DNA : THE CODE OF LIFE

a long, thin, thread-like structure composed of DNA that is wrapped around proteins called histones

• Codes for a specific protein • Controls inherited characteristics • Determines the apperance and functioning of an organism

• Maurice Wilkins & Rosalind Franklin surmised that DNA was helix-shaped • Wilkins showed Franklins X-ray photograph to Francis Crick without her permission • James Watson & Crick used the information from the photograph to build three dimensional models to solve the structure of DNA

• Adenine and Guanine are large molecules (purine bases) • Thymine and Cytosine are smaller molecules (pyrimidine bases)

• the deoxyribose of one nucleotide forms a bond with the phosphate group of another • two long strand are formed • the sides of the DNA strand consist of alternating deoxyribose molecules and phosphate groups • each rung of the DNA ladder is formed by the linking of two nitrogenous bases; a purine and a pyrimidine base • known as a base pair • bases are joined by weak hydrogen bonds, which are easily broken by enzyme action • two hydrogen bonds form between Adenine and Thymine, and three form between Guanine and Cytosine • the following bases are formed: AT GC TA CG • in any DNA molecule there are equal numbers of AT bases and GC bases • one DNA strand is the complement of the other strand as the bases correspond with each other.

it provides the code that gives the instructions for the synthesis of proteins (protein synthesis)

• DNA makes up genes which carry hereditary information • DNA contains coded information for protein synthesis

• The DNA double helix unwinds • Weak hydrogen bonds between nitrogenous bases break and two DNA strands unzip • Each original DNA strand serves as a template on which its complement is built. • Free nucleotides build a DNA strand onto each of the original two DNA strands by attaching to their complementary nitrogenous bases • Two identical DNA molecules are formed and the original each double strand now becomes a twisted helix once again

• Doubles the genetic material so it can be shared between the resulting daughter cells during cell division. • Results in the formation of identical daughter cells ü during mitosis

• to identify crime suspects in forensic investigations • to identify dead bodies • to identify relatives • proof of paternity • to determine the probablity and/or causes of genetic defects • to trace missing persons • to establish the compatibility of tissue types for organ transplants

FOR: 1. Proof of paternity 2. Tracing lost relatives / separated siblings 3. Identifying a missing person 4. Identifying remains of victims of wars/accidents 5. Determine the probability of genetic defects 6. Treatment of genetic defects 7. Solving criminal cases in forensics 8. Identifying origin of products of threatened species in illegal trading AGAINST: 1. Inaccuracy of the DNA profiling process leads to errors 2. Human error in interpretation of the results 3. Data may be used to discriminate against an ill person 4. Cost of profiling may exclude poor communities 5. Forensic labs do not conform to uniform standards 6. DNA samples may be planted at a crime scene 7. Small samples of DNA may be identical in suspects

• mRNA carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm and thus acts as a messenger. • tRNA picks up amino acids in the cytoplasm according to the coding of the anticodon bases and takes them to the ribosomes for protein synthesis. it acts as a transfer molecule. • rRNA forms part of the structure of the ribosomes in the cytoplasm and plays a role in the control of protein synthesis

• the double helix DNA unwinds • the double-stranded DNA unzips/weak hydrogen bonds break to form two separate strands • one strand is used as a template • to form mRNA • using free RNA nucleotides from the nucleoplasm • the mRNA is complementary to the DNA • mRNA now has the coded message for protein synthesis

• each tRNA carries a specific amino acid • when the anticodon on the tRNA • matches the codon on the mRNA • then tRNA brings the required amino acid to the ribosome • amino acids become attached to each other by peptide bonds • to form the required protein

changes in the sequence of nitrogenous bases. happens due to mistakes in DNA replication or transcription.

• mRNA found in the nucleus and functions on the ribosome • tRNA located in the cytoplasm

• mitochondria • nucleus • chloroplast