LIFESCI 7C Study Guide - Winter 2018, Comprehensive Midterm Notes - Protein, Homeostasis, Evolution
LIFESCI 7C
MIDTERM EXAM
STUDY GUIDE
Fall 2018
Week 1
9.1 Principles of Cell Communication
● Cells receive info from physical environment, other cells and respond to signals by changing activity or dividing
● Basic principles of cell communication (receiving and responding to signals first evolved from unicelluar
organisims and apply to all cells
Cells communicate using chemical signals that bind to specific receptors
● Four elements of cell signalling
○ signaling cell The source of the signaling molecule.
○ signaling molecule The carrier of information transmitted when the signaling molecule binds to a
receptor; also referred to as a ligand.
■ Vary immensely: peptides, lipids, gases, etc; carry info from one cell to the next
○ receptor protein The molecule on the responding cell that binds to the signaling molecule.
■ presence/absence of receptors allow signalling to be specific for particular cells
○ responding cell The cell that receives information from the signaling molecule.
● Ex: bacterial density and rate of DNA uptake (increased w/ greater density) → fueled by signalling to indicate
presence of other bacteria
○ → quorum sensing: process by which bacteria are able to determine high/low population density and turn
on specific genes across the entire community; used to control/coordinate many different types of
bacterial behaviors
Signalling involves receptor activation, signal transduction, response, and termination
● When signalling molecule binds to receptor on responding cell….
1. receptor activation The “turning on” of a receptor, which often occurs when a signaling molecule binds
to a receptor on a responding cell.
a. Receptors can be activators, enzymes, channels, etc
2. signal transduction The process in which an extracellular molecule acts as a signal to activate a
receptor, which transmits information through the cytoplasm → chain rxn of molecule activation
a. Signal often amplified at each step in the pathway→ low signal concentration can have large
effect on responding cell
3. response A change in cellular behavior, such as activation of enzymes or genes, following a signal.
4. termination the stopping of a signal; response can be terminated at any point in signalling pathway
a. Protects cell from overreacting to existing signal→ appropriate level of response
b. Allows cell to respond to new signals
● In general elements of signal transduction have been evolutionary conserved over long periods of time in a wide
range of organisms
9.2 Cell Signaling over Long and Short Distances
● In multicellular organisms, distance between communicating cells varies considerably
○ Far cells: signaling molecule transported by circulatory system (endocrine signaling)
○ Close cells: signaling molecule moves by diffusion (paracrine signaling)
○ Physicall attached cells: signaling molecule is not released from the signaling cell at all (contact-
dependent signaling)
○ Self-signaling: autocrine signaling
Endocrine Signaling acts over long distances
● endocrine signaling Signaling by molecules that travel through the bloodstream.
○ E.g. adrenaline, estradiol (estrogen) and testosterone (androgen)
Signaling can occur over short distances
● paracrine signaling Signaling by a molecule that travels a short distance to the nearest neighboring cell to bind
its receptor and deliver its message; moves by diffusion!
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○ growth factor Any one of a group of small, soluble molecules, usually the signal in paracrine signaling,
that affect cell growth, cell division, and changes in gene expression (type of signaling molecule).
■ Type of signalling molecule that tells responding cell to grow, divide, or differentiate
■ Secreted by embryonic cells to influence neighboring cells→ help shape structure of adults’ tisues,
organs, limbs
○ Ex: Neuron-neuron or neuron-muscle short-range signaling
● autocrine signaling Signaling between different parts of a cell; the signaling cell and the responding cell are one
and the same.
○ Ex: specialized cell can use autocrine signaling to maintain this developmental decision; can also be used
by cancer cells to promote cell division
Signaling can occur by direct cell-cell contact
● Transmembrane proteins on surfaces of signalling and and responding cell act as signalling molecule and
receptor→ signaling molecule not released but remains associated w/ plasma membrane of signaling cell
○ Important in embryonic development
● E.g. glial cells (responding cell), Notches (receptors), neurons (signaling cell) and Delta proteins (signaling
molecule)
● Signal molecules that are polar usually have their corresponding receptor on the surface of the cell
○ Nonpolar signal molecules can pass through plasma membrane of responding cell and bind to receptors
inside the cell
9.3: Cell-Surface and Intracellular Receptors
● Receptors: proteins that receive/interpret info carried by signaling molecules
○ Signal molecule=ligand
○ ligand-binding site The specific location on the receptor protein where a signaling molecule binds; bond
is noncovalent and highly specific!
○ Ligand binding to receptor’s ligand-binding cite causes conformational change in receptor
■ Conformational change activates the receptor→ receptor passes message from signaling
molecule to cell interior; triggers chem reactions/other changes in cytosol
Receptors for polar signaling molecules are on the cell surface
● Location of particular receptor depends on polarity of signaling molecule
○ Polar signaling molecule (cannot cross through plasma membrane)→ cell-surface receptors
○ Nonpolar signaling molecule (can cross through plasma membrane) → intracellular receptors
● Receptor proteins for growth factors/other polar ligands=transmembrane proteins w/ extracellular, transmembrane
and cytoplasmic parts
○ ENTIRE receptor protein undergoes conformational change upon binding w/ ligand→ receptor=bridge
between inside/outside of responding cell, carrying hydrophilic signal’s message across hydrophobic core
of plasma membrane
Receptors for nonpolar signaling molecules are in the interior of the cell
● Nonpolar signaling molecules like steroid hormones (endocrine) are hydrophobic and pass through plasma
membrane and into cell easily
○ Once inside steroid hormones bind to receptor proteins in cytosol or nucleus to form receptor-steroid
complexes whcih enter nucleus and act to control expression of genes
○ Steroid receptors ON nucleus often already bound to DNA and only need steroid to turn on gene
expression
● Ex: sex hormones, glucocorticoids, ecdysone, etc
Cell-surface receptors act like molecular switches
● Many receptors act as binary molecular switches: “on” when bound to signaling molecule or “off”
find more resources at oneclass.com
find more resources at oneclass.com