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Double Helix Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral. The two polynucleotide chains run in opposite directions. The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a spiral staircase.
The Backbone DNA is in the form of a double helix. This means that two helices, or sides, twist around a center. The sides of the double helix are referred to as the backbone of the DNA strand. They are made up of molecules of phosphate and sugar. Scientists use complementary base pairing to help identify the genes on a particular chromosome and to develop methods used in genetic engineering (material to eliminate undesirable characteristics or to produce desirable new ones).
.How is the structure of DNA Related to its function
The structure of DNA is a double helix, which can most efficiently be split into two new strands when the DNA is getting ready to copy the DNA, because it "unwinds." Another important part of the structure is the hydrogen bond that connects the complimentary bases.
When DNA splits into individual strands, these bonds are broken, and you now have two strands with complimentary bases. RNA can then be created by using these individual bases, which is how DNA gets its message out of the nucleus (since it's too large in size to fit through the pores in the nuclear envelope).
Nucleotides are organic molecules that serve as the monomers, or subunits of nucleic acids like DNA and RNA.
The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and at least one phosphate group.
3 components
1. Phosphate group :- Composed of one atom of phosphorus surrounded by four oxygen atoms.
2. Sugar (deoxyribose)
3. Nitrogen base=A nitrogen base is a carbon ring structure that contains one or more atoms of nitrogen:
-adenine (A)
-guanine (G)
-cytosine (C)
-thymine (T)
DNA carries the information for making all of the cell's proteins. These proteins implement all of the functions of a living organism and determine the organism's characteristics. When the cell reproduces, it has to pass all of this information on to the daughter cells. Different types of cells replicated their DNA at different rates. Some cells constantly divide. Other cells go through several rounds of cell division and stop.
Finally, some cells stop dividing, but can be induced to divide to repair injury. In cells that do not constantly divide, the cues for DNA replication/cell division come in the form of chemicals. These chemicals can come from other parts of the body (hormones) or from the environment
Process of DNA Replication
1) The first major step for the DNA Replication to take place is the breaking of hydrogen bonds between bases of the two antiparallel strands. The splitting happens in places of the chains which are rich in A-T.
Helicase is the enzyme that splits the two strands. The initiation point where the splitting starts is called "origin of replication".
2) The binding of RNA Primase in the the initiation point of the 3'-5' parent chain.
RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases.
3) The elongation process is different for the 5'-3' and 3'-5' template.
a)5'-3' Template: The 3'-5' proceeding daughter strand -that uses a 5'-3' template- is called leading strand because DNA Polymerase ä can "read" the template and continuously adds nucleotides.
b)3'-5'Template: The 3'-5' template cannot be "read" by DNA Polymerase. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand the RNA Primase adds more RNA Primers. DNA polymerase reads the template and lengthens the bursts. The gap between two RNA primers is called "Okazaki Fragments".
4) In the lagging strand the DNA Pol I -exonuclease- reads the fragments and removes the RNA Primers. The gaps are closed with the action of DNA Polymerase and DNA Ligase. Each new double helix is consisted of one old and one new chain. This is what we call semiconservative replication.
5) The DNA Replication is not completed before a mechanism of repair fixes possible errors caused during the replication. Enzymes like nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps.
HISTORY
Gregor Mendel And Heredity= At 1866 he experimented of pea plants and this led to his idea of inheritance.Though this is very far from what DNA actually is, without this information about inheritance, the idea of heredity would never have developed and without the idea of heredity, nobody would know about DNA.
=The Father of Genetics
Friedrich Miescher= In 1869 Swiss physiological chemist Friedrich Miescher first identified what he called "nuclein" inside the nuclei of human white blood cells. (The term "nuclein" was later changed to "nucleic acid" and eventually to "deoxyribonucleic acid," or "DNA.")
Laying the Groundwork: Investigation on the Structure of the DNA
Phoebus Levene= He characterized the different forms of nucleic acid, DNA from RNA. a biochemist who analyzed DNA and found that it contained adenine, guanine, thymine, cytosine, deoxyribose, and a phosphate group.
Oswald Avery
Oswald Avery, an early molecular biologist and immunochemist, is best known for his discovery in 1944 (with his co-workers Colin MacLeod and Maclyn McCarty) that DNA is the material of which genes and chromosomes are made.
Strengthening the Foundation: Chargaff Formulates His "Rules"
Erwin Chargaff
-Chargaff discovered two rules that helped lead to the discovery of the double helix structure of DNA in 1952.
These two rules paved the way for
Watson and Crick Discovery.
Chargaff’s Rules
1) The first and best known achievement was to show that in natural DNA the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine music

2) The second of Chargaff's rules is that the composition of DNA varies from one species to another, in particular in the relative amounts of A, G, T, and C bases. Such evidence of molecular diversity, which had been presumed absent from DNA, made DNA a more credible candidate for the genetic material than protein.
Linus Pauling= First to propose that DNA was a helix. However, he proposed it was a triple helix rather than the accepted double helix.
Alfred Hershey and Martha Chase= They were the ones that proved DNA, not proteins, were what formed genetic material in 1952.
Maurice Wilkins and Rosalind Franklin= In 1952 at King's College in London, this British scientists used X-ray diffraction to learn DNA structure. Thy aimed a powerful X-ray at concentrated DNA samples and recorded the scattering pattern on film.
James Watson and Francis Crick discovered the structure of the DNA in 1953. first scientists to formulate an accurate description of this molecule's complex. Which was Double Helix.

Protein synthesis
=Proteins are large biological molecules, or macromolecules, consisting of one or more chains of amino acid residues.=Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.
Function of proteins
1.Help fight disease
2.Build new body tissue
3.Enzymes used for digestion and other chemical reactions

Protein synthesis involves two types of nucleic acids:
1.DNA (deoxyribonucleic acid)
2.RNA (ribonucleic acid) =RNA, like DNA, is a polymer formed by a sequence of nucleotides
Three Types of RNA:
1.messenger RNA (mRNA)-carries genetic information from the nucleus to the cytoplasm
2.transfer RNA (tRNA)-brings amino acids to ribosomes during protein synthesis
3.ribosomal RNA (rRNA)- guides the translation of mRNA into a protein
Protein Synthesis involves two processes:
1.Transcription: the copying of the genetic message (DNA) into a molecule of mRNA
2.Translation: mRNA is used to assemble an amino acid sequence into a polypeptide
Outline the DNA Transcription in terms of RNA strand complimentary to DNA strand by RNA polymerase.
Transcription= DNA transcription is a process that involves transcribing genetic information from DNA to RNA. The transcribed DNA message, is used to produce proteins. = occurs in the nucleus of the cell Steps of transcription
1. The DNA helix is opened at the position of the gene.
2. The helix is unwound by RNA polymerase
3.RNA nucleotides are found in the nucleus space.
4. One of the polynucleotide chains act as a template for mRNA
5. Free nucleotides base pair with DNA nucleotides
6.The phosphodiester bonds on the mRNA chain are formed by RNA polymerase
7.mRNA is a single polynucleotide chain but the base thymine is replaced by Uracil.
8. After the mRNA is complete the molecule detaches from the DNA and leaves the nucleus for the cytoplasm ribosomes.
9.The DNA helix reforms
Why? DNA has the genetic code for the protein that needs to be made, but proteins are made by the ribosomes—ribosomes are outside the nucleus in the cytoplasm.
DNA is too large to leave the nucleus (double stranded), but RNA can leave the nucleus (single stranded)reforms.

Describe the genetic code in terms of codons composed of triplets of bases.
1.Translation is carried out in the cytoplasm by ribosomes, molecules of another type of RNA called transfer RNA (tRNA)
2.tRNA is a single strand of RNA that is folded into a “clover leaf” shape. It’s bonded together by complementary base pairings but one area is exposed to correspond to the codons found on the mRNA molecule, this area is the anticodon.
3.At the opposite end is a binding site for one amino acid which corresponds to the codon on the mRNA that matches the anticodon of the tRNA.
4.Ribosomes have binding sites for both the mRNA and the tRNA molecules
5.The ribosome binds to the mRNA and then draws the specific tRNA molecule with anticodons.
6.Only two tRNA molecules bind to the ribosome at once. Each carries with it the amino acid specified by the anticodon.
7.When two tRNA molecules are in place on the ribosome, a peptide bond forms between the amino acid (condensation reaction).
8.Once the peptide bond is formed the first tRNA molecule detaches from the amino acid and the ribosome.
9.The ribosome moves along the mRNA one codon to the next.
10.This process is repeated until a complete polypeptide is formed.
11.The final codon that is reached is the “stop” codon, which tells the ribosome to detach from the mRNA
Define the Terms and Universal as They Relate to The Genetic Code
Degenerate: Having more than one base triplet to code for one amino acid.
Universal: Found in all living organisms Universal and degenerate refer to the genetic code. The standard genetic code is often considered universal because the majority of genes are encoded with exactly the same codon.
What’s Genetic Code?=The genetic code is a set of rules defining how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins. The genetic code is a set of three-letter combinations of nucleotides called codons, each of which corresponds to a specific amino acid or stop signal.
Universal Genetic Code= is the set of rules where materials and information normally encoded with genetic content is transformed into amino acids by rightful living cells. The genetic material is normally DNA sequences where decoding is done and carried out by ribosomes. Degeneracy of codons is the redundancy of the genetic code, exhibited as the multiplicity of three-codon combinations specifying an amino acid. polymerase- A polymerase is an enzyme whose central biological function is the synthesis of polymers of nucleic acids phosphodiester bond- is a group of strong covalent bonds between a phosphate group and two 5-carbon ring carbohydrates over two ester bonds polynucleotide chain -is a chain of many nucleotides. peptide- a compound consisting of two or more amino acids linked in a chain
Polypeptide chain- series of amino acids
4.What unwinds or unzips the DNA helix?=The RNA polymerase
5. What happens to the DNA helix after the mRNA leaves the nucleous?=The DNA helix reforms
6.The process through which proteins are synthesized by the use of ribosome? Translation 7.Messenger RNA is composed of codons
Transfer RNA has a triplet of codon-series of 3 nitrogen bases exons-coding region
.anticodon-3 base sequence found in tRNA that binds a complementary piece of mRNA during protein synthesis.