Unit 4: Cell Communication

Question 1

ligand

Answer 1

A molecule (e.g., hormone, neurotransmitter) that binds to a receptor to initiate a response. Signaling molecules could be proteins, small peptides, amino acids, nucleotides, steroids, fatty acid derivatives, nitric oxide, carbon monoxide. The receptor binding with the ligand often causes a conformational change in the receptor, activating downstream pathways.

Question 2

Receptor

Answer 2

A protein on the cell membrane or within the cell that detects and binds the ligand

Question 3

Signaling cells

Answer 3

Cells that produce ligands

Question 4

Target Cells

Answer 4

Cells that receive the signal

Question 5

Cytoplasmic receptor

Answer 5

Inside the cell, small or nonpolar molecules (e.g., steroids)., Ligand-receptor complex directly influences DNA transcription.

Question 6

Membrane bound receptor

Answer 6

Embedded in the plasma membrane, Large or polar molecules (e.g., peptides), binding triggers intracellular signaling cascades

Question 7

Plasmodesmata

Answer 7

Plants construct channels between cells called plasmodesmata that allow ligands to move directly from one cell to another throughout the plant structure. This is juxtacrine signaling.

Question 8

Autocrine

Answer 8

A cell signals to itself, releasing signals that bind to its own receptors.

Question 9

Juxtacrine

Answer 9

Requires direct contact between cells. Signal molecules are membrane-bound.

Question 10

Paracrine

Answer 10

Signals act on nearby cells.

Question 11

Endocrine

Answer 11

Signals travel through the bloodstream to distant target cells.

Question 12

Quorum Sensing

Answer 12

A process where bacteria communicate using chemical signals to regulate gene expression based on population density. Paracrine, as the signaling molecules act on nearby bacterial cells. Bacteria release small chemical signals into the environment. As the population of bacteria grows, the concentration of signal molecules increases. Once the concentration of autoinducers reaches a threshold, bacteria detect them via receptors and alter their gene expression collectively. This allows bacteria to coordinate group behaviors like bioluminescence

Question 13

Step 1: Reception

Answer 13

• Ligand binds to the receptor
• Most receptor proteins are in the cell membrane but some are inside the cell
• Hydrophilic (polar) ligands bind to plasma membrane receptors
• Small or hydrophobic (nonpolar) ligands can pass through the membrane and attach to intracellular receptors (ex. steroid hormones like testosterone)

Question 14

G-Protein Coupled Receptors

Answer 14

G proteins bind the energy-rich GTP (very similar to ATP- source of energy). GPCR systems are extremely widespread and diverse in their functions. Signaling molecule binds to the receptor. G protein changes conformation an GDP is physically replaced by GTP. G protein diffuses laterally to activate an enzyme. Transduction starts when the enzyme is activated until GTP is hydrolyzed and G protein detaches

Question 15

Ion Channel Receptors

Answer 15

An ion channel receptor acts as a gate that opens and closes when the receptor changes shape, When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor. Ex: acetylcholine receptor, a Na+ channel in skeletal muscle cells → muscle contraction

Question 16

Protein Kinase Receptor

Answer 16

Membrane receptors that transfer phosphate groups from ATP to another protein. Can trigger multiple signal transduction pathways at once. Ex: insulin, cell cycle

Question 17

Step 2: Transduction

Answer 17

• A series of chemical reactions that link ligand binding to the target cell response. It relays signals.
• The goal is to ensure that the target cells have the appropriate response to a ligand binding
• Transduction can have multiple pathways
• Can amplify a signal (make it larger) by activating multiple copies of the next component in the pathway
• Provide more opportunities for coordination and regulation
• At each step in a pathway, the signal is transduced into a different form, commonly a conformational change in a protein

Question 18

Secondary Messengers

Answer 18

Secondary messengers are small molecules/ions that relay and amplify signals received by receptors to proteins.

Question 19

Calcium

Answer 19

Calcium is a common secondary messenger. Ca2+ can function as a second messenger because its concentration in the cytosol is normally much lower than the concentration outside the cell; a small change in the number of calcium ions represents a relatively large percentage change in calcium concentration

Question 20

Protein kinase

Answer 20

Enzymes that use ATP to add phosphate groups (phosphorylate) intracellular proteins. This leads to structural changes that activate or inactive a protein.

Question 21

Phosphorylation Cascade

Answer 21

In this process, a series of protein kinases add a phosphate to the next one in line, activating it. This leads to amplification of the signal. Phosphatase enzymes then remove the phosphates

Question 22

Step 3: Response

Answer 22

There can be many possible responses to a cell signal:
- Activate or inactivate intracellular proteins
- Trigger multiple receptors and different responses
- Example of responses: turn transcription on/off or regulate activity of proteins in cytoplasm
- What can happen if the protein synthesis is altered? Cell behavior is altered - protein production can be altered

Question 23

what can stop the response from happening?

Answer 23

• no more ligands
• ligand stops binding
• reception happens but something goes wrong in transduction (like an interfering molecule) and response doesn’t happen

Question 24

How are steroid and protein hormones different?

Answer 24

steroid hormones are hydrophobic while protein hormones are hydrophilic

Question 25

Second messengers tend to be water-soluble and small. This accounts for their ability to __________

Answer 25

diffuse rapidly through the cytoplasm and amplify the signal efficiently