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What makes up the cell membrane?
- Phospolipid bilayer
- Proteins
- Cholesterol (animals)
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What kinds of proteins make up the cell membrane?
- Peripheral
- Integral (Transmembrane)
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What part of a protein is glycosylated?
The portion facing the extracellular matrix
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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
- Shape
- Receive stimuli
- Site of ECM attachment
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Where does glycoslyation occur, and what is the destination?
- Golgi
- Cell membrane (i.e. not organelles)
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What does flippase do?
It "evens out" enzymes since most are on cytosol side
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What is a lipid raft?
A "microdomain" of the plasma membrane which aggregates proteins and phospholpids for transportation.
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How does a lipid raft travel?
Via vesicle
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Do proteins for organelles get glycosylated? Why or why not?
- No.
- Glycosylation is for cell-cell recognition
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What is an advantage of a compartment/organelle?
- Useful for specialized enzymatic reactions.
- Greater rate of collisions for reactions to occur.
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What is the minimum length of a transmembrane protein?
20 a.a.'s
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What are some functions of transmembrane proteins on the cytoplasmic side?
- Intrinsic or associated enzymatic activity
- Provide cell with shape
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What are functions of transmembrane proteins on the outside?
- Receptors for soluble ligands
- Channel/gate
- ECM attachment (e.g. integrins)
- Cell-cell attachment (e.g. cadherins)
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How are gates/channels activated?
Hormones or action potentials
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What are types of secondary structures for transmembrane proteins?
- Alpha helices
- Beta barrels
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For alpha helices in a gate, where is the hydrophobic side?
Facing the outside surface of the gate
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What transports water thru the membrane?
Aquaporin
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What is the function of membrane cholesterol?
Provides membrane fluidity
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What types of molecular movement are there in the membrane?
- Rotation on axis
- Lateral (sideways)
- Flip-flopping (from one side to the other)
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Describe flip-flopping movement in a membrane.
- Requires energy and is thus uncommon
- Requires the flippase enzyme
- Proteins are too large for this movement
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What can cross a membrane by simple diffusion?
CO2 and O2
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What happens if a cell membrane has no fluidity?
The cell dies
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What are some ways to alter membrane fluidity?
- Change length of hydrocarbon tails
- Change saturation
- Change cholesterol content
- Change temperature
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What does an increase in cholesterol do?
Increases fluidity
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What does an increase in temp do?
Increases fluidity
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What does an increase in saturation do?
Decreases fluidity
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What does an increase in hydrocarbon tail length do?
Decreases fluidity
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What is a ligand?
A signal that is received by the cell usually resulting in a response.
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What is a receptor?
A feature on the cell which receives a ligand
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How does a receptor respond?
- Intrinsically as an enzyme.
- Associated with an enzyme.
- With the cytoskeleton directly.
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What are some responses to a ligand being received?
- Gene expression
- Metabolism
- Movement
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What are effector proteins?
They are proteins activated by intracellular signalling proteins
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What are three types of effector proteins?
- Metabolic enzyme
- Gene regulatory protein
- Cytoskeletal protein (altered cell shape or movement)
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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)
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Which type of signalling requires the most signal molecules?
Endocrine
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Which type of signalling is not soluble?
- Contact dependent
- Maybe Cytonemes?
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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
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What are four end-results of a cell in response to a signal?
- Survive
- Grow + Divide
- Differentiate
- Die
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Describe how acetylcholine can cause two different reponses.
- Heart muscle - decreased rate and force of contraction
- Skeletal muscle - contraction
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What are two types of signals wrt to water?
- Soluble - interact with transmembrane receptors
- Insoluble - interact with cytoplasmic receptors
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Non-soluble signals affect ___.
transcription
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What are examples of non-soluble signals?
Vitamin D, estrogen, testosterone, cortisol, estradiol, retinoic acid, and thhroxine
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Non-soluble signals have a ___ effect due to ___.
- longer-lasting
- their duration in the blood
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Non-soluble signals enter the cytoplasm by ___.
diffusion
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Non-soluble receptor responses include ___.
- Early - first 30 min
- Delyated
- Depends on type of protein and timing of synthesis
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Gene expression regulation falls into two general categories:
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All nuclear receptors bind as either ___ or ___.
Homodimers, heterodimers
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An inactive receptor protein is bound to ___ proteins.
Inhibitory
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Proteins in the primary response can ____.
Activate other proteins for a delayed/secondary response.
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Describe responses to testosterone.
- Early - male characteristics in development
- Delayed - muscle growth
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Describe responses to estrogen.
- Early - female characteristics
- Delayed - retention of bone mass
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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)
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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
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What are examples of second messengers?
cAMP, cGMP, 1,2-diacylglycerol (DAG), IP3, Ca+2
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What second messengers require ATP?
cAMP, cGMP
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What second messengers are derived from phospholipids
DAG, IP3
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Name various proteins/molecules in signalling pathways/cascades.
Anchoring, amplifier, integrator, modular, relay, scaffold, transducer
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Describe an anchoring protein.
Anchors proteins to a structure at a precise location where needed.
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Describe amplifier proteins.
Greatly increases signal they receive.
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Describe Integrator proteins.
Combine signals from two or more pathways before forwarding.
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Describe modular proteins.
Modify the activity of signaling proteins to regulate signal strength.
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Describe relay proteins.
Pass messages to the next signaling component in the pathway.
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Describe scaffold proteins.
Bind to multiple signaling proteins together in a functional complex for quicker and more efficient interaction.
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Describe transducer proteins.
Convert singal to a different form.
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