Microbial Genetics Flashcards
Define genetics
study of genes; how they carry information; how that info is expressed; how that info is replicated
Define chromosomes
made up of DNA and protein; contain genes
Define genes
segment of DNA that encodes for functional products ( ex. proteins)
Define genome
genetic information in the cell
Define genetic code
set of rules that determine how nucleotides sequence converted to amino acid to protein
Define DNA and the 2 essential functions
Genetic blueprint
1) stores genetic information that instructs the cells on how to make proteins ( indirectly plays a role in protein synthesis)
2) replicates and make a copy of itself; copy passed down to daughter cell
What is the central dogma
dna> rna> protein
Define gene expression
combo of transcription and translation
Descrine bacterial dna and chromosomes
single circular chromosome
dna and protein
no histone ( just histone like proteins)
Define short tandem repeats (STRs)
repeating sequences of noncoding DNA
What are the 2 transfers of genetic information
1) vertical gene transfer
2) horizontal gene transfer
Define vertical gene transfer
flow of genetic information from 1 generation to the next.
occur during reproduction from parent to offspring
Define horizontal gene transfer
specific to prokaryotes
the transfer of genes b/t cells of the same generation
transfer from the donor cell to the reciptant cell
allows for recombination cell or recombination chromosome
recombinant genetic information not same as parent
Define recombination
genetic information can be transferred b/t cells of the same generation
What does DNA replications result in
formation of 2 identical complete DNA molecules each having 1 new strand and 1 strand from the original DNA
Define DNA gyrase
enzyme that release strain in region
relaxes supercoiling ahead of the replication fork
Define DNA helicase
enzyme that seperate both strands. unwinds double stranded DNA
Define DNA polymerase
bring complementary nucleotide and bring it growing strand; check if correct nucelotide is attached; synthesizes DNA; proofread and repairs DNA
Define replication fork
structure that forms within the long helical DNA during DNA replication
Define semiconservative
replication of a nucleic acid in which one strand of each double helix is directly derived from the parent molecules
What direction does DNA polymerase add nucleotide
5 to 3 prime direction
What initiates dna polymerase
RNA primer
Leading strand is …
Lagging strand is…..
synthesized continuously
synthesized discontinuosly, creating okazaki fragments
What remove the RNA primers and what joins the Okazaki fragment
dna polymerase remove primers
DNA ligase join okazaki fragments
What are the 6 steps at the DNA replication fork ( figure 7.13)
1) enzymes unwind the parental double helix
2) proteins stabilize the unwound parental DNA
3) The leading strand is synthesized continuously by DNA polymerase
4) the lagging strand is synthesized discontinously. Primase, an RNA polymerase, synthesized a short RNA primer, which is then extended by DNA polymerase
5) DNA polymerase digest RNA primer and replaces it with DNA
6) DNA ligase joins the discontinuous fragments of the lagging strand
Define DNA ligase
makes covalent bonds to join DNA strands; join Okazaki fragments and new segments in excision repair
Define RNA polymerase
copies RNA fromm a DNA template
Define primase
synthesize RNA primer
What direction is DNA replication in prokaryotes
bidirectional
Define DNA gyrase ( topoisomerase I) in prokaryote
release supercoiling
Define topoisomerase IV
seperate 2 loops
What are the 3 types of RNA
1) Ribosomal RNA ( rRNA)
2) Transfer RNA (tRNA)
3) Messenger RNA ( mRNA)
Define ribosomal rna
integral part of ribosomes
role in protein synthesis
Define transfer rna
transports amino acids during protein synthesis
Define messenger RNA
carries coded information from DNA to ribosomes
Describe transcription in prokayotes. What is needed and what direction does it go
- synthesis of complementary mRNA strand
- RNA polymerase
- promoter
- terminator
- proceeds in 5 to 3 prime direction
Define translation
mRNA is translated into the language of proteins
Define codon. How many are there total? How many are sense and how many are nonsense?
group of measured RNA that code for amino acid 64 total codons 61 sense codons- 20 amino acids 1 start codon 3 nonsense codons
What is the start codon
AUG
What are the 3 stop codons
nonsense codon
UAA,UAG,UGA
Where does translation occur
ribosome
What type of codon is tRNA considered
anticodon
What are the 3 steps involved in translation
1) initiation
2) elongation
3) termination
On the ribosome what are the 3 binding sites for tRNA
A site
P site
E site
What are the 3 steps in transcription in eukaryptes
1) in the nucleus, a gene composed of exons and introns is transcribed to RNA by RNA polymerase
2) processing involved snRNPs in the nucleus to remove the intron-deprived RNA and splice together the exon-derived RNA into mRNA
3) After further modification, the mature mRNA travels to the cytoplasm where it directs proteins synthesis
Define exon
code for proteins
Define introns
do not code for proteins
Define small nuclear ribonucleoproteins ( snRNPs)
splice exons together
Define constitutive genes
expressed at a fixed rate
not under control
ex. enzymes involved in glycolysis
Define inducible genes ( repressible genes)
control mechanism-induction and repression
regulates transcription of mRNA
these genes are only expressed as needed
What is the the purpose of the operon model of gene expression
in bacteria it is a genetic regulatory system
set of operator,promoter, and structural genes
What is the structure of operon
operon consists of the promoter and operator sites and structural genes that code for the protein
Define promoter
segment of DNA where RNA polymerase initiates transcription of structural genes
Define operator
segment of DNA that controls transcription of structural genes
Define structural genes
regions of DNA that codes for the specific protein
Define mutation
a permanent change in the base sequence of DNA
may be neutral, beneficial or harmful
Define mutagens
a agent that cause mutations
can be anything physical/ chemical
Define spontaneous mutations
occur in the absence of a mutagens
What are the 2 types of mutations
point mutations
frameshift mutations
Define point mutation
base substitution
change only one base pair
What are the 3 sub types of point mutations
silent mutations
missense mutations
nonsense mutation
Define silent mutations
normal protein
does not change amino acid sequence b/c many codes code for the same amino acid
Define missense mutation
faulty proteins
amino acid is changed
Define nonsense mutations
incomplete protein results in stop codon stop codon ( UAA,UAG,UGA)
Define frameshift mutation
insertion or deletion of one or more nucleotide pairs
shifts the translational “ reading frame”
What are 2 types of mutagens
1) chemicals
2) radiation
Describe chemical mutagens and 2 examples
nucleotide base analogs that replace nucleotides
resemble nucleotide
exp: bromouracil resembles thymine
aminopurine resembles adenine
What chemicals react with DNA
nitrous acid ( adenine to bind to cytosine) we can make antimicrobial agent
What are the 2 types of radiation
1) Non-ionizing
2) ionizing
Describe non-ionizing ( UV radiation)
pyrimidine dimers
Describe ionizing ( xray, cosmic rays, gamma rays)
ionize water and produce free radicals
oxidize nucleotides and breaks sugar phosphate backbone
What is the frequency of mutation
1 in 10 to the power of 9 replicated base pairs
mutagens increase rate to 1 in 10 to the 5th power
What are the 3 ways of DNA repair
1) proofreading
2) mismatch repair
3) repair of thymine dimers
Define proofreading as a form of dna repair
corrected by dna polymerase
reads newly added basepair
Describe mistmatch repair as a form of dna repair
exonuclease
dna polymerase
ligase
Describe repair of thymine dimers as a form of dna repair
nucleotide excision repair ( dark repair) direct repair ( ligth repair) visible light
Define dark repair
DNA polymerase and ligase
Define light repair
photolyase
activated by light
Define genetic recombination
exchange of genes between 2 dna molecules
Define crossing over of genetic material
2 chromospmes break and rejoin
insertion of foreign DNA into the chromosome
RecA protein: does the joining
What 2 process does crossing over occur due to
1) vertical gene transfer
2) horizontal gene transfer
Define vertical gene transfer
from organism to offspring
Describe horizontal gene transfer
from cells to same generation
What are the 3 types of horizontal genetic transfer in bacteria
1) transformation
2) conjugation
3) transduction
Define transformation
genes transferred from 1 bacteria to another as “ naked” DNA
What are the 3 steps in transformation
1) receipient cells take up donor DNA
2) donor DNA aligns with complementary bases
3) recombination occurs between donor dna and recipient dna
Describe conjugation
plasmids transferred from 1 bacterium to another
special plasmid- F factor
F+ cells and F- cells
What is required in conjugation
require cell to cell contact
gram negative-sex pili-projection from the donor’s cell surface
gram positive- sticky surface molecules
Why does antibiotic resistence occur
becuase of conjugation
b/c plasmid can only be transferred by conjugation
Describe transduction
DNA is transferred from a donor cell to a recipient cell via bacteriophage
bacteriophage or phage-virus that infects bacteria
What are the 2 types of transduction
1) Generalized transduction
2) specialized transduction
Define generalized transduction
random DNA packaged inside the phage and transferred
Define specialized transduction
specific bacterial genes are packaged inside the phage and transferred
ex. toxins
What are the 5 steps of transduction
1) a phage infects the donor bacterial cell
2) phage DNA and proteins are made and the bacterial chromosomes is broken into pieces
3) occasionally during phage assembly,pieces of bacterial DNA are packaged in a phage capsid. then the donor cell lyse and release phage particle containing bacterial dna
4) a phage carrying bacterial DNA infects a new host cell, the recipient cell
5) recombination can occur,producing a recombinant cell with a genotype different from both the donor and recipient cells
Describe plasmids
self-replicating circular pieces of DNA
often code for proteins that enhances the pathogenicity of a bacterium
1-5% the size of a bacterial chromosome
What are the 2 types of plasmids
1) conjugative plasmids
2) dissimilation plasmids
Define conjugative plasmids
carries genes for sex pili and transfer of the plasmids
Define dissimilation plasmids
encode enzymes for the catabolism of unusal compounds
Define resistance factors (R factors)
encode antibiotic resistance
ex. mercury resistance,sulfonamide resistance,streptomycine resistance
chlormphenicol resistance, tetracycline resistance
Define transposons
small segments of DNA ( chromosome of plasmids)
can move from one region of DNA to other
contain insertion sequence (IS) code for transposases
complex transposons carry other genes ( antibiotic resistance genes, toxin production genes)
Define transposases
cuts and reseals DNA
