Anatomy of Bacteria

MorphologyStructureFunction

Binary Fission

• “a method of asexual reproduction involving halving of the nucleus and cytoplasm of the cell followed by the development of each half into a new individual”

• septum• progeny cells• generation time

Morphology

• Size

• Shape

• Arrangement

Size

• prokaryotic (bacteria) cells are very small compared to eukaryotic cells

• prokaryotic cells are the most abundant form of life on earth

• prokaryotic cells can survive in conditions that are too extreme for eukaryotic cells

Shape

• Readings question one:

What are the three basic shapes that most bacteria exhibit?

Spiral(Vibrio, Spirillum, Spirochete)

• Vibrio: “curved or bent rods that resemble commas”

• Spirillum: “a corkscrew shape with a rigid cell wall and hair-like projections called flagella that assist in movement”

• Spirochete: “a flexible cell wall but no flagella in the traditional sense. Movement occurs by contractions (undulating) of long filaments (endoflagella) that run the length of the cell.”

Arrangement

• Readings question two:What are the three basic arrangements that most bacteria exhibit?

Additional arrangements:Tetracocci: “grouping of four spherical shaped

cells”Sarcinae: “a cube-like packet of eight spherica

bacteria”

Structure and Function• up until the 1950’s prokaryotes were believed to

simply be “bags of enzymes”• prokaryotes have a simpler construction than

eukaryotes• prokaryotic cell has 5 essential structural

components:– Nucleoid (bacterial chromosome)– Ribosomes– Cell membrane– Cell wall– Capsule

Nucleoid

• bacterial chromosome• typically one large circular molecule of DNA• floats freely in the cytoplasm• genetic control center of the cell• determines all of the properties and functions

of the bacterium

Ribosomes

• proteins and RNA• prokaryotic ribosomes are smaller than

eukaryotic ribosomes• protein synthesis• “granular” appearance

Cell Membrane and Cell Wall

• Readings question three:

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

Capsule

• “the membrane that surrounds some bacterial cells; a loose gel-like structure that, in pathogenic bacteria, helps to protect against phagocytosis”

• glycocalyx• slime layer

Cytoplasm

• Readings question four:• What is the cytoplasm of prokaryotic cells?

• primary structures: nucleoid and ribosomes

• plasmids: extrachromosomal pieces of DNA

Endospores

• “a thick-walled spore within a bacterium”

Endospores

• produced by the bacterium to help it survive in an unfavorable environment

• formed by vegetative cells- “sporulation”• one of the most resistant forms of life

• germination

Clostridium tetani

• deep wound punctures that become anoxic

• tetanus toxin spreads and causes disease

• spastic paralysis and can result in death

Clostridium botulinum

• botulinum toxin in improperly preserved foods

• botulism can result in death due to respiratory failure as a result of muscle paralysis

Clostrideium perfringens

• most prevalent reported cause of food poisoning

• enterotoxins in the intestines

• diarrhea and intestinal cramps with no fever or vomiting

Flagella

• protein structures attached to the cell surface that resemble “whip-like” appendages

• distributed in distinguishing patterns

• flagella of prokaryotic cells differ from eukaryotic cells

Pili (Fimbriae)

• short, hair-like structures on the surface of prokaryotic cells composed of protein

• shorter, thinner, and straighter than flagella• allow bacteria to attach to surfaces• e.g. Neisseria gonorrhoeae

Gram-staining

• Readings question five:

• What is the purpose of gram-staining? What are the characteristics of gram-positive bacteria and gram-negative bacteria?