Controlling metabolism at cellular level: Compartmentation

Metabolism is composed of reaction sequences termed as metabolic pathways. The changes at each step in a metabolic pathway are regulated in order to maintain the stability and survival of the organism. Mainly there are four ways of controlling metabolism. Such one important way of controlling metabolism at cellular level is compartmentation.

When considering a eukaryotic cell; it’s composed of many different compartments known as sub cellular organelles in contrast to a prokaryotic cell. Each organelle contributes a specific metabolic function with different enzymatic activities under different conditions. These metabolic pathways needed to be interconnected to maintain the metabolism. Therefore compartmentation allows the distribution of metabolites and enzymes between the membranes bounded organelles. It’s the method that enables the cell to obtain different metabolic activities at the same time for more energy efficiency. For an example, glycolysis occurs in the cytoplasm and provides the mitochondria substrates such as pyruvates from carbohydrate oxidation. TCA cycle occurs within the mitochondrion matrix while oxidative phosphorylation occurs in mitochondria inner membrane. However, altogether all these three processes are included in one metabolism called ‘cell respiration’. Enzymes of each process are found where the processes take place.

Fat metabolism is another one good example for compartmentation. Fatty acids synthesis takes place in cytoplasm. Cytoplasm contains the required enzymes for the anabolism of fatty acid synthesis. But these fatty acids are degregaded in mitochondria supplying Acetyl Co A for TCA cycle. Mitochondria also contain the enzymes require for the catabolism of fat.

RNA polymerase allows RNA synthesis by using a template of DNA strand. It catalyzes the synthesis of RNA. RNA synthesis takes place in nucleus. DNA transcription also occurs in nucleus. Therefore both the RNA polymerase and DNA templates are available, so that the RNA synthesis is favorable. When considering protein synthesis, all the organelles used for it are close to one another. The nucleolus makes ribosome which synthesizes proteins. Endoplasmic reticulum is near the nucleus to receive Ribosomes and synthesized proteins. The Golgi apparatus is also near the endoplasmic reticulum for storing, packaging and distribution. Therefore all the activities within a cell are cooperated with one another.

Hence, compartmentation helps metabolic controlling by maintaining substrates, regulators and enzymes in separate locations with only favoured access between them.

General facts of parasitic nematodes:- Pin worm, giant round worm, whip worm, pork worm, hook worm

Enterobius sp.

image via human-healths.com

Common name: Pin worm/thread worm/ seat worm

Disease: Enterobiasis (symptoms:- itching in the preanal area)

Host: Human

Habitat: Small intestine

Infective stage: Eggs

Transmission: Ingesting eggs

Parasitic adaptations: Small, sticky, translucent eggs, cuticle

Enterobiu sp -Life cycle 

Trichuris trichuira

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Common name: Whip worm/tap wrom

Disease: Trichuriasis ( Symptoms: Diarrhea, anemia)

Host: Human

Habitat: Colon

Infective Stage: Embryonated eggs

Transmission: Ingesting eggs

Parasitic adaptations: Long slender tapered body, cuticle

Trichinella sp

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Common name: Pork worm

Disease: Trichinosis (Symptoms: nausea, diarrhea, vomiting, fever)

Host: Human, pig, bear, rat

Habitat: Intestine

Infective stage: Cysts (larva)

Transmission: Eating uncooked pork, 

Parasitic adaptations: Long slender body, cuticle

image via dpd.cdc.gov

Ascaris sp

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Common name: Giant round worm

Disease: Ascariasis (Symptoms: Diarrhea, cough, nausea)

Host: Human

Habitat: Intestine

Infective stage: Embryonated eggs ( containing larva)

Transmission: Ingesting eggs

Parasitic adaptations: Long slender body, cuticle, lipid cover around the eggs which is resistant to abrasion and chemicals

Ancylostoma sp

image via plpnemweb.ucdavis.edu

Common name: Hook worm

Disease: Protein deficiency, anemia, cough

Host: Human, cat

Habitat: Intestine

Infective stage: Filari form larva

Transmission: Penetrating the intact skin of the host

Parasitic adaptations: Dental plates in mouth, slender body, cuticle

Plant senescence in brief

Senescence

Senescence is an important program in which the function of a cell/tissue/whole plant naturally leads to its death.

Senescence involves in plant aging.

When tissues senesce they produce enzymes which can recycle the “expensive” materials and reroute the sub-units to somewhere else that growth takes place.

Overall senescence

·         Occurs in the whole plant.

·         Death takes place right after flower and setting.

·         When the flower dies the whole plant dies too.

·         Ex: Asteraceae ( Sun flower)

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Top senescence

·         After the growth season the part above the ground dies remaining the underground part that can grow for several years.

·         Therefore a rhizome is present.

·         Ex: Weed, Grass

       

Deciduous senescence

·         In dry seasons like winter and summer, the leaves falls and trunk remains.

·         Leaves fall due to avoid the heavy transpiration occurs in the dry season.

·         Ex: Deciduous plants

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Progressive senescence

·         Older parts die due to the senescence and the new organs and tissues continue their development.

·         Ex: Green trees

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As above mentioned, senescence can occur in cells as well as tissues.

Cell senescence

·         Can be described according to the senescence in cell membrane and organelle level.

Senescence in cell membrane

Lipid phase change

·         Plasma membrane has the fluid mosaic structure.

·         This structure changes as the liquid crystalline state changes into the solid-gel state.

·         Therefore the membrane gets inflexible and hard.

Degradation and preoxidation of lipids

·         Lipid content gets decreased.

·         It occurs as the lipid synthesis decreases and lipase content increases.

·         Phospholipase, lipoxygenase, MDA and active O₂ content increase.

Increase in Phospholipase activity

·         Mainly the activity of Phospholipase D takes place in plants.

Biomembrane degradation and leakage

·         The equilibrium of ions breaks down.

·         Metabolisms get disordered.

Senescence in organelle level

·         Ribosomes and RER break down.

·         Chloroplasts collapse and mitochondrion cristae are swollen.

·           As the vacuoles break down, all the toxics inside them is released to the cell plasma.

·         Therefore the autophagy takes place and the senescence of organelles activates.

Population dispersion

Dispersion is the pattern of spacing among the individuals within the population. Basically there are three patterns.

-          Clumped dispersion

-          Uniform(regular) dispersion

-          Random dispersion

Clumped

·         Commonest pattern that can observed in populations.

·         Individuals are bunched into groups within the population.

·         This is mainly results from the response to the unevenly distributed resources in their environment.

·         Also there are positive interactions between the individuals.

·         This supplies many advantages to the population such as protection from predators, reproduce and increase the population size and decrease the energetic cost of moving to do work.

Uniform

·         Individuals are uniformly spaced within the population.

·         Mainly results from the competition for resources.

·         Therefore there are aggressive interactions between the neighbours.

Random

·         Individuals are randomly spaced within the community.

·         Not that much common in nature.

·         This occurs as there are no strong interactions between the individuals.

·         They show neutral interactions.

Moulting and cuticle formation of insects

Hormones such as Ecdysone and bursicon play an important role during the events in moulting.

Apolysis

·         Epidermal cells divide and change their shape.

·         These cells separate from the inner surface of the old endocuticle and leave out the sub-cuticular space.

·         This space is consisting of moulting fluid, proteinase and chitinase.

·         These enzymes are inactive in this stage.

Formation of the epicuticle

·         Cuticulin is deposited below the moulting fluid and above the epidermis.

·         This forms the new Cuticulin layer.

·         Inner protein epicuticle is deposited under the Cuticulin layer.

Deposition of new procuticle

·         Deposition of procuticle occurs beneath the Cuticulin layer.

·         After the deposition enzymes in the moulting fluid activate and digest the old endocuticle.

·         Only a thin layer of the old endocuticle is left out.

·         This layer is called as Ecdysial membrane. These lines are located in the median lines of head and thorax.

·         Weak lines appear along this Ecdysial layer.

·         Wax secretion occurs on to the surface of the new cuticle.

Ecdysis

·         Moulting fluid and digested old endocuticle are absorbed.

·         Intake of the air and muscular contractions cause the insect’s body to swell.

·         This leads the old exoskeleton to split open along the weak lines.

·         Insect draws itself out.

·         All parts of the old cuticle are shed.

·         This old cuticle is called as cast skin.

Expansion of the new procuticle

·         New cuticle is soft and pale.

·         At this moment new procuticle expands before it hardens.

Hardening and darkening of cuticle

·         Hardening of the cuticle is known as sclerotization.

·         This forms sclerites which are rigid plates of exoskeleton.

·         It also darkens the cuticle. This is known as tanning.

Deposition of the new endocuticle

·         New endocuticle deposits after the moulting and tanning.

Orientation of insect head: Prognathous, Hypognathous and Opisthognathous

·         Three types of orientation.

                                i.            Prognathous: orientated horizontally. Mouth parts are pointed forward.

                              ii.            Hypognathous: orientated vertically. Mouth parts are pointed down.

                            iii.            Opisthognathous: orientated obliquely. Mouthparts are pointed backward.

Prognathous

·         Mouthparts are pointing forward.

·         Mouthparts are anterior in position.

·         Long axis is horizontal.

·         Mostly carnivore insects have this type of orientation.

·         Ex: Stick insect

Hypognathous

·         Mouthparts are pointing downward.

·         Mouthparts are ventral.

·         Long axis is vertical.

·         Mostly herbivore insects contain this type.

·         Ex: Grasshopper.

Opisthognathous

·         Mouthparts are pointing backward.

·         Mouthparts are directed down between coxae of legs.

·         This is known as proboscis.

·         Long axis is horizontal.

·         Ex: Plant sucking bugs.

Internal gill structures of aquatic vertebrates

INTERNAL GILLS

·         Pouched gills: in agnathans – lamp rays

·         Septal gills: in chondrichthyes

·          Aseptal gills: in osteichthyes

Pouched gills

·         Large sac like branchial pouches which are lined with primary gill lamellae.

·         Water goes through mouth àpharynx àpore shaped internal gill slitsàbranchial pouches.

·         Water leaves the branchial pouches through pore shaped external gill slits.

Septal gills

·         Branchial pouches are narrow chambers.

·         Between the branchial chambers, para branchial chambers are present with external gill slits. External gill slits are small and slit shaped.

·         Distal tips of the interbranchial septa can act as valves to close the external gill slits.

·         Gill lamellae runs along the interbranchial septa towards the body surface.

·         Internal gill slits rise from the pharynx and run into each branchial chamber.

Aseptal (non-septal) gills

·         Operculum covers the gills.

·         A single large opercula cavity is present with one valved external gill slit.

·         Interbranchial septa are greatly reduced.

·         Therefore gill lamellae extend freely into the opercula cavity.

(diagram: http://people.eku.edu)

Comparative anatomy of the animal body covering

INVERTEBRATE BODY COVERING

Protozoan body covering

·         Plasma membrane acts as the body covering.

·         Some have an additional gelatinous outer layer.

·         Some have a complex body covering called Pellicle. Ex:- Paramecium

Pellicle

·         Two membranes are present as outer alveolar membrane and outer alveolar membrane.

·         Between those two an alveolar cavity is present.

·         Some have cilia in the pellicle.

Poriferan body covering

·         Thin.

·         Two types of epidermis.

-          Pinacoderm: outer epidermis. Single layer of Pinacocytes. Pinacocytes are scale like falttened cells.

-          Choanoderm: inner epidermis. Single layer of choanocytes. Choanocytes are oval shaped cells with a flagellum on each.

·         Between those to lies the mesoglea or mesenchyma.

·         It’s a jelly like layer consist of spicules and amoebocytes, enclosing a central cavity called spongocoel.

·         Spicules supply strength and amoebocytes give rise to new cells.

·         Ostia are located on the wall.

Cnidarian body covering

·         Similar to that of Poriferan.

·         Outer epidermis: Cuticle is present.

                             Consist of small cubicle cells.

·         Inner gastrodermis: Mainly consist of columnar epithelial cells.

·         Mesoglea: Jelly like layer.

Platyhelminthes, nematode, annelid and arthropod body covering.

·         Single layer epidermis is present.

·         Cuticle is present on the epidermis.

·         Some arthropods have an inner layer of dermis.

VERTEBRATE BODY COVERING

·         Body covering is called as skin.

·         It has a multilayered structure.

·         Consist of two layers as epidermis and dermis.

Epidermis

·         Multilayered.

·         Avascular.

·         Forms structures such as feathers, claws, scales…etc.

·         From top to bottom of the epidermis;

-          Stratum corneum: Dead keratinized cells are on the surface.

-          Stratum germinativum

-          Basal lamina.

Dermis

·         Fibrous connective tissue with blood vessels, nerves and sensory receptors.

·         Fish scales are derived from the dermis.

Fish skin

·         Relatively thin.

·         Derivatives of the skin;

-          Scales: Bony scales derived from dermis.

             Bone cells come into the dermis and secrete scales. Afterwards they leave. Dentine and enamel layers are later deposited on those scales.

-          Melanophores: Star shaped cells that lie under the epidermis.

-          Glands

                                                                                     I.            Mucous glands: unicellular mucous producing glands. Mucous reduce friction when swimming. Produce mucous cocoon to protect from predators and heat in dry seasons. Also prevent invasion of bacteria.

                                                                                  II.            Poison glands: produce poisonous substances.

                                                                               III.            Light emitting glands: aids to attraction, species recognition and avoid predators.

Amphibian skin

·         Thin, moist skin.

·         Can breathe through the skin.

·         Derivatives of the skin

-          Glands

                                                                         I.            Mucous glands: keep the skin moist

                                                                      II.            Granular poison glands: parotid and parotoid glands.

-          Chromatophores: present in epidermis and dermis. Gives colorization.

·         No scales except for some species.

Reptilian skin

·         Thick, dry skin.

·         Stratum corneum is hardened with dead keratinized cells.

·         Can observe two layers in the epidermis.

-          Outer epidermal generation

-          Inner epidermal generation

·         Therefore they can shed scales or called as molting.

·         Scent producing glands are present in some.

·         No mucous glands.

Bird skin

·         Thin but horny scales are on legs and feet.

·         Claws and beak present.

·         Derivatives of the epidermis:

-          Feathers

                                                                 I.            Contour feathers: Cover the body.

                                                              II.            Flight feathers: Cover the wings. Large and stiffer.

                                                           III.            Down feathers:  lie beneath the contour feathers. Fluffy barbs.

                                                           IV.            Bristle feathers: Short and stiff but the barbs are absent.

·         Stratum corneum is not keratinized like in mammals.

·          Dermis lacks ossification.

·         Glands: mainly secrete lipids.

-          Uropygial gland: Single, branched alveolar gland located above the base of the tail. Produces fatty and waxy secretion. This is later spread over feathers to make waterproof.

-          Wax glands: lie in the external ear canal

Mammalian skin

·         Thick epidermis.

·         Transitional layers can be seen between stratum corneum and stratum germinativum.

·         Stratum corneum is thick and forms foot pads in many mammals.

·         Glands:

-          Sebaceous glands: alveolar branched glands that produce oil and wax.

-          Sweat glands: tubular coiled glands.

-          Mammary glands