Lecture 4 Flashcards
Where in the cell envelope would you find
Hopanoids?
Porins?
D-Alanine and D-Glutamic acid?
- Cell membrane
- Outer membrane
- Link peptidoglycan
THE NUCLEOID
Where genetic content is stored
Eukaryotic cells have a well-defined nucleus delimited by a ____
Nuclear membrane
Prokaryotic cells have a ______ region that extends throughout the cytoplasm
Nucleoid
[pic]
DNA IS ORGANIZED IN THE NUCLEOID
The E. coli nucleoid appears as clear regions that exclude the ribosome and contain the DNA strands
[pic]
The nucleiod forms about ____
50 loops or domains
The midpoint on the DNA is the ____
origin of replication
• Attached to the cell envelope at a point on the cell’s equator
Within each domain, the DNA is supercoiled and compacted by_____ and ______
gyrases & DNA-binding proteins
[PIC]
TRANSCRIPTION AND TRANSLATION
In prokaryotes happen together
-RNA polymerase transcribes DNA into a single strand of RNA
-mRNA immediately binds to a ribosome for translation into a polypeptide
-In prokaryotes, translation is tightly coupled to translation
[pic]
THE RIBOSOME IS A TARGET FOR ANITBIOTICS
[pic has important info]
PROTEIN SYNTHESIS AND SECRETION
Multiple proteins are made from the same
mRNA
In prokaryotes, membrane proteins and secreted proteins are synthesized in association with the cell membrane
• Aided by the signal recognition particle (SRP), which binds to the growing peptide
[PIC]
CELL DIVISION
Bacterial cell division, or fission \_\_\_
requires highly coordinated growth and expansion of all the cell’s parts
- doing all these things at the same time
- transl and transc.
Unlike eukaryotes, prokaryotes synthesize ___ and ____ continually while the cell’s DNA undergoes replication
RNA
Proteins
Bacterial DNA replication
is coordinated with the expansion of the cell wall and ultimately the separation of the cell into two daughter cells
Replication begins at the ___
origin of replication
The DNA double helix unzips and forms two replication forks
At each fork DNA is synthesized by DNA polymerase with the help of accessory proteins (replisome)
As the ______ site is replicated, the two replisomes separate from the DNA
Termination
[pic]
VIDEO
[PIC]
SEPARATION COMPLETES CELL DIVISION
Replication of DNA termination site triggers ___
Growth of the dividing partition of the envelope, Called the Septum
The septum grows __ from the sides of the cells, constricting and sealing off the two daughter cells
Inward
SEPTATION IN COCCI
The spatial orientation of septation has a key role in determining the \_\_\_\_ and \_\_\_\_\_\_ of cocci
Shape & arrangement
If septation occurs in:
• Parallel planes – cells form chains (Streptococcus)
• Random orientations – cells form compact hexagonal arrays (Staphylococcus)
• Right angles to the previous division – cells form tetrads and cubical octads (sarcinae)
[pic]
CELL POLARITY AND AGING
Bacterial cell poles (ends of bacteria) differ in their origin and age a phenomenon called \_\_\_\_
Polar aging
The process of ______ generates daughter cells with chemically different poles
Cell division
“Old” poles continue to age; cell wall material degrades slightly, increasing ____
Chance of cell lysis (disintegration of a cell by rupture of the cell wall/ membrane
Cells with different _______ may differ in the resistance to antibiotics
Polar ages
[pic]
SPECIALIZED STRUCTURES
(PHOTOTROPHS)
Thylakoids
Extensively folded intracellular membrane
• Consists of layers of folded sheets (lamellae) or tubes of
membranes packed with chlorophyls (cells that do photosynthesis) and electron carriers
Carboxysomes
polyhedral bodies packed with the enzyme Rubisco for CO2 fixation
Gas vesicles
to increase buoyancy
[pic]
SPECIALIZED STRUCTURES
Storage granules
- Glycogen, PHB, and PHA for energy
* can store Sulfur, for oxidation
Magnetosomes
- Membrane-embedded crystals of magnetite, Fe3O4
* Orient the swimming of magnetotactic bacteria
Pili
or fimbriae – straight filaments of pilin protein
• Used in attachment
Sex pili
used in conjugation
Stalks
membrane- embedded extensions of the cytoplasm
• Tips secrete adhesion factors called holdfasts
Nanotubes
intercellular connections that pass material from one cell to the next
[pic]
SPECIALIZED STRUCTURES- FLAGELLA
Many bacteria and archaea can swim by means of ________
Rotary flagella
Peritrichous cells (e.g. E. coli, Salmonella)
have flagella randomly distributed around the cell
• Flagella rotate together in a bundle behind the swimming cell
Lophotrichous cells (e.g. Rhodospirillum rubrum)
have flagella attached at one or both ends
Monotrichous cells (e.g. Caulobacter swarmer)
have a single flagellum on one end
Each flagellum is a spiral filament of protein monomers called ______
Flagellin (FliC)
Filament rotates by means of a motor driven by the ___
Proton motive force
Flagella either rotate clockwise (CW) or counterclockwise (CCW) relative to the _____
Cell
[pic]
CHEMOTAXIS
Is the movement of bacterium in response to a chemical gradient
Attractants cause CCW rotation
- Flagella bundle together • Push cell forward
* “Run”
Repellants cause CW rotation
• Flagella bundle falls apart
• “Tumble”
• Bacterium briefly stops, then changes direction
[pic]
The alternating runs and tumbles cause a ______
“Random walk”
Receptors detect attractant concentrations
Sugars, amino acids
Attractant concentration increases and prolongs run
• Termed a “biased random walk”
• Causes a net movement of bacteria toward attractants (or away from repellants)
[pic]
ARCHAEAL CELL STRUCTURE AND FUNCTION ( archaeal aren’t pathogens)
Archaea are the most \_\_\_\_\_\_ diverse of the three domains
Ecological
Extremophiles
Psychrophiles, hyperthermophiles, halophiles, acidophiles, methanogens
Archaea are also abundant in moderate habitats
Open ocean, soil, and surface of plant roots
Surprisingly, the archaeal domain lacks ______
Pathogens
[pic]
DISTINCT ARCHAEAL TRAITS
[important pic with info]
ARCHAEAL CELL MEMBRANE
Depending at where they are living
• Use L-glycerol instead of D- glycerol • Ether linkages instead of ester *More stable; requires more energy to break • Isoprenoid chains * Branched at every 4th carbon
Cross linked lipids
Ends of side chains linked covalently to form a tetraether
Cyclopentane rings
Strengthen membrane at high temperatures
[PIC]
ARCHAEAL S-LAYER AND CELL WALL
Most archaea possess a _______ membrane without any outer membrane
Single
Many also do not have a cell wall, but only an S-layer of proteins plugged into the ______
Tetraether membrane
Some do have a cell wall composed of _____ or ______
Pseudomurein Or pseudopeptidoglycan
• Instead of N-acetylmuramic acid have N-acetyltalosaminuronic acid and beta(1,3) linkage
[pic]
ARCHAEAL GENOMES
Similarities to bacteria
- Circular genome
- Gene size and density
- Has operon
Similarities to eukaryotes
- RNA polymerase has TBP (tata binding proteins), TFB (transcription factor B)
- Has proteins similar to histones
Unique
• Some have reverse gyrases
• Guanosine analog archaeosine
[PIC]
THE BACTERIAL CELL
[PIC]
