Pharmaceutics Flashcards
Recombinant technology: Adv - 3
Adv:
1. Efficient, cheap, & safe production, e.g. insulin, factor VIII
2. Makes rare proteins with therapeutic potential in quantities for pharmaceutical value, e.g. interferon
3. Production of vaccines, e.g. hepatitis B virus, SARS-CoV2, HPV
Recombinant DNA in natural processes - 2
In natural processes:
1. DNA repair
2. Acquire new functions such as multi-drug resistance
Recombinant DNA technology - 3
Recombinant DNA technology:
1. Analyse function of genes and their products
2. Expression/regulation studies
3 Production of industrial & pharmaceutical products
Transcription - 5
- RNA polymerase moves along the DNA unwinding the strand, starting at 5.
- Hydrogen bonds between base pairs break which allows the unzipping of the double helix.
- As RNA polymerase breaks the bonds, it synthesises aprimarytranscript of mRNA using RNA nucleotides. These form hydrogen bonds with the exposed DNA strand by complementary base pairing.
- The primary transcript of mRNA is processed to produce amaturetranscript of mRNA.
- The mature mRNA transcript is now ready to leave the nucleus and travel to the ribosome.
Translation - 7
- mRNA molecule travels through cytoplasm & attaches to the ribosome.
- tRNA molecules transport specific amino acids to the ribosome.
- Each mRNA codon codes for a specific amino acid.
- The anti-codons & codons match up & form complementary base pairs.
- Peptide bonds form between adjacent amino acids to form the polypeptide.
- Used tRNA molecules exit the ribosome & collect another specific amino acid.
- The last codon of an mRNA molecule is a stop codon which signals the end of translation.
DNA transfer: Transformation, Conjugation & Transduction
Transformation: uptake of free DNA (competence), most used in labs
Conjugation: transfer of DNA through cell-cell contact
Transduction: transfer of DNA mediated by a virus
Define: Mobile genetic elements & give examples
Mobile genetic elements: bits of DNA which are efficient in transferring from one to another e.g. plasmids, transposons, prophages
Plasmids: useful genes - 3
Naturally occurring plasmids are not essential, but often encode genes that are helpful
These plasmids may be involved in e.g.:
1. resistance to antibiotics or toxic metals
2. metabolic functions (e.g. growth on lactose, sucrose)
3. production of virulence factors (e.g. toxins such as haemolysin)
Molecular cloning - 2
- Obtain a defined sequence of DNA & produce multiple copies in vivo
- The DNA sequence can be a gene, but may also contain non-coding elements e.g. promoter
Molecular cloning - 7 steps
- DNA fragment is isolated, then using enzymes is inserted into plasmid vector
- Mix recombinant cell with E.coli (easy to transform) in the presence of CaCl2, providing a heat pulse
- CaCl2 is used as both membranes are negatively charged
- Heat pulse generates holes, pushing E.coli to be competent for DNA uptake
- E.coli takes up plasmid (which contains a ampicillin resistance gene)
- The cells are placed in presence of ampicillin, only transformed cells can grow due to resistance
- The plasmid replicates in the plate, ensuring each cell which grows is transformed
Obtaining DNA for cloning (known vs unknown)
Sequence of DNA known:
Polymerase Chain Reaction (PCR) is the most common technique
Sequence of DNA unknown:
May require the creation of a DNA library, followed by “fishing” for the gene of interest
PCR - 6 steps
- Identify target region (e.g. a specific gene)
- Design primers that are complementary to the red and green regions
- Heat up to 94 degrees for 30s, DNA is denatured
- Heat up based on primers so the primers can interact with complimentary sequences
- Thermostable Taq polymerase starts at 3 end and moves to 5, binding nucleotides to make new DNA
- The process is repeated roughly 30 times
Restriction enzymes for cloning - 7
- Recognise palindromic sequences: restriction sites
- Restriction sites for cloning usually are 4 or 6 nucleotides
- Cut both DNA strands, creating sticky or blunt ends
- Named after the organism it originates from, plus a number e.g. EcoR1
- When cleaved produces sticky ends due to paired bases facing each other
- Blunt ends are more difficult to stick together
- e.g. CGGCCG reverse is CGGCCG
Agarose Gel Electrophoresis - Purpose & 4 steps
When cut DNA fragment, to determine it’s the right size Agarose Gel Electrophoresis
1. Load on agarose gel
2. Run for an hour at negative charge
3. Stain with fluorescent dye to visualize under UV light
4. Size can be calculated from position of MW markers
DNA Ligase - 4
- ATP-dependent enzyme that links DNA strands
- Plays a role in DNA repair & replication
- Can ligate compatible sticky ends, as well as blunt ends
- Ligation of sticky ends is more efficient than ligation of blunt ends
Important regions for cloning - 2
Important regions for cloning:
1. Selection marker (genes for antibiotic-resistance or growth on specific media)
2. Region where DNA can be inserted
Cloning -5 steps
- Vector prepared using restriction digest, then purified
- PCR of insert, followed by restriction digest, then purification
- Vector & insert combined using ligase
- Prepare competent cells (heat pulse on E.coli)
- Plate cells on colonies, these are screened using Blue white-screening
Blue-white screening
- Plasmid contains lacZ gene, which encodes the enzyme β-galactosidase (degrades lactose)
- If lacZ gene is intact: β-gal active and converts artificial substrate X-Gal into blue dye
- If DNA insert disrupts lacZ gene: β-gal inactive no conversion of X-Gal into blue color
- Colonies with intact lacZ (no insert) are blue
- Colonies with inactive lacZ (with insert) are white
5 Traits for Hosts for cloning and expression
- Grows rapidly in inexpensive medium
- Non-pathogenic
- Is genetically stable
- Has many tools for genetic manipulation
- Allows high level of expression of genes
Recombinant insulin - 4
- short peptides such as insulin are not very stable (due to degradation) in cytoplasm of E. coli
- peptides can be stabilised by fusion to a large protein
- sequence of insulin can be modified if desired
- e.g. amino acid changes in insulin can be used to make insulin fast- or slow acting
Production of recombinant insulin - 4
- Clone insulin A & B chains separately in E. coli, as fusions with gene encoding β-galactosidase
- Purify fusion proteins & cleave off β-gal
- Combine A & B chains & refold in oxidising conditions in vitro
- oxidising conditions are required to form disulphide bonds for stability & activity of the protein
Modulating insulin-release profile - 3
- Mix with protein to slow release (eg NPH)
- Introduce amino acid changes
- Chemical modification
Glargine (Lantus) - 3
Glargine:
1. One deletion and 3 additions: pI 5.4 to 6.7
2. pI close to neutral pH: soluble at acidic pH but precipitates when injected subcutaneously – released from precipitate
3. Slow release
Detmir (Levemir) - 3
Detemir:
1. Modified – Thr30 deleted & fatty acid on Lys29
2. 98% binds to albumin in plasma, from which it slowly dissociates
3. Slow release
Factor VIII
- Essential blood clotting factor
- Used for treatment of haemophilia
- Very large protein of 2332 AA
- Largest recombinant protein that is used commercially
- Glycosylated
Cloning of Factor VIII
- Very large gene with several introns - requires copies to be made from mRNA
- Initial cloning was done in E. coli
- Plasmid containing F8 gene used to transfect mammalian cell lines
- Plasmid integrates in genome; number of copies amplified, & cell line with highest number of copies used for production
Protein structure
Primary – order of amino acids
secondary – alpha helices &beta sheets
Tertiary – 3d arrangement
Quaternary – Different proteins binding together
Protein stabilization - 7
- Hydrophobic interactions (80% internal), hydrophobic on inside, cause of folding
- Electrostatic (repulsions, ion pairing)
- H-bonding: Inter- & intramolecular
- VDW forces
- Steric effects
- Hydration
- Disulphide bridges, links distant area into specific conformation
Protein aggregation - 2
- Folded protein may become partially unfolded into aggregates
- When proteins unfold, hydrophobic residues are exposed, & interactions between multiple can produce fibular molecules or aggregates
Possible causes of protein denaturation or aggregation - 9
Summary: Energy change, hydrophobic interfaces or disruption of interactions.
1. Freezing/thawing
2. Agitation (interfaces)
3. Sonication
4. Contact with silicone oil
5. Low or high pH
6. Low or high salt
7. Specific salts
8. Chemical changes
9. Heat
Consequences of denaturation or aggregation - 4
- Altered solubility: Causes Hypo-potency or Hyper-potency
- Off target binding due to protein structure change
- Patient may generate neutralizing antibodies (anti-therapeutic antibodies)
- Makes drug ineffective, May break tolerance, Cross react with endogenous protein