Online Counseling Resource YCMOU ELearning Drive… School of Architecture, Science and Technology Yashwantrao Chavan Maharashtra Open University, Nashik – , India

OC-SBT044-U01-01 Introduction Programmes and Courses  SEP – SBT044 – CP01  SEP – SBI044 – CP01  SEP – SGS044 – CP01

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.3 Credits  Academic Inputs by Mrs. Rasika Bhore  M.sc (Microbiology)

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.4 How to Use This Resource  Counselor at each study center should use this presentation to deliver lecture of minutes during Face-To-Face counseling.  Discussion about students difficulties or tutorial with assignments should follow the lecture for about minutes.  Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student.  Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam.  Appear several times, for all the Self-Tests, available for this course.  Student can use handouts for last minutes preparation just before end exam.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.5 Learning Objectives  After studying this module, you should be able to: Discuss how mutations affects DNA & leads to abnormalities. Describe different types of mutations.

School of Science and Technology, Online Counseling Resource… Introduction  DNA is a complex organic molecule of finite chemical stability.  It has maintained an impressive function of replication over generations.  Many times DNA assaulted by natural & unnatural chemicals & radiations that break its backbone & chemically alter bases.  Mutations result when damage changes the coding properties of bases.  Thus mutations can completely destroy the normal functioning of cell. © 2007, YCMOU. All Rights Reserved.6

School of Science and Technology, Online Counseling Resource… Nature Of Mutations  Naturally occurring mutations include almost all conceivable changes in DNA sequence.  Various types of mutations are as follows: Null mutations Mutation by single base change  Transitions  Transversions Frameshift mutations Mutation by chemical mutagens © 2007, YCMOU. All Rights Reserved.7

School of Science and Technology, Online Counseling Resource… Null Mutation  In this type, the function of the gene destroy completely.  Mutation is due to extensive insertions & deletions & even gross rearrangements of chromosome structure.  These changes are due to insertion of Transposon, which typically places many thousands of bases of foreign DNA in the coding sequence of gene.  Many times abnormal recombination also responsible. © 2007, YCMOU. All Rights Reserved.8

School of Science and Technology, Online Counseling Resource… Mutation By Single Base Change  Mutation deals with exchange of one base with another.  This can change genes in ways that are subtle enough to yield useful variants.  Following types of base changes occurs: Transitions: Changes from one purine to another purine or from one pyrimidine to other. Transversions: Changes from purine to pyrimidine or from pyrimidine to purine. © 2007, YCMOU. All Rights Reserved.9

School of Science and Technology, Online Counseling Resource… Frameshift Mutation  An addition or deletion of one or few base pairs that changes the translation reading frame within a protein coding sequence & thus completely disrupts its synthesis is often called a Frameshift mutation. © 2007, YCMOU. All Rights Reserved.10

School of Science and Technology, Online Counseling Resource… Mutation By Chemical Mutagens  Mutagenic chemicals interfere in important way with accurate replication of DNA.  They either act on DNA directly to change its template properties or in some way subvert replication so that a wrong base is inserted.  Chemical mutagens can be divided into 3 classes: 1.DNA reactive chemicals 2.Base analogs 3.Frameshift mutagens © 2007, YCMOU. All Rights Reserved.11

School of Science and Technology, Online Counseling Resource… DNA Reactive Chemicals  Nitrous acid (HNO2) or Alkalating agents like Methyl-nitrosoguanidine, act directly on DNA to change the bases into chemically distinct structures.  The new bases often base pair in a different way from the original bases, in which case the effect of the mutagen is to alter the genetic code directly.  Thus some modified bases can not base pair at all, & sometimes damage completely removes the base from the DNA backbone. © 2007, YCMOU. All Rights Reserved.12

School of Science and Technology, Online Counseling Resource… Base Analogs  It is a second class of chemical mutagens which are similar to the normal bases, incorporated into DNA during normal replication.  Their different structures lead to less accurate base pair formation than normal, causing frequent mistakes during the replication process.  One of the most powerful base analog mutagens is 5-bromouracil an analog of thymine.  It causes mutation by pairing with guanine. © 2007, YCMOU. All Rights Reserved.13

School of Science and Technology, Online Counseling Resource… Frameshift Mutagens  A chemical mutagens consists of a frameshift mutagens like Proflavin, cause deletion or addition of a single base or few bases.  These mutagens might act by binding to bases that loop out of either the template DNA strand or growing strand during DNA synthesis.  By stabilizing the looped-out structure, increases the chances of mutation. © 2007, YCMOU. All Rights Reserved.14

School of Science and Technology, Online Counseling Resource… What We Learn………….  Null mutations destroys the cell functioning completely.  Mutation by single base exchange leads to abnormal replication includes Transitions & Transversions.  Frameshift mutation involves base pair change in translation reading frame.  Chemical mutagens increases probability of mutation.  Alkalating agents which changes the structures of normal bases.  Base analogs are similar to that of normal bases which interfere in binding with complementary base.

School of Science and Technology, Online Counseling Resource… Critical Thinking Questions  What type of mutation occurs if the Adenine is deaminated with Hypoxanthine? © 2007, YCMOU. All Rights Reserved.16

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved. Tips For Critical Thinking Questions  Hypoxanthine is a nitrous acid. Adenine will bind with cytosine instead of thymine after deamination.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.18 Study Tips  Book Title: DNA In Detail Author: J.D.Watson  Book Title: Biochemistry Author: Stryer

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.19 Study Tips DNA mutations

End of the Presentation Thank You !