Human Anatomy and Physiology Module 2 Cells PDF

HUMAN ANATOMY AND PHYSIOLOGY MODULE 2 CELLS I. Cell Structure Anatomy and Physiology – Module 2, Cells 1 Anatomy and Physiology – Module 2, Cells 2 II. Cell Cycle (IMAP) The cell cycl...

HUMAN ANATOMY AND PHYSIOLOGY MODULE 2 CELLS I. Cell Structure Anatomy and Physiology – Module 2, Cells 1 Anatomy and Physiology – Module 2, Cells 2 II. Cell Cycle (IMAP) The cell cycle is the series of events that take place in a cell, leading to its growth, replication of its DNA, and division into two daughter cells. It is a tightly regulated process essential for growth, development, and tissue repair in multicellular organisms. 1. Interphase Interphase is the phase where the cell prepares for division by growing and replicating its DNA. It includes three sub-phases: G1 Phase (Gap 1): The cell grows in size and synthesizes proteins and organelles. The cell performs its normal metabolic functions. The G1 checkpoint ensures the cell is ready to proceed to DNA replication. S Phase (Synthesis): DNA replication occurs, resulting in two identical copies of each chromosome (sister chromatids). Centrosomes, which will help in cell division, also duplicate. G2 Phase (Gap 2): The cell continues to grow and produces proteins necessary for mitosis. The G2 checkpoint ensures that DNA has been accurately replicated and the cell is ready for mitosis. 2. M Phase (Mitosis) Mitosis is the phase where the cell’s nucleus divides, resulting in two identical nuclei. It is followed by cytokinesis, which divides the cytoplasm, forming two daughter cells. Mitosis is subdivided into several stages: a. Prophase: Chromatin condenses into visible chromosomes. Anatomy and Physiology – Module 2, Cells 3  The nuclear envelope begins to break down. The mitotic spindle, made up of microtubules, begins to form, and centrosomes move to `opposite poles of the cell. b. Prometaphase: The nuclear envelope is fully disassembled. Spindle fibers attach to the kinetochores (protein structures on the centromeres of chromosomes). c. Metaphase: (Middle) Chromosomes align at the cell’s equatorial plane, known as the metaphase plate. The metaphase checkpoint ensures that all chromosomes are properly attached to the spindle fibers. d. Anaphase: (Away) Sister chromatids are pulled apart by the spindle fibers toward opposite poles of the cell. This separation ensures that each daughter cell will receive an identical set of chromosomes. e. Telophase: (Tear) Chromosomes reach the poles and begin to decondense back into chromatin. The nuclear envelope reforms around each set of chromosomes. The spindle fibers disassemble. 3. Cytokinesis Cytokinesis is the final step of the cell cycle, where the cytoplasm is divided between the two daughter cells. In animal cells, a contractile ring of actin filaments forms a cleavage furrow that pinches the cell in two. In plant cells, a cell plate forms along the centerline of the cell, eventually developing into a new cell wall. Anatomy and Physiology – Module 2, Cells 4 III. Mitosis vs Meiosis Mitosis and meiosis are two different processes of cell division that serve distinct purposes in the body. Here’s a comparison of the two: Cell Purpose Occurrence Resulting Division Cell Mitosis Mitosis is the process Somatic (body) Two diploid (2n) daughter cells, each by which a single cell cells genetically identical to the original divides to produce two parent cell. genetically identical Each daughter cell has the same daughter cells. It is number of chromosomes as the used for growth, tissue parent cell (e.g., in humans, 46 repair, and asexual chromosomes). reproduction. Does not introduce genetic variation; the daughter cells are clones of the parent cell Meiosis is the process by which Germ cells within Four haploid (n) daughter cells, each a single cell divides the reproductive genetically distinct from one another twice to produce four organs (ovaries and from the parent cell. genetically diverse and testes) Each daughter cell has half the daughter cells. It is number of chromosomes as the essential for sexual original parent cell (e.g., in humans, reproduction and the 23 chromosomes). formation of gametes (sperm and eggs)..Structure of the Cell Membrane Phospholipid Bilayer: Comprised of two layers of phospholipids with hydrophobic tails facing inward and hydrophilic heads facing outward. Proteins: Integral and peripheral proteins embedded in the membrane play roles in transport, signaling, and structural support. Cholesterol: Helps maintain membrane fluidity and stability. Carbohydrates: Attached to proteins and lipids, contributing to cell recognition and interaction. Anatomy and Physiology – Module 2, Cells 5 IV. Membrane Transport Definition: Membrane transport refers to the movement of substances across the cell membrane, which is crucial for maintaining cellular homeostasis and function. Importance: Cells must regulate the entry and exit of ions, nutrients, and waste products to sustain life. Anatomy and Physiology – Module 2, Cells 6 V. Types of Membrane Transport 1. Passive Transport: Movement of substances across the membrane without energy input. a. Diffusion: Movement of molecules from a region of higher concentration to a region of lower concentration. ✓ Simple Diffusion: Direct movement of small, nonpolar molecules like oxygen and carbon dioxide through the membrane. ✓ Facilitated Diffusion: Involves specific carrier or channel proteins to help transport larger or polar molecules (e.g., glucose, ions). b. Osmosis: ✓ Definition: Diffusion of water across a selectively permeable membrane. ✓ Importance: Maintains cell turgor pressure in plants, and balances water levels in animal cells. ✓ Osmotic Pressure: Pressure exerted by the movement of water through osmosis. c. Filtration: ✓ Definition: Movement of water and solutes across the cell membrane due to hydrostatic pressure. ✓ Example: Filtration in the kidneys. 2. Active Transport: Requires energy (ATP) to move substances against their concentration gradient. a. Primary Active Transport: ✓ Mechanism: Direct use of ATP to pump molecules against their gradient. ✓ Example: Sodium-Potassium Pump (Na+/K+ pump) which maintains the electrochemical gradient in cells. b. Secondary Active Transport: ✓ Mechanism: Utilizes the energy from the gradient created by primary active transport. ✓ Cotransport: Includes symport (molecules move in the same direction) and antiport (molecules move in opposite directions). Anatomy and Physiology – Module 2, Cells 7  ✓ Example: Glucose transport in the intestines using the Na+ gradient. 3. Vesicular Transport: Transport of large particles or macromolecules across the membrane using vesicles. a. Endocytosis: ✓ Phagocytosis: "Cell eating"; engulfing large particles. ✓ Pinocytosis: "Cell drinking"; engulfing extracellular fluid. ✓ Receptor-Mediated Endocytosis: Specific molecules are taken in after binding to receptors on the cell surface. b. Exocytosis: ✓ Mechanism: Vesicles fuse with the cell membrane to release contents outside the cell. ✓ Importance: Used by cells to secrete hormones, neurotransmitters, and enzymes. ✓ IV. Factors Affecting Membrane Transport Anatomy and Physiology – Module 2, Cells 8 VI. DNA Replication, Transcription, and Translation A. DNA Replication Purpose: To produce two identical copies of a DNA molecule, essential for cell division. Each new DNA molecule consists of one original strand and one newly synthesized strand. Enzymes o Helicase: Unwinds the DNA double helix. o Topoisomerase: Prevents the DNA from becoming supercoiled. o Primase: Synthesizes RNA primers to initiate DNA synthesis. o DNA Polymerase: has proofreading ability to correct errors during replication, ensuring high fidelity. o Telomeres: Repetitive sequences at the ends of eukaryotic chromosomes, protected by the enzyme telomerase. B. Transcription Purpose: To synthesize RNA from a DNA template. C. Translation Purpose: To synthesize proteins based on the sequence of mRNA. Key Concepts: Ribosome: The molecular machine that facilitates the translation of mRNA into protein Anatomy and Physiology – Module 2, Cells 9 Anatomy and Physiology – Module 2, Cells 10 VII. Membrane Potential A. Resting Membrane Potential The resting membrane potential is the electrical potential difference (voltage) across the membrane of a cell when it is not actively sending a signal. This potential is crucial for the function of neurons and muscle cells, among others. Extraxcellular Na+ Cl- Ca+ Na+- K+ pump Intracellular K+ A- (Amino acids) Key Concepts: Membrane Permeability: The resting membrane potential arises from the selective permeability of the cell membrane to different ions, primarily sodium (Na⁺) and potassium (K⁺). Ion Concentration Gradients: There is a higher concentration of Na⁺ outside the cell and a higher concentration of K⁺ inside the cell. This gradient is maintained by the sodium-potassium pump (Na⁺/K⁺ ATPase), which actively transports Na⁺ out of the cell and K⁺ into the cell. Electrochemical Gradient: The difference in ion concentration across the membrane creates an electrochemical gradient. K⁺ tends to diffuse out of the cell, while Na⁺ tends to diffuse in, but the membrane is much more permeable to K⁺ than to Na⁺, leading to a net negative charge inside the cell. Typical Values: The resting membrane potential in most neurons is around - 70 millivolts (mV). This negative value indicates that the inside of the cell is negatively charged relative to the outside. Role of Ion Channels: Specific ion channels in the cell membrane allow the passage of ions like K⁺ and Na⁺, contributing to the establishment of the Anatomy and Physiology – Module 2, Cells 11  resting potential. The K⁺ leak channels are particularly important for maintaining the resting membrane potential. Importance in Cell Function: The resting membrane potential is essential for the excitability of cells, allowing them to respond to stimuli and generate action potentials, which are crucial for processes like nerve impulse transmission and muscle contraction. This concept is foundational in understanding how cells communicate and function, particularly in the nervous and muscular systems. B. Action Membrane Potential Anatomy and Physiology – Module 2, Cells 12 VIII. Tissues Anatomy and Physiology – Module 2, Cells 13  Cell tissues are groups of similar cells that work together to perform a specific function in the body. In multicellular organisms, tissues are the building blocks of organs and systems, each type with its unique structure and role. In humans and other animals, there are four primary types of tissues: Tissue Location Structure Functions 1. Epithelial Skin Composed of Protection: Forms a protective Tissue lining of the closely packed cells barrier against physical damage, digestive tract, with minimal pathogens, and dehydration (e.g., respiratory tract, extracellular skin). blood vessels, material. Absorption: Specialized epithelial and glands Cells are arranged cells in the intestines absorb in continuous nutrients from food. sheets, either in Secretion: Glands are made of single layers epithelial tissue that secretes (simple epithelium) enzymes, hormones, sweat, or multiple layers mucus, etc. (stratified Filtration and Excretion: Kidney epithelium). tubules, lined with epithelial tissue, filter and excrete waste from the blood. Sensation: Some epithelial tissues contain nerve endings that sense stimuli. 2. Connective Bone Composed of Support and Structure: Provides Tissue Cartilage scattered cells structural support for organs and Anatomy and Physiology – Module 2, Cells 14  Tissue Location Structure Functions Tendons embedded in a the body as a whole (e.g., bones, Adipose tissue large amount of cartilage). (fat) extracellular matrix, Binding and Connection: Blood which can vary in Connects and binds different Extracellular consistency from tissues and organs together (e.g., matrix liquid (as in blood) tendons, ligaments). surrounding to solid (as in bone). Protection: Cushions and protects organs The extracellular organs (e.g., adipose tissue matrix typically stores fat and provides contains fibers insulation). (collagen, elastin) Transport: Blood, a type of that provide connective tissue, transports strength and nutrients, gases, and waste flexibility. products. Storage: Stores energy in the form of fat in adipose tissue. 3. Muscle Tissue Skeletal Muscle: Composed of Movement: Responsible for body Striated, elongated cells movements through contraction voluntary muscle called muscle fibers (e.g., skeletal muscles move attached to that contain bones). bones, contractile proteins Posture Maintenance: Muscle responsible for (actin and myosin). tissue helps maintain posture and body movements. Muscle fibers can supports the body's structure. Cardiac Muscle: be striated (striped) Heat Production: Muscle Striated, or non-striated, contractions generate heat, which involuntary depending on the helps maintain body temperature. muscle found type of muscle Circulation and Digestion: only in the heart, tissue. Involuntary muscle tissues responsible for (smooth and cardiac) are pumping blood. essential for circulating blood and Smooth Muscle: moving food through the Non-striated, digestive system. involuntary muscle found in the walls of hollow organs (e.g., intestines, blood vessels), controlling movements like peristalsis. 4. Nervous Brain Composed of Communication: Neurons Tissue Spinal cord neurons (nerve transmit electrical and chemical Nerves cells) and glial cells signals throughout the body, throughout the (supporting cells). enabling communication body Neurons have a cell between different body parts. body, dendrites Control: Nervous tissue (receiving signals), regulates bodily functions, from and an axon voluntary movements to (transmitting involuntary processes like signals). heartbeat and digestion. Response to Stimuli: Processes sensory input and triggers responses (e.g., reflexes). Anatomy and Physiology – Module 2, Cells 15 Anatomy and Physiology – Module 2, Cells 16