Biochem 2 Studyguide #3
1. Why are triglycerides a better energy storage molecule than glucose? • Their carbons have lower oxidation states, and they are nonpolar molecules so they are stored in an anhydrous form whereas glucose is stored in a hydrated form. This means that you get more energy for a given weight.
2. What is Beta-oxidation?
• The process of breaking down a fatty acid to acetyl CoA
3. What are bile salts, and what is their main function?
• amphipathic cholesterol derivatives made in the liver that act like detergents to break apart big globs of fat in the small intestine into smaller micelles.
• They increase the lipid-water interface so that digestion can be rapid. 4. What are the two types of lipases, and where are they found? • Pancreatic lipase: found in small intestine
• Lipoprotein lipase: found in blood of muscle and adipose capillaries. 5. What is interfacial activation? We also discuss several other topics like What pertains to numbers that are based on per 1,000 people?
• The phenomenon that when pancreatic lipase encounters the lipid-water interface, its activity greatly increases.
6. What is the role of intestinal fatty acid-binding protein?
• Protect cells from the detergent like properties of fatty acids, and increase fatty acid solubility.
7. List the steps of lipid transport after they have been absorbed by intestinal mucosa.
• Packaged into chylomicrons, released into intestinal lymph, move through lymphatic vessels and into large veins, delivered to capillaries of skeletal muscle or adipose tissue.
8. Cholesterol delivered to liver by chylomicrons is incorporated into which lipoprotein?
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Where are fatty acids activated, and what enzymes do this?
• For mitochondrial oxidation: happens on outer mito membrane, and is done by acyl-CoA synthetases (thiokinases)
• For peroxisomal: also done by acyl-CoA synthetases
What determines the rate for fatty acid oxidation?
• Transport of fatty acid chains across the inner mitochondrial membrane. What is the first committed step of fatty acid synthesis?
• Stage 2; carboxylation of acetyl-CoA
What is the enzyme in this step and how is it regulated?
• Acetyl-CoA carboxylase.
• Allosterically stimulated by citrate, and inhibited by long chain fatty acyl Coa’s We also discuss several other topics like Which cultures support independent sleeping for babies?
• inactivated when phosphorylated by AMPK, which is activated by ADP and inactivated by ATP.
• Hormonal control: Insulin removes phosphate (activiating synthesis); glucagon and epinephrine promote phosphorylation.
Which two enzymes use NADPH in fatty acid synthesis?
• Beta-ketoacyl-ACP reductase and enoyl-ACP reductase
What is the major product of the fatty acid synthesis pathway, and what are the total reactants needed? We also discuss several other topics like On which ground was al capone arrested then?
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• Palmitic acid
• 8 acetyl-Coa, 14 NADPH, and 7 ATP
Where does beta-oxidation and FA synthesis occur?
• beta-oxidation: mitochondria
• FA synthesis: cytosol
What is an example of a fatty acid that we cannot produce?
• Linoleic acid (omega-6)
What enzyme uses coenzyme B12, and what is special about this coenzyme? • Methylmalonyl CoA mutase
• It contains a rare carbon-metal bond
Does the carbon in the CO2 produced during FA synthesis come from acetyl-Coa or malonyl-Coa?
What is the acyl carrier in beta-oxidation and FA biosynthesis?
• Beta-oxidation: CoA
• FA biosynthesis: ACP
At what carbons of a FA chain can we not introduce double bonds? • C12 and C15
At the beginning of triglyceride synthesis, what organelles use G3P and/or DHAP to form the glycerol backbone?
• Mito. Uses G3P Don't forget about the age old question of Which city in italy is the largest?
• Peroxisome uses DHAP
• ER can use both.
What is formed when G3P is acylated once? And then a second time? • 1st lysophosphatidate, 2nd forms phosphatidate (a diacylglyceride) What type of glycerophospholipids contains a vinyl ether linkage instead of an ester linkage? Where is this glycerophospholipid synthesized?
• Plasmolagens; made in peroxisomes
What are the precursors for ceramide?
• Palmitoyl-Coa and serine
What are the head groups for cerebrosides/gangliosodes?
• Cerebrosides: 1 sugar (monosaccharide)
• Gangliosides: many sugars (oligosaccharide) + sialic acid
What is cholesterol a precursor for, and what is its structure?
• Steroid hormones (most important) and bile salts.
• 4 fused rings; 3 six member rings and 1 five member ring
Where do the carbons in cholesterol come from?
• Acetate, which comes from acetyl-CoA
What is the first committed step of cholesterol biosynthesis?
• Reduction of HMG-CoA to mevalonate.
• This step requires 2 NADPH, and occurs on membrane of smooth ER in liver What is a key building block of cholesterol synthesis?
• Isopentenyl pyrophosphate
What other molecules are made from this?
• Vit K
• Coenzyme Q
How is cholesterol synthesis regulated?
• By regulating HMG-CoA reductase
• Short term: phosphorylation, which is controlled by cAMP dependent kinase. Glucagon inhibits and insulin activates. Active when dephosphorylated. • Long term (primary control): the concentration of cholesterol controls the rate of enzyme synthesis and degradation. Enzyme synthesis is inhibited by derivatives of mevalonate and dietary cholesterol.
How is cholesterol storage regulated?
• ACAT esterifies cholesterol so it can be stored.
• Activated by high levels of cholesterol.
What stimulates the release of hydrochloric acid and pepsinogen? • Gastrin
When is the hormone secretin released, and what does it do?
• When acidic contents enter the small intestine; it causes pancreas to release bicarbonate to bring pH back to 7.
Why do we degrade internal proteins?
• Use carbon skeletons as energy during starvation
• Get rid of abnormal proteins
• Allow regulation of metabolism.
Why is it important that lysosomal enzymes have acidic pH optima? • Since these dangerous/highly active enzymes are inactive in cytosolic pH, the cell is not harmed if the lysosome leaks.
What sequence do most proteins have that are degraded in lysosomes? • Lys-Phe-Glu-Arg-Gln (KFERQ)
What types of proteins are degraded through ubiquitination (cytosolic degredation) and how are they marked?
• Defective proteins, and proteins with short half lives
• They are marked for degradation by covalently linking them to several ubiquitins via an isopeptide bond.
What types of proteins are degraded by lysozymes?
• membrane proteins, extracellular proteins, and proteins with long half-lives. What determines the half life of proteins?
• The N-terminal residue.
• Short half lives: asp, arg, leu, lys, and phe
• Long half lives: ala, gly, met, ser, and val
What is a PEST sequence?
• A 12-60 residue section of a protein that has a lot of Pro (P), Glu (E), Ser (S), and Thr (T).
• Proteins with this are degraded rapidly.
What amino acids (AAs) are susceptible to being oxidized?
• Lysine, arginine, and proline
What is the first step in AA degradation?
What are the two mechanisms for deamination?
• Transamination, and oxidative deamination
What is the main amino group acceptor in transamination?
Where does oxidative deamination occur?
• Liver mitochondria.
Does Glutamate dehydrogenase use NAD or NADP?
Where does the urea cycle take place?
• The mitochondria and cytosol of the liver
What types of animals get rid of ammonia by converting it to uric acid? • Birds and reptiles
Where do the first and second nitrogen atoms of urea come from? • 1st comes from NH4+ 2nd comes from aspartate in reaction 3. What do the BUN levels tell you?
• If BUN levels are high then you have a kidney problem, if they are low you have a liver problem.
How is urea cycle regulated?
• CPS I: allosterically activated by N-acetylglutamate, which is made from glutamate and acetyl-Coa.
• During starvation or muscle breakdown a lot of glutamate is made, which increases amounts of N-acetylglutamate
• Other enzymes are controlled by substrate availability.
• Long-term regulation is rate of enzyme synthesis and breakdown What are glucogenic AAs converted to?
• Pyruvate, alpha ketoglutarate, succinyl-Coa, fumarate, or OAA
What are ketogenic AAs broken down to?
• Acetyl-Coa or acetoacetate
What are the purely ketogenic AAs?
• Lysine and leucine
Which AAs make up the pyruvate family, and which one is both keto and glucogenic? • alanine, cysteine, glycine, threonine, and serine
• Threonine is both.
What enzyme acts as a chemotheroputic agent, in addition to aiding in AA breakdown?
Which carbon carrier is more versatile, and what does it derive from? - THF, and comes from folic acid.
What are the branched-chain AAs and where are they broken down? - isoleucine, leucine, and valine.
- They are broken down in muscle, adipose, kidney, and brain instead of liver.
Are they keto or glucogenic?
- isoleucine and valine are glucogenic
- leucine is both.
What is the regulatory step of brached-chain AA breakdown?
- step two: oxidative decarboxylation via BCKDH
What are the products of lysine degradation?
- acetoacetate and HMG-Coa
The breakdown of which AA involves the Kynurenine pathway? - tryptophan.
What are the products of tyrosine and phenylalanine breakdown? - fumarate and acetoacetate
What are the four common precursors of all nonessential AAs, except for tyrosine? - pyruvate, OAA, alpha-ketoglutarate, and G3P
What is the nitrogen donor for synthesis of asparagine?
How is glutamine synthesis regulated?
- high levels of alpha-ketoglutarate activate, so ammonia levels don’t get too high.