chapter 4 – part b: prokaryotic (bacterial) cells
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Chapter 4 – Part B: Prokaryotic (bacterial) cells. 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. General characteristics:. Parts: - PowerPoint PPT PresentationTRANSCRIPT
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