2. Bacterial Cell Structure

Cocci

Spheres that can be single or can be associated in arrangements that is useful for identification

Diplococci

Divide and remain in pairs (two little circles)

Streptococci

Divide on one plane to form chains

(A long chain of spheres)

Staphylococci

Divide in random plane making grape-like clusters

Tetrads

Divide in two plane forming a square of 4 cocci

Sarcina

Divide in 3 planes making a cubic packet of 8 cocci

Draw all the cocci shape and arrangement.

• Diplococci

• Streptococci

• Staphylococci

• Tetrads

• Sarcina

Bacilli

Rods, uniform, very predictable

Coccobacili

Short and wide

Diplobacilli

Divide and remain in pairs

Streptobacilli

Divide on one plane to form chains

Palisades

Divide on irregular plane (hinge-like)

Be able to draw bacilli shape and arrangement

• Coccobacilli

• Diplobacilli

• Streptobacilli

• Palisades

What is the size-shape relationship?

• cells usually want a high surface area-to-volume ration (s/v ratio)

• Increased efficiency of nutrient uptake and diffusion of molecules within a cell (advantage)

• Large size and odd shape may be protective mechanisms from predation (advantage)

Plasma Membrane

• Acts as a selectively permeable barrier that regulates the movement of ions, nutrients, and waste into and out of the cell

• In bacteria, acts as the primary site for metabolic energy production (cellular respiration and ATP synthesis) due to the absence of the mitochondria

Inclusions

Aggregates of insoluble nutrient reserves stored in the cytoplasm; reduce internal osmotic pressure while storing carbon, energy, or inorganic compounds for use during nutrient starvation

Plasma Membrane

• Protects the cytoplasm

• A thin structure

• Have amphipathic lipids

  • Hydrophilic: polar ends that interact with water

  • Hydrophobic non-polar tails that are insoluble in water and interact with each other

What are amphipathic lipids?

Membrane Proteins

Integral and peripheral proteins function in transport, cell signaling, enzymatic activity, and cell recognition

Passive Transport

Moves substances down their concentration without ATP

Active Transport

Uses membrane proteins and ATP to move substances against the gradient

Bilateral forms spontaneously in _____ environments. Which side is on the surface?

Aqueous

• Hydrophillic on surface

• Hydrophobic ends buried

What is the plasma membrane mainly composed of?

Phospholipids

Hopanoids

A hydrophobic molecule similar to cholesterol

• distort the bilayer, which impacts the fluidity and shape in the membrane region

• Form functional membrane micro domains that are platforms for protein complex assembly

• Impart more “rigidity” to the membrane

Nucleoid

• NOT a true nucleus

• Not membrane bound

• Location of chromosome and associated proteins

• 1 closed circular, double stranded DNA molecule

• Supercooling and nucleoid proteins aid in folding and structure

Plasmids

• extrachromosomal DNA that is usually small, closed circular DNA molecules

• Exist and replicate independently of chromosome

• Inherited during cell division

• Carry genes that can confer a selective advantage (such as antibiotic resistance)

If a plasmid integrates into the chromosome, that region of DNA is called an…

Episome

DISCUSSION Q:

A bacterium already had a chromosome containing the genes necessary for survival and reproduction. Why would a bacterium need an additional separate DNA molecule such as a plasmid?

• keeps extra genes separate from essential chromosome genes

• Allows plasmids to replicate independently

• Makes it easier for bacteria to gain or lose specific traits

• Allows useful genes to be transferred between bacteria

• Helps bacteria adapt quickly to environmental changes

• Prevents changes to nonessential genes from directly affecting the main chromosome

Ribosomes

• complex protein/RNA structures

  • Sites of protein synthesis

  • Bacterial and archaea ribosome

• Bacterial ribosomal RNA ( R RNA)

  • 16S rRNA in small subunit

  • 23S and 5S rRNA in large subunit

Fimbriae

• short, thin, hairlike, protein appendages

• Can mediate attachment to surfaces, motility, and DNA uptake

The fuzziness all over the cell

Sex Pili

• longer, thicker, less numerous

• Genetically encoded on plasmids

• Required for conjugation

What is conjugation?

Sharing DNA between cells

Ex:

• Cell A shares a trait to Cell B that didnt already have the trait, NOT MIXING

Flagella

• threadlike, locomotor appendages extending outward from plasma membrane and cell wall

Functions of flagella

• motility

• Attachment to surfaces

• Virulence factors

Monotrichous

One flagellum

Polar flagellum

Flagellum at end of cell

Amphitrichous

One flagellum at each end of the cell

Lophotrichous

Cluster of flagella at one or both ends

Peritrichous

Spread over entire surface of cell

How does flagellum move?

Rotates like a propeller

Counterclockwise rotation cause what motion?

Forward

Clockwise rotation disrupts causes to cell to do what?

To stop and tumble