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Transcript
What is a cell Cell is the basic living, structural and functional unit of the body The human body develops from a single cell called the zygote, which results from the fusion of the ovum(Female egg cell) & spermatozoon (Male germ cell) What is a cell Functions of membrane proteins Branched carbohydrate molecules attached to the outside of some membrane protein molecules give the cell its immunological identity. They can act as specific receptors for hormones & other chemical mesengers. Some are enzymes. Some are involved in transport across the membrane. NUCLEUS Largest structure in the cell. Contains hereditary units of the cell, called genes Double membrane called nuclear envelope separates the nucleus from cytoplasm. Nuclear pores in the envelope allow most ions & water soluble molecules to shuttle between the nucleus & cytoplasm. Ribosomes Contain ribosomal RNA & several ribosomal proteins. Structurally a ribosome consists of 2 subunits, one about half the size of the other. They are sites of protein synthesis. Free ribosomes have no attachment to other organelles Other ribosomes are attached to the cellular structure called endoplasmic reticulum. Endoplasmic Reticulum System of membrane enclosed channels of varying shapes called cisterns. Rough ER ribosomes, smooth Er- no ribosomes Provides surface area for many types of chemical reactions & various products are transported from one portion of the cell to another via ER. Ribosomes attached to rough ER synthesize proteins that will be secreted. Smooth ER synthesize lipids & detoxifies a variety of chemicals including alcohol, pesticides, carcinogens. Golgi Complex Stack of 4-6 disc shaped membrane enclosed cisterns. Associated with cisterns are small Golgi Vesicles, which cluster along expanded ends of the cisterns. Golgi complex processes, sorts, packages, and delivers proteins and lipids to the plasma membrane, lysosomes , and secretory vesicles. Proteins & lipids destined for inclusion in the plasma membrane or for use inside lysosomes also pass through the golgi complex. Transport Through Golgi Apparatus Lysosomes One type of secretory vesicles formed by golgi apparatus. Contains digestive enzymes that break down molecules (Eg. DNA, RNA, Carbs, Proteins) inside the cell into smaller particles that are either recycled or extruded from the cell as waste material. Lysosomes in WBC’s contains enzymes that digest foreign materials such as microbes Mitochondria Mitochondria Generates ATP an energy rich molecule which are called the “power houses” of the cell. Mitochondria consists of two membranes. Mitochondria Central cavity enclosed by the inner membrane & cristae = matrix. They are involved in cellular respiration as enzymes required for the process are located on the cristae. Cellular respiration occurs only if O2 is present It results in catabolism of nutrient molecules such as glucose to generate ATP Microfilaments Tiny strands of protein that provide structural support and maintain the characteristic shape of the cell. Microtubules Larger than microfilaments. Involved in the movement of the cell and of organelles within the cell, the movement of cilia & possibly the organization of proteins in the plasma membrane. Transport of substances across cell membranes Passive processes Mechanisms that move substances across a membrane without using cellular energy (released by splitting ATP) Simple Diffusion Simple Diffusion Random mixing of ions and molecules in a solution due to their kinetic energy is called diffusion. Concentration gradient: one area ions are highly concentrated than the other & the difference in the concentration is known as the gradient. One two such areas are connected they cause movement of ions/molecules from area of high conc to low conc called net diffusion. Point of even distribution is called equilibrium. Osmosis Osmosis Osmotic pressure an important force in the movement of water between various compartments of the body. Normally osmotic pressure of the cytosol inside the cells is the same as osmotic pressure of extracellular fluid outside, because the osmotic pressure on both sides is equal the cell volume remains relatively constant. Filtration Site of filtration is in the kidneys. Blood pressure forces small molecules such as creatinine (a waste product) through the plasma membrane of cell lining microscopic blood vessels capillaries. Filtered liquids enter kidneys, from there these harmful substances to be filtered can be eliminated in the urine. Facilated Diffusion ATP is used only as a source of phosphate ACTIVE PROCESSES: Bulk Transport Moves larger substances across plasma membrane Phagocytosis (Cell Eating) Pinocytosis (Cell Drinking) Engulfed material is a tiny droplet of ECF rather than a solid, no pseudopods formed. Membrane folds inward, forming a pinocytic vessicle which allows liquid to flow inward & then surrounds the liquid. The vessicle then detaches from rest of the intact membrane. Receptor Mediated Endocytosis Ligands may be cholestrol, iron & vitamins are needed for chemical reactions that sustain life. Other ligands are either hormones that deliver messages to cells so cells can respond in specific ways or waste products that certain cells have the ability to break down. I. Legand to specific receptor plasma membrane folds in froms endocytic vesicle. II. Merging of endocytic vesicles to form endosome. III. Endosome then separates from ligand. IV. Receptors move back to plasma membrane by exocytosis. V. Portion of endosome containing ingested material with a lysosome & ingested material are broken down by digestive enzymes. Exocytosis Important in nerve cells, which release their neurotransmitter substances by this process. Important in secretory cells, eg. Cells that secrete digestive enzymes or protein hormones, such as insulin. Thank You