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beng100chapter3 - BENG 100 Frontiers of Biomedical...

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1 BENG 100 Frontiers of Biomedical Engineering Professor Mark Saltzman Chapter 3 SUMMARY • Nucleic acids are linear polymers made up of monomer units called nucleotides. Each nucleotide is composed of a pentose sugar, and phosphate group, and a nitrogenous base. DNA nucleotides have deoxyribose sugars whereas RNA nucleotides have ribose sugars. • DNA is the main information storage molecule of the cell. Information is stored in the form of a nucleotide base sequence. A gene is a sequence of DNA bases that code for RNA or a polypeptide chain. • DNA is a double helix with two sugar phosphate backbones and nucleotide bases bridging the two chains. • Base-pairing is accomplished by hydrogen bonding between purines and pyrimidines. Watson-Crick base-pairing dictates the base pairs in DNA are: A-T, C-G. In RNA, the thymine is replaced by a uracil, so base pairs in RNA are: A-U, C-G. • DNA replication occurs every time a cell divides. DNA replication is semiconservative with each daughter cell receiving one parental strand and one newly synthesized strand. DNA polymerization only occurs in the 5’ to 3’ direction. • Errors in replication or environmental factors can give rise to mutations. • The central dogma of molecular biology dictates that DNA must first be transcribed into RNA, which is then translated into protein. • Genes are transcribed into RNA by RNA polymerase. In eukaryotic cells, transcribed RNA must undergo processing to form an mRNA transcript. • mRNA is translated into amino acids using the genetic code. Ribosomes and tRNA are involved in translation of codons to corresponding amino acids. The newly synthesized polymer of amino acids makes up a polypeptide chain. Proteins can be composed of more than one polypeptide chain. • Recombinant DNA technology enables researchers to manipulate DNA for various purposes. Genes can be made to express in other species. • PCR is used to amplify short segments of DNA.
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2 • Plasmids and viruses are used as cloning vectors and expression vectors. • Both non-viral and viral methods can be used to introduce a foreign gene into eukaryotic cells. KEY CONCEPTS AND DEFINITIONS adenovirus - a group of DNA containing viruses, which cause respiratory disease, including one form of the common cold. Adenoviruses can also be genetically modified and used in gene therapy to treat cystic fibrosis, cancer, and potentially other diseases. allele - One of two or more alternative forms of a gene located at the corresponding site (locus) on homologous chromosomes. Different alleles produce variation in inherited characteristics such as hair color or blood type. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one).
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