Cell Communication - Signaling

1
Cell Communication - Signaling

• Local Regulators ? influences cells in close
  proximity.
• Ex. Growth factors (called paracrine signaling)
• Hormones influences cells far away travel thru
  the blood found in plants animals
• Ex. Growth hormone, estrogen (called endocrine
  signaling)
• Neurotransmitters chemical signal in the
  nervous system will bind to a target on another
  cell
• Ex. Acetylcholine, dopamine, serotonin

2
Cell Communication - Signaling

• Local Regulators ? influences cells in close
  proximity.
• Ex. Growth factors (called paracrine signaling)
• Hormones influences cells far away travel thru
  the blood found in plants animals
• Ex. Growth hormone, estrogen (called endocrine
  signaling)
• Neurotransmitters chemical signal in the
  nervous system will bind to a target on another
  cell
• Ex. Acetylcholine, dopamine, serotonin

3
Cell Communication - Signaling
4
Cell Communication Direct Contact

• Cells may chose to communicate through direct
  contact, instead of sending a messenger
• 1) Tight Junctions
• 2) Gap Junctions
• 3) Desmosomes
• 4) Plasmodesmata (plants only)

5
Cell Communication Direct Contact
6
Three Stages of Cell Signaling

• Reception target cell detects the incoming
  signal
• Ex. Signal may bind to a protein (on membrane)
• Transduction when the signal is changed to a
  form/message that can bring about a
  response/change.
• Ex. Usually involves a complex pathway, may
  cause amplification of the message
• Response any activity that occurs as a result
  of the
• signal

7
Overview of Cell Signaling
8
Reception of the Signal

• Recognition b/w signal receptor by shape (lock
  and key)
• Most receptors are peripheral/integral proteins
  (in cell membrane)
• Signal is a ligand ? small molecule that binds to
  a big molecule (receptor protein)

9
Signal Molecules

• Examples of Signal Molecules are .
• A) Receptors on Cell Membrane
• 1) G Protein-Linked Receptors
• neurotransmitters, embryonic development,
  
• vision, smell, bacterial
  infections (Figure 11.7)
• 2) Tyrosine-Kinase Receptors activate many
• signal-transduction pathways
  (Figure 11.8)
• 3) Ion-Channel Receptors - ligand binds
• changes ion concentration, which
  results in a
• cellular response (Figure 11.9)
• B) Receptors that Pass into Cell called
  Intracellular
• Receptors (Figure 11.10)

10
G Protein-Linked Receptor
11
Tyrosine-Kinase Receptor
12
Ion-Channel Receptors
13
Intracellular Receptors
14
Transduction of the Signal

• Usually involves many steps/pathway
• May involve amplifications (many molecules are
  activated)
• Proteins involved may be activated by adding a
  phosphate group ? phosphorylation
• Phosphorylation changes protein shape

15
Protein Phosphorylation

• Protein Kinase an enzyme that transfers P
  groups from ATP to a protein
• Many relay molecules in a signal-transduction
  pathway are protein kinases ? creates a cascade
  of phosphorylation (Figure 11.11)
• About 1 of our genes code for protein kinases
• Abnormal protein kinase activity could lead to
  cancer
• Protein Phosphatases ? enzymes that remove
  phosphate groups from proteins (opposite of
  protein kinases)

16
Protein Phosphorylation Cascade
17
Second Messenger

• Small, non-protein, water-soluble molecule or ion
  that may carry signals via diffusion into and
  through a cell
• Involved in both G protein-linked receptor
  tyrosine-kinase receptor pathways
• Two common secondary messengers are
• 1) Cyclic AMP G protein-linked receptors
• 2) Calcium Ions (2) neurotransmitters,
• growth factors, some hormones

18
Cyclic AMP Secondary Messenger

• Cyclic Adenosine Monophosphatte

19
Calcium Ions Inositol Triphosphate Secondary
Messenger(s)

• Calcium is in low concentration in the cytosol,
  high concentration in the blood, high
  concentration in the ER (actively pumped into ER
  via protein pumps)

20
Cellular Responses

• May regulate..
• 1) Synthesis of Protein/Enzyme -- by
• turning genes on and/or off via
• transcription (Figure 11.17)
• 2) Activity of Proteins/Enzymes in the
• cytoplasm

21
Cellular Response Regulation via Transcription
22
Multiple Steps in Signaling Pathways act to.

1. Amplify the Response few signal molecules can
   lead to the release of many molecules at the end
   of the pathway
2. Specify Signaling Different kinds of cells have
   different proteins therefore, a cells detection
   response to a particular signal depends on its
   collection of proteins