Ch 9 Microbial Genetics Flashcards
Name and describe a purine
Double ringed nitrogenous base; adenine and guanine
Name the 3 parts of a nucleotide
Nitrogenous base, pentose, phosphate group
Name and describe pyrimidines
Single ringed nitrogenous bases; thymine (DNA), cytosine (both), uracil (RNA)
“Students at TCU are PRIMADONNA’S because they are single”
Pyrimidine’s are single ringed, T, C, U
Describe base pairings in DNA and RNA
DNA: A—T and G—C
RNA: A—U and G—C
What is the principle of base pairing
A purine will always H bond and be opposite a pyrimidine in the “rungs” of the DNA
Explain Chargaff’s rule
The conc of A=T; the conc of C=G therefore A + C = T + G
Describe the Watson & Crick model for DNA
Double helix; strands run antiparallel: one side is 5’–>3’ the other is 3’–>5’ (but both sides run from 5’–>3’ direction)
Explain the sugar-phosphate backbone
The 3rd carbon in the sugar of one nucleotide bonds with the phosphate group of another nucleotide below it
What serves as a template to build a new strand from
Each strand of the DNA molecule
Where does theta replication take place
In prokaryotic circular chromosome or plasmid
What does helicase do
Unwinds and separates the parental DNA strands (unwinds helix and breaks the H bonds)
What does DNA polymerase III do
Catalyze the synthesis of new DNA by adding nucleotides to a pre-existing chain can only add to the free 3’ end of the pre-existing primer chain
What does DNA polymerase I do
Removes the RNA primer and substitutes DNA nucleotides in their place, after DNA polymerase III has synthesized its DNA
What does DNA ligase do
Joins all synthesized pieces together; “DNA glue”
What is the origin of replication
Where replication begins; short stretches of DNA having specific sequences
What is the replication bubble
Created when the H bonds between the paired bases break and the two strands of the DNA molecule separate
What is the replication fork
Found at each end of the replication bubble; Y shaped region where the parental strands of DNA are being unwound
Describe the leading strand
Synthesized as one long continuous section in the 5’–>3’ direction; overall direction is the same direction 5’–>3’
Lagging strand
Synthesized in short discontinuous sections in the 5’–>3’ direction; overall direction of synthesis is
3’–>5’
What are the sections of the lagging strand called
Okasaki fragments
Describe the product of semi-conservative replication
2 double stranded DNA molecules, each consisting of half old (original) and half new material; one strand is original, the other is new; produces 2 copies!!
Explain proofreading
During synthesis, DNA polymerase reviews the synthesized strands and corrects mismatched nucleotide pairs or missing nucleotides (deletions)/ extra nucleotides (insertions)
Explain what is meant by “central dogma”
The universal direction of genetic flow: DNA—>RNA—>proteins
What is gene expression
Process by which DNA directs the synthesis of proteins
Producing mRna from DNA is called
Transcription
What is a codon
Triplet code; mRNA that is decoded in groups of 3 bases Ex: AUG/UUU/CAC are all codons
How is tRNA produced
Translation
Explain translation
When mRNA codons are translated by matching its anticodon in base pairing Ex: AUG becomes UAC; UUU becomes AAA; CAC becomes GUG
Explain make-up of rRNA
Major component of a ribosome; 1/2 rRNA + 1/2 enzymatic protein
What is the enzymatic protein in ribosomes
Ribozyme
Prokaryotic vs eukaryotic ribosome size
Pro= 70S euk= 80S
Names of the 3 active sites on a ribosome
P= peptide site E= exit site A= amino site
What binds to the RNA binding sites
tRNA
What are wobbles
Flexible 3rd position bases in the codons; sometimes when a mistake is made it still codes for the same amino acid
Explain the genetic code
Is the universal code for all lifeforms; based on the triplet code; each of the 64 triplet codons corresponds to a specific amino acid or a start or stop signal
Promotor (region)
The DNA sequence where RNA polymerase attaches and initiates transcription
Coding region
The DNA sequence that is transcribed and will code for a polypeptide
Terminator region
The DNA sequence that signals the end of transcription
Nontemplate strand
5’–>3’ Can be called cDNA for complementary
Template strand
3’—>5’ can be called tDNA for template
RNA polymerase
Pries the 2 DNA strands apart and joins together RNA nucleotides complementary to the DNA strand
What direction does RNA polymerase assemble the mRNA molecule? Does it require a primer?
5’–>3’ direction only; does NOT require a primer to start
What is the product produced from transcription
A mRNA 5’–>3’ sequence that can be translated
Where does the mRNA strand go?
Exits the nucleus and moves out to the ribosomes
Translation changes _____ into ____
mRNA into polypeptide ( protein primary level)
Translation is the conversion of the language of ____ to the language of ____
Conversion of the genetic information language of RNA to the language of proteins
What is a point mutation
Nucleotide base pair substitution; results in 1 of 3 mutations
Silent mutation
Codon still codes for the same amino acid (due to a wobble)
Ex: UGU—>UGC both code for cysteine
Missense mutation
Codon codes for a different amino acid Ex: UGU—>UGG will code for tryptophan instead of cysteine
Nonsense mutation
The codon does not code for an amino acid but becomes a terminator codon; premature termination; Ex: UGU—>UGA signals stop instead of cysteine
Frameshift mutation
The reading frame of the mRNA is shifted over one position resulting in a completely different amino acid chain being assembled or premature termination
Frameshift mutation is due to ____ or _____
Insertion (addition) or deletion (removal) of a nucleotide
Operons
Collections of genes in bacteria
Promotor region
RNA polymerase binding site
Operator region
Repressor protein binding site; acts as a control switch to turn on or off the operon
Repressor protein
Allosteric protein with 2 binding sites
Inducer
Molecule that will bind to the repressor protein to change its shape so that it will be unable to bind to the operator region; operon will be “on”
Corepressor
Molecule that will bind to the repressor protein to change its shape so that it will be able to bind to the operator region; operon will be normally “off”
Inducible operons
Most are catabolic operons; producing enzymes that function in the hydrolysis and breakdown of molecules
Are inducible operons normally off or on? What changes that?
Normally off until turned on; the substrate turns the operon on (induces)
In the lac operon, what is the inducer and what is the corepressor
Inducer: lactose;
corepressor: glucose
What is beta-galactosidase
Enzyme produced by the structural genes of the lac operon to hydrolyze the beta bond between glucose and galactose in lactose
Repressible operons
Most are anabolic operons, producing enzymes that function in assembly of molecules
Are repressible operons normally on or off? What changes that?
Normally on until shut off; the product turns the operon off (represses)
In the Arginine operon what is the corepressor?
Arginine
Recombinant
Any organism that contains and expresses genes that originated in another organism
Explain horizontal gene transfer
A DNA transfer the did not directly come from parent cells
Conjugation
Mode of genetic exchange in which a plasmid or other genetic material is transferred by a donor cell to a recipient cell via a direct connection between the two cells
F factor or fertility plasmid
Carries genes for the synthesis of the sex pilus. Only found in gram-negative bacteria. Called a conjugated plasmid
R or resistant factor plasmid
Carries genes for the synthesis of proteins that will allow the bacteria to be resistant to antibiotics or other drugs or heavy metals
VIrulence plasmid
Carries gene for the synthesis of proteins that will allow the bacteria to be more virulent or pathogenic
What are three virulence properties
Ability to infect, invade, produce toxins; (infectivity, invasiveness, toxigenicity)
Transformation
The non-specific acceptance by a bacteria cell of small fragments of soluble DNA from the surrounding environment. Do not need to living cells to accomplish
Explain the difference between an R strain and an S strain
R strain is rough, no capsule
S strain is smooth, has a capsule that allows it to stick and evade
Explain Griffith’s experiment
Mouse + live S = dead mouse
Mouse + live R = mouse is alive
Mouse + heat killed S strain = live
Mouse+ heat killed S strain+live R strain = dead mouse and live S strain on autopsy
What is a competent cell
Cells capable of accepting genetic material through transformation; ability to take up free DNA
Transduction
The process by which a bacteriophage (virus) can carry DNA from a donor bacteria cell to a recipient bacteria cell
Three examples of transduction
Toxin formation in diphtheria botulism and anthrax; enzymes for sugar fermentation; drug resistance
Transposons-jumping genes – transposable elements
Have ability to shift from one part of the genome to another; can relocate a gene from a plasmid to a chromosome and vice versa within its own self
Transposon’s – jumping genes – transposable elements are involved in
Transfer of drug resistance, replacement of damaged DNA, changes in the colony morphology of the bacteria (pigmentation, etc)
