Lecture 3 Flashcards
REVIEW FROM LAST TIME
What piece of lab equipment in Louis Pasteur’s experiment that discovered spontaneous generation?
Swan neck flask
What was the first use of the word vaccination ?
Cowpox to vaccinate for small pox
Cowpox inoculation
INTRODUCTION
Most bacteria share these traits
- Thick, complex outer envelope
- protects the cell, but also mediates exchange with it’s environment
- Compact genome
- Tightly coordinated functions
- Efficiency ; enable high rate of reproduction
What are Archaea?
Like bacteria , they are prokaryotes
- they have a unique membrane and envelope structure
What do eukar. Cells have?
Extensive membrane organelles
MODEL OF A BACTERIAL CELL
Cytoplasm
Gel-like network composed of proteins and other macromolecules
It has ribosomes, so all the translations are happening here
Cell Membrane
Encloses the cytoplasm
Cell wall
Covers the cell membrane
Nucleiod
Non-membrane bound area of the cytoplasm that has the chromosome in the form of looped coils
All genetic info is shared here
Flagellum
External helical filament whose rotary motor propels the cell
[see pic]
[se pic]
What is the cell made up of ?
Water
Proteins
RNA —> rRNA , tRNA, sRNA, mRNA
Lipids—> phospholipids (membrane), lipopolysaccharides (outer membrane)
DNA —> metabolites & biosynthetic precursors, peptidoglycan, inorganic ions, polyamines
CELL MEMBRANE
The structure that defines the existence of the cells
[pic]
What’s the cell membrane made of?
Lipid bilayer
*Double layer of phospholipids
The cell membrane separates?
The cytoplasm from the outside world
Proteins embedded in membrane
- Anchor membrane to envelope
- Sense the outside world
- Transport materials into the cell
Functions of the cell membrane
Mechanical boundary Selective permeable Able to transport nutrients/ waste Site for electron transport chain - respiration - Photosynthesis Involved in lipid synthesis Contain (“sensing” ) receptor protiens
Most membrane proteins ( ~80%)…
Are integral, the rest are peripheral
Polar end
Charged phosphoryl head is hydrophilic ( water loving)
Non-polar end
Fatty acid is hydrophobic ( water hating)
How are the ends connected>
Through a glycerol derivate via ester linkages
[pic]
Ester bonds
Link fatty acids to glycerol backbone in bacteria and eukarya to make plasma membrane lipids
Formation of ester bonds in the synthesis of lipids
[pic]
The cell membrane is a phospholipid bilayer
-The tails face each other- keeps hydrophobic side chains away from water
-the two two layers of phospholipids are called leaflets
[pic]
Phospholipids vary with respect to their fatty acid side chains
.
Chain length of phos.
Between 6 and 22 carbons
Some are partially unsaturated
Contain double bonds
- most unsaturated bonds are cis-both chains on the same side of the bond- cause a “kink”
- some include cyclized carbon rings
FLUID MOSAIC MODEL OF MEMBRANE
Proteins float in 2-D “sea” of phospholipids
So… membrane fluidity is required for proper function of the cell
MEMBRANE FLUIDITY IS AFFECTED BY LIPID COMPOSITION
Increase membrane fluidity
- Use lipid molecules with shorter chain lengths
- ‘’ ‘’. ‘’ That have more double bonds (unsaturation) in the lipid chains- add ‘’kinks’’
Kinks add some space to it and increase fluidity
Decrease membrane fluidity (increase rigidity)
Use lipid molecules with longer chain lengths ( Van der Waals)
“ “ “ “ Fewer double bonds
“ Molecules that hinder movement of phospholipids
- stiff planar rings
- reinforcing agents
-sterols (e.g) cholesterol
*Eukaryotes
Hapanoids
-add strength to membranes
-Structurally similar to steroids
-Prokaryotes
[pic]
When would a cell need to have increased membrane fluidity ?
The temp. If cell is in hotter environment, you’d want to increase
When would a cell need to have deceased membrane fluidity?
When it’s cold, because they will freeze
Bacteria would adapt to increasing temp by?
- Increasing the # of long chain lipids
2. Decreasing the # of double bonds
MEMBRANE COMPONENTS- MEMBRANE PROTEINS
Membrane proteins serve numerous functions including:
Structural support
Detection of environmental signals
Secretion of virulence factors and communication signals
Ion transport and energy storage
Proteins form about _______ the mass of the membrane
Half
Membrane proteins have ________ and ____ regions
Hydrophilic and hydrophobic
“Lock” the protein in the membrane
[pic]
TRANSPORT ACROSS THE CELL MEMBRANE
The cell membrane acts as a \_\_\_\_\_\_
Semipermeable barrier
Selective transport is essential for ____
Survival
Small uncharged molecules such as _____ and _____ , easily permeate the membrane by ______ _______
O2
CO2
Passive diffusion
Water tends to diffuse across the membrane in a process called _____
Osmosis
Some weak ____ and weak ____ can cross the membrane
Acids
Bases
TRANSPORT ACROSS THE CELL MEMBRANE
Transporters
Pass material into and out of cell
____ and ____ molecules require transport through specific transporters
Polar & charged
Passive transport
Molecules move along their concentration gradient
Active transport
Molecules move against their concentration gradient
*requires energy
[pic]
THE CELL WALL AND OUTER LAYERS
How do prokaryotes protect their cell membrane?
.
For most species, the cel env. Includes at least ____ structural supporting layer
One
The most common structural layer is the ______
Cell wall
Many species possess additional coverings such as an ______ _______ or _____
Outer membrane
S-layer. (Which is extra protection)
A few prokaryotes, such as the _______, have a cell membrane with o outer layers
Mycoplasmas
THE CELL WALL IS A SINGLE MOLECULE
Bacteria cell (sacculus) consists of a single interlinked molecule that \_\_\_\_\_\_\_\_
Envelopes the cell
The cell wall forms a cage like structure, that’s highly ____ to ions and organic molecules
Porous
Cell wall confers shape and helps _____
Withstand intracellular turgor pressure
MOST BACTERIAL CELL WALLS ARE COMPOSED OF PEPTIDOGLYCAN (MUREIN)
.
Consists of parallel polymers of disaccharides called ______ cross-linked with peptides of 4 amino acids
Glycan chains
Long polymers of two disaccharides: ____ ( NAG) and ____ (NAM)
N- acetylglucosamine
N-acetylmuramic acid
The peptides can form cross-bridges connecting the parallel _____
Glycan strands
Peptides contains two amino acids in the unusual D form:
D-glutamic acid &. D-alanine
3rd amino acid , ______ , has an extra amine group, which forms an modeling to a cross-bridged peptide
m-diaminopimelic acid
PEPTIDOGLYCAN STRUCTURE
[PIC]
Peptidoglycan
is unique to bacteria
The enzymes responsible for its biosynthesis make
excellent targets for _____
Antibiotics
Penicillin
inhibits the transpeptidase that cross-links the peptides
Vancomycin
prevents cross-bridge formation by binding to the terminal D-Ala-D-Ala dipeptide
Unfortunately widespread use of such antibiotics selects for evolution of ______
resistant strains
So bacteria has evolved to have Beta-lactamase which __
cleaves the lactam ring of penicillin making it inactive
Peptidoglycan structure
[pic]
CELL MEMBRANE OF BACTERIA
Most bacteria have additional envelope layers that provide structural support and protection
There are three major kinds
Three major kinds
- Gram-positive – thick cell wall (e.g. firmicutes)
- Gram-negative – thin cell wall (e.g. proteobacteria)
- Mycobacteria – complex multilayered envelope that includes defensive structures such as mycolic acids (e.g. Mycobacterium tuberculosis)
GRAM-POSITIVE CELL ENVELOPE
S-layer
Made of protein (contains large pores)
-it can let things in and out
[pic]
Thick cell wall
• 3-20 layers of peptidoglycan
• Interpenetrated by teichoic acids for strength
[pic]
[pic]
Cell membrane
[pic]
GRAM-NEGATIVE CELL ENVELOPE
Outer membrane
• Covers peptidoglycan layer
• Confers defensive abilities and toxigenic properties on many pathogens
[pic]
Thin peptidoglycan layer
1-2 sheets
[pic]
Periplasm
area between membranes
[pic]
Inward facing leaflet of OM
Includes lipoproteins that connect the OM to the peptide bridges of cell wall
Outward facing leaflet of OM
- Includes lipopolysaccharide (LPS)
* LPS acts as an endotoxin
OM proteins
Class of transporters called porins that permit entry of nutrients such as sugars and peptides
[pic]
MYCOBACTERIAL CELL ENVELOPE
Examples ;
M. tuberculosis and M. leprae
Exceptionally complex envelopes
• Includes features from both gram-positive and gram- negative
Unusual membrane lipids –
mycolic acids
Unusual sugars -
arabinogalactans
[pic]
MEMBRANE COMPONENTS - MEMBRANE LIPIDS
Membranes
Most membrane lipids are phospholipids
Phospholipids
Are amphipathic - have a polar and a nonpolar end
