Transcription And Lactose

Question 1

Initiation

Answer 1

RNA polymerase recognize promoter and attaches to the promoter site on DNA . Then separate the DNA strands and determines which strand of DNA is used as a template while the other strand is called the non template strand

Question 2

Elongation

Answer 2

The RNA polymerase enzyme adds RNA nucleotides from the 5’ to 3’ end of the growing RNA strand . As the RNA strand elongates , it peels away from its template and DNA strands then re-forms into double helix .

Question 3

Termination

Answer 3

RNA polymerase recognizes termination sequence on the DNA template . Then signal the RNA polymerase to stop transcribing DNA and detach from the DNA template . This will release the newly formed (pre) mRNA molecule .

Question 4

Definition transcription

Answer 4

The synthesis of mRNA using DNA as the template .

Question 5

function lacI , promoter , operator , lacZ , lacY and lacA

Answer 5

• lacI codes for repressor protein
• promoter provide binding site of RNA polymerase
• operator provide binding site of repressor protein
• lacZ codes for B-galactosidase hydrolyzes lactose to glucose and galactose
• lacY codes for permease transports lactose into the cell
• lacA codes for transacetylase transfer an acetyl group from acetyl CoA to B-galactosidase

Question 6

When lactose is absent

Answer 6

The regulatory gene (lacI) codes for repressor protein . Repressor protein can switch off the operon by binding to the operator . Blocks attachment of RNA polymerase . RNA polymerase cannot bind to the promoter . Transcription of structural gene is blocked by repressor-operator complex . lacZ , lacY and lacA genes are not transcribed . Enzymes B-galactosidase , permease and transacetylase are not produced

Question 7

When lactose is present

Answer 7

Lactose molecule enter E. coli . Lactose will be converted into allolactose . Allolactose binds to repressor protein forming allolactose-repressor complex . The binding alters repressor protein conformation . Repressor protein unable to attach to the operator gene . RNA polymerase then binds to the promoter and transcribe the structural genes to produced mRNA . mRNA then translated by ribosome into three enzymes which are B-galactosidase , permease and transcatylase .