The blueprint of life [3] secondary and some special structures of DNA

Let’s pick up where we dropped, the secondary structure of DNA.

IN FACT, a number of different forms of nucleic acid double-helix have been observed and studied, all having the basic pettern of two helically-wound antiparallel strands.

Polymorphism （多样性）of DNA Secondary Structure

―due to conformational changes of sugar-ring on the nucleotide chain.

1. B-form:

right-handed
the structure identified by Watson and Crick,
the most common form,
believed to be the idealized form of the structure adopted by virtually all DNAin vivo (in the living body of a plant or animal), or, at physiological (characteristic of or appropriate to an organism’s healthy or normal functioning) pH and salt concentration.

characterized by:

a helical repeat of 10bp/turn (although now it is known that ‘real’ B-DNA has a repeat closer to 10.5bp/turn);
the presence of base pairs lying on the helix axis and almost perpendicular to it;
having well-defined, deep major and minor grooves.

2. A-form:

right handed
adopted by DNA in vivo under unusual circumstances, (conversed from B-form in low moisture (<75%))
presents in certain DNA-protein complexes

characterized by:

a helical repeat of 11 bp/turn.
the presence of base pairs tilted with respect to the helix axis, and actually lying off the axis.
being the helix formed by RNA and DNA-RNA hybrids. (Similar to some RNA-DNA duplex or RNA-RNA duplex.)

3. Z-form:

left-handed
formed by stretches of alternating pyrimidine-purine sequence, e.g. GCGCGC, especially in negatively supercoiled DNA in high saline (盐) solution.
not easily form even in DNA regions of repeating GCGCGC, since the boundaries between the left-handed Z-form and the surrounding B-form would be very unstale

characterized by:

a zigzag (锯齿型) pattern where its name comes from
12 bp/turn

(1)

A. B, Z-DNA — slide shown by prof.Dong,COMPARISON AMONG A-,B-,Z-DNA

(2)

picture from Instant Notes in Molecular Biology (3rd Edtion)

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Some special structures of DNA

1. Inverted repeats and direct repeats

Inverted Repeat is functionally important as recognition sites on the DNA for the binding of a variety of proteins (e.g. restriction and modification enzymes)

Inverted Repeat is either discontinuous or continuous,

Continuous → palindromic structure (回文结构:inverted repetitions of base sequence over the two strands form a symmetric structure )

Discontinuous→ hairpin & cruciform (发卡、十字结构:self complementary within each of the strands )

hairpin structure & cruciform structure — hairpin structure & cruciform structur

2. DNA triplex (The intramolecular triplex (H-DNA) as an example)

• AG-rich strand vs. CT-rich strand with Hoogsten hydrogen bond

(a quick glance at Hoodsten hydrogen bond:

• Mirror inverted repeat

• a barrier for different DNA and RNA polymerases, and so it is a negative regulator for gene expression.

3. G-quadruplex structure

G-rich sequence(s) to form 4-stranded structure by unusual G-G

H-bonds

Mendel’s Genetics[3]: Variations of the 3:1ratio

Variations of the 3:1 ratio

The simple 3-to-1 monohybrid ratio is not always observed in instances where only one gene is responsible for a particular phenotype.

A number of factors:

Partial or incomplete dominance

Complete dominance means the phenotype of first filial generation(heterozygous) is exactly identical to that of one of the parents(both homozygous). Partial or incomplete dominance means the first filial has phenotype somewhere between that of both parents.

For example, When two pure-bred snapdragons, with white and red petals respectively, cross, their first filial generation has pink petal rather than red or white.

In this case, the homozygous phenotypes are red, or white petals while heterozygous one is between white and red: pink petal.

Thus, it is conceivable that when it comes to the second filial generation, which was produced by the self fertilization of the heterozygous F1, F2 should have three different phenotypes, white, pink, and red. And we can also deduce the ratio of them is 1:2:1.

Codominance

Codominance is similar to incomplete dominance, but here the heterozygote displays both alleles(两种等位基因均被表达).

For example, in humans the MN blood group is controlled by a single gene.

In humans the main blood group systems are the ABO system, the Rh system and theMN system.

Only two alleles exist, M and N. Children whose father is an NN homozygote with N blood and whose mother is a MM homozygote with group M blood are MN heterozygotes and have group MN blood.Both phenotypes are identifiable in the hybrid. And the ratio also switches from 3:1 to 1:2:1.

Lethal alleles

Some alleles affect the viability of individuals that carry them.

In most cases the homozygous recessive does not survive but the heterozygotes may have a normal lifespan.

The best-known example of lethal alleles is the inheritance of yellow coat color in mice.

Yellow fur can arise in strain of mice with different colors, or instance, black. Yellow coat color is dominant to black coat. Mice with BB alleles are back, with BB^yare yellow, with B^yB^y alleles are supposed to be yellow as well, but B^yB^y alleles are lethal and any mice with this genotype die in utero(in the uterus : before birth).

SO it is conceivable that when two yellow mices are mated ratio of the different phenotypes of their first generation is 2 : 1, rather than 3 : 1 or 1 : 2 :1.

NOTE: The allele B^yis recessive in its relation to its effect on viability (only homozygous B^yB^ys die, while the heterozygotes survive ), but dominant in relation to coat color(heterozygotes present in yellow fur in stead of black fur.).

Other examples where alleles are lethal when homozygous but have a dominant effect when heterozygous, include :

tailless Manx cats

genetics — a manx cat, image from the Internet

a breed of domestic cat(Felis catus) originating on the Isle of Man, with a naturally occurring mutation that shortens the tail.

The Manx taillessness gene is dominant and highly penetrant; kittens from two Manx parents are generally born without any tail. Being homozygous for the taillessnees gene is lethal in utero.Thus, tailless cats can only be heterzygous. Because of the danger of having homozygous taillessness gene, breeders avoid breeding two entirely tailless Manx cats together.(wikipedia: Manx (cat))

short-legged Creeper chickens.

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(Annie: If none of the homozygous yellow mice can survive before birth, then where did all the heterozygous yellow mice come from in the first place???????)

Answer: Through mutation. The presence of one mutant allele alters development so as to produce characteristic changes to the animal, but when two of the mutant alleles are present, development is so aberrant as to cause death.

This may occur in utero as described above or resulted in shortened life expectancy as found in several examples in humans, such as Tay-Sachs disease, Huntington’s syndrome（亨丁顿舞蹈症） or sickle-cell anemia（镰刀形红血球病）. (from Instant Notes)

the blueprint of life [2]: primary and secondary structure of DNA

Molecular structure of DNA:

professor Dong first showed us where DNA is:

Then he introduced the molecular structure of DNA with 4 parts:

1. Primary structure of DNA:

Arrangement of nucleotides along a DNA chain.

Annie: So…the primary structure of DNA is a line.

Conventionally, the repeating monomers of DNA are represented by their single letters A, T, G, C.

Professor: There’s a convention to write the DNA sequence with 5′ at the left, that is, in a 5′ to 3′ orientation from left to right.

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2. Secondary structure of DNA—stabilized partial structure formed by polymers of nucleotide

Professor Dong: First, please familiarize yourselves with Chargaff’s Rule:

A+G=T+C & G+T=A+C

↓↓

A=T & G=C

(Chargaff’s Rule)

(Based on analysis of the chemical composition of duplex DNA in the early 1950s, E. Chargaff deduced these rules about the amounts of different nucleotides in DNA.)

Professor: The secondary structure of DNA is a partial structure formed by polymers of nucleotide. The structure is referred to as the double-helix structure.

Two separate chains of DNA are wound around each other, each following a helical (coiling) path, resulting in a right-handed double helix structure.

In 1953, Watson and Click proposed the DNA double-helix structure based on Chargaff’s Rule and DNA Crystallography and X-ray diffraction images of DNA structure by Wilkins and Franklin. (Rosalind Franklin, who was not that well-known as Watson, Click and Wilkins but apparently played a equally significant role in the discovery of the structure.The whole was later nominated Nobel Prize but her, is that even fair?)

—————————————————————————

The backbone of duplex DNA is a serious of phosphodiester group (the covalent linkage of a phosphate group between the 5′-hydroxyl of one sugar and the 3′-hydroxyl of the next, that is , repeats of P-sugar unit) linked by phosphodiester bond.

—————————————————————————

The strands are joined noncovalently by hydrogen bonding between the bases on opposite strands, to form base pairs.

There are around 10 base pairs per turn in the DNA double-helix. The two strands are oriented in opposite directions in terms of their 5’to3′ direction(the nucleotides in one strand is opposite to their direction in the other strand).

More crucially, the two strands are complementary in terms of sequence. The bases hydrogen-bond to each other as purine-pyrimidine pairs which have very similar geometry and dimensions.

A–T: 2 H-bonds ; C–G: 3 H-bonds

5’- A T G T C -3’

¦¦ ¦¦ ¦¦¦ ¦¦ ¦¦¦

3’- T A C A G -5’

Thus, the sequence of one strand uniquely specifies the sequence of the other, with all that which implies for the mechanism of replication of DNA and its transcription to RNA.

——————————————————————————-

Professor Dong added:

Between the backbone stands run the major and minor grooves.

In a detailed analysis of DNA structure, there are two types of grooves that can be seen; the major groove has the nitrogen and oxygen atoms of the base pairs pointing inward toward the helical axis, while in the minor groove,the nitrogen and oxygen atoms point outwards;

Shown by prof.Dong, MAJOR GROOVE A-T

Shown by prof.Dong, MAJOR GROOVE G-C

Major Groove Minor Groove

Depth: 8.5 Å Depth: 7.5 Å

Width: 11.7 Å Width: 5.7 Å

Å

Definition: Symbol for Ångström, a unit equal to 0.1 nanometer, mainly used in expressing sizes of atoms, lengths of chemical bonds, and wavelengths of electromagnetic radiation.

Supplement: The unit is named after the Swedish physicist, Ångström, Anders Jonas.

picture from Instant Notes in Molecular Biology

Professor: The major groove is more dependent on base composition. and major grooves and minor grooves are also recognition and binding sites for certain protein factors, and are involved in the regulation of gene expression.

——————————————————————————

Professor: Summary of “Double Helix” Model (B-DNA):

Right Handed Double Helix

Outside: P-Sugar backbone

Inside: Base pairing linked by H-bonds

Minor and Major grooves

（note: bp=base pair(s)）

the blueprint of life[1]

Of course the blueprint of life is DNA.

DNA is important because it is the genetic material ←contain all the info for the synthesis and functioning of a living form duplicate and passes through to the next generation.

Hearing this Annie questioned herself: DNA is not the genetic for ALL viruses. RNA “blueprints” for the rest of the viruses. Virus, though not even having a cell structure, is a form of life. So why not be fair, and say the blueprint of life are DNA and RNA?

Professor Dong continued,

Proofs:

Bacterial Transformation Experiment

—Griffith, 1928

Professor: So what is the transforming principle?

Annie: It could be a cool type of enzyme that moved the toxic part of S strain onto R strain…

Professor: Well, Enzyme did help a lot in the experiment we’ll talk about later, but it is not the hero of the story.

Annie: So what’s the story?

Professor:

—Avery et al., 1944

slide shown by Prof. Dong ,AVERY REPEATED GRIFFITH’S EXPERIMENT WITH MODIFICATION

Only DNA is responsible for the transformation.

Annie thought: Well, there still existed possibilities that DNA and some other things that were not sugar, lipid or protein cooperated to complete the transformation… The “other things” also contributed to the transformation but could not complete it without DNA? In this case DNA is not the only one that is responsible,

T2 Bacteriophage Infection (Blender Experiment)

—Hershey &Chase, 1952

Experiment 1

Experiment 2

Radioactive labeling of proteins and DNA

The professor continued. So now let’s go deeper and see the chemical composition of DNA.

A 5-carbon sugar , hand in hand with base group and phosphorous group, thought Annie.

It’s not that simple as you learned in high school, said the professor. We need to know the chemical composition of the base group, deoxyribon and phosphorous group as well.

sugar group — slide shown by Prof. Dong,SUGAR GROUP

Professor:

Base — slide shown by Prof. Dong,BASE GROUPS

Annie thought: Pyrimid-ine, Could it have anything to do with the Pyramid in Egypt?

The professor was explaining the structure and Annie didn’t interrupt him with her question.

After class, Annie searched the Internet for an answer, and this is what she found.

The professor continued.

Bonds

P group——phosphester bond–—Sugar—–glycosidic bond—–B group

Mendel’s Genetics[2]: The monohybrid cross

Keywords:

Phenotype

Any character (trait) which can be shown to be inherited, such as eye color, leaf shape or an inherited disease, such a cystic fibrosis, is referred to as a phenotype.

Description: A fly may be described as having a red-eyed phenotype. A child may be described as displaying the cystic fibrosis phenotype.

Genotype

The pattern of genes that are responsible for a particular phenotype in a individual is referred to as genotype.

Dominance

In hybrids between two individuals displaying different phenotypes, only one phenotype may be observed. This phenotype is referred to as the dominant trait and the un-shown one the recessive.

For instance, if the wife has wide eyes while the husband has small eyes, and their little girl has wide eyes, then the wide eyes are dominant to small eyes.

Pure-breeding lines

Organisms which have been inbred for many generations in which a certain phenotype remain the same.Pedigree breeds of dogs or cats are commonplace examples of pure-breeding lines.

A puppy from two purebred dogs of the same breed, for example, will exhibit the traits of its parents, and not the traits of all breeds in the subject breed’s ancestry.

Homozygous: Individuals with two identical copies of a gene.

“True breeding (pure-breedind) organisms are always homozygous for the traits that are to be held constant.”

Heterozygous: Individuals with two different copies of the gene.
Alleles: The different variants of a gene.

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Mendel made a cross between two pure-breeding lines of pea plants, one of which had violet petals and the other white petals. The hybrids produced in this cross were referred to as the F1 (first filial) generation.

In Mendel’s experiment, the ratio of violet pedals and white ones in the second filial were very close to 3 to 1, which applied to the theoretic reasoning shown above.

He did many other experiments focusing on different types of genotypes of the pea plants and the results were shockingly similar. The hidden phenotype in the first filial reappeared in the second filial and the ratio of the dominant to the recessive phenotype were all close to 3 to 1.

The 3:1 ratio is referred to as the monohybrid ratio and is the basis for all patterns of inheritance in higher organisms.

One simple extension of the 3:1 phenotype ratio is a 1:1 ratio, produced when a heterozygous F1 individual is crossed to the homozygous-recessive parent. The process is known as testcross.

Testcross is useful in any condition when it is necessary to determine whether an individual is heterozygous or homozygous. Conceivable that if F2 all have dominant phenotype, then the tested parent is homozygous-dominant; if F2 have a 1:1 ratio of dominant and recessive phenotype, then the tested parent is heterozygous.

Review of Mendel’s Genetics

Here I found a great page story-telling Mendel’s Genetics.Can’t be more suitable as a revision of what we learned about genetics and inheritance in high school. >>Mendel’s Genetics

I believe by reading the link page you have remembered the principles of Mendel’s Genetics. We’ll summarize these principles again in next posts.

While Mendel’s research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms.”

It must be a cliche to summarize the success factors of Mendel’s experiments, but it has to be done, for many of the factors are still important for today’s experimentalists.

Firstly, before the experiment,Mendel spent a long time observing different traits of the peas and decided which traits he was going to focus on in the after experiments. He was prepared, had anticipation and, perhaps already held some hypothesis of what was going to happen.

Then it was the choice of his “lab-rats”. As the link page says,”Mendel picked common garden pea plants for the focus of his research because they can be grown easily in large numbers and their reproduction can be manipulated. ” Based on a large number of offspring, the resulting statistics can be assumed as very close to theoretic statistics. In this case, it’s way more convenient to study the traits of these peas than those of some fragile and rare pole plants.

More important, “pea plants have both male and female reproductive organs. As a result, they can either self-pollinate themselves or cross-pollinate with another plant. In his experiments, Mendel was able to selectively cross-pollinate purebred plants with particular traits and observe the outcome over many generations. This was the basis for his conclusions about the nature of genetic inheritance.”

Reproductive
structures of
flowers

drawing of a flower cross-section showing both male and female sexual structures — the picture is from http://anthro.palomar.edu

Last but not least, Mendel was a pioneer in applying Math(Statistics) to experiment analysis. He rounded the ratio of numbers of different traits to a whole number and discovered the astonishing similarity of all the results.

In high school that’s all the factors, but actually there’s more. For one, Mendel succeeded because all the genes that controlled traits he picked to observe happened to be on different chromosomes. Otherwise, the phenomena of “linkage” would have appeared (which we’ll talk about later)and he should never have had such a groundbreaking discovery.

Illustrations of Wild Animals [insect1]

First of all we need to know the classification of insects.

The following content is all from http://bijlmakers.com/entomology/classification/Insect_classification.htm, a page I find more than helpful for us to use as the introduction of insects.

Classification of Insects

Taxonomy is the study of the principles of scientific classification. In this page we will learn how insects are classified. First we will see where insects belong in the animal kingdom. Then we will find out how the different insects are sorted in groups.

Use the Glossary to look up some of the technical words or terms.

Classification of animals

界(Kingdon)、门(Phylum)、纲(Class)、目(Order)、科(Family)、属(Genus)、种(Species)

The animal kingdom is divided in a number of groups called “phyla” (singular: phylum). Examples of phyla are:

Protozoa (single-celled animals)
Porifera (sponges)
Nemathelminthes (roundworms)
Mollusca (mollusks, snails, etc.)
Arthropoda (crayfish, millipedes, centipedes, spiders and insects)
Chordata, (fish, amphibians, reptiles, birds, and mammals)

Each phylum is subdivided in classes, for example the class Hexapoda (= insects). Classes are subdivided into orders, for example the order Coleoptera (= beetles). Orders are divided into families, families into genera (singular: genus), and genera are divided into species (See Table 1). Within the class Hexapoda there are over 750,000 different species of insects.

The scientific name of a species is always a double name (the genus name, and a specific name). It should be written with a capital letter in the genus name and either in italics or underlined.

Example: Helicoverpa armigera or Helicoverpa armigera

An example of the classification of an insect:

Kingdom — Animal

Phylum — Arthropoda

Class — Hexapoda (= insects)

Order — Lepidoptera (= butterflies and moths)

Family — Noctuidae (= noctuids)

Genus — Helicoverpa

Species — Helicoverpa armigera (= American bollworm)

The phylum Arthropoda

Some characteristics of the Arthropoda are:

They have a so called exoskeleton. They do not have bones, but the hard outer covering supports the muscles.
The appendages are jointed.
The body is formed of a number of segments.

Characteristics of the class Hexapoda (Insects)

Some characteristics of insects are:

Body:

The body is divided into three distinct regions: head, thorax and abdomen

Head:

One pair of antennae.
- The antennae are usually used as tactile organs (= organs pertaining to the sense of touch) or as olfactory organs (= organs of smell).
Eyes:
- Most insects possess one pair of compound eyes and sometimes some simple eyes called “ocelli”.
Mouthparts.
- There is a big variety in types of mouthparts; biting, sucking, stinging, licking, etc.

Thorax:

Three pairs of legs.
- The thorax has three segments. These are called pro-thorax, meso-thorax and meta-thorax. Each segment has one pair of legs. The different parts of the leg are called coxa, trochanter, femur, tibia, and tarsus.
  Note: some insects are legless, or have fewer than 6 legs. Some larvae have leg-like appendages on the abdomen.
Often one or two pairs of wings.
- The wings are borne by the second and/or third of the thoracic segments.
  Note: Some insects are wingless.

Abdomen:

The gonopore (genital opening) is at the posterior end of the abdomen.
No appendages used for moving on the abdomen of adults (except in a few primitive insects).
Sometimes there are some appendages at the end of the abdomen.

Classification of Hexapoda (Insects)

The class hexapoda is divided in two subclasses:

Apterygota (= primitive wingless insects)
Pterygota (= winged and secondarily wingless insects)

The subclass Pterygota is divided in two divisions:

Exopterygota (= insects with a simple metamorphosis, without pupal stage)
Endopterygota (= with a complete metamorphosis, including a pupal stage)

Metamorphosis

After hatching from the egg, an insect grows by a series of molts. After shedding the old skin they expand into a new larger one. This molting continues until the adult stage is reached. At each molt, some externally visible changes occur. This type of growing is called metamorphosis. The division of insects into apterygota, exopterygota and endopterygota is mainly based on differences in the type of metamorphosis.

The apterygota have no metamorphosis. Except for the size, all larval stages closely resemble the adults (which are wingless).

The exopterygota undergo a simple metamorphosis. In molting from egg, via the nymphal stages to an adult, there is a gradual change in the external appearance. The late nymphal stages already show the development of wing pads. But only in the last molt functional wings are developed. The nymphs usually have the same feeding habits as the adults.

In the endopterygota there is a complete metamorphosis. In these insects the external (and internal) changes during the life history are the greatest. The eggs hatch into larvae which feed actively during the different instars. The larvae may or may not have legs. The development of wings is not visible during the larval stages. After several molts a pupa is formed. A pupa is an inactive stage, it does not feed and it does not move. Sometimes the pupa is protected by a cocoon of silk, or it is found in an earthen cell in the soil. During this pupal stage big changes take place internally. After the pupal stage, a highly active winged adult appears. Often, the larvae and the adults live in different types of habitat and use different types of food.

Orders of insects

Orders marked with a (*) are important because they contain some agricultural pests.

Click on the links below to see more information about some orders.

Apterygota

Order Thysanura	Bristletails
Order Diplura	Diplurans (Two-pronged Bristletails)
Order Protura	Proturans
Order Collembola	Springtails

Exopterygota

Order Ephemeroptera	Mayflies
Order Odonata	Dragonflies and Damselflies
Order Orthoptera *	Grasshoppers, Locusts and Crickets
Order Dictyoptera	Cockroaches and Mantids
Order Grylloblattodea	Rock crawlers
Order Phasmida	Stick insects and Leaf insects
Order Dermaptera	Earwigs
Order Isoptera *	Termites
Order Embioptera	Web-spinners
Order Plecoptera	Stoneflies
Order Zoraptera	Zorapterans
Order Psocoptera	Psocopterans (Psocids, Booklice)
Order Mallophaga	Chewing lice (Biting lice)
Order Anoplura (= Siphunculata)	Sucking lice
Order Thysanoptera *	Thrips
Order Hemiptera
suborder Heteroptera *	Bugs
suborder Homoptera *	Cicadas, Hoppers, Psyllids, Whiteflies, Aphids, and Scale insects

Endopterygota

Order Neuroptera	Alderflies, Dobsonflies, Fishflies, Snakeflies, Lacewings, Antlions, and Owlflies
Order Coleoptera *	Beetles
Order Strepsiptera	Twisted-winged parasites (Stylopids)
Order Mecoptera	Scorpionflies
Order Trichoptera	Caddisflies
Order Lepidoptera *	Butterflies and Moths
Order Diptera *	True Flies
Order Siphonaptera	Fleas
Order Hymenoptera *	Sawflies, Ichneumons, Chalcids, Ants, Wasps, and Bees

Identifying insects

When trying to identify an unknown insect you will always first try to determine its correct Order. This can be done with the help of a key. You will need a good hand lens to observe some of the smaller parts of the insect, for example to count the number of segments in the tarsi, or to have a close look at the antennae. Click here to learn more about using a key to identify insect orders.

Good, Bad or Neutral?

We have just seen how insects can be classified in different orders. But there are other ways of grouping insects for example from the farmers’ point of view. Farmers will usually classify insects in 3 groups, depending on their behavior in the farm:

Pests
Beneficial insects
Neutral insects

Pest
Whether an insect species is a pest depends on the situation. A definition of “pest” is: animals causing damage or annoyance to man, his animals, crops or possessions, such as insects, mites, nematodes, rodents, birds. This means that a certain insect could be a pest in one situation, but the same insect would be neutral in another situation. For example the caterpillars of Diamondback moth (Plutella xylostella) feed on cabbage and other plants of the Cruciferae family. A farmer who grows cauliflower or kale will therefore consider it a pest. But for a farmer who grows potatoes or bananas the Diamondback moth is an innocent, neutral insect. As humans we have adapted the nickname pest for other things as well. Let’s say you were looking at apartments and the neighbors around you were making so much noise at all the apartments you checked out. Those people would be called pests and it might change your mind on choosing that apartment.

Beneficial insects
Some insects are beneficial to the farmer, because they are the natural enemies of other insects. Predatory insects feed on other insects and in this way they help control pest insects. For example the Assassin bug kills caterpillars and Ladybird beetles feed on aphids. Other insects are beneficial because they help with the pollination of plants, e.g. bees and bumble bees. There are insects that produce useful products, for example honey (honey bee) or silk (silkworm). And in many countries insects are used as food.

Neutral insects
If an insect is not a pest and not beneficial than we can call it neutral. But again, it really depends on the context. In a rice field a mosquito can be considered a neutral insect (it doesn’t harm the crop), but in your bedroomyou will call it a pest.

The Sea Around Us_Rachel Carson

World consumption of paper has grown 400 percent in the last 40 years. Now nearly 4 billion trees or 35 percent of the total trees cut around the world are used in paper industries on every continent.(source)

For the trees’ sake, please please please please use e-books!

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Rachel L.Carson, most famous for her Silent Spring, also completed many other excellent books on environmental conservation.

As an aquatic biologist early in her career, Rachel explored and admired the mystery of the seas with brain of a scientist. While as a woman worshiped the nature, she explored it with eyes of a sincere admirer.

As a gifted writer, Rachel whispered to us about the sea in the most beautiful descriptions, leading us to the seasons of an strange but engaging world. As a concerned scientist, she sharply stated the harm human activities did to the seas in a serious voice, making us think, facing disruptions of the ecosystem, what is the right thing to do.

Though the book was written in the 1950s and some of the statistics and facts might have been renewed, it is still a must-read book for everyone.

The sea is powerful but also fragile, is beautiful but her beauty could be forever ruined if we don’t start paying attention to the aquatic protection and restoration.

An Inconvenient Truth: film and book

An inconvenient truth is a documentary film directed by Guggenheim. The 2006 movie is based on former Vice President of the U.S Al Gore’s lecture tour in which he educated citizens about Global Warming. Winning two Academy Awards for best documentary feature and best original song, the movies is a great success.

To me, whether it gained public popularity doesn’t matter. The movie has its unique educating meaning and I recommend that everyone should watch it.

Global Warming is not a rumor. It’s time we stop ignoring this fact.

The book An inconvenient truth: the Planetary Emergency of Global Warming And What We Can Do About It written by Al Gore was also published in 2006.

(World consumption of paper has grown 400 percent in the last 40 years. Now nearly 4 billion trees or 35 percent of the total trees cut around the world are used in paper industries on every continent.(source)

For the trees’ sake, please please please please use e-books!)