Microbial Genetics Flashcards
How does DNA relate to the behavior of a microorganism?
-DNA contains inheritable instructions for protein construction (amino acid sequences)
What is the connection between a pathogens DNA and its ability to cause disease?
- all mediated by proteins
- controlled by DNA (template)
What do coding genes control?
-protein amino acid sequences
What do regulatory genes control?
-timing of coding gene expression
Ex. Promoter
-recruits RNA polymerase
What is the mRNA info used for?
-used by ribosome to build proteins during translation
What is a reasonable size for a bacterial coding gene?
1000 bp (base pairs)
How many coding genes does a typical bacterial cell?
- approximately 5000 genes
What does RNA polymerase build?
-builds RNA by reading 1 strand of DNA (template) and building complementary RNA
RNA characteristics
- single stranded or fold to form double stranded regions
- contains protein sequence info
What are the types of RNA?
mRNA, tRNA etc
Is mRNA +sense or -sense?
+ sense
Is template DNA +sense or -sense?
-complementary (-sense)
RNA polymerase binds DNA to make mRNA at DNA sequences called?
-promoters
What are promoters?
-Where RNA polymerase binds to DNA to make mRNA
What part of a promoter can a regulatory protein bind to?
-operator
What type of gene is a promoter?
Regulatory gene
What are the 2 types of transcriptional regulation proteins?
- activator proteins bind regulatory genes and attract RNA polymerase
- repressor proteins bind regulatory genes and block RNA polymerase
Transcription regulation occurs in what two ways?
- Negative Regulation
- positive regulation
Weak promoter characteristics
- weakly attract RNA polymerase
- low baseline rate of transcription
- some become strong promoters when activator proteins attach to them
- found near coding genes
Strong promoter characteristics
- attracts RNA polymerase very well
- high baseline rate of transcription
- some become blocked when reporters or proteins attach to them=transcription repressed
What is induction?
-increases the amount of a specific protein
What is repression?
-decrease the amount of a specific protein
Explain the 2 ways how induction can occur
1) an inducer binds an activator protein causing the activator to bind to a promoter
2) an inducer binds to a repressor protein, causing the repressor protein to detach from the promoter
Explain how repression occurs
-co-repressor binds to a repressor, causing it to attach to a promoter (blocks RNA polymerase)
Example of an inducer and how s causes induction
- lactose (sugar) binds to the Lac repressor protein and causes it to detach from a promoter
- iron
Example of a co-repressor and how is causes repression
-tryptophan (amino acid) binds to the Lac repressor and causes is to bind a promoter
What is an Operon?
- set of genes that are regulated at the same time
- ex. Genes encoding 5 enzymes needed to build tryptophan (amino acid) are turned on or off at the same time
What does the start codon represent?
-beginning of codons
What is the function of a stop codon?
-cause ribosome to release mRNA and polypeptide
What is a messenger (rRNA)?
Amino acid sequence information (from coding DNA genes)
What are codons?
- Nucleic acid words
- 3 bases long
- encoding enough info for 1 amino acid
What is a transfer (tRNA)?
-adaptor molecule that carries amino acids to ribosome
What is an anticodon?
-portion of tRNA that base pairs with a codon in mRNA
What are mutations?
-changes in DNA sequence
Characteristics of a mutation
- may or may not alter proteins
- can be lethal (cell death), detrimental (- effect), neutral, or beneficial (+effect)
- spontaneous or induced
What are point mutations?
-small scale mutations where 1 or a few bases affected
Explain what happens in large scale mutations
-aka chromosomal aberration
- involves large regions of a chromosomes being duplicated, repeated or moved from 1 place to another
- 1000 bp
What are spontaneous mutations?
-replication errors (DNA polymerase errors)
What are induced mutations?
-mutagens (UV, ROS, carcinogenic chemicals) damage DNA and cause increase number of replication errors)
What are mutagens? Examples?
- something that causes mutations
- UV, ROS, carcinogenic chemicals
What is a missense mutation?
- a type of point mutation
- DNA change results in one changed amino acid in a protein
- may have no effect on protein function
- may have drastic effects if amino acid that changed is important for protein function
- ex. Enzyme active site
How do cells detect and repair damaged DNA?
-proofreading proteins detect damaged DNA and direct repair enzymes to the damaged sites
What are the 2 types of gene transfer in unicellular microbes?
- vertical gene transfer
- horizontal gene transfer
Explain the vertical gene transfer process
-parent cell DNA is passes to daughter cells during the cell division process
(Parents to offspring)-most common form of inheritance
Explain the horizontal gene transfer process
-transfer of DNA from 1 cel to another, not during the cell division process
(No parent, daughter cell relationship)
What are the 3 types of horizontal gene transfer?
- transformation
- transduction
- conjugation
What is the typical size of a plasmid?
Range?
How many genes?
- typically 5000 bp
- range: 800-30000 bp
- approx 5 genes
What is the conjugation process?
- transfer of plasmids through a mating bridge
- f plasmid instructs cell to make mating bridge
- sometimes donor cell and recipient cell are connected by sex pious prior to mating bridge
Important components of bacteriophage vision
- phage head
- tail sheath
- tail fiber (binds to host cell)
- DNA
What is a bacteriophage?
- aka ‘phage’
- viruses that infect bacteria
Lytic cycle process
- Phage attaches to host cell and inserts DNA
- Linear dsDNA cyclizes to circular DNA
1) cell synthesizes capsid proteins
2) cell replicates phage DNA. DNA packaged into capsids
3) phage lyses cell, and progeny phases are released
What is a prophage?
-when a phage DNA integrates into a host genome
What is recombination?
-one DNA molecule can insert into another DNA molecule creating a new DNA sequence
What is a transposon?
DNA molecules that inserted and cur out repeatedly (jumping genes)
