Eukaryotic cells are complex structures with specialized compartments called organelles. These organelles work together to keep cells functioning smoothly. Understanding cell structure is key to grasping how cells carry out their roles in tissues and organs.

Prokaryotic and eukaryotic cells differ in size, genetic material organization, and internal structures. These differences impact how each cell type operates. Cell membranes and the cytoskeleton are crucial for maintaining cell shape, movement, and communication with the environment.

Cell Structure and Organization

Organelles in eukaryotic cells

• Nucleus houses genetic material (DNA) controls cellular activities and contains nucleolus for ribosome production
  • Double membrane structure with nuclear pores
  • Chromatin organization (heterochromatin and euchromatin)
• Endoplasmic Reticulum (ER) network of membranes involved in protein and lipid synthesis
  • Rough ER studded with ribosomes synthesizes and modifies proteins
  • Smooth ER produces lipids and detoxifies substances (liver cells)
• Golgi Apparatus modifies packages and distributes proteins produces lysosomes
  • Consists of stacked membrane-bound sacs (cisternae)
  • Adds sugar molecules to proteins (glycosylation)
• Mitochondria generate energy through cellular respiration produce ATP
  • Double membrane structure with inner membrane folds (cristae)
  • Contains own DNA (mitochondrial DNA)
• Lysosomes contain digestive enzymes break down cellular waste and foreign materials
  • Single membrane-bound vesicles
  • Involved in autophagy and apoptosis
• Peroxisomes involved in oxidative metabolism detoxify hydrogen peroxide
  • Single membrane-bound organelles
  • Contain enzymes for fatty acid oxidation
• Ribosomes synthesize proteins found free in cytoplasm or attached to rough ER
  • Composed of rRNA and proteins
  • Two subunits (large and small)
• Cytoskeleton provides structural support and enables cell movement
  • Microfilaments (actin) maintain cell shape and facilitate muscle contraction
  • Microtubules transport vesicles and form mitotic spindle
  • Intermediate filaments provide mechanical strength (keratin in skin cells)
• Centrosomes organize microtubules crucial for cell division
  • Contain two centrioles
  • Form spindle poles during mitosis

Prokaryotic vs eukaryotic cells

• Cell size differs prokaryotes typically smaller (0.1-5 μm) eukaryotes generally larger (10-100 μm)
  • Prokaryotes (bacteria)
  • Eukaryotes (animal and plant cells)
• Genetic material organization varies prokaryotes have circular DNA in nucleoid region eukaryotes possess linear DNA enclosed in nucleus
  • Prokaryotic DNA is often associated with proteins (nucleoid)
  • Eukaryotic DNA is organized into chromosomes
• Membrane-bound organelles absent in prokaryotes present in eukaryotes (mitochondria ER Golgi)
  • Prokaryotes have simpler internal structure
  • Eukaryotes compartmentalize cellular functions
• Cell wall composition differs prokaryotes have peptidoglycan eukaryotes have cellulose (plants) or lack cell wall (animals)
  • Bacterial cell walls provide structural support and protection
  • Plant cell walls consist of cellulose microfibrils
• Ribosomes vary in size prokaryotes have 70S ribosomes eukaryotes possess 80S ribosomes
  • Prokaryotic ribosomes are smaller and simpler
  • Eukaryotic ribosomes are larger and more complex
• Cell division mechanisms differ prokaryotes undergo binary fission eukaryotes use mitosis and meiosis
  • Binary fission is a simpler process
  • Mitosis and meiosis involve complex chromosome segregation
• Energy production sites vary prokaryotes use cell membrane or mesosomes eukaryotes utilize mitochondria
  • Prokaryotic electron transport chain in cell membrane
  • Eukaryotic oxidative phosphorylation in mitochondria

Functions of cell membranes

• Phospholipid bilayer forms basic membrane structure hydrophilic heads face extracellular and intracellular spaces hydrophobic tails form interior
  • Amphipathic nature of phospholipids
  • Fluidity allows membrane flexibility
• Membrane proteins perform various functions integral proteins span entire membrane peripheral proteins attach to surface
  • Integral proteins (transmembrane proteins)
  • Peripheral proteins (surface proteins)
• Passive transport moves molecules along concentration gradient without energy expenditure
  • Simple diffusion (oxygen carbon dioxide)
  • Facilitated diffusion (glucose through GLUT transporters)
• Active transport uses energy to move molecules against concentration gradient
  • Primary active transport (sodium-potassium pump)
  • Secondary active transport (glucose-sodium symporter)
• Bulk transport mechanisms move large molecules or particles
  • Endocytosis (phagocytosis pinocytosis receptor-mediated endocytosis)
  • Exocytosis (neurotransmitter release hormone secretion)
• Selective permeability allows specific molecules to pass through maintains internal environment
  • Ion channels regulate ion flow
  • Aquaporins facilitate water movement
• Osmosis involves water movement across semipermeable membrane influenced by solute concentration
  • Hypotonic hypertonic and isotonic solutions
  • Osmotic pressure in plant cells (turgor pressure)

Importance of cytoskeleton

• Microfilaments (actin filaments) maintain cell shape enable muscle contraction participate in cytokinesis
  • Form stress fibers for cell adhesion
  • Create contractile ring during cell division
• Intermediate filaments provide structural support anchor organelles form nuclear lamina
  • Keratin in epithelial cells
  • Neurofilaments in neurons
• Microtubules facilitate intracellular transport form spindle fibers enable cilia and flagella movement
  • Microtubule-organizing centers (centrosomes)
  • Axonemal structure in cilia and flagella
• Motor proteins interact with cytoskeletal elements for various cellular processes
  • Kinesin moves cargo towards cell periphery (anterograde transport)
  • Dynein transports material towards cell center (retrograde transport)
  • Myosin interacts with actin in muscle contraction
• Cytoskeletal dynamics involve constant assembly and disassembly
  • Treadmilling in actin filaments
  • Dynamic instability of microtubules
• Cell motility mechanisms vary among cell types
  • Amoeboid movement through pseudopodia formation
  • Flagellar and ciliary motion in sperm cells and respiratory epithelium
• Cell polarity establishment creates distinct cellular regions crucial for division and differentiation
  • Apical-basal polarity in epithelial cells
  • Axon-dendrite polarity in neurons