Urea Cycle

Question 1

Amino acids are used to:
* Produce glucose or lipids
* Produce ???
* Provide carbon skeletons
* Produce proteins

Answer 1

energy

Question 2

Eating signals the secretion of gastrin → lowers or increases stomach pH (more acidic).

Answer 2

lowers

Question 3

Low pH in stomach triggers proteolytic activation of pepsinogen → pepsin (breaks down proteins) Peptides/amino acids pass through the ???. Pancreatic zymogens are secreted into the intestine for further digestion of peptides

Answer 3

small intestine

Question 4

Acute pancreatitis: obstruction of pancreatic secretions = proteolytic activation of zymogens within the
pancreas which attack ??? when they have no other proteins/peptides to digest = pain and cellular damage/inflammation.

Answer 4

pancreatic tissue

Question 5

Enteropeptidase is secreted
from the ??? in response to proteins entering the stomach to begin the cascade of events that turn zymogens into active enzymes

Answer 5

small intestine

Question 6

Pancreas can synthesise and
secrete Trypsin inhibitor. Inhibition of trypsin is a key regulatory step in preventing over-activation OR under-activation of zymogens?

Answer 6

over activation

Question 7

amino acids and di-/tripeptides are absorbed into intestinal cells by specific transporters. ??? associated with the intestinal epithelium further digest proteins. Free amino acids are then released into the blood for use by other tissues.

Answer 7

Peptidases

Question 8

first step of amino acid degradation is ??? whereby an amino group is removed

Answer 8

transamination

Question 9

Glutamate, ???, alanine and aspartate are central in nitrogen metabolism as they are all readily converted into TCA cycle INTERMEDIATES

Answer 9

glutamine

Question 10

Gln and Ala are important in the transport of amino groups from ??? tissues and skeletal muscle to the liver

Answer 10

extrahepatic tissues

Question 11

Aspartate or alanine provides the second amino group in the urea
cycle?

Answer 11

Aspartate

Question 12

Excess NH4+ in tissues is added
to glutamate to form glutamine which enables ammonia to be safely transported in the ??? to the liver where NH4+ is released and enters the urea cycle

Answer 12

bloodstream

Question 13

Vigorously working muscles operate nearly ??? and rely on glycolysis for energy = pyruvate –> If pyruvate not eliminated lactic acid will build up
Pyruvate can be converted to alanine for transport into the liver. This alanine in liver can enter the urea cycle and the ??? pathway

Answer 13

anaerobically

gluoconeognesis pathway

Question 14

In ammonotelic organisms, ammonium (NH4+) can be excreted as ???

Answer 14

ammonia

Question 15

In ureotelic organisms, ammonium (NH4+) is converted to ??? for excretion

Answer 15

urea

Question 16

In uicotelic organisms, ammonium (NH4+) is converted to ??? for excretion

Answer 16

uric acid

Question 17

TRUE or FALSE: Animals that excrete nitrogenous wastes as ammonia need access to lots of water as they release ammonia across whole body
surface or through gills

Answer 17

TRUE

Question 18

The liver of mammals and most
adult amphibians converts ammonia to the less toxic urea. Circulatory systems carry urea to the kidneys where it is excreted Conversion of ammonia to urea is energetically EXPENSIVE or INEXPENSIVE; excretion of urea requires less water than ammonia

Answer 18

EXPENSIVE

Question 19

Insects, land snails, many reptiles and birds, mainly excrete uric acid.
Uric acid is relatively NONTOXIC or TOXIC and does not dissolve readily in water. It can be secreted as a paste with little water loss. Uric acid is more energetically expensive to
produce than urea

Answer 19

nontoxic

Question 20

Step 1 leading to urea cycle: NH4+ arrives in liver mitochondria as ???
Free NH4+ is released from glutamate. NOTE: Other amino group enters urea cycle as aspartate

Answer 20

glutamate

Question 21

step 2 leading to urea cycle: Carbamoyl phosphate synthetase I (CPS1) Converts free NH4+ and HCO3- to ???

Answer 21

carbamoyl phosphate

Question 22

TRUE or FALSE CPS1 is allosterically activated by N-acetylglutamate

Answer 22

TRUE

Question 23

Step 1 of UREA Cycle: In mitochondrial matrix, Ornithine combines with NH4+ (from carbamoyl phosphate) to form ???

Answer 23

citrulline

Question 24

Step 2 of UREA cycle: In cytoplasm, Citrulline + ??? combine to form arginininosuccinate and then arginine = Release of fumarate, which enters TCA cycle

Answer 24

aspartate

Question 25

Step 3 of UREA cycle: Arginase catalyses the hydrolysis of arginine to urea and ??? (which continues in the urea cycle)

Answer 25

ornithine

Question 26

hyperammonemia is a defect in the urea cycle where the urea cycle enzymes or intermediates (?) are defective = elevated NH4+ levels =nervous system malfunction and possible death

Answer 26

Enzymes

Question 27

Liver damage caused by excessive alcohol consumption can be fatal, in part because the liver is unable to synthesize ??? and consequently NH4+ appears in the blood

Answer 27

urea

Question 28

TRUE or FALSE: in the catabolism of AAs, the carbon skeleton of the 20 amino acids are converted into one of only 7 molecules

Answer 28

TRUE

Question 29

Most AAs don’t directly enter TCA cycle, instead, many are first converted to ???
e.g. phenylalanine is converted to
tyrosine before entry into the TCA cycle (as fumarate)

Answer 29

other amino
acids

Question 30

Phenylketonuria (PKU) is caused by a defect in phenylalanine degradation from a genetic defect in ??? = buildup of phenylalanine and phenylpyruvate

Answer 30

phenylalanine hydroxylase

Question 31

Phenylketonuria impairs ??? development leading to intellectual deficits and premature death if untreated

Answer 31

neurological

Question 32

phenylketonuria is controlled by limiting ??? intake of phenylalanine (including artificial sweeteners) and dietary non-phenylalanine protein supplementation

Answer 32

dietary

Question 33

Protein within muscle can be degraded to AAs during times of long-term fasting. AAs are secreted from muscle for production of ??? and ??? in the liver

Answer 33

glucose and ketones

Question 34

Glucose derived primarily from glycogen stores in liver via glycogenolysis. Maintaining adequate BGL is essential. When glycogen stores are depleted
(dieting), maintaining BGL requires gluconeogenesis. No intake of food, so muscle protein must be CATABOLISED or ANABOLISED (?) for glucose production = muscle loss rather than loss of fat reserves

Answer 34

CATABOLISED

Question 35

Potential heath risks of Atkins diet:
* ??? (low glucose in blood) causing neural effects
* Ketoacidosis causing acidification of blood
* High serum lipids causing heart disease
* Increased ammonia causing liver damage

Answer 35

Hypoglycemia

Question 36

Atkins diet: Metabolism is similar to fasting but with following result:
* Decreased or increased glucose?
* Increased ketones (secreted in
breath + urine = net calorie loss)
* Increased serum lipids
* Increased NH4+

Answer 36

decreased glucose