Exam 3: Sample Questions Flashcards
- What role does biotin play in acetyl CoA synthesis?
- Prosthetic group on active site that gives pyruvate carboxylase its functionality
- List 3 arachidonic acid products along with one of their affects
- Prostaglandins
- Effect the transit of RBCs through capillaries
-Decrease the production of gastric acid
- Effect the transit of RBCs through capillaries
- Thromboxane
-Involved in blood clotting - Prostacyclin
-Basodialators
-Decrease platelet aggregation - Leukotrienes
-Involved in allergic reactions
-Promotes inflammation
- What is the source of all carbons found in cholesterol?
acetyl CoAs
- Identify the 5 stages of cholesterol synthesis
- Mevalonate production
-From 3 AcCoAs - Isoprenoids
- Squalene
-From 6 isoprenoids - Cyclize squalene to lanosterol
- Cholesterol is formed
- What stage of cholesterol synthesis explains cholesterol not showing up on the fossil record until the earth became aerobic?
- The cyclization during lanosterol formation
- What regulates the transcription and translation of HMGCoA reductase?
Transcription
-Steroid response element that is associated with DNA enzyme
Translation
-Nonsterol mevalonate metabolites
- What enzyme plays a major role in regulating cholesterol synthesis in the body?
- HMGCoA Reductase
- What is the 3C carrier used in fatty acid synthesis?
- Acyl carrier protein (ACL)
- What role does thioesterase play in determining the fatty acid that a particular cell produces?
- Dictates whether the molecule is palmitate or something else during the cleavage stage of fatty acid synthesis
- Write the overall reaction for the synthesis of palmitate.
8AcCoA + 7ATP + 14NADPH ————–> palmitate + 14NADP+ + 6H2O + 7ADP + 7Pi + 8CoA
- Name the 2 enzymes that metabolize/modify arachidonic acid and one of the molecule types that each of the enzymes can form.
- Cyclooxygenase
- Forms: prostaglandins, prostacyclin, thromboxane
- Lipoxygenase
- Forms: leukotrienes
- Describe all the ways that HMGCoA Reductase can be regulated.
HMG CoA synthase
HMG CoA lyase
Feedback inhibition
-cholesterol inhibits
covalent modification
-phosphorylation inhibits
transcriptionally
-decrease cholesterol -> increase gene transcription
- Briefly describe the role of HDL and LDL in regards to cholesterol transport.
- HDL: transports cholesterol to the liver
- LDL: transports cholesterol to tissues
- Compare and contrast chylomicrons and VLDL.
Both aid in transport triglycerides through the blood
Chylomicrons
- Dietary lipids
- Seen in the GI tract
VLDL
- Endogenous
- Seen in the liver
- What is the role of CETP in HDL?
- Antiport
- Transfers CE (cholesterol ester) from HDL to another lipoprotein
- Transfers triglycerides to HDL
- Allows LCAT to esterify more cholesterol
- Low CETP promotes HDL formation
- Moves CE and triglycerides from VLDL.LDL.HDL
- List the 3 ways that the level of cholesterol in cells is regulated.
- Dietary
- HMGCoA Reductase
- ACAT activity
- Target HMGCoA reductase
- ACAT
- Esterifies cholesterol
- LDL receptors
- Downgrade w/ excess cholesterol
- List 3 steroid products of cholesterol metabolism, excluding calcitriol.
- Aldosterone
- Estradiol
- Progesterone
- Cortisol
- Corticosterone
- Identify the 3 organs that are important to calcitriol synthesis.
- Skin
- Splits 7-dehydrocholesterol w/ light
- Liver
- Hydroxylated a C25
- D-binding protein
- Transports D3 to kidneys
- Kidneys
- Form calcitriol
- Identify the 3 ways that glutamate can be made.
- Glutamate Dehydrogenase
- Glutamate Synthase
- BCAA Transaminase
- Identify 2 conditionally essential amino acids. Why are they conditionally essential?
- Arginine
- Glutamine
- b/c they are only required under certain physiological conditions such as septic shock & burn victims
- Describe the mechanism to replace a carbonyl group with an amino group.
Carbonyl tautomerizes
- React tautomer w/ phosphoryl donor
- Nitrogen atom attacks
- Nucleophilic attack on tetrahedral intermediate
- Removal of phosphate group
enamine formation: N replaces O from carbonyl group
- Identify the precursor molecule that is used in both pyrimidine and purine synthesis.
PRPP
- What nucleotide base is thymine made from? What is the primary difference between the two?
- pyrimidine base
- Made from: methylated uracil
- Difference: thymine has an extra methyl group on its structure
- List the 3 enzymes that are important to purine catabolism.
Nucleotidase
- Converts nucleotides to nucleosides
Nucleotide phosphorylase
- Degrades nucleosides to a free base & R-1-P
Phosphoribomutase
- Converts R-1-P to R-5-P
- How is allopurinol used to treat gout?
- b/c it is a purine analog that inhibits xanthine oxidase therefore reducing the amount of uric acid in the tissues
- List 3 methods of regulating purine synthesis.
- PRPP synthesis
- Inhibition by purine nucleotides
- Allows substrate channeling
- Phosphoribosyl amine synthesis
- Inhibition by purine nucleotides
- Example of cumulative feedback inhibition
- IMP
- GMP inhibits xanthylate formation
- AMP inhibits adenylsosunccinate formation
- Substrate Balancing
- ATP used to make GMP
- GTP used to make AMP
- What enzyme plays a role in regulating cholesterol synthesis in the body?
HMGCoA Reductase
- Provide 2 reaction types or processes involved in making non-essential amino acids.
- Transamination
- α-keto acid + amino group -> amino acid
- carbon transfer
- tetrahydrofolate is used to pull amino group off glycine
- non amino acid amino group transfer
- List the methods to regulate NEAA’s
- How is de novo biosynthesis distinguished by de novo pyrimidine biosynthesis?
De novo
- Metabolic precursors
- Prevalence: ubiquitous
- Made possible by: multi enzyme complex
Pyrimidine biosynthesis uses a multi enzyme complex
- 2 used in eukaryotes
- CPS II, Aspartate, transcarbomoylase, dihydroorotase
- OPR transferase, orotidylate decarboxylase
- What ultimately makes an amino acid essential?
- If α-keto acid is not able to be made then it is considered an essential amino acid
- Other than nucleotides, provide 2 compounds or types of compounds that amino acids can serve as the precursor of.
- Histamine: when histidine is decarboxylated
- NAD+ : from tryptophane
- Nitric oxide: from nitric oxide synthase
- Cytochromes
- Heme
- Hormones
- Melanin
- neurotransmitters
- How is pyrimidine synthesis similar to amino acid catabolism?
- What nucleotide cannot be made if there was a deficiency in THF?
DNA —-thymine
- What specific step(s) of atherosclerosis might be prevented by taking antioxidants?
- Damage to endothelial cell lining
- Migration of LDL & platelets
Antioxidants:
- Scavenge free radicals
- Reduce low-grade inflammation
- Reduce blood coagulation & clot formation
- Provide the roles of SAM in amino acid synthesis.
- Preferred methyl donor
b/c of increased transfer potential compared to THF - formed by an adenosyl transfer from ATP
driven by: PPi hydrolysis
produces: active methyl group - induces fruit ripening
- Met synthesis
- Polyamines
- Ornithine conversion to putrescine
- SAM decarboxylation & reaction w/ /putrescine
- Decarboxylated SAM -> putrescine -> spermidine -> spermine
- Provide the roles of THF in amino acid synthesis.
- Carrier of
Methyl
Methylene
Formyl
Methenyl
Formimino - Formed from folic acid
Amino acid synthesis
Neural tube defect prevention
- Provide 3 function of nucleotides other than DNA/RNA synthesis.
- Used to synthesize UDP-glucose
- Energy: ATP & GTP
- Coenzymes: NAD, FAD, CoA
- Regulation: phosphorylation & adenylation
- Group transfers: SAM
- In regards to purine synthesis, what is meant by substrate balancing in regards to IMP metabolism?
IMP conversion to GMP and AMP
- GMP inhibits xanthylate formation
- AMP inhibits adenylosuccinate formation
Substate Balancing
- ATP is used to make GMP
- GTP is used to make AMP
- What causes gout and how is it treated?
Cause: Exceeding the solubility of uric acid
Treatment: Allopurinol
- Inhibits xanthine oxidase
- Reduces the amount of uric acid in tissues
- Explain what is meant by the intestinal-renal axis in regards to arginine synthesis.
Interorgan metabolism plays a major role
Intestinal renal axis
- Small intestine: Gln -> Cit
- Kidney: Cit -> Arg
- How does bacterial regulation of purine synthesis differ from eukaryotes?
Bacteria
- Purines repressor protein
- Block transcription when hypoxanthine of guanylate are high
- Describe the mechanism of ribonucleotide reductase.
- Transfers a free radical from enzyme to substate
- Movement of unpaired electron from tyrosine on R2 to substrate
- Hydrogen removed from C3
- OH refection from C2 as H2O
- C2 reduction by sulfhydryls on R1
- Return hydrogen to C3
- What part of cholesterol is removed to make steroids?
- Aliphatic side chain
- List 3 molecules that amino acids can serve as the precursors for.
- Histidine -> decarboxylase-histamine
- NAD+ -> tryptophan
- Nitric oxide
- Tetrahydrobiopterin
- Serotonin
- Dopamine
- Norepinephrine
- What steroid is termed the hormone grandparent?
- Pregnenolone (precursor)
- Identify the major type of modification that distinguishes the steroids from each other.
- Addition, modification, position of functional groups
- Configuration of steroid nucleus
- Identify the roles of the reductase and nitrogenase in regards to nitrogen fixation.
Reductase
- Role: provides electrons w/ high reducing power
- Function: uses electrons to reduce N2 -> NH4+
Nitrogenase: ATP requirement
Cofactor
- Iron
- Molybidelenum
- Vanadium
- From an evolutionary perspective, what is the major reason why we choose not to synthesize essential amino acids?
A selective advantage
- Need 10+ enzymes to make an a.a.
- Evolutionary advantage
- A period of famine
- Identify the major differences between aminotransferases and amidotransferases in regard to nonessential amino acid synthesis.
Amidotransferases
- Binds glutamine
- Accepts amido group
- Amidoligase
Aminotransferases
- Transaminase
- Transfer amine group between amino acids and keto acid
- What is the major precursor for proline synthesis in the liver?
arginine
- What 2 amino acids play a role in making purines and pyrimidines?
glutamine & aspartate
3 sources for NADPH for fatty acid synthesis
- malic enzyme
- PPP
- isocitrate DH (ICDH)
