Science Reviewer in Biology, Lecture notes of Earth science

Download Science Reviewer in Biology and more Lecture notes Earth science in PDF only on Docsity! 4.4 THE NUCLEUS AND RIBOSOMES NUCLEUS Essential to the life of a cell. It contains the genetic formation that is passed on froto generationm cell to cell and from generation. It specifies the infos that ribosomes use to carry out protein synthesis, it also contains instructions for copying itself. • Has a diameter of about 5 pm. • It appears as an oval structure located near the center of most cells • Command center of cell, usually near center • Seperated from cytoplasm by nuclear envelope -Consists of double layer of membrane -Nuclear pores permit exchange between nucleoplasm & cytoplasm • Contains chromatin in semifluid matrix called nucleoplasm -Chromatin contains DNA of genes, some RNA (ribonucleic acid) and proteins (HISTONES) -It condenses to form choromosomes that is formed during cell division 3 TYPES OF RNA THAT ARE PRODUCED IN NUCLEUS: 1.Ribosomal RNA (rRNA) -produced in the nucleolus, a dark region of chromatin where rRNA joins with proteins to form the subunits of ribosomes. 2.Messenger RNA (mRNA) -a mobile molecule, acts as an intermediary for DNA, a sedentary molecule which specifies the sequeunce of amino acids in protein. 3.Transfer RNA (tRNA) -participates in the assembly of amino acids into a polypeptide by recognizing both mRNA and amino acids during protein synthesis. RIBOSOMES • are particles where protein synthesis occurs • composed of rRNA anf protein -consists of a large subunit and a small subunit -subunits made in nucleolus In eukaryotic cells,some ribosomes occur freely within the cytoplasm either singly or in groups called POLYRIBOSOMES, whereas others are attached to the endoplasmic reticulum. What causes a ribosome to bind to the endoplasmic reticulum? Binding occurs only if the protein being synthesized by a ribosome beings with a sequence of amino acids called a signal peptide. The signal peptide binds a particle (signal recognition particle, SRP) which then binds to a receptor on the ER. Once the protein enters the ER, an emzyne cleaves off the signal peptide, and the protein ends up within the lumen (interior) of the ER, where it folds into its final shape. 4.5 THE ENDOMEMBRANE SYSTEM The endomembrane system consists of the nuclear envelope.the membranes of the endoplasmic reticulum. The Golgi apparatus and several types of vesicles. This system compartmentalizes the cell so that particular enzymatic reactions are restricted to specific regions and overall cell efficiency is increased. The vesicles transport molecules from one part of the system to another. ENDOPLASMIC RETICULUM • consisting of a complicated system of membranous channels and saccules (flattened vesicles) • consists of smooth and rough ER ROUGH ER • studded with ribosomes on the side of the membrane that faces the cytoplasm,giving it the capacity to produce proteins. • Inside its lumen, the rough ER allows proteins to fold and take on their final 3 dimensional shape. • Contains enzymes that can add carbohydrates chains to proteins,forming glycoproteins,that are important in many cell functions SMOOTH ER • Does not have attached ribosomes • In some organs, increased smooth ER helps produce more lipids produces • For ex. In the testes smooth ER helps produces testosterone, steroid hormones • For ex. In the liver smooth ER helps detoxify the drugs • Both rough and smooth ER form vesicles that transport molecules to other parts of the cell notably the golgi apparatus GOLGI APPARATUS • Named after Camillo Golgi who discovered its presence in cells in 1898 • Consists of the stacks of 3 to 20 slightly curved flattened succules whos appearance can be compared to stack of pancakes • It receives the protein filled vesicles that bud from the rough ER and lipid filled vesicles from the smooth ER • It sorts the modified molecules and packages them into vesicles that depart from the outer face this vesicles may be transported to various location within the cell LYSOSOMES • Membrane bounded vesicles produced by the golgi apparatus • They have a very low pH and store powerful hydrolytic digestive enzymes in an inactive state • They assist in digesting material taken into the cell • They destroy non-functional organelles and portions of cytoplasm • White blood cells specialized, to protect the body from foreign entities are well known for engulfing pathogens that are broken down in lysosomes • In Tay-sachs disease, the missing enzyme digest the fatty substance that helps insulate nerve cells and increases their efficiency. The fatty substance accumulates in so many storage bodies that nerve cells die off affected individuals appears normal at birth but begin to develop neurological problems at 4 to 6 months of age. The child suffers cerebral degeneration, slow paralysis, blindness and loss of moto function. Children with these disease live on only about 3 to 4 years ENDOMEMBRANE SUMMARY • Endomembrane system is a series of membranous organelles that work together and communicate by means of transport vesicles the ER and golgi apparatus are flattened saccules and lysosomes are specialized vesicles organells within the endomembrane system can interact because their membranes readily fuse together and because membrane associated proteins enable communication and specialized functions • Products of both rough and smooth ER are carried in transport vesciles to the Golgi apparatus,where they are further modified. Using signaling sequences and molecular address labels, the Golgi apparatus sorts these products and packages them into vesicles that transport them to various cellular destinations. Secretory vesicles take the proteins., LESSON 4.6 OTHER VESICLES AND VACUOLES Peroxisomes-similar to lysosomes , are membrane that bounded vesicles that enclose enzymes. All peroxisome contains enzyme whose action result in hydrogen peroxide. Hydrogen peroxide is a toxic molecule is immediately down to water and oxygen, when it applied to wound bubbling occurs as catalase break down. Peroxisomes produce bile salts from cholesterol and other break down fats The 1962 film of Lorenzo’s oil is based on medical case of peroxisome . Plant cell can also have peroxisome in germinating seed , they oxide acids. Vacuoles-A vacuole is a membrane-bound organelle. They are a kind of vesicle. Vacuoles are closed sacs, made of membranes with inorganic or organic molecules inside, such as enzymes. They have no set shape or size, and the cell can change them as it wants. They are in most eukaryotic cells and do many things. Plant cell Central Vacuole- Typically plant cell have a large central vacuole that may take up to 90 % of the volume of the cell The vacuole is filled with a watery fluid called cell sap that gives support to the cell. LESSON 4.7 THE ENERGY RELATED ORGANELLES Life is possible only because a constant input of energy maintai9ns the structrure of cells , Chloroplast and Mitochondria are the two eukaryotic membrane organelles that specialize in converting energy. Chloroplast-some algal cell have only one chloroplast while some plant cells have many as hundred . chloroplast have 3 membrane system they are bounded by a double membrane . The double membrane enclose the semifluid stroma which contains enzymes and thylakoids . The endosymbiotic theory holds that chloroplast are derived from a photosynthethic bacterium that was enfulged by a eukaryotic cell. One membrane is derived from the vesicle that brought the prokaryote into the cell while the inner membrane is derived from prokaryote. Chloroplast is a type of plastids Mitochondria- Mitochondria are a part of eukaryotic cells. The main job of mitochondria is to perform cellular respiration. This means it takes in nutrients from the cell, breaks it down, and turns it into energy. This energy is then in turn used by the cell to carry out various functions. Mitochondrial diseases are long-term, genetic, often inherited disorders that occur when mitochondria fail to produce enough energy for the body to function properly. One in 5,000 individuals has a genetic mitochondrial disease. So far more than 40 different mitochondrial diseases that affects the brain,muscle kidneys , heart , liver , eyes or pancreas have been identified . in us Between 1000-4000 children per year are born with mitochondrial diseases , it is also possible that many diseases of aging are due to malfunction of mitochondria. 5.1 PLASMA MEMBRANE STRUCTURE AND FUNCTION DIVISION OF LABOR- allows cell to operate more efficiently and respond to changing environmental conditions. MEMBRANE COMPONENTS- include protein molecules that are either partially or wholly embedded in the bilayer. CHOLESTEROL- another lipid found in the animal plasma membrane -related steroids are found in the plasma membrane of plants