Cell and Gen Bio Ch. 11 Part 1 (Textbook)

what are the components of the signal transduction pathway

1. Signal reception

2. Signal transduction

3. Cellular response

explain how yeast mate using receptors

• yeast identify their mates by chemically signaling when they reproduce sexually

• There are two sexes (mating types) of yeast: a and α.

• Each type of yeast secretes a specific factor that only binds to receptors on the other type of cell 

• when exposed to each other’s mating factors, a pair of cells of opposite type change shape, grow towards each other and fuse (mate)

• the resulting a/α cell has genes from both original cells 

quorum sensing

the method by which bacteria coordinate their behavior based on population density

• Bacteria release signaling molecules that increase in concentration as the bacteria population grows, leading to the coordination of a response.

how do signaling substances move through the junctions between plant or animal cells

signaling substances dissolved in the cytosol can pass between neighboring cells

cells communicating with each other via extracellular surface molecules (i.e. carbohydrates of glycoproteins) is especially important in …

1. embryotic development

2. immune response

3. maintaining adult stem cell populations

growth factors 

• local regulators in animals that consist of compounds that stimulate nearby target cells to grow and divide 

• example of paracrine signaling (local regulators work on nearby cells)

1. Target cell

2. Signaling Cell

3. local regulator

4. Paracrine signaling

5. Neurotransmitters

6. Target cell

7. synaptic signaling

describe what happens during synaptic signaling

• A nerve cell releases a neurotransmitter across the synapse, stimulating the target cell, such as a muscle or another nerve cell

• neurotransmitter release is triggered by an electrical signal that travels along the nerve cell

What happens in Endocrine (hormonal) signaling

Specialized endocrine cells secrete hormones into bodily fluids, often the blood.

(effect only some cells)

what determines whether or not a cell can respond to a signaling molecule 

the receptors it has on its surface 

A signaling molecule binds to a receptor, causing it to do what

change shape

ligand

signaling molecule that is specific to a receptor on a cell

after a ligand binds to a receptor, the receptor changes shape, what does this change in shape do

directly activate the receptor, enabling it to interact with other molecules in or on the cell

most signal receptors are 

plasma membrane proteins 

largest family of human cell-surface receptors 

G Protein-Coupled Receptors (GPCR) 

3 major types of cell-surface receptors 

1. G Protein-Coupled Receptors 

2. Receptor Tyrosine Kinases 

3. Ion Channel Receptors 

abnormal functioning of receptor tyrosine kinases is associated with

Breast cancer

Intracellular receptors

• intracellular receptor proteins are found in the cytoplasm or nucleus

• signaling molecules must be small and hydrophobic (i.e. steroid or thyroid hormones)

explain how the hormone aldosterone binds to an intracellular receptor and effects genes

1. Aldosterone (steroid hormone) travels through the plasma membrane

2. Aldosterone binds to a receptor in the cytoplasm, activating it.

3. The hormone-receptor complex enters the nucleus and binds to specific genes

4. the bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA

5. mRNA is translated into a specific protein

transcription factors

specialized proteins that control which genes are turned into mRNA (which genes are “turned on”)

by acting as a transcription factor, the aldosterone receptor carries out what two parts of the signaling pathway

1. reception

2. transduction

Nerve growth factor (NGF) is a water-soluble signaling molecule. Would you expect the receptor for NGF to be intracellular or in the plasma membrane? Explain.

because nerve growth factor is water-soluble, the receptor would be found in the plasma membrane, as only small and hydrophobic molecules are able to cross the phospholipid bilayer

in the transduction stage, proteins are activated or deactivated by what 

the addition or removal of a phosphate group 

when receptors of signaling molecules are in the plasma membrane, what is the transduction stage like

it is usually a multistep pathway involving many molecules

what is the benefit of having a transduction pathway made of several steps

• the signal is amplified with a greater amount of activated molecules

• it allows for more coordination and control than with simpler systems (allows response to be regulated)

as proteins activate one another during transduction, they fall like…

dominoes 

Is the original signaling molecule physically passed along the transduction pathway?

No, in most cases it never enters the cell. When you say that a signal is relayed along the pathway, it means that certain information gets passed along.

protein kinase

an enzyme that transfers a phosphate group from ATP to a protein

RTK (Receptor Tyrosine Kinase) is a specific type of protein kinase that does what

phosphorylates tyrosine on another RTK in a dimer

2 differences between RTKs and cytoplasmic protein kinases 

1. cytoplasmic protein kinases act on proteins different from themselves (unlike RTKs)

2. cytoplasmic protein kinases phosphorylate the amino acids serine or threonine, not tyrosine

phosphorylation cascade

result of each kinase phosphorylating and activating another, leading to the phosphorylation of many proteins.

why does the shape of a protein change with phosphorylation

The shape change results from the interaction of the newly added phosphate groups with charged or polar amino acids on the protein being phosphorylated

protein phosphatases 

enzymes that rapidly remove phosphates from proteins (dephosphorylation)

how to protein phosphatases effect the signal

• they provide the mechanism for turning the signal transduction pathway off when the original signal is no longer present

• make protein kinases available for reuse, enabling the cell to respond to another signal

• turns activities on or off or up or down

second messengers

• small, nonprotein, water-soluble molecules or ions

• rapidly diffuse the signal from the first messenger (ligand)

most common secondary messengers 

cAMP and Ca⁺ ions 

1. The binding of epinephrine to the G protein-coupled receptor in the plasma membrane causes an increase in what?

2. cAMP is produced from

3. the enzyme that converts ATP into cAMP

4. what is the immediate effect of an elevation of cAMP levels

1. cAMP (cyclic AMP)

2. ATP

3. Adenylyl Cyclase

4. the activation of Protein Kinase A

what can inhibitory g-proteins do

block the production of adenylyl cyclase

an increase in the cytosolic concentration of Ca^⁺ ions can cause

• muscle contractions

• exocytosis

• cell division

cells always contain some Ca+, so why can this ion function as a second messenger 

because calcium ion concentration in the cytosol is generally lower than outside the cell 

The pathways leading to calcium release involve what two other secondary messengers

1. IP3

2. DAG

how do signaling pathways regulate protein synthesis

by turning specific genes on or off in the nucleus

list how a signal can lead to the synthesis of a particular protein

• signaling molecule causes a phosphorylation cascade

• once activated, the last kinase in the cascade enters the nucleus and activates a transcription factor

• transcription factor stimulates the transcription of a specific gene

• resulting mRNAs direct the translation of a particular protein in the cytoplasm

4 aspects of response regulation

1. signaling pathways generally amplify the cell’s response to a single signaling event

2. the many steps in a multistep pathway provide control points at which the cell’s response can be further regulated

3. efficiency of the response is enhanced by the presence of proteins known as scaffolding proteins

4. termination of the signal

scaffolding proteins

large relay proteins to which several other relay proteins are simultaneously attached

If two cells have different scaffolding proteins, explain how they might behave differently in response to the same signaling molecule.

the composition and location of their signaling complexes will differ, resulting in different responses to the same signal

How can a target cell’s response to a single hormone molecule result in a response that affects a million other molecules?

A target cell can affect a million other molecules via the protein cascade, which activates many proteins as each phosphorylated protein activates another. Target cells can also affect other molecules via amplification. As a signal proceeds through the pathway, it is amplified at each step, activating more molecules.