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Lecture 12

NURS 364 Lecture Notes - Lecture 12: Single-Nucleotide Polymorphism, Nonsense Mutation, Silent Mutation


Department
Nursing
Course Code
NURS 364
Professor
Deborah Van Kuiken
Lecture
12

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Genes &
Genetic Diseases
NURS 364
Human Karyotype
1 - 22 Autosomal Chromosome
23 - sex chromosome
What Exactly is a chromosome?
Chromosomes
Temporary but consistent state of DNA
They are the carriers of the gene or unit of heredity (DNA).
Chromosomes are composed of two longitudinal sister chromatids
1/10,000 as long as outstretched DNA
7.2 x 10-3 inches
Composition and Structure of DNA?
Anti-parallel structure of
Nucleotide pairings
Double Helix
Pentose sugar (deoxyribose)
Phosphate molecule
Four nitrogenous bases
Adenine with thymine
Cytosine with guanine
Hydrogen bonds
Replication of DNA
Untwisting and unzipping of the weak hydrogen bond between DNA bases leaving a single
strand with each base unpaired.
DNA polymerase
Enzyme that travels along the single DNA strand creating the new complementary DNA
base pair.
Capture new nucleotides
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Double checks itself as it goes along
Genes to Proteins
The central dogma of molecular biology states that information flows in one direction:
Transcription Translat
ion
DNA mRNA Proteins
NUCLEUS CYTOPLASM
Genes to Proteins
Transcription Translation
DNA RNA Proteins
NUCLEUS CYTOPLASM
Mechanisms of Genetic Disorder
Despite wide range of manifestations, there are common mechanisms for genetic disorders:
Mechanism of mutation
At the base level
At the chromosome level
Inheritance
Any inherited alteration of genetic material
Inheritance of an altered gamete cell.
Mutation of gametic cells during meiosis (New Mutation).
Mutation during early embryogenesis.
Mutations at the
base pair/ nucleotide level
Mechanisms of Genetic Disorder
Mechanism of mutation occurring during DNA replication
Point mutations (Single Nucleotide Polymorphism- SNP)
Base pair substitution - substitute one base nucleotide for another
10-30 million SNPs in the Human genome
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Mechanisms of Genetic Disorder
Mechanism of mutation occurring during DNA replication
Point mutations (Single Nucleotide Polymorphism- SNP)
Can result in:
Silent mutation – did not cause a change in the amino acid sequence
Missense mutations – causes a change in the single amino acid
Nonsense mutations – create stop codon
Base Pair Mutation
Examples of a Point mutation
(Single Nucleotide Polymorphism)
Sickle Cells Disease
Caused by a point mutation (SNP) in the β-globin chain of hemoglobin.
The β-globin gene is found on the short arm of chromosome 11.
Examples of a Point mutation
(Single Nucleotide Polymorphism)
Neoplasia (Cancer)
Single Nucleotide Polymorphism (SNP) in genes involved in DNA repair (tumor
suppressor gene) can act as cancer susceptibility genes.
Adverse Drug Reaction
Single Nucleotide Polymorphism (SNP) can alters the structure & function of drug
metabolizing enzymes.
Idiosyncratic Effect from medications
Mechanisms of Genetic Disorder
Mechanism of mutation occurring during DNA replication
Frame shift mutation
Caused by deletion or insertion of one or more base.
Cystic Fibrosis (Chromosome 7)
Tay-Sachs disease
Aberrations in number
of chromosomes
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