Mechanism of Microbial Genetics Flashcards
List the Pyrimidines
- Cytosine (C)
- Thymine (T) in DNA, Uracil (U) in RNA
- They are a 1 ring system
List the Purines
- Adenine (A)
- Guanine (G)
What is DNA made up of
- Phosphate group
- Deoxyribose (sugar)
- Nitrogenous base (A,T, C,G)
What type of bond exist between nitrogen bases in DNA
Hydrogen Bond
What is Genetic Code
set of rules that determine how a nucleotide sequence is converted into AA sequence of a protein
Define Genotype
The organism genetic makeup
- represents potential properties but not properties themselves
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Define Phenotype
actual expressed properties
- manifestation of the genotype
What is the Central Dogma of Molecular Biolgoy
Describes flow of genetic information in cells
DNA-mRNA-Protein
DNA Pol I
Exonuclease
- removes RNA primer and replaces w/ newly syn. DNA
DNA Pol II
Repair Function
DNA Pol III
Main enzyme
- Adds nucleotides in 5’-3’ direction
Helicase
unwinds DNA helix by breaking H bonds between nitrogenous bases
Ligase
seals gaps between Okazaki fragments to create 1 continuous DNA strand
Primase
Synthesizes RNA primers needed to start replication
Sliding Clamp
Helps hold DNA polymerase in place when nucleotides being added
Topoisomerase
helps relieve stress on DNA when unwinding by causing breaks and then resealing DNA
Single-stranded binding proteins (SSB)
binds to single-stranded DNA to avoid DNA rewinding back
DNA replication is Non-specific, explain
Once DNA replication starts it does not until it is done
In what direction is DNA read and in what direction is it synthesized
- 3’-5’
- 5’-3’
Where does DNA replicaiton start? what is the name of the site?
it starts at site called Origin (ori) and proceeds in both directions around chromosome
Explain the process in Initiation during Replicaiton
- DNA replication starts at site called Origin (Ori) site.
- Helicase binds to DNA strand and unwinds in both directions of chromosome to create a Replication Fork
- Single-Stranded Binding Protein (SSB)binds to single strand of DNA to keep it from winding back
- Polymerase synthesis RNA Primer which is required to start replication process.
- DNA Pol I removes RNA primer which then allows DNA Pol III to add nucleotides in 5’-3 direction
Explain the Elongation process
The replication fork has a leading strand and a lagging strand
- In the Leading Strand, nucleotides are added continuoulsy by DNA Pol III
- In Lagging Stran, nucleotides are added in segments called Okazaki Fragments which each has its own RNA Primer.
- DNA Pol I removes the primers so DNA Pol III can add nucleotides
- Ligase seals the gaps between Okazaki Fragments
Explain Termination process in Replicaiton
In bacteria involves the resolution of circular DNA concatemers by Topoisomerase IV to release 2 copies of circular chromosome
list the 3 stop codons
- UGA
- UAG
- UAA
Start Codons
AUG
what is a point mutation
mutation in which a single base is substituted or replace by another
What is an insertion mutation?
addition or one or more bases
What is a deletion mutation
removal of one or more bases
when does spontaneous mutation occur? do they occur naturally or are induced?
occurs during replication process where DNA Pol III
What is a transition mutation
a purine (A or G) or Pyrimidine (C or T) is replaced by other other
what is a transversion mutation
when purine is replaced by a pyrimidine or vice-versa
this is most common mechanism of mutaiton
what is a frameshift mutation
what are the potential outcomes for an insertion or deletion of a base
- Silent mutation: mutation changes original codon to another codon that codes for same AA
- missense mutation: mutation changes original codon into another codon that codes for different AA
- nonsense: mutant stop codon replaces a wild type codons, terminating translation and now have shorter protein
list the kinds of mutations and what do the act on
- physical
- chemical
- biological
They act on DNA directly
what can potentially prevent bacterial cells if there has been a mutagen
an SOS response which temporary induces cell cycle arrest and mutagenesis
explain the effect of a physical mutation, example, and type of mutation that can occure
- UV exposure or radiation
- UV radiation damages DNA by creating covalent linkages between adjacent pyrimidine bases
- inhibits replication and translation
- usually results in deletion mutation
explain the effects of ionizing radition and what type of radiation is it
ionizing radiation can cause a break in phosphate back bone, can be single stranded break or double stranded break
explain effects of non-ionizing radiation and what type of mutagen is it
non-ionizing radiation can lead to thymine dimers that can stall replication and transcription.
it causes frameshift mutation or point mutation
it’s a physical mutation
What are chemical mutations
mutagens that directly/indirectly induce mutation
list the type of chemical mutagens
- Base analogs
- Reactive oxygen species
- Deaminating Agents
- Flat Aromatic Compounds
- Alkylating Agents
what are biological agents of mutations
they come from sources of DNA from elements like transposons and viruses
what is a transposon
sequence of DNA that can relocate and replicate autonomously
list the 3 types of transposons and what they do
- Replicative Transposon keep original locus and translocate a copy
- conservative Transposon is when original transposon relocates
- Retrotransposon transpose via RNA intermediates
what are the significance of a mutation?
- it can help understand the function of a gene
- a mutation can be induced at a specific region to produce a suitable mutagen
- spontaneous mutation can cause bacteria to have to increase antibiotic resistance
- mutations can cause change in phenotype
list 2 ways antibiotic resistance can occur
- through mutations
- acquisition of resistance from other bacteria
how are thymine dimer mutations fixed
they are fixed through photoreactivation (light repair) in presence of visible light
- enzyme called photolyase recognizes the distortion and binds to the dimer
how do you test to detect or select mutations
using Ames Test to ID mutagenic potentially carcinogenic chemicals
- use of Salmonella histidine auxotroph
What is an Auxotroph
Any microorganism that has nutritional requirements that are not present in parents
what does replica plating test for
ID of auxotrophs
list the results of mutation (8)
- missense mutation
- nonsense mutation
- silent mutation
- frameshift mutation
- lethal mutation
- conditional lethal mutation
- suppressor mutation
- inversion mutation
What is Genetic Recombination
The exchange of genes between 2 DNA molecules to form new combinations of genes on a chromosome
explain the steps in DNA Recombination
- DNA from one cell aligns with DNA in the recipient cell
- DNA from donor aligns with complementary base pairs in recipient chromosome, crossing over
- RecA protein catalyzes joining of 2 strands
- recipient chromosome now contains new DNA
how can asexual prokaryotes get genetic diversity (horizontal Gene transfer)
- Transformation: DNA obtained from environment. DNA remains separate as plasmid or incorp into host genome
- Transduction: bacteriophage injects DNA that has hybrid viral DNA and previously infected bacterial cell
- Conjugation: DNA transferred through sex pili
