Chapter 9: What Genes Are - SCB 101 PDF

Chapter 9: What Genes Are Prof. Calkins SCB 101 Recap: What is DNA? Deoxyribonucleic acid; our genetic blueprint which codes for aspects of who we are. DNA contains GENES which code for proteins. Recap: What are different versions of a gene? Alleles Recap: What are the building block...

Chapter 9: What Genes Are Prof. Calkins SCB 101 Recap: What is DNA? Deoxyribonucleic acid; our genetic blueprint which codes for aspects of who we are. DNA contains GENES which code for proteins. Recap: What are different versions of a gene? Alleles Recap: What are the building blocks for nucleic acids? a. Amino acids b. Lipids c. Nucleotides d. Carbohydrates  DNA (deoxyribonucleic acid): What is Contains the genetic code of all life dna? A huge double-stranded molecule made up of nucleotides Nucleotides Each nucleotide is composed of: A sugar (deoxyribose) A phosphate group A Nitrogenous base Adenine (A) Cytosine (C) Guanine (G) Thymine (T) DNA Structure The two parallel strands of DNA are connected by bonds that link the nucleotide base pairs. The DNA “ladder” is twisted into a spiral called the double helix. Recap: What part of the DNA represents the rungs of the ladder? Nucleotides (A,T,G & C) What part represents the sides of the ladder? Sugar-phosphate backbone Complementary Base-Pairing: The sequence of As, Ts, Cs, and Gs on one strand of the double helix determines the sequence on the other strand of the double helix. A always pairs with T G always pairs with C Therefore, one strand serves as a template for the other strand. This allows a new DNA molecule to be built that is identical to the original. Complementary Base-Pairing: Recap: There are four bases in DNA: adenine, thymidine, guanine, and cytosine. How do they pair up? a. A–T and G–C b. A–G and T–C c. T–G and A–C d. G–A and C–T Recap: Which is the correct pairing of nitrogenous bases of deoxyribonucleotides inside a DNA double-helix strand? a.C to A b.T to G c.A to T d.all of the above Nucleotide sequencing The sequence of bases on a DNA strand differs among: Species Subtypes of a species Individuals of the same species Recap: All genes are composed of just four nucleotides. How can different genes carry different types of information? The order of nucleotides differs giving different genes. Recap: Would you expect to see more variation in the sequence of DNA bases between: Two members of the same species? or Two individuals of different species? Recap: Do different alleles of a gene have the same DNA sequence or different DNA sequences? Review: Differences in genotype (DNA nucleotide sequence) can result in differences in phenotype (physical properties). The most basic function of DNA is to code for proteins What makes one allele different from another? All alleles for a particular gene contain the DNA sequence coding for the synthesis of the same protein. Slight differences in the nucleotide sequences of an alleles can cause slight differences in the protein product of the gene. For example: AGGCTTAGA = baby blue pigment in feathers AGGCTAAGA = turquoise blue pigment in feathers Review: Chromosome structure Chromosomes consist of a DNA strand that have been wrapped up and organized into a compact structure. Recap: Choose the correct sequence starting with the smallest unit: a. DNA, gene, chromosome, nucleotide b. Chromosome, gene, nucleotide, DNA c. Gene, nucleotide, DNA, chromosome d. Nucleotide, gene, DNA, chromosome e. Nucleotides, DNA, gene, chromosome Dna replication DNA replication: the duplication of a DNA molecule When would DNA replication occur in the cell cycle? Interphase- S phase Before a cell enters mitosis Occurs rapidly when an embryo is developing Occurs rapidly when a cell becomes cancerous Three steps of dna replication 1. Proteins bind to the origins of replication and unwind the DNA double helix. 2. The enzyme DNA polymerase uses each strand as a template to build another new strand starting from primers. 3. Semiconservative replication occurs, so there are now two new strands of DNA. Each has one old and one new strand. https://www.youtube.com/watch?v=TNKWgcFPHqw Recap: Which is the most accurate description of DNA replication? a. DNA is copied by an enzyme b. DNA is constantly reproduced by the nucleus c. The DNA double helix unzips and new strands form from the original “template” d. There are existing DNA templates in cells that make all DNA replicates Recap: Complementary base pairing in DNA means that DNA is easy to copy. How does this work? a. The base pairs that make up the “rungs” of the DNA molecule will only match with identical copies of themselves A:A, C:C, etc. b. It doesn’t work very well, so many mistakes are made when DNA gets copied as cells divide. c. The base pairs that make up the “rungs” of the DNA molecule will only match up A with T or C with G. d. The base pairs that make up the “rungs” of the DNA molecule match other DNA molecules perfectly. e. DNA isn’t very easy to copy, but there’s no need to do that, so it doesn’t matter. Mutation corrections DNA polymerase proofreading: DNA repair system Corrects almost all mistakes during replication Edits and fixes incorrect complementary base pairs as they form Further repair proteins can correct 99 percent of the remaining errors. This results in only one mistake for every billion bases! mutations Mutation: a change to the sequence of nucleotides in an organism’s DNA Point mutation: when only a single base is altered in a sequence Substitution: one nucleotide is exchanged for another in a sequence. Insertion: one nucleotide is added to the sequence. Deletion: one nucleotide is removed from the sequence. Point mutations Sickle cell disease is a blood disorder caused by one single nucleotide difference for hemoglobin The allele for sickle cell causes the hemoglobin protein to have an altered shape This causes the red blood cells to be concave  Recap: How is the number of mutations minimized in the daughter DNA molecules of semiconservative replication? a.The DNA polymerase molecules that carry out semiconservative replication proofread during the process. b.Repair proteins correct the vast majority of mismatch errors that they detect in newly replicated DNA. c.Replication occurs at hundreds of origins of replication, rather than at only one. d.Both A and B are correct. Recap: How is it possible that a change in just ONE nucleotide can cause huge effects such as sickle cell anemia? DNA codes for proteins, so a change in one nucleotide can change the structure of the protein that it codes for. Sickle cell anemia is caused by an abnormally shaped hemoglobin protein