Me Salva! CIT12 - Citologia - Membrana plasmática

Summary

This lecture introduces cytology, focusing on the structure and function of cells. The speaker explains that cells are fundamental to all living organisms, with unicellular organisms like bacteria and multicellular ones like plants and animals. The cell membrane is discussed in detail, highlighting its phospholipid bilayer, with hydrophilic heads and hydrophobic tails. The fluid mosaic model, proposed by Singer and Nicholson, describes how proteins in the membrane facilitate selective permeability, allowing essential substances like glucose and water to enter the cell. The lecture sets the stage for further topics such as osmosis and active transport.

Takeaways

• 😀 Cytology is the study of cells, which are the basic building blocks of all living organisms.
• 😀 Organisms can be unicellular (like bacteria) or multicellular (like animals and plants).
• 😀 All cells have three main regions: the outer membrane (plasma membrane), cytoplasm, and nucleus (in eukaryotic cells).
• 😀 Prokaryotic cells, such as bacteria, do not have a nucleus, but still contain DNA.
• 😀 The plasma membrane is made up of phospholipids with hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
• 😀 Phospholipids naturally form a bilayer where the hydrophilic heads face water and the hydrophobic tails avoid water.
• 😀 The plasma membrane is semi-permeable, allowing only certain substances to pass through due to the selective permeability of proteins.
• 😀 The model explaining the plasma membrane structure is called the 'fluid mosaic model,' proposed by scientists Singer and Nicholson.
• 😀 Membrane proteins act as channels or enzymes, allowing specific molecules, like glucose, to pass through the membrane.
• 😀 The plasma membrane also plays a role in the transport of substances through processes like osmosis, diffusion, and active transport (e.g., sodium-potassium pump).

Q & A

What is citology?

Citology is the study of cells, which are the basic structural units of all living organisms.

What is the difference between unicellular and multicellular organisms?

Unicellular organisms, such as bacteria, are composed of a single cell, while multicellular organisms, like humans and plants, are made up of many cells.

What are the three main regions of a eukaryotic cell?

The three main regions of a eukaryotic cell are the plasma membrane, the cytoplasm, and the nucleus.

How does a prokaryotic cell differ from a eukaryotic cell?

Prokaryotic cells, such as bacteria, do not have a nucleus, while eukaryotic cells have a defined nucleus that contains DNA.

What is the structure of the plasma membrane?

The plasma membrane consists of a phospholipid bilayer with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repellent) tails facing inward.

What is the significance of phospholipids in the plasma membrane?

Phospholipids create the basic structure of the membrane, with their hydrophilic heads interacting with water and the hydrophobic tails avoiding water, forming a bilayer that acts as a barrier to water-soluble substances.

What does the term 'hydrophilic' mean in relation to phospholipids?

'Hydrophilic' refers to the 'water-loving' property of the head of the phospholipid molecule, which interacts with water molecules.

What is the role of proteins in the plasma membrane?

Proteins embedded in the plasma membrane allow selective passage of molecules, facilitate biochemical reactions, and may also serve as anchors for other substances.

What is the fluid mosaic model of the plasma membrane?

The fluid mosaic model suggests that the plasma membrane is composed of a fluid layer of phospholipids with proteins interspersed, allowing for flexibility and the selective passage of substances.

What is meant by 'selective permeability' of the plasma membrane?

'Selective permeability' means that the plasma membrane only allows certain molecules to pass through, based on their affinity to the proteins in the membrane, which prevents unwanted substances from entering or exiting the cell.