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Nucleotide
Subunit of DNA consisting of a sugar, phosphate group, and nitrogenous base (A,C, G, T) : Sugar/phosphate group = backbone : Nitrogenous bases = ribs
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DNA
- (DeoxyriboNucleic Acid)
- 1. Sugar: Deoxyribose
- 2. Nitrogenous bases: A, C, G, T
- 3. Strands: Double - stranded
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RNA
- (RiboNucleic Acid)
- 1. Sugar: Ribose
- 2. Nitrogenous bases: A, C, G, U
- 3. Strands: Single - stranded
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Watson & Crick
- 1.Discovered molecular structure of DNA
- a. Sugar-phosphate backbone
- b. Nitrogenous base ribs
- c. Complementary base-pairs
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Complementary Base Pairing
- 1. Adenine pairs with Thymine or Uracil
- a. A-T (DNA) or A-U (RNA)
- 2. Cytosine pairs with Guanine
- a. C-G (always)
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Replication
- 2 strands of parental DNA separate, each becoming a template for the assembly of two complementary daughter strands
- Each new DNA molecule = 1 new strand + 1 old strand (maintaining DNA integrity)
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Genotype
Sequence of nucleotide bases in an organism’s DNA.
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Phenotype
Physical expression of nucleotide sequences in an organism.
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Transcription
Transfer of genetic information from DNA to RNA.
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Translation
Assembly of proteins using the information transferred to RNA.
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mRNA
Carries genetic code from DNA into cytoplasm (messenger).
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tRNA
Recognizes genetic code, matching amino acids to it in the correct order (transfer).
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rRNA
With proteins, forms the ribosome, assembling amino acids into proteins (ribosomal).
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Codon
- 3 nucleotide sequence that specifies a particular amino acid; basic unit of genetic code (“word”); on mRNA.
- Each codon code for one of 20 amino acids.
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Anticodon
- 3 nucleotide sequence that is complementary to a codon on mRNA; on tRNA.
- Carries with it one of 20 amino acids.
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Introns
Internal, non-coding regions of RNA (nonsense).
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Exons
Internal, coding regions of RNA (expressed).
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RNA-splicing
Introns are removed and exons are joined together forming a mRNA strand with a continuous coding sequence.
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Mutations
- Any change in the nucleotide sequence of DNA.
- Good mutations: evolution
- Bad mutations: inherited diseases, cancer
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Spontaneous mutations
Results from errors during DNA replication, recombination.
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Mutagens
Agents that cause errors during DNA replication. *Chemical, *Radioactive, *Viral.
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Types of Mutations
- 1) Base substitution: Replacement of one base or nucleotide by another in a DNA sequence.
- 2) Insertions/Deletions: Addition/subtraction of a base or nucleotide in a DNA sequence.
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Base substitution
- Replacement of one base or nucleotide by another in a DNA sequence
- Silent mutation – different base sequence, but same amino acid (no effect)
- Missense mutation – different base sequence with different amino acid (minor to major effect)
- Non-sense mutation – different base sequence, amino acid becomes a stop codon (premature, non-functioning amino acid)
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Insertions/Deletions
- Addition/subtraction of a base or nucleotide in a DNA sequence
- All nucleotides downstream from the mutation will be regrouped into different codons
- Effects are usually disastrous!
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Obligate Intracellular Parasites
Infectious particles that function only when existing inside a living cell.
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Structure
DNA or RNA surrounded by a protein coat.
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Natural History of Viruses
- 1. First discovered in 19th century, origin unknown.
- 2. Not classified in any kingdom (not living).
- 3. Occur in multiple shapes & sizes.
- 4. Capable of mutating.
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Bacteriophages
Viruses that infect bacteria.
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Animal Viruses
- 1. Generally viruses are species specific; some-times even cell specific.
- 2. Viruses seek out cells with receptor sites to which they can attach: ie) Measles – skin cells, Mumps – salivary gland cells, Hepatitis – liver cells, Herpes – nerve cells.
- 3. A virus enters a cell or simply injects its own DNA into the cell. Ie) Viral DNA consists of 3 – 500 genes (eukaryotic DNA consists of 10,000 genes)
- 4. A virus takes over the host’s metabolic path-ways, utilizing host ATP and enzymes. Ie) A single virus can generate 1,000’s of new virus particles.
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Emerging Viruses
- A virus that is in one species and mutates in order to infect a different species.
- ie) Bird flu transmitting through the bird species and infecting the human species.
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