Fosfolipídios e Glicolípidos na Biologia

General Information

• Document is course notes for Cell Biology, 1st year, Pharmacy Faculty, University of Porto, 2006/2007
• Author: Jorge Paulos

Chapter 1 - Evolution of the Cell

• Prokaryotic cells emerged when the first cell acquired a plasma membrane for protection and regulation of substance exchange. This created an internal environment distinct from the external one.
• Eukaryotic cells evolved from prokaryotic cells through the development of vesicles/compartments/endomembranes leading to increased cellular growth, specialisation, metabolic efficiency, and heritable material protection.
• Eukaryotic cells have greater metabolic diversity, easier cell contact and interaction.

Chapter 2 - Chemical Cellular Components and Macromolecules

• Amino Acids: Amino acids are molecules containing both amine and carboxyl functional groups. Their structure is determined by the side chain (radical). The properties of the side chain affect the amino acid's pI (isoelectric point) and polarity.
• Carbohydrates: Can be monosaccharides (simple sugars), oligosaccharides (short chains of monosaccharides), and polysaccharides (long chains). Monosaccharides are important for energy and building blocks.
• Lipids: Lipids are hydrophobic molecules. Some are amphipathic (e.g., phospholipids), with both hydrophobic and hydrophilic parts, crucial for membrane structure. Fatty acids and triglycerides are examples of simple lipids.
• Nucleotides: Nucleotides are composed of a nitrogenous base, a pentose sugar, and one or more phosphate groups. They are important for energy transfer, genetic information storage, and coenzymes.
• Proteins: Proteins are polymers of amino acids. Their structure dictates their specific functions. They can be classified as simple or conjugated depending on their structure, as well as globular or fibrous.

Chapter 3 - Cell Study Methods

• Centrifugation: Separates particles based on their density and size. Differential centrifugation is used to fractionate cellular components. Isopycnic centrifugation separates based on density differences in a gradient.
• Chromatography: Separates molecules based on their interactions with a stationary phase and mobile phase. Different types, like gel filtration and ion exchange chromatography, are used in protein purification.
• Electrophoresis: Separates macromolecules (like proteins) based on size and charge in a gel matrix subjected to an electrical field. SDS-PAGE is a common method for protein separation.

Chapter 4 - Cellular Energy

• Glycolysis: The first step in glucose catabolism in the cytosol, yielding ATP through oxidation and producing pyruvate.
• Fermentation: An anaerobic process that regenerates NAD⁺, allowing glycolysis to continue, yielding lactate or ethanol.
• Krebs Cycle (Citric Acid Cycle): A series of enzymatic reactions completely oxidizing acetyl-CoA, yielding ATP, CO2, and reducing equivalents used in the electron transport chain.
• Oxidative Phosphorylation (Electron Transport Chain): The process where energy from electrons carried by NADH and FADH2 is used to create a proton gradient across the inner mitochondrial membrane, driving ATP synthesis.

Chapter 5 - Genetic Mechanisms

• DNA Replication: Semiconservative process where each new DNA molecule contains one original (parental) strand and one newly synthesized strand. Enzymes involved include DNA polymerase, helicase, primase, and ligase.
• Transcription: The process of converting a DNA sequence into RNA. Three main types of RNA polymerase exist.
• RNA Processing: The modification of primary RNA transcripts (pre-mRNA) into mature mRNA, including capping, splicing, and polyadenylation, to enable translation and prevent degradation.
• Translation: The process of converting an mRNA sequence into a polypeptide chain, using tRNA molecules. Steps involve initiation, elongation, and termination.
• Protein Synthesis: The process of creating proteins from amino acids according to the instructions in DNA.

Chapter 6 - Biomembranes

• Lipid Bilayer: The fundamental structure of biological membranes, composed primarily of phospholipids, cholesterol, and glycolipids.
• Membrane Proteins: Proteins embedded in the membrane, performing various roles like transport, enzymatic activity, and cell signalling, classified as integral and peripheral proteins.
• Membrane Asymmetry: The unequal distribution of lipids and proteins across the two leaflets (inner vs. outer) of the membrane bilayer.
• Membrane Fluidity: The ability of lipids and proteins to move within the membrane, important for membrane function.
• Membrane Transport: Processes for moving substances across the membrane, including passive transport (diffusion, facilitated diffusion), and active transport (using energy). This includes pumps, channels, and transporters.
• Membrane Carbohydrates: Carbohydrates attached to lipids (glycolipids) or proteins (glycoproteins), located on the extracellular side, playing roles in cell recognition and adhesion.

Chapter 7 - Intracellular Organization

• Nucleus: Contains the cell's genetic material (DNA), site for transcription and rRNA synthesis (in nucleolus). DNA packaged into chromatin, crucial for regulation. Contains nuclear pores that allow controlled entry/exit of molecules.
• Endoplasmic Reticulum: Involved in protein synthesis and folding, lipid synthesis, and calcium storage. Rough ER has ribosomes for protein synthesis, while Smooth ER lacks ribosomes and handles lipid metabolism.
• Golgi Apparatus: Processes, sorts, and modifies proteins and lipids, modifying oligosaccharides, and packaging into vesicles for delivery to other cellular compartments, or for secretion.
• Lysosomes: Contain hydrolytic enzymes for intracellular digestion of macromolecules, functioning as a recycling system. The acidic interior allows for optimal enzyme activity.

Chapter 8 - Cellular Junctions and Cell Adhesion

• Cell Adhesion: Mechanisms that enable cells to adhere to each other or to the extracellular matrix, crucial for tissue integrity and function.
• Anchoring Junctions: Provide mechanical attachment between cells (desmosomes, adherens junctions) and cells and the extracellular matrix (hemidesmosomes).
• Communicating Junctions: Allow direct communication between cells, enabling the passage of small molecules (gap junctions).
• Occluding Junctions: Prevent the passage of molecules between adjacent cells (tight junctions).

Chapter 9 - Extracellular Matrix

• Components: The extracellular matrix (ECM) includes a diverse collection of macromolecules (fibrous proteins and proteoglycans.) Collagen is the major fibrous protein giving tensile strength to tissues. Proteoglycans are a family of glycosaminoglycans that provide structural support and interact with other ECM components.
• Functions: Regulates cell growth, movement, differentiation, and differentiation. Contains important signaling molecules.

Chapter 10 - Cellular Communication

• Extracellular Signaling: A cell can communicate and influence others through various mechanisms that depend of the receptor, signaling molecule and intracellular signaling pathway.
• Signal Molecules: Chemical messengers secreted by a cell that act to stimulate a response in target cells. Different types of signaling (paracrine, endocrine, synaptic).
• Receptors: Proteins that bind to signal molecules initiating a cascade of cellular events.
• Intracellular Signaling: The pathways initiated by extracellular signals that ultimately affect the activities of proteins inside the cell that can induce a response.

Chapter 11 - Cellular Cycle

• Cell Cycle: The series of events that take place during the life of a cell, from one division to the next.
• Interphase (G1, S, G2): The period between cell divisions. G1(Gap 1), S (DNA Synthesis), G2 (Gap 2), with checkpoints ensuring proper progression through each phase. The cell monitors its size and internal conditions, the accuracy of the DNA replication and the presence of damaged DNA.
• M-Phase (Mitosis and Cytokinesis): The division stage, separating genetic materials in distinct new nuclear envelops.
• Regulation: The cyclin-dependent kinases (Cdks) and cyclins are crucial regulators, along with other proteins to control the cycle ensuring proper progression and accurate replication

Chapter 12 - Cell Death

• Necrosis: An accidental cell death, often triggered by trauma or other harmful agents, characterized by cellular swelling, membrane damage, and release of cellular content, frequently triggering an inflamation response.
• Apoptosis: A programmed cell death, essential for development, homeostasis, and repair, characterized by distinct morphological changes and tightly regulated enzymatic processes, preventing any release of content to avoid triggering inflammation.

Chapter 13 - Meiosis

• Meiosis: A specialized type of cell division that reduces the chromosome number by half, producing haploid gametes (sperm or eggs) from a diploid parent cell, necessary for sexual reproduction.
• Meiosis I: Separating homologous chromosomes, reducing the chromosome number
• Meiosis II: Separates sister chromatids, similar to mitosis.
• Significance: Important source of genetic variability within a species through homologous recombination(crossing-over).

Chapter 14 - Cancer

• Cancer: A group of diseases characterized by uncontrolled cell growth and proliferation.
• Carcinogenesis: The process of converting normal cells to cancerous cells, involving multiple genetic alterations.
• Tumor: An abnormal mass of tissue that can be benign or malignant (cancerous). Benign tumors do not spread and are often encapsulated, malignat tumors spread aggressively and invade other tissues and organs.
• Metastasis: The spread of cancer cells to distant parts of the body. It requires overcoming the natural mechanisms that keep cells in their original location, and surviving, and growing in different environments.

Chapter 15 - Laboratory Part

• Microscopes: Basic principles of microscopy (light and electron) focusing on power of resolution and magnification. Different types of microscopes.
• Staining: Common methods for visualizing cells during experiments.
• Fixation: Common techniques on dealing with samples for preserving the cells and tissue structure for experiments.