Homework SourseDescribe how the structure of the DNA double helix was disco
Solution
1 The function of DNA? depends to a large extent on its structure. The three-dimensional structure of DNA was first proposed by James Watson and Francis Crick in 1953. It is one of the most famous scientific discoveries of all time.
James and Francis used evidence shared by others, particularly Rosalind Franklin and Maurice Wilkins, to determine the shape of DNA. Rosalind worked with Maurice at King\'s College London. She beamed X-rays through crystals of the DNA molecule and then used photographic film to record where the scattered X-rays fell. The shadows on the film were then used to work out where the dense molecules lie in the DNA. This technique is called X-ray diffraction. The DNA crystals resulted in a cross shape on the X-ray film which is typical of a molecule with a helix shape. The resulting X-ray was named Photograph 51 and Maurice shared it with James and Francis.
In 1953 James Watson and Francis Crick published their theory that DNA must be shaped like a double helix. A double helix resembles a twisted ladder. Each \'upright\' pole of the ladder is formed from a backbone of alternating sugar and phosphate groups. Each DNA base? (adenine, cytosine, guanine, thymine) is attached to the backbone and these bases form the rungs. There are ten \'rungs\' for each complete twist in the DNA helix.
James and Francis suggested that each \'rung\' of the DNA helix was composed of a pair of bases, joined by hydrogen bonds?. According to Erwin Chargaff’s rules, A would always form hydrogen bonds with T, and C with G.
2 - It is not the DNA itself that controls cellular functions, it is the proteins that are coded by the DNA. The nucleotide sequences that make up DNA are a “code” for the cell to make hundreds of different types of proteins; it is these proteins that function to control and regulate cell growth, division, communication with other cells and most other cellular functions. This is why DNA is said to “carry” or “store” information in the form of nucleotide sequences.
The sequences need to be “decoded” and then translated in order to form the protein. This process is called protein synthesis.
- To function correctly, each cell depends on thousands of proteins to do their jobs in the right places at the right times. Sometimes, gene mutations prevent one or more of these proteins from working properly. By changing a gene’s instructions for making a protein, a mutation can cause the protein to malfunction or to be missing entirely. When a mutation alters a protein that plays a critical role in the body, it can disrupt normal development or cause a medical condition. A condition caused by mutations in one or more genes is called a genetic disorder.
In some cases, gene mutations are so severe that they prevent an embryo from surviving until birth. These changes occur in genes that are essential for development, and often disrupt the development of an embryo in its earliest stages. Because these mutations have very serious effects, they are incompatible with life.
It is important to note that genes themselves do not cause disease—genetic disorders are caused by mutations that make a gene function improperly. For example, when people say that someone has “the cystic fibrosis gene,” they are usually referring to a mutated version of the CFTR gene, which causes the disease. All people, including those without cystic fibrosis, have a version of the CFTR gene.
3. Function of DNA
stores an organisms genetic material in the nuclei
-replicates itself when dividing
-provides code or template for the particular sequencing of amino acids that bond together and make a protein
function of RNA
three RNA\'s have different functions :-
One of these active processes is protein synthesis, a universal function wherein mRNA molecules direct the assembly of proteins on ribosomes. This process uses transfer RNA(tRNA) molecules to deliver amino acids to the ribosome, where ribosomal RNA(rRNA) then links amino acids together to form proteins.
4.
5- Translation is the process that takes the information passed from DNA as messenger RNA and turns it into a series of amino acids bound together with peptide bonds. It is essentially a translation from one code (nucleotide sequence) to another code (amino acid sequence). The ribosome is the site of this action, just as RNA polymerase was the site of mRNA synthesis. The ribosome matches the base sequence on the mRNA in sets of three bases (called codons) to tRNA molecules that have the three complementary bases in their anticodon regions. Again, the base-pairing rule is important in this recognition (A binds to U and C binds to G). The ribosome moves along the mRNA, matching 3 base pairs at a time and adding the amino acids to the polypeptide chain. When the ribosome reaches one of the \"stop\" codes, the ribosome releases both the polypeptide and the mRNA. This polypeptide will twist into its native conformation and begin to act as a protein in the cells metabolism.
The steps in translation are:
1. The ribosome binds to mRNA at a specific area.
2. The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.
3. Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain.
4. The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA.
5. The polypeptide forms into its native shape and starts acting as a functional protein in the cell.
6- three different types of mutations are :-
Substitution
A substitution is a mutation that exchanges one base for another (i.e., a change in a single \"chemical letter\" such as switching an A to a G). Such a substitution could:
change a codon to one that encodes a different amino acid and cause a small change in the protein produced. For example, sickle cell anemia is caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced.
change a codon to one that encodes the same amino acid and causes no change in the protein produced. These are called silent mutations.
change an amino-acid-coding codon to a single \"stop\" codon and cause an incomplete protein. This can have serious effects since the incomplete protein probably won\'t function.
Insertion
Insertions are mutations in which extra base pairs are inserted into a new place in the DNA.
Deletion
Deletions are mutations in which a section of DNA is lost, or deleted.
- Reason - Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, some mutations cannot be passed on to offspring and do not matter for evolution. Somatic mutations occur in non-reproductive cells and won\'t be passed onto offspring. For example, the golden color on half of Red Delicious apple was caused by a somatic mutation. Its seeds will not carry the mutation.
The only mutations that matter to large-scale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germ line mutations.
7- three ways of genetic engineering being used in agriculture ;-
1- Golden rice - Genetic modification is often used to make \"healthier\" foods, such as golden rice, which contains beta-carotene – the very same vitamin that makes carrots orange. The result is that people without access to many vitamins will get a healthy dose of vitamin A when the rice is consumed.
2. Bigger, longer-lasting tomatoes - When tomatoes are genetically engineered, they can be made bigger and more robust. These are engineered to produce tomatoes that can remain fresh for longer, can be shipped farther from where they are grown, and can be harvested all at the same time rather than harvesting only parts of a field at each harvest.
3 Salmon that grow faster - Salmon do not produce growth hormones year-round, so scientists have looked toward genetic engineering and found a solution: a modification that allows salmon to grow twice as fast than those that are not engineered
| Substitution A substitution is a mutation that exchanges one base for another (i.e., a change in a single \"chemical letter\" such as switching an A to a G). Such a substitution could: change a codon to one that encodes a different amino acid and cause a small change in the protein produced. For example, sickle cell anemia is caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced. Insertion Deletion - Reason - Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, some mutations cannot be passed on to offspring and do not matter for evolution. Somatic mutations occur in non-reproductive cells and won\'t be passed onto offspring. For example, the golden color on half of Red Delicious apple was caused by a somatic mutation. Its seeds will not carry the mutation. The only mutations that matter to large-scale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germ line mutations. |
