Weak-7 Flashcards
What are the 2 types of cell communication
Local signalling: neighbouring cells communicate
though cell junctions, cell-to-cell recognition or local
regulators
➢ Long distance signalling: distant cells in multicellular
organisms communicate using chemical messengers
(e.g. hormones)
Types of local signalling and what species found in
Direct contact: via cell junctions (animal and plant)
Cell-cell recognition: via surface molecules (animal
cells only)
Local regulators: in paracrine/synaptic signaling
(animal cells only)
What is direct contact describe, and what cells use them.
Animal and plant cells have cell junctions that directly
connect the cytoplasm of adjacent cells • Cell junctions coordinate the function of neighbouring
cells in a tissue
Cell to cell recognition describe,and what cells?
In local signaling, animal cells communicate and recognize
each other via direct contact using surface molecules (e.g.
membrane carbohydrates)
Local regulators .
Local regulators: messenger molecules that travel only short distances (e.g. growth factors, neurotransmitters)
Paracrine and synaptic signaling: animal cells
communicate using local regulators
Cell junction types ,location and what group they fall under
Communicating junctions———
Gap junctions: in animal cells, no cytoskeletal connection
Plasmodesmata: in plant cells, no cytoskeletal connection
Occluding junctions——-
Tight junctions: connect with actin microfilaments
Anchoring junctions——-
Desmosomes: connect with intermediate filaments
Adherens junctions: connect with actin microfilaments
plasmodesmata functions , and location
• Channels connecting neighbouring cells
• Allow cell communication and molecule exchange (e.g.
small molecules and water)
what are junctions found in animals
• Tight junctions: prevent
intercellular communication
• Desmosomes:
anchor cells through ECM
•Gap junctions:
- channels between cells
- allow molecule exchange between cells
Gap junctions------ Functions, what is it made up of? What goes through it? what does it transport? Location?
• Cytoplasmic channels made by membrane proteins
(connexins) connecting adjacent cells
• Necessary for cell-to-cell communication
• Allow small molecule and ion exchange between cells (e.g.
cAMP, Ca+2)
• Located along the apical surfaces of cells of various
tissues (e.g. epithelial cells and heart muscle)
• Transport of Ca+2 between neighbouring smooth muscle
cells through gap junctions
Synchronized contraction of intestine and uterus during
birth
Tight junctions
Location?
function?
What are the two types?
• Underneath the apical surface of epithelial cells
• Inhibit cell-to-cell communication (molecule exchange)
• Create an exclusion zone around the cells
=> prevent leakage of extracellular fluid from a layer of
epithelial cells (e.g skin layer)
• Made by 2 types of transmembrane proteins:
- Claudin and occludin
• Τhe cytoplasmic part of occludin is linked to the actin
microfilaments
Anchoring junction types
• Connect neighbouring cells (Cell-to-cell connection):
- Desmosomes
- Adherens junctions
• Connect cells with ECM (Cell to ECM connection):
- Focal adhesions
- Hemidesmosomes
Desmosomes
Functions?(3)
What do they connect?(3)
• Function like rivets fastening cells together into strong
sheets
• Anchor to the cytoplasm though intermediate filaments
(e.g. keratin)
• Connect cells via transmembrane adhesion proteins
(cadherins)
• Desmosomes connect with:
- Keratin intermediate filaments in epithelial cells
- Desmin intermediate filaments in heart muscle cells and
smooth muscle cells
• Desmosomes attach muscle cells to each other in a
muscle
=> Some ‘muscle tears’ involve the rupture of desmosomes
Adherens junctions
Function/location?
connects what?(2)
• Create an adhesion zone (belt) underneath the apical
surface of epithelial cells
• Connect the plasma membranes of neighbouring cells via
transmembrane adhesion proteins (cadherins)
• Intracellular attachment proteins (catenins, vinculin, αactinin): connect cadherins with actin microfilaments
what are the 2 sections of anchoring junctions
• Connect neighbouring cells (Cell-to-cell connection):
- Desmosomes
- Adherens junctions
• Connect cells with ECM (Cell to ECM connection):
- Focal adhesions
- Hemidesmosomes
Cell –ECM connection types
- Focal adhesions (contacts):
* Hemidesmosomes:
Focal adhesions (contacts):
- Extracellular connection: Connect cells to the ECM through
integrins (transmembrane proteins) - Intracellular connection: Integrin cytoplasmic domain connects
with actin microfilaments through attachment proteins (talin, αactinin, vincoulin)
Hemidesmosomes:
- Found mainly in basal surface of epithelial cells
- Extracellular connection: Stabilise epithelial cells by anchoring
them to the ECM through integrins (transmembrane proteins;
integrin binds to basement membrane laminin) - Intracellular connection: connect with keratin intermediate
filaments through attachment proteins (plectin)
page 28 week 7 diagram
look
page 31 week 7 diagram
look
What is used in Long distance signaling?
• In long-distance signaling, both plants and animals use hormones • Hormonal signaling in animals: - also known as endocrine signaling - specialized cells release hormone molecules which travel via the circulatory system to target cells in other parts of the body
What are the 3 stages of cell signaling
- Reception
- Transduction
- Response
Reception signaling process
• Reception: the signaling molecule binds to a receptor
protein, causing it to change shape (conformational change)
• The receptor protein conformational change initiates the process
of transduction
1.Reception: receptor types
• Receptor types:
- Plasma membrane receptors
- Intracellular receptors
+(The binding between the signal molecule (ligand) and
receptor is highly specific)
Intracellular receptor
types?
what uses these receptors?
examples?
• Intracellular receptors: cytoplasmic or nuclear proteins
• Signaling molecules that are small or hydrophobic and can
readily cross the plasma membrane use these receptors
• Example: steroid hormones bind to intracellular
receptors (e.g. estrogen receptors)
Plasma membrane receptors types?(3)
– G-protein-coupled
– Tyrosine kinases
– Ion channels
G protein-coupled receptors. define? Bound to what? process/function? involved in diseaese? example?
• G protein-coupled receptors: plasma membrane receptors
linked to a G protein
• G-proteins: proteins bound to GTP/GDP
• G proteins act as an on/off switch:
– If GDP is bound to the G protein => G protein is inactive
– If GTP is bound to the G protein => G protein is active
• Involved in many human diseases, including bacterial infections
• Example: cholera toxin and botulinum toxin are bacterial
products that interfere with G protein function
• More than 60% of all medicines used today exert their effects by
influencing G protein pathways
Receptor tyrosine kinases.
function?(2)
Domains?
examples?
• Protein kinases: enzymes that phosphorylates protein
substrates (adds phosphate groups to them)
• Receptor tyrosine kinases: transmembrane receptors
that attach phosphates to tyrosine residues
• 2 domains:
- Extracellular ligand binding domain
- Intracellular domain with tyrosine kinase activity
• Growth factor receptors are commonly receptor tyrosine
kinases (e.g. EGFR, PDGFR, etc)
Receptor tyrosine kinases and clinical correlations?(4)
examples?
what blocks it?
• Abnormal tyrosine kinase receptors may contribute to
some kinds of cancer
- truncated receptors that function in the absence of
signaling molecules (lack the ligand-binding domain)
- overexpression/ amplification of receptors:
- Example: EGFR (Epidermal Growth Factor Receptor)
amplification (overexpression) in many cancers (e.g. breast
cancer)
• Several anti-cancer drugs block tyrosine kinase activity
(herceptin, Gleevec)
Ion channel receptors.
Function?
process?(3)
• Ligand-gated ion channel
receptors: acts as a gate
which opens when the
receptor changes shape
1. Binding of signaling molecule (ligand) to the receptor 2. Receptor changes shape (the gate opens) 3. Specific ions (e.g. Na+,Ca2+) pass through a channel in the receptor
2.Transduction
process?(2)
• Transduction: the signal from the receptor converted to a
form that can cause a specific cellular response
• Transduction usually requires a series of changes in a
series of different target molecules
Signal transduction pathways:
- cascades of molecular interactions that relay signals from
receptors to target molecules in the cell
- At each step in a pathway the signal is transduced into a different form (usually a conformational change in a protein)
Protein Phosphorylation and Dephosphorylation
related to signal transduction
(not sure about this week 7 pg48)
• Many signal pathways include phosphorylation cascades
(e.g. MAPK signaling pathway)
• In this process:
– Protein kinases: enzymes that add a phosphate to
the next protein kinase in line => activate protein
kinases
– Phosphatases: enzymes that remove the phosphates
=> deactivate the protein kinases
Second Messengers.
What are they?
examples?
• Second messengers: small, non-protein, water-soluble
molecules or ions that acts in the signal transduction
pathways
• Examples:
- cAMP
- Ca+2
Cyclic AMP (cAMP). how is it produced? (also I think memorize chart)
Produced from ATP through the enzyme adenylyl cyclase
Cyclic AMP.
What triggers it?
function?
• Many G-proteins trigger the formation of cAMP
• cAMP then acts as a second messenger in the signal
transduction pathways
Calcium ions
function?
importance?
• Calcium ions (Ca+2), when released into the cytosol of a cell,
acts as a second messenger in many different pathways
• Calcium is an important second messenger because cells are
able to regulate its concentration in the cytosol
name 2 other second messengers:
- Diacylglycerol (DAG)
- Inositol triphosphate (IP3)
• IP3
triggers an increase in calcium concentration in
the cytosol
- Response.
function?
• Response: the transduced signal triggers a specific cellular
response
• Cell signaling leads to regulation of cytoplasmic activities
(cytoplasmic response) or transcription (nuclear response)
slide 59 week 7???
look
nuclear response to a signal?
examples?
• Other pathways regulate genes by activating transcription
factors that turn gene expression on or off
• Example: steroid hormone signaling pathways, MAPK
signaling cascade
benefits of multistep signaling pathways?(3)
Multistep signaling pathways have two important benefits:
– Amplification of the signal => amplification of the
response
– Contribution to the specificity of the response
Provide more opportunities for coordination and
regulation
Signal Amplification.
• Each protein in a signaling pathway amplifies the signal by
activating multiple copies of the next component in the
pathway
• At each step, the number of activated products is much
greater than in the preceding step
The Specificity of Cell Signaling.
explain it?
• Different kinds of cells have different types of proteins
• Different proteins allow cells to detect and respond to
different signals
=> Even the same signal can have different effects in cells
with different proteins and pathways
• The different combinations of proteins in a cell give the cell
great specificity in both the signals it detects and the
responses it carries out
what is cross-talk”?
• Pathway branching and “cross-talk” further help the cell to coordinate incoming signals
slide64week7diagram
Scaffolding proteins.
what are they?
Function?
- Large relay proteins to which other relay proteins are
attached - Function: increase the signal transduction efficiency by
grouping together different proteins involved in the same
pathway
more efficient
activation of
signaling pathways
how is signal response terminated?
• Signal response is terminated quickly
– By the reversal of ligand binding
=> Ligand released from the receptor
(summmary) Local signalling
cell junctions, cell-cell recognition, local
regulators
(summary) Distal signalling
hormones
(summary) 3 stages of cell signalling
reception, transduction,
response
(summary) Intracellular receptors
cytoplasmic or nuclear
(summary) Plasma membrane receptors
G-protein coupled,
receptor tyrosine kinases, ion channels
(summary)Second messengers
cAMP, Ca+2, DAG, IP3
