Cell signalling Flashcards
The plasma membrane is composed of ___ and ___ that are held together by _____ ____ interactions
The plasma membrane is composed of PHOSPHOLIPIDS and PROTEINS that are held together by NON-COVALENT HYDROPHOBIC interactions
3 main characteristics of the plasma membrane
It is FLUID, DYNAMIC, and ASYMMETRICAL
3 types of lipids in cell membrane
phospholipid
cholesterol
glycolipid
What are used to lower LDL cholesterol and how?
STATINS are used to lower LDL cholesterol by INHIBITING the enzyme HGM-CoA reductase, which plays a role in the production of cholesterol in the liver
What does CRAC stand for?
“Cholesterol Recognition Amino acid Consesus” sequence, present in some membrane proteins
The first shell of lipid molecules, in direct contact with the membrane protein is termed the __ __
lipid annulus
Predominant anion within the cell?
Cl-
Percentage of genes in a typical genome which encode for membrane proteins
membrane proteins are encoded by more than 20% of the genes in typical genomes
2 types of membrane proteins
- transport and channel proteins (eg. ATPases)
2. receptors (eg. GPCRs)
2 types of cellular transport and their definitions
- Intercellular: transport BETWEEN CELLS and across membrane
- Intracellular: WITHIN THE CELL across different compartments
3 general classes of transport systems across membranes
- uniport
- symport
- antiport
note: symport and antiport are both forms of cotransport)
channel proteins allow for what type of transport?
passive transport
main difference between channel and carrier proteins?
carrier proteins bind to what is being transported, while channel proteins allow for diffusion
Major differences between ion channels and ion transporters:
- rate of flux through CHANNELS can be much greater than turnover number for a TRANSPORTER
- Ion channels are NOT SATURABLE
- Ion channels are GATED (open/closed in response to cellular events)
Ions pass through gated ion channels only when what?
only when the channels are in OPEN CONFIGURATION
2 types of ion gated channels
a) ligan gated: activate/inactivate depending on binding of extracellular ligands to the channel
b) voltage gated: opens when the membrane is depolarized
Primary active transport
the energy released by ATP hydrolysis drives solute movement against an electrochemical gradient
Secondary active transport
after a gradient of ion x (eg. Na+) has been established by primary transport, movement of x down its electrochemical gradient provides energy to drive cotransport of a second solute against its electrochemical gradient
Active transport that uses 25% of energy at rest?
Na+ K+ ATPase
what does Na+ K+ ATPase do?
couples the breakdown of ATP to the simultaneous movement of both Na+ and K+ against their electrochemical gradient (2 K+ in, 3 Na+ out)
Active transport of glucose is driven by a ___ ___ that is generated and maintained by the _____
Active transport of glucose is driven by a Na+ GRADIENT that is generated and maintained by the Na+K+ATPase. THis is known as GLUCOSE SYMPORT.
Describe glucose transport in intestinal epithelial cells
glucose is cotransported with Na+ across the plasma membrane into the epithelial cell. It moves through the cell to the basal surface, where it passes into the blood via GluT2, a passive glucose transporter
What is the name of the basal glucose transporter molecule?
GluT2
Na+K+ATPase pumps Na+ outward to maintain the gradient of Na+ that drives:
glucose uptake
What are the main ways in which cells maintain a very low concentration of free Ca++ in the cytosol in the face of high concentrations of Ca++ in the ECF?
a) Ca++ is pumped out of the cytosol to the cell exterior
b) Ca++ is pumped into the intracellular, membrane enclosed organelles (eg. mito)
Largest group of membrane receptors
GPCRs
Molecules secreted by exocytosis may:
- adhere to the cell surface or incorporate into the extracellular surface
- diffuse into the blood or body fluids as intercellular signal molecules (eg. extracellular vesicles, microvesicles, and exosomes)
- be digestive enzymes
pathway of a secreted protein
- protein synthesis on ribosomes on RER
- Move from RER to Golgi by transport vesicles
- in golgi, undergo protein modification, get sorted, concentrated and packed into secretory vesicles
- secretory vesicles travel from Golgi and fuse with plasma membrane
Exocytosis takes place by fusion of ___ ___ and ___ ___
secretory vesicles and plasma membrane
3 types of extracelular vesicles:
- exosomes
- microvesicles
- appoptotic bodies
What types of extracellular vesicles allow human cells to communicate with eachother?
exosomes
The contents carried by the exosomes are derived from its ___ cell
parental
endocytosis is divided into two types:
- pinocytosis - ingestion of fluid or solutes via VESICLES
2. phagocytosis - ingestion of large particles via VACUOLES
t/f: endocytosis involves the fusion of two cytoplasmic faces
false. It involves the fusion of two non-cytoplasmic faces
Endocytotic vesicles fuse with lysosomes to form ___ ___
secondary lysosomes
formation of the receptor-coated pit
- proteins bind to receptors in invaginations of the membrane called COATED PITS
- Coated pits concentrate receptors mediated for endocytosis in preferences to other receptors
- Pits are coated on their cytosolic side with clathrin
- adaptors link the membrane proteins with the clathrin that forms the outer layer of the coat
- together with accesory molecules, the growing coated pit invaginates. Eventually, the membrane neck is severed to form a closed endocytic vesicle
Clathrin recruitment depends on __ __
particle size
two types of hormones
- steroid (traverse cell membranes)
- polypeptide (act through cell surface receptors)
A ligand does not enter a cell, but generates ___ ___ that regulate physiological functions
second messengers
Define ligand
A molecule that binds to a receptor (eg. adrenaline, sucrose)
Define agonist
a ligand that binds to a receptor and alters the receptor-state resulting in a biological response. Conventionally increase receptor activity
Inverse agonist
a ligand that binds to a receptor and reduces its activity
Antagonist
a ligan that inhibits receptor activation by another ligand, generally an agonist
2 types of G proteins
- large heterotrimeric G-proteins - consist of 3 subunits (Ga, Gb, Gy)
- small G proteins - monomeric
G-proteins alternate between:
inactive guanosine diphosphate (GDP) and active guanosine triphosphate (GTP) bound state
cAMP, IP3 and Ca++ are examples of
second messengers
cAMP signal transduction system
- adrenaline binds to b-adrenergic receptor
- Gs-protein activates adenylate cyclase, which increases cAMP
- cAMP activates protein kinase
What is the first step in taste desensitization?
phosphorylation
Secretory ameloblasts produce many proteins in enamel, including:
amelogenin (AMEL), ameloblastin (AMBN), enamelin (ENAM)
What plays a critical role in regulating the growth of initiall enamel crystals?
phosphorylation of a single serine residue (Ser-16) in AMEL (amelogenin)
