Presentation on theme: "Molecular Structure & Function of Genetic Material"— Presentation transcript:
1 Molecular Structure & Function of Genetic Material Professor Janaki Natalie Parikh
2 D.N.A. StructureD.N.A.: deoxyribonucleic acid: is a double stranded (dbl helix) polymer of a nucleotidesResides in the nucleus (eukaryotes)Made of 3 molecules:Phosphate, Sugar &nitrogenous base
3 DNA 4 bases in D.N.A.: Adenine, Guanine, Thymine & Cytosine Rules for pairing bases together:Adenine Thymine Guanine CytosineOur DNA is composed of literally billions of bases!Genes are long sections (segments) of D.N.A.
4 D.N.A. Function 1. D.N.A. can make a copy of itself, handy during? Mitosis & meiosis2. D.N.A. contains the code for protein synthesis, the manufacture of proteinsProblem, where does protein synthesis take place?Ribosomes, located? Outside the nucleus. D.N.A. can’t leave the nucleus.So how does this get done?
5 R.N.A.R.N.A.: ribonucleic acid, single stranded, free floating throughout the cellSimilar bases, w/ 1 important diffc.Adenine, Guanine, Uracil & CytosineAdenine Uracil Guanine CytosineR.N.A assists in completing protein synthesis
6 Protein Synthesis Proteins: polymers as well, but difft. components? Amino acids. How many are there?20 total. Of these 11 are naturally occuring, the other 9 must be consumed through food, those are known as “essential amino acids” (in kids 10 are essential, 1 loses this status once we produce it)How do we get these essential amino acids?
7 Protein Synthesis Recall our logistical dilemma? Making proteins: multi-step taskCheesy analogy: outside of thenucleus is the “hood”, the nucleus: gated commtyD.N.A.: Doesn’t kNow About the hoodHowever, D.N.A.’s cousin, R.N.A. is another storyR.N.A.: Really kNows About the hood
8 Steps of Protein Synthesis 1.transcription: m.R.N.A. enters nucleus, produces a transcript of D.N.A. code (in R.N.A. language)Let’s try part of a sequence:D.N.A. reads: A T A G A G mRNA?m.R.N.A.: U A U C U C2. translation: t.R.N.A. reads the mRNA transcript & translates the info one codon at a time
9 Codons & Genetic CodeCodons: base triplet that codes for an amino acidNotice: genetic redundancy: more than 1 codon codes for thesame amino acid(we’ll discusssignifcance ofthis redundancysubsequently)
10 Protein Synthesis Back to our 2nd step: mRNA: U A U C U C tRNA: A U A G A GAmino acid: Isoleucine, Glutamic Acid
11 Genetic Redundancy Sometimes mistakes occur in this process (mutation) Problem: even 1 incorrect base can render a protein useless junk (loss of function)Remember genetic redundancy? It’s purpose:Serves as an built-in security mechanism, reducing the chance that a base substitution resuls in loss in protein function
12 Mutations Overview Mutagens: accelerate the rate of mutations Mutations are completely random accidentsMost mutations result in loss in protein function (junk protein), some are neutral, Rarely: new protein function producted(Ecstasy q:
13 Mutations Point mutations: involve 1 single base Base substitution: swapping of nucleotide baseCan possibly be neutral due to genetic redundancyAddition or deletion: extra base insert or a base is omitted from correct sequenceResults in a frameshift mutation (affects multiple amino acids) & can never be neutral
14 Chromosomal Mutations Chromosomal mutations (macrolesions): occur during meiosis, larger scale of significance since whole chromosome involvedNondisjunction: chromosome pair failed to splitResults in a gamete w/ too many, or too few chromosomes
15 Trisomy & Monosomy Trisomy: presence of 3 chromosomes instead of the normal 2 in ahomologous pairMonosomy: presence of 1 chromosome instead ofthe normal 2 in a homologous pairExamples?Down’s syndrome: trisomy of #21
16 Syndromes Klinefelter’s Syndrome: XXY or XXXY Turner’s Syndrome: X0
17 Mutations & Evolutionary Significance In order for a mutation to have an evolutionary impact, it must be inheritable (happens in the gametes)Next, we’ll examine a specific point mutation that had a major impact on human populations