Metabolism

Question 1

How is Vitamin D metabolized?

Answer 1

Fatty Acids are converted to a certain form of cholesterol that can by converted to vitamin D3 in the skin by UV.
Intestine-> also makes D3
D3 is further metabolized by the liver into calciferol
And then again by the kidney giving calcitriol
the active form of Vit D3

Question 2

How is Vitamin K obtained, which forms does it exist in?

Answer 2

Vit K1 is from leafy green vegetables
Vit K2 is synthesized from bacteria in the large intestine and the colon
One form of Vit K is a cofactors for y-carboxylase involved in clotting -> inhibited by Warfarin

Question 3

What are the two main sources of Iron?
Ferric reductase, a membrane-associated enzyme, is mutated and Vitamin C can no longer bind properly to it. Which source of iron does that effect? Why?

Once in the Cell how is Iron stored?
When it is in the blood, how is Iron transported? Where does it transport to?

Answer 3

Absorbed from the intestinal lumen as heme iron, animal products, and nonheme iron, from plant products.
Heme Iron exists in the Fe2+ state.
If Ferric reductase is nonfunctional than this would effect nonheme iron, it would not be able to get into enterocyte in its Fe3+ from. The ferroprotin transports iron in the form Fe2+

The cell stores iron as Ferratin

Iron ins transported in the blood by transferrin, this process is promoted by a low storage of iron in the body. It’s transported to liver, spleen, and bone marrow.

Question 4

What minerals are required in our diet?

What are their main purposes?

Answer 4

Electrolytes: K+, Na+, Cl-

Minerals: Ca2+, (PO4)3-, Mg2+, Fe3+/Fe2+, S-

Trace Minerals: I, Se, Co, Zn
-Manganese, Fluoride, Chromium and Molybdenum

Many minerals serve as cofactors for enzymes
Electrolytes- k is a cofactors, but their main purpose is building and resetting action potentials excitatory cells.

Question 5

What is the proper order of fuel sources from most to least caloric content?

A. Fat, Alcohol, Protein/Carbohydrate
B. Alcohol, Fat, Carbohydrate, Protein
C. Carbohydrate/Protein, Fat, Alcohol
D. Fat, Protein/Carbohydrate, Alcohol.

Answer 5

A. Fat, Alcohol, Carbohydrate/Protein
Fat has 9 calories per gram
Alcohol has 7 calories per gram
Carbohydrates and Proteins both have 4 calories per gram.

Fat has the most energy potential but unsaturated fats are the most healthy of the 3 different kinds. Saturated has more energy potential because of the increased number of Hydrogen-Carbon bonds.

The carbonic skeletons are used for anabolic processes and synthesis.

Question 6

What are the essential fatty acids?

What makes these fatty acids so important?

What are some lipid soluble molecules?

Answer 6

Linoleic Acid - Omega-6
Linolenic Acid - Omega-3
Arachidonic Acid - Omega-6

Saturated fats that are essential-
palmitic acid
Stearin acid

Fatty acids serve as the precursors for certain vitamins, (A, D, E, K), and for membrane lipids: phospholipids and gylcolipids

Lipid Soluble: Thyroxin, Cholesterol, and Steroids.

Question 7

Name 3 examples of secondary transporters and their function.

Answer 7

Calcium-Sodium Exchanger

• piggy backs off of Sodium-Potassium Pump.
• an antiporter
• exports Calcium and imports sodium

Mitochondrial Calcium Transporter
-uniporter, regulates mitochondrial uptake of Ca2+

Lactose permease

• symporter
• uses a proton gradient to bring sugars, primarily Lactose, into the cell. Sugars go against their conc gradient
• proton binds a residue, Glu 269, lactose can bind in the protanated form, structure everts to the inside of the cell and releases lactose, followed by the release of the proton and re-eversion.

Question 8

Lingual Lipase

Answer 8

Digests short and medium-chain fatty acids

Found in the oral cavity

Question 9

Gastric lipase

Answer 9

Digests short and medium-chain fatty acids

Found in the stomach

Question 10

Pancreatic Lipase and colipase

Phospholipase

Cholesterol esterase

Answer 10

Digests triglycerides
Found in the small intestine

Digests phospholipids in the small intestine

Digests cholesterol esters in the small intestine

Question 11

What would happen in Glycolysis if NAD+ was depleted entirely? How does the body solve this issue?
(think about skeletal muscle)

Answer 11

Glycolysis would stop because the reduction of NAD+ to NADH is an important step in adding a Pi to GAP -> 1,3 BPG. This step prepares for the first substrate level phosphorylation event.

This is solved by recycling NADH and oxidizing it back to NAD+ using lactate dehydrogenase, which turns pyruvate into lactate. This is an anaerobic process.

Also the reason lactic acids builds up after exercising.

Question 12

What are the two high-energy intermediates/substrates in Glycolysis?
And their corresponding enzymes?

Answer 12

Phosphoenolpyruvate
-pyruvate kinase
1,3 Bisphosphoglycerate
-phosphoglycerate kinase

Question 13

What is the rate limiting step of Glycolysis?

Answer 13

Fructose 6-phosphate
->
Fructose 1,6 Bisphosphate
By enzyme, phosphofructokinase

Also, the Committed Step

Question 14

In glycolysis: What steps use ATP? What steps give off ATP? Which step uses NAD+?

Answer 14

Steps the use ATP:

• Trapping of glucose in the cell: Hexokinase/Glucokinase. G -> G6P
• Committed step: phosphorylation of Fructose 6-phosphate to Fructose 1,6 Bisphosphate by phosphofrucktokinase

Steps that make ATP:
-1,3 BPG to 3-phosphoglycerate by phosphoglycerate kinase
-PEP to Pyruvate by pyruvate kinase
both done by Substrate level Phosphorylation

NAD+ Reduction step:
-GAP to 1,3 Bisphosphogylcerate

Question 15

What are the regulators of Hexokinase/Glucokinase?

Answer 15

Negative Inhibitor: Glucose 6-Phosphate

GK
Negative Inhibitors- Glucogon, Fructose 6-P
Positive Inhibitors- Insulin, Glucose and Fructose 1-phosphate

Question 16

What are the regulators of phophofructokinase?

Answer 16

Positive: AMP and Fructose 2,6-BP
Negative: ATP and Citrate, H+

Question 17

Regulators of pyruvate kinase?

Answer 17

Negative: Alanine, ATP and glucogon
Positive: Insulin and Fructose 1,6-BP

Question 18

When there is high energy, high ATP & NAD+ and low NADH; which glycotic intermediate is favored?

Answer 18

DHAP

-> converted to glycerol 3-phosphate and eventually stored as triacylglycerols (Fat)

Question 19

What conditions are necessary in order to favor GAP in glycolysis?

Answer 19

Low ATP and High AMP
Low NAD+ and High NADH
Glucose, and Insulin

Question 20

What happens to pyruvate under aerobic conditions, in both fed and fasting states? What about anerobic conditions?

Answer 20

Aerobic and Fed= Acetyl CoA -> TCA cycle and fatty acid synthesis
Alanine -> protein synthesis

Aerobic and Fasting= oxaloacetate and feeds into gluconeogenesis

Anaerobic: lactate recycles via the Cori cycle
Alanine can feed into gluconeogenesis and the Urea cycle.

Question 21

What enzymes of gluconeogenesis essentially reverse the “irreversible” steps of glycolysis?

Answer 21

Glucose 6-phosphatase
Fructose 1,6-Bisphosphatase
Phosphoenolpyruvate carboxykinase
Pyruvate carboxylase

Question 22

Gluconeogenisis happens in both the cytoplasm and mitochondria of liver cells, kidney cells and intestinal cells. What in particular happens in the mitochondria?

Answer 22

Pyruvate gets turned into oxalacetate by pyruvate carboxylase in the mitochondria. Then shuttled out as malate

Question 23

What’s the committed step of gluconeogenesis?

Answer 23

Fructose 1,6-Bisphosphatase

Question 24

Free glucose comes from all these except: 
A.  Glycogenolysis in Muscles 
B.  Glucose 6-phosphatase 
C.  Glycogenolysis in Liver
D.   Debranching enzyme

Answer 24

A. Glycogenolysis in muscles

Question 25

Regulators of gluconeogenesis:

Answer 25

Positive: ATP, Citrate, Acetyl-CoA, Glucogon, Cortisol, Thyroxine
Negative: AMP, ADP, Fructose 2,6 Phosphate

Question 26

Specific regulators of: 
Phosphate 1,6 Bisphosphatase 
Glucose 6 Phosphatase 
Pyruvate carboxylase 
Phosphoenolpyruvate carboxylase

Answer 26

Phosphate 1,6 Bisphosphate: (+) Citrate and Cortisol (-) Fructose 2,6 BP and AMP
Glucose 6-Phosphatase: (+) Cortisol
Pyruvate carboxylase: (+) Acetyl CoA, Cortisol (-) ADP
PEP carboxylase: (+) Glucogon, Thyroxine, Cortisol (-) ADP

Question 27

What is the cori cycle?

Answer 27

Lactate is produced by skeletal muscle and RBCs, it circles the blood and once in the liver gets regenerated/recycled back into Pyruvate. Which feeds into gluconeogenesis and comes out of glucose.

Question 28

What enzymes break 1,4 glycosidic bonds? And which form them?

Answer 28

Glycogen phosphorylase and branching enzyme both break 1,4 glycosidic bonds
Glycogen synthase and transferase form 1,4 glycosidic bonds

Question 29

What enzymes form and break 1,6 glycosidic bonds?

Answer 29

Branching enzyme, glycosyl trannsferase, forms 1,6 glycosidic bonds
Debranching enzyme breaks them