MMSC270 Chap 3 Objectives

List the key differences between the Eukaryotic cell and the Prokaryotic cell

1. Eukaryotic (plant, animal, fungi, or protists) cells contain a membrane-bound nucleus and organelles

2. Prokaryotic (bacteria, archaea) cells lack a membrane-bound nucleus

List the structures all bacteria possess

1. Cytoplasmic membrane

2. cytoplasm

3. Ribosomes

4. one or a few chromosomes

Identify structures most but not all bacteria possess

1. Cell wall

2. A surface coating called glycocalyx

Identify structures some but not all bacteria possess

1. cytoskeleton

2. flagella, pili, and fimbriae

3. An outer membrane

4. Nanowires/nanotubes

5. plasmids

6. inclusions

7. endospores

8. microcompartments

Structure and function of Fimbriae

Short protein projections (on gram positive and negative)

Allows for attachment of cells to surfaces

Structure and function of Pili

Long appendage used for transfer of genetic material between cells

Only in gram negative

Structure and function of flagella

• Structure: Long, whip-like appendages made of flagellin protein, anchored in the cell wall/membrane.

• Function: Movement (chemotaxis – moving toward nutrients or away from harmful substances).

found externally

Structure and function endoflagella

• Structure: Found inside the periplasmic space of spirochetes, wrapped around the cell body.

• Function: Cause a twisting or corkscrew motion, allowing bacteria like Treponema pallidum (syphilis) to move through thick fluids or tissues.

found internally

Structure and function S layer

• Structure: A rigid, crystalline protein layer lying just outside the cell wall.

• Function:

  • Provides protection against environmental stress (enzymes, pH changes).

  • Can act like a suit of armor, helping bacteria survive harsh conditions.

Structure and function Glycocalyx

• Structure: General term for sugar-based (polysaccharide) coating outside the cell wall. Includes both capsule and slime layer.

• Function:

  • Helps bacteria stick to surfaces and other cells.

  • Provides protection from drying out and immune system attack.

Structure and function Slime layer

• Structure: A loose, sticky, unorganized form of the glycocalyx.

• Function:

  • Helps bacteria adhere to surfaces (important in biofilms like dental plaque).

  • Offers some protection but less than a capsule.

Explain how a flagellum works in the presence of an attractant.

• Bacterial flagella rotate like a propeller.

• Movement is controlled by two patterns:

  • Run: Flagella rotate counterclockwise, bundle together, and push the cell forward in a straight line.

  • Tumble: Flagella rotate clockwise, bundle falls apart, and the cell spins in place to change direction.

• When an attractant (like sugar or nutrients) is present, bacteria tumble less and make longer runs toward the attractant.

• This allows them to move toward favorable conditions.

Define Chemotaxis

The directed movement of bacteria toward or away from a chemical stimulus.

• Toward attractants (nutrients).

• Away from repellents (toxins, harmful substances).

Define biofilms

A structured community of microbes attached to a surface and surrounded by a protective slimy matrix (polysaccharides + proteins).

• Example: Dental plaque on teeth.

• Biofilms help bacteria stick, share nutrients, and resist antibiotics.

Describe the 3 possible layers of the cell envelope of bacteria

1. outer membrane (in some bacteria) - extra membrane and functions similar to cytoplasmic membrane

2. Cell wall (In some bacteria) - support and shape

3. (Inner) Cytoplasmic membrane: controls flow of materials in and out of cell

Two main types of bacterial cell envelope and Gram stain color

• Gram-positive bacteria

  - 2 layer, thick peptidogylcan and cell membrane

  • Thick peptidoglycan layer.

  • No outer membrane.

  • Stains purple (crystal violet stays trapped in the thick wall).

• Gram-negative bacteria

  - 3 layer cell envelope, Complex outer membrane, thin peptidoglycan, and cell membrane

  • Thin peptidoglycan layer.

  • Has an outer membrane with LPS (lipopolysaccharides).

  • Stains pink/red (crystal violet washes out, safranin counterstain shows).

Why Gram-negative organisms are more resistant

• Their outer membrane acts as a barrier against many antibiotics, detergents, and disinfectants.

• Porins (small channels) control what enters, blocking large or harmful molecules.

• LPS layer can protect against immune defenses.

Structure and function of plasmids

• Small circular DNA molecules separate from the chromosome.

• Plasmids provide genetic flexibility, for example R plasmids carry genes for resistance to antibodies

Nucleoid / Chromosome

• Region containing the single circular bacterial chromosome.

• Holds genetic instructions for the cell.

Ribosomes

Site of protein synthesis

Composed of rRNA (60%) and protein (40%)

Consists of large (50S) and small subunit (30S)

Small and large together = 70S

Bacterial Ribosome = 70S

Eukaryotic ribosome = 80S

Inclusion bodies

used for food storage

Bacterial microcompartments

Outer shells made of protein, arranged geometrically

• Packed full of enzymes designed to work together in biochemical pathways

Cytoskeleton

Protein filaments that help maintain shape and aid in cell division.

• Unique to non-eukaryotic cells - may be a potential target for antibiotic development

Endospores

• Highly resistant structures produced by some bacteria

• Mechanism for survival not reproduction (used to survive harsh conditions like heat, radiation, chemicals, and starvation)

Size of bacterial vs. eukaryotic ribosomes

• Bacterial ribosomes: 70S (made of 50S + 30S subunits).

• Eukaryotic ribosomes: 80S (made of 60S + 40S subunits).