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Study Guide

LIFESCI 7C Study Guide - Winter 2018, Comprehensive Midterm Notes - Protein, Homeostasis, Evolution


Department
Life Sciences
Course Code
LIFESCI 7C
Professor
Pires
Study Guide
Midterm

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LIFESCI 7C
MIDTERM EXAM
STUDY GUIDE
Fall 2018

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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”
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