DNA Structure & Replication Study Guide PDF

Structure of DNA 1 Structure of DNA. James Watson and Francis H. C. Crick determined the structure of DNA in 1953. DNA is a chain of nucleotides. Each nucleotide is a complex of three subunits. Phosphoric...

Structure of DNA 1 Structure of DNA. James Watson and Francis H. C. Crick determined the structure of DNA in 1953. DNA is a chain of nucleotides. Each nucleotide is a complex of three subunits. Phosphoric acid (phosphate). A pentose sugar (deoxyribose). A nitrogen-containing base. © McGraw Hill LLC 1  Structure of DNA 3 Two polynucleotide strands make up a DNA double helix. The strands are held together by hydrogen bonding between the bases. Complementary Base Pairing. Adenine (A) always pairs with Thymine (T). Connected by two hydrogen bonds. Guanine (G) always pairs with Cytosine (C). Connected by three hydrogen bonds. A purine is always bonded to a pyrimidine. © McGraw Hill LLC 2  Structure of DNA 4 Unwound DNA helix resembles a ladder. Sides of the ladder are sugar-phosphate backbones. Rungs of the ladder are complementary base pairs. The two DNA strands are antiparallel-oriented in opposite directions. The sugars are oriented differently. The 5′ carbon atom is the uppermost on one strand, and the 3′ carbon atom is the uppermost in the other strand. © McGraw Hill LLC 3  DNA Replication 3 Several enzymes and proteins participate in the replication of DNA. Steps of replication: The enzyme DNA helicase unwinds and “unzips” the double-stranded DNA by breaking the hydrogen bonds between paired bases. New complementary DNA nucleotides fit into place along separated strands by complementary base pairing. These are positioned and joined by DNA polymerase. DNA polymerase uses each original strand as a template. © McGraw Hill LLC 4  DNA Replication 2 DNA replication is semiconservative. Each daughter DNA double helix consists of one new strand of nucleotides and one old strand conserved from the parent DNA molecule. The two daughter DNA molecules will be identical to the parent molecule. © McGraw Hill LLC 5  DNA Replication 4 Steps of DNA Replication. Because strands are antiparallel and DNA polymerase can only add new nucleotides to one chain, DNA synthesis occurs in opposite directions. Leading strand follows DNA helicase. Lagging strand synthesized in Okazaki fragments. DNA ligase connects Okazaki fragment and seals breaks in the sugar-phosphate backbone. The two double helix molecules are identical to each other and to the original DNA molecule. © McGraw Hill LLC 6  Transfer RNA Transfer RNA (tRNA) transports amino acids to ribosomes. Boot-like shape due to base pairing within the one strand. Amino acid binds to one end, and the opposite end has an anticodon: Triplet of three bases complementary to a specific codon of mRNA. Order of mRNA codons determines the order in which tRNA brings in amino acids. Codon (mRNA) Anticodon (tRNA) Amino Acid (protein) CGG GCC Arginine © McGraw Hill LLC 7  Messenger RNA 1 Messenger RNA (mRNA) serves to carry genetic information from DNA to the ribosomes for protein synthesis. mRNA is formed by the process of transcription. Transcription begins when RNA polymerase binds to a promoter (in DNA). The DNA helix is opened so complementary base pairing can occur. RNA polymerase joins new RNA nucleotides in a sequence complementary to that on the DNA. © McGraw Hill LLC 8  Messenger RNA 2 When mRNA forms, it has a sequence of bases complementary to the DNA. Wherever A, T, G, or C is present in the DNA template, U, A, C, or G, respectively, is incorporated into the mRNA molecule. The mRNA is a faithful copy of the sequence of bases in DNA. © McGraw Hill LLC 9  Gene Expression 2 Gene expression includes two processes. Transcription. Takes place in the nucleus. A portion of DNA serves as a template for mRNA formation. Translation. Takes place in the cytoplasm. Sequence of mRNA bases (complementary to those in the template DNA) determines the sequence of amino acids in a polypeptide. tRNA assists by bringing amino acids to the ribosome. © McGraw Hill LLC 10  Processing of mRNA Processing of mRNA occurs in eukaryotic cells. Pre-mRNA contains bases complementary to both intron and exon segments of DNA. Introns are noncoding, intergenic, and often regulatory segments that get removed. Exons are portions of a gene that are needed to produce a protein and are joined to form a mature mRNA molecule. A guanine cap is added to the 5′ end. A poly-A tail is added to the 3′ end. The mature mRNA molecule is ready. © McGraw Hill LLC 11  Translation Requires Three Steps During translation, codons on mRNA base pair with anticodons on tRNA molecules carrying specific amino acids. The order of codons determines the order of tRNA entering the ribosome and the sequence of amino acids in a polypeptide. The process must be orderly. Translation involves three steps. Initiation (requires energy). Elongation (requires energy). Termination. © McGraw Hill LLC 12  Levels of Gene Control 6 Translational Control. The longer the mRNA is available in the cytoplasm, the more gene product can be translated. Differences in the poly-A tails and/or guanine caps may determine how long an mRNA is available for translation. Specific hormones may also affect the longevity of mRNA. © McGraw Hill LLC 13  Types of Tissues 2 Four types of tissues in the human body. Epithelial: covers body surfaces and lines cavities. Connective: supports and binds body parts. Muscular: moves the body and its parts. Nervous: receives stimuli, processes that information, and conducts impulses. © McGraw Hill LLC 14  Junctions Between Epithelial Cells Tight junctions—form an impermeable barrier between cells. Gap junctions—allow small molecules to pass between cells and also strengthen connections. Adhesion junctions—act like rivets or “spot welds”; anchor tissues in place and increase their overall strength. © McGraw Hill LLC 15  Connective Tissue 2 Composition of nonfluid matrix. Fibers: Collagen fibers: protein that gives flexibility and strength. Reticular fibers: thin, highly branched collagen fibers that form supporting network. Elastic fibers: contain elastin, a protein that is not as strong as collagen, but more elastic. © McGraw Hill LLC 16  Dense Fibrous Tissues 2 Dense fibrous connective tissue. Contains many collagen fibers packed together. Found in structures such as Tendons—connect muscles to bones. Ligaments—connect bones to other bones. Both loose and dense connective tissue have cells called fibroblasts. Separated by a jelly-like matrix with collagen and elastic fibers. © McGraw Hill LLC 17  Epithelial Tissue 2 On external surfaces, epithelial tissue protects the body from injury, drying out, and possible invasion by microbes. On internal surfaces, epithelial tissue carries out both protective and specific functions. A basement membrane of glycoproteins and collagen joins an epithelium to underlying connective tissue. © McGraw Hill LLC 18  Bone 2 Compact bone. Forms shafts of long bones. Consists of cylindrical structures called osteons. Central canal of each osteon surrounded by rings of hard matrix. Bone cells located in spaces called lacunae between rings of hard matrix. Spongy bone. Contains many bony bars and plates, separated by irregular spaces. Found in ends of long bones. Though lighter, still designed for strength. © McGraw Hill LLC 19  Blood 4 Platelets (thrombocytes). Cell fragments involved with blood clotting. Help to form a plug that seals damaged blood vessels. Injured tissues release molecules to stimulate the clotting process. © McGraw Hill LLC 20  Muscular Tissue 3 Smooth muscle. Cells lack striations; smooth appearance. Occurs in walls of blood vessels and viscera (intestine, stomach, and other internal organs and blood vessels). Cells are spindle shaped, with a single nucleus. Nuclei form an irregular pattern. Not under voluntary control. © McGraw Hill LLC 21  Nervous Tissue 1 Nervous tissue contains neurons (nerve cells) and is present in the brain and spinal cord. A neuron is a specialized cell with three structures. Dendrites—processes that conduct signals toward the cell body. Cell body—contains the cytoplasm and nucleus. Axon—a process that conducts nerve impulses away from the cell body. May have myelin sheath to increase speed. © McGraw Hill LLC 22  Nervous Tissue 2 Neuroglia. Outnumber neurons nine to one. Support and nourish neurons. Four types in the brain. Microglia: engulf bacterial and cellular debris. Astrocytes: provide nutrients. Oligodendrocytes: form myelin sheaths in brain. Schwann cells: form myelin sheaths outside the brain. Ependymal cells: line fluid-filled spaces of brain and spinal cord. © McGraw Hill LLC 23  Homeostasis Homeostasis is the maintenance of a relatively constant internal environment by an organism, or even by a single cell. Even as external conditions change, internal conditions stay within a narrow range. Internal state is often described as one of dynamic equilibrium because internal conditions tend to fluctuate above and below a certain value. © McGraw Hill LLC 24  Disease 2 Acute disease. Occurs suddenly. Usually short duration. Chronic disease. Long term. Develops slowly. Cancers are a group of disorders in which the usual controls of cell division fail, resulting in the production of abnormal cells that invade and destroy healthy tissue. © McGraw Hill LLC 25  Organ Systems of the Body 1 © McGraw Hill LLC 26  Organ Systems of the Body 2 © McGraw Hill LLC 27  Recombinant DNA Technology 1 Recombinant DNA (rDNA). Contains DNA from two or more different sources. To make rDNA, need a vector—piece of DNA that foreign DNA can be added to. Plasmids are accessory rings of DNA in bacteria, commonly used as vectors. They are not part of the bacterial chromosome. © McGraw Hill LLC 28  The Polymerase Chain Reaction 1 The polymerase chain reaction (PCR) can create billions of copies of a segment of DNA in a test tube in hours. Amplifies only specifically targeted DNA sequence. Targeted sequence is usually a few hundred bases in length. Uses DNA polymerase and DNA nucleotides. Three basic steps that occur repeatedly, usually for about 35 to 40 cycles. © McGraw Hill LLC 29  Genome Editing 1 A relatively new advance in DNA technology. Targets specific sequences in DNA for removal or replacement. There are several methods. CRISPR (clustered regularly interspaced short palindromic repeats) is the most widely used. © McGraw Hill LLC 30  Proteomics Proteomics is the study of the structure, function, and interactions of cellular proteins. Proteins differ depending on each cell type. Each cell produces hundreds of different proteins that can vary between or within cells depending on conditions. Computer modeling of the three-dimensional shape of these proteins is important. Protein shape and function is essential to the discovery of better drugs. © McGraw Hill LLC 31  Gene Therapy Gene therapy is the insertion of genetic material into human cells for the treatment of genetic disorders and other illnesses, such as cardiovascular disease and cancer. Various methods of gene transfer have been used. Viruses, genetically modified to be safe, can be used to introduce a normal gene into the body. Liposomes, microscopic globules of lipids, can also be used to introduce normal genes. Sometimes the gene is injected directly into a specific region of the body. © McGraw Hill LLC 32  The Polymerase Chain Reaction 3 PCR is a chain reaction because the targeted DNA is repeatedly replicated. The amount of DNA doubles with each cycle. Automation is possible because of the use of a temperature-insensitive DNA polymerase extracted from Thermus aquaticus, a bacteria that lives in hot springs. The enzyme tolerates the high temperature used to separate the DNA strands (95 degrees Celsius). © McGraw Hill LLC 33  Recombinant DNA Technology 2 Two enzymes needed to introduce foreign DNA into vector DNA. Restriction enzyme—to cleave vector DNA. Hundreds occur naturally in bacteria. Act as a primitive immune system in bacteria to restrict the growth of invading viruses by cutting up viral DNA. Used in cloning as molecular scissors that cut DNA at precise sequences; cut double-stranded DNA at a specific site. DNA ligase—will seal the foreign DNA into the opening in the vector DNA created by the restriction enzyme. © McGraw Hill LLC 34