Presentation on theme: "Prokaryotic vs. Eukaryotic. Prokaryotes Prokaryotes are unicellular organisms and are found in all environments. They are the largest group of organisms,"— Presentation transcript:
Prokaryotes Prokaryotes are unicellular organisms and are found in all environments. They are the largest group of organisms, mostly due to the large numbers of bacteria which make up the bulk of the classification. Characteristics: –No membrane bound nucleus (genetic material dispersed throughout cytoplasm) –No membrane-bound organelles –Simple internal structure –Most primitive cell type (appeared about four billion years ago) Examples: Staphylococcus
Eukaryotes Eukaryotes, in general, are more advanced than prokaryotes. There are many eukaryotic unicellular organisms but there are no multicellular prokaryotes. Characteristics: –Membrane bound nucleus –Numerous membrane-bound organelles –Complex structure –Appeared approximately one billion years ago Examples: –Paramecium –Dinoflagellates –Canines (Dogs
Organelles There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Organelles as specialized structures: –Cilia for example - they act as "oars" to help some cells move Second, membrane bound organelles act as containers, separating parts of the cell from other parts of the cell. Organelles as Containers: –Lysosome - It contains digestive enzymes that if allowed to float free in the cell would kill it. Third, the membranes of organelles can act as sites for chemical reactions. Organelle membranes as sites for chemical reactions: –Chloroplast - Photosyntheis as a chemical process occurs within the structure of this organelle.
Membrane - thin, pliable layer of tissue covering surfaces or separating or connecting regions, structures, or organs of an animal or a plant.
Ribosomes Ribosomes are small dot-like structures in cells. They are often associated with endoplasmic reticulum(ER), to form rough ER. It is here that Protein Syntheis occurs. They are made up of proteins and ribonucleic acid (RNA). Their only function is to build proteins. There are two kinds of ribosomes: –those attached to the endoplasmic reticulum and –those floating in the cell cytoplasm. Attached ribosomes make proteins that are used in the ER or transported within the ER. Free ribosomes make proteins that are used in the cytoplasm. Ribosomes are made in the nucleus of the cell and uniquely enough posess their own form of RNA know as Ribosomal RNA (rRNA). A ribosome can make the average protein in about one minute.
Centrioles They are not found in higher plant cells. Centrioles come in pairs and are composed of short microtubules arranged in a cylinder. The two centrioles are aligned at right angles to each other. During cell division one centriole moves to opposite sides of the cell and may function in cell division. The basic structure of the centriole is nine groups of three microtubules arranged as a cylinder. Each animal cell will have two.
Centrioles (cont’d) The spindle fibers that pull the chromosomes apart during mitosis begin forming in the vicinity of the centrioles. Because of this behavior it was long believed that centrioles were necessary for animal cell division. However, some animal cells can divide when the centrioles have been removed Another possible function of centrioles is that of a cilia and/or flagella template or plan. Centrioles are found in animal cells, and the cells of most protists also contain them. Curiously enough, plant, fungus and red algae cells are fully capable of dividing without centrioles.
Microtubules All eukaryotic cells will contain a network of microtubules. They are made up of protein molecules and provide structure, acting as a "skeleton" or cytoskeleton. They serve as "roads" along which cells can transport organelles and vesicles. Chromosomes are pulled apart during mitosis by microtubules Cilia and flagella are composed of microtubules
Membrane Bound Organelles Organelles made-up of single membranes
Vacuoles The vacuole acts as a container Vacuoles are, in simplest terms, a sac, a single membrane surrounding solid or liquid contents. There are a wide variety of vacuoles, containing a wide variety of substances. Many plant cells contain a large central vacuole (50 -90 % of its volume) filled with water A food vacuole in a single celled amoeba contains the food item that the amoeba has consumed.
Lysosome Lysosomes are sacs that contain digestive enzymes. Lysosomes are used by the cell to digest or breakdown most complex organic molecules. They can either digest substances brought into the cell or they can digest parts of the cell itself. Cells that ingest (eat) other cells surround the ingested cell with a membrane forming a food vacuole. This food vacuole is then fused with a lysosome and the cell is digested.
Lysosomes (cont’d) Often cells need to tear down parts of themselves and reuse the materials, Lysosomes do this. For example, when a tadpole looses its tail in the process of becoming a frog, the tail cells digest themselves by the use of lysosomes. The material from the tail is then used to build legs and other frog parts! The term lysosome comes from two roots, lys which means breakdown or digest and some which means body. Therefore the literal translation is "digesting body".
Vesicles Vesicles are the shipping containers within cells and also carry material out of the cell They are a sac surrounded by a single membrane. They are a liquid filled sac. Some are formed by pinching off the Golgi apparatus. Vesicles that carry material out of the cell are called exocytotic vesicles. Those which bring material into the cell are called endocytotic vesicles.
Endoplasmic Reticulum Endoplasmic reticulum(ER) is a network of folded membranes that extend through the cytoplasm to the nuclear membrane. There are two kinds of ER, rough and smooth. Rough has ribosomes, smooth has no ribosomes. ER is involved in the transport of materials through the cell. Endoplasmic reticulum is an extensive network of membranes that extends from the cell membrane through the cytoplasm to the nuclear membrane. The membranes of the ER surround an inner cavity called the lumen. The membranes of the ER enclose a series of tubes and flattened membranous areas. The ER membranes actually attach to the cell membrane and the nuclear membrane as well as the Golgi bodies in the cytoplasm. The basic function of ER is transport. Proteins produced by the ribosomes are transported to regions of the cell where they are needed or to the Golgi body for export from the cell. Smooth ER involved in detoxification of poisons and lipid synthesis.
Peroxisomes Peroxisomes resemble lysosomes in structure and function. They break down amino acids, fatty acids and alcohol. The function of peroxisomes is very similar to lysosomes, however the reactions in peroxisomes are more specific. These reactions produce hydrogen peroxide which could harm cells if it were allowed to persist. An enzyme (catalase) breaks down the hydrogen peroxide to water and oxygen, both of which can be used by the cell.
Golgi Apparatus Golgi apparatus (sometimes called the Golgi body) The Golgi apparatus consists of stacks of sacs with vesicles pinching off from the edges of the sacs. The function of the Golgi is to "pack up" materials for export from the cell. The vesicles that pinch off from the Golgi apparatus move to the cell membrane and the material in the vesicle is released to the outside of the cell. Some of these pinched off vesicles become lysosomes. The two primary functions of the Golgi apparatus is –: First modification of lipids and proteins; –and second storage and packaging of materials that will be exported from the cell. It is the "shipping department" of the cell
Mitochondria They are the main energy producers in cells. There is a single outer membrane and a folded inner membrane. This results in a sac with two inner compartments which are separated by the inner membrane. The first compartment is between the outer and inner membranes, the outer compartment is inside the inner membrane. Mitochondria are usually shaped like stubby cigars but sometimes they are round.
Mitochondria (cont’d) They use complex molecules and oxygen to produce a high energy molecule known as ATP. To do this mitochondria carry on a process called aerobic respiration. Because of its role in energy production the mitochondria has been called the "powerhouse of the cell". They are very abundant in cells that require lots of energy such as muscle cells.
Mitochondria (cont’d) All the mitochondria in your body came from your mother. Mitochondria are not part of the genetic code in the nucleus of your cells, fathers only give genes to their children. Mothers give genes and cytoplasm to their children in their egg cells, since mitochondria are in the cytoplasm and reproduce themselves they only are inherited from mothers. Geneticists have used this feature of mitochondria to study maternal family lines and rates of evolution.
Chloroplasts Chloroplasts are the site of photosynthesis in eukaryotic cells. Because of their green color chloroplast are the only organelles that can easily be seen with a light microscope. There is a single membrane surrounding the chloroplast. This membrane surrounds a fluid called the stroma. Floating in the stroma are stacks of disks made up of membranes, these are the grana. The grana resemble a stack of coins, however instead of coins this stack is made up of individual hollow disks called thylakoids. Chlorophyll, the green compound which gives chloroplasts their color, is found in the membranes of the thylakoids.
Chloroplasts (cont’d) The light reactions take place on the membranes of the grana. The dark reactions (also called light- independent reactions and/or Calvin- Benson Cycle) take place in the stroma. Chloroplasts, like mitochondria, contain their own DNA and reproduce themselves. Both have these characteristics of prokaryotes (bacteria)
Cilia and Flagella These whiplike appendages extend from the surface of many types of eukaryotic cells. If there are many of them, they are called cilia; if only one, or a few, they are flagella. Flagella also tend to be longer than cilia but are otherwise similar in construction. Cilia and flagella move liquid past the surface of the cell. For single cells, such as sperm, this enables them to swim. For cells anchored in a tissue, like the epithelial cells lining our air passages, this moves liquid over the surface of the cell (e.g., driving particle-laden mucus toward the throat).
Cell Wall a non-living secretion of the cell membrane, composed of cellulose contains pits (openings) that make it totally permeable The cell wall is rigid (up to many micrometers in thickness) and gives plant cells a very defined shape. The cell wall is the reason for the difference between plant and animal cell functions. Because the plant has evolved this rigid structure, they have lost the opportunity to develop nervous systems, immune systems, and most importantly, mobility.
Cell Membrane While the plant cell has a rigid cell wall, an animal cell membrane is a flexible lipid bilayer. The lipid molecules (mostly phospholipids) that make up the membrane have a polar, hydrophilic head and two hydrophobic hydrocarbon tails. There are three different major classes of lipid molecules - phospholipids, cholesterol, and glycolipids. Different membranes have different ratios of the three lipids. What makes the membrane truly special is the presence of different proteins on the surface that are used for various functions such as cell surface receptors, enzymes, surface antigens, and transporters.
Cytoplasm is defined as the material that lies within the cytoplasmic membrane, or the membrane that surrounds a cell. It contains none of a cell's genetic material, because this is contained in the nucleus. It does, however, contain a lot of water, and the other organelles of the cells. It provides a platform upon which they can operate within the cell. It is made up of proteins, vitamins, ions, nucleic acids, amino acids, sugars, carbohydrates and fatty acids. All of the functions for cell expansion, growth and replication are carried out in the cytoplasm of a cell.
The Cell Nucleus The cell nucleus forms the package for our genes and their controlling factors. It functions to: Transport regulatory factors & gene products via nuclear pores. Produce messages (messenger Ribonucleic acid or mRNA) that code for proteins Store genes on chromosomes Organize genes into chromosomes to allow cell division. Produce ribosomes in the nucleolus Organize the uncoiling of DNA to replicate key genes The nucleus is the control center and exists only in eukaryotes. The nucleus contains the genetic information for the cell in the form of DNA and RNA.
A Comparison of Plant and Animal Cells Plant cells have a cell wall, but animal cells do not. Plant cells have chloroplasts, but animal cells do not. Plant cells generally have a more rectangular shape because the cell wall is more rigid. Animal cells have a round or irregular shape because they do not have a cell wall. Plants cells usually have one or more large vacuole(s), while animal cells have smaller vacuoles, if any are present.