BIO 202 Study Guide - Midterm Guide: Membrane Fluidity, Signal Transduction, Protein Kinase A
16 Jun 2018
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Chapter 7: Membrane Structure and Function
3. Discuss the functions of membrane proteins.
- Integral Proteins: at least partly inserted into membranes. Most completely go through membrane; some completely
span it (transmembrane) several times (like sewn into membrane, in and out).
➢ Transport: transport solute either passively or actively
→ Gated Channels: can be triggered or stay closed in the presence of certain molecules (ligands)
ex: ion channel receptors
→ Electrogenic Pump: generates membrane potential (voltage)
ex: proton pumps found in plants
➢ Enzymatic activity: enzymes with exposed active sites can cause a reaction when triggered
➢ Signal Transduction: ligand binds to a protein (receptor) to start a transduction pathway
➢ Cell-Cell recognition: some proteis at as a ID of the ell → specially recognized by membrane proteins of
other cells, short lived compared to ↓
➢ Intracellular Joining: proteins of adjacent cells hook together to form various junctions (gap junction, tight
junction) to make up intracellular junction of cell membranes, more long lasting than ↑
➢ Attachment to cytoskeleton and ECM: protein attached to cytoskeleton helps maintain cell shape and stabilize
location of other membrane proteins.
- Peripheral Proteins: attached to the membrane surface, cytoskeleton, ECM, but NOT inserted
4. Discuss how unsaturated fatty acids and cholesterol affect the fluidity of membranes.
- Membrane fluidity is VERY important to the function of the various proteins on the cell. It cannot be too watery or
thick.
- Unsaturated Fatty Acids: maintain membrane fluidity at low temperature (tails of the phospholipids). They allow more
space between the phospholipid molecules → allow the membrane proteins to wedge themselves inside.
-Cholesterol: acts as a fluidity buffer. It regulates the space between the molecules at different temperatures. At high
temperature it keeps the cell more rigid by restricting movement of phospholipids as it does not easily liquefy. At low
teperatures it keeps the ell’s phospholipids fro pakig together staying between them. It changes the space.
5. Know what hypertonic, hypotonic, and isotonic mean.
- Tonicity: depending on concentration it controls water movement in cells. Can only use these terms when comparing.
- Isotonic: concentration is the same → no net water movement
- Hypertonic: concentration is higher
- Hypotonic: concentration is lower
- In plant cells:
→ when plant cell wall has too much water it is turgid.
→ when plant cells are in an isotonic environment, there is no net movement, so the cell becomes flaccid (limp)
→ when plant cells are in a hypertonic environment, they lose water, the membrane shrinks, called plasmolysis (it
pops)
1. Describe a typical plasma membrane.
- Phospholipid bilayer (2 phospholipids thick, 5-8 nm, so thin) may have
proteins, carbohydrates attached to exterior (glycolipids, glycoproteins),
and sterols through half of membrane (cholesterol, phytosterol). It has
selective permeability, allows only some things to cross.
2. Define and give examples of an amphipathic molecule.
- Amphipathic molecule: molecule having both hydrophobic and
hydrophilic regions
ex: lipids (phospholipids) and membrane proteins
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6. Define and give examples of: passive transport, active transport, osmosis, facilitated diffusion, co-transport
- Passive Transport: no energy required to move substance across membrane. Controlled by the concentration gradient.
➢ Osmosis: water moves from region of low solute concentration to region of high solute concentration
➢ Facilitated diffusion: passive transport aided by channel proteins. Uses harge of aio aids to attrat argo.
→ Aquaporins: membrane channels that allow water to cross cell membrane by H-bonding
- Active Transport: uses energy to move solutes against their gradient (low→high). Usually uses ATP and is performed by
specific membrane proteins.
➢ Sodium Potassium Pump:
→ When 3 Na+ ions bind to this pump; it prompts an ATP to phosphorylate it (adds a phosphate group)
which causes a change in its conformation, opening it to the other side of the membrane, thus releasing
Na+ outside the cell.
→ Now the K+ ion can bind to the pump and when it does the phosphate group given by the ATP goes
away which changes the conformation again to the original conformation.
→ This is a 3Na out 2K+ in ratio.
➢ Co-transport: (coupled transport) when two different substances are moved together. Sometimes the active
transport of a solute indirectly drives transport of another solute.
→ Symport: two different substances are moved in the same direction
→ Antiport: two different substances are moved in different directions
→ ex: plants use the gradient of hydrogen ions (proton pump) to drive the active transport of sugars
(sucrose-H+ cotransporter), glucose transporter that is driven by a Na+ gradient
7. Know the differences between exocytosis and endocytosis.
- Both occur for bulk transport across plasma membrane through the use of vesicles. Used for large molecules
(polysaccharides and proteins) that cannot go through protein channels or diffusion.
- Exocytosis: when cells export/secrete macromolecules through transport vesicles that migrate to the membrane to
release its contents. Exo-EXITING THE CELL.
- Endocytosis: when the cell absorbs an outside macromolecule and encloses it into a vesicle to transport it inside.
8. Describe and give examples of phagocytosis, pinocytosis, and receptor-mediated endocytosis.
- The three types of endocytosis.
➢ Phagocytosis: when a food or other particle is engulfed by the cell and put into a food vacuole, then the vacuole
fuses with a lysosome for digestion.
➢ Pinocytosis: whe a ell gulps drops of extracellular fluid in small vesicles. This is done because the cell needs
the various solutes in the extracellular fluid, formed by infolding of the plasma membrane (pinching off)
therefore there is no specific substance that is transported through this. Can have a coated pit.
➢ Receptor mediated endocytosis: specific type of pinocytosis. Enables the cell to acquire bulk quantities of
specific substances, does’t hae to e a lot of etraellular fluid.
→ Receptors for certain substances are on the cell membrane, these receptors wait for ligands to bind
to them. When a ligand is bound, the receptors clump together and pinches off (coated pit) into a
vesicle (coated vesicle) and it is transported into the cell. Once emptied the vesicle is recycled back to
the cell membrane.
Chapter 11: Cell Communication
1. Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction
system.
- Ligand-receptor interaction: ligands are signal molecules that bind to a receptor protein in a SPECIFIC, NON COVALENT
way, causing a conformational change in the receptor (initial transduction of the signal) resulting in a series of molecular
events (signal transduction pathway) which leads to a physiological response. Two types:
➢ Local signaling: cell to cell interaction, only cells in immediate vicinity is contacted.
→ Synaptic signaling: directly bring the signaling molecule to the receiving cell.
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- Used in neurons, when nerve cell releases neurotransmitters into synapse too trigger response in other
neurons.
→ Paracrine signaling: localized area.
- Secreting cell acts on nearby cells by discharging molecules of local regulator (Ex: growth factor) into
extracellular fluid. Getting a mosquito bite → cells that are bit release a signal → cells around it swells
➢ Long-distance signaling: using hormones to alert whole body. A hormone is an information-carrying molecule.
They have large impact on the condition of the organism as a whole b/c of strength of hormone + receptor (ex:
puberty).
→ Endocrine signaling: hormones released in bloodstream reach every cell in the body, but only those with
specific receptors respond.
2. Compare and contrast G protein-coupled receptors, tyrosine kinase receptors, and ligand-gated ion channels.
Receptor
Ligand-gated ion channels
G protein-coupled receptor (GPCR)
Tyrosine Kinase Receptor
Key
Components
Ligand-gated ion channel receptor,
ions
G protein (peripheral protein),
GPCR, enzyme
2 Receptor tyrosine kinase
proteins, 2 ligands, ATP
How does it
work?
Ligand binds to a site on the
receptor which causes
conformational change. It opens
the gate alloig speifi ios
through. The change ion
concentration triggers a response.
Signaling molecule binds to the
receptor, the inactive G-protein
(GDP) becomes active and moves
to the GPCR to get a phosphate
group. The charged G-protein then
binds to an enzyme to activate it
which sets off a cellular response.
Two ligands to bind to the
RTK’s outside side to reate a
RTK dimer. When the dimer is
activated, the tyrosine groups
are phosphorylated by ATP. A
relay protein binds to the
phosphorylated tyrosines
which causes a
conformational change on the
protein which will lead to a
cellular response.
Transduction
Flux of ions into cell
Activating G protein (GDP to GTP)
Appearance of
phosphorylated tyrosines
Uses/Notes
- Neurotransmitter molecules
released at a synapse between two
nerve cells bind as ligands to ion
channels on the receiving cell,
causing the channels to open. Ions
flow in (or, in some cases, out),
triggering an electrical signal that
propagates down the length of the
receiving cell.
- G-Protein acts as an on/off
switch, the protein itself does not
change, ol the uleotide it’s
bounded to (GDP becomes GTP).
- Used in vision, smell, etc., many
different types.
- The inside of RTK is made of
tyrosine amino acids.
- Can lead to multiple
separate cellular responses
because they have many
phosphorylated tyrosines.
- kinase is an enzyme that
transfers phosphate from ATP
to the hydroxyl R group of
serine, tyrosine, or threonine
3. List the advantages of a multistep pathway in the transduction stage of cell signaling.
- Transduction: everything between activated receptor and ultimate responding molecule, involves multiple steps
- Can amplify signal, a few molecules can produce a large cellular response
- Provides more opportunity for coordination and regulation.
4. Explain how original signal molecule can produce a cellular response without entering the target cell.
- The ligand only needs to bind to a receptor protein to initiate a signal transduction pathway. One signal molecule can
cause a cascade of protein phosphorylation.
5. Define the term second messenger; describe the role of these molecules (Ca++, cAMP, and IP3) in signaling pathways.
- Second messengers: Small non-protein, water-soluble molecules/ions that can spread throughout cells by diffusion.
Still needs a first messenger (ligand) to trigger their diffusion. In response to ligand binding to the receptor → rapid
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Document Summary
Chapter 7: membrane structure and function: describe a typical plasma membrane. Phospholipid bilayer (2 phospholipids thick, 5-8 nm, so thin) may have proteins, carbohydrates attached to exterior (glycolipids, glycoproteins), and sterols through half of membrane (cholesterol, phytosterol). It has selective permeability, allows only some things to cross: define and give examples of an amphipathic molecule. Amphipathic molecule: molecule having both hydrophobic and hydrophilic regions ex: lipids (phospholipids) and membrane proteins: discuss the functions of membrane proteins. Integral proteins: at least partly inserted into membranes. Most completely go through membrane; some completely span it (transmembrane) several times (like sewn into membrane, in and out). Transport: transport solute either passively or actively. Gated channels: can be triggered or stay closed in the presence of certain molecules (ligands) ex: ion channel receptors. Electrogenic pump: generates membrane potential (voltage) ex: proton pumps found in plants. Enzymatic activity: enzymes with exposed active sites can cause a reaction when triggered.
