DNA v DNA is often called the blueprint
DNA v. DNA is often called the blueprint of life. v. In simple terms, DNA contains the instructions for making proteins within the cell.
THE SHAPE OF THE MOLECULE v. The basic shape is like a twisted ladder. v. This is called a double helix. v. It has two strands twisted together.
ONE STRAND OF DNA v. The backbone of the molecule is alternating phosphate deoxyribose phosphate and deoxyribose (sugar) parts. v. The “rungs” are nitrogenous bases
NUCLEOTIDES One deoxyribose together with its phosphate and base make a nucleotide. O O -P O O C C Phosphate C C O Deoxyribose Nitrogenous base
ONE STRAND OF DNA nucleotide v. One strand of DNA is a polymer of nucleotides. v. One strand of DNA has many millions of nucleotides.
FOUR NITROGENOUS BASES DNA has four different bases: v Cytosine C v Thymine T v Adenine A v Guanine G
TWO KINDS OF BASES IN DNA v An. Gels have wings. An. Gels are pure – a way to remember which bases are purines!!!! v Pyrimidines CUT O N C OC CC N N C OC C N C thymine cytosine Guanine O v Pyrimidines are single ring bases. Adenine N N C • Thymine N C C • Cytosine C C N N v Purines are double ring bases. N C • Adenine C C N N • Guanine
N HYDROGEN BONDS C stick to each other because C C of hydrogen bonds. N N v. The two strands of DNA N C O C N Hydrogen bond N C C C N O
BASE PAIRING • Adenine and Thymine always join together A T • • Cytosine and Guanine always join together C G
DISCOVERY OF DNA STRUCTURE v Erwin Chargaff showed the amounts of the four bases on DNA ( A, T, C, G) v In a body or somatic cell: A = 30. 3% T = 30. 3% G = 19. 5% C = 19. 9% copyright cmassengale 11
CHARGAFF ’ S RULE v Adenine must pair with Thymine v Guanine must pair with Cytosine v The bases are held together by weak hydrogen bonds T G A copyright cmassengale C 12
DNA STRUCTURE v. Rosalind Franklin took diffraction x-ray photographs of DNA crystals v. In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays copyright cmassengale 13
ROSALIND FRANKLIN copyright cmassengale 14
REPLICATION FACTS v. DNA has to be copied before a cell divides v. DNA is copied during the S or synthesis phase of interphase v. New cells will need identical DNA strands copyright cmassengale 15
DNA REPLICATION v. Begins at Origins of Replication v. Two strands open forming Replication Forks (Y-shaped region) 3’ v. New strands grow at the forks 5’ Parental DNA Molecule 3’ copyright cmassengale Replication Fork 16 5
DNA REPLICATION v. As the 2 DNA strands open at the origin, Replication Bubbles form v. Prokaryotes (bacteria) have a single bubble v. Eukaryotic chromosomes have MANY bubbles copyright cmassengale 17
DNA REPLICATION v. Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds copyright cmassengale 18
DNA REPLICATION v v v Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides Primase is the enzyme that synthesizes the RNA Primer DNA polymerase can then add the new nucleotides copyright cmassengale 19
STEPS OF DNA REPLICATION
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