The Structure of the DNA Molecule The finger print that is inside your body!

DNA stands for: D: Deoxyribose N: Nucleic A: Acid DNA is too small to see, but under a microscope it looks like a twisted up ladder!

Every living thing has DNA. That means that you have something in common with a zebra, a tree, a mushroom and a beetle!!!!

DNA is made up of steps and rails of a ladder. This is a rail This is a step Green can only go with Red Purple can only go with Yellow

Deciphering DNA's structure. 1.DNA is made up of subunits which scientists called nucleotides. 2.Each nucleotide is made up of a sugar, a phosphate and a base. 3.There are 4 different bases in a DNA molecule: a.adenine ( purine) b.thymine ( pyrimidine) c.cytosine (pyrimidine) d.guanine (purine)

4.The number of purine bases equals the number of pyrimidine bases 5.The number of adenine bases equals the number of thymine bases 6.The number of guanine bases equals the number of cytosine bases 7.The basic structure of the DNA molecule is helical, with the bases being stacked on top of each other Deciphering DNA's structure.

Nucleotides 1.DNA is made up of subunits which scientists called nucleotides. A nucleotide is a chemical compound that consists of 3 portions: a nitrogenous base, a sugar, and one or more phosphate groups.

2. Each nucleotide is made up of a sugar, a phosphate and a base. 3. There are 4 different bases in a DNA molecule: a.adenine ( purine) b.thymine ( pyrimidine) c.cytosine (pyrimidine) d.guanine (purine) Nucleotides

DNA Molecule The DNA molecule is one of the greatest scientific discoveries of all time. First described by James Watson and Francis Crick in 1953, DNA is the famous storehouse of genetics that establishes each organism's physical characteristics.

James Watson and Francis Crick Used data of M.H.F. Wilkins and Rosalind Franklin, early 50 ’ s Wilkins and Franklin studied the structure of DNA crystals using X-rays. The X pattern suggested the structure of DNA was a helix. Distance between the two “ backbones ” of DNA is constant along the length of the molecule

Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G) In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9%

13 Chargaff’s Rule Adenine ThymineAdenine must pair with Thymine GuanineCytosineGuanine must pair with Cytosine The bases form weak hydrogen bonds G C TA

14 Rosalind Franklin copyright cmassengale

15 DNA Structure Rosalind Franklin took diffraction x-ray photographs of DNA crystals. In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

Watson and Crick (1953)

DNA is like a fingerprint because everyone’s is a little different! How would the police look at DNA to figure out who committed a crime? You can tell people apart by their fingerprints……… and their DNA!

Within cells, DNA is organized into structures called chromosomes. DNA Molecule These chromosomes are duplicated before cells divide, in a process called DNA replication.

The genetic information in a genome is held within genes, and the complete set of this information in an organism is called its genotype. DNA Molecule A gene is a unit of heredity and is a region of DNA that influences a particular characteristic in an organism.

Soooo…. How do we tell people apart just by their DNA anyways???

We are ALL a little bit different! Along with the meaningful DNA that encodes for physical traits, we have a lot of "junk DNA." Strings of repeating patterns and filler material. STR stands for short terminal repeating sections, and this area of DNA represents a pattern, 2 to 7 letters long that repeats itself many times. How many times varies between people. This process is called genetic fingerprinting, or more accurately, DNA profiling.

Suspect #1 DNA sample Our DNA has different sizes of pieces so it makes a different pattern when it’s all cut up. Suspect #2 DNA sample In DNA profiling, the lengths of variable sections of repetitive DNA, such as short tandem repeats, are compared between people. This method is usually an extremely reliable technique for identifying a criminal

This is what it really looks like!!! Suspect #1 Suspect #2 Genetic fingerprinting is used in forensic science, to match suspects to samples of blood, hair, saliva or semen.

Which suspect is guilty? Which suspects DNA sample is the red box around? ? Suspect #1Suspect #2

25 DNA Replication

26 Replication Facts DNA has to be copied before a cell dividesDNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphaseDNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strandsNew cells will need identical DNA strands

27 Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase DNA replication takes place in the S phase.

28 DNA Replication Begins at Origins of ReplicationBegins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region)Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forksNew strands grow at the forks ReplicationFork Parental DNA Molecule 3’3’ 5’5’ 3’3’ 5’5’

29 DNA Replication As the 2 DNA strands open at the origin, Replication Bubbles formAs the 2 DNA strands open at the origin, Replication Bubbles form Prokaryotes (bacteria) have a single bubble Eukaryotic chromosomes have MANY bubbles Bubbles copyright cmassengale

30 Replication of Strands Replication Fork Point of Origin

31 Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-CGTATG-3’

32 Answer: DNA 3’-GCATAC-5’