Cell is the basic unit of life All living organisms are composed of one or more cells - the cell is the unit of organization of Life Most cells are very small. Exceptions? Ostrich egg is the largest cell. Nerve cell in a leg of a giraffe may be as long as 3m, but is very thin. Most life on the planet consists of single cells. Multicellular organisms arose relatively recently ~ 600 million years ago. A cell is a small packet or bag of liquid. The liquid is cytoplasm (or cytosol), which is essentially salty water with various organic molecules suspended in it. What is a cell?
Geologic Time Scale The earth is ~4.6 billion years old Humans < 1 mya Dinosaurs until ~65 mya Multicellular life Land plants Insects, amphibians Reptiles Seed plants Eukaryotes ~600 mya Prokaryotes, the first cells
Prokaryotes plasmid Lacking well-defined nuclei and membrane- bound organelles, and with chromosomes composed of a single closed DNA circle. They come in many shapes and sizes, from minute spheres, cylinders and spiral threads, to flagellated rods, and filamentous chains. They are found practically everywhere on Earth and live in some of the most unusual and seemingly inhospitable places.
Plasmids Plasmids, are small, circular pieces of DNA carried by many strains of bacteria. Unlike the chromosome, they are not involved in reproduction. Only the chromosome has the genetic instructions for initiating and carrying out cell division. Plasmids replicate independently and, while not essential for survival, appear to give bacteria a selective advantage. Plasmids have been shown to be instrumental in the transmission of special properties, such as antibiotic drug resistance, resistance to heavy metals, and virulence factors necessary for infection of animal or plant hosts. The ability to insert specific genes into plasmids have made them extremely useful tools in the fields of molecular biology and genetics, specifically in the area of genetic engineering.
Eukaryotes Nucleus is a large membrane-bound organelle. Its function is to sequester the DNA from the rest of the cell. Inside the nucleus, DNA is organized in chromosomes. A chromosome is a tighly coiled and wound strand of DNA packaged with various proteins. Smooth endoplasmic reticulum is a system of membranes and is involved in carbohydrate and lipid synthesis. Rough endoplasmic reticulum is a system of membranes that possesses ribosomes. Proteins are synthesized in the rough ER. Golgi apparatus stores and packages various molecules. When a molecule is needed elsewhere in the cell, a portion of the Golgi membrane closes off and forms a vesicle that can be transported around the cell. Eukaryotic cells have organelles. Organelles are subcellular structures that provide internal compartmentalization and other functions.
Mitrochondria Mitochondria are found in all Eukaryotic cells. Breakdown of glucose begins in the cytoplasm and ends in the mitochondria, where the final products of the breakdown are ATP, water, CO2 and heat. This process requires oxygen - that is why we breath: to provide the oxygen for the mitochondria and to get rid of carbon dioxide produced in the mitochondria. ATP (adenosine triphosphate) is the energy currency of the living world. Every cellular process that requires energy gets it from ATP. Thus, mitochondria are sometimes referred to as "factories of the cell".
Cytoskeleton The cytoskeleton, composed of filaments and microtubules, anchors the organelles and gives a cell its shape. Microtubules move organelles, including vesicles, within a cell. They also move the membrane-embedded proteins around where they are needed.
Comparison Prokaryotes (bacteria) have a cell membrane and cytoplasm and no other organelles. Eukaryotes (plants, animals, fungi, protista) have a number of different cell organelles. The nuclear material in Prokaryotes is a single, circular strand of DNA. The nuclear material in Eukaryotes is organized in multiple chromosomes contained with a nucleus.