Lec 6: Prokaryote structures, function, and features

Question 1

explain peptidolygan and why it helps cells:

Answer 1

Peptidoglycan - confers strength and rigidity, withstanding turgor pressure. Abel to resit turgor pressure. Relatively porous, most substances pass through. Mesh-like glycan polymer of repeating NAG and NAM. losts of variation

Question 2

What is the specific difference between Gram Neg VS Gram Pos prokaryotes?

Answer 2

Gramneg - DAP at 3rd amino acid. Direct cross linkage

Gram pos - have other amino acids at third position. Interpeptide bridges

Question 3

waht does the peptidoglycan provide with crosslinking and antibiotics?

Answer 3

crosslinking involved Penicillin binding proteins (PBP)

Target for penicillin antimicrobials (Beta-lactams)
Lack of PG crosslinking prevents cell division and makes cell fragile

Question 4

waht is a nucleoid? how does it condense DNA? waht does this DNA contain?

Answer 4

Nucleoid - organized zone of DNA. not surrounded by nuclear membrane. DNA condensed by supercoiling and binding by various nucleoid proteins

Nucleotides contain about 60% DNA, 30% RNA and 10 % proteins.
Single circular dsDNA genome (potentially additional plasmids) - more dense than eukaryotes. Genes structured into operons

Question 5

what are the major structures of the prokaryotic cell?

Answer 5

nucleoid
cytoplasm
ribosomes
plasmids
pili (and flagella)
capsule
cell envelope (also called cell wall)
inner membrane
Outer membrane
periplasm

Question 6

waht do ribosomes do in prokaryotic cells? What are they made up of? why are they important?

Answer 6

Ribosomes - site of mRNA translation (protein synthesis) - 3 main structural RNA strands and 52 proteins. Cells are full of them.

Small 30S ribosomal subunit - 1 RNA and 21 proteins
Large 50S subunit - 2 RNA and 31 proteins

Its essential nature and combined structural differences between bacterial and eukaryotic ribosomes made it a target for antimicrobials. - used to only kill bacterial ribosomes, not eukaryotic ones we need.

Question 7

what are plasmids? what do they encode for?

Answer 7

Plasmids - small, mobile circular DNA. extrachromosomal DNA that replicate independently of the host chromosome that carry only non-essential but helpful genes

Shared via conjugation (HGT) in species or outside of species

Mobile genetic elements (e.g. E.coli = >300 different plasmids)

Encode many different genes - antibiotic production or resistance, virulence, metabolic functions, conjugation (able to mobilize the plasmid and transfer the information)

Question 8

waht are some examples of plasmids coding for resistance genes?

Answer 8

antibiotic resistance genes - emergence of multi-drug resistant bacterial infections (e.g. Neisseria Gonorrhoeae - plasmid borne resistance to most relevant antibiotics)

EX2: extended spectrum beta-lactamases (ESBL) and carbapenem resistant enterobacteriaceae. Several studies show healthy populations have high carriage of Entero. Containing mobile plasmids.

Question 9

waht is the capsule made of?

Answer 9

Capsule - polysaccharide layer

Question 10

waht does the cell envelope contain?

Answer 10

Capsule layer

S-layer - protein layer

Outer membrane (Gram -)

Peptidoglycan

Periplasm - space between outer and inner membrane

Inner membrane - ALL OF THEM HAVE THIS

Question 11

What do cell envelopes help do?

Answer 11

shape and protection from osmotic stress

Question 12

waht are the two different types of cell envelopes? briefly explain each

Answer 12

Grap-postiive - cytoplasmic membrane - thick multilayer polysaccharide linked peptidoglycan. PG linked teichoic acids and membrane

Gram - negative - thin 1-2 layers of peptidoglycan. Outer membrane with outer leaflet composed of lipopolysaccharide (LPS). enclosed periplasm. OM anchored to peptidoglycan by Lipoproteins

Question 13

waht is the inner membrane? briefly define it and what it contains:

Answer 13

Inner membrane - selectively permeable barrier AKA plasma membrane, cytoplasmic membrane. Core respiration and synthesis of lipids and cell wall component

Phospholipid bilayer
Integral proteins
Peripheral proteins -
Lipoprotein

Question 14

Waht are the intregral proteins in the inner membrane?

Answer 14

Integral proteins - hydrophobic middle and hydrophilic ends (most common)

Question 15

What are the peripheral proteins in the inner membrane?

Answer 15

Peripheral proteins - loosely attached to inner or outer surface of membrane or other integral proteins

Question 16

What are the Lipoproteins in the inner membrane?

Answer 16

Lipoprotein - anchored into membrane by covalently attached lipids

Question 17

what kind of transport is possible through the inner membrane

Answer 17

Passive diffusion (membrane transport) - simple diffusion through phospholipid bilayer. Small uncharged molecules (e.g. O, CO2, water)

Facilitated diffusion - membrane protein selective for one type of molecule. No energy required (e.g. glucose, Na+, and Cl-) can be size or shape of necessary molecules

Active transport - move solutes against concentration gradients. Uses energy.

Question 18

what kinds of transporters help active trnasport thorugh the inner membrane?

Answer 18

Primary active transport (ATPase) - hydrolyze ATP to transport solutes (e.g. heavy metal efflux in bacteria)

ABC transporters - 2 ATP per cycle, external soluble substrate binding protein. Able to transport more complex molecules (sugars, amino acids, etc.)

Secondary active transport - transport of one molecule linked to import/export of secondary molecules. The concentration gradient of B is driven by the primary active transporter by H+ gradients from ETC and proton pumps. B is typically H+

Question 19

waht are the three types of secondary active transporters?

Answer 19

Antiporter - A goes in B goes out
Symporter - A goes in and B goes in
Uniporter - A goes in, A goes out

Question 20

Explain the outer membrane of prokaryotic cells:

Answer 20

Outer membrane - lipid membrane Lipid Polysaccharide. only present in Gram negatives. Asymmetric lipid bilayer (inner leaflet is phospholipid. Outer leaflet is glycolipid).

Question 21

How is the outer membrane LPS divided? How does this contribute?

Answer 21

Lipid polysaccharide (LPS) is divided into polysaccharide, core oligosaccharide, then lipid A. called endotoxin as it is highly inflammatory to the immune system.

Contributes to the negative charge of the cell surface. Stabilises OM, allows surface attachment. Forms permeability barrier (to bile salts and antibiotics). Allows protection from host defences (e.g. variable O-antigens)

Question 22

waht is Lipid A?

Answer 22

Lipid A - phosphorylates glucosamine disaccharide with multiple fatty acid tails. Main immune stimulating part

Question 23

waht is the core oligosaccharide of the LPS?

Answer 23

Core - highly variable sequence even in species; gram negative. sugars linked to lipid A and O-antigen. crucial for outer membrane structural integrity

Question 24

waht is O-antigen

Answer 24

O-antigen - outermost part, very variable, common for serotyping strains (e.g. e. coli)

Question 25

explain what is inside the outer membrane:

Answer 25

lipoproteins attached by lipid anchor - most abundant is LPP anchoring PG to OM. Integral OM proteins are different IM proteins. - have hydrophobic middles and hydrophilic ends with Beta-barrels. Beta-barrels - largest family is porins. - allow diffusion of small molecules.

Question 26

explain Beta-barrels and their porins:

Answer 26

Beta-barrels - largest family is porins. - allow diffusion of small molecules. Porins can be non-selective, charge selective, and substrate selective. Passive transport and abundance of porins makes outer membrane more permeable than inner membrane (more like a giant sieve)

Question 27

what is particular about the outer membrane's coupling ability?

Answer 27

OM has no access to ATP or PMF. Active transport through OM is physically coupled to the IM protein complex to avoid ATP leaving the cell. Efflux pumps - pump out antibiotics, heavy metals, bile acids, etc.

Question 28

what is the periplasm:

Answer 28

Periplasm - space between IM and OM containing PG. constitutes of 40% of cell volume. Encloses soluble and membrane associated proteins - e.g. enzymes and chaperones.

Question 29

What does the periplasm do?

Answer 29

Acts as pH and osmolality equilibrium with the external environment. Gel-like matrix (osmoregulated periplasmic glucans) - ring of polysaccharides. Likely acts towards macromolecular crowding - allows for many things to pack together in cells. Structural function

Question 30

what is a structural difference between bacteria, archaea, and eurkaryotic cells?

Answer 30

Cytoplasmic membrane: Bacteria have ester bond links and unbranched fatty acid lipids with D-glycerols Archaea - ETHER bond links branched isoprene lipids to L-glycerol. Linked to span entire membrane, through to aid archaea survival in highly acidic habitat (hyperthermophiles too)