Biochemistry

Question 1

List the metabolic challenges to tumour cells

Answer 1

1. Energy sources
2. Protecting against oxidative stress
3. Precursors for biosynthesis

Question 2

Describe the Warburg effect and its role in cancer cell metabolism

Answer 2

• 18F-FDG is a glucose derivative that is radiolabelled and used as a tracer and taken up by glucose utilising cells
  
  • Because of Warburg effect, tumour cells exhibit high capacity to take up 18F-FDG
  • FDG cannot be further metabolised and accumulates in cells resulting in intense radiolabelling in cancer cells (inability of phosphofructo-kinase-1)
    High capacity to take up FDG relates to the metabolic adaptation of cancer cells

Question 3

Why do cancer cells exhibit enhanced glucose uptake?

Answer 3

Cancer cells over-express GLUT-1, a foetal form of glucose transformer

Question 4

Why do cancer cells exhibit enhanced glycolytic flux?

Answer 4

Glycolytic enzymes hexokinase, PFK1 and lactase dehydrogenase (LDH) are over-expressed in cancer cells

Question 5

Why do cancer cells exhibit diminished metabolic flux in TCA cycle?

Answer 5

Pyruvate dehydrogenase (PDH) activity is suppressed in cancer cells -> reduced rate of pyruvate metabolism

Question 6

What usually occurs in hypoxia?

Answer 6

ROS/superoxide production occurs -? ROS damage of nuclear and mitochondrial DNA -? damaged DNA causes activation of tumour suppressor p53 -> p53 induces cell death, DNA repair, senescence and cell cycle arrest

Question 7

How to cancer cells overcome/prevent hypoxia?

Answer 7

Glutathione (reduced) pairs with ROS and become oxidised -> reacts with NADPH to become reduced again (mopping up ROS)

Question 8

How is NADPH produced in the context of cancer cells?

Answer 8

Through the pentose phosphate pathway

Question 9

Explain the production of NADPH in the context of the PPP

Answer 9

hypoxia induces expression of glycogen synthase and glycogen phosphorylase -> hypoxic tumour cells store glycogen -> stored glycogen used to create glucose-6-phosphate -> creates NADPH for reducing glutathione

Question 10

What does the Warburg effect have to do with the PPP and hypoxia?

Answer 10

Warburg effect is the over-expression of GLUT-1 allowing for the excess storage of glucose which then allows for this glucose to be used by PPP to create NADPH

Question 11

What enzymes are involved with glycolysis?

Answer 11

Phosphoglucomutase and Hexokinase II

Question 12

What enzymes are involved with glycogen metabolism?

Answer 12

Glycogen synthase 1, glycogen phosphorylase, glycogen branching enzyme 1

Question 13

What enzyme is involved in the increased glucose uptake?

Answer 13

GLUT1 transporter

Question 14

Hypoxia induces the activation of…

Answer 14

Hypoxia inducible factor (HIF-1)

Question 15

Explain the role of glutamine metabolism in cancer cells

Answer 15

Increased expression of other enzymes to convert glutamine to form other amino acids like serine and glycine and also intermediates of TCA cycle like alpha-ketoglutarate to produce other precursors of biosynthesis of proteins and nucleic acids -> help with cancer cell proliferation

Question 16

How to cancer cells undergo metabolic adaptations to maintain their high cell proliferation rate?

Answer 16

Non-oxidative phase of PPP -> generate precursors for DNA and protein synthesis

Question 17

Explain the role of pyruvate kinase M2 in metabolic adaptation of cancer cells

Answer 17

• PKM2 has a lower activity than normal PK
• Cancer cells over-express pyruvate kinase M2 (PKM2) feeding the glycolysis cycle (going through to lactate rather than the TCA cycle)

Question 17

Explain the role of pyruvate kinase M2 in metabolic adaptation of cancer cells

Answer 17

• PKM2 has a lower activity than normal PK
• Cancer cells over-express pyruvate kinase M2 (PKM2) feeding the glycolysis cycle (going through to lactate rather than the TCA cycle)

Question 18

What are some ways metabolic liabilities can be exploited for cancer cell therapy?

Answer 18

1. dietary restrictions to limit glucose availability
2. inhibitors of glycogen phosphorylase
3. inhibitors of hexokinase
4. inhibitors/activators of PKM2

Question 19

What is GLUT

Answer 19

glucose transporter

Question 19

What is GLUT

Answer 19

glucose transporter

Question 20

What are the kinases in glycolysis and what do they do?

Answer 20

hexokinase and glucokinase - turn glucose into phosphorylate glucose by using ATP trapping in the cell

Question 21

Describe the rate limiting step in glycolysis

Answer 21

fructose 6 phosphate -> PFK1 -> fructose 1, 6-bisphosphate

Question 22

What is the process that changes the rate of glycolysis when in a fed state

Answer 22

fed state -> insulin -> increased PFK2 -> fructose 2, 6-bisphosphate -> increased PFK1 = faster glycolysis

Question 23

What is the process that changes the rate of glycolysis when in a fasting state

Answer 23

fasting state -> glucagon -> less PFK2 -> less fructose 2, 6 bisphosphate -> less PFK1 = slower glycolysis

Question 24

In an anaerobic state what happens in glycolysis after fructose 1, 6-bisphosphate is made?

Answer 24

creation of ATP and converting until pyruvate kinase created pyruvate -> lactate dehydrogenase and NADH -> lactate + NAD+ (build up of lactate causes muscle soreness and NAD keeps glycolysis going)

Question 25

In an aerobic state what happens in glycolysis after fructose 1, 6-bisphosphate is made?

Answer 25

creation of ATP and converting until pyruvate kinase created pyruvate -> moves to mitochondria -> krebs cycle = ATP

Question 26

What is gluconeogenesis?

Answer 26

When in a prolonged fasting state gluconeogenesis allows the cells to make their own glucose for energy production, it is glycolysis in reverse with a couple of extra speedbumbs that requite the use of lactate, amino acids and glycerol

Question 27

Describe the progression of type 2 diabetes

Answer 27

Type 2 diabetes is a progressive disorder - starts with insulin resistance. Can no longer bring about the effect of reducing blood sugar. Body pancreas initially secretes enough insulin to overcome glucose, no longer happens with type 2 diabetes. Insulin-resistant muscle with reduced glucose transport.

Question 28

How does being overweight contribute to risk of diabetes?

Answer 28

Overweight = larger adipocytes Pro-inflammatory state = enlarged adipocytes produce chemotaxis protein (MCP-1) Chronic inflammation = macrophages infiltrate adipose tissue in response to MCP-1 Inhibit GLUT4, cannot access energy from glucose

Question 29

Why is cholesterol important?

Answer 29

Steroid hormones are formed from cholesterol

Question 30

Describe the steps used to synthesise thyroid hormones in the thyroid gland

Answer 30

Thyroglobulin -> thyroglobulin with iodinated Tyr residues -> Thyroxine (T4), Triiodothyronine (T3)

Question 31

Describe the steps of alcohol metabolism

Answer 31

Ethanol --(Alcohol dehydrogenase)--> Acetaldehyde --(Aldehyde dehydrogenase) --> Acetate