What makes up the cell membrane?
- Phospolipid bilayer
- Cholesterol (animals)
What kinds of proteins make up the cell membrane?
- Integral (Transmembrane)
What part of a protein is glycosylated?
The portion facing the extracellular matrix
What are the functions of the membrane?
- Selective barrier
- In eukaryotes, formation of organelles/compartments
- Localization of enzymatic reactions
- Cell-cell communication
- Transmission/reception of signals
- Receive stimuli
- Site of ECM attachment
Where does glycoslyation occur, and what is the destination?
- Cell membrane (i.e. not organelles)
What does flippase do?
It "evens out" enzymes since most are on cytosol side
What is a lipid raft?
A "microdomain" of the plasma membrane which aggregates proteins and phospholpids for transportation.
How does a lipid raft travel?
Do proteins for organelles get glycosylated? Why or why not?
- Glycosylation is for cell-cell recognition
What is an advantage of a compartment/organelle?
- Useful for specialized enzymatic reactions.
- Greater rate of collisions for reactions to occur.
What is the minimum length of a transmembrane protein?
What are some functions of transmembrane proteins on the cytoplasmic side?
- Intrinsic or associated enzymatic activity
- Provide cell with shape
What are functions of transmembrane proteins on the outside?
- Receptors for soluble ligands
- ECM attachment (e.g. integrins)
- Cell-cell attachment (e.g. cadherins)
How are gates/channels activated?
Hormones or action potentials
What are types of secondary structures for transmembrane proteins?
- Alpha helices
- Beta barrels
For alpha helices in a gate, where is the hydrophobic side?
Facing the outside surface of the gate
What transports water thru the membrane?
What is the function of membrane cholesterol?
Provides membrane fluidity
What types of molecular movement are there in the membrane?
- Rotation on axis
- Lateral (sideways)
- Flip-flopping (from one side to the other)
Describe flip-flopping movement in a membrane.
- Requires energy and is thus uncommon
- Requires the flippase enzyme
- Proteins are too large for this movement
What can cross a membrane by simple diffusion?
CO2 and O2
What happens if a cell membrane has no fluidity?
The cell dies
What are some ways to alter membrane fluidity?
- Change length of hydrocarbon tails
- Change saturation
- Change cholesterol content
- Change temperature
What does an increase in cholesterol do?
What does an increase in temp do?
What does an increase in saturation do?
What does an increase in hydrocarbon tail length do?
What is a ligand?
A signal that is received by the cell usually resulting in a response.
What is a receptor?
A feature on the cell which receives a ligand
How does a receptor respond?
- Intrinsically as an enzyme.
- Associated with an enzyme.
- With the cytoskeleton directly.
What are some responses to a ligand being received?
- Gene expression
What are effector proteins?
They are proteins activated by intracellular signalling proteins
What are three types of effector proteins?
- Metabolic enzyme
- Gene regulatory protein
- Cytoskeletal protein (altered cell shape or movement)
What types of interactions are there between effectors and cells?
- Direct contact between transmembrane molecules of two neighboring cells
- Paracrine system (local)
- Synaptic (neurotransmitters)
- Cytonemes (thin cytoplasmic extensions releasing hormones)
- Endocrine (via bloodstream)
Which type of signalling requires the most signal molecules?
Which type of signalling is not soluble?
- Contact dependent
- Maybe Cytonemes?
What are three types of signalling responses?
- Quick; < 1 hour; protein de/activation; synaptic
- Slow; 18-24 hours; transcription/translation; endocrine
- Single cell or group in development; autocrine
What are four end-results of a cell in response to a signal?
- Grow + Divide
Describe how acetylcholine can cause two different reponses.
- Heart muscle - decreased rate and force of contraction
- Skeletal muscle - contraction
What are two types of signals wrt to water?
- Soluble - interact with transmembrane receptors
- Insoluble - interact with cytoplasmic receptors
Non-soluble signals affect ___.
What are examples of non-soluble signals?
Vitamin D, estrogen, testosterone, cortisol, estradiol, retinoic acid, and thhroxine
Non-soluble signals have a ___ effect due to ___.
- their duration in the blood
Non-soluble signals enter the cytoplasm by ___.
Non-soluble receptor responses include ___.
- Early - first 30 min
- Depends on type of protein and timing of synthesis
Gene expression regulation falls into two general categories:
All nuclear receptors bind as either ___ or ___.
An inactive receptor protein is bound to ___ proteins.
Proteins in the primary response can ____.
Activate other proteins for a delayed/secondary response.
Describe responses to testosterone.
- Early - male characteristics in development
- Delayed - muscle growth
Describe responses to estrogen.
- Early - female characteristics
- Delayed - retention of bone mass
What are three classes of cell-surface receptors?
- Ion-channel-coupled (open channel)
- G-protein-coupled (G activates enzyme)
- Enzyme-coupled (intrinsic and associated enzymatic)
What are three types of "players" that affect the cell?
- First messengers - ligands such as hormones
- Intracellular signaling proteins
- Second messengers - not unique to one pathway
What are examples of second messengers?
cAMP, cGMP, 1,2-diacylglycerol (DAG), IP3, Ca+2
What second messengers require ATP?
What second messengers are derived from phospholipids
Name various proteins/molecules in signalling pathways/cascades.
Anchoring, amplifier, integrator, modular, relay, scaffold, transducer
Describe an anchoring protein.
Anchors proteins to a structure at a precise location where needed.
Describe amplifier proteins.
Greatly increases signal they receive.
Describe Integrator proteins.
Combine signals from two or more pathways before forwarding.
Describe modular proteins.
Modify the activity of signaling proteins to regulate signal strength.
Describe relay proteins.
Pass messages to the next signaling component in the pathway.
Describe scaffold proteins.
Bind to multiple signaling proteins together in a functional complex for quicker and more efficient interaction.
Describe transducer proteins.
Convert singal to a different form.
Describe the structure of a G Protein-linked receptor (or G protein-coupled).
- Seven transmembrane spanning domains.
- Large cytoplasmic region that associates/activates with trimeric G proteins
Does the GPCR have intrinsic enzymatic activity?
What are 4 classic downstream targets of G Proteins that regulate different effectors?
- Adenylyl cyclases
- Ion channels
- Protein kinases
What are the basic subunits of a G protein?
alpha, beta, gamma
What about G proteins might explain highly specific responses?
What part of the G protein binds with GDP?
The alpha subunit
When activated, the beta/gamma complex can ___.
move and activate other targets.
What else provides specific signaling specifity?
- Cell-specific receptors, G isoforms, and effectors
- Amount of receptors, G isoforms, and effectors
- Organization of signaling cascades
- Accessory proteins
How do accessory proteins regulate G protein action?
They regulate the strength, efficiency, and specificity of the transmitted signal.
What are some examples of accessory proteins?
- GAP-43 - promotes GDP dissociation
- AGS3 - stabilizes G-alpha-GDP interaction
- Tubulin - directly transfers GTP to G-alpha
What are three types of accessory proteins?
- Activators of G protein signaling (AGS)
- Regulator of G protein signaling (RGS)
- Inhibitors of GDP dissociation
Describe activators of G protein signaling.
Can activate G proteins without the use of a receptor
Describe regulators of G protein signaling.
- Accelerate the GTPase activity of specific G-alpha subunits.
- Quick inactivation - hydrolysis
What is the typical end of a pathway?
What are other roles associated with G proteins?
- Golgi stability (alternative binding partners)
- Cell polarity in the fruit fly and nematode
- Neurite outgrowth and path-finding
What do G protein-linked receptors activate?
- Adenylyl cyclase
- Phospholipase C-beta
What effect does the activation of adenylyl cyclase typically have?
- Increase of cyclic AMP concentration in the cytosol.
- This rise activates PKA.
- PKA enters the nucleus and phosphorylates CREB.
- CREB recruits CBP, and both stimulate gene transcription.
What is produced from the hydrolysis of PIP2?
- inositol 1,4,5-trisphosphate (IP3) - releases Ca2+ from the ER
- diacylglycerol (DAG) - helps to activate PKC
Describe how GPCRs increase cytosolic Ca2+ and activate PKC.
- PLC-beta is activated by G protein (via alpha, beta/gamma, or both).
- Two messenger molecules, P3 and DAG, produced from hydrolysis of PIP2.
- IP3 releases Ca2+ from ER
- Ca2+ and DAG activate PKC
What other purpose does the release of Ca2+ serve?
Prevents polyspermy by creating fertilization envelope