15.1 The Nature of Genes
15.2 The Genetic Code
15.3 Prokaryotic Transcription
15.4 Eukaryotic Transcription
15.5 Eukaryotic pre-mRNA Splicing
15.6 The Structure of tRNA and Ribosomes
15.7 The Process of Translation
15.8 Summarizing Gene Expression
15.9 Mutation: Altered Genes
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| 332034277 | Garrod concluded that inherited disorders can involve specific enzymes. | Garrod found that alkaptonuria is due to an altered enzyme. | |
| 332034278 | Beadle and Tatum showed that genes specify enzymes. | Neurospora mutants unable to synthesize arginine were found to lack specific enzymes. Beadle and Tatum advanced the "one gene/one polypeptide" hypothesis. | |
| 332034279 | The central dogma describes information flow in cells as DNA to RNA to protein. | We call the DNA strand copied to mRNA the template (antisense) strand; the other the coding (sense) strand. |  |
| 332034280 | Transcription makes an RNA copy of DNA. | As per the central dogma, in transcription a DNA template is used to make RNA. | |
| 332034281 | Translation uses information in RNA to synthesize proteins. | An adapter molecule, tRNA, is required to connect the information in mRNA into the sequence of amino acids. | |
| 332034282 | RNA has multiple roles in gene expression. | There are many kinds of RNA: mRNA, rRNA, tRNA, snRNA, SRP RNA, miRNAs. | |
| 332034283 | The code is read in groups of three. | Crick and Brenner showed that the code is non-overlapping and is read in groups of three. This finding established the concept of reading frame. | |
| 332034284 | Nirenberg and others deciphered the code. | A codon consists of 3 nucleotides, so there are 64 possible codons. Three codons signal "stop," and one codon signals "start" and also encodes methionine. Thus 61 codons encode the 20 amino acids. | |
| 332034285 | The code is degenerate but specific. | Many amino acids have more than one codon, but each codon specifies only a single amino acid. | |
| 332034286 | The code is practically universal, but not quite. | In some mitochondrial and protist genomes, a STOP codon is read as an amino acid; otherwise the code is universal. | |
| 332034287 | Prokaryotes have a single RNA polymerase. | Prokaryotic RNA polymerase exists in two forms: core polymerase, which can synthesize mRNA; and holoenzyme, core plus σ factor, which can accurately initiate synthesis. |  |
| 332034288 | Initiation occurs at promoters. | Initiation requires a start site and a promoter. The promoter is upstream of the start site, and binding of RNA polymerase holoenzyme to its -35 region positions the polymerase properly. | |
| 332034289 | Elongation adds successive nucleotides. | Transcription proceeds in the 5'-to-3' direction. The transcription bubble contains RNA polymerase, the locally unwound DNA template, and the growing mRNA transcript. |  |
| 332034290 | Termination occurs at specific sites. | Terminators consist of complementary sequences that form a double- stranded hairpin loop where the polymerase pauses. |  |
| 332034291 | Prokaryotic transcription is coupled to translation. | Translation begins while mRNAs are still being transcribed. | |
| 332034292 | Eukaryotes have three RNA polymerases. | RNA polymerase I transcribes rRNA; polymerase II transcribes mRNA and some snRNAs; polymerase III transcribes tRNA. | |
| 332034293 | Each polymerase has its own promoter. | I promotors are species-specific. II promotors are rather complex. Most III promotors are within the genes themselves. | |
| 332034294 | Initiation and termination differ from that in prokaryotes. | Unlike prokaryotic promoters, RNA polymerase II promoters require a host of transcription factors. Although termination sites exist, the end of the mRNA is modified after transcription. | |
| 332034295 | Eukaryotic transcripts are modified. | After transcription, a methyl-GTP cap is added to the 5' end of the transcript. A poly-A tail is added to the 3' end. Noncoding internal regions are also removed by splicing. | |
| 332034296 | Eukaryotic genes may contain interruptions. | Coding DNA (an exon) is interrupted by noncoding introns. These introns are removed by splicing. | |
| 332034297 | The spliceosome is the splicing organelle. | snRNPs recognize intron-exon junctions and recruit spliceosomes. The spliceosome ultimately joins the 3' end of the first exon to the 5' end of the next exon. | |
| 332034298 | Splicing can produce multiple transcripts from the same gene. | This is due to alternative splicing. | |
| 332034299 | Aminoacyl-tRNA synthetases attach amino acids to tRNA. | The tRNA charging reaction attaches the carboxyl terminus of an amino acid to the 3' end of the correct tRNA. | |
| 332034300 | The ribosome has multiple tRNA-binding sites. | A charged tRNA first binds to the A site, then moves to the P site where its amino acid is bonded to the peptide chain, and finally, without its amino acid, moves to the E site from which it is released. | |
| 332034301 | The ribosome has both decoding and enzymatic functions. | Ribosomes hold tRNAs and mRNA in position for a ribosomal enzyme to form peptide bonds. | |
| 332034302 | Initiation requires accessory factors. | In prokaryotes, initiation-complex formation is aided by the ribosome-binding sequence (RBS) of mRNA, complementary to a small subunit. Eukaryotes use the 5' cap for the same function. | |
| 332034303 | Elongation adds successive amino acids. | As the ribosome moves along the mRNA, new amino acids from charged tRNAs are added to the growing peptide. | |
| 332034304 | Termination requires accessory factors. | Stop codons are recognized by termination factors. | |
| 332034305 | Proteins may be targeted to the ER. | In eukaryotes, proteins with a signal sequence in their amino terminus bind to the SRP, and this complex docks on the ER. | |
| 332034306 | Point mutations affect a single site in the DNA. | Base substitutions exchange one base for another, and frameshift mutations involve the addition or deletion of a base. Triplet repeat expansion mutations can cause genetic diseases. | |
| 332034307 | Chromosomal mutations change the structure of chromosomes. | Chromosomal mutations include additions, deletions, inversions, or translocations. | |
| 332034308 | Mutations are the starting point of evolution. | If no changes occurred in genomes over time, then there could be no evolution. Too much change, however, is harmful to the individual with a greatly altered genome. Thus a delicate bal- ance must exist between the amount of new variation that arises in a species and the health of individuals in the species. | |
| 332034309 | Our view of the nature of genes has changed with new information. | With additional information, our understanding of how genes work adapts. | |
| 332626487 | Garrod concluded that inherited disorders can involve specific enzymes | - discovered that some diseases were the result of recessive alleles and were hereditary - some hereditary diseases appeared to make patients unable to make certain enzymes | |
| 332626488 | Beadle, Tatum, and Neurospora crassa | - Neurospora crassa a bread mold - exposed to radiation to damage their DNA - expected mutations that would damage ability to synthesize necessary compounds - placed on minimal media - isolated and identified many nutritional mutants - came up with one-gene/one-polypeptide hypothesis | |
| 332626489 | Nutritional Mutations | Mutations that affect an organism's ability to synthesize certain nutrients and thus must have them supplemented dietarily. | |
| 332626490 | One-gene/One-polypeptide hypothesis | The hypothesis that one gene codes for one protein. Overly simplistic in actuality. | |
| 332626491 | The Central Dogma (old version) | DNA → RNA → protein | |
| 332626492 | Transcription | The DNA-to-RNA step in the Central Dogma. Takes place in the nucleus (euks) or cytoplasm (proks). | |
| 332626493 | Translation | The RNA-to-protein step in the Central Dogma. Takes place in the cytoplasm in the ribosome. | |
| 332626494 | Retroviruses | A class of viruses that can convert their RNA genome into a DNA copy using the viral enzyme reverse transcriptase, thus violating the Central Dogma and forcing a revision. | |
| 332626495 | The Central Dogma (new version) |  | |
| 332626496 | Template Strand | The strand that is copied during transcription. | |
| 332626497 | Coding Strand | The strand of DNA not used as a template during transcription; it has the same sequence as the RNA transcript (since the template strand has the complementary sequence). | |
| 332626498 | Sense/Antisense | Sense = same sequence (but with different bases for RNA/DNA)(the template sequence). The template strand would be the "Antisense" strand. | |
| 332626499 | Messenger RNA mRNA | - the RNA transcript used to direct the synthesis of polypeptides - its name reflects its use by the cell to carry the DNA message to the ribosome for processing. | |
| 332626500 | Transfer RNA tRNA | - the RNA that is used to "translate" between the language of nucleotides and the language of amino acids during translation - has amino acids covalently attached to one end - has an anticodon that can base-pair with an mRNA on the other end | |
| 332626501 | Ribosomal RNA rRNA | - the class of RNA found in ribosomes; critical to its function - multiple forms of rRNA - found in both ribosomal subunits | |
| 332626502 | Small Nuclear RNA snRNA | - part of the machinery that is involved in nuclear processing of euk "pre-mRNA" | |
| 332626503 | Signal Recognition Particle SRP RNA | - mediates synthesis of proteins by ribosomes on the rough ER - contains both RNA and proteins | |
| 332626504 | Micro-RNA miRNA | - short RNAs - relatively new - major class of regulatory molecules | |
| 332626505 | Codons | - 3-bp blocks - 20 proteins; 2-bp blocks not enough (4²), need 3 - each corresponds to an amino acid in an encoded protein | |
| 332626506 | Crick, Brenner, and the spacing of codons | - Crick+co. used a chemical to create single-base insertions/deletions - either would result in loss of function - same with 2-base alterations - end discovery: 3-base codons, no spacing - importance of reading frame | |
| 332626507 | Reading Frame | How the code is read. | |
| 332626508 | Frameshift Mutations | Mutations that shift the reading frame. | |
| 332626509 | Determining what codons coded what | - Nirenberg artificially synthesized UUU, others - could infer bases, but not order - triple-binding assey allowed them to ID 54/64 - Khorana used organic synthesis to produce artificial RNA molecules of defined sequence, det. the rest | |
| 332626510 | Stop Codons | - three codons that signal for protein synthesis to end - UAA, UGA, UAG | |
| 332626511 | Start Codon | - a single codon that signals for protein synthesis to start - AUG - also codes for methionine (Met) | |
| 332626512 | Degenerate | - some amino acids are specified by more than one codon - HOWEVER, a single codon would never code for more than one amino acid | |
| 332626513 | Degeneracy is not uniform | - some animo acids have only one codon, some have up to six - the degenerate base usually occurs at position 3 of a codon | |
| 332626514 | The code is practically universal, but not quite | - in mitochondrial genes: the stop codon UGA was read as the AA tryptophan; AUA read as methionine and not isoleucine; and AGA and AGG read as stop codons rather than arginine. - differences also found in chloroplasts, ciliates(proks) | |
| 332626515 | RNA Polymerase | - in prokaryotes, exists in two forms: the core polymerase and the holoenzyme - used to synthesize RNA from a DNA polymerase - covers a region of about 74 bp, but only unwinds about 12-14 | |
| 332626516 | Core Polymerase | - can synthesize RNA using a DNA template, but cannot initiate synthesis accurately - composed of four subunits - two identical α subunits that hold the complex together, can find to regulatory molecules - one β subunit, one β' subunit, that form the active site, bind to the DNA template and ribonucleotide triphosphate precursors | |
| 332626517 | Holoenzyme | - can initiate synthesis accurately - contains all subunits of the core polymerase as well as a σ subunit - σ subunit recognizes -35 sequence in promotor and positions the RNA polymerase correctly - unwinds the DNA helix at the -10 site - does not require a primer to work | |
| 332626518 | Promotor | - required for the accurate initiate of transcription - a site that forms a recognition and binding site for the RNA polymerase - short sequence upstream of the start site, not transcribed by the polymerase - two 6-base sequences common to bacterial promotors, -35 and -10 - provides the promotor asymmetry, indicating not only the site of initiation but also direction of transcription | |
| 332626519 | Start Site | - required for the accurate initiate of transcription - the actual site where transcription starts | |
| 332626520 | Terminator | - required for the accurate initiate of transcription - a signal to end transcription | |
| 332626521 | Transcription Unit | - the region from promotor to termination | |
| 332626522 | Upstream/Downstream | - a method of determining positions of things on the DNA relative to the start site - first base transcribed (downstream) is called +1 - bases upstream have negative numbers; -1 | |
| 332626523 | Initiation | - occurs at a promotor - DNA unwound with an RNA polymerase - transcription usually starts with ATP or GTP at the 5' end of the chain, which grows as bases are added - σ factor no longer needed after initiation, snaps off | |
| 332626524 | Clearance/Escape | - process of leaving the promotor - requires enzyme to change shape for synthesis to be more efficient | |
| 332626525 | Transcription Bubble | - region containing the RNA polymerase, DNA template, and growing RNA transcript - within the bubble, first 9 bases of newly synthesized RNA strand temporarily form a helix w/ template DNA - stabilizes positioning of 3' end of RNA so it can interact with incoming base - enzyme covers about 50 bp of DNA around the bubble - moves down the bacterial DNA ~50 nts/sec - transcribed DNA rewound as it leaves the bubble | |
| 332626526 | Termination | - marked by terminator sequences - causes the formation of phosphodiester bonds to cease, the RNA-DNA hybrid within the transcription bubble to dissociate, the RNA polymerase to release the DNA, and the DNA within the transcription bubble to rewind - also requires protein factors to aid in termination | |
| 332626527 | Hairpin | - found in the simplest terminator, consisting of a series of GC bps followed by a series of AT bps - a double-stranded structure in the GC region - followed by 4+ U rnts - formation of hairpin causes RNA polymerase to pause, placing it directly over the Us, the pairing is weak and so the RNA strand dissociates | |
| 332626528 | Prokaryotic transcription is coupled to translation | - mRNA produced by transcription begins to be translated before transcription is finished (coupling) - as soon as a 5' end of the mRNA becomes available, ribosomes are loaded on to begin translation - cannot occur in euks b/c transcription is in nucleus, translation in cytoplasm | |
| 332626529 | Operon | - mRNA produced in proks may contain multiple genes - a grouping of functionally related genes - single transcription unit that encodes multiple enzymes necessary for a biochemical pathway - by clustering genes by function, they can be regulated together | |
| 332626530 | How eukaryotic transcription differs from prokaryotic transcription | - euks have three RNA polymerases differing in structure, function; proks only have one - in nucleus vs. in cytoplasm - euks use transcription factors - euk termination sites not as well defined as prok terminators - euk mRNA end not formed by RNA polymerase II b/c of post-transcription modification | |
| 332626531 | RNA Polymerase I | - found in eykaryotes only - transcribes rRNA | |
| 332626532 | RNA Polymerase II | - found in eykaryotes only - transcribes mRNA, some small nuclear RNAs | |
| 332626533 | RNA Polymerase III | - found in eykaryotes only - transcribes tRNA, some other small RNAs | |
| 332626534 | Eukaryotic RNA polymerase promotors | - three dif polymerases wach need their own promotors - RNA polymerase I promotors specific to each species - RNA polymerase II promotors the most complex, diverse; TATA box a component of most - RNA Polymerase III promotors within the gene itself | |
| 332626535 | TATA Box | - a sequence found in RNA polymerase II promotors upstream of the start site - similar to the prok -10 sequence - part of a "core promotor" composed of different elements | |
| 332626536 | Transcription Factors | - proteins necessary in transcription function - used by RNA polymerase II to form an initiation complex at the promotor | |
| 332626537 | Primary Transcript | - the RNA synthesized by RNA polymerase II - unmodified | |
| 332626538 | Mature mRNA | - the final processed form of mRNA - modified with a 5' cap and 3' poly-A tail | |
| 332626539 | 5' Cap | - first base in a transcript usually A or G - modified with addition of a GTP to the 5' PO₄ group - only 5'-to'5' bond found in nucleic acids - G in GTP modified by addition of methyl group; methyl-G cap - added when transcription is still in progress - protects 5' end of mRMA from degredation - involved in translation initiation | |
| 332626540 | 3' Poly-A Tail | - euk transcript cleaved downstream of a specific site (AAUAAA) prior to termination site for transcription - series of A residues, the 3' poly-A tail, added after the cleavage by poly-A polymerase - 100-200 A's long - not created by RNA polymerase II - not the end of the transcript - protects mRNAs from degredation | |
| 332626541 | Poly-A Polymerase | Part of a complex that recognizes the poly-A site, cleaves the transcript, then adds As to the end. | |
| 332626542 | Colinear | When the sequence of bases in the genes corresponds to the sequence of amino acids in the protein. | |
| 332626543 | Introns | - noncoding DNA that does not appear in mRNA - "intervening sequences" - majority of most eukaryotic sequences - prokaryotes do not have - all begin with same 2-base sequence, end in another 2-base sequence, contain a conserved A nt called the branch point | |
| 332626544 | Exons | - coding regions on the DNA - "expressed sequences" - minority of most eukaryotic sequences | |
| 332626545 | Pre-mRNA Splicing | - how euks deal with introns - occurs in nucleus prior to export of mRNA to cytoplasm | |
| 332626546 | Spliceosome | - comprised of clustered snRNPs and other proteins - responsible for the splicing of introns - recognizes 2-base sequences that tag introns for removal | |
| 332626547 | Small Nuclear Ribonucleoprotein Particles snRNPs | - complexes composed of snRNA and protein - "snerps snip" | |
| 332626548 | Splicing Process | - occurs during trascription - snRnA forms base-pairs with 5' end, at branch site - associate w/ other factors to form spliceosome - cleavage of the 5' end - becomes attached to a 2' OH of branch point A - forms a branched structure called a lariat (noose) - 3' end of first exon then used to displace 3' end of intron, joining exons and releasing intron as lariat | |
| 332626549 | Distribution of introns | - fairly random, no rules govern - exon shuffling hypothesis, that introns the leftovers of functional domains shuffling over time; unsure - possible that introns have no single origin and cannot be explained by a single hypothesis | |
| 332626550 | Alternative Splicing | - the inclusion of different sets of exons - important to an organism's function; ~15% of known human genetic disorders from altered splicing - allows for more proteins to be coded per area | |
| 334521428 | Aminoacyl-tRNA Synthetase | - an enzyme that attaches an amino acid to the tRNA with the correct anticodon - one enzyme for each of the 20 amino acids - but each recognizes more than one tRNA | |
| 334521429 | Acceptor Stem | - one of the functional ends of a transfer RNA - attaches to the amino acid - at the 3' end of the tRNA; always ends in 5' CCA 3'. | |
| 334521430 | Anticodon Loop | - one of the functional ends of a transfer RNA - complementary to the codon - middle "leaf" in tRNA clover | |
| 334521431 | Transfer RNA | - a bifunctional molecule able to interact with both mRNA and amino acids - structure is highly conserved in all living systems - forms a cloverleaf structure based on intramolecular base-pairing that produces dbl-stranded regions - primary structure folded in space to form an L-shaped molecule w/ two functional ends: acceptor stem and anticodon loop | |
| 334521432 | Charging Reaction | - the reaction catalyzed by the enzymes that adds amino acids to tRNAs - joins the acceptor stem to the C-terminus of the amino acid | |
| 334521433 | Ribosomes cannot "proofread" the amino acids attached to tRNA | - they only ensure the codon/anticodon pairing is correct - takes the attached amino acid for granted - thus, it is vital that the charging reaction is done correctly | |
| 334521434 | Terminology for tRNAs | [what the tRNA is charged with]-tRNA^[what the tRNA is supposed to be charged with] ex. X-tRNA^X = supposed to be charged with X amino acid, is charged with X amino acid tRNA^Y = supposed to be charged with Y, not charged yet Y-tRNA^X = supposed to be charged with X, actually charged with Y | |
| 334521435 | The bacterial ribosome has 3 binding sites | - the P site (peptidyl) binrds to the tRNA attached to the growing peptide chain - the A site (aminoacyl) binds to the tRNA carrying the next amino acid to be added - the E site (exit) binds to the tRNA carrying the next amino acid to be added - 5'-E-A-P-3' | |
| 334521436 | The process of the charging reaction | - amino acid reacts with ATP, uses resulting AMP to bind to aminoacyl-tRNA synthetase - tRNA then binds to the enzyme - amino acid transferred to the tRNA, producing a charged tRNA molecule and an AMP | |
| 334521437 | Peptidyl Transferase | - resides in the ribosome's large subunit - necessary for peptide bond formation - is an rRNA | |
| 334521438 | The ribosome bas both decoding and enzymatic functions | - decodes the transcribed message - forms peptide bonds - transcribing function mainly from small subunit of ribosome - peptide bond formation requires peptidyl transferase from the large subunit | |
| 334521439 | Ribosomes are rRNAs held in place by proteins | - comprised of two subunits, one large, one small - faces of subunits lined with rRNA which do the majority of interaction with mRNA, tRNA, and amino acids | |
| 334521440 | The overall process of translation | - mRNA is threaded through a ribosome - tRNAs carrying amino acids bind to the ribosome - tRNAs and mRNAs interact codon-to-anticodon - ribosome and tRNAs position amino acids to form peptide bonds and a growing polypeptide | |
| 334521441 | Translation initiation requires accessory factors, initiation complex | - start codon is AUG/Met; ribosome usually uses the first it meets to signal translation start - in prokaryotes, initiation complex includes tRNA^fMet, small ribosomal subunit, mRNA strand - small subunit fits onto mRNA due to help from RBSes - after complex of mRNA, initiator tRNA, and small ribosomal subunit, large subunit is added - initiator tRNA bound to P site with A site empty - translation can thus begin | |
| 334521442 | RBS | - ribosome-binding sequence - on prokaryotes' initiation complex - helps to position the small subunit onto the mRNA - conserved - on the 5' end of the mRNA - complementary to the 3' end of a small subunit rRNA | |
| 334521443 | Initiation Complex | - in prokaryotes, initiation complex includes special initiator tRNA molecule charged with a chemically modified Met; tRNA = tRNA^fMet - initiation complex also includes small ribosomal subunit, mRNA strand - small subunit fits onto mRNA due to help from RBSes | |
| 334521444 | Eukaryotic Initiation | - differs from proks in 2 ways - initiating amino acid is Met, not fMet - initiation complex much more complicated, has nine or more protein factors, many of several subunits - euk mRNAs also lack an RBS; small subunit binds to mRNA initially by binding to the 5' cap instead | |
| 334521445 | Elongation adds successive amino acids | - with initiation started, second charged tRNA can be brought to the ribosome, bound to the A site - requires elongation factor called EF-Tu; binds to charged tRNA, GTP - peptide bond forms btw amino acid of initiator tRNA and the newly arrived charged tRNA - btw N end of A-site and C end of P-site amino acid | |
| 334521446 | Elongation Cycle | - matching tRNA anticodon w/ mRNA codon - each newly charged tRNA has EF-Tu, GTP - after binding, GTP hydrolyzed and EF-Tu-GDP dissociates; step thought to incr. accuracy of translat - peptidyl transferase located in large subunit catalyzes formation of a peptide bond - P-site tRNA left uncharged - ribosome moves relative to mRNA and tRNAs; codons moved along; uncharged tRNA ejected | |
| 334521447 | Translocation | - moving the mRNA along so that the tRNAs will be in the right sites - takes a GTP as energy - not the ribosome moving, but the mRNA being pulled through the ribosome and along | |
| 334521448 | Wobble Pairing | - fewer tRNAs than codons b/x pairings btw 3' base of codon and 5' base of anticodon less stringent than normal - in some tRNAs, presence of modified bases with less accurate pairing in 5' of anticodon enhances flexibility - effect called "wobble pairin" b/c the tRNAs can "wobble" on the mRNA, a single tRNA can "read" more than one codon in the mRNA | |
| 334521449 | Termination requires accessory factors | - elongation continues until chain-terminating stop codon is reached - stop codons do not bind to a tRNA; instead, bind to release factors, w/ no charging - confused, the peptidyl transferase hands off the polypeptide chain to nothing, which releases it - with nothing else, ribosome dissembles | |
| 334521450 | In euks, translation can occur where? | - in the cytoplasm or on the RER - proteins translated on the RER are targeted there based on their own initial amino acid sequence - ribosomes found on RER are actively translating and not permanently bound to RER | |
| 334521451 | Signal Sequence | - a short short sequence - polypeptide that begins with signal sequence specifically recognized and bound by cytoplasmic complex of proteins called the signal recognition particle - this complex is in turn recognized by receptor protein in ER membrane - process of binding of the two called docking - ribosome not actually bound to ER itself, but the newly synthesized protein entering the ER ties it to | |
| 334521452 | Once within the ER cisternal space, or lumen, the newly synthesized protein... | ... can be modified by addition of sugars (glycosylation) and transported by vesicles to the Golgi apparatus - beginning of protein-trafficking pathway | |
| 334521453 | Base Substitution Mutation | - the substitution of one base pair for another in DNA - may be silent | |
| 334521454 | Missense Mutation | - when a base sequence mutation changes an amino acid in a protein - falls into two categories: transitions, transversions - transitions do not change the type of bases in base pair, i.e. pyrimidine for pyrimidine - transversions does change type of base pairs | |
| 334521455 | Nonsense Mutation | - a base substitution mutation that changes the codon to a stop codon | |
| 334521456 | Frameshift Mutations | - a change in the reading frame - affects pretty much everything after the mutation | |
| 334521457 | Triple Repeat Expansion Mutations | - a mutation where a triplet sequence of DNA is repeated and the repeat is expanded in the disease allele relative to the normal allele - can occur in exons or introns | |
| 334521458 | Chromosomal Mutations | - mutations that are not just point, but can alter the structure of the chromosome itself - consist of deletions, duplications, inversions, translocatons | |
| 334521459 | Chromosomal Mutations Deletion | - the loss of a portion of a chromosome - frameshifts can be caused by one or more small deletions, but if larger, whole regions of the chromosome may also be lost | |
| 334521460 | Chromosomal Mutations Duplications | - duplication of the region of a chromosome may or may not lead to phenotypic consequences - effects depend on location of the "breakpoints" where the duplication occurred; if not within a gene, may have no effect - if duplication occurs next to original region, termed a tandem duplication - important in the evolution of families of related genes | |
| 334521461 | Chromosomal Mutations Inversions | - when a segment of chromosome is broken in 2 places, reversed, put back together - may have no effect if not within a gene | |
| 334521462 | Chromosomal Mutations Translocations | - when a piece of a chromosome is broken off and joined to another chromosome - can change the expression of genes in the region involved |
