RNA Transcription, Translation, and Genetic Variation Module 5.3 PDF

RNA Transcription, Translation, and Genetic Variation Wednesday, 13 November 2024 2:37 PM A. The differences of Eukaryotes vs Prokaryotes in their DNA structure: Eukaryotes: 1. DNA in eukaryotes is found in linear chromosomes inside the nucleus. 2. DNA -> wrapped around histones -> chromoso...

RNA Transcription, Translation, and Genetic Variation Wednesday, 13 November 2024 2:37 PM A. The differences of Eukaryotes vs Prokaryotes in their DNA structure: Eukaryotes: 1. DNA in eukaryotes is found in linear chromosomes inside the nucleus. 2. DNA -> wrapped around histones -> chromosomes. 3. Eukaryotic cells may also possess DNA within mitochondria or chloroplasts. 4. Eukaryotes tend to have larger genomes than prokaryotes, including non-coding and Prokaryotes 1. Prokaryotes possess free floating, singular circular chromosomes, as well as plasmids. 2. Prokaryotic DNA is not membrane bound but floats in the cytoplasm in the cell’s nucleoid region. 3. Plasmids, small circular independent DNA molecules may also be present, which can be transferred between organisms. 4. Prokaryotic genomes are smaller and compact in comparison to eukaryotic DNA, with little repetition. B. Transcription and Translation Polypeptide synthesis (proteins) is the two-stage process used to turn genetic information into structural and functional molecules used inside cells (DNA > Functional Protein). They are made up of amino acids that are "translated" from the expression of certain genes in our DNA. Genes are the basic unit of heredity consisting of a segment of DNA. Stage 1: RNA Transcription DNA uncoils a segment of itself using helicase to show the gene being transcribed. RNA polymerase binds to a specific region on the DNA known as the promoter. The promoter signals where RNA polymerase should start transcribing. The strand being used for transcription is called the template strand while the new RNA strand is called the coding strand. RNA Polymerase moves along the DNA 3' to 5' because they synthesize 5' to 3'. Adenine pairs with Uracil (instead of Thymine) and Guanine with Cytosine. RNA reaches the end of the gene at the terminator sequence and releases the brand new RNA strand. DNA repair itself using ligase. mRNA processed either by splicing or capping to repair mutations or increase stability. It exits the nucleus to find a ribosome to create proteins. Stage 2: Protein Translation Once the processed mRNA reaches the cytoplasm, it binds to a ribosome to begin translation. The ribosome is composed of ribosomal RNA (rRNA) and proteins, with sites for mRNA and transfer RNA (tRNA) binding. Codons are sequences of three nucleotides on the mRNA. Each codon corresponds to a specific amino acid or a stop signal. For example, the codon AUG codes for methionine and also serves as the start codon, signalling the beginning of protein synthesis. 3 Key players: mRNA (Messenger RNA): A template in translation, where the sequence of codons on the mRNA determines the order of amino acids in the protein. rRNA (Ribosomal RNA): structural and functional component of ribosomes, the cellular structures where protein synthesis occurs tRNA (Transfer RNA): adaptors that bring the correct amino acids to the ribosome according to the codon sequence on the mRNA. Each tRNA has an anticodon, a sequence of three nucleotides complementary to the mRNA codon which attaches amino acids that correspond to that codon. Steps: 1. Initiation: The small ribosomal subunit binds to the 5' end of the mRNA at a specific sequence near the start codon (AUG). tRNA then binds to the start codon and a large ribosomal subunit joins the rest of the structure to complete the ribosomal RNA. 2. Elongation: The next tRNA with the complementary anticodon binds to the A site which brings the specific amino acid that matches that codon. The amino acid from the initial tRNA is put onto the new tRNA and creates a polypeptide chain, and shifts the empty tRNA to the P site where it is released. This process continues until the mRNA chain is complete (reaches STOP codon) and the polypeptide is fully complete. 3. Termination: A release factor binds to the stop codon and the ribosome disassembles to be reused in other protein translation. Module 5.3 Page 1 After the creation of the polypeptide, proteins still an additional step to be a functional component. Protein folding is the process where a linear chain of amino acids, synthesized during translation, adopts its unique three-dimensional structure by "folding". This final structure, known as the protein's native conformation, is essential for the protein's biological function. Levels of Protein Structure: 1. Primary Structure: This is the linear sequence of amino acids in a polypeptide chain, held together by peptide bonds. This sequence is determined by the genetic code on the mRNA and is crucial for how the protein will ultimately fold. 2. Secondary Structure: Hydrogen bonds between the backbone atoms in the amino acid chain create local structures. The two common forms of secondary structures are: ○ α-helix: A coiled structure stabilized by hydrogen bonds. ○ β-sheet: A pleated sheet structure where strands align in parallel or anti-parallel arrangements. 3. Tertiary Structure: This is the protein's overall three-dimensional shape, resulting from interactions between side chains (R-groups) of amino acids. These interactions include: ○ Hydrophobic interactions: Nonpolar side chains cluster together to avoid water. ○ Hydrogen bonds: Between polar side chains. ○ Ionic bonds: Between positively and negatively charged side chains. ○ Disulfide bonds: Covalent bonds between cysteine residues, adding stability. 4. Quaternary Structure (only in some proteins): Some proteins are composed of multiple polypeptide chains (subunits). These chains assemble into a single functional unit through interactions similar to those in tertiary structures. C. Genetic Variation Genetic variation refers to the differences in DNA sequences among individuals within a population. These variations are fundamental to evolution and are the raw material on which natural selection acts. Genetic variation enables populations to adapt to changing environments and is key to the diversity of life forms on Earth. Some Sources of Genetic Variation: 1. Mutations: ○ Mutations are changes in the DNA sequence that can occur spontaneously or due to environmental factors, such as radiation or chemicals. They may affect a single base pair (point mutations), insert or delete segments (insertions/deletions), or involve larger chromosomal rearrangements. ○ Mutations can introduce new alleles (alternative forms of a gene) into a population, leading to novel traits that may be advantageous, neutral, or deleterious. 2. Recombination (during Meiosis): ○ Crossing Over: During prophase I of meiosis, homologous chromosomes pair up and exchange segments of DNA through a process called crossing over. This shuffles the alleles between chromosomes, resulting in gametes with unique genetic combinations. ○ Independent Assortment: During metaphase I of meiosis, the way homologous chromosomes line up and are distributed into daughter cells is random. This independent assortment of chromosomes leads to different combinations of maternal and paternal chromosomes in gametes. These sources that create genetic mutation creates a unique genotype, which is a unique gene in that individual. When the genes are expressed for growth and development, we call this expression a phenotype. The variant of a specific gene in one individual is called an Allele. Module 5.3 Page 2  ○ Independent Assortment: During metaphase I of meiosis, the way homologous chromosomes line up and are distributed into daughter cells is random. This independent assortment of chromosomes leads to different combinations of maternal and paternal chromosomes in gametes. These sources that create genetic mutation creates a unique genotype, which is a unique gene in that individual. When the genes are expressed for growth and development, we call this expression a phenotype. The variant of a specific gene in one individual is called an Allele. e.g A person with blonde hair is a phenotype, the genes that express that characteristic is the genotype. The mom who has brown hair has the brown hair allele, while the dad who has blond hair has blonde hair allele. Different ways traits are passed down: 1. Autosomal Inheritance: Traits inherited through autosomal genes are equally likely to be passed to both males and females, as these chromosomes are present in pairs in all individuals, regardless of sex. The allele from each parent can either be dominant or recessive. Dominant trait will express itself even when it's heterozygous. Recessive traits only express itself when it's homozygous. e.g. Recessive exclusive diseases (cystic fibrosis) will only express itself on recessive homozygous individuals. 2. Sex-linked Inheritance: Sex-linked inheritance involves genes located on the sex chromosomes (X and Y in humans). Traits inherited via these genes have different patterns of inheritance in males and females. Males have XY chromosomes while females have XX chromosomes, meaning if there is a trait passed down in the X chromosome, males and females will express it. That also means a trait passed down from the Y chromosome will only affect males. e.g. X or Y linked disease that makes them specific to that allele. 3. Co-dominance: Co-dominance is a form of inheritance where both alleles for a gene are fully expressed in the phenotype of the heterozygote, meaning neither allele is dominant or recessive over the other. That means they both express the trait simultaneously. e.g. AB blood type is expressed because A and B are both dominant. 4. Incomplete dominance: Incomplete dominance is a type of inheritance where the heterozygous phenotype is an intermediate of the two homozygous phenotypes, rather than showing just one or both. Neither allele is completely dominant over the other; instead, they blend to produce an intermediate trait in heterozygous individuals. e.g. Certain species of flowers can express a mix of 2 colours instead of a dominant colour. Predicting traits: Some tools that we can use to predict the traits a new individual can express includes Punnett Squares and Pedigree Charts. How to use Punnet squares: 1. Determine the genotype of parents 2. Draw a grid of 2x2 squares 3. Fill in the alleles 4. Calculate the Percentages. e.g. In a cross between two heterozygous parents for a trait (genotype Aa) where a dominant allele A expresses freckles, what is the probability that their child will also express freckles? A a A AA Aa a aA aa How to use Pedigree Charts: 1. Determine whether the trait is dominant or recessive. If the trait is dominant, one of the parents must have the trait. Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can be heterozygous. 2. Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait. For example, in X-linked recessive traits, males are much more commonly affected than females. In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions). Module 5.3 Page 3