Bacterial Cell Structure and Function

LectureLecture

The Three Domains of Life

Microbiological focus

• Archaea – The Extremophiles

• Bacteria- Cyanobacteria and eubacteria

• Eukarya – Protozoans, fungi, and worms

Prokaryote and Eukaryote Cells

The Structure of the Prokaryote Cell

• Small size ( 0.5 to 2um)

• Large surface area to volume ratio

• A variety of shapes

• Outer cell wall- very thick made of specialized molecules

• Cell membranes may have a different constituency of molecules from eukaryote cells

• Ribosomes smaller

• No organelles, no nuclear membrane

•1 ds circular loop of DNA

Shapes of the Bacteria

• Bacillus

• Coccus

• Vibrio

• Spirillum

• Spirochete

• Pleiomorphism- Some bacterial shapes vary within a culture. This can occur when the nutrients are used and wastes have built up

Bacterial Shapes

Bacillus- E. coli

Fluorescent stain

Freeze fracture

Public enemy # 1- Anthrax

Streptococcus pyogenes- strep throat

Staphylococcus

Arrangement of bacteria

• Groups of two- diplo

• Chains- strepto

• Large groups- like grape clusters- staphylo

• Division on 3 planes- sarcinae- 8 cells arranged in a cube

• Division on two planes produces tetrads

Cell MorphologyCell Morphology

StaphylococcusStaphylococcus

DiplococcusDiplococcus

StreptobacilliStreptobacilli

SpirillumSpirillum

SpriochetesSpriochetes

• Peptidoglycan

•the single most important molecule in the cell walls of bacteria

•One immense- covalently linked molecule

• The molecule forms a chain- the constituents are sugar-amino molecules( glucosamines)

Peptidoglycans - Cell Wall

Gram Positive Bacteria- Cell walls

• The cell wall is made of Teichoic acid- glycerol+ phosphates+ribotol which an alcohol sugar. These polymers extend beyond the cell even beyond the capsule

Gram Negative Bacteria- Cell Walls

The outer membrane found primarily in Gram-negative bacteria is a bilayer that forms the outermost layer of the cell wall and is attached to the peptidoglycan by lipoproteins molecules.

The Cell Membrane

•LPS- this is actually a part of the outer cell membrane and can b be used to help to identiry Gram- bacteria. It is also important to the cell wall and is usually not released until a bacterium is dead. It consists of polysaccharides and lipid A

The toxins gram negative bacteria release are from this portion of the cell membrane. Gram negative bacteria release endotoxin and the result is fever, the dilation of blood vessels, so the blood pressure drops and causes other related effects.

Gram-Positive Bacteria

•The cell wall has a thick layer of peptidoglycan 20 to 80um thick

• 60-90% of the cell wall is peptidoglycan

•Except for the strptococci most gram positive bacterial cell walls contain very little protein

Gram-negative Bacteria

•The wall of a Gram-negative bacterium is thinner but more complex than a Gram-positive bacterium

Only10 to 20 % of the cell wall is peptidoglycan- the remainder consists of various polysaccharides, protein, lipids.

The cell wall contains an outer membrane- the LPS

The Periplasmic Space

•The periplasmic space is between the outer surface of the cell wallo and the cell membrane

•Enzymes and toxins remain in the periplasmic space in sufficient concentrations to help destroy substances that might harm the bacterium.

The Cell Membrane

•The cell membrane consists of molecules called phospholipids.

•Phospholipids have two long tails consisting of hydrocarbon chains ( HYDROPHOBIC)

• Phospholipids have a phosphate head (HYDROPHILIC)

•The membrane is formed by a double layer of these molecules

• The membrane also contains PROTEINS

Internal Structure

Ribosomes- consist of ribonucleic acid ( RNA) and protein. They are abundant in the cytoplasm as

POLYRIBOSOMES

Nucleoid Region- Central

•The nucleoid region contains 1 ds ciruclar loop of DNA.

• The DNA may be attached to the cell membrane as well at some point

•There may be RNA associated with the DNA

Chromatophores- photosynthetic bacteria

•Chromatophores are derived from the cell membrane. They contain pigments used to capture light energy for the synthesis of sugars. Nitrifying bacteria also may have these internal membranes.

•They contain the enzymes necessary for the energy transformation process of photosynthesis

+ Molecules of life

The Nucleoid Region

Mesosomes- Bacteria

Bacterial cells have large infoldings in their membranes.

Mesosomes

Mesosomes provide the surface area for all of the chemical reactions in the cell

• respiration

• metabolic processes

Freeze fracture

Inclusions

•Small bodies in the cytoplasm- some are called granules

Glycogen

pyrrophosphate granules- volutin

Metachromatic granules

Variable colors

• Vegetative cells of bacteria like Bacillus or Clostrium produce resting stages

•These spores are designed for survival and not reproduction.

• These are formed within cells

•They are resistant to heat, drying,acids,bases,disinfectants, and radiation

Spore formation

•Spores form when nutrients are depleged form a culture

• Few spores are formed when nutrients are plentiful and environmental conditions are favorable.

Spore Structure

• An endospore consists of a core, surrounded by a cortex, a spore coat and in some species a thin layer called the exosporium

spore

How do spores survive ?

• They contain dipicolinic acid and a large number of calium ions.

• These materials contribute to heat resistance

• The lose water content enables them to survive.

• Endospores have survived over 10,000 years

• Special methods may be used to skill them during sterilization

• When conditions are favorable they can still germinate

Flagella

• Bacteria that are motile have appendages called flagella

• A bacteria can have one or many flagella

•monotrichous

•amphitrichous

•lophotrichous

•peritrichous

What is this type of bacteria ?

• The diameter of a prokaryote’s flagellum is about one-tenth of that of a eukaryote

•It is made of flagellin

•The basal region has a hook like structure and a complex basal body

• The basal body consists of a central rod or shaft surrounded by a set of rings

• Gram negative bacteria have a pair of rings embedded in the cell membrane and another pair of rings associated with the peptidoglycan and lipopolysaccharide layer of the cell wall. Gram positive have one ring.

Flagellar motion

Flagella rotate like twirling L- shaped hooks such as a dough hook on a kitchen rotor- or a mixer

Turns like a mixer

Twiddling ? HHMM!

• When flagella bundle together they rotate counterclockwise and the bacteria run

• When the flgella rotate clockwise the flagellar bundle comes apart and the bacteria twiddle- tumble randomly

Chemotaxis

• Sometimes bacteria move toward or away from substances in their environment. This is called chemotaxis

• Concentrations of most molecules in the environment form a gradient.

• When a bacteria is running a long an increasing gradient if reduces the frequency of its twiddles

PILI

Attachment pili-

•These are structures on the surface of the bacteria that aid the bacterium in atttching to surfaces

• These acid the bacterium by allowing colonization of the mucus membranes of organisms.

• Some bacteria adhere to red blood cells by attachment pil and cause red blood cells to clum- this is hemagglutination

SEX PILI- Conjugation

• Conjugation pili or sex pili are found only in certain groups of bacteria.

•This structure exists exclusively for the transfer of DNA between bacteria

•The DNA passes between bacteria tend to develop antibiotic resistance

Bacterial Slime Layer or Capsule