Part 2 - lecture 5 - Exam

Question 1

What does AA degredation do?

Answer 1

releases NH3 and remaining carbon skeleton

Question 2

What does the urea cycle do?

Answer 2

Converts toxic NH3 to non-toxic urea for excretion

Question 3

What does AA synthesis do?

Answer 3

Synthesis of non-essential AA and many important biological molecules from AA

Question 4

What are AA used for in the body?

Answer 4

Synthesis of protein, glucose, ketone bodies, many biomolecules, produces fuel with CO2 byproduct

Question 5

What are essential and non-essential AA?

Answer 5

essential - must be taken in diet, non-essential can be synthesized

Question 6

What are the essential AAs?

Answer 6

PVT TIM HALL

Question 7

In what ways can we get AA?

Answer 7

Not stored – must get from diet, synthesize de novo, or produce from protein degradation

Question 8

What is the structure of AA?

Answer 8

Amine and carboxyl function group on an alpha keto acid H2N-CHR-COOH

Question 9

What forms of AA are found in proteins?

Answer 9

L-stereoisomers

Question 10

Where do we get AA from diet?

Answer 10

dietary protein from meat, dairy, grains, beans

Question 11

How are AA obtained from dietary protein?

Answer 11

HCl denatures proteins in stomach which are further broken down by pepsin (activated by HCl) and further breakdown occurs in SI at neutral pH via trypsin and chymotrypsin from pancreas – single AA released by amino- and carboxypeptidases and absorbed by intestinal cells

Question 12

How are AA taken from our own body proteins?

Answer 12

Amine groups from AA are transferred to glutamate and pyruvate to make glutamine and alanine in muscle and are transported to liver or kidney where NH3 groups can be used for urea production

Question 13

What is the rate of synthesis of proteins compared to degradation?

Answer 13

Total of amount of protein in body is constant in healthy adults - rate of synthesis is sufficient to replace degraded protein

Question 14

What enzyme systems are responsible for degrading damaged or unneeded proteins?

Answer 14

Ubiquitin-proteasome proteolytic pathway (ATP dependent) - and Lysosomal protein degradation (no ATP) by acidic pH

Question 15

What type of transport is used to move AA into cells?

Answer 15

Active by use of ATP hydrolysis

Question 16

What is gamma-glutamate?

Answer 16

An AA transporter that attaches to AA by liver enzyme gama-glutamyl transferase (GGT) – gamma-glutamate derived from glutathione

Question 17

What’s the purpose of removing nitrogen from AA?

Answer 17

Breakdown of AA for energy release - allow N to be incorporated into other compounds

Question 18

What protects AA from oxidative breakdown?

Answer 18

the alpha amino group

Question 19

What is the first step in the catabolism of AA? What AA do not participate?

Answer 19

Transamination - transfer of amine group to alpha-ketoglutarate producing glutamate and alpha-keto acid (only threonine and lysine do not participate) - occuring primarily in liver

Question 20

Is transamination reaction reversible?

Answer 20

For essential AA it is unidirection but for non-essential it is reversible

Question 21

What enzymes catalyze the transfer of an amino group from one C skeleton to another? And where are they found?

Answer 21

Aminotransferases or transaminases - found throughout body but especially liver and kidney

Question 22

What are the two most important aminotransferases?

Answer 22

ALT - forms pyruvate

AST - from glutamate to oxaloacetat forming aspartate

Question 23

What is the alanine-glucose cycle?

Answer 23

Primarily used in skeletal muscle to eliminate N and replenish energy by releasing branched AA during prolonged exercise so that C backbones are used for energy while N is used to make alanine which bring C and N to liver to transfer NH3 to ketoglutarate to regenerate pyruvate - newly formed glucose travels through blood to muscle

Question 24

What is the functional form of Vitamin B6 and what is it used for?

Answer 24

Pyridoxal phosphate - coenzyme for aminotransferases - used to remove carboxyl group from glutamate

Question 25

What is demonstrated if the levels of aminotransferase in plasma increases? (normally low)

Answer 25

Damage to cells containing high levels of these enzymes that is causing release to the bloodstream - such as AST and ALT in liver disease

Question 26

What doers glutamate dehydrogenase do?

Answer 26

Liberates amino group as free ammonia by oxidative deamination that primarily occurs in the liver on glutamate (end product of many transamination reactions) -- converts glutamate to alpha-ketoglutarate and NH3 (urea cycle)

Question 27

What raises glutamate dehydrogenase activity?

Answer 27

Caloric restriction or low blood glucose so that more alpha-ketoglutarate can be produced to be used in TCA cycle for ATP

Question 28

Where can we get glutamate from?

Answer 28

Amination of alpha-ketoglutarate or deamination of glutamine to glutamate (glutaminase)

Question 29

What non-essential AA carries ammonia as an amine group?

Answer 29

Glutamine

Question 30

What is the intracellular glutamine cycle?

Answer 30

Scavenge NH3 which has not yet been incorporated into urea and control flux of ammonia to urea or glutamine

Question 31

What is the overall picture of processes involved in AA metabolism?

Answer 31

Transamination and oxidative deamination

Question 32

Where do we get non-essential AA from?

Answer 32

Intermediates of glycolysis, TCA cycle

Question 33

What is the summary of AA catabolism?

Answer 33

Alpha-amino group removed by transamination and oxidative deamination to form ammonia and alpha-keto acid -- some free ammonia excreted but most used to synthesize urea to dispose of -- carbon skeleton of alpha-keto acids converted to intermediates of energy producing pathways - can be metabolized to CO2, water, glucose, or ketone bodies

Question 34

What are the major products when carbon skeleton of AA are degraded?

Answer 34

Pyruvate, AcCoA, acetoacetate, TCA intermediates

Question 35

What are glucogenic AA?

Answer 35

C skeletons degraded to pyruvate or one of TCA intermediates to be used for gluconeogenesis -- can be broken down for energy or converted to glycogen or FA

Question 36

What are ketogenic AA?

Answer 36

Leucine and lysine - C skeletons degrade to AcCoA or acetoacetate which can be catabolized for TCA energy and converted to ketone bodies

Question 37

Which AA can be ketogenic or glucogenic?

Answer 37

Aromatic AAs - tryptophan, phenylalanine, tyrosine, isoleucine

Question 38

What happens if there is excess intake of protein?

Answer 38

Deaminated to result in pyruvate or acetyl CoA for FA synthesis - leads to increased urinary nitrogen which can lead to kidney stones or osteoporosis

Question 39

What happens in the absence of carbs? are they essential nutrient?

Answer 39

Not essential but absence causes ketone body production and degradation of body protein -- whose AA provide for gluconeogensis

Question 40

What hormones stimulate synthesis of glucose from AA in the liver?

Answer 40

Cortisone and cotisol

Question 41

What are the branched-chain AA? and what breaks them down?

Answer 41

Leucine, isoleucine and valine - essential AA needed for building and maintaining muscle mass during times of physical stress "ILIV" broken down by alpha-ketohydrogenase

Question 42

What is PKU?

Answer 42

Phenylketonuria - autosomal recessive disorder where liver enzyme phenylalanine hydroxylas (PAH) is deficient - needed to metabolize phenylalanine from food to tyrosine -- instead there is an accumulation of phenylalanine which converts to phenylketone detected in urine -- can cause brain development problems -- but can be controlled by diets low in phenylalanine and high in tyrosine, low in protein and medication -- detected in newborn screening -- aspartame releases phenylalanine

Question 43

Which AA serves as a sulfur dononr, methyl donor and is required for synthesis of creatine?

Answer 43

Methionine

Question 44

Which AA is an important precursor for dopamine, adrenaline and melanin?

Answer 44

Tyrosine

Question 45

Which AA is used to make nitric oxide?

Answer 45

Arginine

Question 46

Which AA is the preferred nutrient in the brain?

Answer 46

Glutamine

Question 47

Which AA is a precursor for histamine?

Answer 47

Histidine

Question 48

Which AA provides the nitrogen for urea synthesis?

Answer 48

Aspartate

Question 49

Which AA is the precursor for most of body's pyridine nucleotides, serotonin and malatonin?

Answer 49

Tryptophan

Question 50

What is pellagra?

Answer 50

Deficiency in niacin (VB3) and tryptophan causing diarrhea, dermatitis and dementia

Question 51

What is used to produce creatine forenergy of skeletal muscle?

Answer 51

Arginine, glycine and SAM

Question 52

Why do we need the urea cycle?

Answer 52

Ammonia is very toxic especially to CNS, need to be able to remove and convert it to urea which is less toxic so that it can be excreted

Question 53

Where does the urea cycle take place?

Answer 53

Liver

Question 54

Where does the N come from for the urea cycle?

Answer 54

One amine group from oxidative deamination of glutamate and another from aspartate, carbon atom from CO2 or bicarb to give urea = (NH2)2CO

Question 55

What is the carrier of C and N atoms in urea cycle?

Answer 55

Ornithine

Question 56

What are the reactions of the urea cycle?

Answer 56

2 mitochondrial and 3 cystolic 1) - CPSI -- ammonium condenses with CO2 to form carbamoyl phosphate 2) OCT -- Reacts with ornithine to form citrulline which moves to cytosol 3) ASS -- Aspartate and citrulline react to form agininosuccinate 4) ASL -- Which is cleaved to fumarate and arginine 5) ARG1 -- Arginine hydrolyzed to urea and ornithine

Question 57

Is the synthesis or urea reversible?

Answer 57

No - large delta G

Question 58

If urea diffuses from blood to intestine what happens?

Answer 58

Bacterial urease cleaves it into NH3 and CO2 to be put back into urea cycle

Question 59

What regulates the urea cycle?

Answer 59

Induced by high protein diet

Question 60

What is a measure of the kidney's ability to excrete nitrogenous waste?

Answer 60

BUN levels - increase caused by renal failure, congestive heart failure, urinary obstruction

Question 61

What damaged organ can't detoxify ammonia?

Answer 61

Liver disease