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DNA: Types, Structure and Function of DNA
Working with Molecular Genetics Chapter 2. Structures of Nucleic Acids labels in biology.) As diagrammed in Fig. , The proteins of T2 phage were labeled with 35S (e.g. in methionine and cysteine) and the DNA was labeled with 32P (in the sugar-phosphate backbone, as will be presented in DNA The Basics for Beginners! Presented by independent structures containing DNA are known as chromosomes (these structures may be linear or circular), and one complete set of these chromosomes is known as the individual some DNA that does not appear to affect any biological function, this non-coding (or “junk”) DNA contains •Cell structures that have a specific function and are surrounded by a membrane that are found in eukaryotes only. Prokaryotic vs. Eukaryotic Http: DNA called plasmids are also located in cytoplasm. Ribosomes •Each cell contains thousands •Make proteins •Found on endoplasmic
Dna structure and function pdf download
Read this article to learn about the history, types, structure, silent features and functions of DNA:. They were named nuclein. Hertwig proposed nuclein to be the carrier of hereditary traits. Because of their acidic nature they were named nucleinic acids and then nucleic acids Altmann, Fisher s discovered the presence of purine and pyrimidine bases in nucleic acids.
Levene found deoxyribose nucleic acid to contain phosphoric acid as well as deoxyribose sugar. He characterised four types of nucleotides present in DNA. Indna structure and function pdf download, Chargaff found that purine and pyrimidine content of DNA was equal.
By this time W. Astbury had found through X-ray diffraction that DNA is a polynucleotide with nucleotides arranged perpendicular to the long axis of the molecule and separated from one another by a distance of 0.
Indna structure and function pdf download, Wilkins and Franklin got very fine X-ray photographs of DNA. The photographs showed that DNA was a helix with a width of 2.
One turn of the helix was 3. Watson and Crick worked out the first correct double helix model from the X-ray photographs of Wilkins and Franklin. Wilkins, Watson and Crick were awarded Nobel Prize for the same in Dna structure and function pdf download and Crick built a 3D, molecular model of DNA that satisfied all the details obtained from X-ray photographs. They proposed that DNA consisted of a double helix with two chains having sugar phosphate on the outside and nitrogen bases on the inner side.
The nitrogen bases of the two chains formed complementary pairs with purine of one and pyrimidine of the other held together by hydrogen bonds A-T, C-G. Complementary base pairing between the two polynucleotide chains is considered to be hall mark of their proposition. The two chains are twisted helically just as a rope ladder with rigid steps twisted into a spiral.
Each turn of the spiral contains 10 nucleotides. This double helix or duplex model of DNA with antiparallel polynucleotide chains having complementary bases has an implicit mechanism of its replication and copying.
Here both the polynucleotide chains function as templates forming two double helices, each with one parent chain and one new but complementary strand. The phenomenon is called semi conservative replication. In vitro synthesis of DNA has been carried out by Kornberg in DNA duplex model proposed by Watson and Crick is right handed spiral and is called B-DNA Balanced DNA.
In the model the base pairs lie at nearly right angles to the axis of helix Fig. Another right handed duplex model is A-DNA Alternate DNA. Here, a single turn of helix has 11 base pairs. The base pairs lie 20° away from perpendicular to the axis. C-DNA has 9 base pairs per turn of spiral while in D-DNA the number is only 8 base pairs. Both are right dna structure and function pdf download. Z-DNA Zigzag DNA is left-handed double helix with zigzag back-bone, alternate purine and pyrimidine bases, single turn of 45 A length with 12 base pairs and a single groove.
B-DNA is more hydrated and most frequently found DNA in living cells. It is physiologically and biologically active form. However, it dna structure and function pdf download get changed into other forms.
Right handed DNA is known to change temporarily into the left handed form at least for a short distance. Such changes may cause changes in gene expression, dna structure and function pdf download. In many prokaryotes the two ends of a DNA duplex are covalently linked to form circular DNA. Circular DNA is naked, that is, without association with histone proteins, though polyamines do occur. In linear DNA the two ends are free, dna structure and function pdf download.
It is found in eukaryotic nuclei where it is associated with histone proteins. Linear DNA, without association with histone proteins, also occurs in some prokaryotes, e. In semi-autonomous cell organelles mitochondria, plastids DNA is circular, less commonly linear. It is always naked. Chargaff made observations on the bases and other components of DNA.
ii Molar amount of adenine is always equal to the molar amount of thymine. Similarly, molar concentration of guanine is equalled by molar concentration of cytosine. It can be used to identify the source of DNA. The ratio is low in primitive organisms and higher in advanced ones. DNA or deoxyribonucleic acid is a helically twisted double chain polydeoxyribonucleotide macromolecule which constitutes the genetic material of all organisms with the exception of rhinoviruses.
In prokaryotes it occurs in nucleoid and plasmids. This DNA is usually circular. In eukaryotes, most of the DNA is found in chromatin of nucleus. It is linear. Smaller quantities of circular, double stranded DNA are found in mitochondria and plastids organelle DNA. Small sized DNAs occur in viruses, ф x bacteriophage has nucleotides.
Bacteriophage lambda Phage X possesses base pairs bp while number of base pairs in Escherichia coli is 4. A single genome haploid set of 23 chromosomes has about 3. Single-stranded DNA occurs as a genetic material in some viruses e. DNA is the largest macromolecule with a diameter of 2 nm 20Å or 2 x 10 -9 m and often having 3 length in millimetres.
It 15 negatively charged due to phosphate groups. Dna structure and function pdf download is a long chain polymer of generally several hundred thousands of deoxyribonucleotides. A DNA molecule has two un-branched complementary strands.
They are spirally coiled. The two spiral strands of DNA are collectively called DNA duplex Fig. The two strands are not coiled upon each other but the whole double strand DNA duplex is coiled upon itself around a common axis like a rope stair case with solid steps twisted into a spiral.
Due to spiral twisting, dna structure and function pdf download DNA duplex comes to have two types of alternate grooves, major 22 Å and minor 12 Å. In B-DNA, one turn of the spiral has about 10 nucleotides on each strand of DNA, dna structure and function pdf download. It occupies a distance of about 3. A deoxyribonucleotide of DNA is formed by cross-linking of three chemicals ortho- phosphoric acid H 3 PO 4deoxyribose sugar C 5 H 10 O 4 and a nitrogen base.
Four types of nitrogen bases occur in DNA. They belong to two groups, purines 9-membered double rings with nitrogen at 1,3,7 and 9 positions and pyrimidines six membered rings with nitrogen at 1 and 3 positions. DNA has two types of purines adenine or A and guanine or G and two types of pyrimidines cytosine or С and thymine or T. Depending upon the type of nitrogen base, DNA has four kinds of deoxyribonucleotides —deoxy adenosine 5- monophosphate d AMPdeoxy guaninosine 5-monophosphate d GMPdeoxy thymidine 5-monophosphate d TMP and deoxy cytidine 5- monophosphate d CMP.
The back bone of a DNA chain or strand is built up of alternate deoxyribose sugar and phosphoric acid groups. Phosphate group provides acidity to the nucleic acids because at least one of its side group is free to dissociate. Nitrogen bases lie at right angles to the longitudinal axis of DNA chains. They are attached to carbon atom 1 of the sugars by N-glycosidic bonds. Pyrimidine C or T is attached to deoxyribose by its N-atom at 1 position while a purine A or G does so by N-atom at 9 position.
The two DNA chains are antiparallel that is, they run parallel but in opposite directions, dna structure and function pdf download. The two chains are held together by hydrogen bonds between their bases. Adenine Aa purine of one chain lies exactly opposite thymine Ta pyramidine of the other chain. Similarly, cytosine C, a pyrimidine lies opposite guanine G a purine, dna structure and function pdf download. This allows a sort of lock and dna structure and function pdf download arrangement between large sized purine and small sized pyrimidine.
It is strengthened by the appearance of hydrogen bonds between the two. Hydrogen bonds occur between hydrogen of one base and oxygen or nitrogen of the other base. Since specific and different nitrogen bases occur on the two DNA chains, the latter are complementary. Thus the sequence of say AAGCTCAG of one chain would have a complementary sequence of TTCGAGTC on the other chain. In other words, the two DNA chains are not identical but complementary to each other.
It is because of specific base pairing with a purine lying opposite a pyrimidine. This makes the two chains 2 nm thick. A purine- purine base pair will make it thicker while a pyrimidine- pyrimidine base pair will make it narrower than 2 nm. Further, dna structure and function pdf download, A and С or G and T do not pair because they fail to form hydrogen bonds between them. Backbone of each polynucleotide chain is made of alternate sugar-phosphate groups.
The nitrogen bases project inwardly. Nitrogen bases of two polynucleotide chains form complementary pairs, A opposite T and С opposite G. A large sized purine always comes opposite a small sized pyrimidine. This generates uniform distance between two strands of helix.
DNA Structure and Replication: Crash Course Biology #10
, time: 12:59Dna structure and function pdf download
DNA structure: • Maurice Wilkins and Rosalind Franklin at King’s College in London • Linus Pauling, an American Chemist at the California Institute of Technology • James Watson and Francis Crick at Cambridge DNA’s function was so they begun to model build Importance of DNA/RNA 3D Structure Nucleic acids are essential materials found in all living organisms. Their main function is to maintain and transmit the genetic code. This information is stored in the form of long polymer chains. Although the information they carry is one-dimensional, it is essential to understand the 3D structure of nucleic RNA AND ITS STRUCTURE, FUNCTION AND TYPES. With the discovery of the molecular structure of the DNA. double helix in , researchers turned to the structure of ribonucleic acid (RNA) as the next critical puzzle to be solved on the road to understanding the molecular basis of life
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