Lecture 3 DNA and the central dogma DNA replication - Fall 2024 - The American University in Cairo

BIOL1930: Genetics for Everyone Lecture 3 DNA and the central dogma: DNA replication Sunday and Wednesday @3:30 a.m. Dr. Eman AbdelAlim Rabie, PhD Biotechnology Fall 2024 Getting to know Genetics! Module I: Basic concepts in Genetic...

BIOL1930: Genetics for Everyone Lecture 3 DNA and the central dogma: DNA replication Sunday and Wednesday @3:30 a.m. Dr. Eman AbdelAlim Rabie, PhD Biotechnology Fall 2024 Getting to know Genetics! Module I: Basic concepts in Genetics! Module II: Genetic disorders, what could go wrong? Module III: Behavioral Genetics Module IV: The fascinating things Genetics can do! OR Cancer Genetics  Module I: Basic concepts in Genetics! Introduction Sept.1st 1- Introduction to Genetics: from cells to DNA & chromosomes Sept.4th 2- DNA: our genetic material Week 1 Sept.8th&11th 3,4- DNA structure and the central dogma Assignment 1: Posted Sept. 11th Week 2 Sept.15th&18th 5,6- Mendelian Genetics Week 3 Sept.22th& 25th 7,8- Non-Mendelian modes of inheritance Assignment 1: Deadline Sept.22nd Week 4 Sept. 29nd &Oct. 2nd 9- Multifactorial traits In class-exercises and revision on Module I.  Getting the full picture…. “Genetics is the study of genes, genetic variation, and heredity in living organisms.” “Genetics is the study of biologically inherited traits, including traits that are influenced in part by the environment.”-Please review explanation. Heredity (inheritance or biological inheritance) is the passing on of traits from parents to their offspring through reproduction. Through heredity, variations between individuals can accumulate and cause species to evolve. Variation between species Variation between individuals of the same species Chromosomes → DNA → Gene is a section of DNA that contain the set of instructions to produce specific molecule in your body, usually a protein. These proteins control how our body grows and works; they are also responsible for many of our characteristics, such as our eye color, blood type or height. The monomer of DNA is the Nucleotide = Deoxy ribose sugar (ring) + phosphate (grey ball) + one nitrogen base (either A,C,G,T) Two anti parallel polynucleotide strands Nucleotide → Polynucleotide strand → Two anti parallel polynucleotide strands → Double helix DNA Antiparallel: The two strands run parallel but in opposite directions. In one chain the direction is 5' -> 3' while in the opposite one it is 3'-> 5’. The two chains are held together by hydrogen bonds between their bases , i.e. thru “Base-pairing”. Building blocks of biomolecules Starch (Simple sugar) DNA &RNA Protein Fat/triglycerides 20 amino acids→ Different sequences & different lengths →Millions of possibilities! Proteins not only have different sequences & different lengths but also different shapes/folding!  Proteins’ building blocks are 20 aminoacids! Same backbone structure Amino- for amino group (NH2) + -acid for an acid group (COOH) Amino acids link together via peptide bonds * * * *  How? CODE through four nitrogenous bases: A, G, C, T CODE through 20 aminoacids:ARNDCQEGHILKMFPSTWYV  The central dogma of biology “Central dogma is the process in which the genetic information flows from DNA to RNA (transcription), to make a functional product protein (translation).“ The central dogma of biology DNA replication The new DNA strands are formed, with one strand of the parent DNA and the other is newly synthesized, this process is called semiconservative DNA replication. (you keep (conserve) half (semi) of your older self!) DNA replication The two important steps involved in DNA replication: 1. Initiation 2. Elongation Important study source: https://www.nagwa.com/en/explainers/369154351560/#:~:text=DNA%20replication% 20is%20the%20process,can%20see%20in%20Figure%201. DNA replication: Initiation DNA replication: Elongation DNA replication problem! DNA polymerase elongation is unidirectional i.e. DNA polymerase can only build new DNA strand in the 5′ to 3′ direction. ? DNA replication problem solved! In one strand (the template 3‘→5‘) elongation is continuous, hence called continuous replication while on the other strand (the template 5‘→3‘) it is discontinuous replication. They occur as fragments called Okazaki fragments. The enzyme called DNA ligase joins them later. DNA replication problem solved! DNA polymerase proof-reading power! DNA replication DNA replication - YouTube Key points: When a living cell divides, its DNA must replicate so that each new cell receives a copy of DNA. DNA replication is a semiconservative process. In order for a molecule of DNA to replicate, the two strands must first unwind. DNA helicase is responsible for this and “unzips” the DNA molecule by breaking the hydrogen bonds between the nitrogenous bases. DNA polymerase synthesizes new strands of DNA along each template strand by adding complementary nucleotides to the chain. DNA polymerase can only synthesize DNA in the 5′ to 3′ direction. A new strand of DNA is synthesized continuously along the “leading” template strand. A new strand of DNA is synthesized in fragments along the “lagging” template strand. DNA ligase is responsible for joining the fragments of new DNA together to form a continuous complementary strand. DNA polymerase is also responsible for “proofreading” the new strands of DNA to eliminate mutations. If DNA is physically damaged or broken, DNA ligase can function as a DNA repair enzyme, linking the fragments back together through phosphodiester bonds.  Triple Bonus! 1. During replication, Okazaki fragments elongate (a) leading strand towards the replication fork (b) lagging strand towards the replication fork (c) leading strand away from the replication fork (d) lagging strand away from the replication fork 2. The 3’ – 5’ phosphodiester linkage joins (a) two nucleotides (b) two DNA strands (c) a nitrogenous base with pentose sugar (d) two complementary nitrogenous bases 3. DNA replication is (a) conservative (b) conservative and discontinuous (c) semi-conservative and discontinuous (d) semi-conservative and semi-discontinuous  Thank you! Instructor email: [email protected] TA: [email protected]