Download Chapter 10

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,