Exam Assignments Flashcards
what is a codon
codons are groups of three mRNA nucleotides that code for a particular amino acid
What is the central Dogma of molecular biology
DNA to RNA to protein
what accounts for the high accuracy of DNA replication
replication is highly accurate due to the proofreading capability of DNA polymerase
DNA gyrase function
relaxes supercooling ahead of replication fork
DNA ligase function
makes covalent bonds to join new strands, Okazaki fragments, and new segments in excision repair
DNA polymerase
synthesize DNA, proofreading and facilitating DNA repair
topoisomerase
relaxes supercoiling ahead of replication fork, separates DNA circles at the end of DNA replication
why is DNA replication said to be semi conservative
one parental strand and one new strand
define the process of transcription
synthesis of a complementary mRNA strand from a DNA template
what are the three stages of transcription
initiation, elongation, termination
transcription cannot begin until
RNA polymerase binds to the promoter
generally, higher levels of transcription lead to higher levels of
translation
what does a riboswitch do
it is a post transcriptional control mechanism that can initiate or stop translation
how does a riboswitch work
riboswitch is a part of an mRNA molecule that binds to a substrate and changes the mRNA structure
define repression
inhibits gene expression and decreases enzyme synthesis. it is mediated by proteins called repressors that block transcription and the default position of a repressible gene is on
define induction
turns on gene expression. it is initiated by an inducer and the default position of an inducible gene is off
How are genes for lactose catabolism in E. coli transcribed when lactose is available
in the presence of lactose, metabolite of lactose (allolactose) which is the inducer binds to the repressor; the repressor cannot bind to the operator and transcription occurs
what type of operon is allolactose
inducible
are genes for lactose catabolism normally transcribed
no
what specific type of mutagen can result in thymine dimers
Nonionizing radiation (UV radiation)
two DNA repair mechanisms we discussed that are used to correct thymine dimers:
Photolyases and nucleotide excision repair
photolyases
enzymes that use visible light to separate the thymine dimers
nucleotide excision repair
enzymes cut out incorrect bases and fill in correct bases
what is an auxotroph
mutant that has nutritional requirement absent in the parent
describe replica plating
- sterile velvet is pressed on the grown colonies on the master plate and then cells from each colony are transferred from the velvet to new plates with different nutrients
- growth on plates is compared
- a colony that grows on the medium with histidine but could not grow on the medium without histidine is auxotrophic (histamine requiring mutant)
describe the general mechanism of transformation in bacterial cells
genes are transferred from one bacterium to another as “naked” DNA. the recipient cell takes up fragments of DNA from donor cells and the donor DNA aligns with the complementary bases of the chromosomal DNA within the recipient cell. Recombination then occurs between the donor and receipt DNA resulting in a genetically transformed cell
what other types of mechanisms result in DNA transfer among bacteria
transduction, conjucation (F+, HFR)
vertical gene transfer
transfer of genes from an organism to its offspring
horizontal gene transfer
transfer of genes between cells of the same generation
what is the name of the test that indicated the degree to which a substance is mutagenic
Ames test
what is the role of snRNPs
in eukaryotic cells, these removed introns and splice exons together
why is PCR such an invaluable tool for researchers
PCR is a technique that allows for small target samples of DNA to be amplified quickly into large quantities, allowing for analysis by researchers, and it may be used for diagnostic tests for genetic diseases, as well as for detecting pathogens
what is needed in order to preform the polymerase chain reaction
target DNA, nucleotides, primers, DNA polymerase (Tay polymerases) and the thermal cycler
denaturation step in PCR
incubate at 94 degrees C to operate strands
Priming step in PCR
incubate at 60 degrees C to allow primers to attach to ssDNA
extension step PCR
incubate at 72 degrees C to allow DNA polymerase to copy the target DNA
why do we need to use Taq Polymerase in PCR
able to withstand high temperatures required during the denaturation step of PCR, when the strands are seperated
where does Taq polymerase come from
thermos aquaticus
describe the role of restriction enzymes in the creation of recombinant DNA
restriction enzymes recognize and cut DNA at a specific site or nucleotide sequence and are able to cut the same way each time. some cut both strands in the same place creating blunt ends and some make staggered cuts in the two strands producing stick ends
sticky ends have over hangs meaning they leave stretches of ssDNA at the ends of the fragments and are more useful in cloning because they will
hydrogen bond or base pair with another fragment in addition to the joining of the DNA backbones that occurs with the action of the enzyme DNA ligase
what criteria must be met by a vector
vectors must be self replicating
why are screening techniques utilized
in cloning its necessary to select the particular cell that contains your specific gene of interest and this could be difficult to do
blue-white screening technique uses a plasmid containing
ampliilin resistance gene and B-galactosidase gene
White colonies
produced by bacteria that have picked up the recombinant plasmid and will NOT hydrolyze lactose
blue colonies
produced by bacteria with the intact LacZ gene to they will hydrolyze the X gal and produce blue colonies
how can we silence genes
RNA interference
how does RNAi work
inserts DNA encoding siRNA into a plasmid and then is transferred into the cell
siRNAs are able to
bind to MRNA which is then destroyed by RNA-induced silencing complex or RISC
Lytic cycle of T even bacteriophages
attachment
phage attaches by the tail fibers to the host cell
Lytic cycle of T even bacteriophages
penetration
phage lysozyme opens the cell wall; tail sheath contracts to force the tail core and DNA into the cell
Lytic cycle of T even bacteriophages
biosynthesis
production of phage DNA and proteins
Lytic cycle of T even bacteriophages
maturation
assembly of phage particles
Lytic cycle of T even bacteriophages
release
phage lysozymes breaks the cell wall, the cell lyses, and the released bacteriophages infect other susceptible cells in the vin city and viral multiplication is then repeated within those cells
generalized transduction
bacterial genes can be picked up in a phage coat and transferred to another bacterium, any bacterial genes can be transferred during generalized transduction because the host chromosome is broken down into fragments (any of these can be packaged into a phage coat)
specialized transduction
lysogenic phage mediates the packaging of bacterial DNA along with its own DNA in the same capsid so only certain bacterial genes are transferred
