Cell metabolism 2

Question 1

• Explain how the Glycerol-Phosphate Shuttle works

Answer 1

Cytosolic glycerol-3-phosphate dehydrogenase transfers electrons from NADH to DHAP → forming Glycerol-3-Phosphate

Membrane bound form of same enzyme transfers electrons to FAD, forming FADH2, also reforming DHAP from glycerol 3 phosphate

ekectrons are passed to co enzyme Q

Question 2

• What is the purpose of the Glycerol Phosphate Shuttle

- Where in the body is the Glycerol-Phosphate Shuttle, used?

Answer 2

To carry electrons from NADH across to matrix

Skeletal Muscle

Brain

Question 3

• Explain Transamination with an example

Answer 3

Allows production of non-essential amino acids

Alanine + alpha-ketoglutarate → pyruvate + glutamate

when an amine group is transferred from one amino acid to a keto acid forming a new pair of amino and keto acids

Question 4

• Where in the body is the Malate-Aspartate Shuttle used?

Answer 4

Liver

Kidney

Heart

Question 5

Outline the processes in the Malate-Aspartate Shuttle

Answer 5

NADH passed electron to Oxaloacetate (OAA), forming malate and NAD+
malate enters matrix by malate- alpha-ketoglutarate antiporter
malate loses an electron to NAD+, forming NADH and OAA
OAA reacts with glutamate to form alpha-keto-glutarate and aspartate
aspartate leaves matrix via the glutamate aspartate transporter
aspartate reacts with alpha keto glutarate to reform OAA and glutamate
the cycle repeats

Question 6

• Explain how 38 ATP molecules are formed from glucose metabolism

Answer 6

Glycolysis → 2 ATP + 2 NADH → 8 ATP

Pyruvate Conversion → 2 NADH → 6 ATP

6 NADH → 18 ATP

2 FADH2 → 4 ATP

2 GTP → 2 ATP

Question 7

• What is the purpose of Beta-Oxidation and where does it occur?

Answer 7

To produce Acetyl CoA

Mitochondria

Question 8

• Outline the reaction converting Fatty Acids into Acyl CoA

Answer 8

Occurs outside of mitochondrial membrane

Fatty Acid + ATP + HS-CoA → Acyl CoA + AMP (adenosine monophosphate) + PPi

Catalysed by Acyl CoA Synthase

Question 9

• Why is AMP produced?

Answer 9

It is a high energy consuming reaction, so 2 high energy bonds are broken to go from ATP to ADP to synthesise the Acyl CoA

Question 10

• what is the Carnitine Shuttle for?

- Outline the reactions in the Carnitine Shuttle

Answer 10

transport Acyl CoA species into the matrix for beta oxidation

Acyl from Acyl CoA added to the Carnitine to form Acyl Carnitine and CoA, catalysed by Carnitine acyltransferase I

Acyl Carnitine transported into matrix via Translocase

Acyl Carnitine in matrix loses its Acyl group to a CoA to reform Acyl CoA in matrix and Carnitine, via carnitine acyl transferase 2

Carnitine exported into cytoplasm via Translocase

cycle repeats

Question 11

• What are the symptoms of Primary Carnitine Deficiency?

- What is its inheritance pattern

Answer 11

Encephalopathies (damage or disease to brain)

Cardiomyopathies, muscle weakness and hypoglycaemia

Autosomal recessive

Question 12

• When do the symptoms of Primary Carnitine Deficiency usually occur?
• What does a mutation in the gene SLC22A5 do?

Answer 12

During infancy or early childhood

Encodes a carnitine transporter resulting in reduced ability of cells to take up carnitine

Question 13

• what are the reactants for the complete Beta Oxidation of 16C-Palmitoyl CoA
• what are the products from the complete Beta Oxidation of 16C-Palmitoyl CoA?

Answer 13

palmitoyl CoA, 7 FAD, 7NAD+, 7H20, 7 CoA

8 Acetyl CoA, 7 FADH2, 7 NADH

Question 14

• What occurs when fat breakdown predominates over glucose metabolism and why does this accur ?
• what are the ketone bodies?

Answer 14

Ketone bodies are formed, because beta oxidation can’t continue anymore as oxaloacetate is needed, but it is being used to remake glucose in gluconeogenesis (as glucose is low)

during fasting acetyl CoA forms acetoacetate, D-3 hydroxybutyrate and acetone

Question 15

• What is Beta Oxidation?

- What is the beta oxidation equation?

Answer 15

process of producing acetyl CoA from fatty acids
first it is converted to a acyl CoA species
then it undergoes a series of reactions in the matrix including oxidation, hydration, thiolysis

Palmitoyl CoA + 7 FAD + 7 NAD + 7 CoA + 7 H2O → 8 Acetyl CoA +7 FADH2 + 7 NADH

Question 16

• What are the three differences between Beta-Oxidation of Fatty Acids and the synthesis of Fatty Acids?

Answer 16

Carrier Proteins: CoA vs ACP

Reducing Power: NAD+ vs NADPH/FAD

Locations: Mitochondrial Matrix vs Cytoplasm

Question 17

• What is the overall equation for lipogenesis?

Answer 17

Acetyl CoA (C2) + 7 Malonyl CoA (C3) + 14 NADPH + 14 H+ → Palmitate (C16) + 7 CO2 + 6H20 + 8 CoA-SH + 14 NADP+

Question 18

which two enzymes does fatty acid synthesis use?

process of lipogenesis?

Answer 18

acetyl co A carboxylase and fatty acid synthase

fatty acids formed sequentially by darcarboxylation condensation reactions involving malonyl CoA and Acetyl CoA
following each round of elongation, fatty acid undergoes reduction and dehydration by sequential action of
- ketoreductase
- dehydratase
- enol reductase
the gorwing fatty acyl chain is linked to an acyl carrier protein

Question 19

what are the steps to the krebs cycle?

Answer 19

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citrate (6 C)
isocitrate (6 C)
Alpha- Ketoglutarate (5)
succinyl Co A (4)
succinate
fumerate
malate
oxaloacetate
then acetyl added to react with OAA and cycle starts again

Question 20

where are the NADH, CO2, FADH2, and GTP formed

Answer 20

NADH and CO2 between isocitrate and alpha keto glutarate

NADH between alpha keto glutarate and succinyl CoA

GTP between succinyl CoA and Succinate

FADH2 between succinate and fumerate

NADH between malate and Oxaloacetate

Question 21

purposes of amino acid degradation?

Answer 21

remove amine group to be excreted as urea

carbon skeleton either for gluconeogenesis or to feed into TCA cycle

Question 22

• How many net molecules of ATP are generated from metabolism of Palmitate?

Answer 22

7 FADH2 = 7 x 2 =14

7 NADH = 7 x 3 = 21

8 Acetyl CoA = 12 x 8 = 96 (Because it enters the Kreb’s Cycle and undergoes oxidative phosphorylation)

2 Phosphate bonds are hydrolysed at start of beta oxidation to produce Acyl CoA = 2

14 + 21 + 96 - 2 = 129

Question 23

How are ketone bodies synthesised

Answer 23

2 acetyl Co A to acetoacetyl co A via beta thiolase
the HMG - CoA synthase to form HMG coA
forms acetoacetate via HMG CoA lyase

forms either:

D-3 hydroxy butyrate via d-3-hydroxybutyrate dehydrogenase, forming an NAD+ from NADH and H+

or, acetone via acetoacetate decarboxylase

Question 24

• What is the Warburg Effect?

Answer 24

Mutations in genes of Fumerase, Succinate dehydrogenase Isocitrate Dehydrogenase, decreases Kreb’s Cycle activity which enhances anaerobic glycolysis

Preferential generation of lactate from glucose even in increased O2 availability

occurs in cancers

Question 25

What is Acyl CoA dehydrogenase

what are the different lengths

Answer 25

catalyse the initial step in each cycle of beta oxidation

short chain - 6c
medium chain- 6-12
long chain 3 hydroxy acyl CoA dehydrogenase- c13-c21
very long chain- C22

Question 26

what is MCADD

what must someone do if they have been diagnosed

Answer 26

medium chain acyl CoA dehydrogenase deficiency
autosomal recessive

never go without food for more than 10-12 hours
high carb diet
people with illness resulting in appetite loss or severe vomiting may need IV glucose
to make sure body is not dependant on fatty acids