1. Modification of Cell Surface/ Cell Communication
Mader 5.4

2. Learning Objectives:
Learning Objectives: LO 3.34 The student is able to construct explanations of cell communication through cell-to-cell direct contact or through chemical signaling. [See SP 6.2] LO 3.35 The student is able to create representation(s) that depict how cell-to-cell communication occurs by direct contact or from a distance through chemical signaling. [See SP 1.1] LO 3.36 The student is able to describe a model that expresses the key elements of signal transduction pathways by which a signal is converted to a cellular response. [See SP 1.5]

3. Essential knowledge 3.D.2: Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling. a. Cells communicate by cell-to-cell contact. • Plasmodesmata between plant cells that allow material to be transported from cell to cell. b. Cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell. • Neurotransmitters • Plant immune response • Quorum sensing in bacteria • Morphogens in embryonic development c. Signals released by one cell type can travel long distances to target cells of another cell type.

4. Essential knowledge 3.D.3: Signal transduction pathways link signal reception with cellular response. a. Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein. Evidence of student learning is a demonstrated understanding of each of the following: 1. Different receptors recognize different chemical messengers, which can be peptides, small chemicals or proteins, in a specific one-to-one relationship. 2. A receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, which initiates transduction of the signal. To foster student understanding of this concept, instructors can choose an illustrative example such as: • G-protein linked receptors • Ligand-gated ion channels • Receptor tyrosine kinases

5. b. Signal transduction is the process by which a signal is converted to a cellular response. Evidence of student learning is a demonstrated understanding of each of the following: 1. Signaling cascades relay signals from receptors on cell targets, often amplifying the incoming signals, with the result of appropriate responses by the cell. 2. Second messengers are often essential to the function of the cascade. To foster student understanding of this concept, instructors can choose an illustrative example such as: • Ligand-gated ion channels • Second messengers, such as cyclic GMP, cyclic AMP calcium ions (Ca2+), and inositol triphosphate (IP3) 3. Many signal transduction pathways include: i. Protein modifications (an illustrative example could be how methylation changes the signaling process) ii. Phosphorylation cascades in which a series of protein kinases add a phosphate group to the next protein in the cascade sequence

6. Cell Surfaces in Plants and Animals
The extracellular matrix of animal cells are more complex than the cell surfaces of plants or other sessile organisms with cell walls
Plant cell separated by a cell wall constructed of cellulose
Fibroblasts creating an extracellular matrix for the purposes of healing a wound

7. Extracellular Matrix
The extracellular matrix of various tissues varies between being quite flexible, as in cartilage, and being rock solid as in bone

8. Animal Cell Extracellular Matrix
Created by the cells it surrounds
Made from polysaccharides and structural proteins
Gives tissue strength and elasticity
Polysaccharides and proteoglycans work with the proteins in the cell membrane to allow for rapid diffusion of nutrients and hormones

9. How do hormones(ligands) act on target cells
Lipid-based hormones
hydrophobic & lipid-soluble
diffuse across cell membrane & enter cells
bind to receptor proteins in cytoplasm & nucleus
bind to DNA as transcription factors
turn on genes
Protein-based hormones
hydrophilic & not lipid soluble
can’t diffuse across cell membrane
bind to receptor proteins in cell membrane
trigger secondary messenger pathway
activate internal cellular response
enzyme action, uptake or secretion of molecules…

10. Action of lipid (steroid) hormones
target cell
blood S 1 S
cross cell membrane
protein
carrier S 2
cytoplasm
binds to receptor protein
becomes transcription factor 5
mRNA read by ribosome 3 S
plasma membrane 4
DNA
mRNA 6 7
nucleus
protein
protein secreted
ex: secreted protein = growth factor (hair, bone, muscle, gametes)

11. Action of protein hormones
signal-transduction pathway
Action of protein hormones 1
signal
protein hormone P
plasma membrane
binds to receptor protein
activates
G-protein
activates enzyme
cAMP
receptor protein
acts as 2° messenger
ATP
transduction
GTP
transduction: the action or process of converting something and especially energy or a message into another form
activates cytoplasmic signal
ATP
activates
enzyme 2
secondary
messenger system
cytoplasm
activates
enzyme 3
response
target cell
produces an action

12. Ex: Action of epinephrine (adrenaline)
adrenal gland
signal 1
epinephrine
activates G protein 3
activates adenylyl cyclase
receptor
protein
in cell membrane
GDP
cAMP
transduction 4
ATP 2
GTP
activates
protein kinase-A 5
activates GTP
activates
phosphorylase kinase
cytoplasm
released to blood
activates
glycogen phosphorylase 7
liver cell
glycogen 6
glucose
response

13. Benefits of a 2° messenger system1
signal
Activated adenylyl cyclase
receptor protein 2
Not yet
activated
amplification 4
amplification 3
cAMP
amplification 5
GTP
G protein
protein kinase 6
amplification
Amplification!
enzyme
Cascade multiplier! 7
amplification
FAST response!
product

14. Junctions Between Cells
Depending upon the function of tissue, the cells that make up that tissue will be connected to each other in various manners
Junctions
Adhesion Junctions-Skin, Heart, Stomach, and Bladder where tissue gets stretched
Tight Junctions-Intestines, Kidneys, and the blood brain barrier
Gap Junctions-Smooth muscle where ions need to flow between cells to coordinate activity

15. Junctions Between Animal Cells

16. Junctions Between Plant Cells