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7-2: Eukaryotic Cell Structure
- 1. Unit 3: Basic Cell Structure & Function Ms. Petrucci Biology Features of the Cell: The Organelles
- 3. Eukaryotic Cells: Animal Cell
- 4. Eukaryotic Cells: Plant Cells
- 5. Let’s pick it apart…one organelle at a time!
- 6. Wait…What’s an Organelle? • You tell me… – What is an organ? • Think back to chapter 1 – What is an organelle? • specialized structure that performs important cellular functions within a eukaryotic cell.
- 7. Nucleus Contains nearly all of the cells DNA and with it the coded instructions for making proteins and other important molecules
- 8. The Nuclear Envelope The nuclear envelope is layer of two membranes that surrounds the nucleus of a cell
- 9. The Nuclear Pores The nuclear pores allow material to move into and out of the nucleus.
- 10. Chromatin Chromatin is the granular material visible within the nucleus; consists of DNA tightly coiled around proteins.
- 11. Chromosomes Chromosomes are distinct threadlike structures that contain the genetic information that is passed from one generation to the next.
- 12. Nucleolus
- 13. Ribosomes • Proteins are assembled on ribosomes • Ribosomes are small particles of RNA and protein found throughout the cytoplasm
- 14. Endoplasmic Reticulum The ER is the site where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell.
- 15. Rough ER 1 2 Which one is rough? 1 or 2? What makes the rough ER rough?
- 16. Smooth ER 1 2 Which one is smooth? 1 or 2? What makes the smooth ER smooth?
- 17. Golgi Apparatus The function of the Golgi Apparatus is to modify, sort, and package proteins and other materials from the ER for storage in the cell or secretion outside the cell.
- 18. Vesicles
- 19. Specific Vesicle: Lysosomes & Peroxisomes
- 20. Central Vocuole • Why are these flowers red? • Are their vacuoles in animal cells?
- 21. Mitochondria
- 23. Cytoplasm and Cytoskeleton Functions of the Cytoplasm • The cytoplasm has several important functions, including – suspending cell organelles – pushing against the plasma membrane to help the cell keep its shape – providing a site for many of the biochemical reactions of the cell
- 24. Centrioles
- 26. Cell Wall
- 27. What do Plant Cells Have that animal cells do not?? http://www.cellsalive.com/cells/cell_model.htm
Editor's Notes
- Prokaryotic cells are cells without a nucleus. The DNA in prokaryotic cells is in the cytoplasm rather than enclosed within a nuclear membrane. Prokaryotic cells are found in single-celled organisms, such as bacteria, like the one shown in Figure below. Organisms with prokaryotic cells are called prokaryotes. They were the first type of organisms to evolve and are still the most common organisms today. Prokaryotic Cell. This diagram shows the structure of a typical prokaryotic cell, a bacterium. Like other prokaryotic cells, this bacterial cell lacks a nucleus but has other cell parts, including a plasma membrane, cytoplasm, ribosomes, and DNA. Identify each of these parts in the diagram.
- Eukaryotic cells are cells that contain a nucleus. A typical eukaryotic cell is shown in Figure below. Eukaryotic cells are usually larger than prokaryotic cells, and they are found mainly in multicellular organisms. Organisms with eukaryotic cells are called eukaryotes, and they range from fungi to people. Eukaryotic cells also contain other organelles besides the nucleus. An organelle is a structure within the cytoplasm that performs a specific job in the cell. Organelles called mitochondria, for example, provide energy to the cell, and organelles called vacuoles store substances in the cell. Organelles allow eukaryotic cells to carry out more functions than prokaryotic cells can.
- Pick an organelle to being the journey….
- The Nucleus The nucleus is the largest organelle in a eukaryotic cell and is often considered to be the cell’s control center. This is because the nucleus controls which proteins the cell makes. The nucleus of a eukaryotic cell contains most of the cell’s DNA, which makes up chromosomes and is encoded with genetic instructions for making proteins. The nucleus is often the most prominent cell organelle. It contains the genome, the cell’s database, which is encoded in molecules of the nucleic acid, DNA. The nucleus is bounded by a nuclear envelope composed of two membranes separated by an intermembrane space (Fig. 3.5). The inner membrane of the nuclear envelope is lined by a meshwork of proteins called the nuclear lamina which provides rigidity to the nucleus.Atwo-way traffic of proteins and nucleic acids between the nucleus and the cytoplasm passes through holes in the nuclear envelope called nuclear pores. The nucleus of a cell that is synthesizing proteins at a low level will have few nuclear pores. In cells that are undergoing active protein synthesis, however, virtually the whole nuclear surface is perforated.
- Most of the time, chromatin is spread throughout the nucleus, but when a cell divides, the chromatin condenses to form Chromosomes.
- The nucleolus is the area where ribosomes are made. Ribosomes are made of RNA. The nucleolus contains a lot of rRNA (ribosomal RNA)
- Ribosomes Ribosomes are small organelles where proteins are made. They contain the nucleic acid RNA, which assembles and joins amino acids to make proteins. Ribosomes can be found alone or in groups within the cytoplasm as well as on the RER. Ribosomes are the most numerous organelles in almost all the cells.
- Endoplasmic Reticulum The endoplasmic reticulum (ER) is an organelle that helps make and transport proteins and lipids. There are two types of endoplasmic reticulum: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). Both types are shown in Figure below. Endoplasmic Reticulum- The endoplasmic reticulum contains a network of branching and joining tubules 400 to 700 angstroms in diameter (1 angstrom equals 10-9 m). It has been calculated that 1 ml of liver tissue contains about 11 square meters of endoplasmic reticulum. The encircling membranes are about 50 to 60 angstroms thick and have the same substructure as the plasma membrane. Two patterns are found in the cell, the smooth endoplasmic reticulum and the rough endoplasmic reticulum. The rough endoplasmic reticulum is covered by an evenly spaced arrangement of ribosomal granules. The smooth endoplasmic reticulum lacks ribosomes, which synthesize proteins. The smooth endoplasmic reticulum, rich in a wide variety of enzymes, is most common in cells that are involved in the synthesis of lipids, triglycerides, lipoprotein complexes, and steroids.
- RER looks rough because it is studded with ribosomes. It provides a framework for the ribosomes, which make proteins. Bits of its membrane pinch off to form tiny sacs called vesicles, which carry proteins away from the ER.
- SER looks smooth because it does not have ribosomes. SER also makes lipids, stores substances, and plays other roles. The SER contains collections of enzymes that perform specialized tasks, including synthesis of membrane lipids and the detoxification of drugs. Where might you find large amounts of Smooth ER? Liver
- The Golgi apparatus is a large organelle that processes proteins and prepares them for use both inside and outside the cell. It is shown in Figure below. The Golgi apparatus is somewhat like a post office. It receives items (proteins from the ER), packages and labels them, and then sends them on to their destinations (to different parts of the cell or to the cell membrane for transport out of the cell). The Golgi apparatus is also involved in the transport of lipids around the cell. Because of its large size, the golgi apparatus was one of the first organelles of a cell to be discovered. In 1897, a man named Camillo Golgi was researching the nervous system when he noticed an organelle coming out of the Endoplasmic Recticulum, and he named it the recticular apparatus. Once the discovery was announced the organelle was then changed to be named after him, calling it the Golgi Apparatus. Structure: The Golgi Apparatus is a membrane-bound structure with a single membrane found in both plant and animal cells. It is composed of a stack of about six flattened, membranous sacs that look like a stack of pita bread. The membranous sacs are known as cisternae. The cisternae has two faces, the cis and trans face. The trans face is where products leave the Golgi Apparatus in vesicles. The cis face is the part of the Golgi where products are packaged and sent to the required destination determined by enzymes. The Golgi Apparatus is part of the Endomembrane System. FUNCTION: The Golgi Apparatus's function is to refine, package, and deliver proteins synthesized on ribosomes on the Endoplasmic Recticulm. It modifies proteins and lipids and then prepares them for export or for other functions within the cell. The proteins processed are then sent to specific destinations determined by enzymes at the trans face of the Golgi Apparatus. The proteins synthesized are used for a function in transport and cell-cell recognition. The Golgi secretes chemicals in vesicles, called Golgi Vesicles. Other functions include: to produce secretory enzymes, such as the digestive enzymes of the pancreas, transport and store lipids, and form lysosomes. PROCESS: Proteins arrive at the Golgi enclosed in vesicles composed of the ER membrane. These vesicles fuse with the membrane at the cis face. As these vesicles pass from layer to layer through the stacks of the Golgi Apparatus, they are modified chemically. Specific enzymes modify the oligosaccharide chains of the proteins by removing certain mannose residues and adding other sugars.
- Vesicles and Vacuoles Both vesicles and vacuoles are sac-like organelles that store and transport materials in the cell. Vesicles are much smaller than vacuoles and have a variety of functions. The vesicles that pinch off from the membranes of the ER and Golgi apparatus store and transport protein and lipid molecules. Some vesicles are used as chambers for biochemical reactions. Other vesicles include: Vesicles are tiny membrane sacs formed by part of the cell membrane folding inward and pinching off of the Endoplasmic Reticulum and Golgi Apparatus. Vesicles store, transport, and digest cellular products and waste. The vesicles use endocytosis when they are transporting material into the cell, when this occurs the material will join the cell membrane and become a part of it. Vesicles use exocytosis when they are transporting the material out of the cell. Vesicles affect humans because they organize metabolism, they store enzymes, and transport material. Vesicles are found in all cells not just specific ones. Some different types of vesicles are synaptic vesicles, gas vesicles, and matrix vesicles.
- Lysosomes, which use enzymes to break down foreign matter and dead cells. Peroxisomes, which use oxygen to break down poisons. Lysosomes are organelles that contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. The membrane surrounding a lysosome allows the digestive enzymes to work at the 4.5 pH they require. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are created by the addition of hydrolytic enzymes to early endosomes from the Golgi apparatus. The name lysosome derives from the Greek words lysis, which means dissolution or destruction, and soma, which means body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in autolysis. Lysosomes were discovered by the Belgian cytologist Christian de Duve in 1949. Functions The lysosomes are used for the digestion of macromolecules from phagocytosis (ingestion of other dying cells or larger extracellular material), endocytosis (where receptor proteins are recycled from the cell surface), and autophagy (wherein old or unneeded organelles or proteins, or microbes that have invaded the cytoplasm are delivered to the lysosome). Autophagy may also lead to autophagic cell death, a form of programmed self-destruction, or autolysis, of the cell, which means that the cell is digesting itself. PEROXISOMES are omnipresent organelles in eukaryotes that are used in the metabolism of fatty acids and other structures. In 1967, Christian de Duve, a Belgian cytologist, named peroxisomes cellular organelles. They have specific enzymes that get rid of toxic peroxides in the cell. They are made up of one lipid bilayer membrane which separates the contents within peroxisome. This single bilayer contains membrane proteins that are critical for certain functions in the cell such as: bringing proteins into the organelles and helping in proliferation. WHERE ARE PEROXISOMES FOUND? In almost every eukaryote In oxidation reactions (ex. beta-oxidation of very-long-chain fatty acids) Not in prokaryotes In plant and animal cells
- Central Vacuole Most mature plant cells have a large central vacuole. This vacuole can make up as much as 90% of the cell’s volume. The central vacuole has a number of functions, including storing substances such as water, enzymes, and salts. It also helps plant tissues, such as stems and leaves, stay rigid and hold their shape. It even helps give flowers, like the ones in Figure below, their beautiful colors. These flowers are red because of red pigment molecules in the central vacuoles of their cells. The bright colors are an important adaptation. They help the flowers attract pollinators such as hummingbirds so the plants can reproduce.
- The mitochondrion (plural, mitochondria) is an organelle that makes energy available to the cell. This is why mitochondria are sometimes referred to as the power plants of the cell. They use energy from organic compounds such as glucose to make molecules of ATP (adenosine triphosphate), an energy-carrying molecule that is used almost universally inside cells for energy. Scientists think that mitochondria were once free-living organisms because they contain their own DNA. They theorize that ancient prokaryotes infected (or were engulfed by) larger prokaryotic cells, and the two organisms evolved a symbiotic relationship that benefited both of them. The larger cells provided the smaller prokaryotes with a place to live. In return, the larger cells got extra energy from the smaller prokaryotes. Eventually, the prokaryotes became permanent guests of the larger cells, as organelles inside them. This theory is called the endosymbiotic theory, and it is widely accepted by biologists today. The mitochondria are called the “powerhouses” of the cell. This is where cellular respiration occurs. The end product of cellular respiration is energy. Muscle and liver cells have many mitochondria and produce a lot of energy. The mitochondria have 2 membranes. The inner membrane is folded. Here, at the folds, is where the energy is releases. The more folds it has the more energy is released. Foldings increase during exercise and activity while they decrease during rest.
- Plastids Plastids are organelles in plant cells that carry out a variety of different functions. The main types of plastids and their functions are described below. Chloroplasts are plastids that contain the green pigment chlorophyll. They capture light energy from the sun and use it to make food. Chromoplasts are plastids that make and store other pigments. The red pigment that colors the flower petals in Figure above was made by chromoplasts. Leucoplasts are plastids that store substances such as starch or make small molecules such as amino acids. Like mitochondria, plastids contain their own DNA. Therefore, according to endosymbiotic theory, plastids may also have evolved from ancient, free-living prokaryotes that invaded larger prokaryotic cells. If so, they allowed early eukaryotes to make food and produce oxygen.
- Cytoplasm and Cytoskeleton The cytoplasm consists of everything inside the plasma membrane of the cell. It includes the watery, gel-like material called cytosol, as well as various structures. The water in the cytoplasm makes up about two thirds of the cell’s weight and gives the cell many of its properties. The cytoplasm is the jelly-like material that fills in between the nuclear membrane and cell membrane. Eukaryotes cells (containing a nucleus) contains all the organelles such as, mitochondria, the endoplasmic reticulum, the Golgi apparatus, and lysosomes and peroxisomes. Each has specific functions in the cell. Most of the cellular activities occur in the cytoplasm. The cytoplasm contains cytosol, and the the cytoskeleton and many organelles, are suspended in it. Cytosol is a translucent gel outside of membrane-bound organelles, which makes up about 70% of the cell. It is made up of different elements, such as proteins, macromolecules, water, cytoskeleton filaments, enzymes, fatty acids, sugars, and fibers. Much of the cell is composed of dissolved nutrients and helps dissolve waste products. Basically, the cytoplasm/cytosol makes up and holds everything together in the cell. It suspends the contents of the cell in a gel like fatty membrane. It surronds the nuclear envelope and cytoplasmic organelles. The organelles, filled with liquid are separated by the cytoplasm by cell membranes. Crisscrossing the cytoplasm is a structure called the cytoskeleton, which consists of thread-like filaments and tubules. You can see these filaments and tubules in the cells in Figure. As its name suggests, the cytoskeleton is like a cellular “skeleton.” It helps the cell maintain its shape and also holds cell organelles in place within the cytoplasm. The cytoskeleton is responsible for holding the shape and structure of the cell and protecting it, and it also helps with movement and stability. It is found in all cells. The cytoskeleton is made up of microfilaments, microtubules, and intermediate filaments. Microfilaments are about 3-6 nm diameter thread like fibers that are made up of actin (most abundant cell protein). Actin is important with muscle contractions and cytokinesis (forming cell cleavage). Microtubules are longer cylindrical tubes (20-25 nm in diameter) made up of tubulin. This seperates chromosomes during mitosis. The microtubules are responsible for the rigid and organized components of the cytoskeleton. As components of cilia and flagella, they are important in movement of the cell (arranged in patterns in these) and also organelles and vesicles within the cell. Intermediate filaments (8-12 nm diameter) are very stable structures of the cytoskeleton. They anchor and position the nucleus and give the cell its flexibility.
- Centrioles Centrioles are organelles involved in cell division. They help organize the chromosomes before cell division so that each daughter cell has the correct number of chromosomes after the cell divides. Centrioles are found only in animal cells and are located near the nucleus. Centrioles are barrel-shaped structures present in eukaryotic cells except for fungal and plant cells. A pair of centrioles is contained within a structure called centrosome, present near the nucleus. These structures play and important role in the attachment and orientation of microtubules. Microtubules are thin, hollow cylinders that play a major role in cell division, intracellular transport, motility, and are also important to maintain the structural integrity of a cell.Centrioles are the nucleation points for spindle formation during mitosis and meiosis, and also serve as the basal body for cilia and flagella. Given below is a short description of the structure of a centriole, followed by a detailed account of its functions during cell division, and as a basal body.
- The Plasma Membrane (Fluid Mosaic Model) The plasma membrane forms a barrier between the cytoplasm inside the cell and the environment outside the cell. It protects and supports the cell and also controls everything that enters and leaves the cell. It allows only certain substances to pass through, while keeping others in or out. The ability to allow only certain molecules in or out of the cell is referred to as selective permeability or semipermeability. To understand how the plasma membrane controls what crosses into or out of the cell, you need to know its composition. The Phospholipid Bilayer The plasma membrane is composed mainly of phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a phospholipid bilayer. As shown in Figure below, each phospholipid molecule has a head and two tails. The head “loves” water (hydrophilic) and the tails “hate” water (hydrophobic). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outwards, toward either the cytoplasm or the fluid that surrounds the cell. Molecules that are hydrophobic can easily pass through the plasma membrane, if they are small enough, because they are water-hating like the interior of the membrane. Molecules that are hydrophilic, on the other hand, cannot pass through the plasma membrane—at least not without help—because they are water-loving like the exterior of the membrane. Photo: Phospholipid Bilayer. The phospholipid bilayer consists of two layers of phospholipids, with a hydrophobic, or water-hating, interior and a hydrophilic, or water-loving, exterior. The hydrophilic (polar) head group and hydrophobic tails (fatty acid chains) are depicted in the single phospholipid molecule. The polar head group and fatty acid chains are attached by a 3-carbon glycerol unit. Other Molecules in the Plasma Membrane The plasma membrane also contains other molecules, primarily other lipids and proteins. The light blue chain-shaped molecules in Figure here,for example, are the lipid cholesterol. Molecules of cholesterol help the plasma membrane keep its shape. Many of the proteins in the plasma membrane assist other substances in crossing the membrane.
- Cell Wall The cell wall is a rigid layer that surrounds the plasma membrane of a plant cell. It supports and protects the cell. Tiny holes, or pores, in the cell wall allow water, nutrients, and other substances to move into and out of the cell. The cell wall is made up mainly of complex carbohydrates, including cellulose.
- Special Structures in Plant Cells Plant cells have several structures that are not found in animal cells, including a cell wall, a large central vacuole, and organelles called plastids. You can see each of these structures in the figure above. You can also view them in an interactive plant cell at the link below. http://www.cellsalive.com/cells/cell_model.htm