Cell Biology Lecture 2 PDF

Cell Biology Lecture 2 (3g.1) The Cell The cell is the basic structural and functional unit of all tissues in the body, and is considered the basic unit of life. Eukaryotic cells: contain...

Cell Biology Lecture 2 (3g.1) The Cell The cell is the basic structural and functional unit of all tissues in the body, and is considered the basic unit of life. Eukaryotic cells: contain a nuclear envelope and membrane organs, and are found in animals and plants. Prokaryotic cells: lack a nuclear envelope and membrane organs, and are found in bacteria. Cell components: The cell consists of cytoplasm, nucleus, cytosol, organelles, cytoskeleton, and cell membrane that separates the cytoplasm from the external environment.  Membranous Organells Membranous organelles are those organelles that are surrounded by a double membrane, providing them with a distinct internal environment. These organelles play a vital role in regulating various cellular processes Types of Membranous Organelles Mitochondria: - Known as the powerhouses of the cell, they produce ATP through cellular respiration. - They contain their own DNA (mtDNA) and are involved in regulating the cell cycle. Endoplasmic Reticulum (Rough and Smooth ER): - Rough Endoplasmic Reticulum (RER): Has ribosomes on its surface and is involved in protein synthesis. - Smooth Endoplasmic Reticulum (SER): Participates in lipid synthesis and calcium storage. Golgi Apparatus: - Modifies, sorts, and packages proteins and lipids synthesized in the endoplasmic reticulum. - Plays a role in forming vesicles that transport materials to their target locations. Lysosomes: - Contain digestive enzymes that help break down unwanted materials within the cell. - Play a role in cellular recycling processes. Vesicles: - Used to transport materials within the cell or to the outside. - Include types such as secretory vesicles and endocytic vesicles. Peroxisomes: - Contain enzymes that help break down fatty acids and detoxify harmful substances. - Play a role in cellular metabolism.  Cell membrane The cell membrane, also known as the plasma membrane or plasmalemma, is a thin structure that surrounds the cell and acts as a barrier separating the cytoplasm from the external environment. Composition 1. Lipid bilayer (50%) 2. Proteins 3. Carbohydrates Functions Regulation of transport: Acts as a barrier that regulates the passage of ions and solutes through channels and transport proteins. Cell signalling: Contains receptors for proteins and hormones, allowing the cell to interact with the surrounding environment. Cell adhesion: Contributes to the adhesion of cells to each other and to the extracellular matrix, promoting tissue formation.  The Lipid Component The lipid component of the cell membrane is composed mainly of phospholipids and cholesterol, and forms the basic structure of the membrane. Phospholipids: - They exist in the form of a bilayer, where each molecule contains a polar head (hydrophilic) and two nonpolar tails (hydrophobic). - The heads face outward and inward, while the tails point toward the center, forming a barrier that protects the cell. Cholesterol: - It constitutes about 2% of membrane lipids, and is found in the inner and outer layers. - It works to reduce the fluidity of the membrane and increase its mechanical stability, which affects the flexibility of the membrane and helps in processes such as exocytosis and endocytosis. Functions: - The lipid component provides a basic structure for the membrane, acts as a barrier that protects the cell, and contributes to regulating the movement of materials across the membrane The Protein Component of the Plasma Membrane Integral proteins: - These proteins are embedded within the lipid layer, and can extend across the entire membrane, enabling them to interact with the internal and external environment of the cell. - Their functions include transporting ions and substances across the membrane, and acting as channels or carriers. Peripheral proteins: - Located on the inner or outer surface of the membrane, and are not embedded in the lipid layer. - They can be easily removed, and play a role in cell signaling, cell recognition, and adhesion to the extracellular matrix. functions: 1 - Proteins act as channels for the transport of substances. 2 - receptors for cell signals. 3 - contribute to the adhesion of cells to each other and to the surrounding environment. The Carbohydrate Component The carbohydrate component of the plasma membrane consists of sugars attached to proteins or lipids, and forms an important part of the outer structure of the membrane. Glycolipids: are sugars attached to lipid molecules (phospholipids) in the membrane. Glycoproteins: are sugars attached to proteins, and play a role in many cellular functions. Functions: Carbohydrate components form the "cell envelope" (glycocalyx) that contributes to cellular recognition, and helps cells adhere to the extracellular matrix. They also protect cells from injury and facilitate communication between cells.