Lecture 1 Gene Structure and Function

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Lecture 1Gene Structure and Function

• R. D. Gietz Ph.D.
• Department of Biochem Med Genetics
• Ph. 789-3458
• Email. gietz_at_cc.umanitoba.ca

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• Learning Objectives
• To understand the structure of DNA and how it is
  replicated.
• To understand the structure of a gene.
• To understand the Central Dogma of Molecular
  Genetics
• To understand the how the genetic code is used.
• To understand how proteins are produced
  modified.

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DNA is made up of phosphodiester bonds linking
2 deoxyribose sugars. Each sugar is linked to a
nitrogenous base that provides the information
coding part of the molecule.
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The nitrogenous bases come in 4 varieties.
Adenine, which pairs with Thymidine, Guanine
which pairs with Cytosine. Note the two hydrogen
bonds between AT and three between GC.
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DNA structure. DNA is double stranded with the
bases being on the inside of the molecule. The
strands are anti-parallel. (polarity)
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Hydrogen bonding can cause hairpins in DNA and RNA
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DNA is replicated semi-conservatively. This is
what gives replication its high fidelity. One
strand is old and one strand is new produced by
copying from the complementary sequence.
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DNA replication is difficult due to anti-parallel
nature of the molecule. Replication can only
occur in one direction in a biological system.
That is 5 to 3.
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DNA replication is accomplished by DNA
polymerases. In Mammals there are 5, each with a
different job.
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The central Dogma of Molecular Genetics
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Information in DNA is accessed by transcription.
This is done by copying the DNA strand into RNA.
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Transcription is regulated by a promoter elements
that bind protein transcription factors.
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Some promoter elements and Transcription Factors
that control gene expression
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Genes in Humans are not contiguous. Genes are
made up of Exons (coding) and Introns (non
coding). Introns must be removed.
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Splicing signals are found in the gene sequence.
The consensus sequences is found at the
exonintron boundaries as well as in the intron
at the Branch site.
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Splicing mechanism
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RNA is modified to make it more stable. One way
is 5 cap
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mRNA is polyadenylated after transcription. Aids
in transport to the cytoplasm, mRNA stability,
and enhanced recognition by ribosomes
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Genes and Proteins are co-linear. Genes are
processed by splicing. Proteins are processed by
cleavage and modification.
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Translation occurs from the 5 end to the 3 end
giving a colinear protein.
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Peptide bond
Universal Genetic Code
The 5 end of the gene is the same at the N
terminus of protein.
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Gene and protein co-linearity. Gene and protein
processing
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Proteins are modified after production.
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Proteins are localized into different cellular
compartments by signals that are found within the
primary sequence.
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Protein secondary structure. Alpha helix and
beta sheet.
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Proteins have 4 levels of structure
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Proteins can have more complex structures
covalent interactions between subunits as well as
tertiary and quaternary structures.
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Summary 1

• DNA is double stranded.
• Phosphodiester bonds between deoxyribose sugars
  give backbone. Bases are attached to the sugars
  and are complementary AT GC
• Information is encoded by the linear sequence of
  the bases.
• DNA is replicated 5-gt 3
• Information flows from DNAlt-gtRNA-gtProtein

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Summary 2

• Genes are a linear array of 4 nucleotides
• In mammals genes are non contiguous
• Information accessed by making RNA copy
• Transcription controlled by up stream cis acting
  elements and proteins that bind to it.
• Exons are fused at the RNA stage by splicing
  which removes the introns
• RNA is modified by a Cap and polyadenylation

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Summary 3

• Genes and proteins are co-linear
• Triplets are converted into amino acid sequence
• Proteins are modified in numerous ways post
  production.