Karteikarten
p506- 17 (Chapter 19, genetics of living systems)
Karten in diesem Stapel (93)
- 1mutation?a change in the sequence of bases in DNA.
a change in the sequence of bases in DNA
a change in the sequence of bases in DNA - 2Protein synthesis can be disrupted if the mutation occurs within a gene. a point mutation =if only 1 nucleotide is affected
- 3The substitution of 1 nucleotide changes the codon in which it occurs. If the new codon codes for a dif aa, this will lead to achange in the primary structure of the protein.
- 4The degenerate nature of the genetic code may mean that the new codon still codes for the same aa, leading to no change in the protein synthesised. what will determine the impact of the new aa on the function of the protein?the position + involvement of the aa in R group interactions within the protein. E.g. if the protein is an EZ + the aa plays an important role within the active site, then the protein may no longer act as a biological catalyst.
- 5The insertion or deletion of a nucleotide, or nucleotides, leads to aframeshift mutation.
- 6The triplet code means that sequences of bases are transcribed (or read) consecutively in non-overlapping groups of 3. This is the reading frame of a sequence of bases. Each group of 3 bases corresponds to 1 aa. The insertion or deletion of a nucleotide shifts the reading frame of the sequence of bases.This will change every successive codon from the point of mutation.
- 7Multiples of 2 correspond to full codons + therefore the reading frame WILL NOT BE CHANGED, BUT THE PROTEIN FORMED WILL STILL BE AFFECTED AS A NEW AA IS ADDED EFFECTS OF DIF MUTATIONS: no effecton an organism's phenotype bc normally functioning proteins are still synthesised
- 8Damagingbc proteins are no longer synthesised or proteins synthesised are non-functional
This can interfere w/ one or more essential processes. - 9Beneficialv rarely, a protein is synthesised that results in a new + useful characteristic in the phenotype. E.g. a mutation in a protein present in the c surface mems of human cs means that the human immunodeficiency virus (HIV) can't bind + enter these cs. People w/ this mutation are immune to infection from HIV.
- 10causes of Ms?can occur spontaneously, often during DNA replication
but the rate of mutation is increased by MUTAGENS - 11MUTAGENSMUTAGENS
- 12MUTAGEN?a chemical, physical or biological agent which causes Ms
a chemical, physical or biological agent which causes Ms
a chemical, physical or biological agent which causes Ms - 13The loss of a purine base (depurination) or a pyrimidine base (depyrimidation) often occurs spontaneously. The absence of a base can lead to the insertion of an incorrect base through complementary base pairing during DNA replication.Free radicals, which are OXIDISING AGENTS, can affect the structures of nucleotides, + also disrupt base pairing during DNA replication.
Antioxidants? - 14e.g. vitamins A, C, + E (found in fruit + veg), are known anticarcinogens bc of their ability to negate the effects of free radicalsAntioxidants are known anticarcinogens bc of their ability to negate the effects of free radicals.
- 15Physical mutagens: ionizing radiations e.g. X-raysbreak one or both DNA strands. some breaks can be repaired but Ms can occur in the process
- 16Chemical mutagens: deaminating agentschemically alter bases in DNA such as converting C to U in DNA, changing the base sequence
- 17Biological agents: alkylating agentsmethyl or ethyl gs are attached to bases resulting in the incorrect pairing of bases during replication
- 18base analogsincorporated into DNA in place of the usual base during replication, changing the base sequence
- 19virusesviral DNA may insert itself into a genome, changing the base sequence
- 20Green box. EFFECTS OF MUTATIONS: SILENT MSvast majority
= don't change any proteins, or the activity of any proteins synthesised
Therefore, have no effect on an organism's phenotype.
can occur in the non-coding regions of DNA (introns) or code for the same aa due to the degenerate nature of the genetic code. may also result in changes t the primary structure but don't change the overall structure or function of the proteins synthesised - 21Nonsense mutationsresult in a codon becoming a stop codon instead of coding for an aa. The result is a shortened protein being synthesised which is normally non-functional. These Ms normally have -ve or harmful effects on phenotypes.
- 22Missense Msresult in the incorporation of an incorrect aa (or aas) into the primary structure when the protein is synthesised.
- 23A conservative M occurs when the aa change leads to an aa being coded for which has similar properties to the original, means the effect of the M is less severe. In contrast, a non-conservative Mis when the new aa coded for has dif properties to the original, more likely to have an effect on protein structure, + may cause disease
- 24BENEFICIAL MUTATIONS The ability to digest lactose (the sugar in milk) = the result of a recent M. The majority of mammals in the world become lactose intolerant after they cease to suckle.The ability to digest lactose = found primarily in European populations who are more likely to farm cattle. The ability to drink milk + process lactose as an adult helps prevent diseases such as osteoporosis
- 25- this could also have prevented individuals w/ the mutation from starving during famines. Green box. Sickle-c anaemia:= a blood disorder where erythrocytes develop abnormally. The disorder is caused by a M in the gene coding for haemoglobin. There's a substitution of just 1 base.
- 26Thymine replaces adenine, making the sixth aa valine instead of glutamic acid on the beta haemoglobin chain. Glutamic acid =a hydrophilic aa but valine is a hydrophobic aa. When the partial pressure of oxygen is low, + haemoglobin is dissociated from oxygen, the hydrophobic valine aas bind to hydrophobic regions on adjacent haemoglobin ms.
- 27The aggregation of haemoglobin ms deforms the shape of erythrocytes causing them to become sickle shaped. The erythrocytes are less flexible + have difficulty moving through capillaries resulting in reduced oxygen delivery to tissues, which causes anaemia.Gene Ms occur in single genes or sections of DNA whereas chromosome Ms affect the whole chromosome or no. of chromosomes within a c. They can also be caused by mutagens + normally occur during meiosis.
- 28As w/ gene Ms, the Ms can be silent but often lead to developmental difficulties. Changes in chromosome structure include:DELETION: a section of CM breaks off + is lost within the c
Duplication: sections get duplicated on a CM
TRANSLOCATION: a section of 1 CM breaks off + joins another non-homologous CM
Inversion: a section of CM breaks off, is reversed, + then joins back onto the CM - 29Housekeeping genes?the genes that code for the (constantly required) EZs which are necessary for rs present in metabolic pathways like resp
- 30Protein-based HMs (required for the growth + development of an organism or EZs) are only neededby certain cs at certain times to carry out a short-lived response. They are coded for by tissue-specific genes.
- 31The entire genome of an organism is present in every prokaryotic c, or eukaryotic c that contains a nucleus. This includes genes not needed by that c sothe expression of genes + the rate of synthesis of protein products like EZs + HMs must be regulated.
- 32Genes can be turned on or off, + the rate of product synthesis increased or decreased depending on demand. Bacteria can respond to changes, envir, bc ofgene regulation. Expressing genes only when the products are needed also prevents vital resources being wasted.
- 33The stimuli that cause changes in gene expression + the responses produced are more complex in eukaryotes. Gene regulation is needed for cs tospecialise + work in a coordinated way.
- 34a no. of dif ways in which genes are regulated, categorised by the level at which they operate: Transcriptional: genes can be turned on or off Post-transcriptional: mRNA can be modified which regulates translation + the types of proteins producedTranslational: translation can be stopped or started
Post-translational: proteins can be modified after synthesis which changes their functions - 35TRANSCRIPTIONAL CONTROL a no. of mechanisms that can affect the transcription of genes. CHROMATIN REMODELLINGDNA is a v long m + must be wound around proteins called histones in eukaryotic cs in order to be packed into the nucleus of a c.
- 36chromatin =the resulting DNA/protein complex
- 37HETEROCHROMATIN =tightly wound DNA causing chromosomes to be visible during c division
- 38EUCHROMATINloosely wound DNA present during interphase.
- 39Heterochromatin = tightly wound DNA causing chromosomes to be visible during c division vs. euchromatin = loosely wound DNA present during interphase.Heterochromatin = tightly wound DNA causing chromosomes to be visible during c division. Euchromatin = loosely wound DNA present during interphase
- 40The transcription of genes isn't possible when DNA is tightly wound bcRNA polymerase can't access the genes. The genes in euchromatin, however, can be freely transcribed.
- 41Protein synthesis doesn't occur during c division but during interphase between c divisions. = a simple form of regulation that ensures the proteins necessary for c division are synthesised in time.also prevents the complex + energy-consuming process of protein synthesis from occurring when cs are actually dividing.
- 42HISTONE MODIFICATION DNA coils around histones bcthey are positively charged + DNA is negatively charged. Histones can be modified to increase or decrease the degree of packing (or condensation).
- 43The addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces the positive charge on the histones (making them more negative) + this causesDNA to coil less tightly, allowing certain genes to be transcribed.
- 44Phosphorylation or acetylation reduces the histones' positive charge, so DNA coils less tightly, allowing certain genes to be transcribed. Methylation,the addition of methyl groups, makes the histones more hydrophobic so they bind more tightly to e o causing DNA to coil more tightly + preventing transcription of genes.
- 45Methylation makes the histones more hydrophobic so they bind more tightly to e o causing DNA to coil more tightly + preventing transcription of genes.Methylation makes the histones MORE HYDROPHOBIC SO THEY BIND MORE TIGHTLY TO E O CAUSING DNA TO COIL MORE TIGHTLY + PREVENTING TRANSCRIPTION OF GENES.
- 46Epigenetics =describes this control of gene expression by the modification of DNA.
= a term sometimes used to inc all of the dif ways in which gene expression is regulated. - 47Lac operon An OPERON =a group of genes that are under the control of the same regulatory mechanism + are expressed at the same time
- 48Operons are far more common in prokaryotes than eukaryotes bc ofprokaryotes' genomes' smaller + simpler structure
- 49also a v efficient way of saving resources bc if certain gene ps aren't needed, then all of the genes involved in their production can be switched off. Glucose is easier to metabolise +is the preferred respiratory substrate of Escherichia coli + many other bacteria. If glucose is in short supply, lactose can be used as a respiratory substrate. Dif EZs are needed to metabolise lactose.
- 50The lac operon =a group of 3 genes, lacZ, lacY, + lacA, involved in the metabolism of lactose.
- 51They are STRUCTURAL GENES bc they code for 3 EZs + they are transcribed onto a single long m of mRNA.The regulator gene, lacI, is near the operon + codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose.
- 52Fig 1. A repressor protein coded for by a regulatory gene binds to the operator + prevents the binding of RNA polymerase, preventing transcription of the structural genes.The repressor protein is constantly produced + binds to an area called the operator, which is also close to the structural genes.
- 53The binding of this protein prevents RNA polymerase binding to DNA + beginning transcription. = down regulation down regulation= the binding of the repressor protein to the operator prevents RNA polymerase binding to DNA + beginning transcription.
- 54promoterthe section of DNA that is the binding site for RNA polymerase.
- 55When lactose is present, it binds to the repressor protein, causing the repressor protein to change shape so the repressor protein can no longer bind to the operator.so RNA polymerase can bind to the promoter. 3 structural genes are transcribed. The EZs are synthesised
- 56ROLE OF CYCLIC AMP The binding of RNA polymerase still only results in a relatively slow rate of transcription that must be increased or up-regulated toproduce the required quantity of EZs to metabolise lactose efficiently. This is achieved by the binding of another protein, cAMP receptor protein (CRP), that's only possible when CRP is bound to cAMP
- 57The transport of glucose into an E. coli c decreases the levels of cAMP, reducing the transcription of the genes responsible for the metabolism of lactose.The transport of glucose into an E. coli c decreases the levels of cAMP, reducing the transcription of the genes responsible for the metabolism of lactose. If both glucose + lactose are present, then it will still be glucose, the preferred respiratory substrate, that's metabolised
- 58POST-TRANSCRIPTIONAL/ PRE-TRANSLATIONAL CONTROL RNA PROCESSINGThe product of transcription is a precursor m, pre-mRNA. This is modified forming mature mRNA before it can bind to a ribosome + code for the synthesis of the required protein.
- 59A cap (a modified nucleotide) is added to the5' end. A tail (a long chain of adenine nucleotides) is added to the 3' end. These both help to stabilise mRNA + delay degradation in the cytoplasm.
- 60The cap also aids binding of mRNA to ribosomes. The cap also aids binding of mRNA to ribosomes. Splicing also occurs where the RNA is cut at specific points:the introns (non-coding DNA) are removed + the exons (coding DNA) are joined together.
- 61Splicingthe RNA is cut at specific points: the introns (non-coding DNA) are removed + the exons (coding DNA) are joined together. Both processes occur within the nucleus.
- 62RNA editing:The nucleotide sequence of some mRNA ms can also be changed through base insertion, deletion, or substitution. These have the same effect as point mutations + result in the synthesis of dif proteins which may have dif functions. This increases the range of proteins that can be produced from a single mRNA m or gene.
- 63Translational control: following mechanisms regulate the process of protein synthesis: degradation of mRNAthe more resistant the m, the longer it will last in the cytoplasm, a greater quantity of protein synthesised
the more resistant the m, the longer it will last in the cytoplasm, a greater quantity of protein synthesised - 64binding of inhibitory proteins to mRNAprevents it binding to ribosomes + protein synthesis.
binding of inhibitory proteins to mRNA prevents it binding to ribosomes + prevents protein synthesis - 65activation of initiation factors which aid the binding of mRNA to ribosomes activation of initiation factors which aid the binding of mRNA to ribosomes activation of initiation factors which aid the binding of mRNA to ribosomes(the eggs of many organisms produce large quantities of mRNA which isn't required until after fertilisation, at which point initiation factors are activated).
- 66Protein kinases =EZs that catalyse the addition of phosphate groups to proteins.
- 67The addition of a phosphate group to proteinschanges the tertiary structure + so the protein's function.
- 68Many EZs are activated byphosphorylation. Protein kinases are thus important regulators of c activity.
- 69Protein kinases are themselves often activated bythe secondary messenger cAMP.
- 70Post-translational control involvesmodifications to the proteins that have been synthesised. includes
- 71folding or shortening of proteinsmodification by cAMP. E.g. in the lac operon, cAMP binds to the cAMP receptor protein increasing the rate of transcription of the structural genes
- 72addition of non-protein groups such as carbohydrate chains, lipids, or phosphatesaddition of non-protein groups such as carbohydrate chains, lipids, or phosphates
- 73modifying aas + the formation of bs such as disulfide bsmodifying aas + the formation of bs such as disulfide bs
- 74morphogenesis =the regulation of the pattern of anatomical development
- 75Homeobox genesa group of genes which all contain a homeobox
- 76The homeobox =a section of DNA 180 base pairs long, coding for a part of the protein 60 aas long.
highly conserved (v similar) in ps, as, + fungi - 77This part of the protein, a homeodomain, binds to DNA + switches other genes on or off. Therefore, homeobox genes are regulatory genes.This part of the protein, a homeodomain, binds to DNA + switches other genes on or off. Therefore, homeobox genes are regulatory genes.
- 78Many of the homeobox genes present in the mouse + human still have identical nucleotide sequences. Pax6 =one of the homeobox genes. When mutated, it causes a form of blindness in humans.
- 79Hox genesone group of homeobox genes that are only present in animals. responsible for the correct positioning of body parts.
In animals, Hox genes are found in gene clusters: mammals have 4 clusters on dif chromosomes. - 80The order in which the genes appear along the chromosome is the order in which their effects are expressed in the organism. Diploblastic animalshave 2 primary tissue layers
- 81Triploblastic animalshave 3 primary tissue layers
- 82A common feature of animals,are segmented = rings of a worm of vertebrates' backbones
- 83These segments have multiplied over time + are specialised to perform dif functions. somites?The individual vertebrae + associated structures have all developed from segments in the embryo called somites. The somites are directed by Hox genes to develop in a particular way depending on their position in the sequence.
- 84Symmetry Radial symmetry is seen indiploblastic animals like jellyfish. They have no left or right sides, only a top + a bottom.
- 85Bilateral symmetryboth left + right sides + a head + tail rather than just a top + bottom
- 86Asymmetryseen in sponges which have no lines of symmetry
- 87Mitosis (results in c division + proliferation) + apoptosis, both essential in shaping organisms.. The role of mitosis is toincrease the no. of cs leading to growth.
- 88Apoptosisshapes dif body parts, by removing unwanted cs + tissues. Cs undergoing apoptosis can also release chemical signals which stimulate mitosis + c proliferation leading to the remodelling of tissues.
- 89Hox genes regulate...both mitosis + apoptosis.
- 90FACTORS AFFECTING THE EXPRESSION OF REGULATORY GENES STRESS?the condition produced when the homeostatic balance within an organism is upset.
- 91can be due to external factors such as a change in T or intensity of light. Internal factors can change due to the release of HMs or psychological stress.These factors will have a greater impact during the growth + development of an organism.
- 92Drugs can also affect the activity of regulatory genes. thalidomide. given to pregnant women in the 1950s + 1960s totreat morning sickness. it prevented the normal expression of a particular Hox gene. This resulted in the birth of babies w/ shortened limbs.
- 93Thalidomide is currently used in the treatment of some forms of cancer. stop the development of some tumours.prevents the formation of networks of capillaries which are necessary for some tumours to grow + develop.