Genetics Flashcards
The central dogma?
DNA > RNA by transcription
RNA to protein by translation
Define transcription (state its location)
The 3 stages of transcription?
What types of post-transcriptional mods are there for the mRNA strand produced?
Where does the mRNA synthesized during transcription go
synthesis of mRNA copied from DNA base sequences by RNA polymerase II in the nucleus
stages: initiation, elongation, termination
mods: 5’ capping, adding 3’ poly-A tail, splicing to remove introns
mRNA transcript moves out of nucleus into cytoplasm for translation
Process of initiation in transcription?
RNA polymerase II binds to promoter region (at the TATA box)
Protein transcription factors bind to promoter region
RNA polymerase unwinds DNA double helix and initiates transcription
Function of the promoter region, relative location to the gene to be transcribed and functions of transcription factors?
Promoter region:
contains promoter sequences (TATA box) or RNA polymerase binding, also serves as binding site for transcription factors
location: 25-35 base pairs upstream of gene to be transcribed
transcription factors: proteins that can control rate of transcription by promoting or repressing transcription
Process of elongation?
mRNA synthesized from 5’ to 3’ direction
RNA polymerase 2 moves along the antisense (template strand), adding new mRNA nucleotides to the 3’ end of the strand
free mRNA nucleotides (nucleotide TRIPHOSPHATES) aligned opposite to their exposed complementary DNA partner are joined together covalently by using the energy from cleavage of additional phosphate groups
Coding strand goes around the “outside and not actually directly involved
Process of termination?
RNA polymerase II reaches the terminator region on DNA (RNA DOES NOT have the specific sequence to direct RNA polymerase II to terminate at a specific location so the terminator region is DNA)
enzyme and nascent mRNA strand detach from DNA template, DNA rewinds
Then post-transcriptional modification: 5’ capping, adding 3’ polyA tail, splicing to remove introns
How are the post-transcriptional mods done
5’ capping: 7-methylguanosine attached to the 5’ end of the hnRNA to form 5’ cap
3’ polyA tail: polyA tail attached to 3’ end by Poly A polymerase
intron removal: using proteins to form spliceosome for introns to be spliced (only exons remain)
Purposes for post-transcriptional mods?
Protect mRNA against early degradation (increased stability)
facilitate translation
Process of translation?
- RNA passes out from nucleus to ribosomes in cytoplasm where translation takes place
- The ribosome has a large and small subunit which assemble around the mRNA
- Transfer RNA (tRNA) carries individual amino acid
- Codon on mRNA matches anticodon on tRNA
- A site, P site then E site as sequence that tRNA binds at ribosome : APE
- Protein synthesis proceeds with finished amino acid chain emerging from ribosome then folding into conformation
The structure of hemoglobin and no.of genes coding
tetramer (2 alpha subunits, 2 beta subunits)
alpha protein subunits: coded by HBA1 and HBA2 genes
Beta subunit HBB1 coded by HBB gene
3 genes in total
Cause of phenotype in sickle cell anemia?
Hemoglobin gene mutation in HBB subunit (HBB gene mutated to HbS gene)
glutamic acid replaced by valine
valine is hydrophobic so tends to stick together and clump up to avoid aqueous environment
tends to form fibers
cell shape distorted
Why is the sickle-cell phenotype still prevalent in Sub-Saharan Africa
Risk allele helps protect against severe malaria
Cause of thalassemia phenotype and its inheritance pattern?
Produce no or too little hemoglobin (alpha or beta
thalassaemia)
Autosomal recessive
Inheritance pattern of cystic fibrosis?
The symptoms of cystic fibrosis?
Cause of cystic fibrosis phenotype?
Autosomal recessive
Symptoms: salty skin, poor growth, thick sticky mucus, chest
infections
Absence of phenylalanine in CFTR gene (codes for CFTR that
transports chloride across membranes)
Delta F508 (Phe)
Core histone proteins in the nucleosome?
H2A, H2B, H3, H4
Some numerical data about DNA:
1) width of the DNA helix?
2) length of major and minor groove for each turn of the double helix?
3) How many base pairs per turn
4) degrees per rotation of base
1) 20A
2) 34A, 3.4A
3)~10.4
4) 36
Cause of spinal muscular atrophy phenotype?
Exon 7 not included → cannot make SMN1 and so rely on SMN2 to make protein→ shorter SMN Protein ⇒ non functional
CRISPR-Cas9 mechanism in bacteria and its function?
Immune response preventing viral infection
Guide RNA
■ matching sequence with RNA complementary to the DNA of
the invading virus
Tracer RNA
■ constant region of RNA that scaffolds with the Cas 9 protein
Guide RNA + Tracer RNA: sgRNA (single guide RNA)
complex + enzyme (nuclease) ⇒ Cas9
○ RNA locks onto the PAM of viral DNA, Cas9 unzips DNA and matches it to target RNA
○ Cas9 cuts DNA, cell tries to repair the gene but the process is error prone
The applications for dCas9? (meaning of dCas9)
dCas9: dead Cas9 with only the binding activity but not endonuclease activity
1) CRISPR can be used to add transcription factors to promote transcription
2) or CRISPR can be used to directly bind Cas9 to a DNA sequence to silence that gene
3) or attach fluorescent proteins to observe DNA loci activity
Overview 1 clinical trial using CRISPR-Cas9
Curing Leber congenital amaurosis: inherited blindness caused by mutation of CEP290 gene coding for CEP290 protein that helps retinal cilia properly function
CRISPR-Cas9 can help correct the mutation by gene editing
Insulin action that causes glucose absorption? And the consequences?
● Insulin binds to receptor
● The glucose transporter is inserted into the membrane to allow glucose shuttling
● There are more glucose transporters embedded in the membrane
● [Downstream: glucose transporters are transported up into membrane]
● Change in conformation of intracellular domain of insulin receptor
● Increase uptake of glucose into liver cells/ muscle cells
● Increased glycogen synthesis (glycogenesis) as a response to increase in insulin
