A Tour of the Cell Ch. 7
Cell Theory O All organisms are composed of one or more cells. O The cell is the basic unit of structure and organization of organisms. O All cells come from preexisting cells.
Cell Theory O Prokaryotic cells (bacteria) O Have a very simple structure O DO have a plasma membrane O DO NOT have membrane bound organelles
Cell Theory O Eukaryotic Cells (every other cell) O More complex structure O DO have a plasma membrane O DO have membrane bound organelles
The Plasma Membrane O A Thin and flexible boundary between the cell and its environment O Lets nutrients in O Lets waste out
The Plasma Membrane O Has Selective Permeability: Controls the movement of substances entering and exiting the cell
The Plasma Membrane O Is composed primarily of 2 layers of phospholipid molecules O Known as the phospholipid bilayer O Remember: a phospholipid is made up of O Glycerol O 2 fatty acids (non-polar) O Phosphate group head (polar)
The Plasma Membrane O The Fluid Mosaic Model: Other molecules float on and in the membrane O They move, so it is fluid O Like boats and buoys floating on and in a lake O Other components O Proteins O Carbohydrates O Cholesterol
The Plasma Membrane O Proteins O Allow signals to be passed into a cell O Create a pore through which substances can pass O Provide support
The Plasma Membrane O Cholesterol: helps control how fluid or how much the membrane is allowed to bend/flex O Keeps it from flexing too much at higher temperatures O Helps prevent freezing at very low temperatures
The Plasma Membrane O Carbohydrates: Like cellular ID tags O Allows cells to recognize as self and non self O Can identify chemical signals
Cells and Cellular Structures O Cells fall into 2 different categories based on structure: O Prokaryotic O Eukaryotic O Prokaryotic cells are bacteria O Eukaryotic cells are plant cells and animal cells
Cells and Cellular Structures O Basic features of all cells O Plasma membrane O Semifluid substance called the cytoplasm or cytosol O DNA (carry genes) O Ribosomes (make proteins)
Cells and Cellular Structures O Prokaryotic cells are characterized by having O No nucleus O DNA in an unbound region called the nucleoid O No membrane-bound organelles O Cytoplasm bound by the plasma membrane O A cell wall necessary for survival
Cells and Cellular Structures O Eukaryotic Cells O Have membrane bound organelles that compartmentalize function of individual organelles O Have cytoplasm O Have a cell membrane
O The interior of a eukaryotic cell has membranes that enclose organelles O These organelles have specific functions that help the cell stay productive and alive and able to reproduce
O Organelles we ll study O Nucleus O Endoplasmic reticulum O Golgi apparatus O Lysosomes O Vacuoles O Plasma membrane O Mitochondria O Chloroplasts (plants)
The nucleus O The nucleus contains most of the cell s genes and is usually the most visible organelle O The nuclear envelope encloses the nucleus, separating it from the cytoplasm O The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer O Prokaryotes (bacteria) DO NOT HAVE A NUCLEUS
O In the nucleus, DNA is organized into discrete units called chromosomes O Each chromosome is composed of a single DNA molecule associated with proteins O The DNA and proteins of chromosomes are together called chromatin O The nucleolus is located within the nucleus and is where a special type of RNA is made
O ENDOPLASMIC RETICULUM: O The endoplasmic reticulum (ER) accounts for more than half of the total space in many eukaryotic cells O There are two distinct types of ER O Smooth ER, which lacks ribosomes O Rough ER, surface is studded with ribosomes Ribosomes are where proteins are made
O The smooth ER O Synthesizes lipids O Metabolizes (breaks down) carbohydrates O Detoxifies drugs and poisons O Stores calcium ions
O The rough ER O Has bound ribosomes which make proteins for the cell membrane O Is a membrane factory for the cell
O The Golgi Apparatus: Shipping and Receiving Center O The Golgi apparatus consists of flattened membranous sacs O Functions of the Golgi apparatus O Modifies products of the ER O Manufactures certain macromolecules O Sorts and packages materials into transport vesicles
O Lysosomes: Digestive Compartments O A lysosome is a membranous sac of enzymes that can digest macromolecules O Lysosomal enzymes can digest proteins, fats, polysaccharides, and nucleic acids O Lysosomal enzymes work best in the acidic environment inside the lysosome
O Lysosomes, continued O Some types of cells can engulf another cell by phagocytosis; this forms a food vacuole O A lysosome fuses with the food vacuole and digests the molecules O Lysosomes also use enzymes to recycle the cell s own organelles and macromolecules
O Vacuoles: Diverse Maintenance Compartments O A plant cell or fungal cell may have one or several vacuoles O Food vacuoles are formed by phagocytosis O Contractile vacuoles, found in many freshwater protists, pump excess water out of cells O Central vacuoles, found in many mature plant cells, hold organic compounds and water
Central vacuole of a plant
O Mitochondria and chloroplasts change energy from one form to another Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP O Chloroplasts, found in plants and algae, are the sites of photosynthesis
O Mitochondria and chloroplasts have similarities with bacteria O Enveloped by a double membrane O Contain free ribosomes and circular DNA molecules O Grow and reproduce somewhat independently in cells
O The cytoskeleton is a network of fibers that organizes structures and activities in the cell O The cytoskeleton is a network of fibers extending throughout the cytoplasm O It organizes the cell s structures and activities, anchoring many organelles O It is composed of three types of molecular protein structures O Microtubules O Microfilaments O Intermediate filaments
O Roles of the Cytoskeleton: Support and Motility O The cytoskeleton helps to support the cell and maintain its shape O It interacts with motor proteins to produce motility (movement) O Inside the cell, vesicles can travel along monorails provided by the cytoskeleton