slide 7
DNA will be degraded unless it can be replicated and maintained in the recipient cell. there are 3 ways foreign DNA can survive in a recipient cell.
1) The foreign DNA can survive if it is an autonomous replicon. DNA replication starts at a specific site called the origin of replication. If the foreign DNA has a functional origin of replication it can be copied within the host cell and passed on to future generations. Examples of autonomous replicons include: the chromosome, plasmids and temperate bacteriophages (a latent virus) 2) The foreign DNA integrates into the host chromosome or another autonomous replicon such as a plasmid by homologous recombination. 3) The foreign DNA integrates into the host chromosome or another autonomous replicon such as a plasmid by transposition.
conjugation with Hfr cell steps
1. F plasmid integrates into chromosomes by recombination 2. cells join via a conjugation pilus 3. F plasmid partially replicates and moves into recipient cell trolling a copy of donor's DNA 4. conjugation ends with pieces of F plasmid and donor DNA in recipient cell 5. donor DNA and recipient DNA recombine making a recombinant F- cell
GENERAL LIFE CYCLE OF A LYTIC DNA PHAGE AND HOW TRANSDUCTING PARTICLES FORM STAGES
1. bacteriophage attaches to a potential host cell 2. virus DNA is injected into the bacterial cell, bacterial enzymes make viral mRNA 3. cellular chromosome breaks down, phage DNA is replicated, phage mRNAs and proteins are made 4. bacteriophage particles are assembled, some accidentally enclose host DNA rather than virus DNA 5. the infected cell breaks open releasing phage particles. defective viruses that contain host cell DNA are called transacting particles. the protein coat of a transduction cell protects the DNA and helps it to get into a recipient cell by viral attachment and DNA injection mechanisms
conjugation steps
1. donor cell attaches to a recipient with its pilus. the plus draws the cells together. 2. the cells contact one another 3. the plasmid replicates one of its strands and transfers the daughter strand to the recipient 4. the recipient simultaneously synthesizes a complementary strand to become an f+ cell
there are 64 codons in the genetic code. how many are called sense codons, why are they called sense codons?
61 sense codons. they direct the incorporation of specific amino acids into a growing protein chain, the other 3 called nonsense codon
. what is the start codon? tells the ribosome where to begin translation?
AUG
The vast majority of eukaryotic organisms, including most FUNGI, ALGAE and PROTOZOA, have well developed sexual reproduction that includes the formation of diploid cells by the fusion of gametes (haploid sex cells such as sperm and ovum). which microorganism does not form diploid cells?
Bacteria do not form diploid cells, they do not form gametes or undergo meiosis. DNA exchange in bacteria is limited to the one-way transfer of DNA from a donor cell to a recipient.
in bacteria, mitochondria and chloroplast translation starts with?
N-formylmethionine.
The genome of a single stranded RNA virus must be copied by ____________________
RNA-dependent RNA polymerase.
Bacterial transformation was discovered by Griffith in 1928 in
Streptococcus pneumonia.
the genetic code is the key for translating information which is contained within a nucleic acid sequence into information t hat is in the form of a protein sequence. the genetic code consists of ____ codons, each codon is a sequencer of ______ nucleotides and each codon specifies the insertion of one particular amino acid into a growing protein chain.
The genetic code is the key for translating information which is contained within a nucleic acid sequence into information that is in the form of a protein sequence. The genetic code consists of 64 codons, each codon is a sequence of three nucleotides and each codon specifies the insertion of one particular amino acid into a growing protein chain.
Why are there 64 codons for 20 amino acids?
There are 4 letters in the nucleotide language: A, G, C and U (or T). If a codon was two letters long, there would be 16 possible codons: AA, AG, AC, AU, GA, GG, GC, GU, CA,CG,CC,CU, UA, UG,UC, UU. A third nucleotide gives 43 possible sequences, 4 x 4 x 4 = 64. This is sufficient variety to specify 20 different common amino acids.
which codons are the start codons? that tell the ribosome to stop elongating a protein chain because the job is done?
UAA, UAG, UGA
When lactose is present, what happens?
allolactose binds to the repressor and inactivates it. This allows RNA polymerase to transcribe the operon.
a layer of polysaccharides that coats the outer surface of the cell.
bacterial capsule
in steptococcus pneumonia is the________ that can protect the bacterium from the defensive white blood cells of the host animals. thus a capsule makes streptococcus a much more virulent pathogen
capsule
an HFR strain has the F factor integrated into its ________________
chromosome
in conjugation, DNA is transferred from the donor strain to the recipient strain by direct cell to cell contact, the DNA is transferred through a narrow cytoplasmic bridge. The donor cell is not killed by conjugation and in fact does not usually loose any DNA. Conjugation generally involves replication of DNA that is about to be transferred and donation of one copy to the recipient cell.
conjugation
one-way transfer of DNA from a donor cell to a touched recipient
conjugation
An F+ strain of E. coli has a copy of E plasmid in its ______________
cytoplasm
a type of mutation one or more nucleotides are left out
deletion
If one gives the recipient cells a good shock of electricity they are more likely to take up DNA, this procedure is called _________________. It is not clear how electroporation works, but it is useful with a wide variety of bacteria.
electroporation
where can homologous recombination occur?
homologous recombination or cross-over can occur between two pieces of DNA that have very similar sequences both strands of DNA are broken and the ends are rejoined by enzymes of the rec system
a type of mutation one or extra nucleotides are added
insertion
what codons encode methionine in bacteria and eukaryotes?
internal AUG
the genetic code is called a triplet called why? a codon is 3 bases of _________
it takes 3 base pairs of DNA to contain the information needed to specify the sue of one amino acid in a protein. a codon is 3 bases of mRNA
a lac operon in e.coli consists of 3 genes that are involved in the breakdown of the sugar ________________
lactose
The transfer of chromosomal genes by conjugation from an HFR strain occurs in a__________ order.
linear
in eukaryotes and archaea, translation starts with ________________
methionine
there are two amino acids that are specified by only one codon each. methionine is specified by what? tryptophan is specified by what?
methionine is always specified by an AUG codon tryptophan is always specified by UGG
a type of codon change encode a different amino acid, this can inactivate the enzyme
missense mutation
changing a GAG codon (glutamic acid) to GUG (valine). what type of mutation
missense mutation
why is the genetic code degenerate?
most amino acids can be specified for by more than one codon. for example: 2 codons specify aspartic acid: GAU and GAC 2 codons specify phenylalanine: UUU and UUC 4 codons specify valine: GUU, GUC, GUA, GUG
a stable change in the DNA of an organism that can be passed on to the offspring of that organism mutations are rare produces a genotypic change affect the phenotype of the organism, but not all of them
mutations
_________________ viral RNA is complementary to mRNA and must be copied by an RNA-dependent RNA polymerase to make a positive-sense mRNA before translation.
negative-sense
changing a GUU codon to GUC has no effect, both encode valine. what type of mutation
neutral mutation
a type of codon change are minor changes in the DNA that have no effect on an enzyme
neutral mutations
what are nonsense codons for?
nonsense codons cause the termination of translation
a type of codon change encode an early stop codon, this usually eliminates the enzyme
nonsense mutation
Changing CAA (Glutamine) to UAA (STOP). what type of mutation
nonsense mutations
bacterial genes are organized into physically linked coordinately expressed groups of genes called ________________ regulation of gene expression in bacteria
operons
most of the time, the DNA that is transferred by conjugation is a ___________, but some plasmids can mobilize the movement of chromosomal genes into a recipient cell. the plasmid is copied as it is transferred so the donor cell does not loose it.
plasmid
a small circular piece of DNA that can replicate and be maintained within a cell line
plasmid generally carry a few genes that are not essential for cell survival under all conditions may carry genes for antibiotic resistance, production of toxins, and the enzymes for unusual metabolic pathways
_________________ viral RNA is identical to viral mRNA and can be translated directly by the host cell's ribosomes.
positive sense
where does transcription start?
promoter
3 characteristics of a mutation
rare permanent inherited
________________________________ recognize specific sequences of DNA and make breaks in the backbone chain, often producing sticky ends.
restriction enzymes
how do mutations develop
result from errors in DNA base pairing during replication the enzyme that makes the new DNA strand, DNA polymerase, is a very faithful but it's not perfect
Retrovirus RNA is copied by ______________________ to make a DNA copy of the RNA genetic material.
reverse transcriptase
in __________, the DNA travels from cell to cell through a cytoplasmic bridge. a ________, such as the F-pilus, is an appendage that helps that bacterial cells stick together so conjugation can occur.
sex-pilus
a type of mutations one nucleotide is replaced by another
substitution
this type of mutation within a gene can change a codon
substitution
translation starts where?
the AUG near the ribosome binding site
where are the genes for most sex pili located? where are genes that encode all of the proteins needed to make the F-pilus?
the genes for most sex pili are located in plasmids. the genes that encode all of the proteins needed to make the f-pilus are found on the f-plasmid.
why is the genetic code unambiguous?
the genetic code is unambiguous because there is only one amino acid in a particular codon that will specify. CUU encodes leucine
When lactose is absent, what happens?
the lac repressor protein binds to the operon and blocks transcription.
DNA from a donor cell gets incorporated into a defective virus particle called a transducing phage particle. The defective virus attaches to a recipient cell and injects the DNA from the donor strain. Transduction kills the donor strain.
transduction
transfer of DNA from virus-infected cell via a defective phage particle
transduction
DNA is released from a donor strain by lysis of dead cells, the recipient strain takes up the DNA.
transformation
a genetic change produced in a bacterium that is caused by the uptake of naked foreign DNA which becomes a part of the recipient cell's genome.
transformation
in bacteria, there are 3 ways DNA can move from a donor stain to a recipient strain . this one is the uptake of naked DNA
transformation
the recipient cell makes up naked DNA
transformation
a segment of DNA that can be inserted into random site in target by special enzymes called transposases carry a few genes for antibiotic resistance and a gene for a transposes jumping gene for their ability to move around within a genuine
transport
A typical bacterial "mating" experiment require specialized donor and recipient strains and some selective medium. Only a small fraction of the cells in the recipient strain actually acquire donor DNA. (1 in 100,000 on a good day). When DNA from a donor strain gets into a recipient strain, it must be integrated into the genome of the recipient cell, or it will be degraded.
true
An f+ strain will transfer genes that are on the f-plasmid but an HFR strain will transfer chromosomal genes that are near the insertion site of the F-factor
true
Encapsulated strains of Streptococcus produce smooth and shiny appearing colonies when grown on an agar medium. Unencapsulated strains produce colonies that appear to be dry or rough.
true
In 1944 avery and McCarty showed that the transforming substance from the dead virulent strain was DNA. They observed that an enzyme that breaks down DNA destroyed the transforming agent but enzymes that break down proteins did not.
true
THE GENTIC CODE IS UNIVERSAL, WITH A FEW EXCEPTIONS, THE GENETIC CODE IS THE SAME IN ALL LIVING ORGANISMS ON EARTH.
true
The rough strain (R) of Streptococcus can be genetically transformed into the smooth strain (S) by DNA that is released by heat killed S cells. This can happen both in mice and in a test tube, indicating that it can occur in a natural environment, but the mouse is not required.
true
The transfer of chromosomal genes by conjugation from an HFR strain occurs in a linear order. Genes that are close to the integrated F-factor are transferred sooner while genes that are farther from the F-factor are transferred later. You can disrupt the transfer of genes by agitating the mating mix in a blender and until the cells separate. By measuring the time it takes for a particular marker gene to be transferred, you can determine the distance between the integrated F-factor and that marker gene.
true
The trp operon is involved with the synthesis of the amino acid tryptophan. A high level of tryptophan in the cytoplasm causes repression of the trp operon. The trp repressor protein is inactive in the absence of tryptophan. Tryptophan acts as an allosteric activator of the repressor activity.
true
When lactose is present there is always a small amount of allolactose too.
true
bacteria that can take up naked DNA are said to be competent. Some bacteria are naturally competent, including species within the genera: Streptococcus, Staphylococcus, Bacillus, Haemophilus and Pseudomonas.
true
the DNA, what AUG in the mRNA is the real translation start site, where does the RNA polymerase stop transcription, and other necessary signals, are sequences of nucleotides that are often found near structural genes.
true
the genetic code is not punctuated. there are no commas, periods, semicolons, etc
true
transformation is most efficient when the size of the DNA is relatively small, 1000-2000 base pairs. this is just big enough to contain 1-3 genes. circular supercoiled plasmid DNA works better than linear DNA, why? Transformation by plasmids that are 4000 - 5000 base pairs long works reasonably well.
true
how do mutations occur
when DNA polymerase makes an error when synthesizing a new strand of DNA. A mutagenic agent causes damage to DNA that increases the likelihood of an error being made by DNA polymerase. Common mutagens include: x-rays, UV light, and many chemicals (including: coal tar derivatives, LSD and DNA base analogs such as 5-bromouracil).
