Compare and Contrast the Overall Cell Structure of Prokaryotes and Eukaryotes

Chapter 4 Study Guide

1. Compare and contrast the overall cell structure of prokaryotes and eukaryotes.

Prokaryote: “prenucleus”

Eukaryote: “true nucleus”

• One circular chromosome, not in a membrane
• No histones
• No membrane enclosed organelles
• Peptidoglycan cell walls (if bacteria)
• Pseudomurien cell walls (if archea)
• Binary fission
• Bacteria and archea
• Paired chromosomes, in nuclear membrane
• Histones
• Organelles
• Polysaccarhide cell walls (IF they have cell walls at all)
• Mitotic spindle
• Eukaryotes

1. What is the main feature that distinguishes prokaryotes from eukaryotes?

Prenucleus vs. true nucleus

1. Name and describe the three basic shapes of bacteria.

        1. Bacillus- rod shaped

        2. Coccus- spherical

        3. Spiral- spirillum/spirilla, vibrio, spirochete

1. What is the diameter of a “typical” bacterium such as E. coli? How does that compare to the diameter of eukaryotic cells?

Average size: 0.2-1.0 um x 2-8 um, which is smaller than eukaryotes

1. How would you be able to identify streptococci through a microscope? staphylococci?  diplococci?

Streptococci: strepto=chains, cocci= spheres

Staphylococci: staphlo= clusters, cocci= spheres

Diplococci: diplo= pairs, cocci=spheres

1. What is the bacterial glycocalyx, and what is its function?

The bacterial glycocalyx is the outside, sticky cell wall.  It functions to prevent phagocytosis and protect the microbe from dehydration.

1. Why are bacterial capsules medically important?

Bacterial capsules are firmly attached, and prevent phagocytosis (eat foreign microorganism)

1. Compare and contrast flagella, axial filaments, fimbriae, and pili.

Flagella: attached to the outside cell wall by basal body, filament made of flagellin proteins, attached to protein hook, cell can have one or many at one side or both

Axial filaments/endoflagella: found in spirochetes, anchored to cell at one end, rotation causes cell to move, between cell wall and sheath, sheath rotates, organism spirals through medium

Fimbriae: hairlike structures that extend to the outside; thinner than flagella, main function is attachment, found all over cell

Pili: like fimbriae but have different functions; some facilitate transfer of DNA from one cell to another (conjugation) others are used for twitching motility (grappling hook on an edge extends pillus, pillus attaches to structure, pillus disassembled, pulled towards target.

1. Describe the four arrangements of bacterial flagella.

1. Peritrichous: many flagella attached
2. Monotrichous and polar: ONE flagellum attached at ONE end
3. Lophotrichous and polar: tuft of flagella attached to ONE end
4. Amphitrichous and polar: one flagellum attached at BOTH ends

1. In bacterial motility, what is a run?  a tumble?  How does the pattern of “runs” and “tumbles” change when a bacterium is moving toward an attractant?  Toward a repellent?

Bacteria rotate their flagella to run or tumble.

Run: all flagella rotate in the same direction (i.e. all counterclockwise); this moves the bacteria some distance.

Tumble: flagella go in every which way; bacteria doesn’t actually go anywhere, it is just reorienting itself

Toward an attractant: bacteria move toward the stimulus with many runs and few tumbles

Toward a repellant: frequency of tumbles increases as bacteria moves away from a stimulus

1. What are the components of the peptidoglycan backbone?  What kinds of molecules link adjacent strands of peptidoglycan backbone?

Peptidoglycan is a polymer of disaccharide: (NAG) N-acetylglucosamine and (NAM) N-acetylmuramic acid.  Polypeptides (amino acids connected by peptide bonds) link adjacent strands.

1. Compare and contrast the cell walls of gram-positive bacteria and gram-negative bacteria.

GRAM POSITIVE CELL WALLS

• Thick peptidoglycan
• Teichoic acids
• purple

GRAM NEGATIVE CELL WALLS

• Thin peptidoglycan
• No teichoic acids
• Outer membrane
• Periplasmic space
• Pink/red

1. What is osmotic lysis?  What is plasmolysis?  Explain how the peptidoglycan protects the cell from osmotic lysis.

Osmotic lysis: occurs when a cell is in hypotonic solution and cell burst.

Plasmolysis: occurs when a cell is in hypertonic solution and cell becomes raisin like.

1. Why are drugs that target cell wall synthesis useful?

Because they only affect cells with cell walls.

1. Why are mycoplasmas resistant to antibiotics that interfere with cell wall synthesis?

Because they don’t have cell walls!

1. Describe the structure (what it is made of) and functions (what it does) of the prokaryotic plasma membrane.

It is a phospholipid bilayer that encloses the cytoplasm.  It exhibits selective permeability and contains proteins.  The structure can be described by a fluid mosaic model in which the membrane is viscous with proteins (peripheral, transmembrane, integral)

1. How are simple diffusion, facilitated diffusion, active transport, and group translocation similar?  How are they different?

They are similar because they describe movement of solutes across a membrane.

Simple diffusion: movement of a solute from an area of high concentration to an area of low concentration