DNA Structure and Replication (PDF)

Chapters 13 & 14: Discovery of DNA Structure ​ A. Components ​ ​ i. Nucleotides, each consist of ​ ​ ​ a. phosphate group ​ ​ ​ b. deoxyribose sugar ​ ​ ​ c. one of four nitrogenous bases: adenine(...

Chapters 13 & 14: Discovery of DNA Structure ​ A. Components ​ ​ i. Nucleotides, each consist of ​ ​ ​ a. phosphate group ​ ​ ​ b. deoxyribose sugar ​ ​ ​ c. one of four nitrogenous bases: adenine(A), cytosine(C), ​​ ​ ​ guanine(G), thymine(T) i i. Chargaff’s Rule ​ ​ a. A & T found in equal amounts, C & G found in equal amounts ​ ​ b. consistent in all organisms iii. Rosalind Franklin ​ ​ a. used X-ray diffraction to produce first images of DNA ​ ​ b. showed it’s repetitive and helical (spiral) iv. James Watson and Francis Crick ​ ​ a. used numerous data to construct the first model of DNA ​(1953) ​ ​ b. figured out that A pairs with T and G pairs with C ​ ​ c. make hydrogen bonds across the middle of the helix ​ A and G are Purine nucleotides, the base is made of two small rings ​ T and C are Pyrimidine nucleotides, the base is made of one ring ​ Their structure allows for complementary base pairing ​ Only with A & T and with C & G are there opportunities to establish hydrogen bonds ​ 2 between A and T ​ 3 between C and G v. George Gamow ​ ​ a. the genetic code is universal and functional ​ ​ b. the sequence of the bases determines gene function 2. DNA Replication ​ ​ A. Helicase - splits DNA down the center to expose the bases ​ by breaking H-bonds. ​ ​ B. DNA Polymerase – pairs “free” nucleotides with exposed bases. C. The two new strands of DNA consist of exactly half the old strand and half the new strand (semiconservative). DNA replication is semiconservative ​ Meselson and Stahl showed that as DNA replicates, each double helix is made of  one original strand and one new strand ​ i. the leading strand is continuously paired by DNA polymerase ​ ​ ii. The lagging strand is paired in small segments called Okazaki fragments. D. DNA ligase - unites the fragments, making it continuous, like DNA glue 3. RNA A. RNA differs from DNA ​ i. one strand instead of two ​ ii. ACGU instead of ACGT ​ iii. ribose instead of deoxyribose B.​ Three types ​ i. Messenger RNA – carries DNA ​ code or ‘blueprint’ ​ ​ ii. Ribosomal RNA – part of ​ ribosome, assemble proteins ​ ​ iii. Transfer RNA – bring selected ​ amino acids to ribosome to make ​proteins 4.​ Protein Synthesis ​ A. Transcription ​ ​ i. rewriting of the DNA code to mRNA ii. modifications ​ ​ a. Noncoding portions (introns) are cut out. ​ ​ b. Coding portions (exons) are spliced together to make a finished product, are extremely similar in all individuals. c. Since introns differ more between people, they are used for genetic tests (paternity, CSI, genealogy, etc.) B. Translation ​ ​ i. converting mRNA instructions into amino acid sequences to form proteins ​ ​ ii. codon – a set of three bases codes for one amino acid. iii. there are 64 mRNA codons (universal to all living things) ​ ​ a. 61 for amino acids ​ ​ b. 1 for methionine, this is START codon (AUG) ​ ​ c. 3 for STOP signals ​(UAA,UAG,UGA) C. Protein Assembly ​ i. tRNA transfers amino acids into the growing chain ​ ii. Anti-codons on tRNA pair with codons on mRNA to ensure the correct amino acid is put in place 5. Mutations ​ A. any change in the DNA sequence B. could change the shape/structure of the protein ​ C. proteins can be unchanged, faulty, or incomplete  D. Types ​ i. Point – one single base changed (sickle cell - CTC to CAC) ​ ii. Frameshift – several bases move due to deletion/insertion (Tay-Sachs and BRCA) Chapter 16: 1.​ Recombinant DNA A.​ DNA from external sources can be cut out, spliced together, and/or inserted into cells ​ ​ i. bacteria have portable loops of DNA called plasmids which can ​ ​ be used for DNA tech ii. Enzymes involved ​ a. restriction enzymes - cut DNA at determined sequences, removes targeted fragments using “sticky ends” ​ b. DNA ligase - pastes fragments into genome iii. Viruses and plasmids can be used as a vector to insert DNA segments into cells iv. Since DNA code is universal, genes can be transferred from one organism to another. 2.​ Gel Electrophoresis A. can organize and isolate fragments B. restriction enzymes cut DNA into small fragments, perpendicular to how helicase cuts. C. an electric current moves the fragments through the gel ​ i. shorter fragments move further ​ ii. arranges from shortest to longest 3. Genetic Profiling A.​ The pattern of DNA restriction fragments are unique to an individual B.​ gel electrophoresis can be used to compare two samples 4. Polymerase Chain Reaction ​ A. PCR is the cloning/copying of DNA strands (amplification) ​ ​ i. heat is used to break H bonds between base pairs ​ ​ ii. heat resistant taq polymerase pairs exposed bases ​ ​ iii. cooled down to rebuild H bonds B. a few small traces of DNA can be copied into several million in about a day. 5. Cloning by Nuclear Transfer ​ A. nucleus is removed from egg cell of unrelated donor ​ B. nucleus is transferred from a body cell of organism to be cloned into the ‘empty’ egg cell C. clone grows into an embryo in petri dish D. embryo implanted in and carried by surrogate 6.​ Stem cells ​ A. embryonic stem cells are pluripotent, meaning they can grow into virtually any other cell type ​ B. can be induced to replace disease-causing cells 7. Genetically Modified Organisms ​ A. transgenic GMOs - foreign gene ​ is introduced to create favorable trait. B. GM plants ​ i. modified with genes from bacteria or other plants to be ​ pest and drought tolerant, enhance nutrition, add to shelf life, etc ​ ii. e.g BT corn, Flavr savr tomato C. GM Animals i. food production (more meat per animal in less time) ii ii. Herman the Bull - first successful GM mammal, was modified to make a human immune system protein (lactoferrin).​ iii. Other e.g. Enviropig, GloFish 8. CRISPR ​ A. gene editing technique that can ​ delete, insert or substitute targeted ​ genes. ​ B. can modify genomes after cell ​ differentiation and change cell ​ function