Creatine kinase

Question 1

What cells is the artery made of?

Answer 1

Innermost single layer of cells, which are endothelial cells

Many layers of smooth muscle cells surrounding that

Question 2

How does the artery change as you age?

Answer 2

Fatty deposits between the smooth muscle cells causing them to bulge into the lumen of the artery
Calcium deposits settle - ‘hardening’ of the artery

Question 3

What causes blood to clot?

Answer 3

Exposure of blood to collagen

Question 4

What is a major function of the endothelial cells?

Answer 4

Keep the blood within the blood vessel, as if blood leaks out and comes in contact with substances outside, it causes the blood to clot

Question 5

Mr. Adamson’s lawn mower jammed, and he put a lot of effort to try to unjam it. Why did he suffer a myocardial infarction?

Answer 5

Proliferated blood vessel
Blood pressure goes up as demand for O2 to his muscles increase
Blood vessel ruptures
Blood clots
The clot blocks the artery that supplies his heart muscle with O2

Question 6

How do you prove a myocardial infarction?

Answer 6

Measure creatine kinase levels in the blood

Question 7

Why does creatine kinase probe muscle death?

Answer 7

Normally very low levels of creatine kinase in the blood
Muscle cells have a large supply of creatine kinase for substrate level phosphorylation
When the muscle cells die, the creatine kinase is released into the blood

Question 8

Why do cells die from lack of oxygen?

Answer 8

Cells are maintained by the sodium potassium pump, which pumps sodium out and pumps potassium in. There is more salt outside than inside.
This requires ATP, no oxygen supply halts oxidative phosphorylation so ATP is no longer produced
The system goes in reverse, salt moves into the cell, the osmotic potential increases
Water moves in via osmosis, eventually the cell expands and bursts

Question 9

Free energy?

Answer 9

Free energy dependent on equilibrium, substrates and products. If atp and adp are at equilibrium, there is no free energy

Question 10

What does creatine kinase do?

How is this reaction’s direction controlled?

Answer 10

Creatine phosphate + ADP —> creatine + ATP

Depending on the equilibrium, more of which substrate/product there is e.g if there is more creatine phosphate, reaction goes to the right (and vice versa)

Question 11

In what tissues is CK present in high levels and why?

Answer 11

Muscle and brain because they use large amounts of ATP

Question 12

Creatine kinase exists in which 3 dimers?

Answer 12

MM
BM
BB

Question 13

Which creatine dimer corresponds to which muscle?

Answer 13

MM - skeletal muscle
BM - cardiac muscle
BB - brain

Question 14

How can CK activity be detected?

Answer 14

Creatine and creatine phosphate are not easily detectable, so coupled assays may be used
Coupled assays are 2 or more reactions to find something detectable (i.e. the product of the first reaction is the substrate of the next, until a more easily detectable molecule is formed)

Creatine phosphate + ADP ——creatine kinase——> creatine + ATP
ATP + D-glucose ——hexokinase——> ADP + glucose-6-phosphate
Glucose-6-phosphate + NADPH ——G6P dehydrogenase——> 6PG +NADPH + H+

NADPH is detectable as it absorbs UV light

Question 15

What can be used to differentiate between the different dimers?

Answer 15

Gel electrophoresis - because all 3 dimers have similar molecular weights so they must be separated on their charges

Question 16

How does gel electrophoresis separate compounds?

Answer 16

Length of the molecule - smaller travels faster and so further
Charge of the molecule (depending on the amino acid composure)

Question 17

How are the dimers separated?

Answer 17

Based on charge as they are roughly the same size

Question 18

What are the charges on M and B?

Answer 18

M is more positive, B is more negative. So in gel electrophoresis BB travels furthest, then MB, then MM (the least)

Question 19

How can the myocardial infarction be diagnosed (using the dimers)?

Answer 19

If there is much higher levels of CK-MB present in the blood, it suggests cardiac muscle death

Question 20

Can the amount of MB be used to diagnose how large the myocardial infarction was?

Answer 20

Depends if you know all the parameters, e.g. how long it has been since the heart attack and the measurement of the creatine kinase
So generally, no
As creatine kinase is released quickly and broken down quickly by the body when present in the blood

Question 21

What are the features of other proteins that can be used measure the magnitude of the myocardial infarction?

Answer 21

Not present in the blood generally
Small proteins present in the heart muscle
Released during cell death
Not broken down quickly by the body
Amount released/ present is proportional to the magnitude of the myocardial infarction
Readily and rapidly measurable (and cheap too)

Question 22

What other markers can be used for the diagnosis of myocardial damage?

Answer 22

Lactate Dehydrogenase (LDH) - leaks out when cells are damaged
Not specific and only peaks after 6 days
Troponin - there is a specialised myocardium version - look for elevated Troponin I and Troponin T which are specific to cardiac muscle (appears after 48 hours and lasts 5 days)
Serum glutamate oxaloacetate transaminase (SGOT) - starts being released from cells, peaks as CK levels go down