Introduction to Prokaryotic Cells | A-level Biology | OCR, AQA, Edexcel

Summary

This video explores the universal and non-universal features of prokaryotic cells, highlighting key differences from eukaryotic cells. It explains that prokaryotes, including bacteria and archaea, are the most abundant cells on Earth, living in close, beneficial relationships with humans. The video covers shared cell features like the cell membrane, cytoplasm, ribosomes, and genetic material, as well as the unique peptidoglycan cell wall. Optional structures such as flagella, pili, waxy capsules, and mesosomes are also discussed, emphasizing their roles in movement, protection, adhesion, and aerobic respiration. Overall, it provides a clear, detailed overview of prokaryotic cell structure and function.

Takeaways

• 🦠 Prokaryotic cells, including bacteria and archaea, are the most common type of cells on Earth and are smaller than eukaryotic cells, typically 1–5 micrometers in length.
• 🌱 Prokaryotes share universal features with eukaryotes such as a cell membrane, cytoplasm, genetic material (DNA), and ribosomes for protein synthesis.
• 🏗️ The cytoplasm in prokaryotes contains dissolved molecules and solutes, along with glycogen granules and oil droplets for energy storage.
• 🧱 Prokaryotic cell walls are made of peptidoglycan (murine), a polymer of polysaccharides and polypeptides, which differs from plant cell walls made of cellulose.
• 💪 The cell wall protects prokaryotic cells from mechanical damage, changes in water potential, and aids in controlled cell division with the help of the cytoskeleton.
• 🌀 Some prokaryotes have flagella, tail-like structures used for movement, which are chemically distinct from eukaryotic cilia or flagella.
• 🛡️ Certain prokaryotes possess a waxy capsule outside the cell wall that provides extra protection, helps avoid detection by host cells, and allows bacteria to stick together.
• 💈 Pili are hair-like protein projections found in some prokaryotes that help cells attach to each other and their environment, promoting survival and nutrient sharing.
• 🔬 Mesosomes are inward folds of the prokaryotic cell membrane that increase surface area for aerobic respiration, functioning similarly to mitochondrial cristae in eukaryotes.
• 🌍 Prokaryotes live in commensal relationships with humans and the environment, benefiting both the host and the microbes, and can be found on the skin, in the gut, and in airways.

Q & A

What are the main universal features of prokaryotic cells?

Universal features of prokaryotic cells include the presence of a cell membrane, cytoplasm, ribosomes, DNA, and a cell wall made of peptidoglycan.

How do prokaryotic cells differ in size compared to eukaryotic cells?

Prokaryotic cells are much smaller, typically 1–5 micrometers in length, whereas eukaryotic cells can be several tens of micrometers in size.

What is the composition of a prokaryotic cell wall, and how does it differ from a plant cell wall?

The prokaryotic cell wall is made of peptidoglycan (also called murine), which is a polymer of polypeptides and polysaccharides. In contrast, plant cell walls are made solely of cellulose, a polysaccharide.

What is the function of the prokaryotic cell wall?

The cell wall provides protection from mechanical damage, prevents bursting due to osmotic pressure, and is temporarily broken down during cell division to allow formation of daughter cells.

Which organelles or structures are found in all prokaryotes?

All prokaryotes contain a cell membrane, cytoplasm, ribosomes, DNA, and usually a cell wall.

What are some non-universal features of prokaryotes?

Non-universal features include a flagellum for movement, pili for attachment, a waxy capsule for protection and adhesion, and mesosomes for aerobic respiration.

What is the function of pili in prokaryotic cells?

Pili are hair-like protein projections that help bacteria stick to surfaces or connect with other cells, facilitating nutrient exchange and genetic material transfer.

What is a mesosome and what role does it play in prokaryotes?

A mesosome is an infolding of the cell membrane that increases surface area, allowing the cell to carry out aerobic respiration, similar to the cristae in mitochondria.

Why is the waxy capsule important for some prokaryotes?

The waxy capsule protects prokaryotes from detection by host cells, helps bacteria stick together in colonies, and increases their chances of survival by enabling nutrient sharing and genetic exchange.

What are ribosomes and what is their role in prokaryotic cells?

Ribosomes are organelles made of two subunits that translate mRNA into polypeptides (proteins), essential for the cell's protein synthesis.

How do prokaryotic cells store energy internally?

Prokaryotic cells store energy in the form of glycogen granules and oil droplets suspended in the cytoplasm.

Which domains of life are classified as prokaryotes?

Bacteria and Archaea are both classified as prokaryotes, whereas eukaryotes include animals, plants, fungi, and some other organisms.