Key Molecules - MEH

Question 1

NADPH

Answer 1

Coenzyme; the reduced form on NAD+, used in anabolic reactions eg glycolysis.

Question 2

NADP+

Answer 2

Coenzyme; the oxidised form of NADPH, used in anabolic reactions eg glycolysis.

Question 3

NADH

Answer 3

Coenzyme; the reduced form of NAD+, used in catabolic reactions.

Question 4

NAD+

Answer 4

Coenzyme; the oxidised form of NADH, used in catabolic reactions.

Question 5

Glucose 6-phosphate

Answer 5

Made by phosphorylating glucose; the first intermediate in glycolysis. Links to glycolysis, PPP, glycogen synthesis.

Question 6

Ribose 5-phosphate

Answer 6

Produced by PPP; an important intermediate. Used to make DNA, RNA, nucleotides and coenzymes.

Question 7

Galactose 1-phosphate

Answer 7

Intermediate produced when converting galactose to glucose. In galactosemia, accumulation of this affects the liver, kidney and brain.

Question 8

Galactitol

Answer 8

A sugar alcohol caused by excess galactose. In galactosemia, galactose enters other pathways and forms galactitol. This causes cataracts due to lens swelling. It also depletes cells of NADPH, which helps to prevent oxidative damage, resulting in lens proteins denaturing.

Question 9

Galactokinase

Answer 9

Enzyme which breaks down

Question 10

Aspartame transaminase (AST)

Answer 10

A transamination enzyme; catalyses aspartate and alpha- ketoglutarate to oxaloacetate and glutamate. AST levels measured as part of liver function test as it is a marker for liver damage/disease.

Question 11

Alanine aminotransferase (ALT)

Answer 11

A transamination enzyme; catalyses alanine and alpha- ketoglutarate to pyruvate and glutamate. ALT levels measured as part of liver function test as it is a marker for liver damage/disease.

Question 12

Pyruvate dehydrogenase

Answer 12

Enzyme complex (5 enzymes) involved in regulation of entry of pyruvate into the TCA cycle. It is sensitive to vitamin B1 deficiency, as this provides various necessary coenzymes.

pyruvate + CoA + NAD* —> acetyl CoA + NADH + H*

This reaction is irreversible so is a key regulatory step. Enzyme activity regulated by substrate and product concentrations.

Question 13

ATP synthase

Answer 13

Enzyme embedded in inner mitochondrial membrane that produces ATP from ADP and Pi using energy from when H+ ions pass through into matrix down the electrochemical gradient.

Question 14

FAD

Answer 14

Oxidised form of FADH2; a hydrogen carrier molecule. Used/made in catabolic reactions eg ATP production.

Question 15

FADH2

Answer 15

Reduced form of FAD; a hydrogen carrier molecule. Used/made in catabolic reactions eg ATP production.

Question 16

ATP

Answer 16

Energy produced from bond hydrolysis; it is an energy carrier.
ATP —> ADP + Pi (+ energy)

Question 17

ADP and AMP

Question 18

Creatine phosphate

Answer 18

Catalyses creatine + ATP —> creatine phosphate + ADP.

Question 19

Creatine

Question 20

Creatine phosphate

Question 21

Creatinine

Answer 21

Breakdown product of both creatine and creatine phosphate. Usually produced at a constant rate unless muscle is wasting. Excreted via kidneys.

Levels of serum creatinine decrease when muscle is wasting. Can be used to assess kidney function. The conc. in urine can be used as a marker of urine dilution or true urine loss of substances eg pregnancy hormones.

Question 22

alpha- keto acids

Answer 22

The deaminated form of amino acids.

Question 23

Lactase
Sucrose
Pancreatic amylase
Isomaltase

Answer 23

Breaks down lactose.
Breaks down sucrose.
Breaks down amylose in the pancreas.
Breaks down isomaltose.

Question 24

Hexokinase (glucokinase in liver)

Question 25

Phosphofructokinase-1

Answer 25

Key control enzyme involved in glycolysis.

Question 26

Pyruvate kinase

Answer 26

Last enzyme in glycolysis; produces pyruvate from intermediate, producing ATP.

Question 27

CAT 1 and 2

Answer 27

Carnitine acyltransferases - CAT 1 catalyses carnitine + coA —> acyl carnitine + coA (in the cytoplasm)

CAT 2 catalyses acyl carnitine + coA —> carnitine + coA (in the mitochondria)

Question 28

Fatty acid coA synthase

Answer 28

Catalyses the activation of fatty acids by linking it to coA. An active process.

FA + coA + ATP —> fatty acyl-coA + 2Pi + AMP

Question 29

alpha- ketoglutarate dehydrogenase

Answer 29

In TCA cycle, inhibited by NADH.

Question 30

Isocitrate dehydrogenase

Answer 30

In TCA cycle, inhibited by NADH.

Question 31

Alcohol dehydrogenase

Answer 31

Oxidises alcohol to acetaldehyde.

Question 32

Aldehyde dehydrogenase

Answer 32

Oxidises acetaldehyde to acetate (this is then converted to acetyl coA which feeds into TCA cycle).

Question 33

Acetaldehyde

Answer 33

Toxic metabolite made during alcohol metabolism, from oxidation of alcohol catalysed by alcohol dehydrogenase. Accumulation of this is responsible for hangover symptoms.

Question 34

Disulfiram (drug)

Answer 34

Causes symptoms of hangover by inhibiting aldehyde dehydrogenase, which results in accumulation of acetaldehyde. Used as part of treatment for alcohol dependence.

Question 35

O2•-

Answer 35

Superoxide (a free radical) - produced by adding an electron to molecular O2.

Question 36

H2O2

Answer 36

Hydrogen peroxide (not a free radical). Made by adding 2H+ and an electron to superoxide.

Question 37

OH•

Answer 37

Hydroxyl radical. Made by adding H+ and an electron to hydrogen peroxide.

The most reactive and damaging free radical.

Question 38

NO•

Answer 38

Nitrous oxide radical

Question 39

ONOO-

Answer 39

Peroxynitrite (not a free radical but a powerful oxidant).

Made by adding NO• and O2•-

Question 40

Glutathione
How does it work?
How is it reduced back?

Answer 40

A tripeptide synthesised by body to protect against oxidative damage. Thiol group of cysteine donates electron to ROS, reducing the ROS eg H2O2 + e —> H2O

It then reacts with another glutathione (GSH) to form disulphide (GSSG). This requires glutathione peroxidase, which requires trace element selenium.

GSSG reduced back to GSH by glutathione reductase which uses NADPH from PPP.

Therefore NADPH from PPP is essential for protection against free radical damage.

Question 41

Glutathione peroxidase

Answer 41

Catalyses formation of oxidised glutathione (GSSG) from reduced form (GSH) while reducing ROS - this protects against oxidative damage.

Question 42

Glutathione reductase

Answer 42

Catalyses reduction of GSSG (oxidised glutathione) back to GSH (reduced form) using NADPH from PPP; hence NADPH from PPP is essential for protection against oxidative damage.