Mic 201 Lecture

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Mic 201 Lecture 14 Outline Principles of
Microbial Molecular Biology Part I

• Overview of genes and gene expression.
• Macromolecules and genetic information
• What is a gene and what is its function?
• The steps in information flow.
• Prokaryotic and Eukaryotic genetics.
• Exons and introns.
• DNA structure
• The double helix
• Sequence-specific features of DNA structure.
• The effect of temperature on DNA structure.

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Mic 201 Lecture 14 Outline continuation

• DNA replication.
• Templates and Primers.
• DNA polymerases.
• RNA synthesis and processing.

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Molecular Biology the study of the structure and
function of the diverse array of macromolecules
found in the cell.
Genetics is the discipline that deals with the
mechanism by which traits are passed from one
organism to another and how they are expressed.
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What is a gene? What is its function?
Genes Functional unit of genetic information.
Entities that specify the structure of a single
polypeptide or protein chain, a tRNA or a rRNA.
The gene is the element of information that
specifies the sequence of amino acids of the
protein. The information in the gene is present
as a sequence of bases in the DNA.
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The Steps in Information Flow
Informational molecules
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(from the previous picture) There is a linear
correspondence between the base sequence of a
gene and the amino acid sequence on a polypeptide.
One amino acid
CODON
The genetic code
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The genetic code
Protein-synthesizing system
translation
Ribosomes (rRNA and proteins) tRNA enzymes
Proteins
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The central dogma of molecular biology
DNA
RNA
PROTEINS
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Transfer of genetic information in Prokaryotes
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Transfer of genetic information in Eukaryotes
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DNA Structure
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Specific pairing between adenine (A) and thymine
(T) and between guanine (G) and cytosine (C) via
hydrogen bonds.
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DNA structure
Antiparallel strands
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A DNA with 1000 bases contains 1 kb (kilobase) of
DNA.
A double helix 5000 base pairs in length 5 kbp
Sequence-specific features of DNA structure
See next
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Inverted repeats and the formation of a stem-oop
structure
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Linear DNA with complementary single-stranded
ends (sticky ends) can cyclize by base
pairing of the complementary ends.
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A hairpin structure at one end of a linear DNA
molecule
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• DNA replication.

Accurate process the new cells or organisms will
have essentially the same genetic information as
the parent cell.

• Templates and Primers.

DNA double helix with complementary base pairing.
If the DNA double helix is opened up, a new
strand can be synthesized as the complement of
each of the parental strands.
The replication is semiconservative.
The DNA molecule that is copied to form a
complement is called the template.
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DNA replication always proceeds from the 5end to
the 3-hydroxyl end, the 5-phosphate of the
incoming nucleotide being attached to the
3-hyroxyl of the previously added nucleotide.

• DNA polymerases

All DNA polymerases synthesize new DNA in the 5
? 3. Not known DNA polymerase can begin a new
chain. All these enzymes can only add a
nucleotide onto a preexisting 3 OH group.
For a new chain to be started there must be a
primer, a site at which the DNA polymerase can
attach the first nucleotide. In most cases, this
primer is a short stretch of RNA.
A primase synthesize a short stretch of RNA.
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Structure of the RNADNA combination that results
at the initiation of DNA synthesis
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• RNA synthesis and processing.

Messenger RNA (mRNA), transfer RNA (tRNA) and
ribosomal RNA (rRNA).
ALL products of transcription
RNA acts at two levels genetic and functional.
At the genetic level, RNA carries the genetic
information from DNA. At the functional level,
RNA serves a functional and structural role in
ribosomes or an amino acid transfer role in
protein synthesis.
(dont forget the 3 key differences between the
chemistry of RNA and that of DNA)