Biology- Lecture 8- Prokaryotic Cell

The cell theory 

• All organisms made out of cells

• cells are fundamental units of life

• all living organisms are composed of cells

• all cells come from preexisting cells

• cells evolved from a common ancestral cells.

Prokaryotes

Bacteria and Archaea

• they are incomplete with no nucleus

• uni and multicellular

• no membrane enclosed subcellular compartments

  • some exceptions: enclose certain molecules that are not dissolvable- hydrophobic, single layer membrane

• genetic information

Cell size

Limited by the surface area to volume ratio

• prokaryotic cell: 1-10 um

• Eukaryotic cell: 5-100 um

Surface area increases by exponent 2, increases with diameter

Volume increases by exponent 3, increases when diameter increases. If volume doesn’t increase fast, delivering in and out of cell would have issues.

You need space to fit everything in the cell which limits small size of the cell

Microscopy

the scientific approach to study cells

• some based on light that bends, 3D picture, and focus on level within the cell

Eukaryotic cell

Protists, plants, fungi, animals

• membrane- enclosed sub cellular compartments (organelles)

  • nucleus, mitochondria, chloroplasts 

bacteria v archaea

Archaea:

• extreme environments

• able to tolerate extreme conditions such as low pH and high heat (higher motion of molecules)

• celll wall: not peptidoglycan (vary cell wall)

• membrane lipids: ether linked, branched, L- glycerol

• ribosome: eukaryotic like 

• tRNA: eukaryotic like, coming from “house cells”

Bacteria: 

• cell wall: peptidoglycan in cell wall

• membrane lipids: ester linked (fatty acid), unbranched, D-glycerol

• Ribosome: bacteria like, more similar to ribosomes In mitochondria (endosymbiotic theory- mitochondria used to be bacteria)

• tRNA: bacteria like

cell shape and cell arrangements for bacteria

Shapes: 

• coccus- spherical shape and round

• bacillus- longer shape/tube like

• spirillum- helical shape, spaced out waves

• spirochete- very tight waves

Structures: 

• streptococcus- ball like chain structure

• streptobacillus- tubular chain structure

• staphylococcus- random arrangement with round shape, like grapes

Prokaryotic Cell structure

• DNA not enclosed by membrane, it is found in nucleoid since there is no nucleus

  • NAPs= in prokaryotes, nucleoid associated proteins

  • Histones- proteins related to DNA

  • Histones and NAPs allow for structure, expression, and for DNA to be dynamic 

• polysaccharide layer covers surfaces on outside of the cell and hides proteins that are exposed which makes them hard to detect 

• cell wall- made of peptidoglycan,   and outer membrane

Gram negative bacterium

Staining procedure: gram stain requires 2 dyes (dark purple, light pink), identifies positive and negative cells, differs in thickness 

Transcription, translation, and protein secretion

all coupled in prokaryotic cells because there Is no nucleus

• DNA info is rewritten into mRNA, the enzyme RNA polymerase catalyzes this (reads the DNA)

• DNA portions not being used are in condensed form, DNA can condense/de-condense and have lots of proteins involved

bacteria cell wall

peptidoglycan- is a polymer of a disaccharide (glycan) cross-linked by amino acids (peptides). Structures of carbohydrates

Bacteria cell wall- Gram positive and gram negative bacteria

Gram positive bacteria:

• thick peptidoglycan layer- longer

• plasma membrane, penicillin will be more affective on gram positive

• dark purple in gram stain (due to thickness)

  • staphylococcus

  • streotomyces

Gram negative bacteria:

• thin peptidoglycan layer- quicker 

• plasma membrane (inner membrane)

• outer membrane

• light pink in gram stain

  • e. coli

  • salmonella

• lipopolysaccharides: lipids with long chains of sugars, prevent access to membrane and peptidoglycan 

plasma membrane

• Selective barrier enclosing

• intracellular space controls transport in and out of the cell

• glycoproteins and glycolipids on the extracellular side

• compositions vary across different species

• very busy with lots of traffic which makes them very dynamic

• plasma membrane can restructure

cyanobacteria

first photosynthetic bacteria that produced oxygen

• oxygen producing=oxygenic photosynthesis

• membrane inside photosynthesis bacteria resulted from invagination of plasma membrane; efficient photosynthesis, take organic molecules and makes organic molecules

• membranes= invagination of plasma membrane, it is still connected with outer membrane, but more membrane= higher protein= higher efficiency

flagella

made of protein flagellin- allows them to propel forwards, and assemble in hollow structure

• movement: flagellum rotates

• energy: proton motive force which is how they actually move, the rotation of their flagella energy comes from protons through the membrane, high concentration to low concentration

Pili and Fimbriae

protein appendages extending from the cell wall outward, structurally similar, important in adherence to host cells- infectivity and virulence

• Fimbriae: short bristle like protein structure, numerous, attachment to other cells or surfaces

• pili: longer, less numerous, attachment to surfaces

  • sex pilus- transfer of DNA between 2 bacterial cells, non chromosomal info is being shared

    • small DNA circles: playmates, not essential for bacteria to survive but can hold extra genetic properties

    • conjugation- allows spread of plasmids of anti biotic gene that can make resistant bacteria

cytoskeleton

protein filaments: function in cell division, cell movement

• FtsZ (tubular like) cell division: assembled in the middles, allows for cell division, constriction of cell into 2 daughter cells (binary fission)

• MreB (actin like): filaments inside the cells, call shape maintenance, plasmid segregation, repeated proteins, under plasma membrane that form cell structure and transfer in plasmid conjugation

Ester Linkage v ether linkage

Ester: in Bacteria, for surface recognition, less stable, more flexible to bind, unbranched fatty acids with just hydrocarbon

Ether: much more stable, branched fatty acids, hydrocarbon with CH3 (methyl group)

Membrane

Bacteria: double membrane, 2 layer phospholipids 

Archie: membrane monolayer (tetra ethers) connected more stability