Molecular Biology expanding on macromolecules DNA RNA DNA

Molecular Biology - expanding on macromolecules, DNA, RNA • DNA and RNA – Macromolecules – Polymers of nucleotides – Double stranded or single stranded – Sugar-phosphate backbone …think back to Ch. 3

Nucleic Acids • Polymers of 4 specific monomers = nucleotides – Via dehydration synthesis between sugars • Builds chain w/sugarphosphate backbone • Single stranded RNA • Double stranded DNA

• RNA is similar to DNA – Except for the sugar and one base • Uracil (U) in place of Thymine (T)

Structure of DNA • James Watson and Francis Crick, 1953 – Rosalind Franklin • Double helix

Replicating DNA • Based on its structure, Watson & Crick predicted that cells copy genes by matching complimentary bases

• Untwists and replicates both strands simultaneously • Rapid process – Efficient – Builds in two directions • Use of enzymes – DNA polymerase • Links nucleotides to growing daughter strand

Link to genotype & phenotype • Genotype = genetic makeup; contained in DNA • Phenotype = traits; expressed from proteins – Proteins are the link…genes build proteins • How? – DNA sends out instructions as RNA, which synthesizes proteins

… in other words • DNA is our blueprint • The boss or engineer sends a carbon copy, transcribed RNA, for construction • At the construction site, the foreman (ribosomes) translates the plan to the crew, who are not trained to read the plans, but know it in terms of amino acids; the building blocks of proteins

Translating nucleic acid language to polypeptides (chains of amino acids) • Nucleotides (A, T, C, G or A, U, C, G) are the alphabet • Translation code – Words made of 3 letters (triplets) = codons • Polypeptide language – Consists of 20 amino acids

Cracking the genetic code • Rules of communicating – from RNA’s codons to amino acids in proteins

Transcribe the DNA strand: GGT-AAA-TGC ___ - ___ RNA Translate RNA into polypeptides

Transcribe the DNA strand: GGT-AAA-TGC CCA-UUU-ACG RNA Translate RNA into polypeptides Pro – Phe - Thr

• Transcription – Making the RNA • Occurs in steps Initiation Enzyme with start point = promoter Elongation Adds nucleotides to RNA strand Termination Enzyme reaches stop point

DNA → RNA → protein • Flow of information begins in a gene – Nucleotide sequence = DNA – Serves as a template • Template transcribed into – Another nucleotide sequence = RNA • RNA is responsible (translation) for the next sequence – Amino acids = polypeptide • Proteins formed from polypeptide determines cell appearance and capabilities

Potential to look backward • From protein back to gene – E. g. Sickle cell disease caused by different amino acid in hemoglobin protein Caused by change of a single nucleotide = mutation

Mutations • Types of gene mutations – Base substitution • No change • Positive change • Harmful change (sickle cell example) – Base insertion or base deletion • Alters the reading frame • Very bad

Causes of mutations • Errors during DNA replication • Mutagens – Physical agent • e. g. UV, X-rays, or gamma rays – Chemical agent • e. g. ethidium bromide,