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Transcript
Cellular Classification & Organelles: A Look at the Endomembrane System Biology 111 Holyoke Walsh Prokaryotes vs Eukaryotes • The basic structural & functional unit of every organism is one or two types of cells – pro or eukaryote. • Prokaryotes are archaebacteria & eubacteria • Eukaryoes include protists, fungi, animals and plants. Typical Eukaryotic Cell Typical Prokaryotic Cell Commonalities…of all cells!! • • • • Plasma Membrane Cytosol Chromosomes Ribosomes Key Differences? • The location of their DNA; membrane bound organelles • Prokaryote = nucleoid region • Eukaryote = nucleus Prokaryote vs. Eukaryote Prokaryote or Eukaryote?? Prokaryote or Eukaryote?? Prokaryote or Eukaryote?? Cell Membrane Eukaryotes • In addition to the plasma membrane at its outer surface, a eukaryotic cell has extensive & elaborately arranged internal membranes, which divide the cell into compartments. • These provide different local environments that facilitate specific metabolic functions, so incompatible processes can go on simultaneously in a single cell • The plasma and organelle membranes participate directly in the cell’s metabolism b/c many enzymes are built right into the membranes themselves. Cell Membranes..in general • Phospholipid bilayer • Embedded proteins • Each type of membrane has a unique composition of lipids and proteins suited to that membrane’s specific function Ex: enzymes embedded in the mitochondrial organelle function in cellular respiration…which creates the ATP energy our cells need to function! Eukaryotes…genetic info… • Two cellular components involved with the genetic control of the cell are the NUCLEUS & the RIBOSOMES NUCLEUS Ribosomes • Made of some RNA (genetic info) and Protein • Main function is to carry out protein synthesis. Protein Synthesis Summary Protein Synthesis 1. The DNA double helix unwinds to expose a sequence of nitrogenous bases. (A,T,C,G) 2. A copy of one of the strands is made in a process known as transcription. The copy is made of messenger ribonucleic acid (mRNA) which, following transcription, travels out of the nucleus into the main body of the cell, where protein synthesis occurs. 3. The mRNA couples with the protein synthesis apparatus (the ribosome). Another type of RNA, known as transfer RNA (tRNA), brings free amino acids to the ribosome. 4. The anticodon present on the tRNA recognises the codon present on the mRNA, and the ribosome adds the amino acid to the growing chain of linked amino acids (polypeptides), cleaving it away from the tRNA. This process is known as translation. 5. As the polypeptide chain grows, it folds to form a protein. Ribosomes cont… • Cells that have high rates of protein synthesis have particularly high rates of ribosomes • Located in the cytoplasm/ER (structurally identical) • Free ribosomes – function within the cytosol (ie. enzymes that catalyze reactions) • Attached ribosomes – generally destined for insertion into organelles membranes or for export (cells that secrete enzymes) Locate the Ribosomes… Endomembrane System • Many of the different membranes of the eukaryotic cell are part of this system which carry out a variety of tasks in the cell. Ie. synthesis of proteins, metabolism and movement of lipids, & detoxification of poisons • The membranes of this system are related either through physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane) • This system includes: nuclear envelope, the endoplasmic reticulum, golgi apparatus, lysosomes, various vacuoles, and the plasma membrane Endomembrane System Endoplasmic Reticulum • Extensive network accounting for more than half the total membrane in eukaryotic cells • Consists of a network of membranous tubules and sacs called cisternae • The ER membrane separates the internal compartment of the ER, called the ER lumen (cavity) or cisternal space, from the cytosol. • The ER membrane is continuous with the nuclear membrane ER cont… Two types of ER: smooth and rough 1. Smooth ER – lacks ribosomes and involved in diverse metabolic processes such as lipid synthesis, metabolism of carbohydrates, and detoxification of drugs and poisons 2. Rough ER – has ribosomes and is involved in protein synthesis Golgi Apparatus – Shipping & Receiving Center Lysosomes • Membranous sac of enzymes that an animal cell uses to digest macromolecules. • Lysosomal enzymes work best in an acidic environment found in lysosomes. If a lysosome breaks or leaks the enzymes are not very active b/c cytosol has a neutral pH • Lysosomes carry out intracellular digestion in a variety of ways. ie. amoebas use phagocytosis…food vacuole fuses with lysosome and enzymes will then digest the food. FYI: humans use phagocytosis: WBC called macrophage that engulfs and destroys bacteria & other invaders. Vacuoles Types: 1. Food vacuoles – formed by phagocytosis http://www.youtube.com/watch?v=W6rnhiMx tKU 2. Contractile vaculoes – pump excess water out of the cell 3. In plants & Fungi – Central vacuole: stores food, nutrients, water and waste.