Transcript 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
Parts:
1. Cytoplasm --75% water for absorbing
heat from chemical reactions;
Dissolved and suspended molecules in the
cytoplasm
Cytoplasm
Nucleoid
2.
: 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
plasmid
Cell with plasmid and sex pilus
4.
Sex pilus:
Cell that will receive a copy of
the plasmid
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 with plasmid and sex pilus
Conjugation
5.
Ribosomes
Site of protein synthesis
70S ribosomes in bacteria
6.
Fimbriae
Hair-like extensions from cell
Also made of pilin, similar structure to sex pilus
May 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&searchTyp
e=basic&sort=Relevance&query=neisseria&gradeLevels=0
7.
Flagellum
Anchored in plasma membrane
Made of flagellin protein (also called the H antigen)
Ex. E. coli O157:H7 = strain of pathogenic E. coli
Turns like a corkscrew (does not whip back and forth)
Movement:
Runs and tumbles
More runs and fewer tumbles moving toward an attractant
-taxis = movement
chemotaxis = movement in response to chemical
phototaxis = movement in response to light
aerotaxis = in response to oxygen
magnetotaxis = in response to Earth’s magnetic field
Arrangement of flagella:
monotrichous = 1 per cell
amphitrichous = at both ends of cell
lophotrichous = tuft at one end of cell
peritrichous = covering cell
Endoflagella: flagella wrapped around cell and
covered with sheath
Found in spirochetes
Salmonella movie
Flagella
8. Cell envelope:
A. Plasma membrane:
Phospholipids and proteins
Few molecules can move through hydrophobic phospholipids
Many proteins regulate which molecules move into or out of the cell
Function:
Selectively permeable barrier
Aerobic respiration
Photosynthesis
Enzymes for cell wall synthesis
Attachment of chromosome during cell division
Excretion/secretion
Receptor sites (for recognition of molecules outside the cell)
Cell envelope
Plasma (cell) membrane
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)
Cell wall
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
C. Outer membrane (only in Gram – bacteria)
Structure like the plasma membranes
Contains proteins called porins
Contains LPS – lipopolysaccharide
Structure of LPS =
Side chain is O Antigen
Core
Lipid A (buried in hydrophobic region of
outer membrane); is an endotoxin
You don’t want to lyse all Gram negative bacteria at
once because of the danger of shock
Function: an extra barrier
Outer membrane of G- bacteria
Outer membrane of G- bacteria
D. Periplasmic space
Space between membranes and cell wall
Contains:
Binding proteins:ex.To bind glucose molecules
in environment
Degrading enzymes: ex. To degrade macromolecules
Detoxifying enzymes: ex. B-lactamase
Periplasmic space
9. Endospores
Protective structures; not reproductive structures
Sporulation = 1 cell  1 spore
Germination = 1 spore  1 cell
Spore coat resistant to extreme environmental
conditions: heat, dry, UV, chemicals, etc.
Reason that we must use an autoclave to sterilize things
Endospores
Picture of endospores from Bio 225 lab
10. Capsule
Also called glycocalyx, slime layer
Mucus-like, sticky yet slippery
Polysaccharide or polypeptide substance
Function:
Attachment, ex. Plaque on your teeth
Movement – gliding
Evasion of immune system
Protection against dehydration
Capsules
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