3.1 Bacterial Cells

What are the characteristics of life as related to microbes?

Growth, reproduction, responsiveness, metabolism, cellular structure

(Characteristics of life) Describe growth

Increase in size

• In bacteria, archaea, eukaryotes

• Doesn’t occur in viruses.

(Characteristics of life) Describe reproduction

Increase in number

• In bacteria, archaea, eukaryotes

• Host cell replicates in viruses

(Characteristics of life) Describe responsiveness

Increase in number

• In bacteria, archaea, eukaryotes

• Host cell replicates in viruses

(Characteristics of life) Describe metabolism

Controlled chemical reactions of organisms

• In bacteria, archaea, eukaryotes

• Viruses use host cell’s metabolism

(Characteristics of life) Describe cellular structure

Membrane-bound structure that can carry out the functions needed for life

• In bacteria, archaea, eukaryotes

• Viruses lack cytoplasmic membrane/cellular structure

What do all cells have in common?

Plasma membrane, cytoplasm, genetic material (such as DNA), chemical mechanism for using energy (usually atp), enzyme systems, coenzymes

What is the defining difference between prokaryotic and eukaryotic cells?

• Prokaryotic cells don’t have nucleus or membrane-bound organelles

• Eukaryotic cells have nucleus & membrane-bound organelles (complex)

What is the glycocalyx composed of?

• Gelatinous, sticky substance that surrounds the outside of the cell, composed of polysaccharides, polypeptides, or both

• Two types: capsule & slime layer

• Can be found in our intestines when food moves along

What are the two types of glycocalyces?

Capsule & Slime layer

Describe the structure of the capsule

• thick, organized, sticky layer surrounding a bacterial cell.

  • Usually made of polysaccharides (sugars)

  • Located outside the cell wall

  • Well-organized and firmly attached to the cell

  • Helps protect bacteria from immune defenses and drying out

• Ex -> streptococcus pneumoniae & klebsiella pneumoniae

Capsulated strains

Escape immune detection/destruction → can cause disease.

Unencapsulated strains

Easier for immune system to detect/destroy → less likely to cause disease.

What is the structure and function of a slime layer?

A loose, water-soluble, sticky glycocalyx that helps bacteria attach to surfaces and form biofilms

Ex → dental plaque

What is a biofilm?

Aggregates of many bacteria living together on a surface

What are the major functions of the glycocalyx?

Prevents drying out, helps form biofilms, and helps bacteria escape the immune system.

What is motility and why is it useful?

Ability to move

It helps cells move away from harmful environments and toward favorable ones, like food or light

What structure enables motility in many bacterial species?

Flagella — long structures extending beyond the cell surface and glycocalyx.

What are the 3 components of the flagellum? Briefly describe each

• Filament: Long, hollow shaft made of flagellin; rotates like a screw to move the cell.

• Hook: Curved protein structure connecting the filament to the basal body.

• Basal body: Anchors the flagellum to the cell wall/membrane and rotates the filament.

What are the different arrangements of flagella for bacteria?

• Atrichous

• Polar flagella

  • Monotrichous

  • Lophotrichous

  • Amphiatrichous

• Peritrichous

• Spirochetes Flagella

What does atrichous mean?

Bacteria have no flagella

What are polar flagella?

Flagella located at end of cell

What is monotrichous?

One flagellum at one end of cell (polar flagella)

What is lophotrichous?

A cluster of flagella at one end (polar flagella)

What is amphitrichous?

A single or cluster of flagella at both ends of cell (polar flagella)

What is peritrichous?

Many flagella covering all sides of cell

Where are spirochete flagella located?

Inside the cell, between the outer and cell membranes

What are spirochete flagella called?

Axial filament - made of modified flagella called endoflagella

How do spirochetes move?

Their axial filaments rotate causing corkscrew movement

What are runs in flagellar movement?

Straight in one direction

What are tumbles in flagellar movement?

Changes in direction

What is taxis?

Movement in response to stimuli

What is positive taxis?

Movement towards a favorable stimulus

What is negative stimulus?

Movement away from an unfavorable stimulus

What is movement due to light stimulus called?

Phototaxis

What is movement due to chemical stimulus called?

Chemotaxis

What are fimbriae (aka attachment pili) and what do they do?

Rodlike, sticky, bristle-like protein extensions that help bacteria attach, form biofilms, communicate (electrical signals), and sometimes move by pulling. Usually many and shorter than flagella.

What is a conjugation pilus (sex pilus/F pilus)?

Specialized type of pilus/fimbrial structure that transfers DNA between bacteria

How is a conjugation pilus different from fimbriae?

It is longer and fewer in number

What is vertical gene transfer?

parent cell/organism DNA → Child cell/offspring

What is horizontal gene transfer?

DNA transfer to non-child/daughter cell

What is transformation in horizontal gene transfer?

A bacterium takes up DNA from its environment

What is transduction in horizontal gene transfer?

A bacteriophage (viruses only affect bacteria) transfers DNA between bacteria

What is conjugation in horizontal gene transfer?

Direct DNA transfer between bacteria via conjugation pilus

What are the general functions of prokaryotic cell walls?

Provides structure & shape to cell

Protects it from osmotic forces

Assists some cells in attaching to other cells

Assists some cells with resistance to antimicrobial drugs

What are the common shapes of bacterial cells

Coccus, bacillus, coccobacillus, spiral (spirochete, spirillum, vibrio)

Coccus shape bacteria

Spherical

Bacillus shape bacteria

Rod-shape

Coccobacillus shape bacteria

Elongated with rounded edges

Spirochete shape bacteria (spiral)

Flexible & long corkscrew shape

Spirillum shape bacteria (spiral)

Rigid, thick, & doesn’t bend easily

Vibrio shape bacteria (spiral)

Comma-shaped

What are the common arrangements of bacterial cells?

Staphylo, strepto, sarcinae, pallisades

Straphylo arrangement

Arranged in a cluster

Strepto arrangement

Arranged in a chain

Sarcinae arrangement

Arranged in a cuboid packet

Pallisades arrangement

Group of rods

What is the major component of bacterial cell walls?

Peptidoglycan

What carbohydrates are present in peptidoglycan?

Glycan portion made of carbohydrates; Alternating N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM) units; NAG & NAM structurally similar to glucose

What type of molecules crosslink the carbohydrate chains in peptidoglycan?

Peptido “short proteins”

Describe the cell wall of Gram-positive bacteria

• Thick peptidoglycan cell wall

• Teichoic acids help attach peptidoglycan (cell wall) to cell membrane

• Retains crystal violet because of thick peptidoglycan wall

• Stains purple

Describe cell wall of Gram-negative bacteria

• Thin peptidoglycan layer in periplasmic space (closest to cell membrane)

• Outer membrane of cell wall = layer of phospholipids, outermost layer of lipopolysaccharides

• All together makes cell wall!;

• Will not retain crystal violet

What color does gram-negative stain?

Retains safranin = stains pink

What is lipopolysaccharide (LPS)

• a glycolipid, composed of lipid A (toxic) & carbohydrates

  • Lipid A = toxicness released when bacteria die & break apart (lysis) during growth, resists heat & survives standard sterilization techniques

What is an example of a type of bacteria that cannot be stained with Gram staining because they completely lack cell walls?

Mycobacterium

• cell walls made of 60% waxy liquid (mycolic acid), mycoplasma pneumonia

• no peptidoglycan = doesn’t Gram stain

What is cytoplasm?

Everything inside cell (fluid, organelles, structures)

What does cytoplasm include in bacteria?

Cytosol, inclusions, ribosomes, cytoskeletons, sometimes endospores

What is cytosol?

Liquid part of cytoplasm, mostly water with dissolved & suspended substances

What is dissolved and suspended in cytosol?

Ions, carbs, proteins (mostly enzymes), lipids, wastes

Where is DNA located in a bacterial cell?

Nucleoid (area of cytosol in cytoplasm)

Describe the most common structure for bacterial chromosomes?

Single circular chromosome

What is a plasmid?

Smaller circular piece of DNA

Why are plasmids beneficial to bacteria?

Can replicate & have accessory genes that carry genetic info

• Ex → antibiotic resistance genes, pili/toxin production

What are inclusions?

Deposits of reserve supplies of lipids, starch, or compounds with nitrogen, phosphate, sulfur

What are gas vesicles in inclusions?

Gases stored in protein sacs found in aquatic cyanobacteria (blue-green, photosynthetic bacteria)

Define endospore

A form of bacterial cell produced by some species for cell survival or poor growth & environmental conditions

• forms inside vegetative cell; better conditions = endospore germinates to produce vegetative cell

• can survive heat, radiation, & chemicals;

• ex → bacillus & clostridium = pathogenic (cause botulism, tetanus, anthrax, c-diff, gangrene)

Define vegetative cell

Normal, actively/metabolically growing & feeding producing endosperm when bad conditions

What color will endospores stain during the endospore process?

Green

What organelle is the site of protein synthesis?

Ribosomes

What is the process of protein synthesis called?

Translation

What is the total size of a bacterial ribosome?

70S

What is the size of the large subunit of a bacterial ribosome?

50S

What is the size of the small subunit of a bacterial ribosome?

30S

Which rRNA gene is often used for identifying the species of bacteria?

16S

What is the cytoskeleton?

Dynamic network of 3-4 types of protein fibers in cell’s cytoplasm

What are some functions of the cytoskeleton in bacteria?

• Wrap around cell equator for cell division

• Form helix to determine cell shape

• Keep DNA in certain areas

• Provide motility

What color will vegetative cells stain in the endospore process?

Pink