HSC Biology Module 6 - HSC PDF

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BIOLOGY

MODULE 6

1] Mutation Mutation Inquiry question: How does mutation introduce new alleles into a population? Students: 

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Explain how a range of mutagens operate, including but not limited to: – electromagnetic radiation sources – chemicals – naturally occurring mutagens compare the causes, processes and effects of different types of mutation, including but not limited to: – point mutation – chromosomal mutation distinguish between somatic mutations and germ-line mutations and their effect on an organism (ACSBL082, ACSBL083) assess the significance of ‘coding’ and ‘non-coding’ DNA segments in the process of mutation (ACSBL078) investigate the causes of genetic variation relating to the processes of fertilisation, meiosis and mutation (ACSBL078)

A] Causes of Mutations 1] MUTATION  

Mutation – Permanent alteration of the nucleotide sequence of the DNA or RNA Mutations can occur randomly as errors during cell replication and can affect a single or multiple genes. They occur as a result of mutagens – factors that induce mutation.

2] HOW CARCINOGENS FUNCTION   

Mutagens can also function as carcinogens or cancer-causing agents Neoplasm – an abnormal growth of tissue that forms a tumour Cancer – A malignant tumour with the potential of spread to other parts of the body, caused by the uncontrolled division of abnormal cells in a part of the body

I] Types of Neoplasms Benign Neoplasms These form localized masses but do not transform into cancer  Cells divide uncontrollably, yet not as rapid as those of malignant neoplasm  Organism controls the growth of the neoplasm to certain extent  Cells are contained and do not penetrate the blood and lymph vessels  Because neoplasm grows inside a capsule, it does not destroy surrounding Tissues

Malignant Neoplasms These form masses that invade other tissues and transform into cancer  Cells divide uncontrollably  Growth of the neoplasm; uncontrolled cell growth breaks out of capsule and cells can spread to other tissues  Growing neoplasm destroys surrounding tissues

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3] TYPE OF MUTAGENS 

Mut ag e n–Ar ec h e mi c a lo re ne r gya g e ntt ha tc a u s e samut a t i onc ha n gi n gDNAa ndg e ne t i c i n f or ma t i on

I] Chemical Mutagens  Chemical mutagens can cause a change in DNA that alters the function of proteins and, as a result, cellular processes are impaired during DNA replication  Social drugs: Alcohol, tar in tobacco smoke  Environmental drugs: Agent orange, mustard gas Table: Types of Chemical Mutagens Type Function Intercalating Agents Chemicals that insert themselves into the bonds between base pairs and alter the shape of DNA, leading to frame shift mutations Base Analogues

DNA Reactive Chemicals

Denaminating Agents

Chemicals that are structurally similar enough to that of the nitrogenous bases in DNA that they are incorporated into the DNA sequence during replication instead of the usual bases, meaning tht the DNA no longer functions Chemicals that react directly with DNA, such as reactive oxygen species, which cause breakages and cross-links in DNA strands Deaminating agents can remove an amino group (containing nitrogen) from a base, turning it into a different base. For example, nitrous acid can convert cytosine into uracil.

Example  Acridine orange  Proflavin

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Dimethyl

II] Naturally Occurring Mutagens  Na t ur a l l yo c c ur r i n gmut a g e ns–Ar et h os et h a ta r ep a r toft h ee n vi r o nme nta n dduet op h y s i c a l , c he mi c a lo rbi o l o g i c a la g e nt s Non-Biological Mutagens  Include those that are not living or not produced by living organisms  EXAMPLE: o Metals, such as mercury and cadmium o Chr omi u mc a nbef oundnat ur a l l yi ns e di me n t ar yr o c k s ,a ndi sabl et omodi f yt he c he mi c a lnat u r eo ft h eg uani nebas ea nds ot hatade ni nei spai r e dwi t hmodi fi e d guani n er a t he rt h anc y t os i ne Biological Mutagens  Are living molecules that can cause mutations and cancers by interfering with the functions of oncogenes and tumour-suppressor genes  Are end products of metabolism Table: Types of Biological Mutagens Type Function Viruses  Viruses inserts genetic information into the chromosomes of the host

Example  Hepatitis B Virus  HIV

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Bacteria

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Transposable Elements

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cell, changing nucleotide sequences which disrupt cell function by being responsible for leukemia or neoplasm Viruses may also override the cell’s defence mechanisms

Cause inflammation during which free radicals are produced, causing DNA damage and reducing the efficacy of DNA repair systems, thereby increasing mutation Release of free radicals may lead to oxidative stress, where the individual’s immune response does not function properly to fight off viral infections

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Mycotocins Helicobacter

Are sections of DNA that fragment and relocate or multiply within the genome, Can cause errors in replication and interfere with gene functioning, where multiple copies of same sequence can change chromosome crossover points and cause errors in chromosome duplication

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To xi n spr o duc e db yl i v i n g or g a ni s ms ,s uc ha s :  Al k a l oi d sp r oduc e db y p l a n t ss uc habr a c k e n f e r ns  My c ot o xi n spr oduc e d b yf un gi

HSC 2017 QUESTION 34C ( i )

Out l i net hee ffe c to fg e r ml i nemut a t i onso ns pe c i e s Ge r ml i nemu t a t i onsa r epa s s e do nt ot heoffs p r i n g ,i nc r e a s i n gv a r i a t i oni nt hes pe c i e s .

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Ex pl ai nt hei mpac toft r a ns pos abl eg e ne t i ce l e me nt so nt heg e no me Transposable genetic elements are sections of DNA that fragment and relocate or multiply within the genome. As they move, these elements may carry sections of neighbouring genes. This disrupts the normal base sequence of those genes and are likely to disable that gene – the protein the gene codes for is no longer made. After the TE jumps, the gap in the DNA is unlikely to be repaired, again stopping the effective expression of that gene. Duplication of TEs and new locations of copies can disrupt even more genes It can lead to chromosome elongation which disrupts pairing in mitosis and meiosis and consequently cell division. This causes mutations in the chromosomes and alters the genetic make-up of the individual.

HSC 2012 QUESTION 33D - Compa r eandc ont r a s tt hee ffe c t sofge r ml i nemut a t i o nand t r a ns pos a bl eg e ne t i ce l e me nt sonwhol eor g ani s ms . Germ-line mutations occur in gametes and hence are transmitted to offspring and successive generations. Mutations in somatic cells are not transmitted to successive generations. If the mutation is in the coding portion of the genome, it could affect the phenotype, eg a base substitution that changed a codon and hence the amino acid being expressed could change the final protein and hence the phenotype. To function,

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organisms require narrow parameters. If one protein is wrongly made, one biochemical pathway would malfunction and the organism would not function normally. Transposable genetic elements (TE) are foreign DNA sequences that can change their relative position on the genome and/or replicate themselves within the genome. TEs can disrupt the genome they invade by disrupting the base sequence of a functional gene and are likely to disable that gene – the protein the gene codes for is no longer made. After the TE jumps, the gap in the DNA is unlikely to be repaired, again stopping the effective expression of that gene. Duplication of TEs and new locations of copies can disrupt even more genes. It can lead to chromosome elongation which disrupts pairing in mitosis and meiosis and consequently cell division. TEs are not found in all cells of the organism like germ-line mutations. There is a chance that the coding DNA they might disrupt is not expressed in the cells in which they are located. In this way they may not affect the organism. While, the duplication of TEs and their movement through the genome can be problematic for a particular somatic cell, the abnormal functioning of one somatic cell will not necessarily disrupt the organism.

III] Physical Mutagens  Radiation – The movement of energy through space or materials, which can interrupt cellular process and molecules, damaging DNA  Physical mutagens include:  Particle radiation o The energy that is emitted by fast-moving subatomic particles o Produced by nuclear dission and fusion (nuclear power plants and nuclear weaponery)  Electromagnetic radiation o Is a radiant energy emitted by electromagnetic field o Exists on a spectrum, split into low frequency and high frequency radiation; Includes radio waves, microwaves, infrared rays, light, ultraviolet, x ray and gamma radiation o Differs from particle radiation as it does not have mass Two Types of Radiation: Ionizing and Non-ioninsing Type Summary Ionizing Radiation  Includes the shorter wavelengths of UV radiation, x-rays, gamma (γ) rays, alpha (α) particles and (β) particles  The shorter the wavelength and the higher energy of ionizing radiation = Dangerous as it split off electrons, causing damage in cells

Effect Can damage DNA in a number of ways:  Directly: Cause the ionisation of molecules in the DNA, resulting in the sugar-phosphate backbone breaking, or a nitrogenous base changing so that it no longer pairs with its complementary base.  Indirectly: Ionise other molecules in the cell, sometimes producing free radicals which can interact with other molecules to form compounds (such as H2O2) which can damage DNA.  Short term effects of acute radiation syndrome, and long term is cancer

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Non-Ionising Radiation

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Exists at the low frequency end of the electromagnetic spectrum: infrared light, microwaves, radio waves, visible light and ultraviolet spectrum

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Mutagen Effect on DNA

Example of disorder caused by mutation

UV Radiation High energy state of radiation makes it able to disrupt DNA’s hydrogen bonds, so canc ause changes to DNA structure and nucleotide sequences. UV light may be particularly damaging due to the formation of pyrimidine dimers. Melanoma (skin cancer)

Not associated with damage to DNA or with acute radiation syndrome The level of energy emitted is simply too low to have an effect on the chemical bonds of DNA or to cause cellular damage. This is why energy emitted by mobile phone usage is not dangerous or carcinogenic. Can cause susceptible materials to heat up. This why you can use microwaves to heat food as it cause materials to warm without altering the chemical structure of food

Viruses Viruses replicated by inserting themselves into host DNA, changing nucletodite sequences which disrupt cell function. Viral infections may lead to lasting mutational changes.

Cervical cancer

A] Types of Mutation 1] POINT MUTATIONS Definition

Causes

Processes

Effects

Point Mutation Mutation involving a single nucleotide base in single-stranded RNA or nucletotide pair in doubltstranded DNA Change of one nucletotide base in DNA during replication before mitosis or meiosis; may result from exposure to mutagens (electromagnetic, chemical or natural) Substitution, deletion or insertion of a nucleotide, deletions and insertions cause a frameshift as they alter the sequence of codons in mRNA that transcribes the mutated DNA Point mutations can occur in ‘coding’ or ‘noncoding’ parts of the DNA.

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MODULE 6 Mutations in ‘non-docidng DNA may influence gene regulation’ Substitution mutations in ‘coding’ DNA may result in no alteration of the amino acid sequence in the resultant polypeptide (i.e. a silent mutation), or the change of one amino acid that results in an alteration of function of the polypeptide (missense mutation). If the substitute change results in the production of a stop codon, the result will probably be a failure in the production of the polypeptide (i.e. non-sense mutation). Insertions and deletions that cause frameships in the mRNA generally result in non-sense mutations that prevent the formation of functional polypeptides.

I] Base Substitution  Apoi n tmut a t i oni nwhi c honenuc l e o t i dei sr e pl a c e db yo rc h a n g e dt oa not he r .  Ca us e db yc op yi n ge r r oro rbe c a u s eade a mi na t i n gmu t a g e nr e mo v e sa na mi nogr oupf r o maba s e , changing it into a different base.

Typeo fSubs t i t ut i onMut a t i o n Silent

Mi s s e nc e

No ns e ns e

Summar y  Occurs when a substitution results in a new codon that still codes for the same amino acid. Since the amino acid is same as original one, it does not effect the structure and composition of protein, or phenotype.  For example. If the last nucleotide i nt h es e q ue nc ei ss ubs t i t ut e df o r a n yot he r , t hec od onwi l ls t i l lc o de a ndwi l lnoth a v ea n ye ffe c tonfina l pol ype p t i d e  Whe ns ubs t i t u t i onmu t a t i o nsr e s ul ti nt he g e ne r a t i onofac odont ha ts pe c i fie sa di ffe r e nta mi noa c i da ndhe n c el e a dst oa di ffe r e ntpol yp e pt i des e que nc e .  Fore xa mp l e , nor ma la nds i c kc e l l ha e mo gbl i n sd i ffe rduet omi s s e n s e mut a t i oni nwhi c ht hedi s t or t e d s ha peofs i c kl e c e l la ffe c t st he o v e r a l ls h a peofr e dbl o odc e l l s , c a u s i n gt he mt obe c omes i c kl e s ha pe d  Aba s es ubs t i t ut i o nt ha tc h a n g e sac odonf o r a na mi noa c i di n t oas t o pc odon.Thes t op c o donc a us e st r a n s l a t i o nt os t ops h or t e n i n g t hepol ype pt i c ec ha n g e , a ndi nmo s tc a s e s c r e a t e san onf unc t i ona lpr ot e i n  If the substitute change results in the production of a stop codon which cause translation to stop and shortens the polypeptide chain, resulting be a failure in

BIOLOGY

MODULE 6 the production of the polypeptide (i.e. nonsense mutation).

I I ]Fr a me s hi f tMut a t i on  Oc c ur swhe nnu c l e o t i d e sa r ei ns e r t e dorde l e t e dc h a n gi n gt h emu l t i pl eo ft hr e eo r de rc a us i n ga n i n c or r e c tgr oup i n goft henuc l e o t i d e si nt oc odo ns  Re s ul t i n gpo l ype pt i dedi ffe r e ntors h or t e r=Los soff unc t i ona lpr ot e i n

3] STRUCTURAL CHROMOSOMAL MUTATIONS Definition Causes

Processes

Effects

Chromosomal Mutation A chromosome rearrangement resulting in a change in chromosome structure or number Problems in chromosome behavior during meisosis, mitosis or the action of mutagens such as ionizing electromagnetic radiation (glamma rays, x-rays and some ultra violet rays)  Duplication - Involves the replication of a section of a chromosome that results in multiple copies of the same genes on that chromosome.  Deletion – A loss of nucletodite pairs in a gene sequence and casues a frame shift mutation  Inversion – A segment of chromosome breaks off, changes orientation by 180 and is reinserted into the chromosome  Translocation – a segment of chromosome breaks off and joins a chromosome on another homologous pair  Aneuploidy (an entire extra or missing chromosome) results from non-disjunction of homologous chromosomes during cell division, e.g. trisomy  Polyploidy – more than two haploid sets of chromosomes, e.g. triploidy  When they occur in germ-like cells they may be fatal or result in severe disorders of offspring e.g. Dunenne muscular dystrophy, Down syndrome or XX male inherit.  Triploid have three copies of chromosomes. If this result in an uneven number of chromosomes then pairing of homologous chromosomes becomes diffulct during meiosis meaning haploid gametes cannot form properly and sterility

4] CHROMOSOMAL NUMBER MUTATIONS  

Amut a t i oni nwhi c hac e l lc o nt a i n s( who l e )e xt r aormi s s i n gc hr omo s ome s . Two types: Aneuploidy and Polyploidy

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I] Monoploidy  Loss of an entire set of chromsomes II] Aneuploidy  Cell or organism has more than or less than two copies of a particular chromosome  Caused by non-disjunction, when homologous chromosomes do not separate correctly during Meiosis or if sister chromatids fail to separate during meiosis II  As a result, one gamete receives two of the same type of chromosome and another gamete receives no copy.  After fertilisation, the gamete with no copy of sex chromosome has joined with a normal gamete to produce an individual with only one sex chromosome.  E.g. Trisomy (Down syndrome) has an extra copy of chromsomse 21/ three of one type of chromosome I I I ]Pol ypl o i dy/ Tr i pl oi d  Ce l loror g a n i s msha smo r et ha nt woc o pi e sofe v e r yc hr o mos ome=or g a ni s mha st hr e eormor e c o mpl e t es e t so fc hr oms oe s  Ca us e db yn ondi s j unc t i on,whe n:  Fa i l ur eo fc hr omo s omes e pa r a t i ondur i n gme i os i s  Chr omo s o me sdi vi dei nmi t o s i sbutt hec e l ldoe snot  Fe r t i l i s a t i ono fa ne g gb ymor et ha nones pe r m  Ge nomeofas i n gl es pe c i e sdupl i c a t e sdur i n gc e l lc y c l e

HSC 2010 Que s t i on3 3-Co ns t r uc tat abl et oi de nt i f yho we a c hoft hef ol l o wi ngmut at i o nsaffe c t s3 c hr omos o menumbe ri nanor g ani s m:Tr i s omy ,Pol ypl oi dy ,Bas eSubs t i t ut i o n.

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B] Mutations in Non-Coding Regions

BIOLOGY Definition

Mutations in a Region of DNA

MODULE 6 Coding DNA  Is transcribed and translated to make a protein in gene expression  Exon – Coding DNA in eukaryotic DNA that are involved in gene expression

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Mutations within coding DNA are more likely to impair the correct formation of proteins and therefore the phenotype of the individual, as genes in this DNA encode for proteins. DNA point mutations can affect polypeptide synthesis because there is a substitution of nitrogenous bases, resulting in a different amino acid being included in the polypeptie.An insertion or deletion of a nitrogenous base in DNA causes a frameshift so that all the polypeptide synthesis ‘downstrat’ of the mutation is affected If a point mutation occurs in coding DNA one change can have dramatic effects, e.g. sickle cells are caused by changing one T to an A Can effect gene splicing = change function or levels of protein product

Significance

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Mutations of genes becomes serious when proteins involved in DNA repair are affected. These enzymes are responsible for correcting errors in the sequences of bases and if affected, will increase the chance and rate of mutations arising from errors in replication Mutations in tumour suppressor genes may be carcinogenic and mutations that trigger protooncognese can reduce cell death by promoting cell division, which can be fatalistic to an organisms survivial

Non-Coding DNA  DNA that does not code for proteins  This is either an intron or flanking region of a gene.  Introns – Non-coding sequences of DNA separating one exon (coding region) of a gene from another

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DNA mutation in the non-coding section of DNA may have varied impacts on polypeptide production. If the ‘non-coding’ mutation occurs in the part of DNA involved in controlling polypeptide synthesis, a polypeptide may be not produced that would have normally been made.

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