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7.2 Cell Structure Cell Organization The eukaryotic cell can be divided into two major parts: the _________________ and the ___________________. The cytoplasm is the fluid portion of the cell______________ the nucleus. Cell Organization Many cellular structures act as if they are specialized organs. These structures are known as __________________, literally “little organs.” The Nucleus The nucleus is the _____________ center of the cell. The nucleus contains nearly all the cell’s _________ and, with it, the coded instructions for making proteins and other important molecules. This DNA is passed from one _________________ of cells to the next. Most of the time, the threadlike chromosomes are spread throughout the nucleus in the form of______________a complex of DNA bound to proteins. When a cell divides, its_________________________ condense. The nucleus is surrounded by a nuclear ____________ composed of two membranes. The nuclear envelope is dotted with thousands of nuclear ______________, which allow material to move into and out of the nucleus. Most nuclei also contain a small, dense region known as the _________________. The nucleolus is where the assembly of ___________ begins. Organelles That Store, Clean Up, and Support Vacuoles and Vesicles Many cells contain large, saclike, membrane-enclosed structures called ___________________that store materials such as water, salts, proteins, and carbohydrates. In many plant cells, there is a _____________, _______________ central vacuole filled with liquid. The pressure of the central vacuole in these cells increases their rigidity, making it possible for plants to support _________________structures such as leaves and flowers. Vacuoles are also found in some __________________organisms and in some ___________________. Nearly all ____________________ cells contain smaller membraneenclosed structures called _______________. Vesicles are used to store and move materials between cell organelles, as well as to and from the cell surface. Lysosomes __________________ are small organelles filled with _______________ that function as the cell’s cleanup crew. Lysosomes perform the vital function of removing _______________ that might otherwise accumulate and clutter up the cell. One function of lysosomes is the breakdown of ___________, _________________, and __________________ into small molecules that can be used by the rest of the cell. Lysosomes are also involved in breaking down organelles that have _______________ their usefulness. The Cytoskeleton Eukaryotic cells are given their shape and internal organization by a network of protein filaments known as the______________________. Certain parts of the cytoskeleton also help to transport ____________________between different parts of the cell. ______________________and _____________________ are two of the principal protein filaments that make up the cytoskeleton. Microfilaments They form extensive networks in some cells and produce a tough, flexible framework that _______________ the cell. Microfilaments also help cells ___________________. Microtubules . Microtubules are hollow structures made up of proteins known as ____________. They play critical roles in maintaining cell ________________________. In animal cells, structures known as _____________ are also formed from tubilins. _________________________are located near the nucleus and help to organize cell division. __________________________are not found in plant cells. Organelles That Build Proteins Cells need to build new molecules all the time, especially _____________, which catalyze chemical reactions and make up important structures in the cell. Because ______________ carry out so many of the essential functions of living things, a big part of the cell is devoted to their production and distribution. Proteins are synthesized on _____________, sometimes in association with the rough endoplasmic reticulum in eukaryotes. Ribosomes __________________ are small particles of RNA and protein found throughout the cytoplasm in all cells. _____________produce _____________by following coded instructions that come from DNA. Endoplasmic Reticulum Eukaryotic cells contain an internal membrane system known as the _____________ _______________ or ER. The endoplasmic reticulum is where lipid components of the cell membrane are assembled, along with _____________ and other materials that are exported from the cell. The portion of the ER involved in the synthesis of proteins is called __________ endoplasmic reticulum, or rough ER. It is given this name because of the ______________found on its surface. The other portion of the ER is known as _________________ endoplasmic reticulum (smooth ER) because _____________ are ___________found on its surface. Golgi Apparatus Proteins produced in the rough ER move next into the __________ _____________which appears as a stack of flattened membranes. The Golgi apparatus modifies, __________, and packages proteins and other materials from the ER for storage in the cell or release outside the cell. From the Golgi apparatus, proteins are _____________ to their final destination inside or outside the cell. Organelles That Capture and Release Energy All living things require a source of energy. Most cells are powered by food molecules that are built using energy from the ___________. ____________________ and ____________________ are both involved in energy conversion processes within the cell. Chloroplasts ________________ and some other organisms contain chloroplasts. _______________________ are the biological equivalents of solar power plants. They capture the ___________ from sunlight and convert it into food that contains chemical energy in a process called photosynthesis. Inside the organelle are large stacks of other membranes, which contain the _______________pigment ___________________. Mitochondria Nearly all eukaryotic cells, including plants, contain ___________________. ________________________ are the _____________ _____________of the cell. They convert the chemical energy stored in food into compounds that are more convenient for the cell to use. Cellular Boundaries Similarly, cells are surrounded by a barrier known as the cell ____________. Many cells, including most prokaryotes, also produce a strong supporting layer around the membrane known as a _________________. Cell Walls The main function of the cell wall is to provide _________and _______ for the cell. Prokaryotes, plants, algae, fungi, and many prokaryotes _______ cell walls. Animal cells do _________ have cell walls. Cell walls lie outside the cell membrane and most are __________ enough to allow _____________, ____________, carbon dioxide and certain other substances to pass through easily. Cell Membranes All cells contain a cell membrane that regulates what _______________ and ______ _____________the cell and also ______________ and ___________________ the cell. The composition of nearly all cell membranes is a double-layered sheet called the _____ _______, which gives cell membranes a ________ _____________________structure and forms a strong barrier between the cell and its _________________. The Properties of Lipids Many ______ ______________have oily fatty acid chains attached to chemical groups that _______________ strongly with ______________. The fatty acid portions of such a lipid are ___________________, or “water-hating,” while the opposite end of the molecule is _______________________, or “water-loving.” When such lipids are mixed with ________________, their hydrophobic fatty acid “_______________” cluster together while their hydrophilic “_______________” are attracted to water. A lipid ________________ is the result. The ____ ___________groups of lipids in a bilayer are _________________ to water, while the fatty acid tails form an oily layer ______ ___________the membrane from which water is excluded. The Fluid Mosaic Model Most cell membranes contain _________________ molecules that are embedded in the lipid bilayer. __________ ______molecules are attached to many of these proteins. Because the proteins __________ _________in the lipid bilayer can move around and “______________” among the lipids, and because so many different kinds of molecules make up the cell membrane, scientists describe the cell membrane as a “______ _______.” Some of the proteins form _______________ and ______ ____________that help to move material _________________ the cell membrane. Many of the carbohydrate molecules act like chemical ____________ _____, allowing individual cells to identify one another. Although many substances can cross _____________________ membranes, some are too ___________________ or too ________________ charged to cross the lipid bilayer. If a substance is able to cross a ______________________, the membrane is said to be _______________________ to it. A membrane is ____________ to substances that cannot ________________ across it. Most biological membranes are _________ ___________, meaning that some substances _______________ pass across them and others ________. Selectively permeable membranes are also called ____________________ ___________ membranes.