Theme 2: The Complex Proteome
9.1 Principles of Cell Communica4on
• Human proteome represents the full number of proteins that are
expressed by all the hereditary informa6on in our DNA (i.e. our genome)
• Informa6on is o?en conveyed from one cell to another in the form of
small molecules secreted into the environment
• Other informa6on is provided by physical contact with neighboring cells
• Other informa6on is provided by the meshwork of proteins and
polysaccharides that underlies or surrounds most cells in mul6cellular
organisms
9.1.1 Cells communicate using chemical signals that bind to
specific receptors.
• Example: Streptococcus pneumoniae (a.k.a. pneumococcus)- A disease-
causing bacterium that is associated with pneumonia, meningi6s and
some kinds of arthri6s
◦ 1960s- Observed that the rate of DNA uptake by pneumococcal
cells increased sharply once the bacterial popula6on reached a
certain density
• Bacteria could coordinate DNA uptake across the popula6on
so it occurred only at appropriate 6mes
◦ 1990s- Discovery of a pep6de consis6ng of 17 amino acids that is
con6nuously synthesized and released by pneumococcal cells; A
receptor for this pep6de discovered on surface of pneumococcal
cells
• Binding of pep6de to receptor causes a bacterium to
express the genes required for DNA uptake
▪ As popula6on density increases, concentra6on of
pep6de increases un6l it reaches a level high enough
to cause cells to turn on genes needed for DNA uptake
• Four elements of communica6on between all cells:
, ◦ Signalling cell- Source of the signalling molecule, which binds to a
receptor molecule on or in the responding cell
◦ Signalling molecule
◦ Receptor molecule
◦ Responding cell
• Example: In pneumococcus, bacterial cells are both the signalling and
responding cells
9.1.2 Signalling involves receptor ac4va4on, signal
transduc4on, response, and termina4on.
◦ Message is carried from outside the cell into the cytosol or
nucleus
◦ Ini6al signal is o?en amplified
• Example: Pneumococcal cells- Pep6de-signalling molecule binds to a
receptor on the cell surface; When enough receptors are bound by the
signalling molecule, the message is relayed by the signal-transduc6on
pathways to the nucleoid in the cytosol, where genes are turned on that
express proteins involved in DNA uptake from the environment
◦ When the density of bacteria is low, the ini6a6ng signal falls below
a cri6cal threshold and gene expression is turned back off
38.1.3 The endocrine system underlies homeostasis.
• Homeostasis- The maintenance of a steady physiological state within a
cell/organism
• Homeosta6c regula6on depends on feedback from the target organ sent
back to the endocrine gland that secretes the hormone
◦ Feedback- A s6mulus evokes a response, which affects the
s6mulus; The means by which a signal produced by the regulatory
organ can modify its own subsequent produc6on, either inhibi6ng
or s6mula6ng it
◦ Nega4ve Feedback- A change in a system causes a response that
brings the system back to the star6ng point
◦ Consists of a:
• S6mulus- The change itself
• Sensor- Detects the change
9.1 Principles of Cell Communica4on
• Human proteome represents the full number of proteins that are
expressed by all the hereditary informa6on in our DNA (i.e. our genome)
• Informa6on is o?en conveyed from one cell to another in the form of
small molecules secreted into the environment
• Other informa6on is provided by physical contact with neighboring cells
• Other informa6on is provided by the meshwork of proteins and
polysaccharides that underlies or surrounds most cells in mul6cellular
organisms
9.1.1 Cells communicate using chemical signals that bind to
specific receptors.
• Example: Streptococcus pneumoniae (a.k.a. pneumococcus)- A disease-
causing bacterium that is associated with pneumonia, meningi6s and
some kinds of arthri6s
◦ 1960s- Observed that the rate of DNA uptake by pneumococcal
cells increased sharply once the bacterial popula6on reached a
certain density
• Bacteria could coordinate DNA uptake across the popula6on
so it occurred only at appropriate 6mes
◦ 1990s- Discovery of a pep6de consis6ng of 17 amino acids that is
con6nuously synthesized and released by pneumococcal cells; A
receptor for this pep6de discovered on surface of pneumococcal
cells
• Binding of pep6de to receptor causes a bacterium to
express the genes required for DNA uptake
▪ As popula6on density increases, concentra6on of
pep6de increases un6l it reaches a level high enough
to cause cells to turn on genes needed for DNA uptake
• Four elements of communica6on between all cells:
, ◦ Signalling cell- Source of the signalling molecule, which binds to a
receptor molecule on or in the responding cell
◦ Signalling molecule
◦ Receptor molecule
◦ Responding cell
• Example: In pneumococcus, bacterial cells are both the signalling and
responding cells
9.1.2 Signalling involves receptor ac4va4on, signal
transduc4on, response, and termina4on.
◦ Message is carried from outside the cell into the cytosol or
nucleus
◦ Ini6al signal is o?en amplified
• Example: Pneumococcal cells- Pep6de-signalling molecule binds to a
receptor on the cell surface; When enough receptors are bound by the
signalling molecule, the message is relayed by the signal-transduc6on
pathways to the nucleoid in the cytosol, where genes are turned on that
express proteins involved in DNA uptake from the environment
◦ When the density of bacteria is low, the ini6a6ng signal falls below
a cri6cal threshold and gene expression is turned back off
38.1.3 The endocrine system underlies homeostasis.
• Homeostasis- The maintenance of a steady physiological state within a
cell/organism
• Homeosta6c regula6on depends on feedback from the target organ sent
back to the endocrine gland that secretes the hormone
◦ Feedback- A s6mulus evokes a response, which affects the
s6mulus; The means by which a signal produced by the regulatory
organ can modify its own subsequent produc6on, either inhibi6ng
or s6mula6ng it
◦ Nega4ve Feedback- A change in a system causes a response that
brings the system back to the star6ng point
◦ Consists of a:
• S6mulus- The change itself
• Sensor- Detects the change
