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Microbiology 8
Genetics & Mutations
| Question | Answer |
|---|---|
| The region of DNA that contains genes & the regulatory DNA associated with those genes | operon |
| A section of DNA that helps to regulate transcription | operator |
| Components of an operon | a promoter, an operator, and 3 genes that code for enzymes involved in catabolism of lactose |
| Changes in the neucleotide sequences in DNA which occur without addition of agents that cause mutations | Spontaneous mutations |
| the addition or deletion of nucleotides resulting in all genes downstream of a stop codon and in the same operon nonfunctional | Frame shift mutations |
| stable but can undergo a change back to the non-mutant form- a reversion | Spontaneous mutation |
| Base substitutions | usually occur during DNA replication; point mutations occur when only one base pair changes |
| occurs when hydrogen atoms move to alter the bonding of the base pairs | Tautomeric shift |
| have the ability to move to any other location in the genome. | transposons |
| Has a proofreading function | DNA polymerase |
| photoreactivating enzyme breaks the bonds of the thymine dimer, thereby restoring the original molecule | Light repair |
| the damaged segment is excized by an endonuclease. A new strand is synthesized by DNA polymerase | excision or dark repair |
| SOS Repair | last ditch repair mechanism in which 20 enzymes are induced by damaged DNA resulting in DNA polymerase bypassing the damaged part of the strand, but without proofreading the DNA product. Consequently, the synthesized DNA has many mistakes |
| accounts for the mutagenic activity of UV irradiation | SOS Repair |
| Anything that increases the error rate of DNA polymerase III | Mutagen |
| entire chromosome missing in eukaryote cell | aneuploidy |
| 4 positions of chromosonal mutations | insertion, deleted, translocation, inversion |
| bulky adducts | chemicals or their groups that can adhere to DNA bases and can fool polymerase into copying DNA incorrectly |
| Do point mutations change the sequence of a protien? | No b/c some protiens are represented by more than one codon |
| Silent mutation | When the genetic code is redundant and a change in DNA may produce no change in the protien |
| When a point mutation results in a change in sequence of amino acids | missense mutation |
| Mutation that introduces a stop codon into the mRNA and causesprotien chain to shorten | nonsense mutation |
| What causes a frameshift mutation? | faulty replication that leads to insertion or deletion of bases from a chain |
| reading frame | start codon |
| The harm of chemical mutagens | may alter properties of DNA so that base paring does not work |
| How does radiation cause mutations? | UV: Dimers, abnormal bonds within DNA molecule & X-ray: free radicals |
| Alkylating agents | chemicals that modify bases by adding ethyl or methyl groups |
| insert themselves between adjacent bases and cause base additions | intercalating agents |
| look like bases and can be used instead of bases when DNA is being synthesized | Base analogs |
| Method for indirect ditection of mutants | Ames test |
| Detects reversions and involves growing microbes on general purpose media plates - then transfering to different plates and using velvet cloth | Ames test |
| Why is Ames testing called "replica plating"? | b/c a portion of the growing colony is transfered to the new platesat the same location os original plates: like a stamp |
| Colonies that appear non-permissive in Ames test | mutants (revertants) |
| inserting genes into transposable elements, plasmids, or bacteriophage vectors | Artificial transfer |
| used to fire microprojectiles in the form of collodial metal particles w/ DNA at cells | gene guns |
| Electroporation | mixture of cells & DNA are subjected to high voltage, which makes DNA enter cells |
| Competent cells | prepared to accept foriegn DNA |
| Special strains that will accept foreign DNA | Restriction minus |
| Metheylated cells | protection of cell by enzymes |
| When genes are coppied to RNA | gene expression |
| Genes transcribed when needed, otherwise turned off | transcriptional control |
| post-transcriptional control | after synthesis of RNA, splicing is done. By alternative splicing, a cell can create various types of mRNA |
| Translational control | The age of RNA varies and the translation (protien synthesis) goes on longer |
| related genes arranged adjacent to each other in a series, next to regulatory region that controls their expression (operon) | Prokaryote |
| DNA NOT complexed with histone protiens | Prokaryotes |
| Breakdown pathways | inducable - genes expressed when substrate available |
| Inducer of lac operon | lactose, which induces transcription of genes that start the breakdown of lactose |
| trp operon | when trp present, operon on |
| A cell prefers to utilize a substrate that is easier to degrade than one that needs more work | Catabolite repressor |
| post-translational control | the way a protien is folded is controled - activation can be by a clevage of a portion of newly synthesized protien or addition or removal of phosphate group |
| different hydrogen bonding properties can be incorporated into DNA in place of usual purines and pyrimidines | base analogs |
| planar molecules which insert into the double helix and push nucleotides apart resulting in a frame shift mutation | Intercalating agents |
| insertion mutation | results when transposon integrates into a recipient cell's genome |
| Two adjacent thymine molecules on the same strand of DNA joined together through covalent bonds. | thymine dimer |
| an endonuclease cuts out the damaged fragment and a new DNA strand is synthesized | mismatch repair |
| photoreactivating enzyme breaks the bonds of the thymine dimer, thereby restoring the original molecule | light repair |
| excision / dark repair | the damaged segment is excized by an endonuclease. A new strand is synthesized by DNA polymerase |
| Haploid | Condition in which each type of chromosome is represented only once |
| involves inoculating cells on a medium on which the mutant but not the parent can grow; these are the easiest kinds of mutants to isolate | Direct selection |
| is required when the mutant being sought does not grow on a medium on which the parent grows | indirect selection |
| involves the simultaneous transfer of all the colonies on one plate to another and the comparison of the growth of individual colonies on both plates | Replica plating |
| increases the proportion of mutants in a population by killing non mutants in a medium in which only non mutants will grow | penecillan enrichment |
| Ames test | measures whether a suspected carcinogen increases the frequency of reversion; a positive test indicates the suspected carcinogen is a mutagen and therefore a likely carcinogen |
| DNA enters the cell as a single-stranded molecule and is integrated by replacing recipient cell genes by | homologous recombination |
| a process whereby the cells are treated with an electric current that makes holes in the cell envelope through which DNA can pass | electroporation |
| DNA entering unrelated bacteria is recognized as foreign and is degraded by a class of deoxyribonucleases which recognize specific nucleotide sequences termed | Restriction enzymes |
| What would save DNA insid cell from being cleaved? | it is methylated at the potential cleavage sites by a modification enzyme that is paired with the restriction enzyme to form a restriction-modification system |
| Gene Transfer V. Mutations | Gene transfer allows bacteria to survive changing environments by providing cells with a set of new genes.In contrast, mutations only result in a single gene being modified. |
| positive selection | When mutation gives bacteria a survival advantage in a certain environment |
| negative selection | to look for mutants that have lost an ability - involves replica plating technique |
| concluded that living, unencapsulated bacteria had aquired something from dead encapsulated bacteria that had transformed them - that something was DNA | Griffiths |
| Sex pili | hollow tubes of protien that pull 2 attached cells together so that DNA can be passed |
| contains gene for sex pilus | fertility factor |
| When f+ cell encounters f- cell | it forms sex pilus and attaches during conjugation |
| Cells that have the F factor inserted into main chromosome | high-frequency recombination |
| Has DNA that has been combined from 2 sources | Recombinant cell |
| Can initiate conjugation | cell w/ F factor or F+ |
| cAMP | Signaling molecule - alarms for reduction in glucose |
| Point Mutations | Change in single gene - no big deal |
| Silent Mutation | No change in protien |
| Frame Shift | Insertion or deletion of bases from chain |
| Horizontal gene Transfer | Cells of same generation |
| Transposition | removal of a segment of DNA by means of transposable element, or transposon |
| "jumping genes" (Transpons | segments of DNA that move from one site to another - no longer codes for functional protien |
| Result of X-ray exposure | deletion of bases |
| 2 ways to correct errors in base incorporation | Proofreading (DNA polymerase) & mismatch repair (enzymes) |
| Endonuclease | mismatch repair enzyme |
| Wrong base incorporated during DNA replication | Spontaneous |
| How does UV light / thymine dimer formation get repaired? | Photoreactivation, Exciscion (dark) repair, SOS repair |
| Can multiply in only one species of bacteria | plasmids |
Created by:
sloanie32
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