Biochem revision - Week 4 ATP Metabolism

Question 1

How does ATP release energy?

Answer 1

When ATP is hydrolyzed (water is added), and one phosphate is cleaved (removed) to release energy

*ATP is formed through a dehydration reaction in which water is formed

Question 2

What is Gibb’s free energy and what is its formula?

Answer 2

Gibb’s free energy essentially determines which direction a reaction will occur in and if it is favored or not. If a rctn has negative G, it is favored.

Change in G = (Change in H) -T(Change in S)

H - Enthalpy (bond energies)
T- Temperature
S - Entropy (disorder or randomness)

Question 3

What is the role of Myokinase?

Answer 3

Myokinase is an enzyme that adds a phosphate group from one ADP to another to from ATP and a side product of AMP.

This is done during hard exercise to maintain [ATP]

The reaction is favored because [ATP] decreases and so does [AMP] because it is broken down in the liver (products), and [ADP] increases (reactants)

Question 4

Which molecule has the highest phosphoryl transfer potential and how does its breakdown occur?

Answer 4

Phosphocreatine (PCr) has the highest phosphoryl transfer potential. This is in part due to the ratio of PCr to Cr being 2:1 so the conversion to Cr and ATP is favored.

The breakdown from PCr to ATP and Cr is rapidly driven by Creatine Kinase during hard exercise.

Question 5

How do the different concentrations of molecules used in metabolism compare? During exercise, how do these deposits fare?

Answer 5

[PCr] - 20mmol/kg in muscle at rest

[ATP] - 8mmol/kg in muscle at rest

Although PCr stores are 3-4 times larger than ATP, the resynthesis rate is much slower. Thus PCr stores last approx. 7 sec during max. exercise

[ATP] does not drop below 60% of resting levels during exercise due to Myokinase and Creatine Kinase.

Question 6

How do the rates of ATP synthesis rates compare btw different energy systems?

Answer 6

Phosphagen system is has the highest ATP turnover but only lasts up to 1 min during exercise

The glycolytic system has abt half the max. turnover of the PCr system but lasts longer

Mitochondrial resp. has the lowest turnover rate but can last a long time

Question 7

What are the three ways ATP is utilized during exercise?

Answer 7

1. Mechanical E - muscle contraction
2. Heat - maintenance of body temp.
3. Electrical E - electrical nerve impulses (Na+ - K+ and Ca2+ pump)

Question 8

What the steps to carb digestion?

Answer 8

1. Mouth (saliva) and then small intestine (pancreatic juices) where a-amylase hydrolyses glycosidic bonds from starch to oligosaccharides
2. Villi in small intestine then break down oligosaccharides into disaccharides
3. Specific enzymes (lactose, maltose and sucrose) then break down the disaccharides into monosaccharides
4. Monosaccharides are then absorbed into the cytosol of enterocytes and transported into the capillaries that empty into the venous blood and the portal vein that supplies the liver

Question 9

Where is the majority of glycogen stored?

Answer 9

In the liver.

3-7% in the liver
1-1.5% in the muscle

Question 10

What is the process for glycogen synthesis? (Glycogenesis)

Answer 10

1. Glucose reacts with ATP to produce glucose-1-phosphate and ADP
2. glucose-1-phosphate reacts with UTP (Uridine Triphosphate) to produce UDP-glucose that participates in glycogen elongation
3. Glycogenin is the primer that adds residues in a row to itself (it is both a substrate and an enzyme)
4. Glycogen synthase can then take over and adds residues to chain
5. The branching enzyme moves residues to an inner position and forms a branch
6. Synthase resumes work

Question 11

What kind of process in glycogenolysis?

Answer 11

Catabolic, hydrolysis reaction

Question 12

What is the process for glycogen breakdown? (Glycogenolysis)

Answer 12

1. Glycogen Phosphorylase breaks down glycosidic linkages (adding phosphate) until it gets 4 links away from a branch
2. Debranching enzyme carries 3 glucose residues from one branch to the end of the original
3. The same enzyme hydrolyses the linkage at the branch point.
4. This leaves a linear chain for Phosphorylase to hydrolyze.

*In the end, of the 20 (ex.) glucose residues, 19 are converted into glucose-1-phosphate and 1 in converted into glucose

Question 13

What are the 4 regulatory factors that influence the rate of glycogen breakdown i.e Glycogen Phosphorylase activity?

Answer 13

1. Increase in [Pi] - free phosphate is used by glycogen phosphorylase to produce glucose-phosphate
2. Increase in AMP:ATP ratio (activates phosphorylase b (subunit of phosphorylase))
3. Increase in adrenaline (cAMP cascade)
4. Increase in Ca2+ (activates phosphorylase kinase)

Question 14

What does +G mean? Gibbs free energy?

Answer 14

Positive Gibbs free E means that the reaction is not favored and anabolic

Question 15

What is a phosphatase?

Answer 15

Phosphatases are enzymes that catalyze the dephosphorylation of compounds by hydrolysis, in this case, the dephosphorylation and deactivation of glycogen phosphorylase or phosphorylase