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Cells and Cell StructureThecellis structurally and functionally the basic unit of life for all organisms.The termcellcomes from Robert Hooke, who in the seventeenth centuryobserved that cork was made up of small units, which reminded him of the“cells” or cubicles in which monks lived. All cells must arise from preexistingcells, and living organisms may be single-celled or multicellular in composition.Cells may be classified into two types, depending on the presence of aninternal, membrane-boundnucleus: (1)prokaryoticcells, which do not have11C h a p t e r2Cell Biology and DNAAfter completing this chapter you shouldbe able to:1. describe and label the parts of theeukaryotic cell;2. describe the types of cells found inthe human body;3. describe chromosome structure andidentify human karyotypes;4. describe the differences betweenmitotic and meiotic cell division;5. understand the importance ofcrossing over and recombination;6. describe DNA structure, DNAreplication, transcription, andtranslation; and7. calculate the sequence of bases inDNA or RNA when provided with thecomplementary strand, and translatethe codons into amino acids using thechart.O b j e c t i v e sM02_HENS0061_01_SE_C02.QXD6/14/072:19 PMPage 11
12Chapter 2a separate nucleus and are found in bacteria and cyanobacteria and (2)eukaryoticcells, which contain a true nucleus and make up all other forms oflife. It is thought that the prokaryotic cells evolved first and that eukaryoticcells evolved from these simpler forms. All eukaryotic cells share certain struc-tural features in common, including (1) aplasma membrane,separating thecontents of the cell from the outside world; (2)cytoplasm,a gel-like or fluid-likematrix within the plasma membrane; (3)organelles,the various structuresresponsible for cell functions, such as metabolism and protein synthesis; and(4) genetic information, in the form ofDNA(deoxyribonucleic acid), which isstored in the nucleus (Figure 2-1).Two types of cells are found in humans: (1)somatic cellsand (2)gametes.The somatic cells are those cells that make up the body of an organism—everything from hair and skin to lungs, liver, muscles, blood, and bone. Somaticcells are often referred to asbody cells.In contrast, the gametes, or sex cells,are the sperm found in the male testes and the ova (or egg cells) found in thefemale ovaries. The gametes carry the genetic information required to makethe next generation.Chromosome StructureDNA and proteins are found onchromosomes. Chromosomes are located inthe nucleus and are made up of long, threadlike material calledchromatinthatcoils and condenses when a cell is about to divide, making the chromosome vis-ible with a light microscope. Chromosomes are normally single stranded, butthey become double stranded when DNA replicates itself, prior to cell division.

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Term
Spring
Professor
marshall
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