Transcript Molecular biology

CHAPTER 1
INTRODUCTION TO
RECOMBINANT DNA
TECHNOLOGY
MISS NUR SHALENA SOFIAN
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A Brief History
• What is molecular biology?
– The attempt to understand biological
phenomena in molecular terms
– The study of gene structure and function at
the molecular level
• Molecular biology is a melding of aspects
of genetics and biochemistry
• Aims to provide understanding between
various systems of a cell:
– Interrelation between DNA, RNA and protein
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– Regulations of these interactions
Biological Science in Relation to
Molecular Scale
• Combinations of techniques from genetics,
biochemistry and biophysics
• Biochemistry – study of chemical substances
and their vital processes in living organisms
• Genetics – study of the effect of genetic
differences in organisms
• Molecular biology – study of molecular
emphasizing the process of replication,
transcription and translation of genetic
material
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1.1 Transmission Genetics
• Transmission genetics deals with the
transmission of traits from parental
organisms to their offspring
• Chemical composition of genes not known
until 1944
– Gene
– Phenotype
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Mendel’s Laws of Inheritance
• A gene can exist in different forms called
alleles
• One allele can be dominant over the other,
recessive, allele
• The first filial generation (F1) contains
offspring of the original parents
• If each parent carries two copies of a
gene, the parents are diploid for that gene
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Mendel’s Gene Transmission
• Heterozygotes have one copy of each
allele
• Parents in 1st mating are homozygotes,
having 2 copies of one allele
• Sex cells, or gametes, are haploid,
containing only 1 copy of each gene
• Heterozygotes produce gametes having
either allele
• Homozygotes produce gametes having
only one allele
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The Chromosome Theory of
Inheritance
• Chromosomes are discrete physical entities
that carry the genes
• Thomas Hunt Morgan used the fruit fly,
Drosophila melanogaster, to study genetics
• Autosomes occur in pairs in a given
individual
• Sex chromosomes are identified as X and Y
– Female has two X chromosomes
– Male has one X and one Y chromosome
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Hypothetical Chromosomes
• Every gene has its place, or locus, on a
chromosome
• Genotype is the combination of alleles
found in an organism
• Phenotype is the visible expression of the
genotype
– Wild-type phenotype is the most common or
generally accepted standard
– Mutant alleles are usually recessive
– Example?
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Genetic Recombination and
Mapping
• In early experiments genes on separate
chromosomes behaved independently
• Genes on the same chromosome behaved
as if they were linked
• This genetic linkage is not absolute
• Offspring show new combinations of
alleles not seen in the parents when
recombination occurs
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Recombination
• During meiosis, gamete formation,
crossing over can occur resulting in the
exchange of genes between the two
homologous chromosomes
• The result of the crossing-over event
produces a new combination of alleles
• This process is called recombination
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Genetic Mapping
• Morgan proposed that the farther apart
two genes are on a chromosome, the
more likely they are to recombine
• If two loci recombine with a frequency of
1%, they are said to be separated by a
map distance of one centimorgan (named
for Morgan)
• This mapping observation applies both to
bacteria and to eukaryotes
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Physical Evidence for
Recombination
• Microscopic examination of maize
chromosome provided direct physical
observation of recombination using easily
identifiable features of one chromosome
• Similar observations were made in
Drosophila – example?
• Recombination was detected both
physically and genetically in both animals
and plants
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1.2 Molecular Genetics
• The Discovery of DNA: The general
structure of nucleic acids were found by the end
of the 19th century
– Long polymers or chains of nucleotides
– Nucleotides are linked by sugars through
phosphate groups
• Composition of Genes: In 1944, Avery and
his colleagues demonstrated that genes are
composed of nucleic acids
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The Relationship between
Genes and Proteins
• Experiments have shown that a defective
gene gives a defective or absent enzyme
• These lead to the proposal that one gene
is responsible for making one enzyme
• Proposal not quite correct
1. Enzyme may have several polypeptides,
each gene codes for only one polypeptide
2. Many genes code for non-enzyme proteins
3. End products of some genes are not
polypeptides, but RNAs
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Activities of Genes
Genes perform three major roles
• Replicated faithfully
• Direct the production of RNAs and
proteins
• Accumulate mutations thereby allowing
evolution
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Replication
• Franklin and Wilkins produced x-ray
diffraction data on DNA, Watson and Crick
proposed that DNA is double helix
– Two DNA strands wound around each other
– Strands are complementary – know the
sequence of one, automatically know the
sequence of the other
• Semiconservative replication keeps one
strand of the parental double helix conserved
in each of the daughter double helices
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Genes Direct the Production of
Polypeptides
• Gene expression is the process by which
a gene product is made
• Two steps are required
– Transcription: copy of DNA is transcribed into
RNA
– Translation: the RNA copy is read or
translated to assemble a protein
– Codon: a sequence of 3 nucleic acid bases
that stand for one amino acid
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Genes Accumulate Mutations
Genes change in several ways
• Change one base to another
• Deletions of one base up to a large
segment
• Insertions of one base up to a large
segment
• As the change is more drastic, it is more
likely that the gene or genes involved will
be totally inactivated
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