Module 7 - Microbial Genomics Flashcards
What is genomics?
Methods to study the entire genome of a microbe
Why is genomics important?
It provides insight into evolutionary relationships and detection of unknown organisms
What does introduction of DNA into microbes often lead to?
Gene disruption, allowing for studying loss-of-function on phenotype
What is a genome?
An organism’s complete set of DNA (including all genes)
What is genomics?
The collective characterization and quantification of genes (entire genome)
What is genomics?
The collective characterization and quantification of genes (entire genome)
What does genomics focus on?
The structure, function, evolutionary mapping, and editing of genomes
What needs (3) were created based on genomics?
- Improved DNA sequencing techniques
- Formats for storage of very large data sets
- Tools for analysis of large data sets
What needs (3) were created based on genomics?
- Improved DNA sequencing techniques
- Formats for storage of very large data sets
- Tools for analysis of large data sets
When was DNA sequencing first developed?
1970
What is sequencing?
The process of determining nucleic acid sequence
What did Walter Gilbert do?
Developed a chemical degradation method of DNA sequencing
When was Sanger sequencing developed?
Around 1970 (same time as Gilbert sequencing)
When was Sanger sequencing developed?
Around 1970 (same time as Gilbert sequencing)
What did Fredrick Sanger do?
Developed an enzymatic method using DNA polymerase
What is another name for Sanger sequencing?
Dideoxy sequencing, or chain termination sequencing
What are the three steps of Sanger sequencing?
- Clone a gene of fragment of DNA of interest
- Synthesize DNA with DNA polymerase
- Use electrophoresis to separate fragments of DNA at different lengths
What are the three steps of Sanger sequencing?
- Clone a gene of fragment of DNA of interest
- Synthesize DNA with DNA polymerase
- Use electrophoresis to separate fragments of DNA at different lengths
What is Sanger sequencing based on?
The fact that DNA polymerase requires a free 3’ OH group to continue DNA synthesis
What holds the two strands of DNA together?
Hydrogen bonds
What holds two consecutive nucleotides together?
Phosphodiester bonds (between 5’ phosphate group and 3’ hydroxyl group)
What is the significance of the 3’ OH group?
It is essential for chain elongation
What is the significance of the 3’ OH group?
It is essential for chain elongation
What is a nucleotide with a 3’ H called?
A dideoxyribonucleoside triphosphate (ddNTP)
What is the principle of dideoxy sequencing?
ddNTPs will stop chain elongation
What is the principle of dideoxy sequencing?
ddNTPs will stop chain elongation
How is the DNA sequence determined in Sanger sequencing?
By detecting labeled nucleotide at the end of each fragment separated by gel electrophoresis
How is the DNA sequence determined in Sanger sequencing?
By detecting labeled nucleotide at the end of each fragment separated by gel electrophoresis
What are the components (4) of the reaction mixture for Sanger sequencing?
- A template DNA to be sequenced
- A short oligonucleotide primer
- DNA polymerase enzyme
- All 4 dNTPs
How is the primer designed in Sanger sequencing?
To be complementary to the vector sequence
Why is the primer labeled in Sanger sequencing?
To allow for ease of detection of DNA pieces
Why is the primer labeled in Sanger sequencing?
To allow for ease of detection of DNA pieces
How is the Sanger sequencing reaction carried out?
In 4 tubes
What is the different with each tube in Sanger sequencing?
The specific ddNTP used (ddATP, ddTTP, ddCTP, and ddGTP)
What happens when a ddNTP is incorporated in a reaction in Sanger sequencing?
DNA synthesis is terminated
What happens when a ddNTP is incorporated in a reaction?
DNA synthesis is terminated
What happens when a dNTP is incorporated in a reaction in Sanger sequencing?
The DNA chain elongation will continue
What determines how many products will be in each reaction tube in Sanger sequencing?
Based on the number of times a specific nucleotide appears in the template DNA sequence (number of incorporation points)
How does a gel separate DNA fragments?
Larger fragments are at the top, while smaller fragments are at the bottom
How does a gel separate DNA fragments?
Larger fragments are at the top, while smaller fragments are at the bottom
What types of labels can be used in Sanger sequencing?
Radioactive labels, or fluorescent labels
How come fluorescent labels are used more frequently than radioactive labels?
Fluorescent labels are safer, cheaper, and easier than radioactive labels
How come fluorescent labels are used more frequently than radioactive labels?
Fluorescent labels are safer, cheaper, and easier than radioactive labels
How many bases can be sequenced by Sanger sequencing in a day?
700-1000 bases
How many bases can be sequenced by Sanger sequencing in a day?
700-1000 bases
How is a gel read in Sanger sequencing?
From bottom to top (Guitar Hero)
If a gel from Sanger sequencing reads 5’-AGTCT-3’, what is the DNA sequence from 5’ to 3’?
5’-AGACT-3’
If a gel from Sanger sequencing reads 5’-AGTCT-3’, what is the DNA sequence?
5’-AGACT-3’
What is primer walking?
Designing primers such that the 5’ end complements the end of the last DNA segment sequenced
What is primer walking?
Designing primers such that the 5’ end complements the end of the last DNA segment sequenced
What is pyrophosphate?
Two phosphates bonded together
What is pyrophosphate?
Two phosphates bonded together
How is pyrosequencing similar to Sanger sequencing?
It uses DNA polymerase
What happens if a dNTP is incorporated in pyrosequencing?
A pyrophosphate is released, which can be detected
What happens if a dNTP is incorporated in pyrosequencing?
A pyrophosphate is released, which can be detected
What reaction does pyrophosphate undergo in pyrosequencing?
APS + PP –> ATP
What does APS stand for?
Adenosine phosphosulfate
What enzyme catalyzes the reaction of pyrophosphate in pyrosequencing?
ATP-sulfurylase
What does ATP-sulfurylase do?
Converts APS and pyrophosphate into ATP
What does ATP do in pyrosequencing?
It can be used in a luciferase reaction to produce detectable light
What does CCD stand for?
Charged-coupled device
What does CCD stand for?
Charged-coupled device
What happens in pyrosequencing after a wash?
The reaction is repeated with a different dNTP base
When is light detected in pyrosequencing?
Only when the dNTP is complementary to the template base
How many bases can be sequenced by pyrosequencing in a day?
300-500
What is pyrosequencing used for?
Resequencing or sequencing genomes for which a close relative is already available
What is pyrosequencing used for?
Resequencing or sequencing genomes for which a close relative is already available
What are the steps of whole-genome shotgun sequencing?
- Shear the DNA into short pieces
- Sequence the fragments
- Use a computer algorithm to reconstruct
What are the steps of whole-genome shotgun sequencing?
- Shear the DNA into short pieces
- Sequence the fragments (Sanger sequencing)
- Use a computer algorithm to reconstruct
How can the fragments of DNA be sequenced in whole-genome shotgun sequencing?
- Cloning fragments, then Sanger sequencing
2. Directly on fragments using high-throughput sequencing
What do computer programs do in whole-genome shotgun sequencing?
Identify regions of sequence overlap from the fragments
What do computer programs do in whole-genome shotgun sequencing?
Identify regions of sequence overlap from the fragments
How come ~10x genome size is needed for whole-genome shotgun sequencing?
There is a random distribution of fragments generated
How come ~10x genome size is needed for whole-genome shotgun sequencing?
There is a random distribution of fragments generated
How many microorganisms have currently been sequenced?
3,000
How many microorganisms have currently been sequenced?
3,000
What is another name for high-throughput sequencing?
Next-generation sequencing
How many base pairs can high-throughput sequencing sequence at a time?
25-500
How many reads can high-throughput sequencing generated?
Hundreds, thousands, or millions of reads
What is the consequence of high-throughput sequencing having many reads?
High coverage, but a more computationally intensive assembly process
What are some examples of high-throughput sequencing?
Illumina (Solexa), Nanopore DNA sequencing, single molecule real time (SMRT), DNA nanoball, and SOLiD sequencing
What are some examples of high-throughput sequencing?
Illumina (Solexa), Nanopore DNA sequencing, single molecule real time (SMRT), DNA nanoball, and SOLiD sequencing
What DNA sequencing is currently under active development?
Third-generation sequencing
How does third-generation sequencing work?
By reading nucleotide sequences at the single molecule level
What is bioinformatics?
An interdisciplinary field that develops software and methods to understand large and complex biological data
What is bioinformatics?
An interdisciplinary field that develops software and methods to understand large and complex biological data
What is the purpose of annotation?
It allows for researchers to predict ORFs
What does ORF stand for?
Open reading frames
What is the importance of ORFs?
They allow researchers to better determine the start and stop points for a given gene
How can functions for newly discovered proteins be suggested?
Based on observed similarities
What can researchers speculate about a gene by looking at its sequence?
Whether it is a transcriptional factor, transport protein, or some enzyme
True or false: many genes have known proteins associated with them
False: many genes predicted by sequencing data encode gene products whose functions remain unknown
What is functional genomics?
The study of finding out the biological role of unknown genes
What is functional genomics?
The study of finding out the biological role of unknown genes
What types of experiments are part of functional genomics?
Using metagenesis to study phenotypes
How is gene expression generally regulated?
At the transcriptional level
What is a genomic library?
A collection of all the genes in a genome (cloned DNA fragments)
What can a genomic library be used for?
Whole genome sequencing
What does the method for obtaining a genomic library depend on?
The desired outcome
How can an mRNA library be formed?
By using cDNA generated from reverse transcriptase
What does reverse transcriptase do?
Convert RNA into DNA
What does cDNA stand for?
Complementary DNA
What does cDNA do?
It is the complement to the expressed mRNA
How can a true genomic library be formed?
By shearing the genome and cloning the fragments
How are DNA fragments prepared for a genomic library?
Through restriction analysis
How are clones generated for a genomic library?
By ligating the DNA fragments into plasmids, and transforming the cells
What determines how many clones are needed to represent the whole genome in a genomic library?
The size of the genome, and the average size of each cloned fragment
What equation can be used to calculate how many clones are needed for a genomic library?
N = ln(1-p)/ln(1-f)
In the equation for a genomic library, what is N?
The number of cloned fragments
In the equation for a genomic library, what is p?
The probability of generating a complete library
In the equation for a genomic library, what is f?
The average size of a fragment divided by the total genome size
What is the difference between a cDNA library and a true genomic library?
A true genomic library has all the genes, while the cDNA library only has genes that encode proteins
What is the difference between a cDNA library and a true genomic library?
A true genomic library has all the genes, while the cDNA library only has genes that encode proteins
What understanding do expression patterns allow for?
How organisms function under different conditions
What is a transcriptome?
A set of transcribed mRNA molecules in a cell
How can a transcriptome be measured?
Through northern blots
What is the procedure for a northern blot?
- Total RNA is isolated from cells of interest, and separated with gel electrophoresis
- RNA is transferred to a membrane
- RNA is probed with labeled DNA fragments