The Structure and Function of Cells

The Structure and Function of Cells EUKARYOTIC CELL DESCRIPTION/FUNCTION: A. CELL MEMBRANE AND THE FUNCTIONS: CELL MEMBRANE Also called the plasma membrane gives mechanical strength to the cell. Its unique structure enables itself to serve as molecular traffic regulator. It is 5 up to 10 um in thickness. It also exhibits fluid mosaic nature, seal itsef if broken. B. THE CYTOPLASM AND ITS ORGANELLES CYTOPLASM A mass of jelly-like material that is somewhat grayish or colorless, translucent and viscous It can change from semi solid to semi liquid. C. CELL ORGANELLES ENDOPLASMIC RETICULUM (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. ER has two forms: the rough ER and the smooth ER. RIBOSOMES The ribosome is a large complex composed of many molecules, including RNAs and proteins, and is responsible for processing the genetic instructions carried by an mRNA. Ribosomes float freely in the cytoplasm or sometimes bind to another organelle called the endoplasmic reticulum MITOCHONDRIA are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondria have two functionally distinct membrane systems separated by a space: the outer membrane, which surrounds the whole organelle; and the inner membrane, which is thrown into folds or shelves that project inward. These inward folds are called cristae. Mitochondria play a critical role in generating energy in the eukaryotic cell, and this process involves a number of complex pathways GOLGI BODIES OR GOLGI APPARATUS (also called the golgi apparatus or golgi complex) a flattened, layered, sac-like organelle that looks like a stack of pancakes and is located near the nucleus. The golgi body packages proteins and carbohydrates into membrane-bound vesicles for export from the cell. LYSOSOMES are often referred to as the garbage disposal system of a cell. digest foreign bacteria that invade a cell. helping to recycle receptor proteins and other membrane components and degrading worn out organelles such as mitochondria. Lysosomes can even help repair damage to the plasma membrane by serving as a membrane patch, sealing the wound. MICROBODIES Variety of organelles similar to lysosome but contains different enzymes. One of these is the glyxoxysomes present in some plant, another is peroxisomes which contain powerful oxidative enzymes. CYTOSKELETON Microtubules that provide support to the internal system of cell thus, it provides support and shape. Also provides pathways for certain cellular molecules to move. VACUOLES Membrane- bound, fluid- filled spaces found in both animal and plant cell but bigger in plant cell. The vacuolar membrane is also called tonoplast and they contain liquid cell sap. MICROFILAMENTS Are long thread like extremely thin filaments first seen in skeletal muscle cells that gives the cell a striped appearance. CENTRIOLES Small dark bodies located just outside the nucleus of most animal cells. They are cylindrical structures and two of them lie close together. Associated in the spindle fibers of dividing animal cells. PLASTIDS Are cytoplasmic orhanelles found in cells of most plants. NUCLEUS It houses the cells chromosomes and is the place where almost all DNA replication and RNA synthesis occur. The nucleus is spheroid in shape and separated from the cytoplasm by a membrane called the nuclear envelope. CELL WALL a thick, rigid membrane that surrounds a plant cell. This layer of cellulose fiber gives the cell most of its support and structure. cell wall also bonds with other cell walls to form the structure of the plant. CHLOROPLASTS are similar to mitochondria but are found only in plants. Chloroplasts convert light energy from the sun into ATP through a process called photosynthesis. CENTROSOME (also called the microtubule organizing center) a small body located near the nucleus it has a dense center and radiating tubules. The centrosomes is where microtubules are made. During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. GRANUM (plural grana) A stack of thylakoid disks within the chloroplast is called a granum. NUCLEOLUS an organelle within the nucleus it is where ribosomal RNA is produced. DIFFERENCE BETWEEN THE PLANT CELL AND ANIMAL CELL Basis of Comparison Plant cells Animal cells 1. plasma membrane present Present 2. Cell wall present Absent 3. Lysosome Absent Present 4. Plastids Present Absent 5. Vacuoles Small but many Large but fewer 6. Chloroplast present Absent PROKARYOTIC CELL A TYPICAL BACTERIAL CELL DESCRIPTION/FUNCTION: 1. NUCLEOID a nuclear region where the chromosomal matter is found. DNA in the bacterial cell is generally confined to this central region. Though it isnt bounded by a membrane, it is visibly distinct from the rest of the cell interior. Prokaryotic cells genome usually consists of a single, large, circular DNA molecule 2. RIBOSOMES give the cytoplasm of bacteria a granular appearance in electron micrographs. Though smaller than the ribosomes in eukaryotic cells, these inclusions have a similar function in translating the genetic message in messenger RNA into the production of peptide sequences. 3. VESICLES relatively small and enclosed compartments, separated from the cytosol by at least one lipid bilayer. If they have only one lipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar. 4. CAPSULE a layer of polysaccharide (sometimes proteins) that protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells. 5. CELL WALL is composed of peptidoglycan (polysaccharides + protein), the cell wall maintains the overall shape of a bacterial cell. The three primary shapes in bacteria are coccus (spherical), bacillus (rod-shaped) and spirillum (spiral). Mycoplasma are bacteria that have no cell wall and therefore have no definite shape. 6. PLASMA MEMBRANE is a lipid bilayer much like the cytoplasmic (plasma) membrane of other cells. There are numerous proteins moving within or upon this layer that are primarily responsible for transport of ions, nutrients and waste across the membrane. 7. PILI are hollow, hairlike structures made of protein allow bacteria to attach to other cells. A specialized pilus, the sex pilus, allows the transfer from one bacterial cell to another. Pili (sing., pilus) are also called fimbriae (sing., fimbria). 8. FLAGELLA The purpose of flagella (sing., flagellum) is motility. Flagella are long appendages which rotate by means of a motor located just under the cytoplasmic membrane. DIFFERENCES BETWEEN PROKARYOTIC AND EUKARYOTIC CELL Basis of Comparison Prokaryotic cell Eukaryotic Cell 1. Nuclear Membrane Absent Present 2. Chromosomes Single Multiple 3. ER Absent Present 4. Golgi apparatus Absent Present 5. Lysosomes Absent Present 6. Mitochondria Absent Present 7. Ribosome Small Large