Intracellular communications

Question 1

Types of signal transmission

Answer 1

Direct

Indirect

Question 2

Direct signal transmission

Answer 2

1. Gap junctions
2. Contact- Dependent (Juxtacrine signaling)

Question 3

Gap junction

Answer 3

Pore-like communication, ions and small molecules diffused through
Ex. epithelial cells
Ex. heart muscles and smooth muscles

Essentially all tissues that touch each other

Question 4

Contact-dependent (juxtacrine signalling)

Answer 4

Cells make direct physical contact through a signal molecule on the plasma membrane

Important during embryonic development, this type of signalling allows adjacent cells to differentiate into a different cell type

Question 5

indirect signal transmission types

Answer 5

1. Paracrine
2. Hormonal

Question 6

Paracrine signal

Answer 6

Indirect signalling

Signals are transmitted in the interstitial fluid. So only nearby cells affected (does not enter bloodstream)

Examples: inflammation, wound healing

can be autocrine or between neurons

Question 7

Types of paracrine signals

Answer 7

1. Autocrine- cell releases signal that binds to itself causing a response in the cell that originally released it

Important in development where a cell gets its own signal to develop into correct tissues
Ex. interleukins released by the T-helper cells can signal themselves to self-amplify

2. Between neurons
   - Signal can travel far due to the morphology of neurons and fast due to action potential
   - Affects postsynaptic neuron
   - Signals can be released into the bloodstream- “Neuroendocrine”

Question 8

Hormonal signal

Answer 8

indirect signalling

signals are transmitted in the blood circulation

• Hormones released by endocrine cell. Signal molecules travel in the blood stream to target cells
• Not very fast but more flexible as signals can affect any cells that express the receptors
• Hormones get diluted in the blood stream, so receptors must have a very high affinity for the hormone

Question 9

Types of signal molecules

Answer 9

• lipid insoluble
• lipid-soluble
• gaseous (nitric oxide)
• intracellular messengers

Question 10

Lipid insoluble signal molecules

Answer 10

• amino acids (AAs and GABA)
• biogenic amines (catecholamines, histimine, seratonin)
• peptides and proteins
• non-coding RNA

Question 11

Lipid soluble signalling molecules

Answer 11

• biogenic amines (modified amino acids) - thyroid
• steroids (estradiol, testosterone, cortisol)
• eicosanoids (made from arachidonic acid from either COX pathways or Lipooxygenase pathway)

Question 12

What eicosanoids are made by COX pathway?

Answer 12

prostaglandins

prostacyclins

thromboxanes

Question 13

what eicosanoid is made from lipoxygenase pathway?

Answer 13

Leukotrienes

Question 14

Gaseous signal molecules

Answer 14

Nitric oxide released by endothelial cells cause smooth muscle to relax and lead to vessel dilation and increasing blood flow

Question 15

intracellular messengers

Answer 15

• Cyclic AMP
• Inositol triphosphate (IP3)
• Diacylglycerol (DAG)
• Calcium

Question 16

Target cell responses

Answer 16

1. extracellular receptors
2. intracellular responses

Question 17

Extracellular receptors and types

Answer 17

• Lipid-insoluble signal molecules bind to extracellular receptors

3 types:
1. ion-channel coupled receptors
2. enzyme-coupled receptors
3. G-protein coupled receptors (GPCR)

Question 18

Ion-channel coupled receptors

Answer 18

• ligand gated ion channels

Ex. neuromuscular junction
Acetylcholine released from motor neuron binds to nicotinic receptor causing an ion channel to open and allows Na to move inside

Question 19

Enzyme-coupled receptors

Answer 19

Ex. Insulin receptor
- Insulin binds to the tyrosine kinase receptor causing activation (dimerization and autophosphorylation). This activation recruits and activates other intracellular proteins for cell response. Overall, results in the translocation of glucose transporters to the cell membrane, allows cells to take in glucose from bloodstream

Note: kinase- adds phosphate groups

Question 20

G-protein coupled receptors (GPCR)

Answer 20

Trimeric G-protein is first molecular switch

Activated g-protein can :
1. Open a channel
2. Activate an enzyme that generates second messengers to Amplify primary signal
- Adenylyl cyclase generates cAMP
- Phosphodiesterase degrades cAMP
- Phospholipase C generates IP3, diacylglycerol and Ca2+

Question 21

Epinephrine binding to the adrenergic receptor on a skeletal muscle cell (Example of GPCR)

Answer 21

Epinephrine binds to the adrenergic receptor (GPCR), triggers the G-protein which activates adenylyl cyclase that converts ATP to cAMP

cAMP acts as a second messenger which activates breakdown for glycogen. Providing more glucose for muscle cell to generate ATP for muscle contraction

Question 22

GPCR Example: Norepinephreine binds to alpha-1 adrenergic receptor on the smooth muscle around blood vessels.

Answer 22

Activates phospholipase C which cleaves IP3 and diacylglycerol

• IP3 binds to ER receptors, triggering Ca release from ER
• DAG and Ca activate protein kinase c
• Protein kinase C promotes smooth muscle contractions leading to vasoconstriction and increased blood pressure

Question 23

Acetylcholine and GPCR

Answer 23

Acetylcholine activates a GPCR receptor on heart cells, activated the attached complex, opening the K channels, allowing K to leave the cell

Question 24

Intracellular receptors

Answer 24

Lipid-soluble signal molecules can bind intracellular receptors (cytosolic or nuclear). They will diffuse through the membrane and find the receptors

Question 25

Cortisol Example of intracellular receptors

Answer 25

Cortisol (steroid hormone regulating stress response, metabolism, and immune regulation) acts as a signal molecule, binds to receptor forming a Cortisol/receptor complex

Complex moves into the nucleus and activates target genes important in metabolism, immune responses, and stress adaptation