Lecture 3: Mitochondria - Exam 5 Flashcards
What do Deubiquitinating enzymes (DUBS) do?
They release ubiquitin chains from ubiquitin-protein conjugates once they have been targeted to the proteasome and are committed to degradation.
Ubiquitin lysines can also be ubiquitinated, leading to?
Polyubiquitin chains that are best characterized for linkage occurring through K48 and K63**.
The Rpn11 subunit of the proteasome cap is believed to?
Cleave the isopeptide bond between the protein substrate and the ubiquitin chain.
What happens if there is a failure of DUBs releasing ubiquitin chains?
-Inappropriate degradation of the ubiquitin tag along with the substrate.
-Interfere with entry of substrate into the narrow opening leading to the central proteolytic chamber of the proteasome.
What is cell signaling?
The ability of a cell to receive, process and transmit signals with its environment and with itself.
What are receptors?
What are ligands?
Receptors are proteins responsible for detecting stimuli.
Ligands are signaling molecules that trigger a signal cascade by binding to receptor proteins.
What are endocrine signals (e.g. hormones)?
Long range signal produced at distances from their target and carried by the circulatory system to the site of activation.
What are paracrine signals (e.g. growth factors)?
Short range signal produced locally and reaches their target by diffusion to nearby tissues**.
What are juxtacrine signals?
Require physical contact** between sending and receiving cell.
What are autocrine signals?
Sending and receiving mediators are located on the same cell.
What is Kd?
Dissociation constant. The amount of ligand needed to produce a state where exactly half of the receptors are occupied.
What does high affinity refer to?
The lower the Kd value (lower concentration), the higher the affinity of the ligand.
What are agonists? What are antagonists?
Agonists- Ligands that bind to their receptors and activate a signaling cascade.
Antagonists- Ligands that bind to receptors and prevent naturally occurring messengers from binding and activating the receptor.
Describe the downregulation of signaling.
“Turning Receptors off.”
-Reduce the concentration of free ligand available to the receptor… Neurons - Neurotransmitters.
-Reduce the amount of the receptor or the sensitivity of the receptor for the ligand… Receptor Desensitization - Reduced affinity
Describe receptor desensitization – Reduced affinity.
A normal, active receptor binds a ligand and sends a signaling cascade. The possibilities of receptor desensitization:
-Receptor inactivation: A desensitized receptor results in an uncoupling from signaling cascade.
-Receptor internalization: An agonist is bound to the receptor and the receptor is internalized via an endosome.
-Receptor down regulation: The receptor and receptor protein are taken up by a lysosome and broken down.
