unit 4 review
Cell biology is the foundation of life sciences, focusing on the intricate structures and functions within cells. This unit explores organelles, the specialized compartments that perform vital tasks, and how they work together to maintain cellular health and function.
Understanding cell biology is crucial for grasping complex biological processes and diseases. From energy production in mitochondria to protein synthesis at ribosomes, each organelle plays a unique role in keeping cells alive and thriving.
Key Concepts and Terminology
- Cell theory states all living organisms composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells
- Eukaryotic cells contain membrane-bound organelles (nucleus, mitochondria) while prokaryotic cells lack membrane-bound organelles
- Organelles specialized structures within cells perform specific functions essential for cell survival and function
- Cytoplasm gel-like substance inside the cell where organelles and other cellular components are suspended
- Cellular respiration process by which cells break down nutrients to produce energy in the form of ATP
- Occurs primarily in the mitochondria
- Consists of glycolysis, Krebs cycle, and electron transport chain
- Endocytosis process by which cells take in materials from the extracellular environment by engulfing them with the cell membrane (phagocytosis, pinocytosis)
- Exocytosis process by which cells release materials from the cell by fusing vesicles with the cell membrane and expelling the contents
Cell Structure Overview
- Plasma membrane semi-permeable barrier separates the cell's interior from the extracellular environment
- Composed of a phospholipid bilayer with embedded proteins
- Regulates the passage of molecules in and out of the cell
- Cytoskeleton network of protein filaments provides structural support, enables cell movement, and aids in organelle transport
- Consists of microfilaments (actin filaments), intermediate filaments, and microtubules
- Nucleus contains the cell's genetic material (DNA) and controls cellular activities
- Surrounded by a double-layered nuclear envelope with nuclear pores for selective transport
- Contains nucleolus where ribosomal RNA is synthesized
- Ribosomes site of protein synthesis
- Can be found freely in the cytoplasm or attached to the rough endoplasmic reticulum
- Endomembrane system includes the endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles
- Involved in the synthesis, modification, transport, and degradation of proteins and lipids
Membrane-Bound Organelles
- Endoplasmic reticulum (ER) network of membranous channels and sacs involved in protein and lipid synthesis, modification, and transport
- Rough ER studded with ribosomes and involved in protein synthesis and modification
- Smooth ER lacks ribosomes and involved in lipid synthesis, detoxification, and calcium storage
- Golgi apparatus stack of flattened membranous sacs (cisternae) that modifies, packages, and sorts proteins and lipids for transport to their final destinations
- Receives proteins and lipids from the ER
- Modifies proteins by adding carbohydrates (glycosylation) or other molecules
- Lysosomes membrane-bound organelles containing digestive enzymes that break down and recycle cellular waste, damaged organelles, and foreign particles
- Maintain the cell's internal environment by removing non-functional components
- Play a role in programmed cell death (apoptosis)
- Mitochondria double-membrane organelles known as the "powerhouses" of the cell
- Site of cellular respiration and ATP production
- Contain their own DNA and ribosomes for protein synthesis
- Peroxisomes single-membrane organelles involved in the breakdown of fatty acids and detoxification of harmful substances
- Contain enzymes that neutralize toxic compounds (hydrogen peroxide)
Non-Membrane-Bound Organelles
- Ribosomes small, spherical organelles composed of rRNA and proteins
- Site of protein synthesis
- Can be found freely in the cytoplasm or attached to the rough ER
- Centrosome organelle located near the nucleus that organizes the microtubules of the cytoskeleton
- Consists of two centrioles arranged perpendicular to each other
- Plays a crucial role in cell division by organizing the mitotic spindle
- Cilia and flagella hair-like projections from the cell surface that enable cell movement or fluid movement across the cell surface
- Composed of microtubules arranged in a "9+2" pattern
- Cilia shorter and more numerous, beat in a coordinated manner (respiratory tract)
- Flagella longer and typically found in single or pairs, propel the cell through fluid (sperm cells)
- Cytoskeletal elements protein filaments that provide structure, support, and movement to the cell
- Microfilaments (actin filaments) thin, flexible fibers involved in cell movement and contractility (muscle cells)
- Intermediate filaments provide mechanical strength and resistance to shear stress (skin cells)
- Microtubules hollow, cylindrical fibers involved in organelle transport and formation of cilia, flagella, and the mitotic spindle
Organelle Functions and Interactions
- Nucleus controls cellular activities by regulating gene expression and DNA replication
- Nuclear pores allow selective transport of molecules between the nucleus and cytoplasm
- Nucleolus site of ribosomal RNA synthesis and ribosome assembly
- Endoplasmic reticulum (ER) and Golgi apparatus work together in the synthesis, modification, and transport of proteins and lipids
- Proteins synthesized in the rough ER are transported to the Golgi for further modification and sorting
- Lipids synthesized in the smooth ER are transported to the Golgi for distribution
- Lysosomes and peroxisomes work together to maintain cellular homeostasis
- Lysosomes break down and recycle cellular waste and damaged organelles
- Peroxisomes detoxify harmful substances and break down fatty acids
- Mitochondria and chloroplasts (in plant cells) are involved in energy production
- Mitochondria site of cellular respiration and ATP production
- Chloroplasts site of photosynthesis in plant cells, converting light energy into chemical energy
- Cytoskeleton and organelle interactions
- Microfilaments and microtubules aid in organelle transport and positioning within the cell
- Microtubules form the mitotic spindle during cell division, separating chromosomes
Cellular Transport Mechanisms
- Passive transport movement of molecules across the cell membrane without the use of energy
- Diffusion movement of molecules from an area of high concentration to an area of low concentration (oxygen, carbon dioxide)
- Osmosis diffusion of water across a semi-permeable membrane from an area of high water potential to an area of low water potential
- Facilitated diffusion movement of specific molecules across the membrane through protein channels or carriers (glucose, amino acids)
- Active transport movement of molecules across the cell membrane against their concentration gradient, requiring energy in the form of ATP
- Sodium-potassium pump maintains the electrochemical gradient across the cell membrane by pumping sodium ions out and potassium ions into the cell
- Vesicular transport movement of large molecules or particles across the membrane using vesicles (endocytosis, exocytosis)
- Endocytosis process by which cells take in materials from the extracellular environment
- Phagocytosis "cell eating" - cell engulfs solid particles (bacteria, cell debris)
- Pinocytosis "cell drinking" - cell takes in fluid and dissolved molecules
- Receptor-mediated endocytosis specific molecules (hormones, low-density lipoproteins) bind to receptors on the cell surface and are internalized
- Exocytosis process by which cells release materials to the extracellular environment
- Secretory vesicles fuse with the plasma membrane and expel their contents (neurotransmitters, hormones)
- Plays a role in cell signaling and communication
Energy Production in Cells
- Cellular respiration process by which cells break down nutrients (glucose) to produce energy in the form of ATP
- Occurs primarily in the mitochondria
- Consists of three main stages: glycolysis, Krebs cycle, and electron transport chain
- Glycolysis first stage of cellular respiration, takes place in the cytoplasm
- Glucose is split into two pyruvate molecules, producing a net gain of 2 ATP and 2 NADH
- Krebs cycle (citric acid cycle) second stage of cellular respiration, occurs in the mitochondrial matrix
- Pyruvate is converted into carbon dioxide and water, generating 2 ATP, 6 NADH, and 2 FADH2
- Electron transport chain (ETC) final stage of cellular respiration, occurs in the inner mitochondrial membrane
- NADH and FADH2 from glycolysis and the Krebs cycle are oxidized, releasing electrons that are passed through a series of protein complexes
- Proton gradient is created across the inner mitochondrial membrane, driving ATP synthesis through chemiosmosis
- ATP synthase enzyme complex in the inner mitochondrial membrane that generates ATP using the proton gradient created by the ETC
- Protons flow through ATP synthase, causing it to rotate and catalyze the formation of ATP from ADP and inorganic phosphate
- Photosynthesis process by which plant cells convert light energy into chemical energy (glucose)
- Occurs in the chloroplasts of plant cells
- Consists of two main stages: light-dependent reactions and light-independent reactions (Calvin cycle)
Practical Applications and Clinical Relevance
- Stem cell research and regenerative medicine
- Stem cells unspecialized cells that can differentiate into various cell types
- Potential to treat diseases and injuries by replacing damaged or lost cells (spinal cord injuries, Parkinson's disease)
- Cancer biology and targeted therapies
- Cancer uncontrolled cell division and growth due to genetic mutations and abnormal cell signaling
- Understanding the cellular mechanisms behind cancer can lead to the development of targeted therapies (small molecule inhibitors, monoclonal antibodies)
- Drug development and testing
- Knowledge of cellular transport mechanisms and organelle functions is crucial for designing and testing new drugs
- Drug candidates must be able to cross the cell membrane and reach their target organelles or molecules
- Genetic disorders and gene therapy
- Many genetic disorders caused by mutations in genes that encode proteins essential for proper organelle function (lysosomal storage disorders, mitochondrial disorders)
- Gene therapy aims to correct these disorders by introducing functional copies of the affected genes into cells
- Infectious diseases and antibiotic resistance
- Understanding the cellular structure and metabolism of pathogenic microorganisms (bacteria, viruses) is essential for developing effective treatments
- Antibiotic resistance occurs when bacteria evolve mechanisms to counter the effects of antibiotics (efflux pumps, altered drug targets)
- Developing new antibiotics requires knowledge of the unique cellular features of bacteria
- Aging and cellular senescence
- Cellular senescence process by which cells stop dividing and undergo functional changes
- Accumulation of senescent cells contributes to age-related diseases and tissue dysfunction (cardiovascular disease, neurodegenerative disorders)
- Targeting senescent cells or their effects may help to promote healthy aging and prevent age-related diseases