Cells Chapter 3

Cellular Basis of Life Structural units of all living things Human adult has around 75 trillion cells Cells are 60% water, and bathed in a dilute saltwater solution (interstitial fluid) Cell Theory –Cell is the basic structural and functional unit of living organisms –Activity of an organism depends on activities of cells –Biochemical activities of cells are dictated by the relative number of their subcellular structures –Continuity of life has a cellular basis

Anatomy of a Generalized Cell Cells are not all the same! Generalized cell – demonstrates functions common to all cells –All cells have three main regions: Nucleus Cytoplasm Cell membrane

Cell Nucleus “headquarters” or control center of cell Contains DNA –Instructions for building proteins –Necessary for cell reproduction Conforms to shape of cell Three regions/structures –nuclear envelope (double layer) –nucleolus (nucleoli) RNA + protein site of ribosome production –Chromatin (DNA + protein) Form chromosomes

Fluid Mosaic Model Plasma Membrane Selectively permeable Composed of lipids, proteins, and carbohydrates in a phospholipid bilayer

Plasma Membrane Phospholipids –heads = hydrophilic, tails = hydrophobic –O 2 & CO 2 can pass through easily, others cannot Impermeable to water soluble molecules Cholesterol embedded in the bilayer – helps with structural stability LINK

Plasma Membrane Proteins have many functions! –Receptor proteins Receive hormones/chemical messengers –Form pores Water & water soluble molecules to pass through –Selective channels Transport specific ions –Glycoproteins form recognition sites (marker) Cell identification! Glycocalyx: sticky surface of cell due to sugars

Membrane Junctions Some cells loose in body (blood cells, sperm, phagocytic cells) Cells bound together in three ways: –Glycoproteins in glycocalyx act as adhesive –Wavy contours of membranes of adjacent cells fit in tongue-and-groove fashion –Special membrane junctions are formed (vary structurally depending on function!) Tight: impermeable, leakproof, prevent substances from passing through (like a zipper) Desmosomes: anchoring junctions (like rivets), prevents cells from being pulled apart Gap junctions: allow communication

Cytoplasm Cellular material outside the nucleus and inside the plasma membrane “factory area” where cellular activity takes place 3 elements: –Cytosol (fluid that suspends elements) –Organelles (metabolic machinery of cell) –Inclusions (chemical substances present based on the different type of cell) i.e. lipid droplets in fat cells, glycogen granules in liver/muscle cells, pigments in hair & skin cells, mucus, etc.

Pg

Cell Extensions Cilia Flagella

Cell Diversity STRUCTURE DETERMINES FUNCTION Over 200 different cell types in the human body Cells differentiate in development Vary in size, shape, and function

Cell Diversity Figure 3.8a Rough ER and Golgi apparatus No organelles Nucleus (a) Cells that connect body parts

Cell Diversity Nucleus Intermediate filaments (b) Cells that cover and line body organs Figure 3.8b

Cell Diversity Nuclei Contractile filaments (c) Cells that move organs and body parts Figure 3.8c

Cell Diversity Figure 3.8d Lipid droplet (d) Cell that stores nutrients Nucleus

Cell Diversity Lysosomes (e) Cell that fights disease Pseudopods Figure 3.8e

Cell Diversity Figure 3.8f Processes Rough ER Nucleus (f) Cell that gathers information and controls body functions

Cell Diversity Nucleus Flagellum ( g) Cell of reproduction Figure 3.8g

Cell Physiology: Membrane Transport Movement of substances into and out of the cell Cell membranes are selectively permeable –Some substances can pass through but others cannot (only healthy/unharmed cells!) –Due to phospholipid bilayer Two basic methods of transport: –Passive process (no energy required) –Active processes (cell must provide metabolic energy (ATP) ATP

Membrane Transport Passive mechanisms –Simple diffusion –Osmosis –Facilitated diffusion –Filtration Active mechanisms –Active transport (solute pumping) –Vesicular transport Exocytosis Endocytosis

Passive Transport: Diffusion Molecules and ions move away from a region where they are more concentrated to a region where they are less concentrated –Concentration gradient (rate affected by differences in concentration) –Powered by kinetic energy (rate of diffusion affected by size of particles & temperature) Phospholipids control diffusion through membrane. Molecules diffuse if: –Small enough to pass through pores formed by proteins (simple) –Lipid soluble (simple) –Assisted by a membrane carrier

Passive Transport: Diffusion Simple diffusion: unassisted diffusion of solutes through a selectively permeable membrane –Lipid-soluble (fats, fat-soluble vitamins, O 2, CO 2 ) –Pass through membrane pores (small ions such as Cl - ) Osmosis: diffusion of water through selectively permeable membrane –Passes through aquaporins protein (channels) Cytoplasm (a) Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer Extracellular fluid Lipid- soluble solutes (d) Osmosis, diffusion of water through a specific channel protein (aquaporin) or through the lipid bilayer Water molecules Lipid bilayer

Osmosis

Passive Transport: Diffusion Facilitated diffusion –Passage of lipid-insoluble and large molecules (i.e. glucose) –Uses protein carriers or channels –Down concentration gradient Filtration –Water and solutes forced through a membrane (or capillary wall) by fluid (hydrostatic) pressure –Move down pressure gradient –Solute-containing fluid (filtrate) –Not selective (blood cells & proteins too large) –i.e. kidneys

Active Transport Cell uses ATP supply to move substances across the membrane –Substances too large for channels, membrane lacks protein carriers for them, not lipid- soluble, or against concentration gradient Solute pumping (active transport) : require protein carriers (solute pumps powered by ATP) –Very specific –Amino acids, most ions, some sugars, sodium-potassium pump

Active Transport: Vesicular Transport Uses ATP to move substances into or out of cells without their actually crossing the plasma membrane Exocytosis: moves substances out of cell –Secrete hormones, mucus, and other cell products or eject cellular wastes (i.e. secretory cells, nerve cells) –Packaged in golgi into a vesicle Endocytosis: moves substances into cell –Engulf extracellular substances by enclosing them in small vesicle, digested by lysosomes –Phagocytosis: use pseudopods (phagocytes) – protective mechanism (i.e. macrophages, neutrophils) –Pinocytosis: cell “gulps” droplets of ECF (absorption, i.e. small intestine) Phagocytosis

Exocytosis

Endocytosis

Cell Cycle Series of changes a cell goes through from the time it is formed until it divides Two periods: –Interphase (“living”): cell grows & carries on usual metabolic activities DNA replication occurs (S phase) –Cell division: reproduction of the cell

Cell Division Mitosis –Prophase –Metaphase –Anaphase –Telophase Cytokinesis –Division of cytoplasm –Liver (binucleate and multinucleate cells due to no cytokinesis)

Cell Differentiation Process by which cells develop different characteristics in structure & function 200 different cell types!