Biophysics Lec. 3 PDF

The cell  Abdo EIfiky Topics The cell: What is a cell? Cell theory. structure. Cell The membrane....

The cell  Abdo EIfiky Topics The cell: What is a cell? Cell theory. structure. Cell The membrane. cell Membrane transport. Receptors. Dr.AbdoA Elfiky Monday, October 2 21, 2024  Abdo ElIfiky What is a cell? A cell is a pouch or sack of biomolecules that is (orwas) alive. A cell is the smallest unit of an organism that can be considered alive. If you break the cell anything smaller, it's just a into bunch of biomolecules and not consideredalive. The pouch or sack is part of the cell itself and is called the cell membrane. Monday, October Dr. Abdo A EIfiky 22, 2024 3  Abdo EIiky Cell theory Cell theory says (1) all living things are made of cells and (2) allcells come from preexisting cells (cell division). In cell division, a cell replicates its DNA and then splits into two daughter cells. Each of the daughter cells gets a copy of the replicated DNA. Monday, Dr. Abdo A Elfiky October21, 2024  Abdo Elfiky Celltheory (continued) An organism can be single cellular, that is, made up of a single cell (like an amoeba) or multicellular (like people). Cells themselves can grow, by taking in matter and energy to build up their internal structures and increase their membrane size. Single-cell organisms grow as a cell grows. Multicellular organisms grow primarily by adding cells to themselves through cell division. Mondav, October Dr. Abdo A EIfiky 21, 2024 5  Abdo Elfiky Cell theory (continued) There are many different types of cells. The cells of different organisms can be very different from one another. But even within the same organism cells specialize to carry out different functions. Nerve cells are long and thin like wiresto carry nerve impulses throughout the body. Muscle cells can contract to provide movement. Skin cells are flat and strong to protect the body. Bonemarrow manufacture blood cells which carry cells Oxygen through the blood. The processof a young maturing to specialize and cell become a particulartype of cell is known as differentiation. Monday,October Dr. AbdoA EIfiky 21, 2024 6  Abdo Efky CellstrUcture All cells are surrounded by a lipid bilayer membrane that encloses and contains the contents of thecell. many lipids are amphipathic, having both hydrophobic and hydrophilic parts on the same molecule. In an aqueous or polar environment these molecules arrange themselves in complexes (aggregates of molecules) that place their hydrophobic parts inside, away from the water, and their hydrophilic parts on the outside, facing the water. One such complex is a lipid bilayer. Monday, Dr. Abdo A Elfiky October 21, 8 2024  Abdo Elfiky Cell structure (continued) The bilayer forms a membrane around the cell. The polar, hydrophilicportions of lipid molecules face the aqueous environments on both the inside and outside of the cell. The nonpolar, hydrophobic parts lie in the center of the bilayer and form a barrier that blocks many molecules from crossing the membrane. The cell membrane is in fact selectively permeable, meaning that certain types of molecules can pass through the membrane, whereas others cannot. Monday, Dr. Abdo A EIfiky October 21, 2024  Abdo Elfiky Cellstructure (continued) There are two major categories of cells, and all organisms are made up entirely ofone of these two categories of cells eukaryotic and prokaryotic. There are some important distinctionsbetween eukaryotes and prokaryotes. Eukaryotes, in addition to a nucleus, have other membrane-bound, internal structures called organelles. These organelles compartmentalize some ofthefunctions ofthe cell. Monday,October 10 Dr. AbdoA Elfiky 22, 2024  Abdo Efiky Cell structure (continued) oytoplasm microtubules chromatin / nuclearenvelope nucleus mitochondrion, /nuclear pore nucleolus oid centriole. Golgi complex Capsule lysosome vesicle Cell Wal ytoplasmie Membrane cytosol Ribosomes flagellum plasma membrane Flagella rough smooth lendoplasmic endoplasmic ribosomes reticulum reticulum Prokaryotes VS) Eukaryotes Monday, Dr. Abdo A Elfiky October 21, 11 2024 TABLE 8-1 Eukaryotes and prokaryotes compared. Eukaryotes Prokaryotes Nucleus and other membrane-bound No nucleus. Genetic material a4ENy organellescompartmentalize the cell. biomolecules are all together in the cytoplasm. Mostly multicellular; some Unicellular (some have colonial or unicellular. multicelular stage of life). Slower division rates. Rapid division rates.Can adapt quickly to drastic changes in environment. Can carry out more complex and Biochemical reactions are simpler, more efficient biochemicalreactions, and must all occur in the cytoplasm because reactions can be isolated in where more complex reactions might membrane-bound compartments interfere with each other. Also, less where reactants can be brought efficient in bringing reactants closer together. together. Tend to be larger, since able to Tend to be smaller. Nutrients obtained ingest nutrients actively and process primarily through inefficiently, those nutrients with a wide variety of diffusion, and processed with only a reactions for efficient growth and simple set of biochemical reactions. maintenance. Typical size is 10 to 100 um across. Typical size is 0.1 to 10 um across. Plants and animals. Bacteria and archaea. Monday, Dr. Abdo A Elfiky October23, 12 2024  Abdo Efiky The cell membrane In addition to lipids, cell membranes contain a variety of molecules embedded in, or connected to, the lipid bilayer. These include proteins, carbohydrates, glycoproteins (proteinswith carbohydrate attached), and glycolipids (lipids with carbohydrate attached). These molecules are often classified in terms of how deep they are within the membrane. such a molecule is embedded deep into the membrane, we If call it integral, forexample, integral membrane protein. Those that are just on the surface (butare still fundamentally part of the membrane) are called peripheral. If a molecule is embedded allthe way through the membrane, sticking out on both sides, it is called transmembrane. Monday, Dr. AbdoA EIfiky October21, 14 2024  Abdo Elfiky outer face hydrophilic (polar) head hydrophobic of phosphoipid (nonpolar) Sugar side chain fatty acid tail of phospholipid cholesterol integral (intrinsic)proteins peripheral (extrinsic) protein innerface 2007 Encyclopædia Britannica,Inc. Monday, Dr. Abdo A EIfiky October 21, 15 2024  Abdo EIfiky Membrane transport Both the inside and outside of the cell are typically aqueous environments. In order for a molecule to dissolve in an aqueoUs environment such as blood or cytoplasm, the molecule must be polar or hydrophilic. But for a molecule to penetrate the membrane's lipid barrier, the molecule must be lipid soluble,that is,nonpolar or hydrophobic. The hydrophobic portion of the membrane acts as a barrier to keep molecules from passing through. Some small molecules are able to pass through the membrane. Monday, Dr. Abdo A Elfiky October24, 16 2024  Abdo EIfiky Membrane transport (continued) Environment Food particle The cell has a in taken by endocytosis variety of ways to Exocytosis of waste/ transport Food molecules Products of -particles digestion digested through the membrane when Fusion forms it needs to. secondary lysosome aozow 26COug Monday, Dr. AbdoA Elfiky October 21, 17 2024  One method is via membrane Abdo Elfiky transport proteins. These are transmembrane proteins that assist other molecules in getting through the membrane.They may simply provide a channel or tunnel for the molecule to pass through. Or they may bind the Membrane other molecule and thenundergo a transport conformational change that essentially pulls the other molecule (continued) through the membrane. Channel Carrier proteln protein energy, bilayer Passive Active transport transport Dr. AbdoA Elfiky Monday, October 21, 2024 18  Two other methods are endocytosis and Abdo Elfiky exocytosis. Inendocytosis, a portion of the cell membrane folds in toward the cell. At the same time, this portion of membrane engulfs some molecule or molecules from'outside the cell. This portion of membrane then breaks off from the membrane and carriesthe engulfed contents into the cell. Exocytosis is the Membrane opposite process and is used by cells to secrete materials or to eliminate waste. In exocytosis a transport small membrane pouch of material merges (continued) with the cell membrane, releasing its contents outside the cell. OUTSIDE THE CELL 2 CYTOPLASM Vescie Monday, October Dr.AbdoA Elfiky 21, 2024 19  Abdo Elfiky Receptors A receptor is a molecule in the membrane (such as a protein, glycoprotein, glycolipid, or carbohydrate) that has at least a portion of itself on the surface of the membrane. This portion has specificity for some other molecule. This means that only one particular type of molecule can bind tothe receptor. Monday, October Dr. Abdo A Elfiky 20 21, 2024  Abdo Elfiky Receptors (continue) The binding of a specific molecule to its receptor is often a signal for the cell to do something. For example, binding of a certain molecule to a receptor might signal to the cell that it should increase its production of a certain enzyme. Sometimes receptors are also transport proteins. If the receptor is also a transport protein, may then pull that bound molecule it through the cell membrane into the cell. Monday, October 221 Dr. AbdoA Elfiky 22, 2024