Fatty Acids and Amino Acids Flashcards
AA catabolism fate
after proteins –> AA, treated same way dependent on organisms energy needs, they are either
- recycled into new proteins
- oxidised for energy, via removal of AA group or entry into central metabolism
fates of nitrogen in organisms
Humans and great apes excrete both urea (from amino acids) and uric acid (from purines).
Plants conserve almost all the nitrogen.
Many aquatic vertebrates release ammonia to their environment via passive diffusion or active transport
Many terrestrial vertebrates and sharks excrete nitrogen in the form of urea - less toxic and more soluble
Some animals such as birds and reptiles excrete nitrogen as uric acid - insoluble
removal of AA from ammonia
release of free ammonia is toxic, ammonia is captured by a series of transamination reactions
transamination allow transfer of amine to a common metabolite and generate a transportable AA
catalysed by AA-transferases, uses the pyridoxal phosphate cofactor,
α-ketoglutarate accepts amino groups.
o Transfer of one amine toα-ketoglutarate results in synthesis of glutamate (e.g., transamination).
oTransfer of a second amine results in synthesis of glutamine (e.g., glutamine synthetase).
L-Glutamine acts as a temporary storage of nitrogen - can donate the amino group when needed for amino acid biosynthesis.
glutamate safely transported in blood as glutamine
Ammonia Collected in Glutamate Is Removed by Glutamate Dehydrogenase - xxidative deamination occurs within mitochondrial matrix, can use either NAD+ or NADP+ as electron acceptor. Ammonia is processed into urea for excretion, pathway for ammonia excretion; transdeamination = transamination + oxidative deamination
glucose-alanine cycle
Vigorously working muscles operate nearly anaerobically and rely on glycolysis for energy. Glycolysis yields pyruvate.
If not eliminated, lactic acid will build up (in anaerobic conditions) This pyruvate can also be converted to alanine for transport into the liver.
excess glutamate metabolism
Excess glutamate is metabolized in the mitochondria of hepatocytes - glutamate transported via different processes into mitochondrial matrix, ammonia removed to have alpha-keto-glutamate, ammonia converted into carbamoyl phosphate, and this is the 1st step/reaction/substrate for the urea cycle
urea cycle summary
NH4+ from excess glutamate is converted to carbamoyl phosphate. majority of reactions within the urea cycle occur within the cytosol.
citrullene eventually forms arginine and hydrolysed to urea
urea cycle regulation
carbamoyl phosphate synthase I is activated by N-acetylglutamate which is activated by Arginine (acts as allosteric regulator, converts glutamate into carbamoyl phsophate)
Expression of urea cycle enzymes increases when needed.
o high-protein diet
o starvation, when protein is being broken down for energy
end products of AA degradation
Intermediates of the central metabolic pathway
Some amino acids result in more than one intermediate
Ketogenic AA can be converted to acetyl-CoA –> ketone bodies
glucogenic AA can be converted to glucose
AA classification is essential vs nonessential, or ketogenic vs glucogenic
genetic defects in steps of Phe degradation lead to disease
each AA degradation leads to a disease
relationship between enzyme dis-function and disease.
Inborn errors of metabolism
AA synthesis overview
Source of N is Glu or Gln
Derive from intermediates of:
o glycolysis
o citric acid cycle
o pentose phosphate pathway
Bacteria can synthesize all 20.
Mammals require some in diet (essential aa)
AA precursors (7)
CAC: α-ketoglutarate, oxaloacetate
Glycolysis
o pyruvate, 3-phosphoglycerate, phosphoenolpyruvate
Pentose phosphate pathway
o ribose 5-phosphate, erythrose 4-phosphate
synthetic pathway for each amino acid is quite unique
lipids general
organic molecules characterised by low solubility in water and hydrophobic
main: glycerol/triaglycerol, sphingolipids
lipids function
storage of energy: reduced compounds, hydrophobic nature (good packing)
insulation from environment: low thermal conductivity, high heat capacity (absorb heat), mechanical projection (absorb shocks)
water repellant - due to hydrophobic nature, keeping surface of organism dry
buoyancy control - increased density
membrane structure - main structure of cell membranes
cofactors for enzymes - vitamin K (blood clot formation), coenzyme Q (ATP synth in mitochondria)
signalling molecules - paracrine hormones, steroid hormones, growth factors, vitamins A & D
antioxidants - vitamin E
classification of lipids
two major categories based on the structure and function
- Lipids that contain fatty acids (complex lipids)
- can be further separated into: storage lipids (Eg triacylgylycerol) and membrane lipids - Lipids that do not contain fatty acids: cholesterol, vitamins, pigments, etc.
- Main bond for fatty acids, triacylglycerols: ester linkage
- Triacylglycerol: back bone is glycerol
- Other backbone: sphingosine
fatty acids structure
carboxylic acids with hydrocarbon chains with carbons
- saturated: no double bonds between C in chains
- monounsaturated: 1 double bond between C in alkyl chain
- polyunsaturated: 1+ double bond between C in alkyl chain
The cis double bond restricts rotation and introduces a rigid bend in the hydrocarbon tail. All other bonds in the chain are free to rotate.
