HAPP LEC CHAPTER 3

• Cell Structure and Functions:

  • Organelles are specialized structures in cells that perform specific functions
  • Examples of organelles include the nucleus, mitochondria, and ribosomes
• Cytoplasm:

  • Jelly-like substance that holds organelles
• Cell Membrane:

  • Also known as the plasma membrane
  • Encloses the cytoplasm
  • Acts as a selective barrier
• Functions of the Cell:

  • Smallest units of life
  • Cell metabolism and energy use
  • Synthesis of molecules
  • Communication
  • Reproduction and inheritance
• Cell Membrane Structure:

  • Fluid-mosaic model is used to describe the cell membrane structure
  • Contains phospholipids, cholesterol, proteins, and carbohydrates
  • Phospholipids form a bilayer with polar and nonpolar regions
• Movement through the Cell Membrane:

  • Cell membrane has selective permeability
  • Substances like enzymes, glycogen, and potassium are found in higher concentrations inside the cell
  • Substances like sodium, calcium, and chloride are found in higher concentrations outside the cell
• Diffusion:

  • Involves movement of substances down a concentration gradient
  • Solutes move from an area of higher concentration to an area of lower concentration
  • Concentration gradient is the difference in solute concentration between two points divided by the distance between them
• Osmosis:

  • Diffusion of water across a selectively permeable membrane
  • Osmotic pressure is the force required to prevent movement of water across the cell membrane
  • Cells can be in hypotonic, isotonic, or hypertonic solutions
• Facilitated Diffusion:

  • Carrier-mediated transport process that moves substances across the cell membrane from higher to lower concentration
  • Does not require metabolic energy like ATP
• Active Transport:

  • Requires ATP to move substances across the cell membrane from lower to higher concentration
  • Sodium-potassium pump is an example of active transport
• Secondary Active Transport:

  • Uses energy provided by a concentration gradient established by active transport of one substance to transport other substances
  • No additional energy is required beyond the initial active transport
• Endocytosis:

  • Process that brings materials into the cell using vesicles
  • Includes receptor-mediated endocytosis, phagocytosis, and pinocytosis
• Exocytosis:

  • Involves the release of materials from the cell using secretory vesicles
  • Examples include the secretion of digestive enzymes
• General Cell Structure:

  • Cytoplasm is a jelly-like fluid that surrounds organelles
  • Organelles include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, cytoskeleton, centrioles, cilia, flagella, and microvilli
• Cell Nucleus:

  • Located near the center of the cell
  • Bounded by a nuclear envelope with nuclear pores
  • Contains chromosomes made of DNA and proteins
  • Nucleoli are found within the nucleus and produce ribosomal components
• Ribosomes:

  • Organelles where proteins are produced
  • Can be free or attached to other organelles like the endoplasmic reticulum
• Endoplasmic Reticulum:

  • Series of membranes forming sacs and tubules
  • Rough ER is involved in protein synthesis
• Endoplasmic reticulum (ER) is a series of membranes forming sacs and tubules that extends from the outer nuclear membrane into the cytoplasm
• Rough ER is involved in protein synthesis and is rough due to attached ribosomes
• Smooth ER has no attached ribosomes and is a site for lipid synthesis, cellular detoxification, and it stores calcium ions in skeletal muscle cells
• Golgi apparatus consists of closely packed stacks of curved, membrane-bound sacs
• It collects, modifies, packages, and distributes proteins and lipids manufactured by the ER
• The Golgi apparatus forms vesicles, some of which are secretory vesicles, lysosomes, and other vesicles
• Lysosomes are membrane-bound vesicles formed from the Golgi apparatus
• They contain a variety of enzymes that function as intracellular digestive systems
• Vesicles formed by endocytosis may fuse with lysosomes in order to breakdown materials in the endocytotic vesicles
• One example is white blood cells phagocytizing bacteria
• Peroxisomes are small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H2O2)
• Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell
• The enzymes in peroxisomes break down hydrogen
• Mitochondria are small organelles responsible for producing considerable amounts of ATP by aerobic metabolism
• They have inner and outer membranes separated by a space
• The material within the inner membrane is the mitochondrial matrix and contains enzymes and mitochondrial DNA (mtDNA)
• Cells with a large energy requirement have more mitochondria than cells that require less energy
• The cytoskeleton gives internal framework to the cell
• It consists of protein structures that support the cell, hold organelles in place, and enable the cell to change shape
• Protein structures in the cytoskeleton are microtubules, microfilaments, and intermediate filaments
• Microtubules are hollow structures formed from protein subunits
• They help support the cytoplasm of cells, assist in cell division, and form essential components of certain organelles such as cilia and flagella
• Microfilaments are small fibrils formed from protein subunits that structurally support the cytoplasm, determining cell shape