Chapter 4 – Part B: Prokaryotic (bacterial) cells

Chapter 4 – Part B: Prokaryotic

(bacterial) cells

General characteristics:Prokaryote = bacteria

Cells are smaller than eukaryotes, less

organized, no membrane-bound organelles

All molecules in these cells are in close

contact with one another

Cytoplasm

Parts:

1. Cytoplasm --75% water for absorbing heat from chemical reactions;Dissolved and suspended molecules in the cytoplasm

2. Nucleoid: Region where DNA is found (does not have a membrane around it!); DNA is 1 circular chromosome.

3. Plasmids: Extrachromosomal DNA Cell may have one copy or many Extra genes code for new traits, such as antibiotic resistance or production of toxin Passed to another cell by way of the sex pilus

4. Sex pilus: 1 or 2 per cell containing plasmid(s) Long, hollow tube for transfer of a copy of a plasmid Transfer can happen between different species (highly

unusual in nature) Made of protein called pilin

Cell with plasmid and sex pilus Cell that will receive a copy of the plasmid

plasmid

Conjugation

Cell with plasmid and sex pilus Cell with plasmid and sex pilus

5. RibosomesSite of protein synthesis70S ribosomes in bacteria

6. FimbriaeHair-like extensions from cellAlso made of pilin, similar structure to sex pilusMay have several or may cover the cell Important for attachment Ex. Neisseria gonorrhoeae infects urogenital tract by attaching to tissues there

Image from: http://www.biosciednet.org/portal/search/searchResults.php?pageNumber=1&searchType=basic&sort=Relevance&pageNumber=1&searchType=basic&sort=Relevance&query=neisseria&gradeLevels=0

7. FlagellumAnchored in plasma membraneMade of flagellin protein (also called the H antigen)Ex. E. coli O157:H7 = strain of pathogenic E. coliTurns like a corkscrew (does not whip back and forth)Movement:

Runs and tumblesMore runs and fewer tumbles moving toward an attractant-taxis = movement

chemotaxis = movement in response to chemicalphototaxis = movement in response to lightaerotaxis = in response to oxygenmagnetotaxis = in response to Earth’s magnetic field

Arrangement of flagella:monotrichous = 1 per cell

amphitrichous = at both ends of celllophotrichous = tuft at one end of cellperitrichous = covering cell

 Endoflagella: flagella wrapped around cell and

covered with sheath Found in spirochetes

Flagella

Salmonella movie

Cell envelope

8. Cell envelope:A. Plasma membrane:Phospholipids and proteinsFew molecules can move through hydrophobic phospholipidsMany proteins regulate which molecules move into or out of the cellFunction:Selectively permeable barrierAerobic respirationPhotosynthesisEnzymes for cell wall synthesisAttachment of chromosome during cell divisionExcretion/secretionReceptor sites (for recognition of molecules outside the cell)

Plasma (cell) membrane

Cell wall

B. Cell wall:Peptidoglycan

…NAG – NAM – NAG – NAM… aa aa aa aa------aa

aa aa aa

…NAM – NAG – NAM – NAG… aa aa aa aa------aa

aa aa aa

…NAG – NAM – NAG – NAM…

(NAG and NAM molecules are sugars; aa = amino acids)

Peptidoglycan of cell walls

Lysozyme breaks the bonds between the NAG and NAM sugars

Penicillin prevents the crossbridges between aa chains from forming

Penicillin is only effective in actively growing cells

Gram + cell wall can be 40 layers thick; G – is 1 or 2 layers thick

Functions: strength, support, shape

Cells without cell walls:

◦ L-forms: bacteria that have lost their cell walls, many different species can do this

◦ Mycoplasmas

Peptidoglycan determines cell shape

Outer membrane of G- bacteria

C. Outer membrane (only in Gram – bacteria)Structure like the plasma membranesContains proteins called porinsContains LPS – lipopolysaccharideStructure of LPS =Side chain is O AntigenCoreLipid A (buried in hydrophobic region of outer membrane); is an endotoxinYou don’t want to lyse all Gram negative bacteria at once because of the danger of shockFunction: an extra barrier

Outer membrane of G- bacteria

Periplasmic space

D. Periplasmic spaceSpace between membranes and cell wallContains:

Binding proteins:ex.To bind glucose molecules in environment

Degrading enzymes: ex. To degrade macromoleculesDetoxifying enzymes: ex. B-lactamase

Endospores

9. EndosporesProtective structures; not reproductive structuresSporulation = 1 cell 1 sporeGermination = 1 spore 1 cellSpore coat resistant to extreme environmental

conditions: heat, dry, UV, chemicals, etc.Reason that we must use an autoclave to sterilize

things

Picture of endospores from Bio 225 lab

Capsules

10. CapsuleAlso called glycocalyx, slime layerMucus-like, sticky yet slipperyPolysaccharide or polypeptide substanceFunction:

Attachment, ex. Plaque on your teethMovement – glidingEvasion of immune systemProtection against dehydration

This is a photomicrograph of Streptococcus pneumoniae bacteria having been grown from a blood culture. Streptococcus pneumoniae, the bacteria responsible for pneumococcal meningitis, is very common, and normally lives in the back of the nose and throat, or the upper respiratory tract. http://phil.cdc.gov/phil/details.asp

Photomicrograph of Streptococcus pneumoniae bacteria revealing capsular swelling using the Neufeld-Quellung test. This organism causes respiratory infections such as pneumonia and sinusitis, as well as bacteremia, otitis media, meningitis, peritonitis and arthritis. The Neufeld-Quellung test is used in pneumococcus typing. http://phil.cdc.gov/phil/details.asp

The End