L32 - Metabolism 2 Flashcards
What are proteins used for?
cell signaling receptors, signaling molecules, enzymes & intracellular trafficking components, extracellular matrix scaffolds, ion pumps, ion channels, oxygen and CO2 transporters (hemoglobin) + growth and repair
What are amino acids?
the building blocks of protein
What are proteins broken down to?
amino acids that can be used as metabolic substrates, less important than carbohydrate and fat
What are essential AAs?
cannot be made by the body, must come from food
leucine, isoleucine, valine, phenylalanine, threonine, methionine, lysine, tryptophan, histidine, arginine
What are non-essential AAs?
alanine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, tyrosine
Each amino acid has its own specific…
metabolism
How are proteins broken down and how are their components transported?
enzymes in the stomach / SI break down proteins into AAs, which are released into the bloodstream -> AA transporters are membrane-bound proteins that mediate transfer of AAs into and out of cells or cellular organelles
How are amino acids concentrated in the cell?
active transport mechanisms are used
What are the diverse range of functional roles carried out by AATs?
neurotransmission, acid-base balance, intracellular energy metabolism, and anabolic and catabolic reactions
What are amino acids mostly used for?
protein anabolism (i.e. new protein production) and a source of energy, especially in times of starvation
Why are amino acids useful in times of starvation?
because the processing of AAs results in the creation of metabolic intermediates, including pyruvate, acetyl CoA, oxaloacetate and α-ketoglutarate, amino acids can serve as a source of energy production through the TCA cycle
Is amino acid contribution to ATP synthesis generally high or low?
low (except starvation)
How are amino acids used to produce glucose?
pyruvate is transaminated with ammonia, derived from muscle protein catabolism, to produce alanine -> alanine is released from muscle and taken up by liver to produce glucose -> toxic ammonia is converted to urea in the liver
What are hormones?
generally proteins secreted by cells into the blood for transport to a distant target, secreted by most tissues, exert their functions at very low concentrations, degraded rapidly in blood so that their effects are of limited duration
How do hormones work?
bind to receptors on the surface of target cells
generally activate second messenger signalling pathways (i.e. signal transduction), which can induce a cellular response (e.g. activate enzymes)
What is the exocrine function of the pancreas?
functions as an exocrine gland secreting pancreatic juice into the duodenum (digestion, 99% of pancreas)
What is the endocrine function of the pancreas?
within pancreatic islets (1% of pancreas, endocrine function):
β-cells (secrete insulin)
⍺-cells (secrete glucagon)
What is insulin secretion increased by?
high blood glucose levels, amino acids, incretin hormones, feeding-induced parasympathetic neural activity to the pancreas
Does the digestion and absorption of food containing both carbohydrates and proteins provide strong stimulation for insulin release?
yes
What are incretin hormones?
include GIP and GLP-1, which are released by enteroendocrine cells of the SI in response to the presence of glucose in the GI tract
What is an important feature of insulin signalling?
translocation of GLUT4 from the cytosol to the plasma membrane which allows for an increase in glucose uptake
What is glucagon secretion increased by?
low blood glucose levels + increased activity of the sympathetic division of the autonomic nervous system, as occurs during exercise or prolonged fasting
What does glucagon activate?
Gs receptors, which stimulate AC to produce cAMP that activates PKA
What is the role of PKA?
phosphorylates enzymes that control metabolism, leading to their activation (e.g. glycogen phosphorylase) or promote gluconeogenesis (via CREB)
