Chapter 3 Lecture Notes

seperates the cell from its surrounding enviornment and controls what enters and leaves the cell.

thick gel-like substance inside of the cell composed of numerous organelles suspended in a water cytosol; each type of organelle is suited to perform a particular function

large membraneous structure near the center of the cell

sacs and canals made of the same material as the plasma membrane

• theory explaining how cell membranes are constructed
• - molecules are arranged in a sheet
• - the mosiac is fluid, molecules float around and slowly

• double layer of phospholipid molecules
• - heads hydropholic (water loving) 
• - tails are hydrophobic (water-fearing)
• -molecules are arranges in bilayers in water

1. membranous- specialized sacs or canals made of cell membranes

2. non membranous- made of microscopic filaments and other nonmebranous materials

• Ribosomes dot the outer surface of the membranous walls 
• Ribosomes synthesize proteins, which move toward the Golgi apparatus and then eventually leave the cell 
• Function in protein synthesis and intracellular transportation 

• –Functions are less well established and probably more varied than for rough endoplasmic reticulum 
• –Synthesizes certain lipids and carbohydrates and creates membranes for use throughout cell 
• –Removes and stores Ca++ from cell’s interior. 

• Function: synthesize protein 
• –Many are attached to the rough endoplasmic reticulum and many lie free, scattered through the cytoplasm 
• –Each ribosome is a nonmembranous structure made of two pieces, a large subunit and a small subunit; each subunit is composed of rRNA 
• –Ribosomes in the endoplasmic reticulum make proteins for “export” or to be embedded in the plasma membrane; free ribosomes make proteins for the cell’s domestic use 

• Membranous organelle consisting of cisternae stacked on one another and located near the nucleus
• –Processes protein molecules from the endoplasmic reticulum 
• –Processed proteins leave the final cisterna in a vesicle; contents may then be secreted to outside the cell

• Made of microscopic membranous sacs that have “pinched off” from Golgi apparatus 
• –The cell’s own digestive system; enzymes in lysosomes digest the protein structures of defective cell parts, including plasma membrane proteins, and particles that have become trapped in the cell

• Hollow, protein cylinders found throughout the cytoplasm 
• Break down abnormal/misfolded proteins and normal proteins no longer needed by the cell 

• Small membranous sacs containing enzymes that detoxify harmful substances that enter the cells 
• Often seen in kidney and liver cells 

• Made up of microscopic sacs; wall composed of inner and outer membranes separated by fluid; thousands of particles make up enzyme molecules attached to both membranes 
• –The “power plants” of cells; mitochondrial enzymes catalyze series of oxidation reactions that provide about 95% of cell’s energy supply 
• –Each mitochondrion has a DNA molecule, allowing it to produce its own enzymes and replicate copies of itself

spherical body in center of cell; enclosed by an envelope with many pores 

The cell’s internal supporting framework made up of rigid, rodlike pieces that provide support and allow movement and mechanisms that can move the cell or its parts 

• intricately arranged fibers of varying lengths that form a three-dimensional, irregularly shaped network 
• –Fibers appear to support the endoplasmic reticulum, mitochondria, and “free” ribosomes

• 1. Microfilaments are thin, twisted strands of protein molecule. shortening of the cell. 
• 2. Intermediate filaments are twisted protein strands slightly thicker than microfilaments; they form much of the supporting framework in many types of cells 
• 3. Microtubules are tiny, hollow tubes that are the thickest of the cell fibers; they are made of protein subunits arranged in a spiral fashion; their function is to move things around in the cell 

• An area of the cytoplasm near the nucleus that coordinates the building and breaking of microtubules in the cell 
• –Nonmembranous structure also called the microtubule-organizing center (MTOC) 
• –Plays an important role during cell division 
• –The general location of the centrosome is identified by the centrioles 

Cytoskeleton forms projections that extend the plasma membrane outward to form tiny, fingerlike processes

• Microvilli —found in epithelial cells that line the intestines and other areas where absorption is important; they help to increase the surface area manyfolds 
• Cilia and flagella —cell processes that have cylinders made of microtubules at their core; cilia (found in respiratory system) are shorter and more numerous than flagella; flagella are found only on human sperm cells 

• Desmosome Fibers on the outer surface of each desmosome interlock with each other; anchored internally by intermediate filaments of the cytoskeleton 
• Spot desmosomes, connecting adjacent membranes, are like “spot welds” at various points 
• Belt desmosomes encircle the entire cell like a collar 

• membrane channels of adjacent plasma membranes adhere to each other; have two effects: Form gaps or “tunnels” that join the cytoplasm of two cells 
• Fuse two plasma membranes into a single structure 

• Occur in cells that are joined by “collars” of tightly fused material 
• –Molecules cannot permeate the cracks of tight junctions 
• –Occur in the lining of the intestines and other parts of the body, where it is important to control what gets through a sheet of cells