Chapter 5 Flashcards
Ligand
Molecules that bind to proteins reversibly
Chemical messengers 3 Main Categories:
- Paracrines
- Neurotransmitters
- Hormones
Paracrines
Chemicals that communicate with neighboring cells
(Simple diffusion)
- Growth Factors
- Clotting Factors
- Cytokines
Cytokines
Peptides from immune cells, fight infection
Histamine
Paracrine messenger, secreted by mast cells and causes inflammation
Neurotransmitters
Chemicals released through axon terminals between neurons
Presynaptic Neuron
Cell that releases neurotransmitter
Post synaptic cell
Target cell
Hormones
Messengers from endocrine glands, diffuse into blood
Neurohormones
Secreted by neurons called neurosecretory cells, diffuses into blood
(Vasopressin) regulate urine
Lipophilic (hydrophobic)
Lipid soluble, Cross plasma membrane can’t dissolve in plasma
Lipophobic (Hydrophilic)
Dissolve in plasma, but do not cross plasma membrane
Chemical messengers 5 major classes:
- Amino Acids
- Amines
- Peptides/Proteins
- Steroids
- Eicosanoids
Amino Acid messengers
- Glutamate
- Aspartae
- Glycine
- Gamma-aminobutyric acid
Lipophobic, dissolve in water but do not cross plasma membranes
Amine Messengers
From Amino Acids with group (-NH2) and Cateholamines
Catecholamines (catechol group)
Six carbon ring, hydrophilic
- Dopamine
- Nonepinephrine
- Epinephrine
Peptide protein Messengers
Amino acids linked by peptide bonds
Peptide
Less than 50 amino acids
Protein
Longer chains of amino acids
Steroid Messengers
From cholesterol with 4 ring structure, hydrophobic
Eicosanoid Messengers
Paracrines produced by almost every cell in the body, from arachidonic acid. Cross plasma membrane (hydrophobic)
- Prostaglandins- constrict blood vessels cramps
- leukotrienes-Airway contraction
- thromboxanes- platelets
Arachidonic avid
20 Carbon fatty acid
Glutamate and Aspartate synthesis
1) Glucose catabolized to pyruvic acid by glycolysis
2) Pyruvic acid is in turn converted to acetyl CoA, enter Kreb cycle
3) Amine groups added to keen cycle to form glutamate or aspartame
Catecholamines (2)
Tyrosine beta hydroxylase
Dopa decarboxylase
Dopamine beta hydroxylase (dopamine to nonepinephrine)
PNMT (nonepinephrine to epinephrine)
Serotonin
1) tryptophan 5 hydroxylase
2) aromatic L amino acid decarboxylase
Histamine
Histidine decarboxylase
Half life
The amount of time it takes for half of the hormone in the blood to be degraded
Proteins in carriers are protected and have longer half lives (hours)
Affinity
Strength of binding between messenger and its receptor
Magnitude of target cell’s response to Messenger factors (3):
1) messengers concentration
2) number or receptors
3) affinity of the receptor for messenger
Up regulation
When cells have low messengers for long time, increase in number of receptors
Down regulation
When high messenger conc are higher than normal for long time, causing fewer receptors to decrease responsiveness
Receptor Agonist
Ligands that bind to receptors and produce response
morphine- treat pain cause euphoria band addiction
Receptor antagonists
Ligands that bind to receptors that do not produce an response
(naloxone- binds to morphine receptors blocks them, reversing effects) 10x affinity
Dimerization
For steroid hormone to activate a gene, two complexes bind to HRE
Lipophobic messenger receptors categories (3):
- Channel linked receptors
- Enzyme linked receptors
- G protein linked receptors
Channel linked receptors
Ligand gated channel, ligand is messenger
1) fast channels- receptors and ion channels
2) slow channels
Second messenger
Intracellular messenger produced by the binding of an extra cellular messenger to a receptor
G protein linked receptors
Links G protein receptors and other proteins in plasma membrane called effectors
Effectors- ion channels and enzymes
G proteins function
Bind guanosine nucleotides
- alpha 20
- beta 5
- gamma 13
G protein classifications (3):
1) Affect ion channels
2) stimulatory G proteins
3) inhibitory G proteins
2 and 3 activate and inhibit amplifier enzymes
Amplifier enzymes
Enzymes that catalyze the production of second messengers in intracellular fluid
Slow ligand gated ion channels
Regulated by G proteins, causes channels to open or close in response to binding of alpha subunit
Differences:
Can be open or closed
Slow to open or close (minutes instead of milliseconds)
5 major second messengers
1) cAMP
2) cGMP
3) inositol triphosphate
4) diacyglycerol
5) calcium
Phosphatidylinositol second messenger system
Enzyme catalyzed reaction that yield diacyglycerol (DAG) and inositol triphosphate (IP3); calcium
Signal amplification
Cascades cause this by a series of sequential steps for the phosphorylation of proteins
