DNA and RNA Structure PDF

INTRODUCTION TO MOLECULAR GENETICS DNA AND RNA STRUCTURE MARIA LOURDES C. AGUIRRE, Lic. Agr., MRIBio, Ph.D. IAS – BIOLOGY DEPT DNA & RNA  The Vocabulary of DNA  Genetics—The study of genes & heredity  Trait-- inherited characteristic determined by the pre...

INTRODUCTION TO MOLECULAR GENETICS DNA AND RNA STRUCTURE MARIA LOURDES C. AGUIRRE, Lic. Agr., MRIBio, Ph.D. IAS – BIOLOGY DEPT DNA & RNA  The Vocabulary of DNA  Genetics—The study of genes & heredity  Trait-- inherited characteristic determined by the presence and expression of dominant and/or recessive alleles.  Gene-- a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color, etc.) DNA Facts  Chromosomes are made of DNA  Deoxyribonucleic Acid (DNA)  Molecule that stores genetic information in cells  Copies itself exactly for new cells DNA-Deoxyribonucleic Acid  DNA is often called the blueprint of life.  In simple terms, DNA contains the instructions for making proteins within the cell.  Proteins  Responsible for all cell structures and functions  Made of long chains of amino acids  There are 20 amino acids in the body  Proteins are responsible for:  Hair, skin, hormones, muscle movement, antibodies, chemical reactions, oxygenation of cells. Rosalind Franklin and Maurice Wilkins took DNA X-ray photos that were essential to the discovery of the double helix of DNA by James Watson and Francis Crick in 1953. When Watson, Crick and Wilkins got their Nobel prize awards in 1962, Rosalind Franklin was cheated of deserved recognition in part by her early death from cancer in 1958.  Why is the Study of DNA Important?  It’s essential to all life on earth  Medical Benefits—disease detection, treatment, prevention  Development of Crops  Forensics The Structure of the Nucleotide DNA and RNA are long polymers whose monomer units are called nucleotides A nucleotide consists of: 1. Nitrogen containing heterocyclic base Purine Pyrimidine 2. Five-carbon sugar ring Ribose Deoxyribose 3. Phosphoryl group DNA Structure  DNA is a polymer (composed of repeating subunits called nucleotides)  2 long strands  Each a chain of nucleotides  Nucleotides  Consists of…  Phosphate  Carbon sugar (deoxyribose)  Nitrogen base  Nucleotide Structure Ring structures are found in both the base and the sugar – Base rings are numbered as usual – Sugar ring numbers are given the designation ' or prime Covalent bond between the sugar and the phosphoryl group is a phosphoester bond Bond between the base and the sugar is a b-N-glycosidic linkage joining the 1'-carbon of the sugar and a nitrogen atom of the base Adenine and Guanine are PURINES  Adenine and guanine each have two rings of carbon and nitrogen atoms  Purines are a double ring structure (a 6-member ring fused to a 5-member ring) N O N C N C C C N C C N N N C N C C Adenine N C Guanine N Thymine and Cytosine are PYRIMIDINES  Pyrimidines consist of a single 6-membered ring  Thymine and cytosine each have one ring of carbon and nitrogen atoms. N O N N C C O C C O C C C N C N C thymine cytosine Types of Nitrogenous Bases  A = adenine  T = thymine  C = cytosine  G = guanine  DNA Strand  Each nucleotide bonds to the next one to form a strand.  The two strands twist around a central axis to form a double helix.  Sides of the ladder alternate phosphate and sugar (deoxyribose)  Rungs are held together by Hydrogen bonds Base Pair Rule  Adenine can bond only with Thymine  A-T or T-A (2 H bonds)  Cytosine can bond only with Guanine  C-G or G-C (3 H bonds)  This is called the BASE PAIR RULE  Hydrogen Bonding of the DNA Helix A non-covalent attraction aiding in maintaining the double helix structure is hydrogen bonding between base pairs – Adenine forms 2 H bonds with thymine A=T – Cytosine forms 3 H bonds with guanine G≡C This H bonding pattern is called base pairing Diameter of the double helix is 2.0 nm – Distance dictated by the dimensions of the purine-pyrimidine base pairs Nitrogenous Bases  Those 4 bases (ATCG) have endless combinations  Just like the letters of the alphabet can combine to make an infinite number of words.  The two strands are said to be complementary  That means that if you have GAATAC on one side you will have _ _ _ _ _ _ on the other.  Complementary DNA Strands The two DNA strands are complementary strands – The sequence of bases on one automatically determine the sequence of bases on the other strand The chains run antiparallel – Only when the 2 strands are antiparallel can the base pairs form the H bonds that hold them together  Helical Structure of DNA DNA consists of two chains of nucleotides coiled around one another in a right-handed double helix – Sugar-phosphate backbones of the two strands spiral around the outside of the helix like the handrails on a spiral staircase – Nitrogenous bases extend into the center at right angles to the acids of the helix as if they are the steps of the spiral staircase  Schematic Ribbon Diagram of DNA Double Helix 2 strands of DNA form a right-handed double helix Bases in opposite strands hydrogen bond with AT/GC rule 2 strands are antiparallel per their 5' to 3' directionality 1 complete 360º turn of the helix, 10 nucleotides 1 complete turn is 3.4 nm and 1 nucleotide is 0.34 nm  Prokaryotic Chromosomes Chromosomes are pieces of DNA that contain the genetic instructions, or genes, of an organism Prokaryotes (single chromosome) – No true nucleus – Chromosome is a circular DNA molecule that is supercoiled, meaning the helix is coiled on itself – At approximately 40 sites, a complex of proteins is attached, forming a series of loops – This structure is the nucleoid  Eukaryotic Chromosomes Eukaryotes (number and size of chromosomes vary) – True nucleus enclosed by a nuclear membrane – Nucleosome which consists of a strand of DNA wrapped around a disk of histone proteins – DNA appears like beads on a string String of beads then coils into a larger structure called the 30 nm fiber With additional proteins next coiled in to a 200 nm fiber Eukaryotic Chromosome Levels of Structure RNA Structure  Ribonucleic Acid  Consists only of one strand of nucleotides  Has ribose (a 5C sugar) NOT deoxyribose  Has uracil (U) as a nitrogenous base NOT thymine RNA Structure Sugar-phosphate backbone for ribonucleotides is also linked by 3'-5' phosphodiester bonds Base pairing between U and A and G and C can still occur – This H bonding results in portions of the single- strand that become double-stranded Replication  The process by which DNA makes a copy of itself  Why does DNA need to copy?  Cells divide for an organism to grow or reproduce  Every new cell needs a copy of DNA  In DNA replication enzymes work to unwind and separate the double helix and add complimentary nucleotides to the exposed strands Replication  DNA replication is semi-conservative.  When it makes a copy, one half of the old strand is ALWAYS kept in the new strand  This helps reduce the number of copy errors.  Structure to Function in DNA Replication Structure of the DNA molecule suggests the mechanism for accurate replication – An enzyme could “read” the nitrogenous bases on one strand of a DNA molecule adding complementary bases to a newly synthesized strand – Product of this strategy would be a new DNA molecule in which one strand is the original or parent strand, and the other is newly synthesized, a daughter strand – This strategy is called semiconservative replication DNA Replication  DNA helicases—break H-bonds linking bases  DNA polymerases— move along each of the strands, adding nucleotides, according to base pairing rules. DNA Replication  The result is two exact copies of the original DNA  Each new double helix is composed of one original DNA strand and one new strand.  Semi-conservative  Information Flow in Biological Systems Central Dogma tells us that “in cells the flow of genetic information contained in DNA is a one- way street that leads from DNA to RNA to protein” Transcription is the process by which a single- strand of DNA serves as a template for the synthesis of an RNA molecule – Think of making a COPY Translation converts the information from one language of nitrogenous bases to another of amino acids – Think of TRANSLATING into another language  Translation  DNA is in the nucleus  To make proteins, DNA must get its instructions to the ribosomes who make proteins.  To transport its instructions, it uses Messenger RNA (mRNA) DNA by the Numbers  Each cell has about 3 meters of DNA.  The average human has 300 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 0.000000002 meters. The earth is 150 billion meters or 93 million miles from the sun. Coming Soon