8b - Prokaryote Morphology

Summary

This video explores the prevalence and morphology of prokaryotes, which are microscopic, unicellular organisms found in every ecosystem. Despite their small size, they are incredibly abundant, outnumbering all other life forms combined. Prokaryotes can be round, rod, or spiral-shaped and lack organelles but possess a single circular chromosome and ribosomes. They may also have special structures like cell walls, capsules, flagella, and endospores, which aid in survival and adaptation to various environments.

Takeaways

• 🌍 Prokaryotes are incredibly abundant and widespread, existing in every habitat on Earth, including extreme environments.
• 🔬 Despite their ubiquity, only about 10% of prokaryotic species have been described, indicating a vast amount of undiscovered diversity.
• 🌿 Prokaryotes play a significant role in ecosystems, with their numbers in the human colon alone reaching approximately 4 x 10^23.
• 🌿 The total carbon mass of prokaryotes is estimated to be 500 petagrams, which is 15,000 times the mass of all humans combined.
• 🔬 Prokaryotes are unicellular organisms, with three basic shapes: round (coccus), rod-shaped (bacillus), and spiral-shaped (spirillum).
• 🧬 Inside prokaryotic cells, there is a single circular chromosome and often additional small circular DNA pieces called plasmids.
• 🧬 Ribosomes are present for gene expression, but unlike eukaryotes, prokaryotes lack other organelles such as a nucleus, Golgi body, or mitochondria.
• 🛡️ Prokaryotes have a cell wall for support and protection, composed of peptidoglycan in bacteria and various other compounds in archaea.
• 🔍 The Gram stain technique differentiates between gram-positive and gram-negative bacteria based on the amount and structure of peptidoglycan in their cell walls.
• 🏠 Some prokaryotes form endospores, a dormant state that allows them to survive extreme conditions and potentially remain viable for long periods.

Q & A

What is the significance of prokaryotes in terms of their abundance on Earth?

Prokaryotes are incredibly abundant and diverse, being the majority of organisms on the planet. They are present in every habitat on Earth, including places where other organisms might not survive.

How many prokaryotic organisms are estimated to be in the human colon?

There are approximately 4 x 10^23 prokaryotic organisms in the human colon, highlighting their vast numbers even within our bodies.

What is the total carbon mass of all prokaryotes on Earth compared to the mass of all humans?

The carbon mass of all prokaryotes is about 500 petagrams, which is roughly 15,000 times the mass of all humans combined.

Why is the majority of prokaryotic diversity still undescribed by science?

Only about 10% of prokaryotic species diversity has been described, suggesting that there is a vast amount of diversity that remains relatively unknown to science, possibly due to their small size and the challenges in studying such microscopic organisms.

What are the three basic shapes of prokaryotic cells?

Prokaryotic cells can be round (coccus), rod-shaped (bacillus), or spiral-shaped (spirillum). These shapes are reflected in their scientific names.

How does the structure of a prokaryotic cell differ from that of a eukaryotic cell?

Prokaryotic cells lack membrane-bound organelles and a nucleus. They have a single circular chromosome and ribosomes, but no other organelles like mitochondria or Golgi bodies.

What is the function of the nucleoid region in a prokaryotic cell?

The nucleoid region is the area within a prokaryotic cell where the DNA is clumped together. It is not enclosed by a membrane, unlike the nucleus in eukaryotic cells.

What are plasmids and what role do they play in prokaryotic cells?

Plasmids are small, circular pieces of DNA found in prokaryotic cells. They are extra bits of DNA that can carry genes for specific functions and can be transferred between cells.

How do the cell walls of bacteria and archaea differ in composition?

Bacterial cell walls are made of peptidoglycan, while archaeal cell walls are composed of various other polysaccharides and proteins, never peptidoglycan.

What is the difference between gram-positive and gram-negative bacteria in terms of cell wall structure?

Gram-positive bacteria have a thick layer of peptidoglycan and a single cell membrane, while gram-negative bacteria have a thinner layer of peptidoglycan sandwiched between two cell membranes.

What is the primary function of flagella in prokaryotic cells?

Flagella in prokaryotic cells are used for locomotion, allowing the cells to swim through fluids. They differ structurally from eukaryotic flagella and move in a spinning motion.

What is an endospore and how does it help prokaryotes survive extreme conditions?

An endospore is a dormant, non-metabolic state of a prokaryotic cell that allows it to survive extreme conditions by forming a protective coat around its DNA. It can remain dormant until conditions improve, at which point it can resume metabolism.