straight fatty acids

→ Layer structure : Always forms a double layer (bilayer)

→Environment: Moderate conditions

Features: Archaea

→ Chemical bond : Uses Ether links are ultra stable

→ Hydrocarbon tails: Branched isoprenoids

→ layer structure: Can form a monolayer

→ Environment: Extreme heat/ acid

List three roles of the bacterial cytoplasmic membrane

• The bacterial cytoplasmic membrane acts as a dynamic multitasking surface rather than just a passive wall

• The permeability Barrier: controls what enter and exits

• Protein Anchor: hold transport

• Energy conservation: Generates power (ATP) for cells

Detail the steps for making a peptidoglycan cell well.

1. synthesis precursors: NAG abd NAM monomers are made in cytoplasm

2. form dissarcharides: Cells links G and M together

3. Attach peptides; 4 amino acids chain added to NAM

4. Export monomers; Transported out of the cytoplasm

5. form sheets: process repeat to build long sheets

6. Cross link layer : Transpeptidase enzyme connects them for strength

How are molecules transported across the outer membrane? What are some molecules

that should go across, and what are some that shouldn’t and why. What about transport

across the cell wall? Are there molecules that would not cross the cell wall?

• How are molecules transported across the outer membrane?

→ Through proteins holes called porins

→ allowed small nutrients under 500 daltons (water, sugar)

→ Blocked: large molecules over 500 daltons ( too big)

• What are some molecules

that should go across, and what are some that shouldn’t and why.

→ should cross (under 500 daltons)

→ example, water ions and simple sugar

→ why: they are small enough to slip right through the narrow porins channels

Should not cross (over 5000 daltons)

→ Example : Huge proteins, large starches

→ why : they are physically too big to fit inside the small porin tube

What about transport

across the cell wall? Are there molecules that would not cross the cell wall?

→The cell wall acts like a loose chain link fence

→ Small molecules float right through it. It allows items up to 90,000 daltons inside. Giant molecules are completely blocked from passing. they are too bulky to fit through the gaps

Describe how acid-fast bacteria withstand detergents.

acid fast bacteria have a waxy cell wall

• Made of greasy mycotic acid

• Acts like waterproof shield

• Repels water based detergents

• Chemical cannot get inside

Detail what happens when a bacterial cell is treated with a beta lactam antibiotic (such

as penicillin) or lysozyme. Does it matter if the cells are growing or not? What would

change if the cells were gram positive or gram negative?

• Detail what happens when a bacterial cell is treated with a beta lactam antibiotic (such as penicillin) or lysozyme.

→Beta lactam (Penicillin)

→It stops the cell from building its wall

→ The wall becomes weak and thin

→ water rushes inside and the cell bursts

→ it only works on growing cells that are building

• Lyzosyme

→ it physical cuts the existing sugar bonds

→ the wall falls apart immediately

→Water rushes inside and the cell bursts

→it works on all cells whether growing or resting

Does it matter if the cells are growing or not?

→ Yes, growth matters for peniilan but no for lyzosyme

→Penicillin: needs growing cells, it only works when cells are actively building walls

→Lysozyme: Needs any cells. it cuts down pre-existing walls, so it kills resting cells too.

• What would change if the cells were gram positive or gram negative?

→Gram positive cells:

→They have no outer membrane shield

→ both drugs hit the cell wall directly

These cells are very easy to kill

Gram negative cells:

→they have a protective outer membrane

→this membrane physically blocks lysozyme and penicillin

→these cells are naturally protected and harder to kill

Would a molecule 2000 daltons in size have an easier time getting through mycolic acid

layer, outer membrane or cell wall?

• A 2000 Dalton molecule cross the cell wall easiest

→ The cell wall limit is 90,000 daltons

→ a 200 dalton molecule slips right through

→ The outer membrane limit is 500 daltons

→ it blocks a 2000 dalton molecules completely

→ the mycologic acid layer is too waxy

→it blocks large molecules from entering

Describe how the Gram stain can be used to diagnose bacterial meningitis.

• The Gram stain provides a rapid visual identification of the specific bacteria causing meningitis infections

→ detectors collect a spinal fluid sample first

→ they put the sample on a glass slide

→ they run a quick Gram stain test

→The stain colors the hidden bacteria cells

→ doctors look at it under a microscope

→ they intactly see the bacterial shape and color

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THe 3 cell types ( wall shields)

• Gram positive

→ Layer: Thick wall, stains purple

→ Stain color : purple

• Gram negative:

→Layer: inner + thin cell wall+ outer membrane

→ stain color : Pink /red

→ LPS : Lipoplysaccharide

→ Gram shield rule: bacteria need more lysozyme to burst

• Acid-fast

→ Thick, waxy mycotic acid layer, stains red

How antibiotics destroy walls

• Lysozyme: cops up existing sugar bonds, kills all cells

• Penicillin (B- lactam) blocks enzymes from building wall cross links

• Vancomycin: Caps peptide ends to block

Size Gates (daltons)

• Outer membrane (porins): tiny openings only <500 daltons pass

• Cell wall (fence) ; Loose , up to 90,000 daltons pass

• Inner membrane: no size limits, Required active energy pumps

Capsules & slime

Capsule: organized shield, stops white blood cells from eating them

Membranes & Stability

The basics

• Shared features: Both Bacteria and Archaea have cytoplasm and a lipid bilayer

• Heads: hydrophilic ( likes water)

• Tails: Hydrophobic ( hates wate)

Bacteria vs Archaea

• Bacteria: uses Ester linkages to hold lipids

• Archaea: uses Ether linkages ( stronger/ more stable)

• Archaea extra: Has branched lipids and can form a monolayer to survive extreme heat

Fluidity control

• Prokaryotes: Use Hopanoids for stability

• Eukaryotes: Use cholesterol for stability

The cell wall & Peptidogylycan

• How it built

→ 1. NAG & NAM made in cytoplasm

→ 2. Forms a G-M unit

→ 3. 4 Mino acid teal hooks to NAM

→ 4. Move out of the cell

→ 5. Tied together by enzymes

• Transglycosylase: Links sugar horizontally

• Transpeptidase: Links peptides vertically

• Attacks & defense

→ Lysozyme ( saliva) : cleaves existing G-M sugar bonds

→ Penicillin: Block the transpeptidase enzyme active site

→ Vancomycin: Caps the peptide tail so the enzyme can’t touch it

Mycolic acids, Capsules & Transport

• Mycolic acid (waxy layer)

Bacteria: found in Mycobacterium

• Size limits (what can pass)

→ Porins ( outer membrane) : passive holds. Only fits things < 500 daltons

→ Cell wall: loose, fits large things up to 90,000 daltons

→ Inner membrane: locked tight