BS1040 Topic 1 Lecture 4 Bacterial Cell Structure

What are common properties shared by all cells?

Membrane boundary, DNA inheritance, transcription and translation, cellular metabolism, energy generation by redox reactions and proton gradients producing ATP.

Who defined "prokaryote" and "eukaryote"?

Stanier and van Niel in 1962.

What does "eukaryote" mean?

True nucleus.

What does "prokaryote" mean?

Before nucleus.

What are the key structural features of eukaryotic cells?

Linear chromosomes in a membrane-bound nucleus, histone proteins, and multiple membrane-bound organelles (mitochondria, chloroplasts, ER, Golgi, vacuoles).

What are the key structural features of prokaryotic cells?

No nucleus, single circular chromosome in nucleoid, no organelles, may have internal membranes for ATP generation.

What enzyme transcribes DNA into mRNA?

RNA polymerase.

What is the function of ribosomes?

Translate mRNA into proteins.

Where does transcription occur in eukaryotes?

In the nucleus.

Where does transcription occur in prokaryotes?

In the cytoplasm; transcription and translation occur simultaneously.

What is a monocistronic transcript?

mRNA that codes for a single gene product (common in eukaryotes).

What is a polycistronic transcript?

mRNA that codes for multiple genes organized in an operon (common in prokaryotes).

Do prokaryotic genes have introns?

No, prokaryotic genes lack introns.

What is an operon?

A cluster of genes under control of a single promoter, producing a polycistronic mRNA.

What size are eukaryotic ribosomes?

80S (60S large + 40S small subunits).

What size are prokaryotic ribosomes?

70S (50S large + 30S small subunits).

Why are prokaryotic ribosomes medically important?

They are sensitive to aminoglycoside antibiotics.

Why do small cells grow faster?

Higher surface area-to-volume ratio allows faster nutrient exchange and waste removal.

What is Thiomargarita magnifica?

The largest known bacterium (up to 20 mm long), discovered in 2009; polyploid, chemolithotrophic gammaproteobacterium storing sulfur.

What are general characteristics of bacteria?

Prokaryotic, no nucleus, small, simple structure, binary fission, strong cell walls, diverse morphologies, and divided historically by Gram stain.

What is Gram staining used for?

Differentiating bacteria based on cell wall structure using crystal violet and safranin dyes.

Who developed the Gram stain and when?

Hans Christian Gram, 1884.

What color do Gram-positive bacteria appear after staining?

Purple (retain crystal violet).

What color do Gram-negative bacteria appear after staining?

Red/pink (retain safranin after crystal violet is washed out).

What is peptidoglycan?

A polymer of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by peptides, giving structural strength to the bacterial cell wall.

How thick is the Gram-positive peptidoglycan layer?

20-80 nm, with extensive cross-linking.

What are teichoic acids?

Phosphate-rich polymers in Gram-positive walls that add rigidity; lipoteichoic acids link to membrane, teichoic acids link to peptidoglycan.

How thick is the Gram-negative peptidoglycan layer?

5-8 nm, thinner than in Gram-positive bacteria.

Do Gram-negative bacteria have teichoic acids?

No, they do not.

What is the outer membrane of Gram-negative bacteria composed of?

Phospholipids, proteins (porins, lipoproteins), and lipopolysaccharide (LPS).

What is lipopolysaccharide (LPS)?

A molecule in the outer membrane consisting of lipid A (endotoxin), core sugars, and O-antigen; key virulence factor.

What part of LPS is toxic?

Lipid A, which can trigger endotoxic shock when released by bacterial lysis.

What is the bacterial capsule?

A thick polysaccharide or glycoprotein layer surrounding some bacteria, protecting against phagocytosis and desiccation.

What are functions of the capsule?

Protection, virulence, adhesion, antigenic variation, and resistance to immune attack.

What is the capsule of Bacillus anthracis made of?

Protein (unusual among bacteria).

Why is the capsule important in vaccines?

It is antigenic; e.g., Neisseria meningitidis ACWY vaccine targets capsular polysaccharides.

What is a flagellum?

A whip-like structure that enables bacterial motility.

How does a flagellum move?

Rotation driven by a proton motive force; can rotate clockwise or counterclockwise.

What is chemotaxis?

Directed movement toward attractants (like sugars) or away from repellents.

What is a Type III secretion system (T3SS)?

A needle-like protein complex in Gram-negative bacteria used to inject virulence proteins into host cells or assemble flagella.

What is the function of pili (fimbriae)?

Hair-like surface structures for attachment, biofilm formation, motility, or genetic exchange (conjugation).

What is the pilin protein?

The main structural subunit of pili or fimbriae.

What is conjugation?

Transfer of genetic material (plasmids) between bacteria through a pilus.

What are spores?

Dormant, highly resistant structures formed by certain bacteria (e.g., Bacillus, Clostridium) under adverse conditions.

How long can bacterial spores survive?

Over 10,000 years or more.

What makes spores so resistant?

Low water content, calcium-dipicolinic acid complex, protective enzymes, and thick coats.

What triggers spore germination?

Favorable environmental conditions and nutrients.