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Biology Summary Chapter 2 2.1 - to sustain life, cell must create and maintain molecules and structures that then perform the essential tasks to perform cell functions including o obtain food and energy o convert energy into a form that works within a cell o construct and maintain the molecules that make up cell structures o carry out chemical reactions o eliminate wastes o reproduce o keep records of how to build structures Prokaryotes are cells that lack a true nucleus, instead, the DNA in these cells is concentrated in nucleoid Eukaryotes are cells containing a true nucleus and other organelles. - larger - contain complex internal structure Organelles are specialized structures within a cell with specific functions - a great deal of diversity exists among eukaryotic cells organelles in a eukaryotic cell divide its interior into compartments allows different chemical reactions taking place at once without interfering with one another many organelles contain highly folded membranes that increase the surface area on which chemical reactions can be co-ordinated and increases overall rate of reaction within the cell Freeze Fracture Technique - technique used by scientists to expose the nucleus for study - provides valuable details about organelle and membrane structure - could view two layers of the double membrane around nucleus Electron Micrograph - a close up scan of the organelle - could show the nuclear pores and reveal their flower-like structure Drawing - artist render information from electron microscope - compose a 3-D drawing of nuclear envelope 2.2 - almost all cell processes require proteins proteins make up about half of the dry mass of cellular material - many proteins function as enzymes ie blood protein hemoglobin carries oxygen and carbon dioxide cells produce proteins only in the amounts and at the times required Protein synthesis is the process of making proteins which involves transcription and translation. 1. Transcription occurs in nucleus - cell transcribes (copies) the coded information from the gene of DNA - cell must unwind and unzip that section of DNA and make an RNA copy of it - transcription is the process of making a copy of the information along one strand of DNA to produce a strand of mRNA 2. mRNA moves into cytoplasm - mRNA carries the coded message from DNA in nucleus to ribosomes in the cytoplasm 3. Translation starts when mRNA attaches to a ribosome - Translation is the process of using the coded mRNA instructions for a sequence of amino acids to produce a polypeptide that take place on a ribosome - Ribosome then translate mRNA and attach mRNA to either a cytoplasmic ribosome or to a ribosome attached to the endoplasmic reticulum 4. tRNA brings amino acids to the ribosome - dissolved amino acids in the cytoplasm must be transferred to ribosome for assembly into a polypeptide - tRNA, transfer RNA recognizes one amino acid and attaches it to one side of itself - on other side of tRNA molecule, 3 nucleotide bases match one of the triplet codes on the mRNA 5. An incoming tRNA positions its amino acid to join the polypeptide chain - tRNA carrying the next amino acid in the mRNA code forms a temporary bond with the mRNA at the ribosome - this places the amino acid in the correct position to form a peptide bond with the amino acid on tRNA molecule already at the ribosome - 15 amino acids are added to polypeptide chain per sec 6. An outgoing tRNA releases its amino acid and detaches from the mRNA - A ribosome has room for only 2 tRNA molecule at a time - When ribosome moves along the mRNA to the next coding unit, outgoing tRNA transfers the polypeptide chain to the other tRNA - Frees up space for a new tRNA molecule at the ribosome - The outgoing tRNA can now collect another amino acid 7. Translation ends when a ribosome reaches a “stop” instruction - - - - When ribosome reaches the “stop” codes at the end of an mRNA strand, it releases the complete polypeptide Then ribosome separates into its subunits which detaches it from the mRNA Polypeptide must still complete its folding process before becoming a finished protein process of transcription and translation in prokaryotes and eukaryotes follow similar basic steps but protein synthesis in prokaryotes is simpler prokaryotic ribosomes are smaller than eukaryotic ones, lie close to DNA, so the beginning of an mRNA strand can attack directly to a ribosome while the rest of strand is still being transcribed allows prokaryotes to produce proteins rapidly each lysosome in animal cell or vacuole in plant cells contain over 40 different digestive enzymes after the lysosome leaves Golgi body, its membrane actively pumps in hydrogen ions to make its interior environment more acidic which activates the lysosomal enzymes when active, these enzymes can break apart macromolecules in a stepby-step process Lysosomal digestion is the step-by-step process of breaking macromolecules within lysosomes, also called intracellular digestion - - down after a cell engulfs materials by endocytosis, a lysosome fuses with the ood vacuole formed to fill the vacuole with digestive enzymes and break down the captured material a lysosome fuses with and digests worn out organelles recycle their components back to cytoplasm enzymes make possible reaction that would otherwise not proceed Enzyme is a protein that functions as an organic catalyst that helps a particular reaction go forward without being used up in the process 2.3 cell makes a different enzyme for each reaction it requires an enzymatic reaction may either combine molecules to produce a new product or break a molecule into smaller parts enzyme’s shape allows its substrate to attach at the active site chemical bonds within a substrate will then be broken then the enzyme releases the products and can start the process again - a multicellular organism contains a large number of different kinds of specialized cells Tissue is a group of specialized cells that have the same structure and perform the same function Ie muscles Organ is a group of different tissues working together Ie leaf of a plant Heart muscle cells - pump blood throughout the body - small size of heart muscle cells gives them a large surface area, increasing their access to critical materials - have a branched shape that allows them to form an interconnected network of cells - can conduct electric impulses and contract in unison - contain many large mitochondria to power their action - contain actin and myosin filaments that allow them to contract Parietal cells - within indentations in the lining of stomach (gastric pits) cells secrete the juices necessary for digestion - parietal cells there produce hydrochloric acid - activates an enzyme secreted by other cells lining the gastric pit and allows digestion - parietal cells contain tiny canals that run from cell membrane facing the gastric pit deep into cytoplasm - each canal lined with small extensions of cell membrane called microvilli - with little increase to cell size, the folded fringe of membrane maximizes the surface area for pumping hydrogen ions out into the canals - requires large number of mitochondria Podocytes - cells excrete toxic nitrogen-containing waste in the form of ammonia, which the liver converts to less toxic substances: uric acid or urea - kidney function is to cleanse the blood of this nitrogen waste - podocytes cells act as main filtration barrier in nephron of the kidneys - has long thin processes that interlock with the process of another podocyte around the capillaries entering the kidneys - arterial blood pressure pushes small molecules from the capillaries into the kidney through think membranes between prodocyte processes - podocytes keep blood cells, platelets, and proteins from leaving the blood - before urine leaves kidneys, other specialized kidney cells extract amino acids, glucose, and required salts from the liquid Squamous epithelial cells - in lungs, extremely thin, flat cells line the tiny sacs (alveoli) where gas exchanges take place - lies directly against the thin cells from capillary walls - provide shortest distance possible (1m) for oxygen to diffuse into and carbon dioxide to diffuse out of body - stem cells are blank slate of the human body undifferentiated (nonspecialized) cells that can give rise to any type of cell until they differentiate, stem cells can reproduce themselves indefinitely ie rapidly dividing cells of a week-old embryo people retain a limited number of stem cells the body uses reserves of stem cells to replace worn-out or damaged cells mainly found in bone barrow, blood, muscle tissue, lining of digestive tract, brain, and retina of the eye - proper development and maintenance of all tissues requires that some cells be removed or replaced Apoptosis is a process in the development and maintenance of all tissues in which some cells turn on an orderly self-destruct process (programmed cell death) - most cells with DNA damage and many infected with viruses die by apoptosis - when a cell dies dies from injury, the cell contents scatter into its environment - in body, this leads to inflammation of the area - in apoptosis, a series of enzyme reactions degrade the contents of a cell - cell shrinks and small bulges appear along cell membrane - special phagocytotic cells engulf and digest these cell fragments - phagocytotic cells also release chemicals that inhibit inflammation - some cells with damaged or defective DNA don’t make the correct chemicals to induce apoptosis - failure of apoptosis can result in cancer ie leukemia - too much apoptosis can lead to degenerative diseases ie muscular dystrophy 2.4 Finding New Cancer Treatments - investigators map the process by which apoptosis works, looking for ways to activate the apoptotic mechanism in tumour cells - possibility that cancer cells could be induced to self-destruct may provide basis for various treatments - look at how treated cells in a culture die - track this by tagging cellular structures sensitive to changes that take place during apoptosis with fluorescing dyes - so can see how a particular treatment is working newly discovered that some cancer cells don’t produce an important cell membrane receptor that allows the killer cells of the immune system to signal a damaged cell to begin apoptosis Insulin - diabetes caused by deficiency of insulin, because the islet cells in pancreas have been damaged or destroyed - or by inability of cells to respond to insulin - when eating, the cells in intestines transfer nutrients into blood stream when blood glucose level rises, healthy islet cells synthesize quantities of insulin and secrete it into blood stream insulin is a hormone that binds to cell membrane receptors, mainly on muscle and liver cells this signals the cells to take up glucose and amino acids also causes protein synthesis to start as soon as blood glucose levels fall, insulin production shuts down cells then have stored the nutrients they need until the next meal - without insulin, when cells fail to receive its signal, glucose and amino acid transport into cells and protein synthesis within cells shut down - body uses lipids as an alternative energy source to glucose large quantities of lipid products start circulating in blood some of these form deposits in blood vessels, impeding circulation, others are acidic and damaged tissues blood contains so much glucose that kidney cells can’t filter it back into blood glucose in urine draws water with it by osmosis, causing cells to become dehydrated and circulation to collapse - Biotechnology and human insulin - huge demand for insulin - insulin used to be extracted from the islet cells of beef cattle or pigs - animal insulin similar enough to human insulin that it can function, but will develop allergic reaction - insulin biotechnology involves the use of living organisms to manufacture products for humans - pharmaceutical industry genetically engineers bacteria to manufacture human insulin - bacteria given DNA instructions for making human insulin molecules and then manufacture insulin along with other proteins they need - on-time insulin delivery - - regardless of their source of injected insulin, diabetics have to deal with swings in blood sugar levels use computerized “smart” pumps to test a diabetic’s blood level and automatically dispenses the correct amount of insulin viral vector technology splice DNA instructions for making a molecule similar to insulin into the DNA of a harmless virus when virus enters liver cells, the cells begin to make the desired insulinlike molecules engineered insulin only 40% as potent as natural insulin, but sufficient enough to control blood glucose levels Newer forces driving research - AIDS (acquired immunodeficiency syndrome) and hepatitis C. are examples of recently identified diseases - AIDS caused by HIV (human immunodeficiency virus) - Hepatitis C caused by HCV (hepatitis C virus - HCV transmitted through direct contact with infected blood - Spread among people who share injection needles - Damages liver cells - Symptoms include fatigue, jaundice (yellowing of skin or eyes), nausea, hair loss, and build up of toxins in blood - Can lead to chronic inflammation of liver, liver cancer, death - Need liver transplants