Lecture 14 Flashcards
What is meant by genetic heterogeneity?
-phenomenon where a single phenotype or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus) mutations. -a phenotype can be the result of mutation in different genes e.g. deafness: 120 independent genes may result in deafness when mutated = genetically heterogenous trait
What are the three processes in transcription?
-initiation-promoter recognition -elongation -termination
What determines where RNA synthesis begins?
RNA polymerase binds to promoter regions and this determines where RNA synthesis begins -+1= start of transcription everything to the left= upstream, right= downstream promoters always upstream from the initiation point
What is a promoter?
special DNA sequences recognised by the RNA polymerase 20-200 bases
What is this?
-for RNA polymerase to bind we have to have the other proteins
Describe:
enhancer- enhances transcription
yellow-influenced by protein binding or not binding
pink-where RNA polymerase binds
-DNA flips back, brings the enhancer in contact with the transcription complex and that will start tanscription
-what proteins in a cell at a time can switch genes on/off
What does binding of a repressor protein do?
-blocks transcription
What does binding of an activator protein do?
-stimulates transcription
What happens at the transcription initiation?
RNA polymerase binds and DNA is denatured in this region
• DNA strands separate • First RNA nucleoside triphosphate is placed
at the site
-once RNA polymerase is bound- has to melt the DNA so it’s single stranded = opens up the strand
What happens at transcription elongation?
- RNA polymerase moves along DNA template strand adding bases 5’ 3’ to growing RNA strand
-bases are complementary to the DNA
template
What happens at transcription termination?
RNA polymerase reaches a chain termination sequence
This is a sequence which can form a loop
..CGTCCGA….TCGGACG.. ..GCAGGCA….AGCCTGC..
RNA polymerase and mRNA are released
RNA formed from the end sequence will bend on itself- then RNA poilymerase drops off
What is reverse transcriptase?
some viruses have only RNA(instead of DNA as well), they employ enzyme reverse transcriptase to manufactire DNA out of RNA, this DNA can take over the machinery of the cell they’re infecting, take RNA make single-stranded DNA and make it double stranded by special PCR techique
What is the difference in mRNA production in prokaryotes and eukaryotes?
- Prokaryotes the primary transcript is mRNA,so just have a single step since mRNA is the primary RNA in prokaryotes
- In eukaryotes the primary transcript is modified
and processed into mRNA,ot of processing before primary transcript is made into mRNa
Where does the RNA processing take place?
-in the nucleus before it leaves to the cytoplasm
What is the first step of RNA processing? (ends)
- The ends of the transcript are treated for stability and binding to the ribosome
- treated at its ends- modification there allows it to find its way through the nuclear membrane and to the ribosomes
modifications at both 3’ and 5’ end
5’- special methyl guanosine 7 Me G
3’- a whole sequence added of upto 200 adenines =capping(7 Me G) and tailing (adenine)
What is the step no 2 in RNA processing? (splicing)
The mRNA is commonly spliced, the introns are removed and the exons (expressed sequences) joined up to make the final transcript
-there are sequences in the hnRNA that are cut out, the intervening sequences=introns= sequences that are transcribed but won’t go to be translated
-the sequences left behind are the expressed sequences= exons
hnRNA into mRNA by capping and tailing then splicing then mRNA
-alternative splicing of the same primary transcript may create different mRNA molecules
Can we get more protein types from one primary transcript?
-yes, the case of alternate splicing in trypomyosin
which of the introns are cut ot varies with tissue type example tropomyosin in skeletal muscle miss exon 2
- then get variance of the protein in different tissues
- more protein types from the same primary transcript
How is sex determination in drosphila connected to alternative splicing?
sxl gene produces tra protein as a consequence of that the sxl protein has an influence on the splicing of the RNA transcript
-in sex determination in drosphila- associated with differential splicing in the pathway
How mamy bases per amino acid?
3
64 possible combinations
=degenerative= more than one combo for an amino acid
=the third base not as important
- for RNA= codons
- DNA= triplets
Does every DNA sequence that is transcribed get translated?
No!
-mRNA is the only RNA to be translated into a polypeptide
ribosomal RNA for example, transfer RNA, micro RNA(doesn’t get translated)
