Nucleic Acids l Ribonucleic acid RNA Single stranded
Nucleic Acids l Ribonucleic acid (RNA) – Single stranded – Builds proteins – Acts as enzymes – Three types • m. RNA • t. RNA • r. RNA 2
DNA is often called the blueprint of life q Nucleic acids store and transmit hereditary information q In simple terms it contains the instructions for making proteins in the cell. q
DNA BY THE NUMBERS • Each cell has about 2 meters of DNA. • The average human has 75 trillion cells. • The average human has enough DNA to go from the earth to the sun more than 400 times. • DNA has a diameter of only 0. 00002 meter. The earth is 150 billion meters or 93 million miles from the sun
The Shape of the Molecule l DNA is a very long polymer. l The basic shape is like a twisted ladder or spiral staircase. l This is called a double helix.
DNA STRUCTURE Adenosine Mono Phosphate (AMP) Phosphate HO H+ Nucleotide OH P O Base N H O 5’CH 2 4’ NH 2 H N O 1’ Sugar 3’ OH 2’ H N N
H DNA STRUCTURE Phosphate OH P HO CH 2 O O O • The outer parts of the ladder are made of sugars and phosphates. • The steps of the ladder are made of pairs of nitrogen bases. H Sugar OH Base NH 2 N N H
DNA Four Nitrogenous Bases Cytosine q Thymine q Adenine q Guanine q C T A G
ONE STRAND OF DNA phosphate sugar One strand of DNA is a polymer of nucleotides. q One strand of DNA has many millions of nucleotides. q The backbone of the molecule is alternating phosphate and deoxyribose, a sugar. q The teeth are nitrogenous bases q base nucleotide
Two Types of Bases in DNA l Purines are double ring bases. O Guanine NH N NH 2 Adenine N N
Two Kinds of Bases in DNA l Pyrimidines ring bases. O CH 3 are single Thymine O (DNA) N O N NH N O Uracil (RNA) NH NH 2 Cytosine N O Uracil is found in RNA (more later) l
Nucleotide Bases Pyrimidines C = Cytosine T = Thymine U = Uracil Purines A = Adenine G = Guanine Nitrogenous bases Pyrimidines NH 2 O C N C CH N C HN CH C N O CH 3 C C HN CH CH H H N H Cytosine C Thymine (in DNA) T Uracil (in. RNA) Uracil (in UU O O O CH CH Purines O NH 2 N C C HC C N H N N CH N HC N H Adenine A C N NH 2 Pentose sugars HOCH 2 O 3’ OH 5” OH H NH Guanine G 5” 4’ C C 2’ HOCH 2 1’ H H H Deoxyribose (in DNA) H H 4’ 3’ OH 12 OH O 2’ 1’ H OH Ribose (in RNA)
TWO STRANDED DNA q. Remember, DNA has two strands that fit together something like a zipper. q. The teeth are the nitrogenous bases but why do they stick together?
Hydrogen Bonds The bases attract each other because of hydrogen bonds. l Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. CH N O + O N Thymine N N- N - H H + H Adenine N N 3 l
Chargaff’s Rule l Adenine must pair with Thymine l Guanine must pair with Cytosine l Their amounts in a given DNA molecule will be about the same T A G C
THE CODE OF LIFE… • The “code” of the chromosome is the SPECIFIC ORDER in which the bases occur. A T C G T A T G C G G…
DNA STRUCTURE DETERMINATION • Edwin Chargaff – 1949 biochemist – Showed that the amount of A=T and G=C • Wilkins and Franklin – 1952 X-ray picture of DNA • Watson and Crick – 1953 proposed a 3 -D model accounting for the data.
- - - A C G C - - 3. 4 nm 1 nm - - - Minor groove G T A - The Watson - Crick Model Of DNA T G C T A C G A T Major groove A T C G G C 0. 34 nm T A - - -
DNA REPLICATION • • The preparation of exact copies of a molecule. DNA replication is essential for life It allows organisms to create copies of themselves. DNA is wrapped tightly around histones and coiled tightly to form chromosomes
WHY IS ACCURACY OF NUCLEOTIDE SEQUENCE IN THE DNA OF A GENE IMPORTANT? Nucleotide sequence in messenger RNA (m. RNA) Transcription Nucleotide sequence in a protein (t. RNA) Translation Structure and function of the protein Form and function Characteristics or traits (normal health or problems)
DNA Replication q DNA must be copied to produce 2 IDENTICAL new complementary strands following the rules of base pairing: A-T q Each strand of the original DNA serves as a template for the new strand G-C
DNA REPLICATION Semi-conservative Model: Meselson and Stahl showed the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand. Parental DNA Template New DNA
Uses energy from ATP to unwind the DNA by breaking the Hydrogen bonds SSB SSB Areas where the DNA separates are called replication forks
• SCHEMATIC REPRESENTATION OF Structure resembles DNA POLYMERASE a human right hand • Template DNA thread through the palm • Thumb and fingers wrapped around the DNA • Polymerase has “proofreading” role • Backtrack and correct errors • Only about one error per billion nucleotides
Multiple Replication Forks During Eukaryotic DNA Synthesis
- Slides: 25