Lecture 6- Regulation of Gene expression

Question 1

structure of a gene

Answer 1

-contains a promoter, coding sequence, and a terminator

Question 2

Within the promoter

Answer 2

• is the controlling site

- where induction (increased expression of a gene) occurs

Question 3

Operon

Answer 3

-regulates genes
-one promoter serving several genes
ex- typtophan and lactose

Question 4

Operator

Answer 4

• the operon’s switch for controlling transcription
• where the repressor binds
• determines whether RNA polymerase binds to the promoter and produces proteins or not

Question 5

Repressor

Answer 5

• switches the operon off
• blocks attachment of RNA polymerase, therefore blocks transcription
• is specific
• is allosteric: 2 different shapes, active and inactive

Question 6

co-repressor

Answer 6

molecule that binds to repressor to switch an operon off

-tryptophan

Question 7

Tryptophan absent

Answer 7

• RNA polymerase binds to promoter
• transcribes mRNA to make more tryptophan
• operon on, repressor off

Question 8

Tryptophan present

Answer 8

a lot of tryptophan-> tryptophan acts as a co-repressor

• tryptophan binds to repressor and activates it
• repressor attaches to operator
• RNA polymerase can no longer transcribe

Question 9

Tryptophan operon

Answer 9

• example of repressible operon

- turned off by the end product of metabolic pathway

Question 10

Lactose operon

Answer 10

• example of an inducible operon
• usually inactive
• can be turned on by the precursor/first chemical of the metabolic pathway

Question 11

Lactose not present

Answer 11

• repressor binds to operator and blocks RNA polymerase

- mRNA cannot be made and proteins/enzymes cannot be made

Question 12

Lactose present

Answer 12

• lactose binds to repressor, changing repressor’s shape and making it unable to bind to operator
• RNA polymerase binds to promoter and transcribes to make mRNA
• mRNA is used to make the enzymes that break down lactose

Question 13

Regulatory genes

Answer 13

• codes for production of allosteric repressor protein that can switch off operon
• ex: lacI

Question 14

Structural genes

Answer 14

ex- the enzymes for lactose, break down lactose

Question 15

Mutations

Answer 15

• a permanent change in DNA

- source of new genes

Question 16

Mutagens

Answer 16

-physical and chemical agents that promote mutations
ex:
-ionizing radiation
-ultraviolet radiation
-chemical mutagens 
-pyrimidine dimer
-spontaneous mutations

Question 17

Point mutation

Answer 17

• change in single nucleotide pair of a gene
• change of a single nucleotide in the DNA’s TEMPLATE STRAND leads to altered mRNA and abnormal protein
• some have no effect on the encoded protein due to the redundancy of the genetic code

Question 18

Silent mutation

Answer 18

• no effect on amino acid sequence

- no observable effect on phenotype

Question 19

Missense mutation

Answer 19

• changes one amino acid

- may have little effect, or big effect

Question 20

Nonsense mutation

Answer 20

• causes translation to be ended early

- leads to a non functional protein

Question 21

Insertion

Answer 21

additions of nucleotide pairs in a gene

Question 22

Deletions

Answer 22

removal of nucleotide pairs in a gene

Question 23

Insertions and Deletions

Answer 23

both alter the reading frame of mRNA

-more disastrous effect

Question 24

Frame-shift mutation

Answer 24

• when insertion/deletion is not a multiple of three
• results in extreme missense mutations
• non functional protein