Prokaryotic and Eukaryotic Cells PDF

Prokaryotic and Eukaryotic cells Assist. Prof. Yalda Hekmatshoar Email: [email protected]  Definition of a cell A cell is the smallest unit that is capable of performing life functions, All living things are made of cells Smallest living unit of structure and...

Prokaryotic and Eukaryotic cells Assist. Prof. Yalda Hekmatshoar Email: [email protected]  Definition of a cell A cell is the smallest unit that is capable of performing life functions, All living things are made of cells Smallest living unit of structure and function of all organisms is the cell  Life functions Reproduction and heredity Growth and development Metabolism – Chemical and physical life processes Movement and/or irritability – Respond to internal/external stimuli –Self propulsion Cell support, protection and storage mechanisms –Cell walls, vacuoles, granules, inclusions Transport of nutrients and waste  From simple microscopy, it has long been clear that living organisms can be classified on the basis of cell structure into two groups: ✓Prokaryotes (Bacteria and Archaea) –Pro= Before –Karyon= Kernel= nucleus ✓No nucleus ✓Eukaryotes (Everything else) –Eu= True Prokaryotes Prokaryotic cells were here first and for billions of years were the only form of life on Earth. Have no distinct nuclear compartment to house their DNA, Most prokaryotic cells are small and simple in outward appearance, ✓Most prokaryotic cells are 0.5–5µm,much smaller than the 10–100 µm of many eukaryotic cells. They live mostly as independent individuals or in loosely organized communities, rather than as multicellular organisms.  They are typically spherical or rod-shaped and measure a few micrometers in linear dimension. Molecular Cell Biology Lodish 5th edition  They often have a tough protective coat, called a cell wall, beneath which a plasma membrane encloses a single cytoplasmic compartment containing DNA, RNA, proteins, and the many small molecules needed for life. In the electron microscope, this cell interior appears as a matrix of varying texture without any discernible organized internal structure Molecular Cell Biology Lodish 5th edition  Prokaryotic cells live in an enormous variety of ecological niches, and they are astonishingly varied in their biochemical capabilities—far more so than eukaryotic cells. on plants & animals in plants & animals in the soil in depths of the oceans in extreme cold in extreme hot in extreme salt on the living on the dead ❖ Organotrophic species can utilize virtually any type of organic molecule as food, from sugars and amino acids to hydrocarbons and methane gas. ❖ Phototrophic species harvest light energy in a variety of ways, some of them generating oxygen as a by-product, others not. Molecular Biology o the cell, six edition ❖Lithotrophic species can feed on a plain diet of inorganic nutrients, getting their carbon from CO2 , and relying on H2 S to fuel their energy needs or on H2 , or Fe2+ , or elemental sulfur, or any of a host of other chemicals that occur in the environment. Molecular Biology o the cell, six edition ❖Prokaryotes (cells without a distinct nucleus) are biochemically the most diverse organisms and include species that can obtain all their energy and nutrients from inorganic chemical sources, such as the reactive mixtures of minerals released at hydrothermal vents on the ocean floor—the sort of diet that may have nourished the first living cells 3.5 billion years ago. ❖ DNA sequence comparisons reveal the family relationships of living organisms and show that the prokaryotes fall into two groups that diverged early in the course of evolution: the bacteria (or eubacteria) and the archaea. ❖ Together with the eukaryotes (cells with a membrane-enclosed nucleus), these constitute the three primary branches of the tree of life. ❖Most bacteria and archaea are small unicellular organisms with compact genomes comprising 1000–6000 genes.  The two groups of prokaryotes are called ✓bacteria (or eubacteria) ✓archaea (or archaebacteria).  The living world today is considered to consist of three major divisions or domains : ✓ bacteria, ✓Archaea, ✓eukaryotes Molecular Biology o the cell, six edition Archaea ✓are often found inhabiting environments that we humans avoid, such as bogs, sewage treatment plants, ocean depths, salt brines, and hot acid springs, Although they are also widespread in less extreme and more homely environments, from soils and lakes to the stomachs of cattle.  In outward appearance they are not easily distinguished from bacteria. At a molecular level, archaea seem to resemble eukaryotes more closely in their machinery for handling genetic information (replication, transcription, and translation), bacteria more closely in their apparatus for metabolism and energy conversion. Molecular Cell Biology Lodish 5th edition Eukaryotes Eukaryotes keep their DNA in a distinct membrane-enclosed intracellular compartment called the nucleus. (The name is from the Greek, meaning “truly nucleated,” from the words eu, “well” or “truly,” and karyon, “kernel” or “nucleus.”) Plants, fungi, and animals are eukaryotes  Eukaryotic cells, ✓ Are bigger and more elaborate than prokaryotic cells, ✓ Their genomes are bigger and more elaborate, ✓ The greater size is accompanied by radical differences in cell structure and function. ✓ Many classes of eukaryotic cells form multicellular organisms that attain levels of complexity unmatched by any prokaryote. Because they are so complex, Keep their DNA in an internal compartment called the nucleus. The nuclear envelope, a double layer of membrane, surrounds the nucleus and separates the DNA from the cytoplasm. Molecular Cell Biology Lodish 5th edition ✓ Their cells are, typically, 10 times bigger in linear dimension and 1000 times larger in volume. ✓ They have an elaborate cytoskeleton— ❖a system of protein filaments crisscrossing the cytoplasm and forming, together with the many proteins that attach to them, a system of girders, ropes, and motors that gives the cell mechanical strength, controls its shape, and drives and guides its movements. ✓ And the nuclear envelope is only one part of a set of internal membranes, each structurally similar to the plasma membrane and enclosing different types of spaces inside the cell, many of them involved in digestion and secretion. Modern Eukaryotic Cells Evolved from a Symbiosis ✓ All cells contain (or at one time did contain) mitochondria. ✓ These small bodies in the cytoplasm, enclosed by a double layer of membrane, take up oxygen and harness energy from the oxidation of food molecules—such as sugars— to produce most of the ATP that powers the cell’s activities. ✓ Mitochondria are similar in size to small bacteria, and, like bacteria, they have their own genome in the form of a circular DNA molecule, their own ribosomes that differ from those elsewhere in the eukaryotic cell, and their own transfer RNAs. ✓ It is now generally accepted that mitochondria originated from free-living oxygen-metabolizing (aerobic) bacteria that were engulfed by an ancestral cell that could otherwise make no such use of oxygen (that is, was anaerobic). Escaping digestion, these bacteria evolved in symbiosis with the engulfing cell and its progeny, receiving shelter and nourishment in return for the power generation they performed for their hosts. This partnership between a primitive anaerobic predator cell and an aerobic bacterial cell is thought to have been established about 1.5 billion years ago, when the Earth’s atmosphere first became rich in oxygen. What prokaryotic and eukaryotic cells have in common They both –have DNA as their genetic material –are covered by a cell membrane –contain RNA –are made from the same basic chemicals Carbohydrates, proteins, nucleicacids, minerals, fatsandvitamins –have ribosomes –regulate the flow of the nutrients and wastes that enter and leave them _ have similar basic metabolism like photo synthesis and reproduction –require a supply of energy Molecular Cell Biology Lodish 5th edition