FINAL MC Flashcards
What are the Advantages of Protein Expression in Yeast vs bacteria?
- Protein folding
- Post translational modifications such as phosphorylation, adding sugar residues
- Secretion (proteins targeted to various organelles or exported for harvesting)
- Vectors can be maintained as PLASMIDS or INTEGRATED
What are the disadvantages of Protein Expression in Yeast vs bacteria?
-Higher number of recombination events
-Longer growth time
-Post translational modifications such as glycosylation may be different when compared to human proteins
(hyper glycosylation of secreted glycoproteins can be observed)
What are the advantages of yeasts vs other eukaryotes?
- LESS EXPENSIVE, EASIER TO GROW, HIGH THROUGHPUT- you get a lot for the amount of time you spent.
- Shorter cell cycle than tissue culture
- Transformation/DNA manipulations easier
- HIGHER PROTEIN YIELD
- Protein pharmaceuticals free of human disease (don’t have to worry about yeast becoming infected with some virus or something that can infect a human that consumes)
- Fewer regulations compared to tissue culture
- More extensive genetics
What are the disadvantages of yeasts vs. other eukaryotes
- Glycosylation in yeast can be different (usually adds extra glycosol groups to proteins)
- In the ER membrane there is protein generation/modifications and sometimes they get stuck there so they can’t secrete
- it is a lower eukaryote so not as many genes
Which of the following is NOT an advantage of yeast expression systems?
A) High protein Yield
B)Hyper glycosylation of protein products
C)Vectors can be maintained as plasmids or integrated into the chromosome
D)Fewer regulations compared to tissue culture systems
B) hyper glycosylation of protein products
What are the transformation methods for yeast?
1) Spheroplast preparation-production of wall-less yeast cells with enzymes and fused with PEG in the presence of CaCl2 and DNA (NOT USED OFTEN)
2) Lithium acetate wash-mimic any electrical charges with the lithium acetate wash, PEG, and heat shock to get DNA into the cell
3) Electroporation: heat shock and hope the DNA gets into the cells
Selection of transformants for yeast
- complementation markers (URA3, LEU2, TRP1, HIS3)
2. Dominant Selection Markers (resistance to antibodies such as G418, hygromycin, or Zeocin)
Yeast can be transformed by.... A) Electroporation B) Use of dominant markers C)Spheroplast production D) Lithium acetate treatment and heat shock E) A, B, and C F) A, C, and D
F
Why use P. Pastoris for Protein Expression?
Like Saccharomyces cervisiae:
- Easy to manipulate
- Faster, easier, less expensive than other eukaryotic systems
Advantages over Saccharomyces:
-10-100 FOLD HIGHER HETEROLOGOUS PROTEIN EXPRESSION LEVELS
Grows to extremely high cell densities
Intracellular or secreted protein:
- Pichia Pastoris secretes low levels of native protein
- Easier Purification
Insulin
is being produced by S. Cerevisiae under the product NOVOLOG
Hep. B virus surface antigen
is being produced by Pichia Pastoris under the product Hep. B vaccine
MCSF- macrophage colony stimulating factor
is being produced in S. cervesiae under the produce Leukine
Bone Marrow transplants
treat with high levels of GMCSF-cytokine that causes immature bone marrow cells to become mature immune cells. High doses goes to the blood, only treat for a few days then collect blood and put into the patient
Xylanase
Industrial Enzyme produced in yeast
-breaks down hemicellulose
Uses:
- pulp and paper
- textile industry
- animal feed
Cellulase
Industrial enzyme produced in yeast
-breaks down lignin/cellulose
Uses:
- animal feed
- ethanol production
What are some other uses of other industrial enzymes used in yeast?
production of wine
extraction of olive oil
fermentation of tea, coffee, and cocoa
Yeasts are used to produce many valuable therapeutics for human use. What is one advantage of yeast over E. coli in terms of production of recombinant proteins.
A)High protein yield
B) ability to glycosylate proteins so that they resemble human proteins
C) variety of promoters available including constitutive and inducible promoters
B) ability to glycosylate proteins so that they resemble human proteins
Why use PLANTS for the generation of recombinant proteins?
Plants LIKE YEAST are not contaminated by bacterial or mammalian borne pathogens
Engineer plants that are resistant to pesticides and herbicides, grow larger, or stay fresh longer.
- Bt corn and soybeans express a toxin from Baccillus Thuringiensis
- HT (herbicide tolerant) corn and soybeans express C4 EPSPS, making crop resistant to the herbicide glyphosate
Easy way to administer drugs/vaccines to individuals.
- problem is that it expensive, its to grow in third world countries, people would have to eat a good amount to get the protection that they
- Vitamin A-expressing bananas
- rice that expresses a vaccine for Cholera
Arabidopsis Thaliana
- WEEDS
- compared to tobacco it has a relatively small genome
- produces many seeds
- cheap and easy to grow
- small so do not need a lot of growing space
- short life span (6 weeks seed to germinate and develop into mature plants)
- small genome compared to other plants
- genome has been sequenced
- efficient transformation with Agrobacterium Tumefaciens
Plant Tranformation Agrobacterium tumefaciens
- clone your gene of interest into agrobacterium. Its in specific plasma called a TI plasmid
- Biolistic or microparticle bombardent: gene uncoats your DNA onto gold or tungsten particles that act as bullets, and use very high pressurized chamber with vacuum. This will cause wounds and allow DNA to get into cell.
- Protoplast fusion
- Have a screen for both to make sure its in the cell
Stable vs. Transient transformants by using the Gene gun
Stable transformants: can be generated if bombarding undifferentiated cells; select for cells that received DNA. Tissue culture required
Transient Transformants: can be generated if bombarding WHOLE PLANTS, as not all cells of the plant will receive DNA
Stable vs. Transient transformants by using AGRO
Stable transformants generate by floral dip and collection of seeds
Transient transformants generated by leaf infiltration
Stable transformants
maintain same DNA throughout life
transient Transformants
usually top leaves of the plants get more DNA
Selectable marker genes for stable transformants
allow for the selection of transformed cells by their ability to grow in the presence of antibiotics or herbicides
- antibiotics: kanamycin and hygromycin
- herbicides: glyphosphate and glufosinate
Screenable marker fore genes for stable transformants
allows not only for the selection of transformed cell, but gives an estimate of where trangene expression is located and the levels of transgene expression
- Enzymes such as beta-glucuronidase (GUS), chloramphenicol acetyl transferase (CAT), luciferase, GFP, or beta-galactosidase
- Enzyme activity is determined by histochemical staining or fluorometric assay
Mammalian Cell transfection
- Procedure to introduce foreign nucleic acids into cells to produce genetically modified cells
- study gene function and regulation as well as protein function
- produce recombinant protein
Types of transfection
-Transfection same process of transformation just called that bc its in mammalian cells
1) stable:
- genetic materials are integrated into the host genome
- genes expressed after host cells replicates
2) Transient:
- genes only expressed for a finite period of time
- Genes can be lost by environmental factors or cell replication
Why do mammalian cell transfection?
Gene Therapy:
- good for diseases that don’t have pharmaceutical inhibitor that would restore function of the gene
- Adding a gene into cells to replace a defective gene or lack of a gene
- Therapy for neurological diseaeses, chronic diseases, and some forms of cancers since ether don’t have great treatment options
- Cure diseases, the patients still have the mutation that caused the disease but decreased symptoms
iPS cells
- commonly taken from the skin
- transfect cell with the addition of three or four transcription factors to revert differentiated cells
- can give rise to any fetal or adult cell type
- many possibilities
RNA interference:
- mRNA is made but it actually chews up the mRNA so the protein isn’t made or isn’t made in its normal levels.
- Any disease where decreasing a genes product is beneficial
- Decreases gene product, post-transcriptional
Mammalian Cell Transfection Methods Characteristics
METHOD used will depend on your cell type and purpose
-ideally, methods should have high transfection efficiency, low toxicity, minimal effects on physiology, easy to use, and reproducible
Biological method of mammalian cell transfection
Ex: virus-mediated (transduction)
-high-efficiency, easy to use, effective on cells, slices and in vivo
Chemical method of mammalian cell transfection
Ex: cationic polymer, cationic lipid (most commonly used), calcium phosphate
-No viral vector (TRansduction), high-efficiency, easy to use, easily purchased, effective on cells and slices
Physical method of mammalian cell transfection
Ex: direct injection, electroporation, biolistic particle delivery, laser-irradiation, etc.
-Straight forward, no need for vector, physical relocation of nucleic acids into cell, less dependent on cell type and condition, single cell
Which type of transfection depends upon the integration of foreign DNA into the host genome? A) Stable B) Transient C) Direct D) Indirect
A) Stable
Which method involves using virus to deliver foreign DNA into the host genome? A) Transfection B) Transduction C)Electroporation D) Nucleofection
B) Transduction
Which method is NOT suitable for incorporating nucleic acids into mammalian cells? A) Transduction B) Cationic Lipids C) injection D)Electrical Current E) They are all suitable F) none are suitable
E) THey are all suitable
What is the solution to this problem:
Problem: You want to express a protein, but you aren’t sure whether it would be best expressed in E. coli, mammalian cell culture, yeast cells, insect, or plants.
Or what type of fusion tag would work best and if it would be better C or N terminally.
clone genes in frame into a Gateway donor vector (ENTRY Clone), and then move easily into multiple expression vectors
The purpose of Gateway cloning is to:
A) streamline the act of moving a gene into multiple vectors/hosts
B) Quantitate transcription of all the genes on the genome
C)Clone a gene of interest into E. Coli in the easiest, quickest manner
D)Rapidly determine the nucleotide sequence of a gene
A) streamline the act of moving a gene into multiple vectors/hosts
Look at gate way cloning and chart at the end of 4/6 lecture
!
What is evaluated when measuring gene expression of eukaryotic organisms?
the presence and/or amount of mature mRNA
-should always follow-up with protein expression assays to assess translational regulation
Bacteria transcription and translation
RNA polymer sometimes transcription factors bind to promoters
- mRNA is translated by a ribosome into protein. This occurs in the cytoplasm of the bacteria
- single ORF
-bacteria contain multiple genes controlled by a single promoter, a single mRNA transcript is made, and multiple proteins are made (operon)
Eukaryotic transcription and translation
Have a promoter and Ribosome binding site (RBS). ORF is broken up into segments
- Contains exons and introns
- introns could code for alternative splicing sites NOT JUNK or miRNA coding regions
- Transcription occurs and still have RBS, eons, and introns. mRNA is turned into mature mRNA by adding a 5’ cap and 3’ poly A tail and introns spliced out
- All occurs in the nucleus of the eukaryotic cell. Then shuttled out via the ribosome. The 5’ cap prevents degradation/stabilizes from exonucleases. Also, the 5’ cap is used for binding of the Ribosome
-SIGNALING for nuclear export. Also, used for processing/splicing removal of introns from pre-mRNA
Eukaryotic mRNA isolation
- Lyse cells and treat with DNase. Treat with DNase because you want RNA contaminated with RNA
- Run cellular content over OLIGO (DT) COLUMN to bind poly(A) RNA. Oligo (dt) column similar to affinity chromatography. Has a string of T’s that bind to the 3’ Poly A tail/
- mRNA is immobilized on the column
- all other cellular impurities, including ribosomal, and tRNAs run through - Wash column
- Elute mRNA from column so you have nice pure mRNA. mRNA is a very small portion 1-2% of the total mRNA in the cell.
Problems with RNases
- resistant to chelation
- resistant to autoclaving
- found on skin, in water, in samples (everywhere)
Solutions when dealing with RNases
Diethylpropcarbonate (DEPC) treatment inactivates RNases, but DEPC doesn’t last forever
- Wear Gloves ( and change often)
- Purchase RNase free water and buffers
- Use RNase free micropippette tips that have an aerosol barrier
- work quickly and keep samples cold
How do you make cDNA from mRNA
1) add primers (oligo d(t) primer), which binds to 3’ poly A tail. Then add reverse transcriptase. You end up with a hybrid molecule where one strand is mRNA and one is cDNA. FIRST STRAND cDNA Synthesis
2) Nicking Step: add RNase H-randomly which chew up the mrNA sequence called the nicking step
3) Second Strand cDNA synthesis: add DNA polymerase such as Vent, then add dNTPs and DNA ligase
Type of Primers for the first step of the first strand cDNA synthesis
- Oligo (dT) primers, 12-20 nt in length, which bind the poly(A) tail of mRNA
- Specific primers specifically designed to anneal to the cDNA sequence of interest. Use only if wanting to generate specific cDNA.
- Random Hexamers: randomly generated 6 nt oligos that will anneal randomly to mRNA. Get better cDNA so preferred
Reverse Transcription has low processivity: it will not copy all of a long mRNA (likely have to use more than one primer per mRNA molecule)
-Processivity: the average number of nt added by a polymerase per association/dissociation with the template
Why is quantifying gene expressions (mRNA levels) of interest?
- find out what gives a cell certain characteristics (i.e., disease vs. healthy, brain vs lung)
- identify genes that combat a certain stressor (i.e. drug)
- identify genes in a regulatory pathway
**you can miss genes that are regulated at the translational level (or by microRNAs). This is, just because the message is present, doesn’t mean that the protein is present(always follow up with protein study)
What would you do?
Baker’s yeast (Saccharomyces cerevisiae) has the ability to grow under aerobic and anaerobic conditions. You have been given a project to determine which genes are utilized under each condition. You want to be able to look at all genes at once.
So what technology would you use?
deep sequencing or high throughput sequencing is replacing microarray
What is the purpose of using microarrays?
is to examine the transcriptional regulation of whole genome at once
Microarray process
placed on a chip, use PCR to synthesize oligos or bunch of pieces of DNA that represent all genes in the organism. Then Robot spot on individual locations on that chip ssDNA Then use robots, will spot onto a glass chip
Cy3 and Cy5 experiment
Cy3 fluoresces Green (aerobic)
Cy5- Red (anaerobic DNA)
Mix together in equal ratios and allow to hybridize to the slide. Allow them to bind Robot do all of this.
- Fluorescent molecules bonded to nucleotides which are incorporated into cDNA during reverse transcription
- Fluorescent molecules absorb at a particular wavelength of light and emit at a different one; the experiment is set up with two dyes with separate emission peaks
Cy3 and Cy5 are examples of:
A) Fluorescent molecules that can be bound to nucleic acid for microarray analysis
B) specialized nucleotides that are used for microarray analysis
C) enzymes that assist samples in hybridizing to the microarray plate
A) Fluorescent molecules that can be bound to nucleic acid for microarray analysis
What sample is added to a microarray chip? A) mRNA B) cDNA C) gDNA D) protein
B) cDNA
Example: you are studying gene regulation of light versus dark cycles in zebrafish
What is the :
Biological replicate
Test RNA from several fish. Statsitics for variation among living entities
-testing for a specific gene
Example: you are studying gene regulation of light versus dark cycles in zebrafish
What ist he technical replicate
Test mRNA from one zebrafish on more than one chip (and/or more than one spot). Stats for variations arising from experimental procedure
-to make sure that the confidence for that particular zebra fish is 100% correct. Gonna run 3 samples from each zebrafish so 3 different times so that all of them match/make sense
Affymetrix Microarrays
-Affymetrix makes “gene chips” for model organisms. These have some advantages over “homemade” chips.
Affymetrix: single dye: single sample per slide -Oligo Probes -available for model organism -easier to compare multiple conditions
Homemade Microarrays
Double dye: always compare 2 samples/conditons
- longer probes
- custom
If you only have a couple genes to study some other techniques that could be used are?
- Northern Blotting; time consuming and outdated
- Reverse Transcriptase PCR; simple, hard to quantify cDNA amount with convetional RT-PCR
Quantitative PCR or Real Time PCR
same thing
-can be used to measure amounts of DNA or mRNA (quantitative reverse transcriptase PCR) present in sample
RT-PCR
reverse transcriptase PCR (non-quantitative)
qPCR detection methods
quantitative (real time) reverse transcriptase PCR
PCR signal (i.e. product) is detected in “real time” or as it appears in the reaction
New PCR products/amplicons= the products
1st method:
SYBR green: a dye that intercalates into double stranded DNA and fluoresces upon excitation
-Advantages: cheap, easy to use
-Disadvantages: can bind to primer dimers and non-specific PCR products (i.e. false positives)
-CAN AMPLIFY INTO ANYTHING
-Primer design is imperative
2nd Method:
TaqMan: fluorescent-labeled probe with quencher hybridizes to template DNA. When the probe is displaced by Taq polymerase, the quencher is released and the fluorescence is detected.
-Advantage: only specific PCR products are detected
-Disadvantages:expensive- need a different probe for each reaction
LOOK AT qPCR
!11 write out on to piece of paper
How do you quantitate for PCR results?
compare another sample to get relative values
-Standard curve to get absolute values
qPCR controls
No RT control: to make sure you don’t have DNA contamination of original sample.
Negative control: to make sure your reagents are not contaminated
Internal control (housekeeping) standardize for number of cells
- same copy number and constitutively expressed in all cells
- exs: GAPDH, Tubulin, Beta-actin genes
If you wish to examine the effects of a chemical on the transcription of all genes in an organism’s genome, which method would be best to use? A) northern blotting B) qPCR C) RT-PCR D) Microarray
D) microarray
If you wish to quantify the transcriptional level of a single gene, which method would be best? A)Northern Blotting B) qPCR C) RT-PCR D) Microarray
B) qPCR
What dye, sometimes used in qPCR, only fluoresces when it’s incorporated into double stranded DNA A) cy3 B) cy5 C) SYBR green D) Taq Man
C) SYBR GENE
What type of probe, sometimes used in qPCR, only gives a signal once the dye is released from the quencher? A) Cy3 B)Cy5 C) SYBR Green D) Taq Man
D) Taq Man
Dicer
-is an ATP-dependent RNAIII-like protein which progressively cleaves the long dsRNA in small dsRNA