Intro To Cells/Prokaryotes Flashcards
Describe the contributions Robert Hooke and Anton van Leeuwenhoek made to the cell theory.
Robert Hooke:
- first to use term cell
- observed cork under microscope
- observations laid foundation for idea that organisms are made of cells
Anton van Leeuwenhoek:
- improved microscope lenses to observe living cells
- first to document single-celled organisms
- prove life exists at microscopic level
Describe the contribution Louis Pasteur made to the cell theory.
- showed that cells arise from preexisting cells
List four structural characteristics common to all cells.
- Cell membrane – A phospholipid bilayer that controls entry and exit of substances.
- Cytoplasm – A gel-like substance where cellular processes occur.
- Genetic material (DNA or RNA) – Carries instructions for growth and function.
- Ribosomes – Sites of protein synthesis.
List three significant structural differences between bacterial cells and eukaryotic cells.
- Nucleus – Bacteria lack a membrane-bound nucleus; eukaryotes have one.
- Organelles – Bacteria lack membrane-bound organelles (e.g., mitochondria); eukaryotes have them.
- Cell wall composition – Bacteria have peptidoglycan in their cell walls; eukaryotic plant cells have cellulose, and fungi have chitin.
Describe the structure and function of bacterial cell features.
• Cell wall – Provides structural support and protection; made of peptidoglycan.
• Chromosome – A single circular DNA molecule containing genetic information.
• Plasmids – Small, circular DNA fragments that carry extra genes (e.g., antibiotic resistance).
• Ribosomes – 70S ribosomes (smaller than eukaryotic ones) that synthesize proteins.
• Pili – Hair-like structures used for genetic exchange (conjugation).
• Fimbriae – Short, bristle-like structures that help bacteria adhere to surfaces.
• Capsule – A sticky outer layer that helps bacteria evade the immune system and adhere to surfaces
Contrast gram-positive and gram-negative bacteria. Why is penicillin ineffective against gram-negative bacteria?
• Gram-positive bacteria:
• Thick peptidoglycan layer.
• Stains purple with Gram stain.
• More susceptible to penicillin (which targets peptidoglycan synthesis).
Gram-negative bacteria:
• Thin peptidoglycan layer.
• Outer membrane contains lipopolysaccharides (LPS).
• Stains pink with Gram stain.
• Penicillin is ineffective because the outer membrane prevents access to peptidoglycan.
Explain the role of antibiotics (such as penicillin and tetracycline) in the microorganisms that produce them.
Antibiotics are natural defense mechanisms used by certain microbes (e.g., fungi and bacteria) to inhibit the growth of competing microbes.
Example: Penicillium mold produces penicillin to kill bacteria and reduce competition for resources.
How do tetracycline and penicillin help fight bacterial infections? Why don’t they harm human cells?
Penicillin: Inhibits peptidoglycan synthesis, preventing bacterial cell wall formation.
Tetracycline: Binds to bacterial ribosomes (30S subunit), preventing protein synthesis.
Why they don’t harm human cells:
• Human cells lack peptidoglycan, so penicillin has no effect.
• Human ribosomes differ from bacterial ribosomes (80S vs. 70S), so tetracycline doesn’t bind to them.
What events increase the likelihood of antibiotic resistance?
- Overuse of antibiotics – Creates selective pressure for resistant bacteria.
- Incomplete antibiotic courses – Leaves behind resistant bacteria.
- Use of antibiotics in agriculture – Increases resistance genes in bacterial populations.
- Horizontal gene transfer – Resistant bacteria transfer genes via plasmids.
- Mutation – Random genetic changes can confer resistance.
Compare the abundance of prokaryotic and eukaryotic organisms in terms of numbers and biomass.
Prokaryotes (bacteria & archaea) outnumber eukaryotes by far in both numbers and biomass.
Bacteria thrive everywhere – from deep oceans to human bodies.
They make up a significant portion of Earth’s biomass and are essential for ecosystems (e.g., decomposition, nitrogen fixation).
List the general characteristics of bacteria that contribute to their success.
- Rapid reproduction – Short generation times allow fast adaptation.
- Diverse metabolism – Can live in extreme environments (e.g., anaerobic, high temperature).
- Genetic adaptability – Can exchange genes through horizontal gene transfer.
- Resistant structures – Some form endospores to survive harsh conditions.
- Symbiotic relationships – Many bacteria live in or on other organisms, benefiting from them.
Define symbiosis and distinguish between the three types of symbiotic relationships with examples.
Symbiosis: A close, long-term interaction between two different species.
- Mutualism (+/+) – Both organisms benefit.
• Example: Gut bacteria (help digest food & produce vitamins). - Commensalism (+/0) – One benefits, the other is unaffected.
• Example: Bacteria on human skin that do not harm or help us. - Parasitism (+/-) – One benefits, the other is harmed.
• Example: Pathogenic bacteria like Salmonella, which cause disease.
