Biochemistry: Metabolism

What is the function of glucokinase and hexokinase in glycolysis? What's the difference between these two enzymes?

The function of these enzymes is to trap glucose into the cell through phosphorylation. Glucokinase is the hexokinase of liver cells and B inslet pancreatic cells, and it has a higher Km than hexokinase. Hexokinase is in cells in general.

Can a liver cell use both hexokinase and glucokinase?

Yes, because hexokinase works at low glucose levels, and glucokinase works at high glucose levels.

Why won't the Citric Acid Cycle function in the absence of oxygen?

Even though oxygen is not directly required to complete a cycle of the Citric Acid Cycle, the cycle stops functioning in its absence because a buildup of NADH and FADH2 prevent unfilled electron carriers from being available to accept electrons.

What is the reason for the naming of the Citric Acid Cycle?

The Citric Acid Cycle is so named because when the two reactants of the cycle, oxolacetate and acetyl CoA, combine to form the first reactant of the cycle, that reactant is citrate/citric acid.

Is pyruvate a reactant of the Citric Acid Cycle? What is the enzyme responsible for catalyzing the reaction?

No, pyruvate, the product of glycolysis, is converted pre-CAC into acetyl CoA by pyruvate dehydrogenase.

What are the 8 steps of the Citric Acid Cycle (reactants and products per Acetyl CoA)?
How many GTP, FADH2, NADH, and CO2 are formed per Acetyl CoA?

1) Oxaloacetate + Acetyl CoA form Citrate
2) Citrate isomerizes to Isocitrate (which happens when a water molecule is moved around)
3) Isocitrate forms alpha-ketoglutarate, carbon dioxide, and reduced NADH
4) alpha-ketoglutarate forms succinyl CoA, carbon

What is the "slow step" (aka rate-limiting step) of the Citric Acid Cycle? What type of reaction occurs?

Step 3, isocitrate --> alpha-ketogluturate, is the rate-determining step of the CAC mechanism. In this reaction, oxidative decarboxylation occurs.

How many carbons does Acetyl CoA contribute to oxaloacetate in the Citric Acid Cycle? Is the number of carbons that Acetyl CoA contains different from the number of carbons that Pyruvate has?

2 carbons, which are lost through oxidative decarboxylation during steps 3, isocitrate --> alpha-ketoglutarate, and 4, alpha-ketoglutarate --> succinyl-CoA of the CAC.
Yes, pyruvate has 1 extra carbon, which is lost when pyruvate is oxidized to acetyl CoA

Which reaction of the Citric Acid Cycle occurs in the inner mitochondrial membrane? Where do the other reactions occur?

Fumarate formation from succinate. (This is because the complex that forms fumarate is is in Complex II of the electron transport chain, and it's involved in oxidizing FADH2 for the ETC.)
The other reactions occurs in the mitochondrial matrix.

What is a humorous mnenomic to remember the reactants of the citric acid cycle?

Please, can I keep selling seashells for money, officer?

How many ATP are produced from 1 NADH molecule? 1 FADH2 molecule? 1 GTP molecule?

1 NADH molecule yields 2.5 ATP
1 FADH2 molecule yields 1.5 ATP
1 GTP yields 1 ATP

How many ATP, NADH, FADH2, and CO2 are produced by pyruvate dehydrogenation per pyruvate? How many are produced by the Citric Acid Cycle per Acetyl CoA?

1 ATP, 1 NADH, 0 FADH2, and 1 CO2
1 GTP (--> ATP), 3 NADH, 1 FADH2, and 2 CO2

What are the enzymes that regulate the pyruvate dehydrogenase complex in response to metabolic needs of the cell?

In PDC, pyruvate dehydrogenase is negatively regulated by pyruvate dehydrogenase kinase and positively regulated by pyruvate dehydrogenase phosphatase. PDK is activated with higher levels of ATP and NADH; PDP is activated with lower levels of ATP and NADH

What steps of the Citric Acid Cycle are regulated by ATP and NADH?

The formation of citrate from oxaloacetate and acetyl coa is negatively regulated by the presence of NADH and ATP and positively regulated by the presence of NAD+ and ADP.
The formation of alpha-ketogluturate from isocitrate is negatively regulated by NAD

Why is it helpful to think of the energy stored in ATP like a loaded spring?

A loaded spring is a spring that has been compressed and held in place. Once that spring is released, then it moves quickly in the direction opposite to its compression.
It's helpful to think of ATP as a loaded spring because the energy capacity of ATP is

Based on the standard models for nucleic acids, all of the following could logically replace adenine in ATP except (choose 1): guanine, thymine, cytosine, uracil

Thymine because it is a DNA nucleic acid. ATP is a ribose-based (RNA based) nucleic acid.

What is the postprandial state, and how does it relate to anabolism and catabolism?

The postprandial state is a period of time (3-5 hours) post-meal that the human body spends breaking down food to form biomolecules. This is an example of anabolism. Catabolism doesn't occur during the postprandial state because there is plenty of energy

When nutrients are absorbed in the small intestine, where do most nutrients travel first (an organ)? Where do fats travel?

Most nutrients travel to the liver. Fats are absorbed by lacteals in SI villi, and they are then deposited into lymphatic vessels in the form of chylomicrons. These then travel through the lymphatic system to the thoracic duct.

When blood glucose rises, what hormone is released? What 3 areas of the body does this hormone act on, and what are the major effects?

Insulin
Skeletal muscle -> uptake of glucose, synthesis of proteins and glycogen
adipose tissue --> synthesis of fatty acids and triacylglycerols
liver --> synthesis of glycogen

Does the brain depend on insulin stimulation to use glucose? Does the white or gray matter use more glucose?

No. The gray matter uses more glucose than the white matter.

In addition to glucagon, several hormones have "counter-regulatory effects" to insulin on the 3 areas of the body insulin most affects. Name these and describe their effects.

cortisol, epinephrine, norepinephrine, growth hormone
These hormones effect skeletal muscle, adipose tissue, and the liver. Skeletal muscle sends amino acids to the liver for gluconeogenesis. Adipose tissue sends fatty acids to the liver for gluconeogenes

What cells produce insulin and glucagon and where are they located in the human body?

Beta-cells produce insulin and Inslets of Langherns in alpa-cells produce glucagon in the pancreas

Name catecholamines and glucocorticoids. How do they work together to increase blood sugar?

...