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
Dec 18, 2015
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/sugar-phosphate 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 stepsInitiation
Enzyme with start point = promoter
ElongationAdds nucleotides to RNA strand
TerminationEnzyme 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,