Weak-7

Question 1

What are the 2 types of cell communication

Answer 1

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)

Question 2

Types of local signalling and what species found in

Answer 2

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)

Question 3

What is direct contact describe, and what cells use them.

Answer 3

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

Question 4

Cell to cell recognition describe,and what cells?

Answer 4

In local signaling, animal cells communicate and recognize
each other via direct contact using surface molecules (e.g.
membrane carbohydrates)

Question 5

Local regulators .

Answer 5

Local regulators: messenger molecules that travel only
short distances (e.g. growth factors, neurotransmitters)

Paracrine and synaptic signaling: animal cells
communicate using local regulators

Question 6

Cell junction types ,location and what group they fall under

Answer 6

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

Question 7

plasmodesmata functions , and location

Answer 7

• Channels connecting neighbouring cells
• Allow cell communication and molecule exchange (e.g.
small molecules and water)

Question 8

what are junctions found in animals

Answer 8

• Tight junctions: prevent
intercellular communication

• Desmosomes:
anchor cells through ECM

•Gap junctions:

• channels between cells
• allow molecule exchange between cells

Question 9

Gap junctions------ Functions, 
what is it made up of?
What goes through it?
what does it transport?
Location?

Answer 9

• 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

Question 10

Tight junctions
Location?
function?
What are the two types?

Answer 10

• 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

Question 11

Anchoring junction types

Answer 11

• Connect neighbouring cells (Cell-to-cell connection):

• Desmosomes
• Adherens junctions

• Connect cells with ECM (Cell to ECM connection):

• Focal adhesions
• Hemidesmosomes

Question 12

Desmosomes
Functions?(3)
What do they connect?(3)

Answer 12

• 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

Question 13

Adherens junctions
Function/location?
connects what?(2)

Answer 13

• 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

Question 14

what are the 2 sections of anchoring junctions

Answer 14

• Connect neighbouring cells (Cell-to-cell connection):

• Desmosomes
• Adherens junctions

• Connect cells with ECM (Cell to ECM connection):

• Focal adhesions
• Hemidesmosomes

Question 15

Cell –ECM connection types

Answer 15

• Focal adhesions (contacts):

* Hemidesmosomes:

Question 16

Focal adhesions (contacts):

Answer 16

• 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)

Question 17

Hemidesmosomes:

Answer 17

• 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)

Question 18

page 28 week 7 diagram

Answer 18

look

Question 19

page 31 week 7 diagram

Answer 19

look

Question 20

What is used in Long distance signaling?

Answer 20

• 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

Question 21

What are the 3 stages of cell signaling

Answer 21

1. Reception
2. Transduction
3. Response

Question 22

Reception signaling process

Answer 22

• 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

Question 23

1.Reception: receptor types

Answer 23

• Receptor types:

• Plasma membrane receptors
• Intracellular receptors

+(The binding between the signal molecule (ligand) and
receptor is highly specific)

Question 24

Intracellular receptor
types?
what uses these receptors?
examples?

Answer 24

• 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)

Question 25

Plasma membrane receptors types?(3)

Answer 25

– G-protein-coupled – Tyrosine kinases – Ion channels

Question 26

``` G protein-coupled receptors. define? Bound to what? process/function? involved in diseaese? example? ```

Answer 26

• 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

Question 27

Receptor tyrosine kinases. function?(2) Domains? examples?

Answer 27

• 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)

Question 28

Receptor tyrosine kinases and clinical correlations?(4) examples? what blocks it?

Answer 28

• 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)

Question 29

Ion channel receptors. Function? process?(3)

Answer 29

• 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 ```

Question 30

2.Transduction | process?(2)

Answer 30

• 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

Question 31

Signal transduction pathways:

Answer 31

- 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) ```

Question 32

Protein Phosphorylation and Dephosphorylation related to signal transduction (not sure about this week 7 pg48)

Answer 32

• 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

Question 33

Second Messengers. What are they? examples?

Answer 33

• Second messengers: small, non-protein, water-soluble molecules or ions that acts in the signal transduction pathways • Examples: - cAMP - Ca+2

Question 34

``` Cyclic AMP (cAMP). how is it produced? (also I think memorize chart) ```

Answer 34

Produced from ATP through the enzyme adenylyl cyclase

Question 35

Cyclic AMP. What triggers it? function?

Answer 35

• Many G-proteins trigger the formation of cAMP • cAMP then acts as a second messenger in the signal transduction pathways

Question 36

Calcium ions function? importance?

Answer 36

• 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

Question 37

name 2 other second messengers:

Answer 37

- Diacylglycerol (DAG) - Inositol triphosphate (IP3) • IP3 triggers an increase in calcium concentration in the cytosol

Question 38

3. Response. function?

Answer 38

• Response: the transduced signal triggers a specific cellular response • Cell signaling leads to regulation of cytoplasmic activities (cytoplasmic response) or transcription (nuclear response)

Question 39

slide 59 week 7???

Answer 39

look

Question 40

nuclear response to a signal? | examples?

Answer 40

• Other pathways regulate genes by activating transcription factors that turn gene expression on or off • Example: steroid hormone signaling pathways, MAPK signaling cascade

Question 41

benefits of multistep signaling pathways?(3)

Answer 41

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

Question 42

Signal Amplification.

Answer 42

• 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

Question 43

The Specificity of Cell Signaling. explain it?

Answer 43

• 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

Question 44

what is cross-talk”?

Answer 44

• Pathway branching and “cross-talk” further help the cell to coordinate incoming signals slide64week7diagram

Question 45

Scaffolding proteins. what are they? Function?

Answer 45

- 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

Question 46

how is signal response terminated?

Answer 46

• Signal response is terminated quickly – By the reversal of ligand binding => Ligand released from the receptor

Question 47

(summmary) Local signalling

Answer 47

cell junctions, cell-cell recognition, local | regulators

Question 48

(summary) Distal signalling

Answer 48

hormones

Question 49

(summary) 3 stages of cell signalling

Answer 49

reception, transduction, | response

Question 50

(summary) Intracellular receptors

Answer 50

cytoplasmic or nuclear

Question 51

(summary) Plasma membrane receptors

Answer 51

G-protein coupled, | receptor tyrosine kinases, ion channels

Question 52

(summary)Second messengers

Answer 52

cAMP, Ca+2, DAG, IP3