The Cell Notes 1 of 11

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Katherine McDowell
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1 The Cell The basic unit of structure and function in living things The smallest units in living things The smallest units in living things that show the characteristics of life Organisms can be made of one cell or of many The 2 Basic Cell Types There are 2 types of cells: prokaryotic and eukaryotic Figure 5-3 Prokaryotic Lack any internal membrane-bound structures (membranes do not separate different areas of the cell from each other) Make up the smallest single-celled organisms, bacteria Eukaryotic Present in all living things except bacteria Have many kinds of internal membrane-bound structures Most important internal-membrane structure is the nucleus The nucleus is the structure in which the cell s hereditary material (DNA) is located Eukaryotic translates into true nucleus Eukaryotic cells are more compartmentalized The Cell Notes 1 of 11

2 Similarities between Prokaryotic and Eukaryotic Both are surrounded by a membrane that helps to keep their internal environment constant and different form their external environment Both types carry out the same life processes, using the same kinds of organic compounds- CHO, fats, proteins and nucleic acids and the same kind of metabolic machinery Cell Size The diameter of prokaryotic cells can range between 1 and 10 micrometers Eukaryotic cells are 10 times larger ( micrometers) The small size of cells has do to with the necessity of getting materials into and out of the cells at rates that will meet the cell s needs Nutrients must be able to get into a cell at rates that will meet the cell s needs for nutrients Wastes must also be able to move out of a cell rapidly, so that they do not build up to harmful levels What limits the rate of exchange of material between the contents of the cell and its surroundings is the cell s surface area-to-volume ratio (how close the parts of the cell are to its environment) The Cell Notes 2 of 11

3 Cell Structure Eukaryotic cells have many specialized internal structures called organelles Some organelles are enclosed in their own membrane while other organelles are not Cell Wall The cell wall is a rigid structure that encloses most bacteria, various microorganisms and all plants The cell wall lies just outside the cell membrane The cell wall give the cell its shape and provides protection for the cell In plans, this wall is composed largely of cellulose but in other organisms, it may contain other compounds The cell wall has many small openings that allow materials to pass to and from the cell membrane Thin strands of cytoplasm will occasionally stretch through the walls of bordering cells which will allow materials to pass directly from one cell to another Animal cells do not have a cell wall The Cell Membrane The cell membrane is also known as the plasma membrane The cell membrane separates the cell from its surrounding environment This membrane controls the movement of materials into and out of the cell This allows the cell contents to be chemically different from the environment The cell membrane keeps the internal conditions of the cell constant or maintains homeostasis The Cell Notes 3 of 11

Structure of the Cell Membrane The cell membrane is a two layered structure that is composed of lipids, proteins and CHO The 2 layers are made of lipids with proteins implanted in them Some of the

4 Structure of the Cell Membrane The cell membrane is a two layered structure that is composed of lipids, proteins and CHO The 2 layers are made of lipids with proteins implanted in them Some of the proteins are on the outer surface of the membrane and some are in the inner surface and some extend through the membrane Fig. 5-6, page 84 CHO, which are linked chemically to some membrane proteins or lipids, branch from the external surface of the membrane Lipid and protein molecules of the membrane move along the membrane The proteins of the cell membrane serve many functions: transport proteins (control the movement of substances through the membrane); receptors (binding sites for specific messenger molecules that signal the cell to begin or to stop some metabolic activity); act as enzymes; bind the membrane to neighboring cells or to structural elements in the cytoplasm of the cell The cell membrane is selectively permeable or only some substances can pass through it freely Other substance can pass through only at certain times Selective permeability allows the cell to regulate the chemical composition of the cell and is a result of the chemical and electrical properties of the membrane s molecules The Cell Notes 4 of 11

5 The Nucleus The cell nucleus is a round membrane-bound structure that serves as the control centre for cell metabolism and reproduction Without this largest organelle, the cell would die The nuclear envelope is the membrane that surrounds the nucleus The nuclear envelope is actually 2 membranes that lie close to each other and, like the cell membrane, is selectively permeable The inner and outer membrane are fused at certain points creating pore These pores control the movement of certain substances into and out of the nucleus This selective permeability of the nuclear membrane allows the contents of the nucleus or the nucleoplasm, to remain chemically different from the rest of the cell Nucleoli are dense, granular bodies that disappear at the beginning of cell division and reappear at the end and are made up of DNA, RNA and protein Nucleoli, which are located within the nucleus, are the production sites of ribosomes The nucleoplasm consists of chromatin, which is DNA attached to various proteins Chromatin (when in the form of long, thin threads) make up the structures of chromosomes (DNA in chromosomes are the hereditary material of the cell) The Cytoplasm Cytoplasm is the watery material lying within the cell between the cell membrane and the nucleus Many of the chemical reactions of cell metabolism take place in the cytoplasm The cytoplasm also contains a variety of organelles that have specific functions in the cell membrane The Cell Notes 5 of 11

6 Endoplasmic Reticulum The endoplasmic reticulum is a system of fluid-filled canals or channels, enclosed by membranes There are 2 types; rough endoplasmic reticulum (r.e.r.) in which the surface is lined with ribosomes and smooth endoplasmic reticulum (s.e.r.) which are not lined with ribosomes The canals of the endoplasmic reticulum are paths for the transport of materials through the cell The membranes of the network provide a large surface area on which many chemical reactions occur The compartments of the endoplasmic reticulum allow for many chemical reactions to take place at the same time Some of the endoplasmic reticulum are joined to the outer membrane of the nuclear envelope Ribosomes Ribosomes are small particles which are the sites of protein production or synthesis in the cell The are found lining the membranes of the endoplasmic reticulum and the cytoplasm Certain cells that produce proteins to be released from the cell, the ribosomes are usually attached to the outer membrane surface of the endoplasmic reticulum The proteins pass through the canals, which carry the proteins to the cell membrane and out of the cell Proteins that are to be used within the cell are produced on the ribosomes that are free in the cytoplasm These proteins are usually enzymes that functions in the cell s cytoplasm The Cell Notes 6 of 11

7 Golgi Bodies Golgi bodies are stacks of flattened membrane sacs and serve processing, packaging and storage centers for the products released from the cell Animal cells usually have only Golgi body, which is commonly located near the nucleus Plant cells may have hundreds of Golgi bodies Lysosomes Lysosomes are small, saclike structures surrounded by a single membrane and contain strong digestive (hydrolytic) enzymes Lysosomes are produced by the Golgi bodies and are found in most animal cells and in some plant cells In single-celled organism, lysosomes are involved in the digestion of food within the cell In multi-cellular organism, lysosomes serve several different function: o Break down worn-out cell organelles o In some animals, they are part of the body s defense against disease (White blood cells) o Involved in developmental processes (ex. Tadpole to frog- loss of tail- through lysosome involvement of digestion and absorption of the tail) The Cell Notes 7 of 11

8 Mitochondria Mitochondria are round or slipper-shaped organelles that release the energy in food molecules for use by the cell Known as the powerhouse of the cell because most of the energy needed by cells is released in the mitochondria Mitochondrion (singular) have a double membrane: the inner membrane is highly folded which form cristae that extend into the middle of mitochondrion The cristae provide a large surface area on which many chemical reactions occur Cells that need large amounts of energy contain a large number of mitochondria (ex. Muscle cells) The process by which the energy of food is released in the mitochondria and elsewhere in the cell is called cellular respiration Mitochondria contain their own DNA and are capable of duplicating themselves Microtubules Microtubules are long, hollow, cylindrical structures found in the cytoplasm They are the skeleton for the cell Microtubules are found in centrioles, cilia and flagella They may also be involved in the movement of the chromosomes during cell division Microtubules are composed of a protein called tubulin which are layered in a helix giving the microtubules its form The Cell Notes 8 of 11

9 Microfilaments Microfilament are long, solid, threadlike strands found in some cells Mainly composed of actin (a protein) and are linked with cell movement Microfilaments can contract and are involved in the movement of the cell called cyclosis or cytoplasmic streaming Some microfilaments are not made of actin and serve as the supporting structure of the cell Centrioles Centrioles are involved in cell division in animal cells Located as a pair of cylinders near the nucleus in animal cells that lay at right angles to each other Fig page 88 Cilia and Flagella These are hairlike organelles with the ability for movement Flagella has the same structure as cilia but is longer There are usually a few flagella on a cell but cilia may cover the entire cell surface In multi-cellular animals, cilia serve to move substances over the surface of the cells Cilia and flagella are derived from structures called basal bodies which is similar to that of centrioles The Cell Notes 9 of 11

10 Vacuoles Vacuoles are fluid-filled organelles enclosed b a membrane Vacuoles found in plant cells are filled with a fluid called cell sap Vacuoles serve as a place for digestion (in some organisms and simple animals); contractile vacuoles (excess water from the cell collects and pumped out from the cell into the environment); storage (for certain cell products) Plastids Plastids are membrane-enclosed organelles that are found only in the cells of photosynthetic, eukaryotic organism Plastids are not present in the cells of animals or fungi Plastids are bounded by a double membrane and have systems of membranes with the organelle 2 types of plastids: o Leucoplasts: colourless, starch and other plant nutrients are stored o Chromoplasts: contain pigments that five colours to fruits, flowers and leaves The most important chromoplast are chloroplast which contain the green pigment chlorophyll The chloroplasts are the site of photosynthesis, the food making process that uses light energy Chloroplasts contain their own DNA and have the ability to duplicate themselves The Cell Notes 10 of 11

7-2 Eukaryotic Cell Structure

7-2 Eukaryotic Cell Structure 1 of 49 Comparing the Cell to a Factory Eukaryotic Cell Structures Structures within a eukaryotic cell that perform important cellular functions are known as organelles. Cell biologists divide the eukaryotic