Genetic Molecule: DNA and RNA, Discovery and Structure

Discovery of DNA

1Discovery of DNA 1870 - Friedrich Miescher extracted DNA from the nucleus of a cell. He called it nucleic acid. 1900's - chromosomes were discovered to be the carriers of hereditary information.

2. 1940's - Erwin Chargaff analyzed the relative amounts of the 4 nucleotides in DNA in a variety of species of organisms. . In doing so he realized that the amount of Thymine always equaled the amount of Adenine, and the amount of Guanine always equaled the amount of Cytosine.

A T Y P.q A Y adenine thymine Adenine = Thymine 4 C guanine cytosine Guanine = Cytocine Chargaff's Rule1950's - Alfred Mirsky found that the total amount of DNA in any cells is always the same, no matter what type of cell!

41950's - Rosalind Franklin & Maurice Wilkins used X-Ray diffraction to infer that DNA molecules have a helical shape and are composed of repeating units. Photo 51

51951 - Francis Crick & James Watson built a 3D model of the structure of DNA which is still accepted today. They were awarded the Nobel Prize for their work!

DNA Structure

1 6Structure of DNA

• Cells contain a central nucleus.
• Within the nucleus is the chromatin, which is the genetic material of the cell. Endoplasmic reticulum Nucleolus Chromatin Nucleoplasm Nuclear pore Nuclear envelope

8Chromosome Buzzle.com Centromere Chromatid Chromatid We call it chromatin in non-dividing cells. However, when a cell divides, the chromatin condenses into rod-like structures called chromosomes.

DNA Structure Components

9DNA Structure -Histone Chromosome Nucleosome Gene DNA- Cell Nucleotide Nucleotide base pairs: Nucleus Guanine Cytosine Adenine Thymine @ 2015 Terese Winslow LLC U.S. Govt. has certain rights

• DNA is wrapped around histone proteins to form nucleosomes.
• Nucleosomes are the folded and wrapped into condensed bundles called chromosomes.
• This allows a LOT of DNA to occupy a relatively small space!

10 Chromosomes are composed of nucleic acid (DNA) and proteins called histones. · The average chromosome consists of about 85 million nucleotides!A gene is a segment of DNA within a chromosome which regulates a specific function within the cell and codes for one polypeptide (protein). Most genes are about 1000 nucleotides long.

Types of Nucleic Acid

11Two Types of Nucleic Acid

• DNA is Deoxyribonucleic Acid. It is a double-stranded molecule.
• It's job in the cell is to control all cellular activities, including cell reproduction and protein synthesis.
• DNA undergoes mutations and so is also responsible for evolution (change) of a species.

13RNA is Ribonucleic Acid. It is a single-stranded molecule. RNA is synthesized from DNA. RNA works with the DNA to control the synthesis of proteins in the cell. (0)123RF® RNA ORARF Helix of Sugar- Phosphates (2)123RF" Nitrogenous Bases (2)123RF® (2)123RF (0)123RF® (2)123RF® 14 (0)123RF®DNA Nucleotides All DNA nucleotides consist of:

• the five carbon sugar deoxyribose
• a phosphate group
• one nitrogen-containing base. The nitrogenous base may either be a single ring pyrimidine or a double-ring purine. NH O HO-P-O N O I .O OH OH OH pyrimidine 0 N HN -N 0 -0- P-0 0 H H 0- エ H OH OH purine

15· DNA nucleotides only differ in which Nitrogenous base is attached. · The four nitrogenous bases in DNA are adenine, guanine, cytosine and thymine. Pyrimidines NH3 O C C CH3 HN C I C CH C CH N O H Cytosine C Thymine T Purines O NH2 1 N C -C N HC I .C C N N NH2 H H Guanine G C N - N NH HC I .C C N N C H N CH I Adenine A

16DNA nitrogenous bases: adenine thymine guanine cytosine 3' 5' A T base pair G C T A major groove C G A T T A minor groove G C A T sugar- phosphate backbone 5' 3' (a) (b) 5' 0 NH2 O 0 N T OH -( 0 O N 3' 5 O N O 1 5' 4 1 3 2' O NH2 ---. O D O 2' o 'P C N ---. HN G N 3' O N 1 5' 1' O .---. H2N 3 O .--. HON 0. P T NH ---. N A N 3' O. N N O 5' 4 1 O 4 3 2' .H2N O .00 C N C o 0 NH .---. N N 3' O G N 5' N ·O O- 4' 1 NH2 3 2 O A-OO 5' 3' OH O O 4 2' C N 2'0 O O C 00- N 5 O'4 .00 N HN 2' A N 4 3' O 4 5 O 1 20 P - (c)

DNA Molecule Structure

17DNA Molecule

• DNA consists of TWO antiparallel strands of nucleic acid, which are held together with Hydrogen Bonds between the nitrogenous bases.
• Antiparallel means that they run in opposite directions.
• The "backbone" of the DNA "ladder" consists of alternating sugar and phosphate groups, while the "rungs" of the DNA ladder are the nitrogenous bases bonded together.
• The "ladder" is twisted to form a double helix.

18nitrogenous bases: adenine thymine guanine cytosine 3' 5' A T base pair G C T A major groove C G A T T A minor groove G C A T sugar- phosphate backbone 5' 3' (a) (b) 5' 0 NH2 O 0 N T OH -( 0 O N 3' 5 O N O 1 5' 4 1 3 2' O NH2 ---. O D O 2' o 'P C N ---. HN G N 3' O N 1 5' 1' O .---. H2N 3 2' O .--. HON 0. P T NH ---. N A N 3' O. N N O 5' 4 1 O 4 3 2' .H2N O .00 C N C o 0 NH .---. N N 3' O G N 5' N ·O O- 4 5 4' 1 NH2 3 2 O A-OO 5' OH O O (c) 3' O 4 .00 N 00- N 5 O'4 4 C N 2'0 O O C 1 5 P - 20 O 1 3' N A HN 2'

Complementary Base Pairing

19Complementary Base Pairing

• The nitrogenous bases only bond in a specific manner: a purine base must bond with a pyrimidine base.
• Adenine always bonds with Thymine (2 H bonds).
• Guanine always bonds with Cytosine (3 H bonds). - Therefore the two strands are always 3 rings apart! Adenine Thymine H2N 3' 5' O OH . N N NH O 0 O N O O P O O H2N O C N 0 O NH N O N O Cytosine NH2 5' HO Guanine 3' 20