Cell signaling

Question 1

What are the five basic steps of cell signalling?

Answer 1

Signal → Receptor → Transduction → Response → Deactivation

Question 2

What is a ligand?

Answer 2

A molecule that binds to a receptor to initiate signalling.

Question 3

What is a receptor?

Answer 3

A protein that specifically binds to a signalling molecule.

Question 4

What is the function of transduction in signalling?

Answer 4

To relay and amplify the signal inside the cell.

Question 5

Name one example of a cell response.

Answer 5

Activation of a gene or an enzyme.

Question 6

What does deactivation ensure?

Answer 6

That the signal does not persist indefinitely, maintaining homeostasis.

Question 7

Give one example of a signalling molecule.

Answer 7

Insulin.

Question 8

What type of macromolecule are most receptors?

Answer 8

Proteins.

Question 9

Where are most cell receptors located?

Answer 9

On the cell membrane (for hydrophilic ligands) or inside the cell (for hydrophobic ligands).

Question 10

Why is cell signalling essential for multicellular organisms?

Answer 10

It allows coordination of growth, development, metabolism, and immune responses.

Question 11

What is autocrine signalling?

Answer 11

A cell targets itself.

Question 12

What is paracrine signalling?

Answer 12

Signalling to nearby cells.

Question 13

What is endocrine signalling?

Answer 13

Hormone-based signalling over long distances via the bloodstream.

Question 14

What is juxtacrine signalling?

Answer 14

Direct contact between adjacent cells.

Question 15

What determines a cell’s ability to respond to a signal?

Answer 15

The presence of the correct receptor.

Question 16

Give an example of endocrine signalling.

Answer 16

Insulin released by the pancreas affecting liver cells.

Question 17

What ensures signal specificity?

Answer 17

Ligand-receptor binding and context-dependent pathways.

Question 18

Can a single signal cause different responses in different cells?

Answer 18

Yes, depending on the receptors and intracellular machinery.

Question 19

Why is communication critical in multicellular organisms?

Answer 19

To coordinate complex activities like tissue growth, immune response, and homeostasis.

Question 20

What kind of ligand binds to membrane receptors?

Answer 20

Hydrophilic or large ligands (e.g., peptide hormones).

Question 21

What kind of ligand binds to cytoplasmic receptors?

Answer 21

Small, nonpolar ligands like steroid hormones.

Question 22

Where are cytoplasmic receptors located?

Answer 22

In the cytoplasm or nucleus.

Question 23

How do cytoplasmic receptors often act?

Answer 23

As transcription factors.

Question 24

Do membrane receptors affect gene expression directly?

Answer 24

No, they usually activate intracellular signalling cascades.

Question 25

What’s a key feature of membrane-bound receptors?

Answer 25

They relay the message from the membrane and transduce message to the cytoplasm.

Question 26

Which receptor type leads to faster signalling?

Answer 26

Membrane receptors => affect enzyme or protein activity

Question 27

Which receptor type leads to longer-lasting effects?

Answer 27

Cytoplasmic receptors => change gene expression

Question 28

What do GPCRs activate?

Answer 28

G proteins, which then activate other enzymes like adenylyl cyclase.

Question 29

What is the role of receptor Tyrosine Kinases?

Answer 29

To phosphorylate enzymes and proteins (at tyrosine residues) and activate signalling proteins. Often trigger phosphorylation cascades.

Question 30

Which receptor type forms a dimer upon activation?

Answer 30

receptor Tyrosine Kinases.

Question 31

What second messenger is often made by GPCRs?

Answer 31

cAMP.

Question 32

What is a key feature of GPCR signalling?

Answer 32

Amplification via second messengers.

Question 33

Which receptor directly alters ion gradients?

Answer 33

Ion channel receptors.

Question 34

Which receptor is the largest receptor family in animals?

Answer 34

GPCRs.

Question 35

What is signal transduction?

Answer 35

Signal transduction is the process of converting an external signal into a functional response inside the cell.

Question 36

What is a phosphorylation cascade?

Answer 36

A chain of protein kinases that activate each other through phosphorylation, amplifying the signal.

Question 37

What is signal amplification?

Answer 37

It refers to the phenomenon where one signal molecule leads to the activation of many intracellular molecules, greatly increasing the strength of the signal.

Question 38

What activates second messengers in many signalling pathways?

Answer 38

G protein-coupled receptors (GPCRs) and other transmembrane receptors.

Question 39

What enzyme produces cAMP from ATP?

Answer 39

Adenylyl cyclase.

Question 40

What does IP₃ do once produced?

Answer 40

It binds to receptors on the endoplasmic reticulum, causing the release of Ca²⁺ into the cytoplasm.

Question 41

What is the role of calcium ions in signalling?

Answer 41

They act as a second messenger that activates various proteins and enzymes.

Question 42

What terminates a phosphorylation cascade?

Answer 42

Protein phosphatases remove phosphate groups, inactivating the kinases.

Question 43

What is a direct transduction pathway?

Answer 43

A pathway where the receptor itself initiates the cellular response without secondary messengers.

Question 44

Why is signal transduction important?

Answer 44

It allows cells to interpret and respond to external signals appropriately.

Question 45

What is an example of a receptor using direct transduction?

Answer 45

Protein kinase receptors (e.g., receptor tyrosine kinases).

Question 46

What is indirect signal transduction?

Answer 46

A pathway that involves second messengers to propagate the signal inside the cell.

Question 47

What receptor type often uses indirect transduction?

Answer 47

G protein-coupled receptors (GPCRs).

Question 48

How do second messengers amplify the signal?

Answer 48

They activate multiple targets inside the cell, creating a cascade effect.

Question 49

Which type of transduction is typically faster?

Answer 49

Direct transduction is usually faster but less flexible than indirect.

Question 50

Which transduction pathway allows for more regulation and variability?

Answer 50

Indirect transduction pathways.

Question 51

Is calcium a direct or indirect messenger?

Answer 51

It’s a second messenger in an indirect transduction pathway.

Question 52

What enzyme often terminates an indirect transduction signal?

Answer 52

Phosphodiesterases (e.g., they break down cAMP).

Question 53

What’s the key advantage of indirect transduction?

Answer 53

It allows for signal amplification and fine-tuned regulation.

Question 54

What are the three main types of cellular responses to signals?

Answer 54

Changes in gene expression, ion channel activity, and enzyme activation.

Question 55

How do signals affect gene expression?

Answer 55

By activating transcription factors that regulate DNA transcription.

Question 56

What is an example of a rapid cellular response?

Answer 56

Opening an ion channel in response to a neurotransmitter.

Question 57

What is an example of a long-term cellular response?

Answer 57

Changes in gene expression leading to differentiation.

Question 58

What type of receptor is common in neurons?

Answer 58

Ligand-gated ion channels.

Question 59

How does enzyme activation occur in signalling pathways?

Answer 59

Often through phosphorylation by kinases.

Question 60

What molecule deactivates kinases?

Answer 60

Protein phosphatases.

Question 61

Can one signal produce multiple responses?

Answer 61

Yes, depending on the receptor type and downstream pathways.

Question 62

What determines the type of response a cell will produce?

Answer 62

The receptor and intracellular machinery specific to the cell type.

Question 63

Why are cellular responses tightly regulated?

Answer 63

To ensure appropriate reactions to stimuli and avoid pathological outcomes.

Question 64

What is positive feedback in signalling?

Answer 64

A mechanism that enhances or amplifies the response to a stimulus.

Question 65

What is negative feedback?

Answer 65

A mechanism that reduces or terminates a signalling response.

Question 66

What’s a biological example of positive feedback?

Answer 66

Oxytocin release during labor contractions.

Question 67

What’s a biological example of negative feedback?

Answer 67

Insulin release lowering blood glucose, which in turn suppresses insulin secretion.

Question 68

Why are feedback loops important in signalling?

Answer 68

They help maintain balance and prevent overreaction.

Question 69

Which feedback loop is more common in maintaining homeostasis?

Answer 69

Negative feedback.

Question 70

How do feedback loops affect the duration of a signal?

Answer 70

They can shorten (negative) or prolong (positive) the signal response.

Question 71

Can a signalling pathway contain both types of feedback?

Answer 71

Yes, some complex pathways use both to fine-tune responses.

Question 72

What role do feedback loops play in disease?

Answer 72

Disrupted feedback can lead to conditions like cancer or diabetes.

Question 73

What type of feedback is usually involved in cell cycle checkpoints?

Answer 73

Positive feedback to reinforce progression once a threshold is passed.