The Genetic Code & Protein Synthesis
In protein synthesis the information
held in the sequence of bases in a gene is translated into a sequence of amino acids in a polypeptide chain.
Friedrich Miescher
identified DNA in the 1860s
Messenger RNA (mRNA) carries
information from the DNA in the nucleus out into the cytoplasm. It is formed when a smell length of the DNA double helix unzips.
RNA is closely related to DNA but
it doesn't form complex molecules. The sequence of bases along a strand of RNA is related to the sequence of bases on a small part of DNA in the nucleus - different types of RNA take different roles in the process of protein synthesis.
DNA is transcribed
1. to give a length of mRNA
Erwin Chargaff
1940s - created a rule for DNA bases
Rosalind Franklin
1952 - created a photo of DNA structure
tRNA in the cell attaches
2. to specific amino acids
A mRNA moves
3. out of the nucleus and becomes engulfed by a ribosome
tRNA molecule carrying
4. amino acid lines up against matching mRNA on the ribosome
Peptide links are formed between
5. the amino acids brought by the tRNA
When the polypeptide is released
6. into the cytoplasm, the tRNA units also unbind and return to the cytoplasm to pick up more amino acids. The ribosome may read the mRNA again.
Section 1 00:00:02 What are the similarities and differences between the structures of DNA and RNA? DNA is found in the nucleus of a cell, and it contains the instructions that are needed for making proteins. RNA plays a key role in moving the instructions that are found in the DNA to the ribosomes, where the proteins are actually made. DNA and RNA share many similarities, but their 00:00:25 differences allow them to do different jobs in the cell. Next, we're going to look at just the DNA structure. Section 2 00:00:02 In these next few slides, we're going to go over a little bit about the structure and the function of nucleic acids. And the nucleic acids we're going to discuss are DNA and RNA. Their function is to store and transmit hereditary information and they're very, very long macromolecules. DNA is a double-stranded helical polymer. 00:00:27 It contains the sugar deoxyribose, a phosphate group, and the bases adenine, cytosine, thymine and guanine. It is found in the nucleus of cells and it's responsible for the protein synthesis that is the function of cells. OK, RNA, ribonucleic acid, is a single-stranded nucleic acid. It contains the sugar ribose, a phosphate group, and it has the bases adenine, cytosine, guanine, and uracil. 00:01:05 It is responsible for moving the information that's in the DNA in the nucleus out of the nucleus and over to the ribosomes, which is where protein synthesis occurs. Those two little black dots there, are ribosomes. Also, these little black dots, all over here, are ribosomes. There are millions of ribosomes in the cell. So RNAs job is to get the information that's in the DNA over to the ribosomes because that's where 00:01:34 protein synthesis occurs. OK, now for DNA structure. The molecule that makes up DNA, that gets repeated over and over again billions of times to make an actual DNA molecule, is called a nucleotide. And the nucleotide, building block of DNA, it consists of a deoxyribose molecule, which is this portion right here. It's a sugar. 00:02:03 And there are five carbons in here, where these little points are and there's no Cs, that's actually a carbon atom, carbon atom, carbon atom, carbon atom. So you've got 1, 2, 3, 4, 5 carbon atoms and there normally would be an oxygen here, but there's not, so that's why it's called deoxyribose. OK, it also consists of a phosphate group, which is this part right here. 00:02:28 And a nitrogenous base. Right here's the nitrogenous base. In this case, the base is guanine, G-U-A-N-I-N-E, but it could be adenine or cytosine, guanine, or thynine. So a DNA nucleotide will always have a phosphate group and a deoxyribose sugar. They are the same, but the third portion of the nucleotides is going to be one of the four nitrogenous bases. 00:02:59 And then they're all connected together to make up one nucleotide. Now, a little more on the structure of DNA. These nucleotides link together. Here's a nucleotide. This is the sugar. Here is the nitrogenous base, in this case, adenine. And then over here is the phosphate group, right there. 00:03:22 Now, you can see that here's another nucleotide that's attached to it. This is another nucleotide attached right here. Here's another nucleotide, and here's another nucleotide. So what DNA is is a long chain of nucleotides that actually, is connected then to another long chain of nucleotides. On the outside of the molecule, are these sugar and phosphate molecules and they tend to twist and make the 00:03:54 whole molecule look like this twisted latter. This right here, phosphate, sugar, phosphate, sugar, phosphate, sugar, this is kind of analogous to this portion of the diagram. And then this side here phosphate, sugar, phosphate, sugar would represent this side of the model. In the middle, you have the nitrogenous bases. So those nitrogenous bases would be in the middle here. 00:04:23 And they're all connected by hydrogen bonds. Which by themselves are very weak, but when you multiply them billions of times you have a very strong bond that's holding this whole double helix together. Now when DNA reproduces, the two strands unzip, enzymes add new bases to each strand, and then you have two new strands which make up two new identical molecules of DNA. And we'll go into that a little bit more in some of the 00:04:55 future slides. Section 4 00:00:02 What are the similarities and differences between the structures of DNA and RNA? Nucleotides are the building blocks of DNA. A nucleotide contains deoxyribose, which is this sugar right here, and it's called deoxy because it's missing the oxygen there, a phosphate group right here, and a nitrogenous base right here. And all three of them are connected together. 00:00:31 That is a nucleotide. Now, DNA and RNA have very similar structures. You're going to see that in the next segment. But the differences allow them to actually perform different jobs in the cell. So the next thing we're going to do is look at RNA structure. Section 5 00:00:02 The genetic code is found in the DNA, which is inside the nucleus, but proteins are made on the ribosomes that are outside of the nucleus. So the information has to get from the DNA in the nucleus outside of the nucleus over to the ribosomes. That's what the RNA does in order to help the cells make proteins. The structure of RNA is very similar to that of DNA, but 00:00:26 there are a few differences. One of the differences is that RNA has a sugar in it that is called ribose. Here is where the ribose sugar is. It's a 5 carbon sugar-- one, two, three, four, five. This one does have the oxygen, whereas in DNA, deoxyribose sugar does not have the oxygen. So there's the sugar. 00:00:56 The next thing it has here is a phosphate group, which is very similar to the phosphate group in DNA. Phosphate-- this is the ribose right here. And then it also has a nitrogenous base-- that's this section of the molecule right over here. And a nitrogenous base in RNA could be either adenine, cytosine, guanine, or in this case, uracil. 00:01:25 That's what this one is, uracil. In this slide, we're going to begin to look at how the RNA helps the cell make proteins. Recall that RNA is a single-stranded chain of nucleotides. Its function is to move the genetic information in the DNA out of the nucleus over to the ribosomes. When proteins are made, the two strands of DNA separate 00:01:50 and they're used to make a strand of RNA. One strand of DNA is used to make a strand of RNA. When it's finished, then the DNA strands are put back together and the RNA moves out of the nucleus over to the ribosomes. In this picture, you have three bases here in the RNA. Remember? It's always a little clue here that this is RNA, because you 00:02:14 see the uracil there. So these three bases are-- they're called the codon, and what that means is that these three bases tell the ribosomes to go out and grab a specific amino acid. In this case, the amino acid that's coded for by C, G, and A is argenine, and the abbreviation for that amino acid is Arg. 00:02:41 The next codon would begin with this U and then it would have 2 more bases on it, and whatever amino acid that that codon is calling for would come into the ribosome. And eventually, all of the amino acids would be attached to each other in a long chain and they would make the protein. The next slide has us looking at a comparison, then, between the RNA structure and the DNA structure. 00:03:11 RNA-- ribonucleic acid, the sugar is ribose. DNA-- deoxyribonucleic acid, the sugar is deoxyribose. RNA is a single strand of nucleotides-- thousands of them, but all in a single strand. With DNA, you have two strands that are linked together in this twisted helix shape. 00:03:40 The bases in RNA are cytosine, guanine, adenine, or uracil. The bases in DNA are cytosine, guanine, adenine, or thymine. Remember, you're only going to see thymine in DNA and you only going to see uracil in RNA. All right, so this is pretty much a wrap up of what the basic structures here of these two molecules. Section 7 00:00:02 What are the similarities and differences between the structures of DNA and RNA? DNA contains the instructions needed for protein synthesis. RNA moves the instructions to the ribosomes where the protein synthesis actually occurs. And the structures of DNA and RNA are quite similar, but their key differences allow for specialized functioning. We're going to next look at the discovery of how the base 00:00:30 pairs in DNA and RNA work together. Section 8 00:00:01 These next slides are going to examine how DNA was actually discovered to be the inheritable material and what the role of RNA is in heredity. This work is really the result of the work of many, many scientists over a period of over 100 years. One of the men involved in this is named Phoebus Levene. And his contribution was that he was studying biochemistry, and he discovered deoxyribose, which is the sugar in DNA, and 00:00:32 ribose, which is the sugar in RNA. He realized that they were in these two molecules. He also proposed what's called the polynucleotide theory, that DNA and RNA were actually composed of repeating units of nucleotides. Erwin Chargaff was studying cells and the DNA inside of cells, and he realized that no matter what cell type he studied, the amount of adenine was always equal to the amount 00:01:03 of thymine, and the amount of cytosine in a particular cell type was always equal to the amount of guanine. So he came up with something that is still currently referred to as Chargaff's rules. The amount of adenine in a particular cell type is always going to equal the amount of thymine, and the amount of cytosine will always equal the amount of guanine. A equals T. C equals G. Chargaff's rules. 00:01:30 Now, James Watson and Francis Crick are the two who are credited with coming up with the first actual accurate model of a DNA molecule. They did, however, rely on the work of many previous scientists in order to come up with that model. One of the scientists who really helped quite a bit in helping them to figure out what the actual structure was was Rosalind Franklin. 00:01:57 She had been working with a new type of photography called X-ray crystallography, or diffraction photography. Her picture gave them the correct orientation for the phosphates, the sugars, and the bases. They also used Chargaff's rules in order to determine how those bases were paired with each other. And for that, they got the Nobel Prize. Then, in the 1960s, two scientists named Marshall 00:02:27 Nirenberg and Heinrich Matthaei were studying RNA because people knew now what the DNA actually had to code for the proteins, but they didn't really know what the role was that RNA played in actually getting the proteins produced. They were studying E coli, which is a lab strain of bacteria. And they conducted something that's referred to as the 00:02:50 poly-U experiment. They took a whole bunch of uracil, threw it in an experimental chamber, and they ended up producing these chains of phenylalanine. That was how they discovered that RNA is actually the agent responsible for transmitting the DNA messages for protein synthesis. The next slide here is going to go in a little bit into the 00:03:19 impact of all this research. And there are three areas, science, society, and the environment, that this research has really had a big influence on. The first here, the Human Genome Project. This project was started in the '90s, 1990s, and its intention was to sequence all the DNA in the human genome so that we would know where these genes are and what it is that 00:03:46 they actually code for, the proteins that they code for. So this project was supposed to identify 300 billion base pairs that make up the human genome, and within those base pairs, identify the 22,000 to 25,000 genes that determine the sequence of codons which ultimately determine the sequence of amino acids and proteins. The project is finished, but the analysis of this data will continue for quite some time. 00:04:16 The Human Genome Project can provide clues to understanding human biology. And it has the potential to revolutionize how diseases are diagnosed, how they're treated, and possibly even prevented. In society, genetic testing is something that can happen in order to help people who are possibly concerned that they have a genetic disease in their family. 00:04:41 You can go to a genetic counselor, find out information, find out a risk assessment for what your chances are of actually passing these genes onto your offspring. DNA typing, it's been around since the 1980s, and it's been used to connect perpetrators to crimes. It also has been used in paternity . Testing in the environment, understanding of DNA has 00:05:07 allowed for selective breeding of plants and animals. It's possible to breed animals that have very desirable traits, for example, chickens that can lay more eggs. Also, genetically modified organisms have been produced through DNA technology. And the genetically modified organisms, that is an organism that has been changed genetically to have some favorable characteristic. 00:05:35 For example, it's possible to grow tomatoes that can be grown in areas where they haven't been able to be grown before, for example, drought resistant tomatoes. Places where they don't get a whole lot of rainfall and couldn't really grow tomatoes before, now you can grow those crops. So these are just some of the areas where DNA research has really impacted science, society, and the environment.
DNA & RNA
The triplet code (three bases) on DNA/RNA is known as
a codon (which can either signal start/beginning of sequence or used to code amino acid).
mRNA is formed
as a complementary strand to the DNA - mirror of the original base sequence.
The coding or antisense strand of the DNA acts
as a template for the formation of the mRNA. The mRNA then moves out of the nucleus transporting the instruction from the genes to the surface of the ribosomes (which are the site of protein synthesis).
Peptide links are formed
between the amino acids, joining them together to form a polypeptide chain which in turn can be used to form a larger protein.
Human Genome Project
The Human Genome Project was an international research effort to determine the sequence of the human genome and identify the genes that it contains. The Project was coordinated by the National Institutes of Health and the U.S. Department of Energy. Additional contributors included universities across the United States and international partners in the United Kingdom, France, Germany, Japan, and China. The Human Genome Project formally began in 1990 and was completed in 2003, 2 years ahead of its original schedule. The work of the Human Genome Project has allowed researchers to begin to understand the blueprint for building a person. As researchers learn more about the functions of genes and proteins, this knowledge will have a major impact in the fields of medicine, biotechnology, and the life sciences. The main goals of the Human Genome Project were to provide a complete and accurate sequence of the 3 billion DNA base pairs that make up the human genome and to find all of the estimated 20,000 to 25,000 human genes. The Project also aimed to sequence the genomes of several other organisms that are important to medical research, such as the mouse and the fruit fly. In addition to sequencing DNA, the Human Genome Project sought to develop new tools to obtain and analyze the data and to make this information widely available. Also, because advances in genetics have consequences for individuals and society, the Human Genome Project committed to exploring the consequences of genomic research through its Ethical, Legal, and Social Implications (ELSI) program. In April 2003, researchers announced that the Human Genome Project had completed a high-quality sequence of essentially the entire human genome. This sequence closed the gaps from a working draft of the genome, which was published in 2001. It also identified the locations of many human genes and provided information about their structure and organization. The Project made the sequence of the human genome and tools to analyze the data freely available via the Internet. In addition to the human genome, the Human Genome Project sequenced the genomes of several other organisms, including brewers' yeast, the roundworm, and the fruit fly. In 2002, researchers announced that they had also completed a working draft of the mouse genome. By studying the similarities and differences between human genes and those of other organisms, researchers can discover the functions of particular genes and identify which genes are critical for life. The Project's Ethical, Legal, and Social Implications (ELSI) program became the world's largest bioethics program and a model for other ELSI programs worldwide. For additional information about ELSI and the program's accomplishments, please refer to What were some of the ethical, legal, and social implications addressed by the Human Genome Project?
Codons form a unit of the genetic code that determines a specific
amino acid
The tRNA molecules each
carrying an amino acid line up alongside the mRNA on the surface of the ribosome building up a long chain of amino acids.
Depending on the organism, the number OF _____ in a cell may change.
chromosomes
genetic code was based on
codons
Transfer RNA (tRNA) is
found in the cytoplasm - it picks up particular amino acids from the vast numbers always free there.
Segments of DNA transferred from parent to offspring are called
genes
DNA is coiled into chromosomes in a cell's
nucleus
James Watson & Francis Crick
rapidly put together several models of DNA and attempted to incorporate all the evidence they could gather
Once the RNA sequence is known
the DNA sequence is simple to deduce, from the way the bases pair.
The messages are relayed from the nuclear DNA to
the active synthetic enzymes on the ribosomes by ribonucleic acids.
The DNA is combined within the chromosomes in
the nucleus of a cell. The ribosomes where proteins are synthesised are found the cytoplasm and as no nuclear DNA has even been detected there the message can't be carried out directly.
genetics
the study of heredity in organisms
Genetic code is based on genes
which is a sequence of bases on a DNA molecule for coding a sequence of amino acids in a polypeptide chain.
