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Genetics!
How is this all one unitโฆ
DNA
โ Purine Bases (Ag for Silver) โ Adenine & Guanine โ Two-Ring โ Pyrimidine Bases โ Thymine (Uracil) & Cytosine โ Single-Ring โ DNA Denaturation โ Separating the strands by the H bonds โ NOT harmful & reversible โ Directionality โ 5โ end is top of nucleotide (where the Phosphate sticks up) โ Five = phosphate โ Organized in tightly wounded chromosomes โ Circular in prokaryotes โ Linear in eukaryotes Phosphate Nitrogenous Base Phosphodies ter Bond Deoxyribose (Pentose Sugar) 3โ 5โ 5โ 3โ
REPLICATION
โ In both strands: ยฝ is new DNA and ยฝ is the parent template strand โ Semi-conservative process
- Topoisomerase relaxes supercoiling of the chromosome
- 2 Replication Complexes attach to the Origin of Replication (ORI Sequence) a. Replication Complex: Enzymes ATTACHED to each other and maintain the same speed of operations b. Each chromosome will have more than one i. Simultaneous process at different points in the chromosome
- The Replication Complexes travel in opposite directions creating Replication Bubbles
- Helicase breaks hydrogen bonds creating separate strands a. Stabilized by single-stranded binding proteins
- RNA Primase places RNA primers at the beginning of each building chunk where DNA Polymerase III can continue adding nucleotides
- DNA Polymerase III builds daughter strand by adding complementary bases a. Polymerization: an ANABOLIC process i. Every additional base pair is an endergonic reaction 1. Energy is used from the exergonic reaction of reducing ATP to Adenine (GTP, CTP, & TTP too!) b. Strand only grows in 5โ โ 3โ direction
โ Only the gene needed is unzipped โ The one and only enzyme that does all: RNA Polymerase (RNAP) โ NO EDITING: unnecessary โ Transcription bubble contained in RNAP โ RNAP binds to the promoter region โ TATA Box in any direction โ Enhancer region โ Transcription factors โ Initiation complex binds to promoter region and triggers transcription โ Terminator Region POST-TRANSCRIPTIONAL PROCESSING โ Splicing: cut out the introns to make mature mRNA transcripts โ Eukaryotic genes are not continuous โ Exons = the โreal geneโ โ expressed/coding โ Introns = the โjunkโ โ In between โ Alternative splicing โ One gene can code for more than one protein โ Different introns within the same gene โ Protecting the ends of the mRNA as it travels from the nucleus through the cytoplasm โ Add 5โ GTP cap โ Add poly-A tail on 3โ end โ mRNA will last longer and produce more protein
Translation: Creating a Polypeptide
โ Codon: each group of consecutive 3 nucleotides that code for 1 amino acid โ Directionality โ โ N-AA 1 -AA 2 -AA 3 -AAi-C
โ Highly conserved genetic code: a 3 base combination will code for the same amino acid across ALL species โ Defense against mutation: more than 1 codon for the same Amino Acid โ Start Codon: 5โ AUG 3โ (methionine) โ Stop Codons (5โ โ 3โ): UAA, UAG, UGA โ Stop translation as there is no tRNA to bind to here โ Transfer RNA Structure (tRNA): โ โClover leafโ โ Anticodon determines amino acid โ Ribosomes facilitate coupling of tRNA anticodon to mRNA codon
- Initiation a. Ribosomes latches onto mRNA where it sees 5โ AUG 3โ first at P site i. First anticodon is 3โ UAC 5โ
- Elongation a. Ribosome will move down one codon b. tRNA will enter through A site and latch onto the codon c. The Amino Acid from the tRNA in the P site will detach and create a polypeptide bond with the amino acid in the A site d. The tRNA without an Amino Acid will leave in the E site i. E for Exit
- Termination a. Reach a stop codon and no tRNA attaches
The Exception to the Central Dogma: Viruses
โ Virus: Genetic material within a protein capsid/envelope/capsule โ Injects genetic material into the cell
Prokaryotes
โ No nucleus (or other organelles) โ No post transcriptional processing โ Direct translation โ As mRNA gets made, it is fed into a ribosome
General Gene Stuff
โ Phenotype: Version of a trait โ Allele: Version of a Gene โ Genotype: Combination of Alleles โ 2 Chromosomes = 2 Copies of each gene = 2 alleles for each trait โ Dominant allele renders 2nd^ allele irrelevant (will be expressed no matter what) โ Functioning Protein โ Recessive Allele typically makes a malfunctioning allele โ True-Breeding: Homozygous โ Carrier: Heterozygous โ Punnett Squares โ Dihybrid Cross: Maintain Gene Order and FOIL for gametes โ Polyhybrid Cross: figure out probability of each trait and then x โem all โ Autosomal Chromosomes (Regular, 2 of each #) & Sex Chromosomes (X, Y) โ Pedigree โ Square = Genetically Male โ Circle = Genetically Female โ Shaded = Has Phenotype โ Skipped Generation: when children have the trait, but the parents donโt โ Can use? or _ for second allele when dominant and indertiminable โ Determining Inheritance Patterns โ Skipped Generation? = Autosomal Recessive, X-Linked Recessive โ Sex Distribution? โ Only Males (all dads with sons) = Y-linked โ All moms with sons = X-linked recessive โ All females with dads = X-linked dominant
Mendelโs Laws
- Law of Dominance a. Dominant Allele? Dominant Phenotype!
- Law of Segregation a. During meiosis, alleles segregate
i. Homologous chromosomes separate b. Each allele for a trait is packaged into a separate gamete i. Can only give 1 allele per gene to your kiddo
- Law of Independent Assortment a. Different loci (genes) separate into gametes independently b. Each gene is going to randomly out its allele i. Many possibilities for gametes 1. Ex. YyRr โ YR, Yr, yR, yr c. Exception: if genes are on same chromosome & close together i. Will usually be inherited together ii. Rarely crossover separately
Non-Mendelian Inheritance
โ Incomplete Dominance: 2 Dominant Alleles โ Heterozygote shows a novel, intermediate, blended phenotype โ Ex. RR = Red, WW = White, RW = Pink โ Codominance: 2 Dominant Alleles โ New Phenotype that is BOTH simultaneously (SEPARATE BUT EQUAL) โ Multiallelic Trait: has more than 2 alleles coding for 1 gene โ Ex. Blood Type Phenotype Genotype Antigens Antibodies Donation Status To From A AA, AO A Anti-B A, AB A, O B BB, BO B Anti-A B, AB B, O AB AB A & B None AB A, B, O, AB O OO None Anti-A, Anti-B A, B, O, AB O โ Pleiotropy: 1 Gene affects many traits โ Most genes! โ Lethality โ Presence of 2 specific alleles is LETHAL even if the phenotype is possible โ Polygenic Inheritance: Many genes affect 1 trait โ Epistasis: One gene can completely mask another gene
