The Discovery of Cells

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2 The Discovery of Cells Microscope observations! General Cell & Organelle Discovery 1600s Observations made by scientists using more powerful microscopes in the 1800s led to the formation of the cell theory.

3 All substances that enter or leave a cell must cross the surface of the cell THE CELL MEMBRANE. A cell s ability to move substances across its membrane can be estimated by finding its surface area-to-volume ratio. Cells with greater surface area-to-volume ratios can exchange substances more efficiently.

4 Eukaryotic Cells A eukaryote is an organism made up of one or more eukaryotic cells. **All multicellular organisms are made of eukaryotic cells.** DNA is in an internal compartment: nucleus. Organelles have membranes (are compartmentalized).

5 Organelle: Small structure in the cytoplasm that carries out specific activities inside the cell. Each organelle in a eukaryotic cell performs distinct functions. ***The complex organization of eukaryotic cells enables them to carry out more specialized functions than prokaryotic cells.

6 Cell Membrane Outer layer Acts as a barrier Made of: - phospholipids, - proteins - carbohydrates

7 Cytoplasm Region of the cell inside the cell membrane. **Includes the fluid inside the cell called the cytosol and holds all the organelles** Jelly-like substance within a cell

8 Ribosomes: makes proteins Ribosomes: makes proteins Attached Ribosomes- Make proteins for EXPORT Free Ribosomes-Make proteins for use within that cell. Remember DNA RNA Proteins

9 Directing Cellular Activity DNA contains instructions for making proteins which control most of the activity of the cell. The DNA of eukaryotic cells is stored in the nucleus. DNA instructions are copied as RNA messages, which leave the nucleus. DNA NEVER LEAVES THE NUCLEUS In the cytoplasm, ribosomes use the RNA messages to assemble proteins.

10 Nucleus Surrounded by nuclear membrane: it is a double membrane. Nuclear pores: located in the nuclear envelope act as channels (holes/tunnels) to allow certain molecules to move in and out of the nucleus. Nucleolus: structure within the nucleus where ribosome parts are made. These ribosome parts are transported out of the nucleus into the cytoplasm where they are assembled to form a complete ribosome.

11 The Nucleus

12 Ribosomes Each ribosome in a cell is made of RNA and many different proteins. Free Ribosomes: are suspended in the cytosol ~Make proteins that remain inside the cell. Bound/Attached Ribosomes: are attached to the membrane of another organelle are called Endoplasmic Reticulum (ER). ~make proteins that are exported from the cell. Ribosomes can switch between being bound or free, depending on what proteins the cell needs to make.

13 Protein Processing Proteins that are sent outside the cell are packaged in vesicles: small, membrane-bound sacs that enclose the proteins and keep them separate from the rest of the cytoplasm. ***The Endoplasmic Reticulum and Golgi Apparatus are organelles involved in preparing proteins for extracellular export.

14 Endoplasmic Reticulum An extensive system of internal membranes that moves proteins and other substances through the cell. The membranes of the ER are connected to the outer membrane of the nuclear envelope. The endoplasmic reticulum is divided into two portions: Rough ER and Smooth ER.

15 Endoplasmic Reticulum (ER)

16 ER with attached ribosomes: Rough ER It has a rough appearance when viewed with an electron microscope. Ribosomes on the rough ER make proteins that are packaged into vesicles & exported ER with NO attached ribosomes: Smooth ER it has a smooth appearance when viewed with an electron microscope. Enzymes of the smooth ER make lipids and break down toxic substances.

17 Protein Processing Golgi Apparatus Set of flattened, membrane-bound sacs. Helps modify, sort, and package cell products for distribution.

18 Golgi apparatus

19 Protein Processing, continued Making and Exporting Proteins The ribosomes located on the rough ER make proteins which then cross into the membranes of the ER. The ER membrane then pinches off and forms a vesicle around the proteins. Vesicles transport the proteins from the rough ER to the Golgi apparatus, where they are modified by enzymes and repackaged in new vesicles. These new vesicles transport the modified proteins to the cell membrane to be released outside the cell.

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21 Storage and Maintenance Lysosomes Vesicles help maintain homeostasis by storing and releasing a variety of substances as the cell needs them. A lysosome is a vesicle produced by the Golgi apparatus that contains enzymes that break down large molecules. Lysosomes recycle old or damaged organelles and digest food particles to provide nutrients for the cell.

22 Storage and Maintenance, continued Vacuoles A vacuole is a fluid-filled vesicle found in the cytoplasm of many plant cells. Plant cells contain a large compartment called the central vacuole, which stores water, ions, nutrients, and wastes. When water fills the central vacuole, the cell becomes rigid, allowing the plant to stand up. When the vacuole loses water, the cell shrinks, and the plant wilts.

23 Storage and Maintenance, continued Other Vacuoles Some protists have contractile vacuoles which pump excess water out of the cell in order to control the concentration of salts and other substances. A food vacuole is another type of vacuole. It is formed when the cell membrane surrounds food particles outside the cell and pinches off to form a vesicle inside the cell.

24 Energy Production, continued Chloroplasts Organelle found in plant and algae cells that uses light energy to make carbohydrates from carbon dioxide and water. Surrounded by two membranes and have several stacks of flattened sacs (thylakoids) where energy production takes place. Plant cells may have several chloroplasts.

25 Energy Production, continued Mitochondria Organelles that use energy from organic compounds to make ATP. Most of the ATP needed by a cell is produced inside mitochondria. *Both animal and plant cells contain mitochondria*. A smooth outer membrane and a folded inner membrane surround a mitochondrion. ATP is produced by enzymes on the folds of the inner membrane.

26 Mitochondrion