The Structure of DNA and RNA Replication, Transcription, Translation

DNA & RNA are polymers of nucleotides There are three types of nucleic acids in nature. Adenosine triphosphate (ATP) Energy Storage Deoxyribonucleic Acid (DNA) Ribonucleic Acid (RNA) DNA and RNA are involved with the genetic aspects of the cell DNA and RNA are polymers of nucleotides

The Building Blocks of DNA Nucleic Acids The Building Blocks of DNA Deoxiribonucleic Acid – this where genetic information is stored DNA is a kind of nucleic acid, a polymer built from monomers called nucleotides Ribonucleic Acid (RNA) – another group of nucleotides, plays a role in protein synthesis. Nucleotides – are the building blocks (monomer) of nucleic acid polymer Only 4 types of nucleotides make – up DNA

DNA - Nucleotides Each DNA molecule has three parts:

DNA - Nucleotides The chemical bonds occur at specific locations in order to produce a functional unit. Be able to draw this!!!! All bonds within the nucleotide involve sharing electrons and are therefore COVALENT BONDS! (test question)

DNA - Nucleotides Nitrogenous Base – 4 nucleotides found in DNA differ only in their nitrogenous bases Pyrimidines: single ring structure Thymine (T) Cytosine (C) Purines: double ring structure Adenine (A) Guanine (G)

DNA - Nucleotides AT CG At Coral Gables

Monomers to Polymers The pattern (Pentose (sugar) - Phosphate- Pentose (sugar) -Phosphate) This is called – Pentose Phosphate Backbone Nitrogenous bases (AG ; CT) line – up along this backbone Nucleotides of a nucleic acid polymer can combine in many different sequences Sequences are essentially unlimited

Monomers to Polymers

The Double Helix Double Helix – Model created by Watson and Crick; in which two strands of nucleotides wound about each other Sugar phosphate backbones on the outside; Nitrogenous base on the inside. Electrical charges related to the molecules of the two strands cause the twisting action of the DNA model

The Double Helix

Complementary Base Pairs Base Pairing Rules A with T (2 hydrogen bonds) C with G (3 hydrogen bonds) AT CG (Coral Gables) Bonded by weak Hydrogen Bonds

Antiparallel The 2 single strands that make up the double-stranded molecule run in opposite directions to each other.

DNA Replication DNA replication occurs before cell division This ensures that cells carry the same genetic information This is also the method for inheritance.

DNA Replication When a cell divides; a complete set of genetic instructions are created for each cell Genetic material uses the template principle to make more DNA There are 2 types of molecules important for the process of DNA replication: Enzymes: helicase and a group of enzymes called DNA polymerase Free nucleotides found free floating in the nucleoplasm (A,T,C,G)

Called Daughter Strands DNA Replication During DNA copying: Two strands of the double helix separate Each strand acts like a picture negative Nucleotides line up one at a time across the existing strand (as per base pairing rule) Enzymes link the nucleotides together to form two new DNA strands Called Daughter Strands

DNA Replication Helicase – the enzyme that initiates the separation of DNA into 2 single strands by breaking the hydrogen bonds Helicase begins at a point or at an end of DNA molecule, and moves on complementary base pair at a time Unpaired nucleotides on each of these single strands can now be used to create 2 double stranded DNA molecules identical to the original

DNA Replication

DNA Replication DNA Polymerases – Catalyze covalent bonds between nucleotides of the new DNA strand This happens really fast and it is really accurate An error occurs in only one of a billion nucleotides As this happens on one side the other strand goes through the same process in the opposite direction DNA replication is described as a semi-conservative process because half of the pre-existing DNA molecule is always conserved (saved). DNA Polymerases

Protein Synthesis DNA controls the proteins produced in a cell. Some proteins are enzymes The production of enzymes can have a dramatic effect on the biochemistry of the cell Protein synthesis involves 2 major reactions: Transcription Translation

Protein Synthesis As we know a gene is a sequence of bases along DNA chain A gene is like a sentence; it’s a section of DNA that codes for a polypeptides Specific strings of nitrogenous bases make-up a gene

RNA (ribonucleic acids) Any nucleic acid whose sugar is ribose rather than deoxyribose (DNA) Another difference is that the Nitrogenous Base Thymine is replaced by Uracil (U) Similar to thymine Also Pair with Adenine RNA forms single strands NOT a double helix (like DNA) RNA can twist

Messenger RNA (mRNA) Transcription – The process of converting a DNA sequence to a form a single stranded mRNA molecule. mRNA molecule leaves the nucleus and is involved with the making of protein

Messenger RNA (mRNA) Remember the nucleoplasm contains free nucleotides for DNA replication and for creating RNA Each of the RNA nucleotides contain the sugar ribose not deoxyribose Also the nucleotide thymine is replaced by uracil

The Transcription Process Messenger RNA (mRNA) The Transcription Process Begins with an area of DNA of one gene becoming unzipped Like DNA replication but only the section of the gene get unzipped Only one of the 2 strands of DNA will be used to create the mRNA molecule Enzyme RNA polymerase catalyzes the reaction As RNA polymerase moves along the DNA starnd is acting like a template RNA nucleotides float into place using the RNA base pairing rules

The Transcription Process

The Transcription Process Triplet – any set of 3 bases that determine the identity of one amino acid The genetic code for an amino acid is written in a language of 3 bases A set of 3 bases contains enough information to code for one of the 20 amino acids When the triplet is found in a mRNA molecule its called a codon (codon triplet)

Translation There are three different kinds of RNA molecules and all are transcribed from a gene mRNA Ribosomal RNA (rRNA) – each ribosome is composed of rRNA and ribosomal protein Transfer RNA (tRNA) – each type of tRNA transfers one of the 20 amino acids to the ribosome

Translation Genetic Translation – the synthesis of polypeptides on ribosomes This is how the flow of information from gene to protein is based on Several codons form a sentence – that translates into polypeptide

Translation Anticodon Located at one end of the folded tRNA molecule It is a specific triplet of bases Are complementary (or matched up with) a specific codon in mRNA Recognition follows base pair rules (AU / CG) At the other end is the site where a particular amino acid recognizes both tRNA and its amino acid partner and links both together. Requires

Translation Ribosomes bind to mRNA in the cytoplasm and move along the molecule in a 5’ – 3’ direction until it reaches a start codon (AUG) Anticodons on tRNA molecules align opposite appropriate codons according to complementary base pairing Each tRNA molecule carries a specific amino acid (according to the genetic code) Ribosomes catalyze the formation of peptide bonds between adjacent amino acids (condensation reactions) The ribosome moves along the mRNA molecule synthesizing a polypeptide chain until it reaches a stop codon At this point translation ceases and the polypeptide chain is released

Translation

Triplet Code There are specific codons to represent amino acid Some amino acids are coded by more than one codon But no codon represents more than one amino acid

Triplet Code

This coding is shared by ALL organisms (almost all) Triplet Code There is also a code for stop These come at the end of a sequence There are sequence that do not code form an amino acids This coding is shared by ALL organisms (almost all) Production of human insulin in bacteria is an example of the universality of the genetic code allowing gene transfer between species

Polymerase Chain Reaction (PCR) PCR is a means by which DNA replication can be carried out artificially in a lab setting. Developed in the 1970’s Only replicate short segments Used to study and analyze DNA Used in crime scenes (forensic situations)

Thermus Aquaticus (Taq) A bacteria enzyme that is used in PCR that is stable at high temperatures Bacteria occurs in hot springs In addition the bacteria’s polymerase is also resistant to high temperatures Taq polymerase The use of Taq polymerase has allowed scientist to produce multiple copies of DNA quickly using the PCR technique