Cell Physiology: Structure and Function PDF

# Cell physiology: Structure and Function ## Levels of Organization - **Chemical level:** Atoms combine to form molecules (e.g. DNA) - **Cellular level:** Molecules assemble to form organelles (e.g. smooth muscle cell). - **Tissue level:** Similar cells come together to form tissue (e.g. smooth mus...

# Cell physiology: Structure and Function ## Levels of Organization - **Chemical level:** Atoms combine to form molecules (e.g. DNA) - **Cellular level:** Molecules assemble to form organelles (e.g. smooth muscle cell). - **Tissue level:** Similar cells come together to form tissue (e.g. smooth muscle tissue). - **Organ level:** Different types of tissue are organized to perform specific functions (e.g. Stomach). - **System level:** Organs come together to form organ systems (e.g. Digestive system). - **Organismal level:** Organ systems work together to form a functional organism (e.g. Human). ## Cell Physiology: Understanding the Fundamental Units of Life Cell physiology focuses on the functions and processes occurring within cells. This field explores the complex mechanisms within cells and their roles in living creatures. Key areas of study include cell structure, metabolism, communication, and reproduction. Understanding cell physiology is crucial for comprehending the fundamental processes that sustain life. ### Cell structure **Cell membrane or plasma membrane:** - Separates the internal environment of the cell from its surroundings. - Plays a crucial role in maintaining cell homeostasis by regulating the movement of substances in and out of the cell. - Composed of a phospholipid bilayer, with two layers of phospholipid molecules. - Each phospholipid molecule has a hydrophilic head and hydrophobic tails. - The hydrophilic heads face outward towards the aqueous environments while the hydrophobic tails face inward creating a selectively permeable barrier. - Embedded proteins within the phospholipid bilayer have various functions: - **Transporters**: allow specific molecules to cross the membrane. - **Receptors**: transmit signals from the exterior to the interior of the cell. - **Structural support**: provide structure, aid in adhesion or enzymatic functions. **- Nucleus:** - Control center of the cell. - Contains genetic material (DNA). - Enclosed within a nuclear membrane. - Regulates gene expression and orchestrates cell activities. - Contains: - **Ribosomes**: essential for protein synthesis. - **Chromosomes**: composed of chromatin and DNA bound to histones. **- Mitochondria:** - Known as the powerhouses of the cell. - Responsible for producing cellular energy in the form of ATP. - They have a double membrane and contain their own DNA. - Replicate independently within the cell. **- Endoplasmic Reticulum (ER):** - Network of membranous tubules and sacs involved in the synthesis, folding, and transport of proteins and lipids. - Classified as: - **Rough ER**: covered with ribosomes and primarily responsible for protein synthesis. - **Smooth ER**: without ribosomes and plays a role in lipid metabolism and detoxification of drugs and toxins. **- Golgi Apparatus:** - Acts as a central delivery system within the cell. - Receives proteins and lipids from the ER. - Modifies and packages them into vesicles for transport within or outside the cell. - Forms secretory vesicles which are discharged via exocytosis. - Plays a role in the synthesis of complex carbohydrates. **- Lysosomes:** - Vesicular organelles containing digestive enzymes. - Break down cellular waste, foreign substances, and damaged organelles through autophagy. - Important for maintaining cellular homeostasis and cellular defense mechanisms. **- Vacuoles:** - Large, membrane-bound sacs. - Act as storage compartments for water, ions, nutrients and waste products. - Formed during endocytosis when portions of the cell membrane are pinched off. **- Peroxisomes:** - Scavengers for reactive oxidative species (e.g. H2O2). - Contain the antioxidant catalase enzyme which breaks down hydrogen peroxide into water and oxygen. - Breakdown lipids and detoxify certain chemicals. - Self-replicating. **- Ribosomes:** - Small, complex structures responsible for protein synthesis.. - Found free in the cytoplasm or attached to the endoplasmic reticulum. - Composed of two subunits: a large and a small subunit, each made up of proteins and ribosomal RNA (rRNA). **- Centrioles:** - Paired barrel-shaped organelles located just outside of the nucleus. - Help during cell division (mitosis and meiosis). - Absent in adult nerve cells. **- Cilia:** - Microscopic, hair-like structures found on the surface of many cells. - Functions depend on their location. - In the respiratory tract: help move mucus and debris out of the lungs. - In the female reproductive system: aid in the movement of eggs through the fallopian tubes. **- Flagella:** - Whip-like structures used by many microorganisms for movement.. - Found in various organisms (e.g., bacteria, algae, protozoa, and sperm cells). **- Microvilli:** - Finger-like plasma membrane protrusions. - Found in various tissues (e.g., the small intestine, kidney tubules, and inner ear). - Increase the surface area of cells, allowing for more efficient absorption and secretion processes.