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Feb 25, 2018CraigTheCool posted a message on Say the first word that pops into your head after reading the last person's postPosted in: Forum Games
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Jan 19, 2018Posted in: Forum Games
The flow of information from DNA to RNA to proteins is a central principle in biology.
If you opened a book on the main themes in biology, you would find that one of them is the relationship between DNA, RNA, and proteins.
In living things, certain segments of DNA , or genes, are essentially directions for building proteins. You can think of those DNA segments as blueprints.
RNA uses those DNA segments (genes) to build proteins, as a construction contractor uses blueprints for building structures.
What does RNA build? Proteins. Once completed, like workers in a company, each type of protein carries out a specific type of job.
RNA molecules are transcribed from DNA codes and translated into 3-D protein structures.
You can think of this process as having two parts:
- First, DNA is transcribed into RNA.
- Then, RNA is translated into proteins.
DNA makes RNA in the nucleus. RNA is a copy of certain DNA segments, or genes , that are the instructions on how to build a protein. The process of making RNA from DNA is called transcription.
RNA carries the code it has transcribed from DNA to ribosomes in the cytoplasm to build either a single protein or a part of a protein called a polypeptide in a process called translation. Many proteins are made out of various combinations of polypeptides.
Many different types of proteins exist in living things.
The human body produces about 100,000 proteins. Why does the body need so many? Most activities in and out of cells are carried out by actions of proteins. The earlier example makes it clear: Proteins are like workers in a big company. Just like the workers, proteins can be organized into groups based on the jobs they have.
Proteins can be enzymes, or they can be used for transport or storage.
On a cloudy morning, a female tufted puffin dives into frigid arctic waters. She uses her wings in pursuit of small fish. After a several successful runs, she returns to her nest with her catch neatly lined up in her bill.
All of the specialized equipment that the puffin uses in her hunting—her wings, her ability to withstand the cold water, and her keen eyesight—use a lot of ATP . As the energy is used, ATP changes into ADP. For this to happen, the body uses ATPase, an enzyme , or one class of proteins. Enzymes speed up reactions in living things.
Other classes of proteins include those that transport substances and those that store substances.
Proteins can cause movement and can be formed into structures.
To humans, an Asterias sea star is a fascinating creature to look at, seemingly harmless and slow moving. To a mussel, it is a vicious predator. The sea star climbs onto its bivalve prey, using hundreds of tube feet to pull the two shells apart. With no way to move, the mussel eventually weakens, and the tight seal of its shells cracks open. The sea star thrusts its stomach inside out into the mussel, where the predator begins eating its prey alive.
The movements of both the sea star's and mussel's muscles can only occur through the actions of actin and myosin—two types of contractile proteins that can move back and forth. These proteins work inside muscle cells.
Another class of proteins forms structures. For example, fibroin is a structural protein used in spider webs. keratin is a structural protein found in the hair that forms a rhino's horn and in a bird's feathers.
The immune system and maintenance of metabolism include the actions of many proteins.
One day you are feeling fine and healthy, the next day your throat is a bit itchy, and the day after that you're stuck in bed with a fever. You are under attack by the flu virus. During the extra sleep you are getting, protein antibodies in your bloodstream work aggressively to tag and destroy the pesky virus. A few days later, your immune system is victorious, and you are back on your feet. Antibodies are not cells. They are defensive proteins produced by cells in the immune system.
As you already know, an organism's metabolism is a complex balance of several factors, many of which are regulatory proteins. serotonin is a protein hormone that is involved in the regulation of sleep, mood, and appetite, among other things.
Keep in mind that proteins do many jobs both in and out of the cellular environment.
To summarize, parts of the DNA code are transcribed into RNA, and RNA is used to build proteins.
To summarize the big picture:
- Many types of proteins are used by organisms.
- Some proteins work in cells, while others work out of cells.
- All proteins are made in the same way.
- DNA is transcribed into RNA.
- RNA is translated into proteins.
- DNA is transcribed into RNA, which is translated into proteins.
- By now you are probably going to be dreaming about the pathway from DNA to RNA to proteins—that isn't a bad thing, considering it is the underlying theme of this entire unit.
- In addition to understanding this pathway, it is extremely important to remember the tremendous diversity in the types of proteins produced. Proteins are responsible for jobs in all parts of an organism, from moving substances within a cell, to signaling others outside the cell, to making structures such as hair. Whether proteins work in or out of a cell, all are produced inside a cell.
DNA is a double-stranded nucleic acid. The entire DNA molecule is twisted into a helix shape.
The information contained in the structure of DNA defines all of what an organism is and is capable of doing. A red-headed woodpecker has all red feathers on its head because its DNA has the genes that code for it. An aspen tree loses its leaves in the fall because its genes instruct it to do so. This coded genetic information is passed along from one generation to the next. This lesson focuses on the physical structure of the DNA molecule itself.
Think of DNA as a ladder. DNA has two long strands, like the uprights of a ladder. Each long strand is called a backbone. Cross-connections unite the two backbones, just as a ladder has rungs.
Now, imagine that the whole ladder is twisted to form a double spiral or, as it is known more often, a double helix.
he basic unit of the DNA molecule is a nucleotide.
A single strand of DNA has three distinct columns of repeating parts.
Starting from the outer edge, there are phosphates, sugars, and nitrogenous bases. Scientists define these units as nucleotides.
A nucleotide consists of one of each of a phosphate, a sugar, and a nitrogenous base. Phosphate and sugar make up the backbone of the molecule.
Learn more about the physical makeup of a DNA molecule. You may also turn to page 92 of your reference book to explore two different views of a DNA molecule.
DNA consists of four types of nitrogenous bases.
DNA consists of only four different types of nitrogenous bases, and they are organized into two groups. The purines, adenine and guanine , have two rings in their chemical structure. The pyrimidines, thymine and cytosine , are smaller with only one ring in their structure. Each base is commonly abbreviated as the first letter of its name:
- adenine (A)
- guanine (G)
- thymine (T)
- cytosine (C)
To make all living things on earth, one might expect to find a code made up of thousands of different parts. Yet the entire DNA code comes down to these four bases.
Nitrogenous bases pair up in a specific way.
In the center of the DNA molecule, the nitrogenous bases from the two strands line or pair up. The bases always pair up according to the following rules:
- adenine (A) with thymine (T), and vice versa
- guanine (G) with cytosine (C), and vice versa
Two DNA bases that are paired up are called complementary bases. Because all bases have to be complementary, it is also said that the two DNA strands are complementary to each other. Therefore, if you know the order of bases of one strand, you can figure out what the bases are on the other.
Hydrogen bonds form between the nitrogenous bases of either strand.
What holds the two DNA strands together? Why don't they simply fall apart and unwind? Just like the uprights of a ladder never touch, neither do the backbones of the DNA. That leaves the bases again. It is here that the two strands are bonded to each other—specifically, hydrogen bonds are between the paired bases. As you learned in an earlier lesson, a double hydrogen bond connects the nitrogenous bases A and T, while a triple hydrogen bond links G and C.
DNA differs among organisms based on the order and number of its bases.
You keep reading that DNA is each organism's unique genetic blueprint and that segments of DNA are genes. So, if all DNA has identical phosphates and sugars, the differences in DNA from organism to organism must be in the nitrogenous bases. The genetic differences among organisms are inherent in the number and the order of the nitrogenous bases in DNA.
From Tyrannosaurus rex to a tortoise to a termite, the critical difference is primarily in two aspects of the organism's DNA:
- the order of bases
- how many bases there are
Several scientists contributed to the discovery of the structure of DNA.
It wasn't much more than 50 years ago that the structure of DNA was unknown. Scientists the world over were using various techniques to try to uncover the mystery.
The first piece of the puzzle came in 1949, after scientist Erwin Chargaff collected data on the occurrence of the four nitrogenous bases in the DNA of various organisms. He discovered that the number of guanine bases equals the number of cytosine bases and that the number of adenine bases equals the number of thymine bases. In human DNA, for example, adenine and thymine each appear about 30 percent of the time, while guanine and cytosine appear about 20 percent of the time. Chargaff's work helped lead later scientists to realize the base-pairing makeup of DNA.
Several scientists contributed to the discovery of the structure of DNA.
A few years later, in the early 1950s, Rosalind Franklin, a scientist working in London, took X-ray photographs of a DNA molecule. Her photos gave strong clues to DNA's double-helix shape, but she was not quite able to make the connection before being diagnosed with cancer caused by exposure to X rays. She died in 1958 at the age of 37.
Read more of Franklin's life and work at Rosalind Elsie Franklin: Pioneer Molecular Biologist.
Several scientists contributed to the discovery of the structure of DNA.
American James Watson and Englishman Francis Crick used Chargaff's conclusions, Franklin's X-ray images, and their own understanding of chemistry to fully discover the 3-D structure of DNA. They used wires and tin parts to make a large model of the molecule, which helped them visualize how all the parts fit together. They won the Nobel Prize in Physiology or Medicine 1962.
The structure of DNA is two complementary strands twisted into a double helix.
Here's a list of features that all DNA molecules share:
- two complementary strands
- sugar-phosphate backbones on each strand
- hydrogen bonding in the middle of the strands between the nitrogenous bases
- strict base pairing rules: adenine with thymine and guanine with cytosine
- an overall shape of a twisted double helix
RNA is a nucleic acid found in a cell that is involved in protein production. There are many different types of RNA.
DNA is often called the brain of the cell and receives much attention and praise.
It is RNA , however, that brings the all-important DNA to life by manufacturing the thousands of different proteins an organism uses to live.
Like DNA, RNA is a nucleic acid. Unlike DNA, there is more than one type of RNA in the cell. Each type has a unique function or role, and the structure of each type of RNA helps it accomplish its function. Fundamentally, however, every RNA molecule has a similar overall nucleic acid chemical structure—a phosphate-sugar backbone attached to nitrogenous bases. In RNA, the sugar is ribose , while in DNA it is deoxyribose.
RNA has the nitrogenous base uracil, not thymine.
Aside from having a different sugar molecule, RNA and DNA differ in other ways. RNA does not have the pyrimidine base thymine, which is present in DNA.
In its place, RNA uses another pyrimidine base called uracil. Whenever a molecule of RNA pairs up with DNA, uracil pairs with the purine base adenine.
Of the four types of RNA you will learn about in this lesson, three have only a single strand of RNA—in that way, RNA most differs from DNA, which has two strands.
Messenger RNA (mRNA) is a single-stranded molecule.
This lesson only makes slight mention of the function of each type of RNA. Their roles in the cell will be explored further in upcoming lessons.
The first type of RNA is mRNA . Its structure is relatively simple: It's a piece of single-stranded RNA. It is made directly from DNA, so it is a copy of the genetic code of DNA.
A molecule of mRNA can be between 300 to 9,000 nucleotides long.
The process by which mRNA is made from DNA is called transcription.
Transfer RNA (tRNA) is shaped like a cross.
A molecule of tRNA has a different shape than a molecule of mRNA. tRNA is often described as a cross or even the letter t (that makes it easy to remember). Its shape is a long, single-stranded piece of RNA. In some places, the bases pair up and make regions of double strands.
Like all RNA, tRNA is made in the cell's nucleus from DNA. A molecule of tRNA can be between 70 to 90 nucleotide sequences long, and its job is to identify which amino acids the mRNA is coding for and bring them in.
To do the work of making proteins, all of these different kinds of RNA migrate out of the nucleus. Protein synthesis takes place in the cytoplasm.
Ribosomal RNA (rRNA) is part of the structure of a ribosome.
Molecules of rRNA , which can be between 100 to 4,000 nucleotide sequences long, are formed in the nucleus and migrate to the cytoplasm. In the cytoplasm, rRNA combines with many small proteins to make up a ribosome.
Each ribosome has two subunits, a larger one and a smaller one. The lesson on translation will discuss the role that ribosomes play in protein production.
Turn to pages 104–105 of your reference book to read about these three types of RNA and their structures.
Double-stranded RNA (dsRNA) does not play a role in protein production.
In October 2006, American scientists Andrew Z. Fire and Craig C. Mello won the Nobel Prize for Physiology or Medicine. They discovered another kind of RNA, one that is double stranded and keeps other kinds of RNA from performing their tasks.
In the cell, dsRNA is cut into pieces and combined with proteins to make a complex called a small interfering RNA. Its function is to destroy certain mRNA strands. If an mRNA molecule is destroyed, the protein it was going to make never gets made. In this case, one type of RNA destroys the mRNA, so that the gene that coded for the mRNA is silenced, or not expressed, in the organism.
By destroying some mRNA strands, dsRNA plays an important role in regulating protein production. Therefore, dsRNA is important in controlling which genes are expressed and which genes are not expressed.
Gene-silencing dsRNA has many potential health benefits for people.
Recent discoveries about the actions of gene-silencing dsRNA might lead to a cure for cancer or other maladies.
Scientists have already been successful in turning off certain genes in the roundworm and fruit fly. They feel it is within their reach to turn off those genes that cause disorders in people.
Also, many viruses operate using RNA. The virus injects its RNA into its host's cells, and the cells translate the viral information.
However, with gene silencers, viral RNA can be targeted and destroyed before it ever reaches translation. Think of how the world would change if such a thing happens.
Compare DNA and RNA to highlight their similarities and differences.
Now that you've looked into the structures of DNA and RNA, review how they are the same and how they differ.
The cell uses many types of RNA. Each type has its own specific structure that relates to its function.
This lesson presented four different types of RNA: mRNA, tRNA, rRNA, and dsRNA. Each has structure that relates to the role it plays in the cell. Knowing those structures will help you understand the detailed processes that will be discussed in upcoming lessons. Before a cell can divide, its DNA must be replicated.
You're probably familiar with the ferocious predators of the animal world—tigers, sharks, and piranhas—but how familiar are you with killer plants? Deep in an Australian jungle, a bird releases its waste onto the branch of a tree. In its waste is the seed of a strangler fig (Ficus destruens).
Just like those of any other plant, the roots of the strangler fig search for soil. However, since the seed starts its life high in the branches of another tree, its roots climb down, or strangle, the trunk of its host until they reach the ground. Yet, this isn't as deadly of an embrace as it looks. The real trouble comes as the top of the strangler fig grows thick with leaves, blocking sunlight from the host tree.
Strangler figs grow quickly, and growth includes the making of new cells. Before each mitotic division, the DNA has to be copied, or replicated. The process of DNA replication is similar in all organisms.
Replication begins when the DNA double helix unwinds.
To begin replication , the double helix unwinds. The nitrogenous base pairs pull apart from each other at a replication fork, exposing the two strands.
The unwinding of the helix does not start at one end of the molecule, as you might think. Rather, it starts at many points along the DNA stand. The new DNA is made at each of these unwound segments, eventually fusing into each other. In this way, replication can be accomplished rapidly.
As the double helix continues to open, new nitrogenous bases are added on both sides.
With each strand pulled apart from the other, forming a replication fork, nitrogenous bases on both sides are exposed. Using the base-pairing rules, new nucleotides come in and match up on both strands.
Each single strand is a template for a new strand because of base pairing. The two helixes wind as they go, very shortly after the new bases are added.
Replication produces identical copies of the DNA molecule.
At the end of replication, two identical copies exist
Both copies consist of one original strand plus one newly made strand. Therefore, once DNA unwinds to replicate, it only rewinds with the new strands. The two original strands are separated forever.
Explore the replicating DNA molecule on-screen, and then turn to pages 94–95 of your reference book to read about DNA replication.
More than 30 different types of proteins are involved in the replication process.
Unzip. Bring in bases. Make new strands. Those steps are the basics; however, the process actually occurs through the actions of more than 30 proteins. Like workers on an assembly line, each protein has its specific job to make sure the process as a whole is accomplished.
In the beginning of this unit, remember learning about organisms that need many types of proteins to live? In replication, there is a certain enzyme that cuts one strand to start the unwinding. Another enzyme helps keep the separated strands from binding back together.
Helicase and DNA polymerase are examples of enzymes used in replication.
Two examples of enzymes used in replication are helicase and DNA polymerase.
Helicase acts to unwind DNA, moving down the molecule. It is often referred to as the protein that unzips DNA.
Once the DNA is unwound, DNA polymerase is the protein that brings in the new nitrogenous bases and pairs them up on the original strands. DNA polymerase molecules are the central proteins involved in making or synthesizing new DNA.
Reminder: An enzyme is a protein that speeds up a chemical reaction.
Some enzymes check for mistakes in replication.
Despite the often extremely large numbers of nitrogenous bases copied, replication takes place with a very high level of accuracy. The precision of replication is essential to the well-being of an organism. Mistakes in replication can lead to major problems in a cell.
Several proteins work together to check and repair mistakes in replication. If the wrong base is put in, the proteins will cut it out, bring in the right one, and fix the other parts of the molecule. These proteins act as a DNA repair mechanism.
DNA in a cell can replicate in a surprisingly short time.
After eating a nice meal, you sit back and let your body digest it, right? Well, sort of. Your body doesn't do all of the work on its own. Millions of bacteria call your intestines home, where they help digest your food.
A common bacterium is called Escherichia coli, otherwise known as
E. coli. Maybe you've heard of E. coli in the news. When E. coli gets out of your intestines and into other parts of your body, it can make you sick. There are various strains of E. coli—some are helpful, while others are harmful.
For E. coli to reproduce, its DNA has to be replicated. A bacterium only has one circular chromosome. To replicate its entire DNA strand takes about 42 minutes. All of the DNA in a typical human cell takes about 8 hours to replicate because it is so much longer. In a human, 25 million new cells are made every second, or 2 trillion new cells per day.
DNA replication results in an exact copy of the original DNA strand.
Billions of times a day, cells of your body, and of the bacteria living within you, divide. Before this can happen, the entire DNA code has to be replicated each and every time. Replication occurs when DNA's double helix opens. Each strand becomes a template for a new strand. New nitrogenous bases are brought in, and two new, identical strands are produced. Many proteins are involved in this process.
White-rot fungus produces enzymes that digest compounds in plastic, weapons, and toxic waste.
Fungus has a bad reputation. Most people associate it with mildew or athlete's foot. Like many misconceptions, this one is not completely accurate.
Scientists developed an interest in white-rot fungus (Phanerochaete chrysosporium) when they discovered it was good at breaking down and digesting a large variety of compounds. In nature, white-rot fungus usually breaks down wood, but scientists have found it can also digest compounds similar to many human-made chemicals. It may even break down chemicals that are serious waste problems, such as plastic and toxic waste.
The discovery that a fungus might be a safe solution to some waste problems is certainly an exciting one. But how does it do it? The answer is that it uses certain powerful enzymes. Organisms use enzymes to break down and digest food. And what are enzymes? Why, proteins, of course.
The leafy sea dragon produces enzymes that digest fish larvae and sea lice.
If you're planning a scuba trip to Australia, you'd better be on the lookout for dragons. These dragons aren't the kind that can fly and breathe fire—rather, they are leafy sea dragons (Phycodurus eques).
These fish (which hardly look like fish at all) are covered in appendages that look exactly like leaves of kelp. They move very slowly and live in large masses of kelp. Known as one of the best-camouflaged creatures on the planet, leafy sea dragons blend perfectly into their habitat.
Leafy sea dragons feed on fish larvae and other tiny creatures called sea lice. To digest the morsels, they use specific enzymes. And how do they produce these protein compounds? The same way the fungus does—through translation.
The pitcher plant produces enzymes that digest rats.
In a dense patch of Borneo's rain forest, a light rain trickles down onto the colorful vegetation. A baby rat scurries to find shelter before the dampness turns into a downpour. It finds a large, rubbery plant that seems to be a perfect hiding spot.
A strong, attractive smell further lures the unsuspecting rodent to peer into the pitcher plant. The cloudiness fogs the 3½ L of liquid death at the bottom of the plant. The rat slides into the predatory pool.
The liquid is not simply evidence of rain. It contains powerful enzymes that start digesting the frantic rat alive. The baby rat tries to climb the sides of the pitcher plant, but a special waxy coating prevents its progress. How does the plant produce enzymes strong enough to digest a rat? Yes, you've got it now—through translation.
Carnivorous plants create a variety of unique proteins.
The enzymes of these very different organisms are built using the same language: the genetic code.
It would seem highly unlikely that the enzymes made by white-rot fungi, leafy sea dragons, and pitcher plants would have anything in common. Not only are all the enzymes produced through translation, but they are also all based on the same exact genetic code .
The only difference between the enzymes is the order of their amino acids. The order is determined by the order that tRNA molecules bind to the mRNA in a ribosome.
Each codon on an mRNA molecule is the basis for which amino acid is next in the chain; thus, a sequence of codons is the key to making enzymes. Codons match up with specific amino acids, creating the genetic code.
The genetic code connects codons from an mRNA strand to an amino acid.
Let's examine a table of the genetic code. As a reference, you may download a copy of the table, listed as The Genetic Code under Materials in Lesson Resources, or turn to page 103 of your reference book.
The table is organized to show the possible base combinations in mRNA. Each codon codes for an amino acid.
Four codons are different. They code for start and stop signals in translation.
There are specific codes to start and stop translation.
The start codon for of any protein is always AUG, and AUG codes for the amino acid methionine (met in the table). Therefore, every protein starts with the amino acid methionine.
To stop translation, one of three stop codons is used—UAA, UAG, and UGA. No amino acid corresponds to the stop codons.
The genetic code is used to construct every single organism on earth.
Think about the genetic code. What can it mean about life on earth if each bacterium, crawling bug, leafy plant, feathery bird, scaly reptile, and furry mammal is built from the same code?
It is evidence for a connection between all organisms. The genetic code is universal—that is, all organisms share it. A saguaro cactus uses the same genetic code to build itself as your body does. In the upcoming units, you will continue to explore how scientists piece together the puzzle called life.
The genetic code translates mRNA codons into specific amino acids.
The codons on mRNA each correspond to specific amino acids, which is called the genetic code. The information is organized into a usable table.
The genetic code shows the sequences of three nitrogenous bases for codons and their connection to the specific amino acids they represent.
It is fascinating to think that the genetic code is the same for all organisms, including white-rot fungi, leafy sea dragons, and pitcher plants.
Jan 14, 2018CraigTheCool posted a message on The Above Avatar is Your Substitute Teacher. What Is the Lesson?Posted in: Forum Games
How to be a member of the best evil team in Pokemon
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Dec 17, 2016CraigTheCool posted a message on Community Creations: Extended Pistons (Vanilla-Friendly, No Mods), by tryashtarPosted in: News
I am going to make a multiplayer world with my friends and use this a mailing system.
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