CELLS Structure

Cell Membrane Surrounds the cell to separate it from its external environment Composed of a phospholipid bilayer that has proteins embedded in it Cholesterol is also an important component of cell membranes since it keeps the membrane intact yet fluid The membrane acts as a selective barrier by controlling what substances enter and leave the cell

Membrane Structures Microvilli (microvillus): extensions of the cell membrane used to increase the surface area of the cell Cilia (cillium): short, hair-like extensions on the cell membrane used for movement Flagella (Flagellum): long, whip- like structures used for movement

Cell Interior Cytoplasm:  A semi-fluid substance in which all of the cell’s organelles are suspended  Located between the nucleus and the cell membrane  Contains the cytoskeleton Cytoskeleton: a network of microtubules that support the cell and give it shape

Nucleus Nucleus: the control center of the cell and where the cell’s DNA is located Nuclear Membrane:  Separates the nucleus from the cytoplasm  Contains pores so that substances may enter or leave the nucleus Nucleolus: structure within the nucleus that is responsible for making rRNA Nucleoplasm: similar to the cytoplasm, it is a semifluid substance in which the DNA and nucleolus are suspended

Organelles Endoplasmic reticulum (ER):  Extensive network of membranes  There are 2 types: Rough ER: contains ribosomes that make proteins destined to leave the cell Smooth ER: makes lipids, steroids, and is involved in detoxification; important in cells that are responsible for ridding the body of toxic substances (i.e. liver)

Organelles (cont.) Ribosomes:  Structures involved in protein synthesis  Found attached to the RER or suspended in the cytoplasm Mitochondria: structures used to make ATP (energy compound) Golgi complex (apparatus):  Series of flat membrane-bound sacs  Packages proteins made from the RER and sends them in membrane- bound vesicles to their destination

Organelles (cont.) Vacuole:  Membrane-bound compartment that serves many functions (i.e. absorbs water, stores proteins, stores wastes, etc.)  Plant cells have one large central vacuole whereas animal cells contain several small vacuoles

Organelles (cont.) Lysosome:  Membrane-bound organelles filled with hydrolytic enzymes  These enzymes are used to break down substances (i.e. carbohydrates, proteins, lipids, old organelles, etc.) Pinocytotic Vesicles:  Membrane-bound compartments used to bring substances across the cell membrane  The membrane of these vesicles is actually part of the cell membrane that has “pinched” off

Cell Division Structures Centrosome:  Structure used during cell division  Spindle apparatus attaches here  Made up of a pair of centrioles Centrioles:  Made up of 9 sets of triplet microtubules