lecture 2- med micro

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Questions and Answers

What is the primary function of the cytoplasmic membrane in prokaryotic cells?

To provide structural support to the cell

To act solely as a barrier to toxins

To regulate movement of molecules in and out of the cell (correct)

To store genetic information

Which of the following statements about the prokaryotic cell wall is true?

It separates the cytoplasm from the external environment.

It is composed entirely of phospholipids.

It is rigid and maintains the integrity of the cell. (correct)

It is a flexible structure that allows cell shape changes.

What distinguishes Gram-positive bacteria from Gram-negative bacteria?

The thickness of the peptidoglycan layer in the cell wall (correct)

The ability to undergo binary fission

The presence of a nucleus

The composition of ribosomes

What is the role of the glycocalyx or capsule in prokaryotic cells?

It aids in motility and adherence. Signup and view all the answers

What unique structural component is found in the bacterial cell wall?

Peptidoglycan Signup and view all the answers

Which molecule is primarily responsible for the negative charge of Gram-positive bacterial cell walls?

Teichoic acid Signup and view all the answers

Which transport mechanism does NOT require energy in prokaryotic cells?

Active transport Signup and view all the answers

What is the primary function of basic dyes in bacterial staining?

To provide contrast by staining negatively charged components in the cells Signup and view all the answers

What can happen if a Gram stain smear is decolorized for too long?

Gram-positive cells may appear pink Signup and view all the answers

Which two main groups of bacteria are identified by Gram staining?

Gram positive and Gram negative Signup and view all the answers

What differentiates the Acid-Fast stain procedure from Gram staining?

It stains organisms with high lipid content in their cell walls Signup and view all the answers

What is the primary stain used in the Acid-Fast staining procedure?

Carbol fuchsin Signup and view all the answers

What feature distinguishes the Gram negative cell wall from the Gram positive cell wall?

Presence of an outer membrane Signup and view all the answers

What role does Lipid A play in the structure of lipopolysaccharides (LPS)?

Anchors the LPS molecule in the lipid bilayer Signup and view all the answers

Why are Gram negative bacteria generally less sensitive to many medications?

A protective outer membrane that restricts access Signup and view all the answers

Which component of Gram negative bacteria elicits symptoms associated with endotoxin when introduced to a host?

Lipid A Signup and view all the answers

What is the role of porin proteins in the Gram negative cell wall?

To transport nutrients and small molecules across the outer membrane Signup and view all the answers

Which antibacterial compound primarily targets peptidoglycan synthesis?

Penicillin Signup and view all the answers

How does penicillin inhibit the growth of bacteria?

By preventing the formation of peptide interbridges in peptidoglycan Signup and view all the answers

What characteristic of the O-specific polysaccharide side chain is important for identifying certain bacterial strains?

It varies in number and composition across species Signup and view all the answers

Which of the following statements about the periplasm in Gram negative bacteria is true?

It is filled with a gel-like fluid involved in various cellular activities Signup and view all the answers

What is the primary function of fimbriae in bacteria?

Attachment to surfaces Signup and view all the answers

Which type of plasmid carries genetic information that provides antibiotic resistance?

R-plasmids Signup and view all the answers

Which of the following statements about ribosomes is true?

Prokaryotic ribosomes are 70S in size. Signup and view all the answers

What process allows the transfer of DNA from one bacterial cell to another via a sex pilus?

Conjugation Signup and view all the answers

Under what conditions do endospores typically germinate?

Favorable environmental conditions Signup and view all the answers

What is the main characteristic of endospores?

They can remain dormant for extended periods. Signup and view all the answers

What type of genetic material do plasmids typically consist of?

Circular double-stranded DNA Signup and view all the answers

Which of the following diseases is caused by an organism that produces endospores?

Tetanus Signup and view all the answers

How do certain antibiotics affect bacterial ribosomes?

They bind to 70S ribosomes and inhibit protein synthesis. Signup and view all the answers

What is the significance of plasmids in genetic technology?

They carry genes that can be used for genetic engineering. Signup and view all the answers

What type of bacteria is generally more susceptible to lysozyme?

Gram-positive bacteria Signup and view all the answers

Which structure is primarily responsible for bacterial motility?

Flagellum Signup and view all the answers

What differentiates a capsule from a slime layer?

Capsules are distinct and gelatinous Signup and view all the answers

Which of the following bacteria lack a rigid cell wall?

Mycoplasma Signup and view all the answers

What role do sterols play in mycoplasma cells?

They strengthen the cell membrane. Signup and view all the answers

What is the function of pili in bacteria?

Motility and adherence Signup and view all the answers

Which bacteria can cause disease only when they have a capsule?

Streptococcus pneumoniae Signup and view all the answers

What are flagella primarily composed of?

Flagellin Signup and view all the answers

How are dental plaque biofilms primarily formed?

By encapsulated bacteria Signup and view all the answers

What prevents lysozyme from effectively reaching the peptidoglycan layer in Gram-negative bacteria?

The outer membrane Signup and view all the answers

Study Notes

Prokaryotic Cell Structures

Cell envelope: Includes the cytoplasmic membrane, cell wall, and glycocalyx/capsule.
Cytoplasmic membrane: Acts as a barrier between the cell's interior and exterior environment.
Cell wall: A rigid structure that prevents the cell from bursting, maintaining cell contents.
Glycocalyx/capsule: A layer outside the cell wall, offering protection and attachment.
Appendages: Include flagella (for motility) and pili (for adherence).

Cytoplasmic Membrane

The boundary of the cell, made of a phospholipid bilayer.
Embedded membrane proteins move constantly (fluid mosaic model).
Regulates the movement of proteins and other molecules (ions) in and out of the cell.
Selectively permeable, allowing only certain molecules to pass.
Movement across the membrane is regulated by simple diffusion and osmosis (no energy required) or active transport (uses energy).

Cell Wall

A rigid structure that maintains cell integrity and determines the shape of the organism.
Cell wall architecture distinguishes Gram-positive and Gram-negative bacteria.
Contains unique structures and molecules, some recognized by the immune system as signs of invaders.
Antimicrobial agents target some of these wall structures.

Peptidoglycan

Found in bacterial cell walls.
A polymer of NAM and NAG.
Its structure is a key difference between Gram-positive and Gram-negative bacteria.
A major target for antibiotics.

Gram-positive Cell Wall

Thick peptidoglycan layer (around 30 layers).
Permeable to many substances (sugars and amino acids).
Composed of peptidoglycan and teichoic acid.
Some also contain lipoteichoic acids attached to the cytoplasmic membrane.
The teichoic acids give the cell a negative charge.

Gram-negative Cell Wall

Thin peptidoglycan layer.
Outer membrane, a unique lipid bilayer with many proteins, including lipoproteins.
The outside leaflet is composed of lipopolysaccharides (LPS).
This layer acts as a protective barrier, making Gram-negative bacteria less sensitive to many medications.
Contains porin proteins.

Lipopolysaccharide (LPS)

Extremely important medically.
Also known as endotoxin due to its toxic activity.
Elicits symptoms associated with Gram-negative bacterial infections.
Two notable parts: Lipid A (anchors LPS in the lipid bilayer; immune system recognizes it as an invader which is associated with endotoxic activity) and the O-specific polysaccharide side chain (O antigen).

Antibacterial Compounds Targeting Peptidoglycan

Differences in prokaryotic and eukaryotic cells allow for development of antibacterial agents that target prokaryotic life processes.
Some compounds interfere with peptidoglycan synthesis or alter its structural integrity, weakening the rigid molecule and causing cell bursting.

Penicillin

Interferes with peptidoglycan synthesis.
Binds to proteins/enzymes, preventing cross-linking of adjacent glycan chains (peptide interbridge formation).
More effective against Gram-positive cells due to outer membrane preventing penicillin reaching peptidoglycan layer.

Lysozyme

An enzyme found in bodily secretions (tears, saliva).
Breaks bonds linking NAM and NAG in peptidoglycans.
Destroys the structural integrity of glycans.
More effective against Gram-positive bacteria due to outer membrane of Gram-negative bacteria

Bacteria Lacking a Cell Wall

Example: Mycoplasma
Lack a rigid cell wall, leading to variable shapes.
Some cause mild pneumonia.
Not affected by penicillin or lysozyme.
Cell membrane is stronger, containing sterols.

Comparison of Gram-positive and Gram-negative Bacteria

Summary table of key differences and structural components (see table 3.2 in the document).

Structures Outside the Bacterial Cell Wall: Capsules and Slime Layers

Many bacteria have external layers.
Distinct, gelatinous layer is a capsule.
Diffuse, irregular layer is a slime layer.
Capsules and slime layers allow attachment and protection, and can lead to biofilm formation.
Important in adherence, pathogenesis, and biofilm formation (e.g. streptococcus mutans and dental plaque).

Other Surface Layers/Structures

Flagella: Long protein structures for motility. May be peritrichous (all over the cell) or polar (at one or both ends). The filament is composed of flagellin.
Pili/Fimbriae: Shorter protein appendages for attachment to surfaces, important in pathogenesis (e.g., enterotoxigenic E. coli). "Sex pili" transfer DNA.

Internal Components of Bacterial Cells: Nuclear Material

Chromosome: A single, circular, supercoiled DNA molecule containing all genetic information. It resides in the nucleoid.
Plasmids: Extra-chromosomal, double-stranded DNA molecules with additional genetic material.
Plasmids carry genes for additional traits such as antibiotic resistance.

Ribosomes

Organelles involved in protein synthesis.
Composed of large and small subunits (prokaryotic are 70S; composed of 30S and 50S subunits; eukaryotic are 80S).
Differences in ribosome structure are used as targets for certain antibiotics.

Endospores

Dormant bacterial cells formed during unfavorable conditions.
Extremely resistant to heat, desiccation, chemicals, and radiation.
Germinate into vegetative cells under favorable conditions.
Cause some medically important diseases, such as tetanus, botulism, gas gangrene, and anthrax.

Methods to Observe Bacterial Cells

Often need to be immobilized and stained for observation due to rapid movement and transparency.
Staining provides contrast between bacteria and surrounding medium.
Simple staining uses a single dye and differential staining distinguishes cell types(Gram stain, Acid-fast stain).

Dyes and Staining Techniques

Basic dyes: Positively charged, used to stain negatively charged cell components (nucleic acids, proteins). Examples include methylene blue, crystal violet, safranin, and malachite green.
Acidic dyes: Negatively charged, used for negative staining (stain background).
Differential staining: Distinguishes cell types, such as Gram staining.

Differential Staining

Gram Staining: Distinguishes Gram-positive and Gram-negative bacteria based on their cell wall structure.
Acid-fast staining: Distinguishes acid-fast bacteria (e.g., Mycobacterium) that have waxy cell walls from non-acid-fast bacteria.

Fluorescent Dyes and Tags

Fluorescence: Used to observe total cells, subsets of cells (live or dead), or cells with specific proteins.
Various dyes bind to certain compounds in cells.
Examples: Acridine orange binds DNA; CTC dye binds to respiration proteins in live cells; Bac light in live vs dead cells; Calcofluor white binds to fungi and some bacterial cell wall components.

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