MMT: fuel metabolism II

Question 1

What is different about fuel intake in neonates due to breastfeeding?

Answer 1

More intake of lipids!

Question 2

What is the major carbohydrate in breast milk?

Answer 2

Lactose

Question 3

What does lactose synthase do?

Answer 3

Convert UDP galactose (from UDP glucose) to lactose

Question 4

Fats from the diet are transported via…

Answer 4

Chylomicrons

Question 5

Lactose is composed of which monomer(s)?

Answer 5

Glucose and galactose

Question 6

Lactase cleaves what linkage?

Answer 6

B-1,4

Question 7

Describe lactose intolerance.

Answer 7

A deficiency in lactase leads to more lactose making it to the large intestine, where bacteria ferment it and lead to gas/irritation

Question 8

What can cause lactose intolerance?

Answer 8

A primary deficiency or temporary deficiency from infections

Question 9

How do we get galactose into glycolysis?

Answer 9

1. Galactokinase forms galactose-1-phosphate
2. Galactose 1-phosphate uridyl transferase takes a UDP molecule from UDP glucose and puts it onto the galactose 1-phosphate to form UDP galactose and glucose 1 phosphate
3. Glucose 1 phosphate can enter glycolysis!
4. Epimerase converts UDP galactose to UDP glucose to be reused

Question 10

Should a mother who has a child with classic galactosemia be breastfed?

Answer 10

No!!

Question 11

Foremilk quenches ___, while hindmilk quenches ___?

Answer 11

Thirst; hunger

Question 12

In the small intestine, what version of triglyceride is present?

Answer 12

2-monoacylglycerol

Question 13

Chylomicrons leave the small intestine via which lipoprotein?

Answer 13

ApoB48

Question 14

How do chylomicron remnants get recycled?

Answer 14

They have ApoE, allowing them to return to the liver for re-processing

Question 15

What kinds of fatty acids are most abundant in breast milk?

Answer 15

Saturated fatty acids! The essential fatty acids are also present

Question 16

What makes omega 6 and 3 essential fatty acids?

Answer 16

Humans cannot synthesize double bonds in unsaturated fatty acids beyond the delta9 position, so we can’t make omega 3 and 6. Therefore, we must get them from the diet.

Question 17

Which two amino acids specifically are essential in infants and kids?

Answer 17

Arginine and cysteine

Question 18

How do we excrete amino groups from proteins?

Answer 18

As urea via the urea cycle

Question 19

What are the major steps of the urea cycle?

Answer 19

1. Amino acid transfers the amino group onto a-ketoglutarate to form glutamate
2. NH4 is removed from glutamate, which then converts back to a-ketoglutarate and can re-enter the cycle
3. NH4 is converted to urea for excretion

Question 20

Where does the urea cycle occur?

Answer 20

The liver

Question 21

Which amino acids are strictly ketogenic?

Answer 21

Leucine and lysine

Question 22

What major molecule is made via the methionine cycle?

Answer 22

SAM, a huge methyl carrier for a bunch of reactions

Question 23

What are the major intermediates in the methionine cycle?

Answer 23

Methionine > SAM > homocysteine

Question 24

After homocysteine is produced by the methionine cycle, it becomes…

Answer 24

a-ketobutyrate and cysteine

Question 25

Why is cysteine not an essential amino acid?

Answer 25

We make some of it from homocysteine! Neonates do need more than what we can make though, so they need it in the diet

Question 26

A-ketobutyrate can become…

Answer 26

Propionyl CoA and ultimately succinyl CoA

Question 27

What does phenylalanine hydroxylase do?

Answer 27

Convert phenylalanine to tyrosine using BH4

Question 28

Issues with phenylalanine hydroxylase are associated with what condition?

Answer 28

PKU

Question 29

What does fumarylacetoacetate do?

Answer 29

Convert 4-fumarylacetoacetate to acetoacetate and fumarate

Question 30

Issues with 4-fumarylacetoacetate are associated with…

Answer 30

Tyrosinemia type I

Question 31

What are the branched chain amino acids?

Answer 31

Valine, isoleucine, leucine

Question 32

How do we break down branched chain amino acids?

Answer 32

They are transaminated (amino group removed), forming their a-ketoacid. Branched chain a-ketoacid dehydrogenase then processes these into their metabolic components (propionyl CoA, acetyl CoA, acetoacetate)

Question 33

Maple syrup urine disease is associated with deficiency in which enzyme?

Answer 33

Branched chain a-ketoacid dehydrogenase

Question 34

What major carbohydrate tends to be introduced when starting solid foods?

Answer 34

Fructose

Question 35

What step does fructose skip in glycolysis?

Answer 35

PFK

Question 36

What is essential fructosuria?

Answer 36

Deficiency in fructokinase. Pretty benign and just results in fructose in the urine

Question 37

What is hereditary fructose intolerance?

Answer 37

Deficiency in aldolase B. Issues arise after eating fruits and symptoms include jaundice, vomiting, hypoglycemia, and poor feeding.

Question 38

Why does aldolase B deficiency cause hypoglycemia between feedings?

Answer 38

A buildup of F1P due to not being able to break it down traps phosphate in an unusable form. This blocks glycogen breakdown and gluconeogenesis, removing the buffering elements the body has in place and leading to hypoglycemia

Question 39

How do we treat aldolase B deficiency?

Answer 39

Avoid fructose and sucrose

Question 40

Fructose is mostly metabolized by…

Answer 40

The liver

Question 41

What enzyme is associated with MODY2?

Answer 41

Glucokinase

Question 42

What is MODY2?

Answer 42

Deficiency in glucokinase means pancreatic beta cells cannot sense glucose levels, preventing release of insulin. This causes neonatal diabetes mellitus