Biology of two common phyto-pathogenic Oomycetes

Phytophthora infestans

Obligate parasite.

Infect potatoes and tomatoes with late blight disease.

   

Life cycle

Mycelium:  Non septate, coenocytic

Asexual reproduction

In the host tissue inter-cellular somatic hyphae colonizes and club shaped haustorias penetrate the tissues, feeding the parasite.

Sporangiophores are produced from the hyphae and emerge through stomata.

Sporangiophores produce lemon-shaped sporangia laterally and at the terminal end/apex of the sporangiphore. A Sporangium possesses a papilla on its tip.

Outcome of the sporangium depends on the temperature and humidity.

Low humidity or high temperature: Sporangium germinates by a germ tube that later results the somatic hapha.  

High humidity (when raining) or low temperature (12⁰C or below: Cytoplasm of the sporangium divides and gives rise to biflagellate Zoospores. Either by dissolution of papilla or through its opening tip, zoospores are released to outside. Zoospores directly penetrate host tissue and undergo encystment in cells. They develop into germ tubes that later result the hyphae.

Sexual reproduction

Plasmogamy occurs as oogonium punches the antheridium, going through that antheridium, oogonium grows above it. The antheridium therefore appears as a funnel at the base around the oogonium. Karyogamy and meiosis occurs respectively. Oospore is spherical and adapted to adverse environmental conditions. It results out a sporangiophore that again develops into a sporangium.

via www.apsnet.org

Plasmopara viticola

Obligate parasite.

Infect grape vines with Downy mildews.

Life Cycle

Mycelium is non septate and coenocytic.

Life cycle is much similar to Phytophthora infestans as both are oomycites.

Asexual reproduction

Somatic hyphae develops in inter cellular space host tissue penetrating with haustoria.

Hyphae give rise to sporangiophores that emerge through stomata, branching and producing sporangia at each apex of the branches.

Sporangia may either germinate directly into mycelium or produce kidney shaped, biflagellate zoospores, depending on humidity and temperature just like the Phytophthora infestans. Zoospores encyst in cells, germinate and result the somatic hyphae.

Sexual reproduction

Sexual phase is taken place at unfavorable conditions. Plasmogamy occurs by gametangial copulation as oogonium and anthredium come close together. Karyogamy results zygote that later gives the spherical oospore. Oospore divides by meiosis and undergoes germination producing a sporangium.

More about downy mildew http://fruit.cfans.umn.edu/grape/IPM/downy.pdf

Insect Abdomen: Appendages found on the abdomen

Insect abdomen is the third functional region of insect body. It is located behind the thorax and contains 6-10 segments. There are various types of appendages arise from the abdomen.

Cerci

Located close to anus.

-Blattodea: simple and jointed cerci

Via ediacaran.mech.northwestern.edu

-Orthoptera: simple and not jointed cerci

-Dermaptera: Sclerotized, forceps like cerci

Dermaptera forcep like cerci via gallurapestcontrol.com

-Thysanura: Long filamentous cerci

Long filamentous cerci of Thysanura

-Ephemeroptera larvae: Wing like cerci that helps to move forward in water.

Wing like cerci -Ephemeroptera larva

Styles

Can be seen in Cockroach and Lepisma. It is regarded as the vestige of the walking limb.

via microscopy-uk.org.uk

Median caudal filament

This is a thread like projection arising from he center of the last abdominal segment between the cerci.

Abdominal Prolegs

Can be seen in Lepidopera.

via entomology.umn.edu

Abdominal Gills

These are respiratory organs and found in nymphs of some aquatic insects.

Cornicles

These are located dorsally on the abdomen as paired secretory structures.

      

Female External Genitalia

Ovipositors are used for oviposition and it is formed by the modification of 8-9 abdominal segments. Thysanura, Orthoptera, Thysanoptera and some Hymenoptera insects contain true ovipositors.

Ovipositor places egg inside caterpillar 

Egg is released (naturecloseups.com)

-The ovipositor is modified as a poison injecting sting ( Wasps, bees..etc)

via amazingnature.us

-Hind end of the abdomen is extended to work as an ovipositor

Male genitalia

Modification of 9^th abdominal segment makes the copulatory organ of males which is consist of aedeagus and pair of lateral claspers to grasp and hold the abdomen of the female during mating. 

Special reactions/tests for Urea, Formamide, Oxamide, Salicylamide, Succinimide, Phthalimide

Urea

Urea nitrate and oxalate: Take a concentrated solution of urea, to one portion, add a few drops of con. HNO₃: the white crystalline urea nitrate (m.p. is 163°) is precipitated; to another portion, add con. Oxalic acid solution and scratch with a glass rod. White crystals of urea oxalate (m.p. is 171°) are separated. In an excess of water both salts dissolve.

Biurate reaction: Take 0-2 g of urea into a dry test-tube and heat gently above the melting point. NH₃ is evolved. After 2 minutes the liquid rapidly solidifies with the formation of biuret.

2NH₂CONH₂à NH₂CONHCONH₂ + NH₃

Dissolve the solid residue in a few ml. of warm 10% NaOH solution. Stand it to cool and add 1 drop of dil. CuSO₄ solution. A purple coloration is obtained. A pink/purple coloration is due to containing two -CONH- groups attached to one another, or to the same carbon atom or nitrogen atom. Therefore the same colouration is also given by malonamide, oxamide and by proteins/peptides.

Urease test: Urease enzymes can hydrolys Urea to Ammonium carbonate. The reaction is specific. It is used for solutions of urea to which the biuret test cannot be applied.

Action of hypobromite: Add sodium hypobromite solution to a solution of urea. The brisk effervescence is given.

NH₂CONH₂ + 3NaOBr à N₂ + CO2 + 3NaBr + 2H₂O

Formamide

Boil 1 ml of formamide in a test-tube. NH₃is evolved from it.  CO is produced, but cannot be ignited in the presence of the NH₃.

Oxamide

Biuret test: Oxamide does not need any preliminary treatment to proceed with the test. Shake 1 g of oxamide with 1ml of 10% NaOH solution. Add 1 drop of very dilute CuSO₄ solution to it and mix well. A pink coloration is produced.

Sulphuric acid test: Heat 0-3 g of Oxamide with con. H₂SO₄. CO and CO₂ are evolved.

Salicylamide

FeCl₃ coloration: Take the solid into a test tube. Add FeCl₃ solution and shake. An intense violet coloration is produced as the Phenolic groups are present.

Succinimide

Reduction: Take about 1 g of succinimide and an equal amount of Zn dust into a dry hard-glass test tube and mix well. Heat strongly. Soak a pinewood splinter in con.HCl and place it in the mouth of the tube. The splinter is turned red by the vapour of pyrrole which is formed by reduction.

Fluorescein reaction: Take about 1 g of Succinimide, 1 g of resorcinol and 2 drops of con. H₂SO₄ into a dry test tube and fuse all of it together. Cool and add water. Then add NaOH solution in excess. A green fluorescent solution is produced.

Phthalimide

Phthalein reaction: Take about 1 g of Phthalimide, 1 g of phenol and 2 drops of con. H₂SO₄ into a dry test-tube and fuse all together very gently. Let it cool and add water. Then add NaOH solution in excess. A red coloration is produced which is decolorized by acids.

Fluorescein reaction: Repeat the above test, using resorcinol instead of phenol. A green fluorescent solution is produced on the addition of NaOH solution.

Physical properties of common organic compounds (In brief)

One of the easiest ways to get an idea about an unknown organic substance is to check for its physical properties first. Physical properties are appearance, state, odour, colour, solubility in water etc. Below are some general physical properties of common organic substances.

Odour

Fruity odour: Esters, ethers.

Odour of almonds: Benzaldehyde, Nitrobenzene, Benzonitrile,

Pungent odour: Pyridine, Formic acid, Acetic acid, Benzoyl chloride, Benzyl chloride, Acetyl chloride.

Many phenols give a unique Phenolic odour. Also some derivatives of salicylic acid such as Salicylaldehyde.

Colour

Orange: Ortho-Nitro-aniline, Alizarin.

Yellow:  Quinones, m-nitroaniline, o-nitrophenol, and many other nitro-compounds. Also Iodoform.

Red: i,2-Naphthoquinone.

Blue: Commonly Copper salts.

Solubility in water

Soluble in cold water: Lower aliphatic alcohols, lower aliphatic aldehydes & ketones, lower aliphatic nitriles, lower aliphatic acid chlorides, aliphatic amines, pyridine, salts of amines, glycine, some phenols, aliphatic acids, sulphonic acids, ammonium salts and alkali salts of all acids, methyl esters of certain acids such as  formic, oxalic, succinic and tartaric. Also some aliphatic amides and imides, such as succinimide.

Almost insoluble in cold water: Higher ketones, most esters, ethers, higher alcohols, higher phenols, Benzyl alcohol, metaformaldehyde, Aromatic aldehydes, aromatic acids, aromatic amides, aromatic imides, aromatic amines, aromatic nitriles, aromatic acid anhydrides, aromatic acid chlorides, sulphonamides, sulphonyl chlorides, starch, anilides, uric acid, hydrocarbons.

Hydrolysed with water: Acids, esters can hydrolyse easily. Acid anhydrides, acid chlorides, salts of amines and nitrophenols.

Using  litmus-paper on a solution

Weakly acidic: Phenols. Except for nitrated phenols, phenols do not liberate CO₂ from Na₂CO₃ solution.

Weakly alkaline: Alkali salts of some weak acids and pyridine.

Polymerase Chain Reaction ( PCR )

This is a method to produce very large numbers of copies of specific DNA sequences without cloning. Therefore PCR can amplify specific sequences or add sequences such as  endonuclease  recognition  sequences as primers to cloned DNA.

PCR consists of 5 main components.

-Target DNA

-Single stranded Oligonucleotides (primers)

-d NTPs (dATP, dCTP, dTTP, dGTP)

-Taq DNA polymerase

-Termocycler

There are three main steps in PCR.

Step1:  Denaturation. The mixture of excess primer and DNA fragment is heated to about 95° C causing the double strands of target DNA to be denatured into single strands.

Step 2: Annealing of Primers. The temperature is dropped down between about 35⁰- 65°C

As the temperature decreases the single strands of DNA reassociate into double strands. Large excess of primer allows two primers anneal or bind to their complementary sequences on the target DNA leaving the rest of the fragment single-stranded.

Step 3: Primer Extension. The temperature is raised to 70⁰- 75°C Taq  polymerase is added. Taq polymerase extends the primer into a complementary copy of the entire single-stranded fragment, in the 5’-3’ direction.  As both the DNA strands are replicated, two copies of the original fragment are gained.

This process is repeated many times. At each time, the number of DNA copies doubles. This is continued until enough copies are gained for the analysis. 

Differences between physisorption and chemisorption

Different kinds of bacteriophages (phages)

M13

Filamentous.

About 870nm in length and 6nm in width.

Consists of single stranded DND (ssDNA).

Three kinds of capsomeres build the capside.

Infects E. coli by adsorbing to the cell and entering through F pilli. Therefore only infect F⁺ and HFr cells. Also male specific.

Does not kill the host. Particles are released by budding, therefore when the particles are released, the host cell is alive.

An efficient vector in gene cloning as it can hold longer pieces of foreign DNA.

T phage

Structure is composed of icosahedral head, double stranded DNA and a tail.

Infects E.coli

 Main types of T phages are T2, T4 and T12.

In the infection linear DNA of the phage is released to the host cell and becomes circular by replicating that later produces a long DNA chain known as ‘Concatamen’. This coils into the phage’s head by headfull mechanism while packaging.

Infection kills the host cell as the new particles are released outside by bursting the host cell.

Lambda (λ)

Composed of head and tail.

Head is consisting of double stranded linear DNA.

At both 5’ ends of the DNA strand, 12 complementary base pair, single stranded segments are present. These two ends are known as “cos ends”.

Because of the cos ends, phage chromosome circularizes before replication. Concatamen is produced during the replication and during the packaging, Terminase enzyme cuts off the cos ends.

Host cell is E.coli.

MS2

Contains the smallest known genome.

Super coiled single stranded DNA.

Infect only through sex pilli. Therefore male specific.

Infect E.coli.

Phi×174(ΦX174)

Contains a single stranded circular DNA.

After adsorption, synthesizes the complementary strand and becomes double stranded.

Use as a positive control in DNA sequencing.

G4

Structurally similar to ΦX174 phage.

Can infect susceptible E.coli cells. 

Serotonin the neurotransmitter

Serotonin i.e. 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter that is said to be helping to relay signals from one area of the brain to another. However its primary functions are found in gastrointestinal tract as 90% of total serotonin is located in the enterochromaffin cells in the gut. 

Serotonin is made via a unique biochemical conversion process that begins with Tryptophan. Tryptophan is a building block to proteins. In the synthesis of serotonin, Tryptophan hydroxylase the enzyme combines with tryptophan to form 5-hydroxytryptophan metabolite that later converts to Serotonin.

Via wikipedia.org

As mentioned earlier serotonin helps to distribute messages across the brain. Brain cells related to mood, appetite, sleep, memory, learning, temperature regulation, sexual desire and some social behaviour are influenced either directly or indirectly by serotonin due to the widespread distribution in the brain. 

It can also affect the functioning of the cardiovascular system, muscles, and various elements in the endocrine system.

When it comes to mental health, it is widely believed that a serotonin deficiency plays a role in depression but there is no way to measure its levels in the living brain. Therefore, there have not been any studies proving that brain levels of this or any neurotransmitter are in short supply when depression or any mental illness develops. People who suffer from depression shows lower serotonin levels in blood levels but still it is not revealed that whether the blood levels reflect the brain's level of serotonin.

Antidepressant medications such as SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors) that work on serotonin levels are believed to lower the symptoms of depression, but their exact function is not fully understood.

Recent studies show that when the Mycobacterium vaccae, which occurs naturally in soil and is often breathed in when spending much time nature, is injected into mice, it stimulates neuron growth and causes serotonin levels in blood to increase. So that the bacteria could have antidepressant benefits but it is not yet revealed whether it has an effect on human.

Simple facts about Betalain

Betalains are alkaloid pigments which are found in some families of plants belonging to the order Caryophyllales, but in no other plants.

They are named after the Beet family of plants (Beta).

Betalains are not found in plants containing anthocyanin pigments. Structurally they are unrelated. Unlike anthocyanins, they are not pH indicators as their colour is stable over a wide range of pH.  They are oxidised over time going brown in colour. This can be prevented by 0.1% ascorbic acid.

They have also been found in some fungi too e.g. Fly Agaric (mushroom)

Betalains can be divided into two types as betacyanins and betaxanthins; based upon their molecular structure.

Betacyanins

Usually appear red to red violet in colour (absorbance in 535-550nm)

Betaxanthins

Usually appear yellow in colour (absorbance in 475-480nm)

Betalains are found in the vacuole and they are water-soluble.

Also they cause colour in both flowers, fruits and sometimes vegetative organs



Beetroot contains 2 Betacyanins. Thay are Betanin and a derivative.

Not much is known about the role of betalains. Commercially they are sometimes used as food colourants. As a food dye it’s cheap and no all allergic side effects are figured out yet.

Basic structure of betalain

Use of colorimeter for the determination of the concentration of a solution

Absorbance is important in determining concentration of a substance in a sample through colorimeter analysis. Colorimeter measures the intensity of colour and light transmittance by the sample to achieve the concentration. When a beam of light passes through a coloured solution, the amount of light absorbed depends on the nature of the molecules absorbing the light, their concentration and thickness (path length) of the solution. The ratio of transmitted intensity to original intensity s known as the “transmittance”, T.

Transmittance (T) = I/I₀

I = intensity of the transmitted light

I₀ = intensity of incident light

The Beer- Lambert law states that there is a logarithmic dependence between the transmittance and the absorbance. Therefore the transmittance is expressed in terms of absorbance;

Absorbance (A) = -log₁₀ T

                             = -log₁₀ (I/I₀)

According to this, the absorbance becomes linear with concentration considering;

A = ℰ ℓ C

ℰ = Molar absorbance coefficient

ℓ = path length

C = concentration of the solution

Therefore in dilute solution,

A = -log₁₀ (I/I₀) = ℰ ℓ C

Molar absorbance coefficient indicates the absorbance under a standard set of conditions, i.e. the light travelling 1cm through a solution of 1moldm^-3. In a material with a low absorption coefficient, light is poorly absorbed and vise versa. This depends on the material and on the wave length of the light.

When using the colorimeter the path length i.e. the width of the glass cell is constant. Also the concentration of one solution used at one specific wave length. Therefore ℰ is also constant through the measurements. This shows out clear relationship between the absorbance and the concentration.

A ∝ C as ℓ and ℰ are constant

The glass cell/ container with plane parallel faces are transverse by monochromatic radiation in the colorimeter. If the glass cell is filled with non absorbing solution, there is 100% transmittance; therefore the absorption would be zero.

Colorimeter applies only in relation to the visible region. Also Beer- Lambert law is applicable for 0.800-0.200 absorbances.

In the experiment, firstly the absorbance reading of the colorimeter should be zeroed using distilled water as distilled water is used to prepare the solutions. 

Also before taking the measurements of the absorbance value in each solution, the glass cell should be washed with distilled water in order to prevent interferences to the reading. It is important not to touch the two smooth surfaces of the glass cell and wipe out the additional drops remain on the surfaces of the glass cell, using a tissue. Otherwise the beam of the radiation would be scattered incorrectly and interfere the accuracy of the reading.

When filling the cell, air bubbles should not be remained inside the cell as it would decrease the absorbance value.

When refilling a glass cell with a different solution, small amount of the new solution should be used to rinse the cell before filing as it would give more accurate results.

Spectrophotometer also uses a monochromatic light to pass though a solution and measure its absorbance. The principle of spectrophotometer and colorimeter is same but a colorimeter can only use one wavelength at a time and have a fixed number of wavelengths that can be used. Also they have to be in visible range only.

A spectrophotometer on the other hand can not function like a colorimeter but take a spectrum of a solution across the entire wave spectrum especially in UV – IR. Therefore use of spectrophotometer is beneficial than a colorimeter and useful to determine concentration of unknown solutions.

Applications of conductivity measurements: Calculating the solubility product of a partially soluble salt (Lab report)

Theory

The solubility of poorly soluble salts is expressed as the solubility product. That is the product of the concentration of ions in the solution which are in equilibrium with the solid ion. These concentrations can be determined via conductivity measurements. In this practical PbSO₄ is used.

                                 PbSO₄ ⇌ Pb²⁺ + SO₄^2-

Assume concentration of solid is a constant.

Concentration of Pb²⁺= concentration of SO₄^2- = C

                             \  Ksp = [Pb²⁺_aq] [SO₄^2-_aq]

                                    Ksp = C²

The measurement of the specific conductivity, K of the saturated solution leads to a value of the concentration.

                      i.e.       C = K/ Λ₀

                      As,   Ksp = C²

                               Ksp = (K/ Λ₀)²

 Λ₀ for PbSO₄ = 3.02 × 10^-2 m²Smol^-

Λ₀ = Molar conductivity at infinite dilution

Procedure

About 2g of finely powdered PbSO₄ was measured using the electric balance into a clean, dry watch glass.

It was added to a clean beaker. The watch glass was washed with distilled water and that washed water was also added to the beaker.

To remove impurities it was shaken by adding distilled water. It was kept aside for a while, for the salt to be collected at the bottom of the beaker. Then the upper layer was decanted and repeated this step for several times.

An empty reagent bottle was kept in a water bath at 24⁰C in order to maintain the temperature of the reagent bottle at 25⁰C.

Then the well- washed salt was added to the reagent bottle and added 100mL of distilled water.

After awhile without disturbing the solid, the clear upper solution was decanted into a clean beaker and the conductivity was measured.

Results

K of distilled water at 25⁰C = 4.2 µS/cm

K of PbSO₄ at 25⁰C = 39.2 µS/cm

Calculations

Corrected conductivity of PbSO₄ = (39.2 – 4.2) µS/cm

                                                           = 35.0 µS/cm

                                                                  = 35.0 × 10^-2 Sm^-

C = K/ Λ₀

C = 35.0 × 10^-2 Sm^- / 3.02 × 10^-2 m²Smol^-

C = 0.11589 molm^-3

C = 0.11589 × 10^-3 moldm^-3

PbSO₄ ⇌ Pb²⁺ + SO₄^2-

Ksp = [Pb²⁺_aq] [SO₄^2-_aq]

Ksp = C²

Ksp = (0.11589 × 10^-3 moldm^-3)²

         = 1.3430 × 10^-8 mol² dm^-6

Conclusion

Exact given Ksp at 25⁰C is 1.6 × 10^-8 mol² dm^-6. Practically obtained Ksp at 25⁰C is 1.3430× 10^-8 mol² dm^-6

As the both values are closer we can use conductivity measurements in order to calculated KSP.

Discussion

The precipitate was washed in order to remove impurities that may affect the results. It should be washed several times to obtain a well- washed precipitate. During this process, precipitate can be also removed. Therefore all 2g of the sample wouldn’t be left.

When maintaining the temperature  of 25⁰C, the water bath was kept at a temperature about 24⁰C. this is because we measure the temperature of the water bath assuming the temperature inside the reagent bottle is at 25⁰C. But actually the temperature of the solution inside would be slightly higher than the temperature of the water bath as the glass of the reagent bottle separates both. Therefore the temperature of the water bath was kept at lower temperature to obtain the required temperature for the solution.

Reagent bottle should be shaken time to time when it was kept in the water bath. This is to increase the dissociation and reach the equilibrium. If not, we might have not measured the conductivity at the equilibrium and that will alter the true Ksp value.

The calculated Ksp value is slightly smaller than the exact given Ksp value due to errors occurred during the experiment. Mainly the personal errors. Such as temperature maintaining errors, measuring errors and personal carelessness.

When preparing the solutions, the distilled water was added. Distilled water also contains ions it self. Therefore additional conductivity from the distilled water would be raised in the solution. For this reason the conductivity of the solution is corrected by deducting the conductivity of water. 

Physiology of Synapse:- Excitatory synapses and Inhibitory synapses

Synapse is simply a junction between two neurons. There are two types of synapses in central nervous system.

·         Excitatory synapses

·         Inhibitory synapses

Excitatory synapses

Pre synaptic knob secretes as excitatory substance. (Ex: Acetyl choline, Noradrinalin, Gutamic acid)

Transmission:

Nerve impulse à pre synaptic knob releases acetyl choline (Ach)àAch diffuse across synaptic cleftàAch combine with receptor sites of post synaptic membraneàpermeability of post synaptic membrane changesà permeability to Na⁺ increases and Na⁺ enter the post synaptic knobà Excitatory post synaptic potential (EPSP) is obtainedàthreshold potential is reachedà action potential is formedà distribution of action potential

A combined EPSP depolarize the membrane to a threshold value to generate an action potential is known as summation. Summation can occur in two ways as temporal summation which is obtained by repeat discharge of single pre synaptic knob and spatial summation which is obtained by numerous pre synaptic knobs.

Inhibitory synapses

Pre synaptic knob secretes an inhibitory substance. (Ex: alpha butric acid and glycine)

This inhibitory synapses function in two ways as post synaptic inhibition and pre synaptic inhibition.

Post synaptic inhibition

Nerve impulseà pre synaptic knob release an inhibitory substance (GABA)àGABA diffuse across synaptic cleftà GABA binds with receptor sites on post synaptic membraneà permeability of post synaptic membrane changesà permeability to K⁺ and Cl^- ions increaseà K⁺ leaves and Cl^- ions enteràInhibitory post synaptic potential (IPSP) is obtainedà membrane hyperpolarizedà no action potential initiated

Pre synaptic inhibition

Nerve impulseà pre synaptic knob release inhibitory substancesàhyperpolarize the pre synaptic  excitatory membraneà prevent excitatory substances releasingà no excitation occurs on post synaptic membrane     

Sequence of events take place during action potential in brief

>In resting state, membrane is permeable to K⁺ and relatively impermeable to Na⁺.

>When a stimulus depolarize the membrane into the threshold value the voltage gated Na⁺ channels open, vastly increasing the membrane’s permeability to Na⁺.

>Na⁺ enters the cell across the membrane under the influence of both concentration gradient and the electric gradient.

>Na⁺ makes the membrane more depolarized and that makes more voltage gated sodium channels to open.

>As the membrane potential approaches equilibrium potential of Na⁺ the driving force of Na⁺ is reduced. Therefore less number of Na⁺ reach into the cell.

>After a short time the voltage gated Na⁺ channels are inactivated and stop the taken in of the Na⁺.  Here the membrane potential rise to +45mV.

>As this occurs, the voltage gated K⁺ channels open and greatly increases the permeability to K⁺ ions. Therefore K⁺ leaves the cell under the influence of concentration gradient and electric gradient.

>As K⁺ leaves, the positive charge inside the cell is reduced. After awhile the equilibrium potential of K⁺ is obtained and the membrane is hyperpolarized. Now the membrane potential is -75mV. Hyperpolarization is due to the delay of closing the K⁺ channels compared to Na⁺ channels.

>The voltage gated K⁺ channels close and by then the Na⁺ channels recovered by inactivation.

Basics of electroplating

Electroplating is the process of depositing a layer of metal electrolytically on to a surface.The articles to be plated make the cathode of an electrolytic cell and a rod of the plating metal makes the anode.

Normally pure metals are used. E.g. Cu, Ni, Cr, Au, Ag, Pt, Zn

But there are exceptions such as Alloys (Cu-Zn, Ni-Cr) and metal with polymers or ceramics (metal-PTEF, metal- Ceramic)

Requirements for electroplating  

-Proper bonding between the plating material and the surface.

-Evenness of the plating.

-Cleanliness

-Leak holes must not be left.

-Texture: should have high brightness.

-Resistant to chemicals in the environment that can cause damage.

Essential parts of electroplating

Difference between Mⁿ⁺ and complex ions

Complex ions release metal ions slowly. Therefore its concentration is low. It’s important to obtain a smooth ending.

Additional electrolyte can be used to increase the conductivity of the system but it will not effect the solution’s ions. Sodium sulphate is an additional electrolyte.

Additives

Additives increase the quality of the electroplating.

-Brighteners: Saccaric acid, Thiourea

-Levelers:  Formaldehydes

-stress relievers: organic substances

-wetting agents: Sodium lauryl suphate

Factors affecting the quality of the electroplating

-Nature of the electrolyte

-Concentration of the electrolyte

-Purity of the electrolyte

-Nature of the additives

-Concentration of the additives (should be low)

-pH of the solution

-Temperature

-Current density

-Geometry of the electrode(whether it’s round or flat)

-Shape of the bath

-Flow conditions (stirring is good)

Hull cell
To study the quality of electroplating dependence on the current density.

Haring-Blum cell

To determine the throwing power of the electroplating process. 

Biosynthesis and function of aromatic amino acids in plants

Most aromatic amino acids in plants are formed by three main types of aromatic acids;

•    Phenylalanine
•     Tyrosine
•     Tryptophan

These three important aromatic amino acids are exclusively synthesized by Shikimic acid pathway that is unique to plants and microbes. This pathway got its name by an important intermediate forms,called Shikimic acid.

Shikimic acid pathway starts from the condensation of Erythrose-4-phosphate with Phosphoenolpyruvate (PEP). PEP is provided by the glycolysis while Erythrose-4-P comes from either oxidative pentose phosphate pathway or Calvin cycle. Therefore Shikimic acid pathway is combined with other important metabolic pathways of the cell. 

The condensation produces 3-deoxy-D-arabinoheptulosonic acid-7-phosphate (DAHP). DAHP undergoes another series of reactions including condensation with another molecule of PEP to give out Chorismic acid. Shikimic acid forms as an intermediate in this reaction and regarded as the key intermediate.

Chorismate is a central intermediate giving rise to two products; Prephenate and Anthranillic acid. Shikimic acid pathway is shown simply as below.

The synthesis of aromatic amino acids is important as these amino acids are the precursors for the synthesis of defense and repair compounds.

Phenylalanine

·         Flavonoids: in plant pigments (eg: Anthocyanine), act against pathogens. Antioxidants.

·         Coumarins: Has appetite-suppressing properties.

·         Liginin: In lignicolous fungi

Tyrosine

·         Tocopherol: Antioxidant in cornifers.

·         Plastoquinone: Important in photosynthesis.

·         Cyanogenic glucosides: Phytoanticipants. Important in plant defense against herbivores due to bitter taste and release of toxic hydrogen cyanide upon tissue disruption.

Tryptophan

·         Alkaloides: provides protection as it prevents insects and herbivores eating the plant.

·         Plant growth regulators

Diversity of bacteria according to nutritional requirments, temperature, Oxygen conditions and water activity

Nutritional type	Energy source	Carbon source	Examples
Photoautotroph	Light	Inorganic carbon, i.e. CO2	Some purple and green bacteria (Chromatium)
Photoheterotroph	Light	Organic compounds	Some purple and green bacteria (Rhodospirillum)
Chemoautotroph (Lithotroph, Lithoautotroph)	Inorganic compounds; H2, H2S, NH3	CO2	Many Archaea and few bacteria (Nitrosomanas)
Chemoheterotroph (Heterotroph)	Organic compounds	Organic compounds	Few Arcaea and many bacteria (Pseudomonas)

Type	Minimum (0C)	Optimum (0C)	Maximum (0C)
Psychrophile	Below 0	10-15	Below 20	Contain unsaturated fatty acids in plasma membrane to tolerate.
psychrotroph	0	15-30	Above 25	Able to grow at low T but prefer moderate T
Mesophile	10-15	30-40	Below 45	Most bacteria especially the ones associated with warm-blooded animals.
Thermophile	45	45-70	Above 100	Contain Saturated fatty acids in plasma membrane. High glucose and carbon content as well as high melting point for DNA.
Hyperthermophile	80	80-115	Above 115	Contain phytane and modified proteins in plasma membrane. High glucose and carbon content as well as high melting point for DNA.

Type	Aerobic condition	Anaerobic condition
Obligate aerobe	Growth	No growth
Microaerophiles	Growth; when the O2 is at very low level	No growth
Obligate anaerobe	No growth; O2 is toxic	Growth
Facultative anaerobe/ facultative aerobe	Growth; Not essential to grow but utilized when available	Growth
Aerotolerant anaerobe	Growth; neither essential nor utilized	Growth

Type	Speciality
Halophile	Require NaCl for growth
Halo tolerant	Able to grow at moderate salt concentrations but grow best in the absence of NaCl
Osmophile	Able to grow in high levels of suger
Xerophile	Able to grow in dry conditions