Cell Communication

1
Cell Communication

• How External Signals Give Rise to Specific
  Intracellular Responses

2
Three Stages of Cell Signaling

• Reception or Binding Environmental
  signal/molecule binds to receptor
• Transduction Propagation and amplification of
  the signal from the receptor through a series of
  molecules in a signal-transduction pathway
• Cellular Response Change in cellular activity as
  a result of the signal

3
Signaling Molecule

• Ligand
• binds to receptor and induces change in its
  structure
• reversible reactionR L RL

4
Types of Receptors

• Cytoplasmic receptors
• bind to signals that diffuse across plasma
  membrane, including small and/or non-polar
  molecules

5
Types of Plasma Membrane Receptors

• Ion Channel Receptors
• when signal binds, gated proteins open a
  channel to allow ions to enter or leave cell
• signal is large and/or polar

6
Types of Plasma Membrane Receptors
Two insulin molecules must bind
Receptor forms an activated dimer

• Protein Kinases
• catalyze the transfer of phosphate to target
  protein
• signal is large and/or polar

Kinase domain catalyzes phosphorylation of
responder
7
Types of Plasma Membrane Receptors

• G Protein-Linked Receptors
• signal is large and/or polar
• when signal binds, receptor interacts with G
  protein
• G protein, carrying GTP, binds to an effector
  protein
• effector protein influences cell activity

Animation 15-01
8
Signal Transduction Pathway Involving G
Protein-Linked Receptor
Ligand-Receptor complex activates G protein
Effector converts reactants to products
G protein subunit activates effector protein
9
Applying Your Knowledge

• Protein Kinase Receptor
• Ligand
• G Protein-Linked Receptor
• Cytoplasmic Receptor
• Ion Channel Receptor

• Which one binds to a non-polar signaling
  molecule?
• Which one catalyzes a phosphorylation reaction?
• What is the name of the signaling molecule?

10
Types of Signal Transduction Pathways

• Direct Transduction Effect of receptor, occurs
  at plasma membrane

Activated Adaptor protein causes Ras activation
by GTP binding
Activated MAP kinase enters the nucleus to
influence gene activity
Receptor activates Adaptor protein by
phosphorylation
11
RAS Mutations Cause Cancer
In a normal cell, RAS is activated when growth
factor binds to the receptor
In a cancer cell, a mutated version of RAS is
locked in its GTP-binding form, causing cell
division in the absence of growth factor
12
Types of Signal Transduction Pathways

• Indirect Transduction Pathway includes a second
  messenger between receptor and effector

Cyclic AMP (cAMP) is a common second messenger
13
Cellular Responses
Second messenger DAG and calcium activate Protein
Kinase C

• Ion Channels are Opened

Slow Block to Polyspermy
Phospholipase C catalyzes the production of IP3
and DAG from PIP2
Second messenger IP3 opens calcium channels
14
Changes in Cell Function

• Enzyme Activities are Changed

15
Cellular Responses

• Different Genes are Transcribed

16
Applying Your Knowledge

• GDP
• Receptor
• cAMP
• GTP
• Effector

• When considering a pathway that leads to changes
  in enzyme activity, which term best describes the
  enzyme?
• Which one represents a common secondary
  messenger?
• Which one is attached to a G protein in its
  inactive state?