Cell Structure and Function 1

Introduction 1.The cell is the structural and functional unit of all living organisms. 2.All human cells originate from a single fertilized egg (zygote). 3.During development, cell division and specialization give rise to trillions of cells with a wide variety of cell types, such as nerve, muscle, bone, fat and blood cells. 4.Each cell type has important characteristics to perform a particular function. 2

Cell Structure and Function How we learn about cells? 1.Because most cells are too small to be seen with the unaided eye, it is necessary to use microscopes to study cells. 2.Light microscopes allow us to visualize some general features of cells. 3.Electron microscopes allow us to study the fine structure of cells. 4.Microscopic techniques only allow us to study cell structure. Therefore, other techniques such as tissue culture must be employed to study cell function. 3

Cell Structure and Function Cells are enclosed by a plasma membrane Each cell is surrounded by a thin plasma membrane, which isolates the cell's contents from the external environment. Functions of plasma membrane 1.Enclose and support the cell contents. 2.Control the movements of substances into and out of the cell. Structure of plasma membrane 1.The plasma membrane is made up of lipid, protein and carbohydrate components. 4

Cell Structure and Function Cytoplasm 1.The cytoplasm is the cellular material inside the plasma membrane and outside the nucleus. 2.The fluid portion of the cytoplasm contains various inorganic and organic chemicals that are dissolved and/or suspended. This fluid suspension is called the cytosol. 5

Cell Structure and Function Cytoplasm contains organelles 1.Organelles are small structures within cells that are specialized for particular functions. 2.Most organelles have membranes that are similar to the plasma membrane. 6

Cell Structure and Function Ribosomes 1.Ribosomes are the sites of protein synthesis. 2.Each ribosome is composed of a large subunit and a smaller one. 3.Ribosomes can be found free in the cytoplasm (free ribosomes) or associated with membranes called the endoplasmic reticulum (attached or bound ribosomes). 7

Cell Structure and Function Endoplasmic reticulum The endoplasmic reticulum consists of broad, flattened, interconnecting membrane-limited sacs (cisternae) and tubules Rough endoplasmic reticulum (RER) 1.Is endoplasmic reticulum with attached ribosomes. 2.The cisternae of RER are arranged in parallel. 3.The function of RER is the synthesis of proteins. Smooth endoplasmic reticulum 1.Is endoplasmic reticulum that lacks ribosomes. 2.Consists of membrane-limited vesicles and branched tubules. 3.It manufactures lipids and carbohydrates. 8

Cell Structure and Function Endoplasmic reticulum 9

Cell Structure and Function Golgi apparatus 1.It is composed of slightly curved smooth-surfaced cisternae that run in parallel. 2.The cisternae are slightly expanded at either ends. 3.Numerous small vesicles are associated with the ends of the cisternae. 4.The Golgi apparatus modifies (adds sugars to proteins) and packages proteins to form secretory vesicles which fuse with the plasma membrane as secretion occurs. Thus, secretion is the main role played by Golgi apparatus. 10

Cell Structure and Function Mitochondria 1.They are usually rod-shaped structures. 2.Each mitochondrion has inner and outer membranes separated by intermembrane space. 3.The outer membrane is a smooth, but the inner membrane has numerous folds called cristae. 4.They produce the energy in the form of ATP. 11

Cell Structure and Function Lysosomes 1.Lysosomes are membrane-bounded vesicles that pinch off from Golgi apparatus. 2.Contain a great variety of hydrolytic enzymes that are used for intracellular digestion. 3.Their hydrolytic enzymes are capable of digesting foreign materials, such as bacteria. 12

Cell Structure and Function Centrioles 1.Animal cells contain two centrioles that are oriented perpendicular to each other. 2.Each centriole is a small cylindrical organelle with a microtubular structure. 3.Synthesize microtubules of cilia and flagella and spindle fibers during cell division. 13

Cell Structure and Function Nucleus 1.It contains our genetic information. 2.It consists of three distinguishable parts: The nuclear envelope. Chromatin. Nucleolus. 14

Cell Structure and Function Nuclear Envelope 1.The nucleus is bounded by a nuclear envelope which separates the nuclear material from the cytoplasm. 2.It consists of two parallel membranes, the outer nuclear membrane and the inner nuclear membrane. 3.The nuclear envelope is interrupted at many sites by small nuclear pores. 4.It controls the passage of materials. Chromatin 1.The nucleus contains a granular-looking material called chromatin. 2.Chromatin is a complex of DNA and proteins called histones. 15

Cell Structure and Function Nucleolus 1.It is a dense region within the nucleus. 2.Lacks a surrounded membrane. 3.It manufactures the subunits of ribosomes. 16