Unit II: Cells & Membranes Flashcards
Explain the mechanism of Ca2+ ATPase.
Calcium concentration in cytoplasm is 100 nanoM, extra cellular fluid is 2milliM. Concentration gradient is thus pointed into cell for even diffusion of Ca+ ions.
Transmembrane domain consists of a bundle of alpha helices, substrate goes through center of helical bundle, as outside of alpha helix bundle is hydrophobic and inside is hydrophilic.
Over the course of transfer it undergoes a conformational change just like facilitated diffusion protein. Can hydrolysis ATP into ADP and Phosphate (hence, P-type, as it undergoes phosphorylation). This phosphorylation causes a conformational change in the protein and undergoes a cycle.
Binds ATP in one conformation. Hydrolyses it and gets Phosphorylated, which causes an all obstetric conformational change favoring other conformation. Protein then hydrolysis off the phosphate group, and is allowed to return to initial conformation.
Since ATP is getting hydrolyzed, THIS SYSTEM HAS ENERGY, thus the hydrolysis of ATP gives cycle a favored direction.
In E1 there is a high affinity for Ca2+ (accessible from cytoplasm). In E 2 (accessible by extra cellular fluid) Ca2+ affinity is low.
This lets protein transfer Calcium against the concentration gradient and export Calcium ions from the cell.
What are the types of transport proteins? What are the differences between them? What are some shared characteristics?
Passive Diffusion, diffusion of solute across membrane as a result of equalizing concentration. Has hyperbolic kinetics (can be saturated, since they have specific binding sites, similar to enzymes).
Facilitated Diffusion, in which facilitates transport of specific solutes across membrane. Conformational Change in protein after solute binding means there never is a hole that goes all the way through the membrane. Carries out transport in both directions according to concentration. ex. Glucose transferred by GLUT ( GLUcose Transporter, 7- different types.), important in liver!
Active Transport- can move solutes AGAINST concentration gradient, powered by hydrolysis of ATP. ATPases are transporters that use ATP. Outputs 3 Na + ions for 2 K+ ions taken in. Responsible for voltage difference in neurons, etc. Ex. Na+ ATPase, Ca2+ ATPase, H+ ATPase (Targeted by Proton Pump inhibitors). See Mechanism of Ca ATPase.
Co-transport
Open Ion channels ex. aquaporin (important in the kidneys)
Gated Ion Channels
All are multipass integral membrane proteins. Provide a path for solute across the membrane.
Types of Active Transporters
F-Type found in mitochondrial inner membrane, and synthesizes ATP from ADP and Phosphate. Recycles spent ATP from ion channels, etc.
V-Type found in lysosomes and endosomes in mammals. Pumps proteins from the cytoplasm into the organelle, creating a low pH (4.5) in organelles.
ABC transporters carry organic molecules, not just ions. Have common ATP-binding cassette motif. Cystic fibrosis is caused by an irregularity in CFTP. ABCA1: one type is responsible for transporting chloride/bicarbonate, and another for cholesterol.
What are the different classifications of hormone signaling? In order of decreasing distance
Endocrine- cell releases hormone into the bloodstream, hormone received by most of body.
Paracrine- very short distance, sender cell secretes hormone released into tissue, has multiple recipients depending on how far it spreads. Ex. Mosquito bite
Juxtracrine- Paracrine with a target cell that is attached to the sender cell. Important in development.
Synaptic- neurons release neurotransmitters
Autocrine- cell secretes hormones that it receives itself, prominent in cancer. 44minutes in
Types of receptors how is signal transmitted? How is it amplified?
Nuclear- activated by binding ligands removing proteins that inhibit receptor. Binding ligands result in a conformational change that allows hormone to enter the nucleus and interact with DNA to change gene expression (transcription) causing changes in mRNA, which changes protein synthesis, eventually causing a change in biological response as a result of changes in proteins. Interacts in a sequence specific manner. HRE (Hormone Response Element) is DNA sequence that allows particular gene to interact with receptor. Is a slow reaction. Slide 14
G-proteins- type of alpha subunits determine downstream effect of activated G-protein, activates secondary messengers.
Cytokine
Cyclic AMP
Made by adenyl cyclase in plasma membrane from ATP. Cyclase regulated by GPCRs
Broken down into AMP by cAMP phosphodiesterase
Diffuses through cytoplasm and nucleus
Concentration is <1 microMolar
Only function is to serve as regulatory molecule as a secondary messenger.
G protein receptor mechanism
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