DNA Structure

DNA Structure and basic properties Lecture 1

An introduction to DNA TopologyDNA

DNA inside the Nuclues

The human cell contains 23 pairs of chromosomesIf we scale the cell nucleus to the size of Basketball then the DNA scales to 200km in length.The cell nucleus is only 10 micrometres in diameterThe bacteria is made up of only one DNA molecule (which is a closed loop)

DNA: the molecule of lifeDNA stands for Deoxyribonucleic acid DNA is often called the blueprint of life (the secret of life).

In simple terms, DNA contains the instructions for making proteins within the cell.

Its double helix structure was discovered by Crick and Watson 1953 (Nobel prize)

4Why is DNA called the blueprint of life?Why is DNA so important ?Mainly because of:its central importance to all life on Earth (it contains all genetic information)

genetic testsmedical benefits such as cures for diseases,

genetically modified Food5

5About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.Chemical structureThe DNA consists of two long molecules arranged into a ladder like structure called the double HelixThe two Backbones (strands) are bonded together by ladder rungs which are made up of pairs of bases.Structure(video)

Each strand consists of: 2) Four Base Chemicals (Attached in Pairs)1) A Sugar Phosphate Backbone

7patSome animationshttp://video.parajsa.com/video/1681/How-DNA-Works

DNA packingDna in crowded in the cell

Circular DNADNA of Bacteria consists of closed loopIt is made up of two circular strands which wrap around each otherThe backbones are circular and the base pairs are the same as in the case of linear DNA (human)

Bacteria and Virus Bacteria and viruses are often made up of a single DNA circular molecule!

Coiling and SupercoilingSupercoil (Animation)

Super coiling means coiling of a coil

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Circular DNA, has one helical turn every 10.5 bp in relaxed, form

Super coiling appears when two points are twisted in opposite directions

From relaxed to super coiledAn electron micrograph of The DNA molecule inRelaxed and super-coiledStates

DNA replicationFor a cell to divide, it must first replicate its DNAEach strand of the original double-stranded DNA serves as template for the reproduction of the complementary strand.

DNA in Cell (replication 1)

Replication2(Youtube)

Replication(circular) (DNA Tube)

15What is DNA topology about?

An electron micrograph Corresponding mathematical object

Knotted DNACircular DNA molecules can be knotted as

Knotting may lead to cell Death.

Certain Enzymes are responsible of that phenomena (topoinsomerase)

More pictures

Topology

Enzyme actionEnzymes are proteins that catalyze (i.e., increase or decrease the rates of) chemical reactions

In enzymatic reactions, the molecules at the beginning of the process are called substrates, after the transformation they are called the products

Almost all processes in a biological cell need enzymes to occur at significant ratesTopoisomerase (video 1)Topoisomerase (video 2)

Topological EnzymologyMathematics: Deduce enzyme binding and mechanism from observed products

*07/16/96*##DNA (Some facts)Molecular basis of heredity. It is a complex giant molecule that contains, in chemically coded form, the information needed for a cell to make proteins. In other words it determines the order in which amino acids are joined to make a specific protein in a cell. DNA is a ladder-like double-stranded nucleic acid, which forms the basis of genetic inheritance in all organisms, except for a few viruses that have only RNA. DNA is organized into chromosomes and, in organisms other than bacteria, it is found only in the cell nucleus.DNA is a ladder-like molecule, which means that it is made up of two halves (the ladder sides), formed of chains of nucleotide subunits. Each nucleotide contains a deoxyribose sugar, a phosphate, and a base. A set of three bases known as a codon acts as a blueprint for the incorporation of a particular amino acid, the subunit of a protein molecule. The two halves are joined together by the bases a purine (adenine or guanine) or pyrimidine (cytosine or thymine) forming pairs (the rungs). The bases form into two specific base pairs: adenine with thymine and guanine with cytosine. The sequence of base pairs along the DNA acts as a code carrying information about the sequence of amino acids in proteins. Three base pairs in sequence (triplet) name an amino acid and the next three name the next amino acid that needs to be joined and so on, to make a specific protein. The specific way in which the pairs form means that the base sequence is preserved from generation to generation. Hereditary information is stored as a specific sequence of bases.

Reference: http://encyclopedia.farlex.com/Circular+DNA