PRINCIPLES OF HEREDITY
PRINCIPLES OF HEREDITY GENE 310
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This 10 page Class Notes was uploaded by Elvera Macejkovic V on Wednesday October 21, 2015. The Class Notes belongs to GENE 310 at Texas A&M University taught by Clint Magill in Fall. Since its upload, it has received 20 views. For similar materials see /class/225931/gene-310-texas-a-m-university in Genetics (Graduate Group) at Texas A&M University.
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Date Created: 10/21/15
GENE 310 Lecture outline for protein structure Proteins are polymers chains of amino acids 20 different amino acids are used to make proteins all have an amino NH3 group and a carboxylic acid COOH they differ in the quotside chainquot which can be simply an H glycine or a complex double ring structure most side chains are uncharged but two are acidic and 2 basic at typical cellpH values two amino acids contain sulphur S in the side chain the protein is formed by linking the N in the amino group of one amino acid to the C in the COOH of the previous amino acid this creates a peptide bond and the units are also called peptides the chains vary in length from a few to thousands of units the primary structure of a protein is the sequence of amino acids the quotbeginningquot of the chain has a free NH3 amino terminal and the quotendquot of the chain has a free carboxyl COOH ie there is a quotdirectionquot proteins are very information rich molecules secondary structure results from natural folding where helixes sheets barrels etc that form due to interactions within the chain of amino acids tertiary structure refers to the 3 D structure that may also include cofactors quaternary structure refers to the fact that many proteins contain multiple polypeptide chains Enzymes are proteins that catalyze speci c metabolic reactions each reaction requires a different enzyme each enzyme is the product of one or more genes an active site often a groove or cleft in the surface of the 3 D folded protein acts as a quotmagnetquot for the substrates in the reaction the enzyme lowers the energy of activation allowing the reaction to proceed the enzyme is not changed in the reaction and can be used over If you are interested in exploring the structures of the amino acids and proteins try the following WEB sites httDwww ediiChemisfrvChem22 aminnaoid aahtm htt rowlrockefelleredu aainfo structhtrn htt wwwbiochemuclacuk bsm dbbrowser c 2 aastructhtrnl munm m m Sex airlined Genes Leann Oudm Mulhpl muhamsms am far murmg saxuar rapmduchan samna malts danars wnmm a fmlxty m plasma a m1 af DNA that mag far pmtum that anahh a wpy nanacanna mm ad that an nut an a plasmid a in already mntam a many implants my many fung quotmm afferent mm A vs a at an a twa gen 104 m arder a was ganahahy either mating typz can in man damn ah ramah Rupiah m kamfex af ganana mfarmztmn Sam 2mm h campuann af h agg may tnggex mal ah famasa davdapment ny plan mm famasa and ma gamatas ha 5am a pas but samzhma In argzm Farmed an ha 5 pr n away ax a Sam plant ax mm whm pa m adqu m ha ussd and agg m mad In th nah A m spams hm stncdy a1 and famasa plan s ax zpnmt xn grashappexs an many a bug femalas hm an mn number af Lhramasamas and man an add r Femalz grashappexs hm 2 pm Lhra ma wh a1 hm u and an that remains unpaired In 1 190 a h u h m a m 05A When Mdllung nahwd h m ha ch mystery chmmasam anx Lhmmasam and th ham mm m gvas 115 0 ch xao system af sax datemumtmn femalas actually hm 2 X s so ah ha aggs Ea an x 5mm anly wnh an x hal h mng m h 112 th sperm praducgd by a mal and up XXfemalas and ham x0 mks m 15 a1 50 hm an x chmm mm but rather man ng n0 partner m mewsAS ha pm wnh a much smanar Lhramasam am a v Lhramosmn Th v mmmns my fzw gang and than that m pagan m dffexent fmm ha many gang fauna an an x Lhramasam aggs samwnhx armwnhv MamWW mamamammukamnsammkmmssxmm Mm munm m W Th typ hf saxdnmnmahan is called h my system xh hmh ch w and my system h mal 5 sad m ha ha hatemgamzhc sun smog h praduu m m uent lands af gamztas h a ma h mm is h hatemgamzhc sax rather than mug x and v whuzh wauld h mn mng male hm am sad m he 22 whd fmmla an zw m a v Lhmmmm h w 1 ma and has very fzw gang rmnasam sha a ah h v ch uld Shaw 2 mal m ma pmm af 1 halandnc mhexxtanoz Hamm smog Lh mg m m 1 ex an very fzw gang ah ha y mer than a a1 dzvela mm gang ah ha x Lhmmasam am sad m h saxdmked genas Saxrhnked gang Shaw umqu pmm af mhmmno when h sax af Offspring is taken mm mam hm hm anly ah mpy 0f sax hum gen 50 chm 5 ha maskmg af 139an by annuan allelas mks m thus 5m m h hznuzygaus Many mu knawn mus Shaw pmm af mhmmncz emu af 2 saxrlmked hmm x meanmg ch ran 1 hmm m fmmla JCalarhhndnasS Bmh radmn aha gmhmhg Vlsmn pigments an baded by gang ah ha x 41hr mawm Wth Va happen m a urns hatwem 2 mm wha is defuhv m ah afthm gang and a ma wnh narma on r vmaha man 3 narma v 1 mlarhlmd but a daughter hmmh 12 sans mlarhlmd Duffexmus m ch nuns afnarma v mm m mal versus mm affspnng is a gand dug that sax39hnkb gang may in mvalvod Ahaut s m mm man an mlarhhnd but 7th 1 m 23o mm Calarhhnd mm hm a wlarhhnd mhw 2 Durban Muscular nymaphy DMD is 7th fauna m mm 5mm 12 15mm befar rapmduchan About 13 am an h usult af haw mmmm when ch mather is hat 2 mm Far a camping dmlptmn m m WW m whimvimlwnxgmmSedmkkmsSxmhm Ma 4 a h pt 042003 551 PM 3Hemophilia A the lack of clotting factor 8 is another well known case of a sex linked recessive Many female descendents of Mary Queen of Scots are carriers while many males in this I39Royal Pedigreequot suffered from hemophilia See the following links for the pedigrees htt wsrvclasvir iniaedu r h u ro lhemahtml htt u li uffaloedu li raries ro ects cases hemohtm By contrast dominant genes on the X chromosome such as normal color vision tend to I show upquot more often in females than in males This becomes especially apparent when the trait is very rare in the whole population Human examples include a sex linked type of hypertrichosis excessive body hair and a type of defective tooth enamel You should be sure that you can predict the progeny expected from all possible crosses involving sex linked genes Flwrnm Mm Page 3 of 3 GENE REGULATION IN HIGHER ORGANSIMS Although eukaryotes do not have operons and are much more difficult to study experimentally examples of gene regulation and knowledge of the molecular mechanisms involved are coming to light Although eukaryotic regulation is relatively more complex many of the principles from the lacoperon can be applied For example a number of promoters that allow tissue specific expression thorough interaction with transacting factors have been defined One quite useful application in plants has been the ability to place structural genes under the control of seed specific promoters so that the protein can be made and stored in seeds The local company Prodigene www9r0digenecom is a pioneer in this research and is now selling corn that contains a valuable protein called avidin that is widely used in basic biology research A bushel of corn can provide as much avidin as would normally be isolated from a boxcar full of eggs the usual source of this protein Even better the corn can be stored without spoiling and the avidin can still be isolated in active form Lets look at a few examples from humans where gene regulation can be seen to occur even if all the molecular details are not available One interesting example involves the same enzyme that we called 5 galactosidase in bacteria In humans the enzyme is simply called lactase Since human milk is 7 lactose it is fortunate that almost all babies are born with lactase On aging however many adults lose the ability to digest lactose they become lactose intolerant If these individuals consume lactose they tend to develop gas cramps and even diarrhea the ability of adults to digest lactose is culturedependent In general in dairyoriented cultures adults maintain lactase whereas in nondairy cultures they do not For example among Finns and Swedes 96 of the adults are lactose tolerant while among Eskimos and Asians 8898 of adults are intolerant Adults in seemingly dairyoriented cultures where the lactose is predigested by microbes to make cheese or yogurt also tend to be intolerant It is not clear if synthesis of the enzyme is shut down as a consequence on nonexposure to milk or simply as a function of aging It does not appear to be easy to turn the lactase gene back on once it has been shut off A clear case of developmental regulation can be seen in our genes for hemoglobin the molecule in red blood cells that function to transport oxygen All hemoglobins are made of four polypeptide chains which almost always occur in two pairs The 4 chains of amino acids globins surround the ironcontaining heme group which binds to 02 Adult humans typically have HbA which has two alpha 0L and 2 beta 5 globin chains Tha alpha and beta chains of amino acids come from different genes There are actually 2 adjacent alpha genes on chromosome 16 in man and one beta gene on chromosome 11 We also make a small amount of alpha2delta2 hemoglobin as adults the delta globin gene is beside the beta globin gene These genes are turned on in bone marrow only which is where all of our blood cells originate During most of the gestation period a fetus has fetal hemoglobin or HbF HbF is a combination of alpha2gamma2 gene products There are two gamma genes just before the beta gene on chromosome 11 they differ by just one nucleotide so that one has the amino acid glu where the other has asp The gamma genes are turned on starting at about 6 weeks after conception and begin to turn off before birth During this time the active globin genes are found in the liver Several embryonic forms of hemoglobin HbE are made during the first 6 weeks following conception Active genes are transcribed in the yolk sac during very early development Along with alpha genes there are zeta and epsilon genes eXpressed during this developmental period The various forms of Hb have differing affinities for 02 the embryonic forms function in a relatively low 02 environment and the fetal globins must be able to take 02 from the mothers blood as compared to adult Hb where the O2 is absorbed in the lungs There are a number of genetic defects where not enough hemoglobin is made These can result from defects in the genes or from defective regulation The common name for these diseases is thalassemia If no alpha globin is made the disease is alphaOthalassemia and if some but less than the normal amount is made the disease is called alphathalassemia Beta0 and Beta types of thalassemia also occur In all cases individuals who are heterozygous for one normal gene and one defective allele may have a minor degree of anemia but are essentially normal Heterozygotes are often said to have thalassemia minor while homozygous defective individuals have thalassemia major Ifn0 alpha globin is made the condition is known as hydrops fetalis and is usually lethal within 24 hours after birth When no beta globin is made the condition is called Cooley s anemia or sometimes Mediterranean anemia reflecting the fact that it is relatively common in that area of the world In fact it is the cause of many thousands of childhood deaths per year around the globe Patients have all the problems associated with severe anemia Their system tries to get along with fetal hemoglobin but these genes naturally turn off Very limited O2 transport can be handled by alpha4 globin but soon the only solution is blood transfusions every 23 weeks After some years of transfusions the buildup of iron damages the liver heart and kidneys so that patients seldom survive into their thirties The OMIM entry for 50 thalassemia is lthtt wwwaninlmnih 0v280 entrez dis 0mimc iid1 1 00gt In cases where an HLA match can be found a bone marrow transplant can effectively cure the symptoms Many different defects in the promoter or Bglobin structural gene have been described that lead to deficiency of globin production including deletions new stop codons and changed intron splice signals An interesting observation was made in patients who have a condition called quotHereditary Persistence of Fetal Hemoglobin HPFH These individuals get along relatively well with only fetal hemoglobin being made even as adults In some cases the whole beta gene and the adjacent delta gene have been shown to be entirely missing in these individuals This suggests that there may be some regulatory factor within or between these genes that normally functions to turn off the fetal gammatype globins HPFH also has spurred efforts to try to turn on the fetal Hb genes in adults with thalassemia major One compound that can do so at least for short a time is 5azacytidine a base analog that is rather toxic so can not be used without very careful monitoring The rationale for testing 5azacytidine came from its known ability to cause demethylation of DNA It turns out that many of the Cs in the promoters of genes that are inactive are methylated 5mC but that when the same gene is active the same Cs are not methylated This includes our globin genes At this point it is still very difficult to determine whether methylation is a method for silencing genes or a consequence of the gene already being inactive In any case removing the methyl from SmCs leads to increased transcription Again however just as no method for selectively methylating specific promoters has been identified 5azaC is not specific in removing methyl groups Thus other genes that should remain inactive may be turned on when attempting to treat thalassemia The treatment is used only in patients who can no longer have transfusions In general the models for eukaryotic gene regulation are similar to the lacoperon except that multiple transacting factors may attach to the same promoter some of them stimulate transcription while other tend to decrease transcription Thus transcription of a tissue specific or developmentally eXpressed gene may depend on a delicate balance of multiple interacting factors We know that hormones are key factors in gene regulation in plants and animals There are two types of hormones peptides and steroids As the name implies peptide hormones are chains of amino acids and include molecules such as insulin nerve growth factor human growth hormone and many others Peptide hormones do not enter the target cell but instead interact with receptors found on the cell surface Once they bind a reaction occurs on the inner side of the membrane to release another compound that is referred to as a quotsecond messengerquot In many cases the 2quot 1 messenger is cAMP the same compound that signaled welloff conditions in bacteria to prevent induction of the lac operon if both glucoses and lactose are present The second messenger can then interact with other proteins to cause a phosphate to be added or removed from another protein setting up a cascade of steps eventually leading to active transcription factors that interact directly with DNA Much research is underway to understand these signal transduction pathways Steroid hormones such as estrogens and testosterone can directly enter the cell Inside they still tend to interact with specific receptors in order to regulate transcription Since hormones tend to stimulate mRNA synthesis the target sequence in the promoter that is recognized by the transcription factor hormone amp receptor or second messenger molecule is generally referred to as an enhancer element Many genes also have been found to have interacting quotsilencersquot Where binding of a transcription factor can prevent transcription To be thorough it should be noted that gene eXpression can also be regulated by regulating translation or even after translation by adding glucoses phosphates etc to specific proteins Many proteins such as insulin are first made as larger molecules that require specific cuts by other proteases to become active Likewise some proteins have a much longer quotlifetimequot than others so the rate of turnover can also be important in regulating gene eXpression
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