Session 1 Flashcards

Question

How is superoxide produced?

Answer 1

Produced by adding Superoxide electron to molecular oxygen. Also Important source of other ROS

Answer 2

Not a free radical but can | react e.g. with Fe2+ to produce free radicals. Readily diffusible.

Answer 3

It’s the most reactive and so reacts with anything.

Answer 4

Oxygen molecule gains an electron to become superoxide. Superoxide gains two H+ and an electron to become hydrogen peroxide. Hydrogen peroxide gains an electron and a H+ and the. Splits to form a water molecule and a hydroxyl radical.

Answer 5

Two main types of damage: • ROS reacts with base Modified base can lead to mispairing and mutation • ROS reacts with sugar (ribose or deoxyribose) Can cause strand break and mutation on repair

Answer 6

1. ROS reacts with DNA 2. DNA damage 3. Failure in repair can lead to mutation 4. Mutation can lead to cancer

Answer 7

The amount of 8-oxo-dG present in cells can be used as measurement of oxidative damage. When damaged by ROS deoxyguanosine becomes 8-oxo-dG.

Answer 8

Two ways: By damaging backbone: 1. ROS reacts with protein. 2. If it reacts with backbone it can cause fragmentation. 3. This leads to protein degradation By damaging side chain: 1. ROS reacts with protein 2. If it reacts with a side chain it could result in a modified amino acid e.g making a ring opened species or carbonyl. 3. This causes change in the protein’s structure. This can result in protein degradation, loss of function or gain of function.

Answer 9

* Play important role in folding and stability of some proteins (usually secreted proteins or in extracellular domains of membrane proteins) * Formed between thiol groups of cysteine residues * Inappropriate disulphide bond formation can occur if ROS takes electrons from cysteines causing misfolding, crosslinking and disruption of function (e.g. enzyme)

Answer 10

• Free radical (e.g. *OH) extracts hydrogen atom from a polyunsaturated fatty acid in membrane lipid. • Lipid radical formed which can react with oxygen to form a lipid peroxyl radical. • Chain reaction formed as lipid peroxyl radical extracts hydrogen form nearby fatty acid • Hydrophobic environment of bilayer disrupted and membrane integrity fails

Answer 11

``` Endogenous: • Electron transport chain • Nitric oxide synthases • NADPH oxidases Exogenous: • Radiation Cosmic rays UV light X-rays • Pollutants • Drugs Primaquine (anti-malarial) • Toxins Paraquat (herbicide) ```

Answer 12

* NADH and FADH2 supply electrons (e−) from metabolic substrates * electrons pass through ETC and reduce oxygen to form H2O at Complex IV * Occasionally electrons can accidently escape chain and react with dissolved O2 to form superoxide.

Answer 13

* iNOS: Inducible nitric oxide synthase. Produces high NO concentrations in phagocytes for direct toxic effect. * eNOS: Endothelial nitric oxide synthase (Signalling) * nNOS: Neuronal nitric oxide synthase (Signalling)

Answer 14

It’s an enzyme that produces nitric oxide. It converts arginine to citrulline and nitric oxide.

Answer 15

Signalling molecule • Vasodilation • Neurotransmission • S-Nitrosylation Use in phagocytes for direct toxic effect.

Answer 16

It has toxic effects at high levels

Answer 17

NADPH Oxidase converts NADPH to NADP+ to convert an oxygen molecule into superoxide. Superoxide can combine with nitric oxide to make peroxynitrite or be made into hydrogen peroxide which can be converted into hypochlorite; both of which can be used to kill bacteria.

Answer 18

Genetic defect in NADPH oxidase complex causes enhanced susceptibility to bacterial infections • Atypical infections • Pneumonia • Abscesses • Impetigo • Cellulitis

Answer 19

Superoxide dismutase (SOD) • Converts superoxide to H2O2 and oxygen • Primary defence because superoxide is strong initiator of chain reactions Catalase • Converts H2O2 to water and oxygen • Widespread enzyme. Important in immune cells to protect against oxidative burst.

Answer 20

• Tripeptide (glycine, cysteine and glutamate) synthesised by body to protect against oxidative damage • Thiol group of Cys donates e− to ROS. GSH (reduced form)then reacts with another GSH to form disulphide (GSSG). • Glutathione peroxidase requires Selenium • GSSG reduced back to GSH by glutathione reductase which catalyses the transfer of electrons from NADPH to disulphide bond phosphate pathway • NADPH from pentose phosphate pathway is therefore essential for protection against free radical

Answer 21

Glutathione reductase converts NADPH, from the pentose phosphate pathway, to NADP+ in order to convert one GSSG to two GSH(reduced form).

Answer 22

- Starts from Glucose-6-phosphate - It’s an important source of NADPH required for: Reducing power of biosynthesis Maintenance of GSH levels Detoxification reactions - Produces ribose-5-phosphate required for synthesis of nucleotides, RNA and DNA. - No ATP synthesised. CO2 produced. - The rate limiting enzyme is glucose-6-phosphate dehydrogenase.

Answer 23

Free radical scavengers reduce free radical damage by donating hydrogen atom (and its electron) to free radicals in a nonenzymatic reaction. Vitamin E • Lipid soluble antioxidant Vitamin E • Important for protection against lipid peroxidation. Vitamin C • Water soluble antioxidant • Important role in regenerating reduced form of Vitamin E ``` Others: Carotenoids. Uric acid. Flavonoids. Melatonin. ```

Answer 24

``` When there is a defect in one of three enzymes involved in the metabolism of galactose (galactokinase, uridyl transferase or UDP - galactose epimerase) so galactose builds up. This results in galactose concentration being higher than normal in the blood. Symptoms: Hepatomegaly + Cirrhosis Renal failure Vomiting Seizure + Brain damage Cataracts Hypoglycaemia ```

Answer 25

Aldose reductase converts galactose to galactitiol using NADPH. This consumes excess NADPH which could be used to reform GSH but without it this cant happen reducing the body’s defence against ROS damage.

Answer 26

High concentration of galactitol causes osmotic pressure combined with ROS damage resulting in crystalline protein in the lens of the eye being denatured

Answer 27

Glucose-6-phosphate dehydrogenase converts glucose 6 phosphate to 6-phosphogluconate and when it does this is reduces NADP to NADPH. NADPH is required for reduction of oxidised glutathione (GSSG) back to reduced glutathione (GSH). If there is a lack of G6PDH then there is less NADPH and so less GSH resulting in oxidative stress.

Answer 28

``` Protein damage due to ROS causes aggregates of cross linked haemoglobin in RBCs. Dark staining within RBC resulting from precipitated haemoglobin. • Bind to cell membrane altering rigidity • Increased mechanical stress when cells squeeze through small capillaries • Spleen removes bound Heinz bodies resulting in “blister cells” • Clinical sign of G6PDH deficiency. This results in haemolysis of the RBCs. ```

Answer 29

Paracetamol at prescribed dosage is safely converted into glucuronide and sulphate. When there is too much paracetamol this pathway becomes saturated and the paracetamol is instead converted into NAPQI which is toxic. Glutathione then deals with the the NAPQI but is used up, depleting the cells store of glutathione. Acetylcysteine works as an antidote by replenishing glutathione levels.

Answer 30

``` Amino acids Proteins Purine and pyrimidines (DNA and RNA) Smaller amounts of others: • Porphyrins (haem) • Creatine phosphate • Neurotransmitters (e.g. dopamine) • Some hormones (e.g. adrenaline) ```

Answer 31

``` • Breakdown product of creatine & creatine phosphate in muscle • Usually produced at constant rate depending on muscle mass (unless muscle is wasting) • Filtered via kidneys into urine • Creatinine urine excretion over 24h proportional to muscle mass. • Provides estimate of muscle mass • Also commonly used as indicator of renal function (raised level on damage to nephrons) ```

Answer 32

In 70kg male: 2kg nitrogen stored as body proteins 16g nitrogen in an amino acid pool which can be used to make body proteins or other N-containing compounds. These their N-containing compounds make up about 60g of nitrogen. Nitrogen can be lost through waste products such as faeces and urine which we lose about 14g nitrogen and through loss of skin hair and nails about 2g of nitrogen. We gain nitrogen through dietary proteins which is roughly 16g a day.

Answer 33

N equilibrium Intake = output No change in total body protein. Normal state in adult.

Answer 34

Positive N balance Increase in total body protein. Normal state in growth & pregnancy or in adult recovering from malnutrition.

Answer 35

``` Negative N balance Intake < output Net loss of body protein. Never normal. Causes include trauma, infection, or malnutrition. ```

Answer 36

In your body there’s is a pool of free amino acids. These can come from new amino acid synthesis, dietary protein digestion or proteolysis of cellular proteins. These can be used to synthesise more proteins or sent to the liver. At the liver they are broken down and the amino group is converted to urea to be excreted in urine as we don’t want it to form ammonia which is very toxic to cells. Depending on the carbon skeleton left over the amino acid can be divided into glucogenic and ketogenic amino acids. The glucogenic amino acids can be used for gluconeogenesis and the ketogenic amino acids can be used for ketone bodies. Both of which are used for energy.

Answer 37

Glucogenic: Alanine Ketogenic: Lysine Both: Tyrosine

Answer 38

Occurs during extreme stress (starvation) Occurs under hormonal control Insulin and growth hormone increase protein synthesis and decrease protein degradation whereas glucocorticoids (e.g cholesterol) decrease protein synthesis and increases protein degradation.

Answer 39

Excessive breakdown of protein can occur in Cushing’s syndrome (excess cortisol). Weakens skin structure leading to striae formation.

Answer 40

20 amino acids | 9 essential amino acids

Answer 41

``` If Isoleucine Learned Lysine This Threonine Huge Histidine List. Leucine May. Methionine Prove Phenylalanine Truly Tryptophan Valuable Valine ```

Answer 42

Children and pregnant women have a high rate of Presteigne synthesis so also require dietary arginine, tyrosine and cysteine

Answer 43

• Protein of animal origin considered “High quality” (Contain all essential amino acids) • Proteins of plant origin generally considered “lower quality” since most are deficient in one or more essential amino acids. • Therefore essential that vegetarian diet obtains protein from a wide variety of plant sources

Answer 44

* Intermediates of glycolysis (C3) * Pentose phosphate pathway (C4 & C5) * Krebs cycle (C4 & C5)

Answer 45

``` Thyroid hormone - Tyrosine Hydrogen sulphide - Cysteine Serotonin - Tryptophan Histamine - Histidine GABA - Glutamate Nitric Oxide - Arginine Sphingosine - Serine Creatine - Gycine ```

Answer 46

Transamination | Deamination

Answer 47

An aminotransferase enzyme is used to move the amine group from the amino acid to a keto acid. The new amino acid formed is more easily able to enter the urea cycle. • Most aminotransferase enzymes use α-ketoglutarate to funnel the amino group to glutamate. • Exception to rule is aspartate aminotransferase which uses oxaloacetate to funnel amino group to aspartate • All aminotransferases require the coenzyme pyridoxal phosphate which is a derivative of vitamin B6

Answer 48

``` Alanine aminotransferase (ALT) Converts alanine to glutamate ``` ``` Aspartate aminotransferase (AST) Converts glutamate to aspartate ```

Answer 49

``` As part of a over function test. Levels particularly high in conditions that cause extensive cellular necrosis such as: • Viral hepatitis • Autoimmune Liver Diseases • Toxic injury ```

Answer 50

• Liberates amino group as free ammonia • Mainly occurs in liver & kidney • Keto acids can be utilised for energy • Also important in deamination of dietary D-amino acids (found in plants and microorganisms)

Answer 51

Several enzymes can deaminate amino acids • Amino acid oxidases • Glutaminase • Glutamate dehydrogenase

Answer 52

* High nitrogen content * Non-toxic * Extremely water soluble * Chemically inert in humans (bacteria can break it down to release NH 3) * Most urea is excreted in urine via the kidneys * Also performs useful osmotic role in kidney tubules

Answer 53

* Occurs in liver and involves 5 enzymes * Amount of urea cycle enzymes normally related to need to dispose of ammonia * High protein diet induces enzyme levels * Low protein diet or starvation represses levels * Cycle is inducible but not regulated

Answer 54

Urea cycle down regulated due to malnutrition. So when when lots of protein is digested the urea cycle doesn’t have enough enzymes working the urea cycle so toxic ammonia builds up.

Answer 55

Autosomal recessive genetic orders caused by deficiency in one of the enzymes in the urea cycle. Mutations cause a partial loss of enzyme function. Leads to: • hyperammonaemia • accumulation/excretion of urea cycle intermediates

Answer 56

``` Symptoms • Vomiting • Lethargy • Irritability • Mental retardation • Seizures • Coma ```

Answer 57

* nature of defect | * amount of protein eaten

Answer 58

• Severe urea cycle disorders show symptoms within 1 day after birth. If untreated, child will die. • Mild urea cycle enzyme deficiencies may not show symptoms until early childhood

Answer 59

* Low protein diet | * Replace amino acids in diet with keto acids

Answer 60

• Readily diffusible and extremely toxic to brain • Blood level needs to be kept low (25-40 µmol/L) Several potential toxic effects: • Interference with amino acid transport and protein synthesis • Disruption of cerebral blood flow • pH effects (alkaline) • Interference with metabolism of excitatory amino acid neurotransmitters (e.g. glutamate and aspartate) • Alteration of the blood–brain barrier • Interference with TCA cycle (reacts with α-ketoglutarate to form glutamate)

Answer 61

Glutamine • Ammonia combined with glutamate to form glutamine • Glutamine transported in blood to liver or kidneys where it is cleaved by glutaminase to reform glutamate and ammonia. • In liver ammonia fed into urea cycle. In kidney excreted directly in urine Alanine • Amine groups transferred to glutamate by transamination • Pyruvate then transaminated by glutamate to form alanine • Alanine transported in blood to liver where it is converted back to pyruvate by transamination. • Amino group fed via glutamate into urea cycle for disposal as urea whereas pyruvate is used to synthesise glucose which can be fed back to tissues

Answer 62

Heel prick test • Sickle cell disease • Cystic fibrosis • Congenital hypothyroidism ``` Inborn errors of metabolism • Phenylketonuria (PKU) • Maple syrup urine disease • Isovaleric acidaemia (IVA) • Glutaric aciduria • Homocystinuria ```

Answer 63

``` Most common inborn error of amino acid metabolism Deficiency in phenylalanine hydroxylase Autosomal recessive. Affected gene is on chromosome 12 Accumulation of phenylalanine in tissue, plasma & urine Phenylketones in urine Musty smell Symptoms: • Severe intellectual disability • Developmental delay • Microcephaly (small head) • Seizures • Hypopigmentation ``` Treatment • Strictly controlled low phenylalanine diet enriched with tyrosine • Avoid artificial sweeteners (contain phenylalanine) • Avoid high protein foods such as meat, milk, and eggs

Answer 64

* Noradrenaline * Adrenaline * Dopamine * Melanin * Thyroid hormone * Protein synthesis This is due to a lack of tyrosine, as the phenylalanine’s hydroxylase cant convert phenylalanine to tyrosine. Instead it’s converted to phenylpyruvate which is made into phenylacetate and phenyllactate (these are phenylketones which accumulate in blood and urine)

Answer 65

``` • Problem breaking down methionine • Excess homocystine (oxidised form of homocysteine) excreted in urine • Autosomal recessive disorders. • Incidence ~1 in 344,000 Treatment • Defect in cystathionine β-synthase • Affects connective tissue, muscles, CNS, CVS Treatment: • Low-methionine diet • Avoid milk, meat, fish, cheese, eggs • Nuts, and peanut butter also contain methionine • Cysteine, Vit B6, Betaine, B12 & Folate supplement ```

Answer 66

Normally methionine is converted to homocysteine and then that is converted to cystathionine by cystathionine β-synthase, which will go on to become cysteine. Homocysteine can go back to methionine and this is promoted by beating, vit B12 and folate. cystathionine β-synthase requires an active for of VitB6 as a co-factor. In homocystinuria there’s a defect in the cystathionine β-synthase so homocysteine is not sufficiently converted to cystathionine causing methionine and homocysteine to accumulate which is what causes disease symptoms.

Session 1 Flashcards

(90 cards)