DNA Replication and Protein Synthesis PDF

DNA REPLICATION Basic Information about DNA DNA Stands for Deoxyribonucleic Acid – It carries genetic instructions for the growth, development, functioning, and reproduction of all living organisms. Double Helix Structure – DNA is shaped like a twisted ladder, with sugar-phosphate backbones on th...

DNA REPLICATION Basic Information about DNA DNA Stands for Deoxyribonucleic Acid – It carries genetic instructions for the growth, development, functioning, and reproduction of all living organisms. Double Helix Structure – DNA is shaped like a twisted ladder, with sugar-phosphate backbones on the sides and nitrogenous base pairs (A-T, C-G) forming the rungs. Contains Four Nitrogenous Bases – Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G) through hydrogen bonds. Nearly 99.9% of Human DNA is Identical – Despite variations that make individuals unique, human DNA is remarkably similar across the species. Basic Information about DNA DNA is Found in the Nucleus and Mitochondria – Most DNA is in the cell nucleus, but mitochondria (the cell’s powerhouse) also have their own small amount of DNA, inherited maternally. If Stretched Out, DNA is Extremely Long – A single human cell contains about 2 meters (6.5 feet) of DNA, and all the DNA in your body could stretch from the Earth to the Sun hundreds of times! Replication is Semi-Conservative – During DNA replication, each new DNA molecule consists of one original strand and one newly synthesized strand. Basic Information about DNA DNA Can Self-Repair – Specialized enzymes, like DNA polymerases, help detect and fix errors during replication to maintain genetic integrity. Genes are Segments of DNA – DNA is made up of genes that provide instructions for making proteins, which control most biological functions. Your DNA is Unique (Unless You Have an Identical Twin!) – Every person (except identical twins) has a unique DNA sequence, making it a powerful tool for identification in forensic science. ENZYME Helicase – Unwinds and separates the double-stranded DNA by breaking hydrogen bonds S that between the base pairs. works Topoisomerase (Gyrase) – Relieves the supercoiling tension during ahead of the replication fork by cutting and rejoining DNA DNA strands. Replicati Single-Strand Binding Proteins (SSBs) – Prevent the separated strands from on reannealing or forming secondary structures. ENZYME Primase – Synthesizes a short RNA primer to provide a starting point for DNA polymerase. S that DNA Polymerase III – Adds new works nucleotides to the growing DNA strand in the 5' to 3' direction, extending from the during RNA primer. DNA Polymerase I – Removes the RNA DNA primers and replaces them with DNA nucleotides. Replicati Ligase – Seals gaps between newly synthesized DNA fragments (Okazaki on fragments on the lagging strand) by forming phosphodiester bonds. PROTEIN SYNTHESIS - TRANSCRIPTION The process of Transcription takes place in the cytoplasm in prokaryotes and in nucleus in eukaryotes. It uses DNA as a template to make an RNA (mRNA) molecule. During transcription, a strand of mRNA is made that is complementary to a strand of DNA. PROTEIN SYNTHESIS - TRANSLATION The RNA sequence is translated into a sequence of amino acids as the protein is formed. During translation, the ribosome reads three bases (a codon) at a time from the RNA and translates them into one amino acid. There are 20 Amino Acids – 11 are non-essential and 9 are essential. Non-essential Amino Acids can be synthesized by the body such as alanine, asparagine, arginine, aspartic acid, glutamic acid, cysteine, glutamine, proline, glycine, serine, and tyrosine. Essential Amino acids cannot be synthesized by the body. These include isoleucine, histidine, lysine, leucine, phenylalanine, tryptophan, methionine, threonine, and valine. Gene Mutations Gene mutations are changes in the nucleotide sequence of DNA. There are several types of gene mutations, and they can be classified based on how they affect the genetic code. Here are the main types, along with examples using genetic codons: Types of Gene Mutation 1. Point Mutation (Substitution) A single nucleotide is replaced with another, which may lead to a change in the amino acid sequence. Types of Point Mutations: Silent Mutation – No change in the amino acid due to redundancy in the genetic code. Example: Normal codon: AGA (Arginine) Mutation: AGG (Arginine) No change in the protein. Types of Gene Mutation Missense Mutation – A change in a nucleotide alters the amino acid. Example: Normal codon: GAG (Glutamic acid) Mutation: GUG (Valine) This occurs in sickle cell anemia (mutation in the β-globin gene). Nonsense Mutation – A change results in a stop codon, leading to premature termination of protein synthesis. Example: Normal codon: UAC (Tyrosine) Mutation: UAG (Stop codon) Leads to truncated, non-functional proteins, as seen in Duchenne muscular dystrophy. Types of Gene Mutation 2. Frameshift Mutation Insertion or deletion of nucleotides shifts the reading frame of codons, altering the protein sequence. Insertion Mutation – A nucleotide is added, changing the reading frame. Example: Normal sequence: AUG-AAA-GGC Mutation (inserting G): AUG-GAA-AGG-C... Leads to abnormal protein function, such as in Tay-Sachs disease. Types of Gene Mutation Deletion Mutation – A nucleotide is removed, shifting the codons. Example: Normal sequence: AUG-AAA-GGC Mutation (deleting A): AUG-AAG-GC... Can lead to conditions like cystic fibrosis (CFTR gene deletion F508). Types of Gene Mutation 3. Expanding Repeats Mutation A repeated sequence of nucleotides expands, causing genetic disorders. Example: Huntington’s Disease – CAG repeat expansion in the HTT gene Normal: CAG-CAG-CAG (10–35 repeats) Mutant: CAG-CAG-CAG... (36+ repeats) Leads to neurodegenerative symptoms.