Biochemistry Unit 4 Exam
72 flashcards · Other · by John Mark Webb
What are the fats in foods?
triacyl glycerols
What are some sources of fatty acids?
fats consumed in the diet fats from cells (triacylglycerides) fats synthesized in one organ for transport to another
What is a triacylglyceride?
the major form of dietary lipid in fats and oils, whether derived from plants or animals composed of three fatty acids esterified to a glycerol molecule
What is a fatty acid?
a carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group
What is a glycerol?
three carbon chain with alcohols attached to it
How do fats get from our mouth to our cells?
bile salts are amphipathic compounds that act as biological detergents they convert dietary fats into mixed micelles of bile salts and triacyglycerols
What happens to the glycerol backbone? DETAILED.
glycerol is converted to glyceraldehyde 3-phosphate so it can enter glycolysis it only makes about 5% of energy from triglycerides glycerol kinase glycerol 3-phosphate dehydrogenase triose phosphate isomerase step 2 makes dihydroxyacetone phosphate step 3 makes glyceraldehyde 3-phosphate
Describe the metabolism of fatty acids in detail. Include: Fatty Acyl-CoA formation, beta-oxidation, carnitine shuttle
First, a fatty acid is converted to a fatty acyl-CoA in a two step process. This conversion is catalyzed by fatty acyl-CoA synthetase and inorganic pyrophosphatase. Second, the fatty acid enters the mitochondria via the carnitine shuttle. After fatty acyl–carnitine is formed at the outer membrane or in the intermembrane space, it moves into the matrix by facilitated diffusion through the transporter in the inner membrane. In the matrix, the acyl group is transferred to mitochondrial coenzyme A,…
How many ATP does the metabolism of fatty acids produce?
# of bonds * 4 ATP = ATP from beta-oxidation # of bonds + 1 = # of acetyl-CoA * 10 ATP = ATP from Krebs cycle In beta-oxidation, every bond makes 1 FADH2 and 1 NADH. ONE round of Krebs cycle produces: 3 NADH 1 FADH2 1 GTP (ATP) In even-numbered fatty acids: # of bonds + 1 = # of acetyl-CoA FADH2 = 1.5 ATP NADH = 2.5 ATP
Explain the beta-oxidation of a monounsaturated fatty acid.
there is one double-bond already so there is 1 less FADH2 produced which means there is -1.5 ATP total an isomerase is used to make a cis bond trans makes normal amount of acetyl-CoA monounsaturated fats require an isomerase to enter step 2 of beta-oxidation
Explain the beta-oxidation of a polyunsaturated fatty acid.
polyunsaturated fats require an isomerase AND a reductase to enter step 2 of beta-oxidation the reductase uses NADPH
Explain the beta-oxidation of an odd-numbered fatty acid.
the last 3-carbon piece is glucogenic requires three more steps at the end of beta-oxidation: carboxylation epimerization mutation into succinyl-CoA this enters Krebs cycle
Explain the beta-oxidation of a short fatty acid.
it may undergo omega-oxidation in the endoplasmic reticulum of liver and kidney cells produces dicarboxylic fatty acyl intermediates, which can undergo beta-oxidation
Explain the beta-oxidation of a fatty acid that is methylated at the beta-carbon.
if a fatty acid is methylated at the beta-carbon, beta-oxidation cannot occur alpha-oxidation must occur in peroxisomes alpha-oxidation produces propionyl-CoA the final product is NOT acetyl-CoA
How is fatty acid oxidation regulated?
two main hormones: insulin and glucagon increased [insulin] = disabled carnitine acyl-tranferase I increased [glucagon] = enabled carnitine acyl-tranferase I the disabling of carnitine acyl-tranferase I occurs if there is production of malonyl-CoA, which happens when [insulin] is high [insulin] increases when there is high blood glucose [glucagon] increases when there is low blood glucose
What is a ketone body?
water-soluble molecules that contain the ketone groups produced from fatty acids by the liver mitochondria in hepatic cells (fatty acyl CoA is converted into ketone bodies) three main ketone bodies: acetone (exhaled by the lungs) acetoacetate beta-hydroxybutyrate
How are ketone bodies formed?
there are 5 enzymes involved in the formation of ketone bodies: thiolase HMG-CoA synthase HMG-CoA lyase acetoacetate decarboxylase beta-hydroxybutyrate dehyrdrogenase sequential 1, 2, 3 produce acetoacetate 4 produces acetone 5 produces beta-hydroxybutyrate while using an NADH
Under what conditions are ketone bodies formed?
ketone body synthesis occurs normally under all conditions increased ketone body synthesis occurs when: under starvation low levels of insulin (type 1 diabetes) high rate of gluconeogenesis (depletion of oxaloacetate = increase in acetyl-CoA) in general, ketone bodies are synthesized only during conditions of high circulating free fatty acids
Why are ketone bodies necessary?
glucose is the sole energy source for the brain free fatty acids cannot cross the blood-brain barrier so the brain cannot use them for energy ketone bodies can be used for energy by the brain when glucose levels are lower than normal
Describe how amino acids get from our mouths to our cells.
gastric glands of the stomach lining have parietal cells that secrete HCl gastric glands of the stomach lining have chief cells that secrete pepsinogen gastric glands of the stomach lining have gastric mucosa that secretes gastrin as the acidic stomach contents pass into the small intestine, the low pH triggers secretion of the hormone secretin (from duodenum) into the blood, stimulating the pancreas to secrete bicarbonate to abruptly increase the pH to about 7 exocrine cells of pancreas (mostl…
What are the goals of amino acid oxidation?
to separate alpha-amino groups from the carbon skeleton and then... transport alpha-amino group to the liver to recycle the amine (aa and nucleic acid biosynthesis) and convert to urea (urea cycle) use the carbon skeleton for energy (conversion to CO2) and conversion to glucose (gluconeogenesis)
Under what conditions does amino acid oxidation occur?
during the normal synthesis and degradation of cellular proteins, some amino acids that are released from protein breakdown and are not needed for new protein synthesis undergo oxidative degradation when a diet is rich in protein and the ingested amino acids exceed the body’s needs for protein synthesis, the surplus is catabolized; amino acids cannot be stored during starvation or in uncontrolled diabetes mellitus, when carbohydrates are either unavailable or not properly utilized, cellular pro…
What are the two primary carriers of ammonia to the liver?
alanine (from muscle) glutamine (from muscle and other tissues)
How are the two primary carriers of ammonia produced?
alanine is formed in the skeletal muscle when excess amino groups are transferred to pyruvate glutamine is synthesized by the enzyme glutamine synthetase from glutamate and ammonia
Where are the two primary carriers of ammonia produced?
alanine is produced in skeletal muscle glutamine is produced in most other tissues besides hepatocytes
Describe the urea cycle in detail.
there are FOUR enzymatic steps in the urea cycle ornithine transcarbamoylase - catalyzes carbamoyl phosphate donation of carbamoyl group to ornithine to form citrulline (release of Pi) argininosuccinate synthetase - (requires ATP) catalyzes second amino group from aspartate in a condensation reaction between the amino group of aspartate and the ureido (carbonyl) group of citrulline forms argininosuccinate argininosuccinase - (only reversible step in urea cycle) cleaves argininosuccinate to form…
What is the purpose of the urea cycle?
to convert toxic ammonia to urea for excretion by the kidneys
How is the urea cycle connected to the citric acid cycle?
fumarate produced in the argininosuccinase reaction is also an intermediate of the citric acid cycle cytosolic fumurase converts fumarate to malate, which can then reenter the mitochondria for the Krebs cycle
Which reactions in the urea cycle acquire nitrogen?
both require ATP carbamoyl phosphate synthetase I (occurs in mitochondria) argininosuccinate synthetase (step 2 of urea cycle)
What are benzoate and phenyl butyrate used for medically?
treatment for deficiencies in urea cycle enzymes
Name the essential (from diet) and nonessential amino acids.
ESSENTIAL histidine isoleucine leucine lysine methionine phenylalanine threonine tryptophan valine NONESSENTIAL alanine asparagine aspartate glutamate serine
Which amino acids are conditionally essential?
arginine cysteine glutamine glycine proline tyrosine
Name the ultimate fates (final products) for each of the 20 amino acids.
those that form glutamate (then alpha-ketogluturate): arginine glutamine histidine proline those that form succinyl-CoA: isoleucine methionine threonine valine those that form fumarate: phenylalanine tyrosine those that form oxaloacetate: asparagine aspartate those that form pyruvate: alanine cysteine glycine serine threonine tryptophan those that form acetyl-CoA: isoleucine leucine threonine tryptophan those that form acetoacetyl-CoA: leucine lysine phenylalanine tryptophan tyrosine
Which amino acids are glucogenic? These will form glucose.
only two are not glucogenic: leucine and lysine arginine glutamine histidine proline glutamate isoleucine methionine threonine valine phenylalanine tyrosine asparagine aspartate alanine cysteine glycine serine tryptophan
Which amino acids are ketogenic? These will form ketone bodies.
seven total, two ONLY ketogenic: leucine and lysine leucine lysine phenylalanine tryptophan tyrosine isoleucine threonine
Which amino acids are both glucogenic and ketogenic?
phenylalanine tryptophan tyrosine isoleucine threonine
Name three cofactors commonly used in biochemistry as carbon atom transfer agents.
biotin tetrahydrofolate S-adenosylmethionine
What is PKU? What causes it?
a disease that is caused by a genetic defect in phenylalanine hydroxylase, the first enzyme in the catabolic pathway for phenylalanine that converts it to tyrosine this disease is when there is an elevated level of phenylalanine in the blood
What is the role of oxidative phosphorylation in mammals?
the reduction of O2 to H2O in the mitochondria with electrons donated by NADH and FADH2 so that energy in the form of ATP can be produced
What is the role of oxidative phosphorylation in plants?
photophosphorylation oxidation of H2O to O2 with NADP+ as the electron acceptor while requiring light energy
Where does oxidative phosphorylation occur in mammals? In plants?
mammals = mitochondria (within the inner mitochondrial membrane) plants = chloroplasts
What is the reaction summary for oxidative phosphorylation?
NADH => Q => Cyt b => Cyt c1 => Cyt c => Cyt (a + a3) => O2 NADH + 11H+N + 1/2 O2 => NAD+ + 10H+P + H2O
Compare and contrast the two oxidative phosphorylation systems in mammals and plants. DETAILS.
Photophosphorylation differs from oxidative phosphorylation in requiring the input of energy in the form of light to create a good electron donor and a good electron acceptor
Describe redox chemistry in biological systems.
The term reducing equivalent is used to designate a single electron equivalent transferred in an oxidation-reduction reaction.
Name common biochemical electron transfer reaction types.
direct, which uses iron and copper (Fe3+ + e- => Fe2+) transfer as a H atom (H+ + e-) by the use of FADH2 transfer as a hydride (H-) by the use of NADH
Name the four most commonly occurring electron carriers in biochemistry.
NAD+ (NADH) NADP+ (NADPH) FAD (FADH2) FMN (FMNH2)
Name three other electron carrier types we see in oxidative phosphorylation.
ubiquinone or coenzyme Q cytochromes (iron-heme containing protein) iron-sulfur proteins
Describe complexes I-IV in detail for mammalian oxidative phosphorylation.
ALL are membrane bound in the mitochondria Complex I NADH dehydrogenase proton pump driven by electron transfer catalyzed reaction is vectorial catalyzes two simultaneous reactions: NADH + H+ + Q => NAD+ + QH2 transfer of 4 protons from matrix => inter membrane space Complex II succinate dehydrogenase NOT A PROTON PUMP succinate to fumarate FAD to FADH2 net reaction: succinate => ubiquinone Complex III ubiquinone : cytochrome c oxidoreductase proton pump ubiquinone => cytochrome c utilizes the…
Describe the role of complexes I-IV.
Complexes I and II catalyze electron transfer to ubiquinone from two different electron donors: NADH (Complex I) and succinate (Complex II) Complex III carries electrons from reduced ubiquinone to cytochrome c Complex IV completes the sequence by transferring electrons from cytochrome c to O2
What function do ubiquinone and cytochrome c play in oxidative phosphorylation? What are their counterparts in plant oxidative phosphorylation?
ubiquinone (plastoquinone of plant chloroplasts) can accept one electron to become the semi-quinone radical (•QH) or two electrons to form ubiquinol (QH2) and, like flavoprotein carriers, it can act at the junction between a two-electron donor and a one-electron acceptor cytochrome c of mitochondria is a soluble protein that associates through electrostatic interactions with the outer surface of the inner membrane
What is an F-type ATPase? How does it function? What is its purpose?
F-type ATPase has two distinct components: F1 is a peripheral membrane protein Fo is an integral membrane protein it phosphorylates ADP to make ATP which is possible due to energy derived from a gradient of protons which cross the inner mitochondrial membrane from the intermembrane space into the matrix through the Fo portion of the enzyme
What are the two key NADH shuttles in oxidative phosphorylation? Why are they important?
malate-aspartate shuttle (liver, kidney, heart) glycerol-3-phosphate shuttle (skeletal muscle, brain) NADH equivalents moved in by the malate-aspartate shuttle enter the respiratory chain at Complex I and yield a P/O ratio of 2.5 NADH equivalents moved in by the glycerol 3-phosphate shuttle enter at ubiquinone and give a P/O ratio of 1.5
What can you say about the regulation of oxidative phosphorylation?
it is generally limited by the availability of ADP as a substrate for phosphorylation relative concentrations of ATP and ADP control not only the rates of electron transfer and oxidative phosphorylation but also the rates of the citric acid cycle, pyruvate oxidation, and glycolysis
Can you comment briefly on the "other topics" discussed? (brown fat, oxidative stress, etc.)
brown fat brown because high amount of mitochondria which contains many cytochromes produces heat, not ATP keeps newborns warm provides path for protons to return to matrix to make heat thermogenin, also called uncoupling protein 1 (the product of the UCP1 gene), provides a path for protons to return to the matrix without passing through the FoF1 complex oxidative stress it may serve instead to reduce the frequency with which electrons “leak” out of the system, moving from succinate to molecula…
How does a zymogen become an enzyme?
a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the active site) for it to become an active enzyme
Why is there an elaborate mechanism for getting active digestive enzymes into the GI tract?
synthesis of the enzymes as inactive precursors protects the exocrine cells from destructive proteolytic attack (the breakdown of proteins or peptides into amino acids by the action of enzymes)
What is the purpose of a low pH in the stomach?
it causes an autocatalytic cleavage of pepsinogen, a zymogen, to convert it to pepsin, which only occurs at low pH pepsin hydrolyzes ingested proteins at peptide bonds on the amino-terminal side of the aromatic amino acid residues Phe, Trp, and Tyr as the acidic stomach contents pass into the small intestine, the low pH triggers secretion of the hormone secretin into the blood secretin stimulates the pancreas to secrete bicarbonate into the small intestine to neutralize the gastric HCl, abruptl…
What four amino acids play central roles in nitrogen metabolism?
glutamate glutamine alanine aspartate
How is alanine produced and used?
alanine is formed when an amino group is transferred to a pyruvate in the skeletal muscle it travels in the blood to the liver, carrying the amino group in the liver, alanine is converted back to pyruvate pyruvate is then used in gluconeogenesis (in the liver) to send glucose back to the muscles
Where is the first amino group to enter the urea cycle derived from?
ammonia (in the mitochondrial matrix)
Tryptophan is a precursor to what three molecules?
niacin (precursor of NAD+ and NADP) serotonin (neurotransmitter) indoleacetate (plant growth factor)
What six amino acids are converted to pyruvate?
threonine glycine serine cysteine alanine tryptophan
What is a cofactor?
transfers one carbon in reactions
What seven amino acids are degraded to acetyl-CoA?
tryptophan lysine phenylalanine tyrosine leucine isoleucine threonine
What five amino acids are degraded to alpha-ketogluturate?
arginine histidine proline glutamine glutamate
What four amino acids are degraded to succinyl-CoA?
methionine isoleucine valine threonine
What causes maple syrup urine disease?
a defective branched-chain alpha-keto acid dehydrogenase complex in which the three branched-chain amino acids (valine, isoleucine, leucine) are not degraded in the liver simply put, no oxidative decarboxylation can occur
What two amino acids form oxaloacetate?
asparagine aspartate
What are the steps of triglyceride mobilization by hormones?
hormone binds its receptor in the adipocyte membrane stimulates adenylyl cyclase, via a G protein, to produce cAMP, activating PKA PKA phosphorylates hormone-sensitive lipase (HSL) phosphorylates perilipin molecules on surface of lipid droplet hydrolyzes triglycerides to fatty acids fatty acids leave adipocyte fatty acids enter myocyte fatty acids oxidized to CO2
What four enzymes are necessary for beta-oxidation?
acyl-CoA dehydrogenase enoyl-CoA hydratase beta-hydroxyacyl-CoA dehydrogenase acyl-CoA acetyltransferase (thiolase)
What do the four enzymes in beta-oxidation do?
acyl-CoA dehydrogenase adds a trans double bond between the alpha and beta carbon enoyl-CoA hydratase adds a OH to the beta carbon beta-hydroxyacyl-CoA dehydrogenase oxidizes –OH on beta carbon to =O acyl-CoA acetyltransferase (thiolase) adds CoA-SH between alpha and beta carbon,
How does insulin disable carnitine acyl-transferase I?
it activates phosphatase which dephosphorylates ACC which catalyzes acetyl-CoA to malonyl-CoA which directly inhibits carnitine acyl-transferase I this makes sure that fatty acid synthesis does not occur during fatty acid beta-oxidation