Notes on Nucleic Acids 2 types of nucleic acids: DNA – deoxyribonucleic acid RNA – ribonucleic acid Chapter 8

organic compounds large, made of subunits called nucleotides  Click image for interactive journey into human DNA

Each DNA nucleotide is made up of 3 parts: 1. Phosphate group 2. Deoxyribose – 5 carbon sugar 3. Nitrogen base – either adenine, thymine, cytosine, or guanine

Nitrogen bases Purines – adenine (A) and guanine (G)

Pyrimidines – thymine (T) and cytosine (C)

The bases are held together by weak hydrogen bonds Base pairings in DNA:A – T C – G

A model of DNA was constructed in 1953 at Cambridge University in England

Scientist – James Watson, ( )James Watson Field of study – biology Country - America

Scientist – Francis Crick ( )Francis Crick Field of study – biophysics Country - England

Their model is described as a double twisted helix (looks like a twisted ladder) Watson and Crick published their proposed DNA double helical structure in a paper in the journal Nature in April In this paper Watson and Crick acknowledged that they had been "stimulated by.... the unpublished results and ideas" of Wilkins and Franklin.

Scientist – Maurice Wilkins, ( )Maurice Wilkins Field of study – biophysics Country - England

Scientist – Rosalind Franklin, ( )Rosalind Franklin Field of study – Molecular Biology (x-ray diffraction) Country - England  Click image for interpret- ation of the X-ray

The process by which DNA builds an exact copy of itself - replication first the double helix must be unwound – this is done by enzymes called helicases then DNA polymerases (enzymes which move along each DNA strand) add nucleotides to the exposed bases

Replication occurs every time a cell divides, therefore passing the DNA code on into every cell

Genes are the DNA-encoded information that specifies particular proteins; Each gene is made of a specific sequence of nucleotides

The working structures of genes are made of RNA RNA structure: 1. Consists of a single strand of nucleotides

2. Ribose – a 5 carbon sugar 3. Uracil (U) instead of thymine (T) uracil is paired with adenine

RNA base pairings:A – U C – G

Three types of RNA 1. mRNA – messenger RNA 2. tRNA – transfer RNA 3. rRNA – ribosomal RNA All are needed for processing the information from DNA into proteins (gene expression)

Differences in DNA and RNA: DNARNA 1. double stranded single stranded 2. thymine uracil 3. nucleus only cytoplasm 4. deoxyribose sugar ribose sugar

Gene expression occurs in two stages: 1. Transcription – information in DNA is transferred to mRNA 2. Translation – the information in mRNA is used to make a protein

Roles of DNA & RNA in transmitting genetic information Story time: the analogy… Comp Book– Draw the Flow Map: DNA expression in the cell You need your pencil plus three colors: –Pencil will draw cell membrane/ cell parts/ labels –RED: DNA molecules –BLUE: any RNA molecules –PURPLE: protein

DNA  RNA

RNA  protein

1. Transcription (DNA  RNA) occurs in nucleus begins with the enzyme RNA polymerase which binds to the promoter

Promoter – a specific sequence of DNA that acts as a “start” signal for transcription Terminator – a sequence of bases that tells the RNA polymerase to stop adding nucleotides

Transcription Video

mRNA – is an RNA copy of a gene used as a blueprint for a protein carries hereditary information from DNA and delivers it to the site of translation acts as a template for the assembly of amino acids

tRNA – acts as an interpreter molecule translating mRNA sequences into amino acid sequences

rRNA – plays a structural role in ribosomes

2. Translation (RNA  proteins) occurs in a ribosome —both free ribosomes & ribosomes attached to ER uses nucleic acids to synthesize proteins

involves all three RNA types: —rRNA in the ribosome

—mRNA containing the genetic message —message is made of codons AUG-AAA-UAC-CCU-CCA-GCG-GGA

Codon – a series of three-nucleotide sequences each codon corresponds to an amino acid or signifies a start or stop signal Write this down!

—tRNA carrying specific amino acids to be joined a.a.

AUG-AAA-UAC-CCU-CCA-GCG-GGA mRNA  tRNA UAC tRNA GGA AUG GGU Pro tRNA UUU ribosome Met Lys Tyr Ser Translation (Example) Growing polypeptide         

Translation: mRNA, tRNA & rRNA in cooperative action …to make proteins!!!

AUG-AAA-UAC-CCU-CCA-GCG-GGA mRNA  tRNA UAC tRNA GGA AUG GGU Pro tRNA UUU ribosome Met Lys Tyr Ser Translation (Repeated) Growing polypeptide         

Translation Video

A “Polysome” Can you ID the 3 RNAs?

Awesome summary video from Click here to viewhere