Lecture Set 10 - Cells and the Cell Membrane - Fall 2024 PDF

The Cell Cell: An autonomous self-replicating unit that may constitute an organism or may be a subunit of a multicellular organism. The cell is the lowest level of structure capable of performing all of the activities of life independently.  Cell Theory All organisms are made up o...

The Cell Cell: An autonomous self-replicating unit that may constitute an organism or may be a subunit of a multicellular organism. The cell is the lowest level of structure capable of performing all of the activities of life independently.  Cell Theory All organisms are made up of cells. The cell is the fundamental unit of life. Cells come from preexisting cells. General Properties of All Cells All cells are surrounded by a plasma membrane. The semifluid substance within the membrane (i.e.*, inside the cell) is called the cytoplasm. All cells at some point contain chromosomes which have genes in the form of DNA. All cells also have ribosomes, tiny structures that make proteins using the instructions contained in genes. The abbreviation “i.e.” stands for id est, which is Latin for “that is.” The abbreviation “e.g.” stands for the Latin phrase exempli gratia, meaning “for example.” Bacterial cell  The Cell Interior  Cytoplasm: Material within the cell but outside of the nucleus, includes the organelles.  Cytosol: Material within the cytoplasm but outside of the membranous organelles  Organelle: A structurally and functionally discrete compartment or structure of the cell in which specific metabolic processes are localized.  The Cytoplasm Versus Cytosol Cytoplasm: Material within Cytosol: the cell but Material within outside of the the cytoplasm nucleus, but outside of includes the the organelles. membranous organelles  Prokaryotic and Eukaryotic Cells Cells can be classified as prokaryotic or eukaryotic. Prokaryotic cells lack a nucleus and have no internal compartmentalization. Eukaryotic cells have a nucleus and internal membrane-bound organelles.  Prokaryotic and Eukaryotic Cells Prokaryote Eukaryote Gr. pro “before” and karyon Gr. eu “true” and karyon “kernel” “kernel” Found only in Bacteria and Found in the Kingdoms Archaebacteria Animalia, Plantae, Protista, and Fungi No membrane-bound nucleus Possesses a membrane-bound nucleus Genetic material found in Genetic material contained nucleoid region within a nucleus No membrane-bound organelles Contains cytoplasm with a cytosol and membrane-bound organelles  Organelles Organelles work together Generally considered structures of eukaryotic cells to maintain the cell's (except ribosomes) structure and carry out its functions effectively. Most are membrane-bound (except ribosomes). Nucleus: The control center of the cell that contains the genetic material (DNA) and coordinates activities like growth, metabolism, and reproduction. Mitochondria: The powerhouse of the cell, producing energy (ATP) through cellular respiration. Ribosomes (both prokaryotes and eukaryotes): Sites of protein synthesis Endoplasmic Reticulum (rough and smooth): Sites of protein and lipid synthesis. Golgi Apparatus: Prepares proteins and lipids for secretion. Lysosomes: Cellular digestion Chloroplasts (in plant cells): Conducts photosynthesis to convert light energy into chemical energy (glucose). Typical Features of an Animal Cell Typical Features of a Plant Cell Typical Features of a Prokaryotic Cell ls Are Structurally and Functionally Diver ls Are Structurally and Functionally Diver Cells are small (mostly). Exceptions: bird eggs, neurons, some algal cells  The Plasma Membrane All cells are cells are enclosed by a plasma membrane. The plasma membrane: Is made of a phospholipid bilayer. Allows cells to maintain constant internal environment Is a selectively permeable barrier Often has proteins for receiving signals and binding molecules and and interacting with other cells. Cells Are Open Systems Cells Are Open Systems  Plasma Membrane Plasma Membrane: The external, limiting lipid bilayer membrane of a cell. 1. Composed mainly of phospholipids, cholesterol (only animal cells), and protein. 2. About 5 to 7 nm thick. 3. Controls chemical traffic into and out of the cell 4. Is selectively permeable Fun fact: Nanometer (nm) = 10-9 meters  Plasma Membrane Membrane function is determined by its composition and structure Phospholipids Proteins Cholesterol (only animals)  Cell Membranes Are Comprised of a Complex Mixture of Lipids and Proteins Phospholipids are Polar Amphipathic Nonpola r Phosphatidylcholine is a common phospholipid in cell membranes. The major lipids found in cell membranes are phospholipids. Phospholipids have both hydrophobic, nonpolar regions and hydrophilic, polar regions. Phospholipid s are amphipathic Froggies are amphibians that live both on land and in water  Phospholipid Bilayers In water, the polar phospholipid heads and nonpolar tails associate with one another to form a bilayer.  Membranes Are Bilayers of Phospholipids Water Van der Waals (hydrophobic) interactions between the fatty acid tails help stabilize the membrane. Water  Fluid Mosaic Model of Membran e Structure Proposed in 1972 by Singer and Nicolson. Describes the plasma membrane as a mosaic of proteins “floating” in a fluid bilayer of phospholipids.  Fluid Mosaic Model of Membran e A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in Structure place by plaster/mortar, and covering a surface. Proposed in 1972 by Singer and Nicolson. Describes the plasma membrane as a mosaic of proteins “floating” in a fluid bilayer of phospholipids.  The Fluid Mosaic Model The cell membrane is made of different parts working together, like a mosaic which is made of many different tiles. The different parts of the cell membrane include: Phospholipids, Cholesterol (animals), and Proteins. View Narration Transcript Link View Extended Audio Description Link  Cellular Membranes - Lipids Membranes may vary in lipid composition. Phospholipids tails can vary in chain length, degree of saturation (double bonds), and phosphate groups. Animal cell membranes may be up to 25% cholesterol.  Cellular Membranes - Lipids Phospholipid bilayers are flexible, and the interior is fluid, allowing lateral movement of molecules. Fluidity is affected by temperature and lipid composition. (rare )  Cell Membranes - Fluidity Low Melting Point High Melting Point (takes less energy to melt) (takes more energy to melt)  Cell Membranes - Proteins Membranes also contain proteins; the number and types of proteins varies with cell function. Proteins can comprise up to 50% of the mass (or more) of the plasma membrane.  Cell Membranes - Proteins There are two types of membrane proteins: Integral membrane proteins have hydrophobic and hydrophilic regions or domains. Some extend across the lipid bilayer; others are partially embedded. Peripheral membrane proteins lack exposed hydrophobic groups and do not penetrate the bilayer.  Cell Membranes - Proteins Peripher Peripheral membrane al proteins do not interact Protein with the hydrophobic interior of the bilayer Integral membrane proteins interact with both the hydrophobic interior and the Integr hydrophilic exterior of al Peripher the bilayer Protei al n Protein  Cell Membranes - Proteins (lack exposed (have both hydrophobic hydrophobic groups ) and hydrophilic regions)  Integral Membrane Polar Proteins Amin o Acids Nonpolar Amino Acids Polar Amin o Acids  Integral and Peripheral Proteins Many membrane proteins are able to move laterally along the membrane.  Proteins in the Membrane Proteins of the membrane include: transporters that move ions and molecules. receptors that allow the cell to receive signals from the environment. enzymes that catalyze chemical reactions in the cell. Soaps Are Modified Fatty Acids That “Dissolve” Oil and Dirt