Essential Question How do cell structures enable a cell to carry out basic life processes? Cell Organization Eukaryotic cells can be divided into two parts: 1. Nucleus 2. Cytoplasm-the portion of the cell outside of the nucleus The nucleus and the cytoplasm work together to keep the cell functioning properly. Prokaryotic cells also have cytoplasm, butdo not have a nucleus 1
Cell Organization Organelles Specialized structures found in cells Act like little organs (literal definition) Found in eukaryotic cells A cell is like a factory Different organelles = specialized machines and assembly lines within a factory Cells also follow instructions and produce products The Nucleus Control center of the cell The nucleus contains nearly all the cell s DNA and the coded instructions for making proteins and other important molecules. Prokaryotic cells don t have a nucleus, but they do have DNA with instructions Nucleus is surrounded by a nuclear envelopewhich is made of two membranes Dotted with thousands of nuclear pores Allows material to pass into/out of the nucleus Ex. Proteins, RNA, other molecules 2
The Nucleus Chromosomes Carry genetic information, found in the nucleus Threadlike Most of the time spread throughout nucleus in the form of chromatin (DNA bound to proteins) When a cell divides, the chromosomes condense and can be seen under a microscope Nucleolus Also contained in most nuclei (plural of nucleus) Small dense region Where the assembly of ribosomes begins Organelles that Store, Clean Up, & Support Vacuoles & Vesicles Vacuoles Large, saclike, membrane-enclosed structures Vacuoles store materials like water, salts, proteins, and carbohydrates. Plant cells There is one large central vacuole filled with liquid Increases their rigidity (stiffness) letting them support heavy structures like leaves and flowers Unicellular organisms & animals Can pump water out of a cell Vesicle Store and move materials between cell organelles Also move things to and from the cell surface 3
Organelles that Store, Clean Up, & Support Lysosomes Small organelles filled with enzymes Lysosomes break down lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell. They are also involved in breaking down organelles that have outlived their usefulness. Remove junk that would build up Many human diseases are linked to lysosomes that are not functioning properly Found in both animals and a few specialized plant cells Organelles that Store, Clean Up, & Support Cytoskeleton Gives eukaryotic cells their shape and internal organization Certain parts help transport materials between different parts of the cell May also be part of moving the cell (flagella or cilia) The cytoskeleton helps the cell maintain its shape and is also involved in movement. Network of protein filaments two main types 1. Microfilaments Threadlike structures made of protein called actin Produce tough flexible framework to support the cell Help cells move Microfilament assembly/disassembly responsible for cytoplasmic movements that allow cell to move across surfaces 2. Microtubules See next slide 4
Organelles that Store, Clean Up, & Support 2. Microtubules Hollow structures made up of proteins known as tubulins Play critical role in maintaining cell shape Also important in cell division Form the mitotic spindle to help separate the chromosomes In animals cells, centrioles are formed from tubulins Organelles located near nucleus Help organize cell division Not found in plant cells Help build projections from cell surface Cilia and flagella Enable cells to swim rapidly through liquid Organelles that Build Proteins Cells are always building new things, especially proteins Catalyze chemical reactions Make up important structures in the cell Carry out many important functions of living things Much of the cell is devoted to building and distributing proteins 5
Organelles that Build Proteins Ribosomes (http://www.youtube.com/watch?v=d3foxt4mrom) Small particles of RNA and protein found throughout the cytoplasm in all cells Where proteins are assembled Produce proteins by following coded instructions on DNA Cells that are very active in protein synthesis have large numbers of ribosomes Organelles that Build Proteins Endoplasmic Reticulum (ER) Internal membrane system found in eukaryotic cells Where lipid parts of the cell membrane are put together along with proteins and other materials that are exported out of the cell Two parts: 1. Rough ER Portion of the ER that synthesizes proteins Has ribosomes on its surface giving it a rough texture New proteins leave the ribosomes and enter the rough ER where they may be chemically modified Proteins made on the rough ER include those that will be released, or secreted, from the cell as well as many membrane proteins and proteins destined for lysosomes and other specialized locations within the cell. Rough ER is abundant in cells that export large amounts of protein 2. Smooth ER 1. Ribosomes are not found on the surface 2. Contains collections of enzymes that perform specialized tasks 6
Organelles that Build Proteins Golgi Apparatus Stack of flattened membranes Only in eukaryotic cells Where proteins produced in the rough ER go next As they leave the rough ER they are given molecular address tags to make sure they get to the right spot The tags are read by the cell Proteins are bundled into vesicles that bud from the ER and carry them to the Golgi Apparatus The Golgi apparatus modifies, sorts, and packages proteins and other materials from the ER for storage in the cell or release outside the cell. Acts as a customization shop, where finishing touches are put on before proteins go to their final stop (inside or outside of the cell) Bellringer What process within the cell does this picture represent? 7
Organelles that Capture and Release Energy Chloroplasts Biological solar power plants Present in plants and some other organisms Chloroplasts capture the energy from sunlight and convert it into food that contains chemical energy in a process called photosynthesis. Two membranes surround chloroplasts Inside the organelle are large stacks of other membranes that contain chlorophyll (a green pigment) Organelles that Capture and Release Energy Mitochondria Power plants of the cell Present in nearly all eukaryotic cells Mitochondria convert the chemical energy stored in food into compounds that care more convenient for the cell to use. Like chloroplasts, it has two membranes Inner membrane is folded up inside the mitochondria Inheritance In humans, all or nearly all come from the cytoplasm of the ovum (egg cell) Which means your mitochondria comes from your mom Genetics Chloroplasts and mitochondria contain their own DNA molecules Possible that they are descended from independent microorganisms Endosymbiotic theory (chapter 19 in bio honors text) 8