Biochemistry Flashcards
definition of glycogenesis
synthesis of glycogen from glucose
definition of glycogenolysis
breakdown of glycogen to form glucose
definition of gluconeogenesis
de novo synthesis of glucose from metabolic precursors
what is liver glycogen
broken down between meals and released to maintain blood glucose levels for red blood cells and brain
what is muscle glycogen
provides energy via glycolysis and the TCA during bursts of physical activity. not availale for maintenance of blood glucose levels
what is the primary source of glucose overnight when hepatic glycogen is depleted?
gluconeogenesis
what does UDPG stand for?
uridine diphosphate glucose
what enzyme synthesises glycogen from UDP-glucose
glycogen synthase
can glycogen synthase start new molecules of glycogen?
no, it can only extend the chains of glycogen and cannot introduce new branches
what enzyme catalyses glycogenolysis?
glycogen phosphorylase
what happens in the liver during glycogenolysis?
glucose-6-phosphate can be de-phosphorylated and the resulting glucose is released into the blood stream
what happens in (skeletal) muscle during glycogenolysis?
glucose-6-phosphate cannot be de-phosphorylated but instead is used to provide energy via glycolysis and the TCA cycle
what are the precursors of gluconeogenesis?
- lactate
- amino acids
- glycerol
what is the cori cycle?
lactate (as a precursor of gluconeogenesis) produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which is then released into bloodstream
what are lipids?
a collection of different compounds, predominantly hydrocarbons that contain long fatty acids and are insoluble in water
examples of simple lipids
fatty acids, triglycerides, waxes
examples of compound lipids
phospho-, glyco-lipids, lipoprotein
examples of steroids
cholesterol, steroid hormones
what are triglycerides
= triacylglycerols
main storage form in adupose tissue
hydrophobic
consist of glycerol and 3 fatty acids
what is the structure of fatty acids?
straight chains, aliphatic, usually contain an even number of C atoms
can be saturated, unsaturated or polyunsaturated
double bonds are usually in cis formation
how long are fatty acids that are liquid at room temperature?
up to 8 carbon atoms
are plant fats liquid or solid?
liquid
they contain large proportions of unsaturated fatty acids
are animal fats liquid or solid?
solid
they contain mainly palmitic and stearic acid
what are the main products of fat digestion?
- glycerol
- fatty acids
monoglycerides
how is fat absorbed?
- short and medium length fatty acids enter portal blood
- long chain FAs and monoglycerides are re-synthesized to triglycerides
- coated with a layer of chylomicrons
what are chylomicrons?
a layer of protein, phospholipid and cholesterol
what is the function of Chylomicrons?
transport lipids absorbed from the intestine to adipose, cardiac, and skeletal muscle tissue, where their triglyceride components are hydrolyzed by the activity of the lipoprotein lipase, allowing the released free fatty acids to be absorbed by the tissues.
what is lipidolysis?
breakdown of lipids
what initially cleaves fatty acids and glycerol during lipidolysis when energy is needed
hormone sensitive lipases
where does fatty acid conversion to CoA derivatives initially occur?
the cytoplasm
where does further oxidation of fatty acids occur?
mitochondrial matrix
how do fatty acids get from the cytoplasm to the mitochondria?
the carnitine shuttle
- acyl-carnitine transporter facilitates antiport of acyl-carnitine to the mitochondrion and carnitine out
where does beta oxidation take place?
mitochondria
how many times is beta oxidation repeated?
8 times
what is the net yield of beta oxidation?
120 ATP
what reactions occur in the breakdown of glycerol?
activated to glycerol-3-phosphate by glycerol kinase
then
dehydrogenated to dihydroxyacetone
how and where are ketone bodies formed?
formed in liver mitochondria from acetyl-CoA from beta oxidation
what happens to ketones in starvation or diabetes?
high levels in blood, accumulation leads to severe acidosis
