4.1 gene expression and operon structure

Question 1

central dogma of molecular biology

Answer 1

explain flow of genetic information DNA –> RNA –> protein

Question 2

transcription start site

Answer 2

green for Go! what allows transcription of DNA to mRNA to start

Question 3

transcription stop site

Answer 3

red for stop! what stops transcription process

Question 4

how does transcription begin

Answer 4

• when RNA polymerase binds to the promoter element
• RNA polymerase scans along the DNA strand until it reaches the transcription start site
• mRNA copy is made from the information from the transcription start site through the open reading frame, all the way to the terminator sequence.

Question 5

while eukaryotic genes contain ___ bacteria genes do not

Answer 5

interons
– means there is no need to splice the mRNA (removing non-coding parts)

Question 6

why is the no need to splice mRNA convenient for bacteria

Answer 6

remember that bacteria do not have a nuclear membrane, means the DNA is in cytoplasm of the cell
– therefore as soon as mRNA is transcribed it can also be simultaneously available for translation
– therefore they occur at the same time in a bacterial cell

Question 7

mRNA orientation

Answer 7

5’ to 3’ because transcribed on 3’ end of DNA

Question 8

basic makeup of an mRNA strand / process to translation

Answer 8

1. starting at the 5’ end, ribosome binding site.
2. once ribosome has bound to mRNA, it will scan along the mRNA until it encounters the first AUG (translation start site)
3. ribosome continues moving along the mRNA, reading in triplets and grows peptide strand.
   4.mRNA will be transcribed until reaches one of the 3 stop codons.
4. will cause translation to stop, the ribosome to disassociate from mRNA, and the protein to be released from the ribosome.

Question 9

AUG encodes what

Answer 9

methionine

Question 10

bacterial genes can be coexpressed

Answer 10

promoter can control the expression of multiple genes

Question 11

group of genes controlled by a single promoter is called.

Answer 11

an operon

Question 12

operon description

Answer 12

like in a gene that encodes a single polypeptide, there is a single site for RNA polymerase to bind (start site)

– difference is that this single mRNA encodes multiple proteins– this mRNA is referred to as polycistronic

Question 13

polycistronic

Answer 13

‘poly’ = many
‘cistron’ used to refer to operon reading frame

Question 14

what are the components in an operon

Answer 14

promoter, operator, structural genes

Question 15

the operon is a convenient mechanism for genetic regulation..

Answer 15

clever way to ensure that genes that encode proteins that are needed for the sae process are co-expressed

Question 16

what are sigma factors

Answer 16

– proteins that contribute the most to regulation of bacterial gene transcription

Question 17

role of sigma factors

Answer 17

recognize particular DNA sequences, to bind to them, and to recruit the core RNA polymerase to the DNA, forming the holoenzyme so that transcription can be initiated

Question 18

the sigma factor places..

Answer 18

the RNA poly at a discrete site through recognition of the DNA sequences located 10 and 35 base pairs up from the transcription start site (before it)

Question 19

sigma factor 70 directs transcription

Answer 19

sigma factor binds to promoter region, recuiting RNA polymerase, and the process of transcription of the operon begins.

Question 20

activator proteins

Answer 20

interact with DNA sequences in and around promoter
– in doing so, they make the promoter region MORE attractive to RNA polymerase – activates more transcription

Question 21

repressor proteins

Answer 21

often interact with the operator region and HINDER the ability of RNA polymerase to move alone the DNA strand, blocking transcription,.