Chapter 3 Notes: Cell Structure and Function PDF

CHAPTER 3 NOTES: CELL STRUCTURE AND FUNCTION 3.1 The Cellular Level of Organization The cell marks the boundary between the nonliving and the living. Cells can be classified as either prokaryotic or eukaryotic. The Cell Theory The cell theory states that all organisms are made up of...

CHAPTER 3 NOTES: CELL STRUCTURE AND FUNCTION 3.1 The Cellular Level of Organization The cell marks the boundary between the nonliving and the living. Cells can be classified as either prokaryotic or eukaryotic. The Cell Theory The cell theory states that all organisms are made up of basic living units called cells and that all cells come only from previously existing cells. Cell Size Cells are quite small. The smaller the cell, the greater its surface-area-to-volume ratio, which improves its ability to take in and expel nutrients and wastes at its surface. 3.2 Prokaryotic Cells Prokaryotic cells lack a membrane-bounded nucleus. The domains Archaea and Eubacteria consist of prokaryotic cells. Cell Envelope In bacteria, the cell envelope consists of the plasma membrane, the cell wall, and, if present, the glycocalyx. All cells are surrounded by a plasma membrane consisting of a phospholipid bilayer embedded with proteins. Inside the Cytoplasm Semifluid cytoplasm is composed of water, salts, and dissolved organic molecules. While prokaryotes lack a membrane-bound nucleus, their DNA is located in a region of the cytoplasm called the nucleoid. On the surface of the Cell Some bacteria have a capsule surrounding the cell wall, rotating flagella for motion, and fimbriae for attachment to surfaces. 3.3 Eukaryotic Cells Eukaryotic cells are structurally very complex. The principal distinguishing feature of eukaryotic cells is the presence of a nucleus. Cell Walls Most eukaryotic cells have a permeable but protective cell wall around the plasma membrane. Organelles of Eukaryotic Cells The term organelle refers to any well-defined subcellular structure that performs a particular function. Cellular organelles process the nutrients and raw materials that enter the cell. The Nucleus The nucleus stores genetic material, DNA, that governs the characteristics of the cell and its metabolic functioning. Chromatin consists of DNA and associated proteins. In the nucleus, the nucleolus produces ribosomal RNA. The nucleus is enclosed in a double membrane called the nuclear envelope with pores to permit transport of proteins and ribosomal subunits. Ribosomes are small organelles in the cytoplasm where protein synthesis occurs. The Endomembrane System The endomembrane system consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, and several vesicles (tiny membranous sacs). The Endoplasmic Reticulum The endoplasmic reticulum (ER) is a complicated system of membranous channels and flattened vesicles that is physically continuous with the outer membrane of the nuclear envelope. The rough reticulum (RER) is studded with ribosomes and synthesizes and processes proteins. The smooth ER has no ribosomes; it synthesizes lipids and performs various other functions. The Golgi Apparatus  The Golgi apparatus consists of a stack of 3-20 slightly curved sacs; it collects, sorts, packages, and distributes materials such as proteins and lipids in the cell. Lysosomes Lysosomes contain hydrolytic digestive enzymes and are the garbage disposals of the cell factory. Vacuoles A vacuole is a membranous sac that is larger than a vesicle and stores substances. Peroxisomes Peroxisomes are membrane-bound vesicles that enclose enzymes that break down fatty acids. The enzymes present in a peroxisome depend on the function of the cell. Energy-Related Organelles Chloroplasts use solar energy to synthesize carbohydrates, which are broken down by the mitochondria to produce ATP molecules. Chloroplasts Plant and algal cells contain chloroplasts, which allow them to use solar energy to produce organic molecules. Mitochondria Most eukaryotic cells contain mitochondria, which are the power plants of the cell. They convert broken-down nutrients into ATP. They also play a role in the aging process. 3.4 The Cytoskeleton The cytoskeleton maintains the shape of the cell and allows its parts to move. The protein components of the cytoskeleton interconnect and extend from the nucleus to the plasma membrane in eukaryotic cells. Actin Filaments Actin filaments are long, thin, flexible fibers that play a structural role when they form a dense, complex web just under the plasma membrane. To produce movement, actin filaments interact with motor molecules. Intermediate Filaments Intermediate filaments are a ropelike assembly of fibrous polypeptides that vary according to the type of tissue. These dynamic structures support parts of the cell and provide mechanical strength. Microtubules Microtubules are small, hollow cylinders organized by the centrosome. They help to maintain the shape of the cell and act as tracks along which organelles can move. Centrioles Centrioles are contained in the centrosome and composed of microtubule triplets. They may be involved in the process of microtubule assembly and disassembly. Cilia and Flagella Cilia and flagella are hairlike projections that can move either in an undulating fashion, like a whip, or stiffly, like an oar. 3.5 Origin and Evolution of the Eukaryotic Cell The fossil record suggests that the first cells were prokaryotes. Scientists believe that eukaryotic cells evolved from prokaryotic cells in a particular manner. This idea is called the endosymbiotic theory. It is supported by many similarities in the characteristics of some organelles and the RNA base sequence of the ribosomes in chloroplasts and mitochondria.