Anatomy of Cells Introduction to Biology The Discovery of Cells • 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. • Leeuwenhoek examined as many types of cells as he could. 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 • 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 Water vapor H2O o Nitrogen N2 o Carbon dioxide CO2 o Methane CH4 o Ammonia NH3 Origin of Cellular Life • How did life arise from such a harsh environment? • Two scientists designed a model of what conditions were like on Earth at this time. o This is called the Miller-Urey Apparatus Miller-Urey Apparatus • This apparatus simulated three important conditions on Earth: – The high amount of lightning – Heat and gases released by volcanic activity – Water vapor present in the atmosphere. Results of Miller-Urey Apparatus • Simple compounds including water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2) were used to simulate the atmosphere. • After 2 weeks, 10-15% of the carbon had been used to form sugars, amino acids, and parts of nucleic acids. o These simple organic compounds could have produced the proteins, lipids, and carbohydrates that make up life today. The First Cells • The first life forms on Earth were likely single-celled prokaryotic organisms. o Prokaryotic organisms are single-celled organisms that do not have a nucleus. • Their DNA or RNA is usually floating freely inside the cell. o Prokaryotic cells also do not have any membrane bound organelles. Pili Nucleoid Ribosomes Plasma membrane Cell wall Bacterial chromosome Capsule 0.5 µm Flagella A typical A thin section through the rod-shaped bacterium Bacillus bacterium 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. • Pili – Hollow, hair-like structures that can be used to exchange genes. • Flagella – Spin to produce movement. • Cell membrane – Controls what leaves or enters the cell Antibiotics • Antibiotics are anti-bacterial chemicals that originally came from mold. • Each antibiotic works in different ways. o Penicillin disrupts the bacteria’s ability to produce a cell wall, causing it to burst due to an influx of water into its cytoplasm. Antibiotic Resistance • Bacteria can mutate and evolve quickly, due to their small size and fast reproduction rate. • Sometimes, a mutation will result in their ability to resist the action of antibiotics. o Over time, this mutation can spread throughout an entire colony, creating a strain of antibiotic-resistant bacteria. • Resistant bacteria will not be affected by the antibiotics in the same way. Eukaryotic Cells • Eukaryotes are organisms with much larger and more complex cells than prokaryotes. • DNA is in a nucleus that is bounded by a nuclear membrane. • Have membrane-bound organelles • The largest eukaryotic cells are 0.1mm to 1.0mm in size. Why haven’t they evolved any larger? LE 6-7 Surface area increases while • Volume represents the Total volume remains constant size of the cell. • Surface area represents the amount of cell membrane to transport food, waste, water, and 5 oxygen. 1 1 Total surface area Total volume Surface-to-volume ratio LE 6-7 Surface area increases while • A cell with a volume of Total volume remains constant 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 6 number of sides x number of boxes) Total volume (height x width x length 1 X number of boxes) Surface-to-volume ratio 6 (surface area ÷ volume) LE 6-7 Surface area increases while • A larger cell with a Total volume remains constant volume of 125mm3 will only have a surface area of 150mm2. • This cell will not be able to transport wastes and 5 nutrients fast enough. 1 1 Total surface area (height x width x 150 number of sides x number of boxes) Total volume (height x width x length 125 X number of boxes) Surface-to-volume ratio 1.2 (surface area ÷ volume) LE 6-7 Surface area increases while • If the larger cell is instead Total volume remains constant broken down into 125 smaller cells, it will once again have enough surface area. • This is why multicellular 5 organisms exist! 1 1 Total surface area (height x width x 6 150 750 number of sides x number of boxes) Total volume (height x width x length 1 125 125 X number of boxes) Surface-to-volume ratio 6 1.2 6 (surface area ÷ volume) 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. • Prokaryotic cells have cytoplasm as well, even though they do not have a nucleus. Eukaryotic Cell Anatomy • A eukaryotic cell has internal membranes that partition the cell into organelles. o Organelles are small structures within cells that have specific jobs. • Plant and animal cells have most of the same organelles, although there are a few differences. ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER Nucleolus NUCLEUS 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 Rough NUCLEUS Nucleolus endoplasmic reticulum Chromatin Smooth Centrosome endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate CYTOSKELETON filaments Microtubules Mitochondrion Peroxisome Plasma Chloroplast 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 • The nucleus contains most of the cell’s genes and is usually the largest organelle. • The nuclear envelope is a membrane that encloses the nucleus, separating it from the cytoplasm. • In the same way that the main office controls a large factory, the nucleus is the control center of the cell. • The nucleus contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules. The Nuclear Membrane • The nuclear envelope is dotted with thousands of nuclear pores, which allow material to move into and out of the nucleus. • The nucleus mainly contains chromatin— the cell’s DNA instructions joined with proteins. The Nuclear Membrane • 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 on 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 function of the endoplasmic reticulum (ER) is to assist in the production, processing, and transport of proteins and in the production of lipids. • 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 Synthesizes lipids o Metabolizes carbohydrates o Stores calcium o 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 Rough ER → Golgi → Cell membrane → Released by cell 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 Vacuoles o Lysosomes o Cytoskeleton Vacuoles • Vesicles and vacuoles are membrane-bound sacs that store many materials. • 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! 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 Cytoskeleton • The cytoskeleton is a network of protein filaments that give the cell shape.