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Questions and Answers
What is unique about the cell membrane of eukaryotic cells compared to prokaryotic cells?
How do prokaryotic cells, such as bacteria, replicate?
What determines the shape of a bacterium?
How do certain cocci arrange themselves?
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What is the term for bacteria that are variable in shape?
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What is the primary function of the nucleoid in a prokaryotic cell?
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Which of the following is a characteristic of prokaryotic DNA?
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What is the function of pili (fimbriae) in bacteria?
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What is the purpose of antibiotics that target prokaryotic ribosomes?
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What is the role of capsular polysaccharides in vaccine development?
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What is the approximate concentration of bacteria per milliliter required to see one bacterium per microscopic field using the oil immersion lens?
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What is the function of teichoic acids in gram-positive bacteria?
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What is the location of the peptidoglycan layer in gram-negative bacteria?
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What are the components of ribosomes in prokaryotic cells?
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What is the region of the cytoplasm that contains DNA in prokaryotic cells?
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Study Notes
Cell Membrane and Replication
- Eukaryotic cell membranes contain sterols, whereas prokaryotes (except Mycoplasma) do not.
- Prokaryotic cells replicate by binary fission, while eukaryotic cells replicate by mitosis.
Structure of Bacterial Cells
Shape and Size
- Bacteria are classified by shape into three basic groups: cocci, bacilli, and spirochetes.
- Some bacteria are variable in shape and are said to be pleomorphic (many-shaped).
- The shape of a bacterium is determined by its rigid cell wall.
Arrangement of Bacteria
- Certain cocci occur in pairs (diplococci), some in chains (streptococci), and others in grapelike clusters (staphylococci).
- These arrangements are determined by the orientation and degree of attachment of the bacteria at the time of cell division.
Gram Stain
- It takes approximately 100,000 bacteria/mL to see 1 bacterium per microscopic field using the oil immersion (100×) lens.
- The sensitivity of the Gram stain procedure is low.
Medically Important Bacteria That Cannot Be Seen in the Gram Stain
- Meningococcemia is an exception, where high concentrations of Neisseria meningitidis can occur in the blood.
Special Components of Gram-Positive Cell Wall
- Teichoic acids are found in Gram-positive bacteria and can induce septic shock.
- Teichoic acids mediate the attachment of staphylococci to mucosal cells.
- Gram-negative bacteria do not have teichoic acids.
Periplasmic Space
- The periplasmic space is the area between the inner and outer membranes.
- It contains the peptidoglycan layer and a gel-like solution of proteins.
Cytoplasmic Membrane
- The cytoplasmic membrane is a lipid bilayer with selective permeability.
- It is the site of ATP production.
Cytoplasm
- The cytoplasm has two distinct areas: an amorphous matrix and an inner, nucleoid region composed of DNA.
- The cytoplasm contains ribosomes, nutrient granules, metabolites, and plasmids.
Structures Inside Cytoplasm
- Ribosomes consist of rRNA and protein.
- Protein synthesis occurs at ribosomes and can be inhibited by certain antibiotics.
- Prokaryotic ribosomes (70s) are different from eukaryotic ribosomes (80s), allowing antibiotics to selectively target prokaryotic ribosomes.
Nucleoid
- The nucleoid is the area of the cytoplasm where DNA is located.
- Bacterial DNA is a single, circular molecule that contains about 2000 genes.
- Bacterial DNA has no introns, unlike eukaryotic DNA.
Plasmids
- Plasmids are extrachromosomal, double-stranded, circular DNA molecules that can replicate independently of the bacterial chromosome.
- Plasmids carry genes for antibiotic resistance, heavy metal resistance, UV light resistance, pili, and exotoxins.
Structures Outside the Cell
- Capsule is a gelatinous layer covering the entire bacterium, composed of polysaccharide.
- Capsule is a determinant of virulence, limits phagocytosis, and is used in specific organism identification and vaccine production.
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Description
Compare and contrast the characteristics of prokaryotic and eukaryotic cells, including cell membrane composition, replication methods, and cell division.