Biochem week 11-12

Activity 1:

Briefly explain the amplification feature of signal transduction and provide a specific example.

Also called enzyme or signal cascade. A single signal molecule will activate an enzyme (enzyme 1) which will in turn activate several second enzymes (enzyme 2), each second enzyme activate several other enzymes (enzyme 3), etc.

Binding of a molecule of epinephrine to 1 β-adrenergic receptor activates several G proteins, which in turns activate adenylyl cyclase producing many cAMP. These will activate several PKA enzymes, which will then activate thousands of glycogen-degrading enzymes.

See lecture 11-1 slide 9 and 11-2 slide 12

Activity 2:

Briefly describe the meaning of integration in signal transduction and its different effects on the cell.

Integration in signal transduction represents the combination of multiple signals to give a specific response. The difference in the combination of signals will be provide 4 main types of response: survival, division, differentiation or death.

See lecture 11-1 slide 12

Activity 3:

Put these RTK activation steps in the correct order:

(1) The receptor phosphorylates downstream proteins

(2) The receptor auto-phosphorylates

(3) Ligand binds to extra cellular domain of receptor

(4) The receptor dimerises

3 -> 4 -> 2 -> 1

See lecture 11-3 slide 4

Activity 4:

Using your knowledge of integration in signal transduction, explain why a mutation in an RTK could lead to cancer. You can use a specific example to explain this concept.

A mutation in an RTK in the ligand binding domain can lock the receptor in the active conformation. Provided that this RTK is part of the signal that incites a “divide” response, the cell constantly receives a “divide” signal regardless of the presence of the ligand, which could lead to uncontrolled division. (example of ErbB2 could be used)

See lecture 11-3 slide 7

Activity 5:

Name 4 of the 7 processes that affect steady-state concentration of a protein.

1. Initiation of primary RNA transcript synthesis

2. Processing of primary RNA into mRNA

3. Degradation of mRNA

4. Protein synthesis

5. Posttranslational modification of protein

6. Targeting and transport of protein

7. Degradation of protein

See lecture 12-1 slide 5

Activity 6:

What are the 2 types of gene expression in bacteria? Explain how they are different.

The 2 types of gene expression are constitutive and regulated. Constitutive gene expression means the genes are constantly expressed at unchanging levels. Regulated gene expression means the expression of genes is either induced (turned on) or repressed (turned off)

See lecture 12-1 slide 6

Activity 7a:

Which of these statements about positive regulation is TRUE:

a. Involves activators

b. Involves repressors

c. Increases gene expression

d. Decreases gene expression

Activity 7b:

Which of these statements about negative regulation is TRUE:

a. Involves activators

b. Involves repressors

c. Increases gene expression

d. Decreases gene expression

See lecture 12-1 slides 7 and 10

Activity 8:

Make these statements correct by changing one (1) word:

· An operator is a cluster of genes sharing a promoter and regulatory sequences. (operon)

· The lac operon relies on positive regulation and susceptible to lactose concentration for expression. (negative)

· In eukaryotes, negative regulation is the most common regulation due to chromatin structure. They require activator proteins. (positive)

See lecture 12-1 slide 11; 12-2 slide 4

Activity 9:

Explain the regulation of the lac operon.

Lactose metabolism is regulated by lactose availability whereby the transcription of genes for enzymes responsible for lactose metabolism is repressed in the absence of lactose, but the transcription is no longer repressed when lactose is present in the environment.