I. Organelles: tiny structures within cells with specialized functions. They are listed below.
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II. The Plasma Membrane: a phospholipid bilayer that surrounds all cells. It determines what leaves and enters a cell.
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III. The Nucleus (Plural, Nuclei):
A. A double membrane enclosed organelle that contains chromatin (DNA and proteins) which rests in nucleoplasm (a gel-like substance).
B. It is only present in eukaryotic cells.
C. Surrounded by the nuclear envelope (a double membrane).
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IV. The Mitochondrion (Plural, Mitochondria):
A. An oval shaped organelle surrounded by a double membrane (an inner and outer membrane). Each membrane is composed of a phospholipid bilayer.
B. Produces ATP (adenosine triphosphate) through a process called cellular respiration. ATP: the cell’s main energy carrying molecule. It fuels most cellular activities. Therefore, the mitochondrion is referred to as the “power house” of the cell.
C. Has its own DNA.
V. The Golgi Apparatus:
A. Stacks of flattened membranes, resembling a stack of pancakes.
B. A site which receives products from the ER for modification and shipment.
1. Modification: it receives products from the ER via vesicles which travel to the cis side of the Golgi apparatus, fuse with it, and empty its contents into its lumen (the inner part of the flattened membranes). Note: the cis side of the Golgi apparatus is the side that lies closest to the ER. Once the Golgi apparatus receives products from the ER, modification begins (sugar molecules and phosphate groups are often added).
2. Shipment: it ships finished products via vesicles on the trans side. Vesicles deposit contents to other parts of the cell or fuse with the plasma membrane to release contents outside of the cell. Note: the trans side of the ER is the side that releases vesicles.
VI. The ER (Endoplasmic Reticulum):
A. A maze of connected, flattened membranous sacs that’s continuous with the nuclear envelope.
B. The lumen/cisternal space: the hollow part of the ER tubes.
C. A site which produces proteins and lipids. The proteins and lipids produced are transported to the Golgi apparatus via vesicles where they are finished and shipped out to other regions in the cell (for instance, the cell membrane).
D. There are 2 types of ER: rough ER (RER) and soft ER (SER).
1. RER: a type of ER covered in ribosomes. Because ribosomes produce protein and RER is covered with ribosomes, RER produces protein. The proteins produced in the RER include secretory proteins and membrane proteins.
2. SER: a type of ER that is not covered in ribosomes. It produces lipids.
VII. Lysosomes:
A. A membrane enclosed organelle with a spherical shape and digestive enzymes speckled throughout. Their enzymes are hydrolytic (they split bonds).
B. They’re only present in animal cells. They’re not present in plant cells because plant cells unlike animal cells have vacuoles, and vacuoles serve the same function as lysosomes (both are digestive organelles). Thus, plant cells don’t need lysosomes.
C. The site of intracellular digestion (i.e. the cell’s garbage disposal). They break down unwanted molecules (proteins, polysaccharides, lipids, nucleic acids) and worn out organelles for recycling within the cell or excretion from the cell. They destroy pathogens (disease causing microorganisms such as bacterium and viruses). They release nutrients from ingested food particles.
VIII. Vacuoles:
A. A membrane bound organelle found in both animal and plant cells; however, they are larger in plant cells.
B. They are similar to vesicles in that they can also ship materials from one location to another; however, they cannot engage in endocytosis.
C. They store materials inside of cells.
D. In plant cells, vacuoles serve similar digestive functions as lysosomes. Each plant cell contains a large vacuole which stores water
IX. The Cytoplasm:
A. The gel-like substance which rests between the plasma membrane and the nuclear envelope. Without a cytoplasm, a cell would deflate.
B. Composed of cytosol, water, ions, organic molecules (proteins, simple sugars, amino acids, nucleic acids, fatty acids, derivatives of glycerol).
X. The Nucleolus:
A. A dark area/round body located inside the nucleus, which serves as the site of ribosome synthesis.
B. The ribosomes produced are transported out of the nucleus through the pores in the nuclear envelope to the cytoplasm.
XI. Peroxisomes: small, round membrane enclosed vesicles that provide a safe environment for a variety of reactions to occur. For instance, the breakdown of fatty acids and amino acids via oxidation reactions. Such reactions produce hydrogen peroxide (H2O2), which is broken down into oxygen and water. Hydrogen peroxide is toxic to cells but produces no damage because it is confined.
XII. Vesicles:
A. Small membrane enclosed organelles.
B. They ship materials. For instance, from one organelle to another (e.g. from the ER to the Golgi apparatus). They pinch off from the membrane of one organelle and fuse with the membrane of another in a process called endocytosis.
XIII. The Cytosol: an aqueous gel that’s part of the cytoplasm (the fluid part of the cytoplasm). The part of the cytoplasm that’s not contained within intracellular membranes (membrane bound organelles include the nucleus, the ER, the Golgi apparatus, lysosomes, chloroplasts, and vacuoles). If you removed the plasma membrane from a eukaryotic cell and removed all of its membrane enclosed organelles, you would be left with the cytosol.
XIV. The Cytoskeleton:
A. A system of protein fibers/filaments (slender threadlike objects) that lie in the cytoplasm, giving shape.
B. Composed of 3 major filament types:
1. Actin filaments/microfilaments (the thinnest): the most abundant filaments in muscle cells. Microfilaments are so thin that they disassemble and reform fast, allowing the cell to change shape and move; they function in cellular movement.
2. Intermediate filaments: the most abundant filaments in epidermal cells of the skin. Their function is structural because they hold the organelles in place.
3. Microtubules (the thickest, resemble hollow tubes): function as railroad tracks for intracellular movements. For instance, vesicles travel on these filaments in order to move through cells. They are also responsible for the separation of chromosomes during cell division.
XV. The Cell Wall:
A. Present in plant cells and bacteria.
B. Provides cells with structure/shape and protection because it’s rigid and covers the plasma membrane.
C. Cellulose is a major organic molecule present in the wall. Its presence in plants is the reason why celery crunches when you bite into it!
XVI. Chloroplasts:
A. Large, green organelles. Found only in plant and algae cells, not in animal and fungi cells.
B. Contain a green pigment called chlorophyll. The pigment captures light energy which drives photosynthesis reactions.
C. The site where photosynthesis occurs, a process which gives plant cells energy. Chlorophyll molecules (which reside in chloroplasts) use the energy of sunlight to produce energy rich sugar molecules.
D. Have an outer membrane, an inner membrane, and chlorophyll containing membranes (membranes that surround a green pigment called chlorophyll).
E. Contain their own DNA.
XVII. Review:
A. What membrane bound organelles are found inside eukaryotic cells?
Answer: nucleus, mitochondria, chloroplasts, ER, Golgi apparatus, lysosomes, peroxisomes, vesicles, vacuoles.
B. A protein is made at a ribosome on the RER and will eventually be excreted out of a cell. Describe its path.
Answer: once made on the RER, the protein will travel to the cis side of the Golgi apparatus via a vesicle. Once modified in the Golgi apparatus, it is shipped out of the trans side of the Golgi apparatus via a vesicle which fuses with the plasma membrane.
C. What are 3 organelles inside a plant cell that are not inside an animal cell?
Answer: cell walls, chloroplasts, a large central vacuole.
D. Name a few organelles found in both plant and animal cells.
Answer: a nucleus, plasma membrane, mitochondria, cytoplasm, cytoskeleton, ER, Golgi apparatus, peroxisomes.