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58 Cards in this Set

  • Front
  • Back
How do you control regulatory enzyme activity
- Hormonal control - insulin and glucagon
- Covalent modification - phosphorylation/dephosphorylation
- Allosteric modification - availability of substrate
- Gene expression
- Sensitivity to energy needs of system - ATP/ADP ratio
In fed state in liver glucose is converted to _
Fatty acids - stored in adipose
Glycogen - stored in liver
Enzyme responsible for glycogen synthesis and how its regulated
Glycogen synthase
Insulin dephosphorylates it in fed state - ACTIVATES
Glucagon phosphorylates it in fasting state - INACTIVATES
Glycolysis does what and major regulatory enzyme
Conversion of glucose to pyruvate
Enzyme responsible for conversion of pyruvate to acetyl CoA and how its regulated
Pyruvate dehydrogenase - insulin dephosphorylates - ACTIVATES
glucagon phosphorylates - INACTIVATES
Which enzyme responsible for conversion of acetyl CoA to palmitoyl CoA and how its regulated
Acetyl CoA carboxylase - acitvated by insulin by dephosphorylation - RATE LIMITING STEP OF LIPOGENESIS
How does malonyl CoA prevent futile cycling
Malonyl coA prevents transport of fatty acyl CoA into mitochondrion - prevents beta oxidation occuring at the same time as FA synthesis thus preventing futile cycling
Which enzyme breaks down TAG in fed state and how its regulated
In fed state LIPOPROTEIN LIPASE breaks down TAG into glycerol and FA - STORAGE
Insulin induces synthesis if LPL
Which enzyme breaks down TAG in fasting state and how its regulated
In fasting state TG are broken down by HORMONE SENSITIVE LIPASE which reacts to drop in insulin (not glucagon since glucagon receptors are in liver only)
It breaks it down to glycerol and FA and FA can go to muscle where they burned for energy or they can go to liver where they are burned for energy or used for synthesis of ketone bodies
Which hormone stimulates glycogenolysis and how its regulated
GLUCAGON stimulates glycogenolysis in fasting state - uses covalent modification and gene induction
Glycogen stimulates adenylyl cyclase which starts phosphorylation cascade - glycogen phosphorylase is phoshorylated and it takes off glucose monomers from glycogen and adds P to make G-6-P which is converted to glucose in liver by G-6-Pase (defficiency - Von Gierkes disease)
Which hormone stimulates gluconeogenesis and how its regulated
GLUCAGON stimulates gluconeogenesis by covalent modification and gene induction
Pyruvate dehydrogenase in instead of pyruvate kinase in glycolysis
Acetyl CoA Carboxylase requires 3 factors - name them
What stimulates production of ketone bodies
Fatty acids inhibit production of malonyl CoA by inhibiting acetyl CoA carboxylase, so instead ketone bodies can be synthesized from acetyl CoA in the liver
Describe main enzymes for ketone bodies synthesis in liver
- THIOLASE - in liver only - condenses to acetyl CoA to make acetoacetyl CoA
- HMG CoA synthase - condenses acetyl CoA with acetoacetyl CoA to make HMG CoA
- HMG CoA lyase - breaks down HMG CoA to acetoacetate which can be converted to beta - hydroxybuturate and released to the blood where it can be picked up by brain in time of starvation
Sequence and source of fuel used by muscle in time of exercise and/or fasting
1. Glucose from the blood
2. Glucose from muscle glycogenolysis
3. FA from adipose tissue
4. Ketone bodies from liver
During fasting what is the source of alanine
Skeletal muscle releasing AA - go to liver and are source for gluconeogenesis to make glucose
Describe protein digestion in stomach
In stomach PEPSIN is a major proteolytic enzyme which cleaves proteins to smalle polypeptides
- Pepsin is produced and secreted by chief cells of the stomach as inactive zymogen PEPSINOGEN
- HCl produced by parietal cells of the stomach causes nonconformational change in pepsinogen that enables it to cleave itself to active form - PEPSIN
Describe protein digestion in intestine
- In intestine pancreatic secretions - bicarb and proteolytic enzymes
- Bicarb raises pH
- ENTEROPEPTIDASE cleaves trypsinogen and makes trypsin and trypsin can further cleave trypsinogen
Trypsin also cleaves CHYMOTRYPSINOGEN to make active CHYMOTRYPSIN
Proteases produced by intestinal cells finish breaking proteins to amino acids
3 routes of amino acids to blood from intestine
1. Secondary (driven by hydrolysis of ATP) active Na dependent transport - uptake by cell of Na and AMINO ACID by same carrier protein. Na is pumped from cell into blood by Na/K ATPase while amino acid travels down concentration gradient into blood
2.Facilitated diffusion - from intestinal epithelial cells to portal circulation
3. Gamma glutamyl cycle -
Name two genetic defects in membrane transport systems
Result in decreased absorption of amino acids from intestine and resorption of amino acids by kidney and increased excretion in urine - Hartnup disease and cystinuria
- Defective transport of cysteine - cysteine is synthesized in body and oxidized in cystine which can crystallize forming kidney stones
Hartnup disease
Transport of neutral amino acids is defective resulting in defficiency of essential amino acids because they are not absorbed from diet
Cystic fibrosis
- Chloride channel protein defficiency
- Poor absorption of proteins and lipids
- Glistening, bulky, foul smelling stools
Name 2 pure ketogenic amino acids
Leucine and lysine
Name all ketogenic acids
Aromatic acids - phenylalanine, tyrosine, tryptophan
Ketogenic amino acids are converted to
Acetyl CoA or acetoacetate
Cystathionine synthase defficiency - homocysteine does not react with serine to form cysteine. Homocysteine that accumulates is oxidized to homocystine and excreted in the urine
Can also have defficiency of methionine synthetase (converts homocysteine to methionine) or dietary defficiency of cofactors - folate and B12
Maple syrup urine disease
Alpha keto acid dehydrogenase is defective - enzyme complex that decarboxylates transamination products of branched chain amino acids
Urine has odor of maple syrup
PKU - phenylketonuria
Defective conversion of phenylalanine to tyrosine - defect in phenylalanine hydroxylase. Phenylalanine accumulates and is converted to phenylketones - musty odor of urine
Homogentisic acid accumulates (product of phenylalanine and tyrosine metabolism) - HOMOGENTISATE OXIDASE IS DEFECTIVE
Homogentisic acid oxidizes and products polymerize forming dark colored pigments which accumulate in tissues and can be associated with DEGENERATIVE ARHTRITIS
Fate of amino acids in fed state
- Protein synthesis
- Conversion to glucose (if low carb diet)
- Excess converted to fat
Fate of amino acids in fasting state
- Converted to glucose or ketone bodies
- Burned for energy
B6 - pyridoxal phosphate defficiency
- Dermatitis, apathy, irritability, susceptibility to infections, convulsions in infants
- Blocks amino acid deamination
- Used for transamination and deamination reactions
Transamination reactions
Transfer of AMINO GROUP from one amino acid (which is converted to corresponding alpha keto acid) to alpha keto acid (converted to corresponding amino acid)
Cofactor for transamination reactions
PLP - pyridoxal phosphate derived from vitamin B6
How does muscle get rid off extra N
Alanine is sent to the liver for gluconeogenesis (glutamine can also be used)
Which enzymes when elevated indicate leakage from liver because of inflammation
ALT - alanine transaminase
AST - aspartate transaminase
Defects in urea cycle lead to what
Abnormal mental development and mental retardation
High blood concentrations of ammonia lead to tremors, slurred speech or blurred vision. Very high concentrations can lead to coma and death
- Acquired - ammonia detoxificaiton is impaired - circulating levels of ammonia increased - alcoholism, hepatitis or biliary obstruction
- Hereditary - defficiency in enzymes of urea cycle - rare, mental retardation within one week of birth
Describe mechanism of ammonia toxicity
Glutamate dehydrogenase catalyzes oxidative deamination of glutamate - ammonium ion is released and alpha ketoglutarate is formed.
IF ammonium is high - reaction will push to the left and there will be lack of NADH and alpha ketoglutarate - which will slow down citric acid cycle and ATP production in ETC
Which amino acid speeds up urea cycle
Folate is most abundant in
Green leafy veggies
Most folate is taken up by _
Who needs folate most
Pregnant and nursing women especially with history of giving birth with neural tube defects
In folate which nitrogens are most important
N5 and N10 because they bind directly to the carbon that is being transfered
Folate has 3 important oxidation states - what are they
What can tetrahydrofolate do
Take one carbone from one molecule and transfer to another molecule
Factors that cause folate defficiency
- Malnutrition - not enough of veggies or overcooking of veggies, damage to duodenum (folate is absorbed in duodenum)
- Chronic alcoholism - damage to intestinal cells and brush border enzymes, defect in enterohepatic circulation, liver damage, decreased kidney reabsorption
46 y. o female with chronic alcoholism and malnutrition, c/o fatigue and muscle weakness - what findings?
- Anemia
- Macrocytic RBC's
- Polysegmented neutrophils
- Reduced folic acid in blood
Megaloblastic anemia
- Due to folate defficiency or borderline B12 defficiency
- Caused by shortage of T for DNA synthesis so slowing down division of rapidly dividing cells (RBC)
- Tetrahydrofolate shuttles single C off serine to U to make T (DNA base)
Name 2 drugs that interfere with folate, reduce DNA synthesis and so are used as chemo drugs
- 5- FLUOROURACIL - blocks methylation of U to T
-METHOTREXATE- blocks recycling of folate
SIDE EFFECT - anemia
Vit B12
- Essential vitamin
- Made by bacteria only - NOT in plants - meat + dairy
- Stores in liver for 3-6 years
Function of B12
Methylation of homocysteine and formation of SAM
S- adenosylmethionine - made from methionine and ATP
Defficiency of SAM causes what
Megaloblastic madness - extreme irritability caused by B12 defficiency - also numbness, tingling, gate disturbance, blind spots and alteration of sense and smell
Methyl trap hypothesis
If there is low B12 - folate gets methylated and is trapped forming folate defficiency
Lack of intrinsic factor in stomach causes
Defect of B12 absorption in intestine and PERNICIOUS ANEMIA
- Caused by either B12 defficiency or B12 dependent conversion to succinyl CoA