Undergraduate
  1. General chemistry  1.1. Introduction to Chemistry  1.2. Atomic Structure  1.2.1. Subatomic particles  1.2.2. Atomic Model  1.2.3. Quantum numbers  1.2.4. Electron Configuration  1.2.5. Periodic trends  1.2.6. Isotopes and their applications  1.3. Chemical bond  1.3.1. Ionic bond  1.3.2. Covalent bonds  1.3.3. Metal Bond  1.3.4. Hybridization  1.3.5. Molecular geometry and VSEPR theory  1.3.6. Bond polarity and dipole moment  1.4. Stoichiometry  1.4.1. Mole concept  1.4.2. Empirical and molecular formula  1.4.3. Limiting reactant and excess reactant  1.4.4. Percent Yield and Purity  1.4.5. Dilution calculation  1.5. States of matter  1.5.1. Gas Laws  1.5.2. Matter and Intermolecular Forces  1.5.3. Solid and Crystal Structures  1.5.4. Phase diagram  1.5.5. Plasma and supercritical fluid  1.6. Chemical reactions  1.6.1. Types of Chemical Reactions  1.6.2. Balancing Chemical Equations  1.6.3. Thermochemical reactions  1.6.4. Reaction energy profiles  1.7. Solutions and Mixtures  1.7.1. Concentration units  1.7.2. Syndrome properties  1.7.3. Solubility and Solubility Rules  1.7.4. Henry's Law and Raoult's Law  1.7.5. Partition coefficient  1.8. Chemical equilibrium  1.8.1. Law of mass action  1.8.2. Le Chatelier's principle  1.8.3. Reaction quotient  1.8.4. To use this online calculator for Equilibrium Constant, enter Equilibrium Constant (Eq.) and hit the calculate button. Here is how the Equilibrium Constant calculation can be explained with given input values -> 0.05 = 0.05/0.  1.8.5. Acid-base balance  1.9. Acids and bases  1.9.1. Arrhenius, Brønsted–Lowry, and Lewis definitions  1.9.2. pH and pOH  1.9.3. Acid-base titration  1.9.4. Buffer Solution  1.9.5. Acid-base indicator  1.9.6. Polyprotic Acids and Bases  1.10. Electrochemistry  1.10.1. redox reactions  1.10.2. Galvanic and Electrolytic Cells  1.10.3. Nernst equation  1.10.4. Electrolysis  1.10.5. Faraday's laws of electrolysis  1.11. Thermodynamics  1.11.1. Laws of Thermodynamics  1.11.2. Enthalpy, entropy and Gibbs free energy  1.11.3. Spontaneity of reactions  1.11.4. Thermodynamic cycles (Hess's law, Carnot cycle)  1.12. Kinetics  1.12.1. Rate law and reaction order  1.12.2. Activation Energy and Catalyst  1.12.3. Collision theory  1.12.4. Reaction mechanism  1.12.5. Transition state theory
  2. Organic chemistry  2.1. Structure and relationships  2.1.1. Hybridisation in Carbon Compounds  2.1.2. Resonance and aromatization  2.1.3. Molecular orbitals  2.1.4. Inductive and mesomeric effects  2.2. Hydrocarbons  2.2.1. Hydrocarbons  2.2.2. Alkene  2.2.3. Alkynes  2.2.4. Aromatic compounds  2.2.5. Cycloalkanes and Conformation  2.3. Functional Group  2.3.1. Alcohols and phenols  2.3.2. Ethers and epoxides  2.3.3. Aldehyde and ketone  2.3.4. Carboxylic acids and derivatives  2.3.5. Amin  2.3.6. Esters and amides  2.3.7. Thiols and sulfides  2.4. Stereoscopic  2.4.1. Isomerism in Stereochemistry  2.4.2. Chirality and optical activity  2.4.3. Structural analysis  2.4.4. Diastereomers and Enantiomers  2.5.1. Substitution reactions  2.5.2. Elimination reactions  2.5.3. Addition reactions  2.5.4. Radical reactions  2.5.5. Rearrangement reactions  2.5.6. Pericyclic Reactions  2.6. Spectroscopy and structural analysis  2.6.1. Infrared Spectroscopy  2.6.2. Nuclear magnetic resonance spectroscopy  2.6.3. Mass Spectrometry  2.6.4. UV-visible spectroscopy  2.6.5. X-ray crystallography  2.7. Polymer chemistry  2.7.1. Addition and Condensation Polymers  2.7.2. Polymerization mechanism  2.7.3. Biodegradable Polymer  2.7.4. Conducting and smart polymers
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Ligands and coordination compounds  3.1.2. Crystal field theory  3.1.3. Molecular Orbital Theory in Coordination Compounds  3.1.4. Jahn–Taylor distortion  3.2. Main Group Chemistry  3.2.1. Alkali and alkaline earth metals  3.2.2. Halogens and Noble Gases  3.2.3. Transition metals and their complexes  3.2.4. Lanthanides and Actinides  3.3. Solid state chemistry  3.3.1. Crystal lattices and unit cells  3.3.2. Defects in solids  3.3.3. Electrical and magnetic properties  3.3.4. Superconductivity  3.4. Bio-inorganic chemistry  3.4.1. Metal ions in biology  3.4.2. Enzymatic reactions with metals  3.4.3. Metal poisoning and detoxification  3.4.4. Metalloproteins and Metalloenzymes
  4. Physical chemistry  4.1. Quantum Chemistry  4.1.1. Wave–particle duality  4.1.2. Schrödinger Equation  4.1.3. Quantum Numbers and Orbitals  4.1.4. Atomic and molecular spectroscopy  4.2. Statistical mechanics  4.2.1. Maxwell–Boltzmann distribution  4.2.2. Partitioning functions  4.2.3. Bose–Einstein and Fermi–Dirac statistics  4.3. Chemical thermodynamics  4.3.1. Gibbs Free Energy  4.3.2. Phase transition  4.3.3. Thermodynamic efficiency  4.4. Surface chemistry  4.4.1. Absorption and Catalysis  4.4.2. Colloids and Emulsions
  5. Analytical Chemistry  5.1. Classical methods  5.1.1. Gravimetric Analysis  5.1.2. titrimeter  5.2. Instrumental methods  5.2.1. Chromatography  5.2.2. Spectroscopy  5.2.3. Electroanalytical methods  5.2.4. X-ray diffraction
  6. Industrial Chemistry  6.1. Petrochemistry  6.2. Chemical engineering principles  6.3. Green Chemistry  6.4. Pharmaceuticals and Drug Synthesis
  7. Biochemistry  7.1. Carbohydrates  7.2. Proteins and enzymes  7.3. Lipids and membranes  7.4. Nucleic acids  7.5. Metabolism and Bioenergetics  7.6. Enzyme kinetics and mechanism

Undergraduate → Biochemistry ↓


Lipids and membranes


In the field of biochemistry, it is important to understand the role and structure of lipids and membranes. Lipids are a diverse group of biomolecules that are primarily hydrophobic or amphipathic, meaning they contain both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts. They serve many functions in biological systems, including energy storage, structural components of cell membranes, and signaling molecules.

On the other hand, cell membranes are composed primarily of lipids and proteins. They act as barriers, separating the interior of cells from the external environment and controlling the movement of substances in and out of cells. Let's take a closer look at the fundamental aspects of lipids and membranes.

Types of lipids

Lipids can be classified into several classes based on their structure and function. The primary lipid types include triglycerides, phospholipids, and sterols.

Triglycerides

Triglycerides are the most common type of lipid and are primarily used for energy storage. They are composed of a glycerol backbone bonded to three fatty acid chains. In chemical terms, they can be represented as:

CH2(OH)-CH(OH)-CH2(OH)

Triglycerides are synthesized by a reaction called esterification, where each hydroxyl group on the glycerol molecule reacts with the carboxyl group of a fatty acid, forming ester bonds and releasing water.

Phospholipids

Phospholipids are essential components of cell membranes. Phospholipids contain two fatty acid tails and a phosphate group attached to a glycerol backbone. The phosphate group is hydrophilic, while the fatty acid tails are hydrophobic. This amphiphilic nature allows phospholipids to form bilayers in aqueous environments, creating a stable barrier for cells.

Head Group: O- Phosphate Group: PO4^3- Fatty Acid Tails: CH3-(CH2)n-COOH

This structure leads to the formation of the lipid bilayer, a two-layer arrangement of phospholipids that is critical to the function and structure of cell membranes.

Sterols

Sterols such as cholesterol are another important type of lipid. Cholesterol has a complex ring structure and is amphoteric. It is an essential component of animal cell membranes, providing fluidity and stability. Cholesterol can be synthesized by the body or obtained from dietary sources.

Cholesterol: C27H46O

Unlike triglycerides and phospholipids, which are composed of long chains, sterols have a four-ring core structure.

Cell membrane

Cell membranes are dynamic structures composed of a lipid bilayer in which proteins are embedded. They are often described by the fluid mosaic model, which pictures the membrane as a flexible layer consisting of a mosaic of different proteins floating within or on top of the lipid bilayer.

Lipid bilayer

The lipid bilayer forms the basic structure of the cell membrane. The hydrophilic heads of the phospholipids face outward, toward the aqueous environment, while the hydrophobic tails face inward, away from the water. This arrangement forms a selective barrier that allows the passage of some substances while restricting others.

|---- Hydrophilic Head ----|---- Hydrophobic Tail ----|

Membrane proteins

Proteins within the membrane have many functions, including transport, signal transduction, and acting as enzymes. There are two main types of membrane proteins: integral and peripheral.

Integral proteins extend across the lipid bilayer and have open areas on both sides of the membrane. They play an important role in transport, forming channels or pores through which molecules can pass.

Peripheral proteins are associated with the exterior of the lipid bilayer, and often interact with integral proteins or the hydrophilic heads of lipids.

Visualization of the fluid mosaic model

Extracellular space Cytoplasm

The above view shows a simplified fluid mosaic model of a cell membrane.

Functions of lipids and membranes

Lipids and membranes play diverse and important roles in biological systems. Here are some of the major functions they perform:

Energy storage

Lipids, especially triglycerides, serve as the main storehouse of energy in living organisms. When energy is needed, triglycerides can be broken down into glycerol and free fatty acids, which are then oxidized to form ATP, the energy currency of cells.

Structural role

Phospholipids and sterols provide structural integrity to the cell membrane. The lipid bilayer forms a flexible but stable barrier, while cholesterol regulates membrane fluidity.

Barrier and transportation

The lipid bilayer acts as a selective barrier, allowing some molecules to pass through while blocking others. Membrane proteins facilitate the transport of ions, nutrients, and waste products across the membrane.

Signal transduction

Membrane proteins are involved in transmitting signals from the external environment to the interior of the cell, a process vital for cell communication and function.

Examples of lipids and membranes in biological systems

Adipose tissue

Adipose tissue or body fat is composed primarily of adipocytes, which store energy in the form of triglycerides. When energy is needed, hormones stimulate the breakdown of these triglycerides to release fatty acids into the bloodstream.

Red Blood Cells (RBCs)

The membrane of red blood cells is rich in phospholipids and proteins, which provide the necessary flexibility and integrity, facilitating oxygen and carbon dioxide transport in blood vessels.

Myelin sheath

The myelin sheath is a lipid-rich layer that insulates nerve fibers, allowing for the rapid transmission of nerve impulses through neurons in the nervous system.

Hormones

Steroids such as estrogen and testosterone are lipids derived from cholesterol. They function as hormones, regulating a wide range of bodily processes from metabolism to reproduction.

Conclusion

Lipids and membranes are fundamental components of biological systems, playing essential roles in energy storage, formation of cellular barriers, and signaling. The dynamic and versatile nature of lipids allows them to participate in many biological processes, making them vital to life.


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Lipids and membranes

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