Lecture 13: Gene Expression

Question 1

Why does the regulation of genes matter

Answer 1

• helps us get from fertilized eggs, to a clump of non-specialized cells, to complex organisms (via cell cycle)
• differentiation

Question 2

Gene Similarity: Humans and Monkeys

Answer 2

• explains why we have great genetic similarity with monkeys but are still very different species

i.e. Human and Gorilla are 98% genetically similar (98% of the genome is similar)

Question 3

All somatic cells are

Answer 3

are genetically identical

Question 4

So how can cells be different

Answer 4

cells express various combinations of genes
= makes them different from each other (gene expression)

Question 5

How is gene expression controlled

Answer 5

• transcriptional regulation

additional controls:
- posttranscriptional
- translational
- post translational

Question 6

Gene Expression for Prokaryotes

Answer 6

Prokaryotic gene expression reflects life history:
- rapid, reversible response to environment (hence they have to produce the appropriate proteins fast)

Question 7

Regulation of G.E. for prokaryotes

Answer 7

Operon: A cluster of prokaryotic genes and DNA regulatory sequences

• RNA polymerase binds at promoter for operon (cluster of genes including genes to be transcribed and regulator sites (i.e. promoter))
• Many genes may be transcribed into 1 mRNA
• Cluster of genes is transcription unit (transcribed all together at once)

Question 8

Operon

Answer 8

• Operator: regulatory DNA sequences in operon

*Regulator proteins bind the operator
- coded by genes outside operon

1) Repressor proteins
2) Activator proteins

Question 9

Repressor Protein vs Activator Proteins

Answer 9

repressor proteins: prevent operon genes from being expression (don’t transcribe genes)

activator proteins: turn on expression of genes from operon
- activates transcription and allows it to work

Question 10

LAC OPERON

Answer 10

• lactose metabolism in E. coli (requires lacZ,lacY,lacA)
• lac operon contains all three genes and regulatory sequences (prokaryotes have this)
• Lac operon OPERATOR sequence is between the promoter and lacZ

Question 11

where is the operon

Answer 11

between promoter and first gene of transcriptional unit

Question 12

lac Z codes for
What about Y? A?

Answer 12

Z- B-galactosidase (breaks lactose down)

Y- permease (lets it in cell (transport))

A- transacetylase (lets it in the cell (transport))

Question 12

lac repressor

Answer 12

• codes for proteins, that, when it binds to the operator, it turns off the transcription of genes
• lac operon: codes for metabolism of lactose

Question 13

lac Operon E. coli
- not present

Answer 13

• active lac repressor binds to the operator of the lac operon to BLOCK transcription

Question 13

what happens when lactose is absent

Answer 13

• Lac repressor
• stops lac operon expression (bc prokaryotes shouldn’t be making enzymes for digestion of lactose, costs them energy)
• encoded by lacI, synthesized in active form (3D structure that can easily bind to operator sequence)
• binds operator
• prevents transpcription

Question 14

Purpose of binding operator
(lactose is not present)

Answer 14

• ## lac repressor will bind to the operator to turn off RNA polymerase, prevents it from transcribing lac operon

Question 15

What happens when lactose is present

Answer 15

• ALLOCATOSE: made from lactose
• Induver: of lac operon by binding to Lac Repressor
• allocastlase but try to migrate 2/n
• Inducible operon because inducer increases expression

Question 16

Operon

Answer 16

0- some of lactose is converted by alloactose. SALLACTOSE
- reror inactivation a sp that to vammpt bind the operators

Question 17

Positive regulation for lac operon

Answer 17

• lac operon operators when lactose but not when glucose is on? Why”
• glucose more efficient energy than source of 2n^2

Question 18

Cutatbolite Activator Protein

Answer 18

• activator that stimulates the order gene ecpression(2)