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MED-103 Biology I (2024-25) > Topic 7: cell communication > Flashcards

Topic 7: cell communication Flashcards

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1
Q

Define signal transduction pathways

A

Convert extracellular signals into cellular responses

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2
Q

2 types of cell communication

A

1) Local signaling: neighboring cells communicate
2) Long-distance signaling: distant cells in multicellular organisms communicate via chemical messengers

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3
Q

Types of local signaling

A

1) Direct contact: cell junctions
2) Cell-cell recognition: surface molecules
3) Local regulators: synaptic signaling

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4
Q

Describe direct contact

A
  • Both plants/animals have cell junctions directly connecting cytoplasm of adjacent cells
  • Coordinate function of neighboring cells in a tissue
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5
Q

Describe cell-cell recognition

A
  • Animal cells recognize each other via direct contact using membrane carbohydrates/receptors
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6
Q

Describe local regulators

A
  • Messenger molecules travel short distances
  • E.g. growth factors + neurotransmitters
  • Paracrine = secreting cell acts on target cell
  • Synaptic = nerve cell into synapse onto target cell
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7
Q

Cell junction types

A

COMMUNICATING JUNCTIONS:
- Gap junctions = animals + no cytoskeletal connection
- Plasmodesmata = plants + no cytoskeletal connection
OCCLUDING JUNCTIONS:
- Tight junctions = connect with actin filaments
ANCHORING JUNCTIONS:
- Desmosomes = connect with intermediate filaments
- Adherens junctions = connect with actin microfilaments

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8
Q

Describe plasmodesmatas

A
  • Channels connecting neighboring cells
  • Allow cell communication + molecule exchange of small molecules/water
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9
Q

Describe gap junctions

A
  • Cytoplasmic channel = connect adjacent cells
  • Made of membrane protein = connexin
  • Allow exchange of small molecules + ion exchange e.g. cAMP + Ca2+
  • Located = apical surface of cells e.g. epithelial + heart muscle
  • Transport Ca2+ between neighboring smooth muscle cells = allows synchronized contraction of intestine + uterus during birth
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10
Q

Describe tight junctions

A
  • Located = underneath apical surface of epithelial cells
  • Inhibit cell-cell communication + exchange
  • Prevent leakage of extracellular fluid from epithelial cells
  • Made by transmembrane proteins = claudin + occludin
  • Cytoplasmic part of occludin linked to actin filaments
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11
Q

Types of anchoring junctions

A

CELL-CELL CONNECTION:
- Desmosomes = intermediate
- Adherens = actin
CELL - ECM CONNECTION:
- Focal adhesion = actin
- Hemidesmosomes = intermediate

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12
Q

Describe desmosomes

A
  • Fasten cells together = strong sheets
  • Anchor to cytoplasm via intermediate filaments e.g. keratin in epithelial + desmin in heart/smooth muscle cells
  • Connect cells via transmembrane adhesion proteins = cadherins
  • Attach muscle cells to each other = muscle tears are ruptured desmosomes
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13
Q

Describe adherens junctions

A
  • Located = create adhesion zone under apical surface of epithelial cells
  • Connect plasma membranes of neighboring cells via transmembrane proteins = cadherins
  • Intercellular attachment proteins = connect cadherins + actin microfilaments
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14
Q

Describe focal adhesions

A
  • Extracellular connection = connect cells to ECM via integrins
  • Intracellular connection = integrin connects with actin via attachment proteins
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15
Q

Describe hemidesmosomes

A
  • Located = basal surface of epithelial
  • Extracellular connection: stabilize epithelial by anchoring to ECM via integrins to basement membrane laminins
  • Intracellular connection: connect with keratin intermediate filaments through attachment proteins
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16
Q

Define basement membrane

A

Specialized ECM type = separates endothelial cell from underlying connective tissue

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17
Q

Define connective tissue

A

Consists of ECM secreted by fibroblasts

18
Q

Define long-distance signaling

A
  • In plants + animals
  • Hormonal signaling AKA endocrine signaling
  • Specialized cells release hormone = travels to target cell in body
19
Q

3 stages of cell signaling

A

1) Reception
2) Transduction
3) Response

20
Q

Explain reception

A
  • Signaling molecule = ligand = binds to receptor protein = change shape
  • Binding is highly specific
  • Conformational change initiates process of transduction
21
Q

2 Types of receptors

A

1) Plasma membrane receptors
2) Intracellular receptors

22
Q

Describe intracellular receptors

A
  • Cytoplasmic + nuclear proteins
  • Used by signaling molecules that = small + hydrophobic + readily cross membrane
  • E.g. steroid hormone + intracellular receptors = estrogen/androgen + ERs/ARs
23
Q

What are the clinical correlations of intracellular receptors?

A
  • Tamoxifen
  • Drug used for ER+ breast cancer
  • It is estrogen antagonist = binds to ER and prevents estradiol binding
24
Q

Explain how steroid hormones act via intracellular receptors

A

1) Hormone passes through membrane
2) Binds to receptor protein in cytoplasm = activate
3) Hormone-receptor complex enters nucleus = bind to specific gene
4) Bound protein stimulates transcription of gene>mRNA
5) mRNA translated to specific protein

25
Q

3 Types of plasma membrane receptors

A
  • G-protein-coupled
  • Tyrosine kinases
  • Ion channels
26
Q

Describe G-protein-coupled receptors

A
  • Linked to G protein = bound to GTP/GDP
  • G protein acts as on/off switch:
    > GDP when bound = G protein inactive
    > GTP when bound = G protein active
27
Q

What is the involvement of G protein receptors in human disease?

A
  • E.g. bacterial infections
  • Cholera + botulinum toxin = bacterial products = interfere with G protein function
  • > 60% meds exert effects by influencing G protein pathways
28
Q

Describe receptor tyrosine kinases

A
  • Protein kinases = enzymes that phosphorylate protein substrates
  • These are transmembrane receptors that attach phosphates to tyrosine residues
    1) Extracellular = ligand binding domain
    2) Intracellular = tyrosine kinase activity
  • Growth factor receptors = tyrosine kinases receptors
  • Growth factors bonding to receptor = activation of signal transduction pathways = MAPK
29
Q

What is the clinical correlation of receptor tyrosine kinases?

A
  • Abnormal TKR = contribute to cancer
  • Receptors that function in absence of signaling molecules = lack ligand binding domain
  • Overexpression of receptors = EGFR amplification in cancers e.g. breast cancer
  • Anti-cancer drugs block tyrosine kinase activity e.g. Herceptin + Gleevac
30
Q

Describe ion channel receptors

A
  • Act as gates = open when receptor changes shape
    1) Binding of signal molecule + receptor
    2) Receptor changes shape = opens
    3) Specific ions pass through channel
31
Q

Explain transduction

A
  • The signal from the receptor converted to form that can cause specific cellular response
  • Requires signal transduction pathways = molecular interactions that relay signal from receptors > target
  • Each step = signal transduced to different form = conformational change
32
Q

Describe protein phosphorylation + dephosphorylation

A
  • Some signal pathways = phosphorylation cascades
    1) Protein kinases = enzyme add phospahte to next protein kinases in line = activate protein
    2) Phosphatases = enzyme removes phosphates = deactivate protein
33
Q

Define second messengers

A
  • Small + non-protein + water-soluble molecules/ions = act in signal transduction pathways
  • E.g. cAMP + Ca+2 + DAG + IP3
34
Q

Describe cAMP

A
  • Cyclic AMP = produced by ATP via enzyme adenylyl cyclase
  • G proteins trigger the formation
  • cAMP acts as second messenger in pathway
35
Q

Describe calcium ions

A
  • When released into cytosol = act as secondary messenger in many pathways
  • Ca2+ = important messenger = cells able to regulate concentration cytosol
36
Q

What is the function of IP3?

A
  • Triggers an increase in Ca concentration in cytosol
37
Q

Explain how second messengers work together

A

1) Signal molecule binds to receptor = activation of phospholipase C
2) Phospholipase C cleaves plasma membrane phospholipid PIP2 = DAG + 1P3
3) DAG = second messenger in other pathways
4) IP3 = diffuses through cytosol + binds to IP3 gated calcium channel = open
5) Ca2+ out of endoplasmic reticulum = Ca2+ increase in cytosol
6) Ca2+ activate next protein in 1 or more pathways

38
Q

Explain response

A
  • Transduced signal triggers specific cellular response
  • Cell signaling = regulation of cytoplasmic activities + transcription
39
Q

Describe the cytoplasmic response to a signal

A
  • Signaling pathways regulate variety of cellular activities e.g. glycogen breakdown>glucose
    1) Reception = binding of epinephrine to G-protein linked receptor
    2) Transduction:
  • Inactive G protein > active
  • Inactive adenylyl cyclase > active
  • ATP > cAMP
  • Inactive protein kinase A > active
    3) Response = glycogen > glucose 1 phosphate
40
Q

Describe the nuclear response to a signal

A
  • Pathway regulates genes by activating transcription factors = turn gene expression on/off
  • E.g. steroid hormones signaling pathway + MAPK signaling cascade
41
Q

What are the benefits of multistep signaling pathways?

A

1) Amplification of signal= amplification of response
2) Contribution to specificity of response
- Therefore provides more opportunities for coordination + regulation

MED-103 Biology I (2024-25) (10 decks)

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