Lecture #12- Genetic Expression

Question 1

define Central Dogma

Answer 1

• refers to the flow of information in the cell
• unidirectional flow of info in cell
• from DNA -> transcription -> mRNA -> translation -> protein

Question 2

draw out the structure of a prokaryotic gene

Answer 2

• all genes must have a promoter, where RNA poly assemble
• sequence of DNA that regulates initiation of transcription

Question 3

How does the cell know that is a gene: in prokaryotes

Answer 3

• there are conserved sequence elements that direct gene expression
• eg. TATA box: commonly found in promoters = A and T rich sequence found 10 ntds before the transcription
• transcription factors (TF): proteins that can read DNA, bind to TATA box to recruit RNA poly
• eg. sigma factor

Question 4

How does the cell know that is a gene: in eukaryotes

Answer 4

• euk make more complex decisions than prok therefore there are lots of different DNA elements that regulate transcription and lots of different transcription factors = combinatorial control

Question 5

What is transcription, define both template and coding

Answer 5

DNA -> RNA
- DNA is read 3’ - 5’ because RNA is made 5’ -> 3’

template: DNA strand that runs 5’ -> 3’ and used in transcription
coding: strand not used in transcription, complementary and antiparallel to template
enzyme of transcription is RNA poly

Question 6

draw the gene expression in bacteria

Answer 6

pg. 5

Question 7

Draw transcription initiation complex

Answer 7

pg6

Question 8

what is elongation

Answer 8

• as mRNA is elongated, the area that is unwound ic called the transcription bubble
• DNA double helix reforms and the single stranded RNA hangs out of the complex, and another RNA polymerase can being there fore a gene can undergo transcription many times simultaneously

Question 9

what is termination and draw transcription termination

Answer 9

• RNA sequences that signal the end = terminators
• transcribed from specific DNA sequences; signal the end of transcription
• terminators often form hairpin loops which help release the RNA polymerase and the mRNA chain

Question 10

What is post-transcriptional processing

Answer 10

• only in euk
• modifications are required to increase the stability of the transcript in the cytosol
  three post-transcriptional modifications:
  1. addition of a methyl-guanosine cap at the 5’ end
  2. addition of 100-200 adenosines to the 3’ end, known as the poly-A-tail
• this is to prevent the unwanted degradation of RNA

Question 11

for euk where does transcription and translation take place

Answer 11

transcription - nucleus
translation - cytoplasm

Question 12

What is RNA splicing

Answer 12

• its the removal of introns
• exons: a.a coding regions which contain expressed sequences found in both gene’s DNA and mRNA
• introns: non a.a coding regions which contain intervening sequences found ina gene’s DNA
• enzyme is spliceosomes

Question 13

list the mRNA start codon and stop codons

Answer 13

Start: AUG
STOP: UAG, UAA, UGA

Question 14

What is tRNAs and their function

Answer 14

• functional RNA molecule
• fxn is to carry the correct a.a to the ribosome
• just the adaptor not NOT the translator

Question 15

What is Aminoacyl tRNA synthetases

Answer 15

• the translators
• correct matching of tRNA and its associated a.a
• pairs correct a.a to tRNA based on anticodon sequence

Question 16

what is the ribosome and draw out their function

Answer 16

• made up of a large - catalytic subunit that contains rRNAs
• and small subunit - mRNA recognition
• catalyze peptide bonds