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,