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Transcript
Anatomy of Cells The Discovery of Cells • DON’T WRITE THIS • Robert Hooke discovered cells when he looked under a microscope at a think slice of cork. • In Holland, Anton van Leeuwenhoek examined pond water and a sample taken from a human mouth. • He drew the organisms he saw—which today we call bacteria. (Rotifers) • Leeuwenhoek examined as many types of cells as he could. He even observed his own semen! Overview: The Importance of Cells • The early discoveries of cells are summarized in the cell theory, a fundamental concept of biology. • The cell theory states: o All living things are made up of cells. o Cells are the basic units of structure and function in living things. o New cells are produced from existing cells. Origin of Cellular Life • DON’T WRITE THIS NOW • The Earth formed about 4.6 billion years ago. o For about 500 million years, the Earth was continually bombarded by chunks of rock and ice in the solar system. • The early atmosphere of Earth contained: o o o o o Water vapor H2O Nitrogen N2 Carbon dioxide CO2 Methane CH4 Ammonia NH3 Two Types of Cells 1- Prokaryotes First life forms • Single celled • No true nucleusDNA/RNA is just floating around the cell • No membrane bound organelles 2- Eukaryotes • Evolved from single celled organisms • True nucleus with membrane bound organelles • Usually multi-cellular, but not always. Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm Flagella A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM) Parts of a Prokaryotic Cell • Nucleoid – Area where DNA or RNA is located. Not enclosed in a membrane like a nucleus. • Ribosomes – Small structures that use DNA or RNA instructions to produce proteins. • Flagella – Spin to produce movement. • Cell membrane – Controls what leaves or enters the cell • Do have cytoplasm – jelly like substance that is made up of mostly water and dissolved substances. Why are cells so small? • To have a large surface area to volume area. • Let me explain: LE 6-7 • Volume represents the size of the cell. • Surface area represents the amount of cell membrane to transport food, waste, water, and oxygen. 1 Total surface area Total volume Surface-to-volume ratio Surface area increases while Total volume remains constant 5 1 LE 6-7 Surface area increases while Total volume remains constant • A cell with a volume of 1mm3 will have a total surface area of 6mm2. • This provides plenty of area for the cell to absorb what it needs. 5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 Total volume (height x width x length X number of boxes) 1 Surface-to-volume ratio (surface area volume) 6 LE 6-7 • A larger cell with a volume of 125mm3 will only have a surface area of 150mm2. • This cell will not be able to transport wastes and nutrients fast enough. Surface area increases while Total volume remains constant 5 1 1 Total surface area (height x width x number of sides x number of boxes) 150 Total volume (height x width x length X number of boxes) 125 Surface-to-volume ratio (surface area volume) 1.2 LE 6-7 • If the larger cell is instead broken down into 125 smaller cells, it will once again have enough surface area. • This is why multicellular organisms exist! Surface area increases while Total volume remains constant 5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 150 750 Total volume (height x width x length X number of boxes) 1 125 125 Surface-to-volume ratio (surface area volume) 6 1.2 6 Eukaryotic Cell Organization • The eukaryotic cell can be divided into two major parts: the nucleus and the cytoplasm. • The cytoplasm is the fluid portion of the cell outside the nucleus. o Organelles are small structures within cells that have specific jobs. ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) LE 6-9b Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata The Nucleus • This is the Boss of the cell • The nuclear envelope is a membrane surrounding the nucleus. • Contains the DNA The Nucleus • The nucleus also contains a small dense region called the nucleolus. • The nucleolus produces ribosomes, which are needed to build proteins. Organelles that Build Proteins • Because proteins carry out so many of the essential functions of living things, a big part of the cell is devoted producing and transporting them. • Proteins are synthesized(made) in ribosomes, which can be found in two places: o Freely floating in the cytoplasm o Attached to the endoplasmic reticulum Ribosomes: Protein Factories • Ribosomes are particles made of RNA and protein o Ribosomes produce proteins by following coded instructions that come from DNA. o Each ribosome is like a small machine in a factory, turning out proteins on orders that come from its DNA “boss.” Endoplasmic Reticulum • The endoplasmic reticulum (ER) is a huge membrane that is connected to the nuclear membrane. • There are two distinct regions of ER: o Smooth ER, which lacks ribosomes o Rough ER, with ribosomes studding its surface Smooth Endoplasmic Reticulum • The smooth endoplasmic reticulum: o o o o Synthesizes lipids Metabolizes carbohydrates Stores calcium Detoxifies poison • The smooth endoplasmic reticulum does not contain any ribosomes, so it is unable to synthesize proteins. Rough Endoplasmic Reticulum • The rough ER o Holds ribosomes o Produces any proteins needed by the cell. The Golgi Apparatus • The Golgi apparatus is a series of flattened membrane sacs in the cytoplasm. • Functions of the Golgi apparatus: o Modifies, sorts, and packages materials into transport vesicles for storage or transport out of the cell. o A typical path for a protein produced by the cell: o DNARNARibosomeRough ER → Golgi → Cell membrane → Released by cell Cell/Plasma Membrane • The plasma/Cell membrane is a selective barrier. o Allows passage of oxygen, nutrients into the cell, and waste out of the cell. • The general structure of a biological membrane is a bilayer(double)of phospholipids o This allows the cell to control what goes in and out. LE 6-16-1 Nucleus Rough ER Smooth ER Nuclear envelope LE 6-16-2 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi LE 6-16-3 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle Plasma membrane trans Golgi Organelles that Store, Clean Up, and Support • These are organelles that help the cell maintain its shape, clean up wastes, and store material needed later. o Lysosomes o Vacuoles o Vesicles Vacuoles • vacuoles are membrane-bound sacs that store many materials. • Mostly found in plant cells • Plant cells often have one large central vacuole. This fills with water, making the cell rigid. o When they are empty and dry, plants wilt! o Hold cell sap ( full of sugars and water) Lysosomes • Lysosomes serve as the cell’s cleanup crew. • A lysosome is full of enzymes that can digest proteins, lipids, polysaccharides, and nucleic acids. o Can also breakdown old organelles so they can be re-used. Animation: Lysosome Formation Vesicles • Spherical Sacs that transport materials within a cell. Cytoskeleton • The cytoskeleton is a network of protein filaments that give the cell shape. o Can also help transport materials across the cell. • Centrioles are part of the cytoskeleton that help move chromosomes during cell division. Organelles that Capture and Release Energy • All life requires energy. • Organisms either can get their energy from sunlight via photosynthesis, or by eating other organisms via cell respiration. • Photosynthesis occurs in chloroplasts. • Cell respiration occurs in mitochondria. Chloroplasts • Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis • Chloroplasts are found in leaves and other green organs of plants and in algae Mitochondria • Mitochondria are the power plants of the cell. • They convert the chemical energy stored in food into smaller molecules for the cell to use. • Mitochondria have two membranes, outer and inner. • The inner membrane is folded up to increase the amount of surface area to do chemical reactions. Cell Wall • The cell wall is made of cellulose and serves as support and protection for the cell. • Animals do not have cell walls, but plants, fungi, and algae do. • The cell wall is outside of the cell membrane. The Cell: A Living Unit Greater Than the Sum of Its Parts • Cells rely on the integration of structures and organelles in order to function • For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane