Lecture 14 - Activation and Inhibition of Proteins Pt. II

Question 1

What are some ways that a message can be passed on during signal transduction?

Answer 1

1. Proteins
2. Chemical signals (second messengers)
3. Sequential phosphorylation

Question 2

What do the multi-step pathways of signal transduction help provide?

Answer 2

opportunities for coordination and regulation of the cellular response

Question 3

Which of the two mechanisms of signal transduction are most common to many receptors?

Answer 3

second messengers, and phosphorylation

Question 4

What receptors use second messengers?

Answer 4

many different receptors, especially GPCRs

Question 5

What are second messengers?

Answer 5

intracellular molecules that change in concentration in response to receptor activation

Question 6

How do second messengers work?

Answer 6

transmit signals form the receptor to other relay molecules because they are not attached to the membrane

Question 7

What does Phosphorylation and Dephosphorylation do to proteins?

Answer 7

Turn protein activity on and off, or up and down

Question 8

How does phosphorylation occur?

Answer 8

Protein kinases transfer phosphates from ATP to protein

Question 9

How does a phosphorylation cascade occur?

Answer 9

Via the use of many different protein kinases

Question 10

How does dephosphorylation work?

Answer 10

Protein phosphatases rapidly remove the phosphates from proteins to carefully control signal transduction

Question 11

What are some ways that signal transduction is tightly regulated?

Answer 11

1. Ligand dissociation
2. Internalisation (removal of receptor from cell surface via endocytosis)
3. Phosphatases

Question 12

How does signal transduction occur in GPCRs?

Answer 12

1. GPCRs use G proteins to start signal transduction
2. GPCR activates the G protein which communicates with other proteins in the cell
3. Different types of G proteins cause different effects

Question 13

What are some examples of G proteins?

Answer 13

Question 14

How does Glucagon (A peptide ligand) receptor signal transduction occur?

Answer 14

1. Glucagon receptor is a GPCR
2. Glucagon binds receptor
3. Receptor activation causes G Protein activation + leads to further signal transduction events
4. Leads to Glycogen breakdown + lipolysis

Question 15

How does GLP-1 receptor signal transduction occur?

Answer 15

1. GLP-1 receptor is a GPCR
2. GLP-1 binds receptor
3. Receptor activation causes G protein activation and further signal transduction
4. Leads to insulin secretion

Question 16

What is GLP-1?

Answer 16

A peptide ligand that is produced in the gut, and acts on pancreatic Beta-cells

Question 17

How are adaptor proteins phosphorylated? (starts signal transduction in RTKS)

Answer 17

1. agonist ligand binds
2. receptor changes conformation and becomes activated
3. receptor autophosphorylation occurs
4. adaptor protein is phosphorylated

Question 18

How does signal transduction occur in RTKs?

Answer 18

1. Agonist ligand binds
2. Adaptor protein is phosphorylated
3. Adaptor proteins communicate with other proteins in the cell
4. Different types of adaptor protein result in different effects

Question 19

How does insulin receptor signal transduction in muscle and adipose cells occur?

Answer 19

1. Insulin binds to insulin receptor (an RTK)
2. Receptor activation causes phosphorylation of adaptor protein + further signal transduction events
3. Leads to GLUT-4 translocation
4. Permits entry of glucose into cell

Question 20

What is insulin?

Answer 20

An endogenous peptide ligand

Question 21

How does insulin receptor signal transduction in liver cells occur?

Answer 21

In liver cells, receptor activation causes phosphorylation of an adaptor protein and further signal transduction events. However this leads to Glycogen synthesis in the liver rather than glucose entry

Question 22

How do ligand gated ion channels differ from other receptor classes?

Answer 22

• Instead of the use of relay proteins like G proteins or adaptors being used ions directly flow through the channels to produce effects
• Faster signalling compared to GPCRs and RTKs

Question 23

How are ligand gated ion channels activated?

Answer 23

Binding of an agonist ligand causes a conformational change to activate receptor

Question 24

How can cellular responses be controlled by receptors?

Answer 24

Depending on where receptors are expressed

Question 25

Why can different cells detect and respond differently to the same ligand?

Answer 25

Because they have different collections of receptor and relay molecules

Question 26

How can the same ligand and receptor pairing result in different effects in different cells?

Answer 26

different cells use different combination of relay molecules for signal transduction

Question 27

What is the role of the pathway branching and ‘cross-talk’ in cellular signalling?

Answer 27

Helping coordinate signals from incoming ligands