Prokaryote L3

How big are prokaryotic cells

Usually about 0.2–2 µm.

2 Why does cell size matter for prokaryotes

Smaller cells have a larger surface area-to-volume ratio, making transport of nutrients and waste more efficient.

What is the advantage of a larger surface area-to-volume ratio

It allows faster nutrient uptake and waste removal, which can support faster growth.

Do prokaryotes have a nucleus

No. Their DNA is located in a region called the nucleoid.

What is the nucleoid

The region of a prokaryotic cell where its DNA is located.

What does the prokaryotic genome usually look like

Usually one circular chromosome that is not paired with another chromosome.

What are plasmids

Small circular pieces of DNA separate from the main chromosome.

What do plasmids usually contain

Genes that are not essential for survival but can give the cell an advantage.

Why are plasmids important

They can be easily passed between cells, allowing useful traits to spread.

Do prokaryotes have membrane-bound organelles

No. Prokaryotes do not have membrane-bound organelles.

What are prokaryotic ribosomes made of

rRNA and proteins.

What are the two subunits of a prokaryotic ribosome

30S + 50S = 70S.

What is the function of ribosomes

Protein synthesis.

What is the fluid mosaic model

The plasma membrane is a flexible phospholipid bilayer with proteins embedded in it.

How are phospholipids arranged in the plasma membrane

Non-polar tails face inward and polar heads face outward.

What does selectively permeable mean

The membrane controls what enters and leaves the cell.

What are some functions of membrane proteins

Transport, energy generation, movement, and sensing the environment.

How does the plasma membrane help generate energy

It helps with respiration and harvesting light energy to create a proton motive force.

What are bacterial membrane lipids made of

Glycerol + phosphate + fatty acids.

What are archaeal membrane lipids made of

Glycerol + phosphate + isoprene-based side chains.

With Archaea’s unique membrane lipid. What does their phospholipid form in the cytoplasmic membrane

The side chains in their phospholipids covalently link to each other to form a monolayer.

What is the main function of the prokaryotic cell wall?

Maintains cell shape and protects the cell from osmotic forces.

What is peptidoglycan?

The main structural component of bacterial cell walls.

What are the two sugars in peptidoglycan?

NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine).

What is the difference between NAM and NAG?

NAM has a short peptide attached to it, while NAG does not.

How are peptidoglycan chains connected?

Sugar chains are connected by short peptide chains.

What is the main difference between Gram-positive and Gram-negative cell walls?

Gram-positive cells have a thick peptidoglycan layer, while Gram-negative cells have a thin peptidoglycan layer.

What is found in Gram-positive cell walls besides peptidoglycan?

Teichoic acids.

What do teichoic acids do?

Help with cell wall structure, cation transport, and antigenic specificity.

How are the peptides in Gram-positive and Gram-negative peptidoglycan connected?

Gram-positive bacteria can have an interbridge between peptides, while Gram-negative bacteria have a more direct connection.

What is the difference between a cell wall and a cell membrane?

The cell wall provides shape and protection, while the cell membrane controls what enters and leaves the cell.

What is the difference between Gram-positive and Gram-negative cell envelopes

Gram-positive: one cytoplasmic membrane + thick peptidoglycan. Gram-negative: cytoplasmic membrane + thin peptidoglycan + outer membrane.

What is the outer membrane of Gram-negative bacteria made of

Phospholipids, proteins, and lipopolysaccharides (LPS).

What is LPS

A major component of the Gram-negative outer membrane. It contains lipid A and sugars.

What does the structure of LPS look like

Lipid A is the base and the polysaccharides are on top.

What is Lipid A

The endotoxin part of LPS that can cause fever, inflammation, and other harmful effects.

What are porins

Proteins in the outer membrane that allow small molecules to enter and leave by diffusion.

What is the periplasm

The space between the cytoplasmic membrane and outer membrane of Gram-negative bacteria. It contains thin peptidoglycan and various proteins and enzymes.

What colour do Gram-positive bacteria appear after Gram staining

Purple.

What colour do Gram-negative bacteria appear after Gram staining

Pink.

What is the purpose of Gram staining

To distinguish bacteria based on differences in their cell walls.

What is a fimbria

A short, protein-based structure used mainly for attachment to surfaces or other cells and NOT movement

What are pili

Protein structures usually found in small numbers that can be used for movement, attachment, and gene exchange.

What is a conjugation pilus

A long, hollow protein tube that connects two bacteria and allows DNA, such as plasmids, to be transferred.

What is the difference between fimbriae and pili

Fimbriae are mainly used for attachment, while pili can be used for attachment, movement, and DNA transfer.

What is a glycocalyx

A sticky substance outside the cell made of polysaccharides, proteins, or both.

What is a capsule

A tightly attached, organized form of glycocalyx.

What is a slime layer

A loosely attached, less organized form of glycocalyx.

What are some functions of the glycocalyx

It helps protect cells from drying out and can help pathogens avoid recognition by the immune system.

What are inclusions

Structures inside prokaryotic cells that usually store nutrients or energy reserves.

What are examples of materials stored in inclusions

PHB can store carbon and energy, while sulfur and polyphosphate can store other nutrients.

What are gas vesicles

Structures that allow some aquatic microbes to control their buoyancy and move to different depths in the water.

What are endospores

Stable resting structures produced by some Gram-positive bacteria that can survive harsh conditions.

Which bacteria can produce endospores

Some Gram-positive bacteria, including Bacillus and Clostridium.

When do bacteria form endospores

When nutrients run out and the cell begins to starve.

What happens during sporulation

The vegetative bacterial cell transforms into an endospore.

What happens when an endospore encounters better conditions

It germinates and becomes a new vegetative cell.

Are endospores physiologically active

No. They are not physiologically active while in their resting state.

What conditions can endospores resist

Drying, heat, radiation, and lethal chemicals.

How long can endospores remain viable

They can remain viable for extremely long periods of time.

Why are endospores difficult to destroy

They have a complex structure with multiple protective layers surrounding the DNA core.

Why is movement beneficial for prokaryotes

It allows cells to move toward better environments or away from harmful ones.

What is taxis

Directed movement toward or away from a stimulus.

What is an attractant

A stimulus that causes a microbe to move toward it.

What is a repellent

A stimulus that causes a microbe to move away from it.

What is chemotaxis

Movement toward or away from chemicals using chemoreceptors.

What is phototaxis

Movement toward or away from light using photoreceptors.

How do microbes respond to an attractant during chemotaxis

They favor longer runs and fewer tumbles, causing movement toward the attractant.

What is a tumble

A change in movement direction that allows the cell to sense and respond to its environment.

What happens to movement when there is no chemical stimulus

Movement is more random, with runs and tumbles occurring without a specific direction.

Why do phototrophs move toward specific wavelengths of light

Different wavelengths have different properties, so cells move toward wavelengths they can use to obtain energy.

What is the role of sensory receptors in taxis

They detect environmental stimuli and affect the movement of the cell.

What are bacterial flagella

Long structures that propel bacteria through their environment.

How do bacterial flagella move bacteria

They rotate like a molecular motor rather than moving in an undulating motion.

What is the bacterial flagellum made of

The filament is made of many copies of a protein called flagellin.

What powers the rotation of bacterial flagella

The proton motive force powers the rotor.

How does the proton motive force power bacterial flagella

Protons move down their concentration gradient through the motor, providing energy for rotation.

What is the difference between bacterial and archaeal flagella

Archaeal flagella, called archaella, are smaller and are made of several different proteins.

What powers archaeal flagella

ATP hydrolysis powers their rotation.

What is the difference between bacterial and eukaryotic flagella movement

Bacterial flagella rotate, while eukaryotic flagella move with an undulating motion.

What is gliding motility

Movement across a surface without using flagella.

What does atrichous mean

The bacterium has no flagella.

What does monotrichous mean

The bacterium has one flagellum at one end.

What does lophotrichous mean

The bacterium has a tuft of flagella at one end.

What does amphitrichous mean

The bacterium has flagella at both ends.

What does peritrichous mean

The bacterium has flagella distributed all over the cell.

What is binary fission

A type of cell division in which one prokaryotic cell divides into two cells.

What happens during binary fission

The cell elongates, DNA is replicated, the membrane and cell wall constrict at the center, and the cell separates into two cells.

How do prokaryotes produce genetic variation

Through mutations and the transfer of DNA between cells.

What is transformation

A bacterium takes up DNA released into the environment by another cell and incorporates it into its own DNA.

What is conjugation

DNA is transferred directly from one bacterium to another through a pilus.

What is transduction

Viruses that infect bacteria can pass DNA from one bacteria to another