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Transcript
The Cell CELL STRUCTURE & FUNCTION THE CELL THEORY A. All living organisms are made up of one or more cells B. The cell is the basic unit of life C. All cells come from the division of pre-existing cells The Cell Membrane • functions in transport of materials in and out of cell, cell recognition, maintaining cell integrity, and homeostasis. • is called selectively permeable (also known as semipermeable and differentially permeable) - means that the membrane will let some substances cross but not others of the same size The Fluid Mosaic Model: Cell notes.docx — Page 1 • Cells are surrounded by a thin membrane of lipid and protein. • Scientists today agree Please Label this Diagram upon The Fluid Mosaic Model of cell membrane structure. The cell membrane is a remarkable structure that has properties of a solid and a liquid. • The solid part (the “mosaic”) is the different proteins embedded in the bilayer. The fluid part is the lipids and how they give the membrane flexibility. • Membranes made mostly of phospholipids molecules. Phospholipids have two ends with different properties in water. The phosphate head is HYDROPHILIC “water-loving” while the lipid (fat) tail is HYDROPHOBIC “water-fearing”. The cell Membrane consists of two phospholipids layers called a BILAYER. • There are proteins embedded in the phospholipid bilayer and they form a mosaic pattern. These proteins have different functions. Cell notes.docx — Page 2 o Receptor Sites – some proteins on the surface serve as a receptor site so certain molecules can attach to the surface. o Protein Channels – these proteins provide the mechanisms for lipid insoluble materials to cross the membrane. (e.g. water) o Channels with ATP – some substances (ions, amino acids, glucose) actually bond to the proteins and are propelled through the membrane with the expenditure of ATP energy. • The carbohydrates strung together in chains are attached to proteins ("glycoproteins") or lipids ("glycolipids") of membrane. These carbs function as identification markers for cell recognition (allows the immune system to identify which cells belong to the body and which are invaders). The Nucleus: • is a large, centrally located organelle surrounded by the nuclear envelope. The nuclear envelope is a double membrane (2 phospholipid bilayers) that has pores, called nuclear pores, in it for molecules to enter and exit. The envelope is a continuation of the membrane of the Cell notes.docx — Page 3 endoplasmic reticulum. • controls all of the cellular functions (metabolism, growth, differentiation, structure, and reproduction) in the cell • contains the DNA and it is the site of RNA production. The DNA is contained in a number of chromosomes, which consist of long strands of DNA tightly wound into coils with proteins called histones. Chromosomes function in the packaging of DNA during nuclear division and the control of gene expression. • contains one or more DARK CIRCLES, known as the NUCLEOLUS. The nucleolus is the site of RIBOSOMAL RIBONUCLEIC ACID (rRNA) SYNTHESIS. rRNA is one of two components that is needed to produce a ribosome. Endoplasmic Reticulum (ER) • is a system of MEMBRANOUS TUBULAR CANALS that begin just outside the nucleus and branches throughout the cytoplasm. Rough E.R. Smooth E.R. • When ribosomes are Cell notes.docx — Page 4 attached to the ER, it is called Rough Endoplasmic Reticulum (RER). The Rough ER is the site of protein synthesis. • If no ribosomes are attached to the ER, it is called Smooth Endoplasmic Reticulum (SER). The function of smooth ER is to synthesize lipids (Lipids are required for the growth of the cell membrane and for the membranes of the organelles within the cell and are often used to make hormones). The smooth ER is also used to detoxify drugs and chemicals in the cell (takes place in peroxisome vesicles which are often attached to smooth ER). • The channels of the reticulum provide both storage space for products synthesized by the cell and transportation routes through which material can travel through to other parts of the cell. Phospholipids and cholesterol, the main components of membranes throughout the cell, are synthesized in the smooth ER. Ribosome: Cell notes.docx — Page 5 • consist of rRNA and proteins • each ribosome is made of 2 non-identical subunits • rRNA is produced in the nucleolus and joined with proteins -- then migrate through the nuclear pore to the cytoplasm for final assembly • Ribosomes attach themselves to the endoplasmic reticulum • The ribosome and the Rough Endoplasmic Reticulum are both sites for PROTEIN SYNTHESIS. Polysomes: • free-floating structures within the cytoplasm • generally produce proteins that will be used inside the cell • consist of clusters of ribosomes bunched together, each of which is transcribing the same type of protein Golgi Apparatus Cell notes.docx — Page 6 • The Golgi Apparatus (“X” in diagram), named after an Italian anatomist of the nineteenth century, are stacks of flattened, hollow cavities enclosed by membranes, which are often continuous with the membrane of the endoplasmic reticulum. • The stack is made of a half-dozen or more saccuoles. Looks like a flattened stack of hollow tubes. Each sac in the organelle contains enzymes that modify proteins as they pass through. • Thus, the Golgi apparatus functions in modification, assembly, packaging, storage and secretion of substances. • The Golgi apparatus receives newly manufactured protein (from the ER) on its inner surface. Within the Golgi apparatus, the proteins are sorted out, labeled, and packaged into vesicles. These vesicles can then be transported to where they are needed within the cell, or can move to the cell membrane for export to the outside of the cell by exocytosis. Vacuoles and Vesicles: Storage Depots Cell notes.docx — Page 7 • A VESICLE is a small vacuole. • vacuoles and vesicles are formed by: 1) pinching off from the Golgi apparatus 2) endocytosis of the cell membrane 3) extension of the ER membrane • Vesicles and vacuoles are used for transport and storage of materials. Lysosomes: Cellular “Stomachs” • Special vesicles which are formed by the Golgi apparatus. • The three main functions are: 1) Cellular digestion 2) Autodigestion or disposal of damaged cell components like mitochondria 3) Breakdown of a whole cell (by releasing their contents into the cell cytoplasm). For this reason, they are sometimes called “suicide sacs.” • Lysosomes help destroy invading bacteria. Mitochondria: the Cell’s Powerhouse Cell notes.docx — Page 8 • are the 2nd largest organelles in an animal cell, after the nucleus a.________________ b.________________ • Are sausage-shaped or filamentous structures surrounded by a double-layered membrane. • has two membranes: an outer and an inner. The inner is convoluted into shelf-like folds called cristae. The enzymes responsible for cellular respiration are arranged, in assembly-line fashion, on the cristae. This is where energy is produced. • main function is to perform CELLULAR RESPIRATION. Cellular respiration is when the cell converts glucose (a carbohydrate)into ATP, the cell's primary energy molecule. The overall formula for cellular respiration is: Carbohydrate + O2 CO2 + H2O + ENERGY (i.e. ATP) • In the end, 38 molecules of ATP are formed for every molecule of sugar that is used up in respiration. Cell notes.docx — Page 9 THE SURFACE AREA TO VOLUME RATIO & CELL SIZE • Cells cannot get too large. When cells get too large, they must divide. One of the main reasons that cells do this is because of the way that a cell's volume changes with respect to its cell surface area. • As the size of a cell increases, its surface to volume ratio decreases. This means that, as a cell gets larger, each cubic unit of cytoplasm is serviced by proportionally less cell membrane. Cell Size 1 2 4 8 Surface area 6 24 96 384 Volume 1 8 64 512 SA:V ratio 6:1 3:1 1.5:1 0.75:1 • How do cells get around the limits of the surface to volume ratio? 1. Divide. 2. Get long and thin rather then round and fat. e.g. nerve cell 3. Folds in the cell membrane: e.g. microvilli of intestine. Cell notes.docx — Page 10