11.1 Signal Transduction I

Question 1

Cell communication is based on the production of small molecules by one cell and their detection by another. These molecules can be:

Answer 1

Steroids, cholesterol based, peptides, small pieces of proteins, etc.

Question 2

What kind of signaling systems have local effects?

Answer 2

For local or short distance signaling, contact-dependent signaling is used.

Question 3

What kinds of signaling systems have distant targets?

Answer 3

For long distance targets, either synaptic or endocrine signaling is used

Question 4

What type of signaling systems require very high affinity binding of ligands to receptors?

Answer 4

Endocrine signaling uses high affinity binding of ligands to receptors. This is because the signals are spread throughout the body through the circulatory system. And their concentrations are relatively low. The signal must bind tightly to the receptor and the receptor must be sensitive.

Question 5

What type of signaling systems allow signaling to an individual cell or small group of cells?

Answer 5

Synaptic signaling is very specific and selective for one specific type of target cell. This means it signals directly to an individual cell or group of cells.

Question 6

What class of signaling receptors are generally transcription factors?

Answer 6

Most of the intracellular class of receptors use transcription factors.

Question 7

What is a general characteristic of signaling molecules that interact with internal receptors?

Answer 7

Small, hydrophobic molecules that contain a DNA binding motif. Many are shaped like a cholesterol molecule.

Question 8

How can signaling pathway elements be targeted to the cell membrane?

Answer 8

Phosphoinositides in the membrane next to where the signaling pathway is taking place. The PIs patch together in the membrane and allows for localized interactions between the membrane and the signaling pathway

Question 9

What general types of accessory proteins stimulate and down-regulate signaling by GTP binding proteins?

Answer 9

Guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs) are used to “catalyze” the replacement of GDP with GTP or opposite in the G-protein systems.

Question 10

What are the effects of positive feedback loops on signaling systems?

Answer 10

Prolonged response of the cell to a signal due to long term exposure to it. Or the response can be a type of “all or none” response where suddenly all cells respond at once.

Question 11

What are the effects of negative feedback loops on signaling systems?

Answer 11

There is a delay in the activity of the signal or there is an overall dampened effect of the signal.

Question 12

Receptor desensitization

Answer 12

Cell surface receptors for specific signaling systems are desensitized to the signal it is receiving.

Question 13

Cell communication

Answer 13

Communication based on the production of molecules by 1 cell and their detection by another cell.

Question 14

Receptor

Answer 14

Proteins that bind signaling molecules and receive the signal.

Question 15

Ligand

Answer 15

Molecules that bind to a receptor

Question 16

Contact dependent signaling

Answer 16

Signaling over the shortest distance is the signals between 2 neighboring cells that touch.

Example: signaling thro gap junctions

Question 17

Cells of the heart coordinate their contraction by signaling with calcium using ______ junctions.

Answer 17

The calcium travels through Gap junctions.

Question 18

Paracrine signaling

Answer 18

Moderate distance of signaling. Signaling molecules secreted from one cell are detected by another thro relatively localized areas.

Example: Autocrine signaling

Question 19

Autocrine signaling

Answer 19

A type of paracrine signaling in which the cell produces receptors that are activated by a molecule it is also secreting. This type of system is used in both positive and negative feedback loops so that cells can control their own behavior. (Important in cancer biology where cancer cells signal themselves to grow)

Question 20

2 types of long distance signaling

Answer 20

1. synaptic signaling (by neurons)

2. Endocrine signaling

Question 21

What type of signaling system do most signaling events use?

Answer 21

Endocrine signaling

Question 22

Signaling using insulin, testosterone, estrogen and growth hormones all use what type of signaling system?

Answer 22

Endocrine signaling

Question 23

Endocrine signaling uses the _______ system to carry signals. This causes the signals to become __________ .

Answer 23

1. Circulatory system (or blood system)

2. Distributed throughout the entire body, nonspecifically

Question 24

High affinity binding is used by what signaling system?

Answer 24

Endocrine signaling

Question 25

Endocrine signaling is fast or slow?

Answer 25

Slow due to the signaling molecule traveling thro the entire body or blood.

Question 26

Regulation of digestion, organismal growth, development and differentiation use ________ signaling.

Answer 26

Endocrine signaling

Question 27

Signaling molecules are diluted in what type of signaling pathway?

Answer 27

Endocrine

Question 28

What type of long distance signaling pathway has signaling molecules that are not diluted?

Answer 28

Synaptic signaling. This is because after the signal is transmitted along a neuron, the signal does not have to travel far across the synaptic cleft to be able to bind to the target cell.

Question 29

What signaling process is quick? An example of an event that uses this.

Answer 29

Synaptic signaling of a neurotransmitter across synaptic space. Changes in the diameter of blood vessels

Question 30

A target cell usually has _____ types of receptors.

Answer 30

Several different or even dozens of types of receptors

Question 31

It often takes ______ in order to tell a cell to survive.

Answer 31

More than a single type of signal in order to tell a cell that is needs to survive.

Question 32

A single signaling molecule can bind to receptors on ______ types of cells. Example of this.

Answer 32

2 different types of cells and each cell can respond differently even tho the receptor is the same. Acetylcholine neurotransmitter causes a different effect on salivary glands and cardiac muscles due to different internal signaling pathways inside the cell.

Question 33

Specific cell response can depend on the _______ of the signal that reaches the cell.

Answer 33

Concentration

Question 34

Signaling molecules involved in embryogenesis are often called _________. Why are they called this?

Answer 34

Morphogens. Because they alter the morphogenesis or shape of the tissues they are affecting.

Question 35

Morphogen

Answer 35

A molecule that when non-uniformly distributed, determines the pattern of tissue distribution in the process of morphogenesis - namely in developmental biology/embryogenesis. This concentration gradient can determine the fate of each cell and the location of cell types in a tissue.

Question 36

What are the 2 general types of receptors?

Answer 36

1. Intracellular receptors | 2. Cell-surface receptors

Question 37

Intracellular receptors

Answer 37

Bind to ligands that enter a cell with no assistance (therefore they are typically small and able to pass thro a membrane). They are hydrophobic and often transported to a target cell using a carrier system (preventing the aqueous environment of the cell to have an effect)

Question 38

Cell-surface receptors

Answer 38

Transmembrane proteins with extra cellular domains. Often a ligand can bind to the outside portion of the receptor and never enters the cell.

Question 39

What type of cell receptors are more adaptable and variable?

Answer 39

Cell-surface receptors. There are cell surface receptors for a huge variety of molecules.

Question 40

What is an example of a nuclear receptor used in nuclear export (discussed in 1st section of the course)?

Answer 40

Ran system

Question 41

All members of the nuclear receptor family are what type of receptor?

Answer 41

Intracellular receptors

Question 42

Nuclear receptors bind directly to _____ meaning they are ________ .

Answer 42

DNA | Transcription factors

Question 43

What do all nuclear family of receptors share?

Answer 43

They all share a conserved DNA binding motif.

Question 44

Nuclear receptors are normally present in an _________ state in a complex containing an inhibitory protein.

Answer 44

Inactive state

Question 45

The initial binding of the ligand to the nuclear receptor complex causes ___________.

Answer 45

The displacement of the inhibitory protein allowing for interaction with the coactivator proteins

Question 46

Activation of nuclear receptors can have: - immediate/early cell response - longer term secondary responses

Answer 46

Both

Question 47

The 3 types of cell surface receptors:

Answer 47

1. Ion-channel coupled receptors 2. G-protein coupled receptors 3. Enzyme coupled receptors

Question 48

Ion-channel coupled receptors

Answer 48

Open or closes pores in the cell membrane in response to ligand binding. The opening of the pores usually generates rapid changes in ion concentration within the cell such as calcium or sodium or potassium.

Question 49

G-protein coupled receptors

Answer 49

Huge class of proteins that work by activating another set of membrane associated proteins which is the complex of 3 proteins which uses GTP as a secondary signaling mechanism.

Question 50

Enzyme coupled receptors

Answer 50

The receptor has an enzymatic function of its own that becomes functionally active when ligands bind to it.

Question 51

To localize proteins to unique places in a cell, the cell uses ________ proteins.

Answer 51

Anchoring proteins

Question 52

Scaffold protein

Answer 52

Scaffold proteins interact and bind to multiple members of a signaling pathway, tethering them into complexes. This can help to localize pathway components to specific areas of the cell (plasma membrane, cytoplasm, nucleus, golgi, endosomes, mitochondria) and help to regulate signal transduction

Question 53

What are the 3 types of scaffold proteins?

Answer 53

1. Very large protein that serves as the scaffold with multiple binding domains interacting with the activated receptor and downstream signaling proteins 2. The receptor itself has a large domain acting as the scaffold 3. Activation of phosphorylated lipids in the adjacent membrane

Question 54

Almost all signals will involve the phosphorylation of proteins on 1 of 3 different amino acids. List in order of frequency:

Answer 54

Serine, Tyrosine and Threonine

Question 55

The activity of a specific protein can be either increased or decreased by _____________ depending on the type of protein.

Answer 55

Phosphorylation

Question 56

Phosphate groups added to amino acids during signaling events are added using a phosphate provided by _____ and catalyze by _______ .

Answer 56

ATP | Kinase enzymes

Question 57

Phosphate groups are removed to turn off signaling pathways by enzymes called ____________ .

Answer 57

Phosphatases

Question 58

The addition of GTP to a protein replacing GDP is enhanced by ______________ .

Answer 58

GEF (Guanine nucleotide exchange factor)

Question 59

What happens in the absence of a feedback loop?

Answer 59

The signal generated by receptor activation might be simply the reflection of the number of ligands that bind to a receptor.

Question 60

What is an example of a system in our bodies that uses the concept of receptor desensitization?

Answer 60

Sense of smell - rapidly desensitized in order to allow the olfactory system to respond to new odors. Important for animals detecting new smells even in the presence of another one

Question 61

How do you desensitize a receptor system?

Answer 61

1. Sequester in an endosome 2. Degrade and destroy it 3. Inactivate downstream signaling elements