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Questions and Answers
What happens to all bases after a base addition?
Move one position to the right.
What happens to all bases after a base deletion?
Move one position to the left.
Which type of mutations could frame shift mutations lead to?
What is the result of adding a C between the C and U in the base sequence GCG-CUA-GAG?
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What are the three components that each nucleotide is composed of?
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What is the result of deleting the C in the second codon of the base sequence GCG-CUA-GAG?
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What connects complementary bases in DNA?
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DNA replication occurs during the G period of Interphase.
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Helicase untwists and unzips the DNA helix by breaking the _______ bonds.
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Match the following RNA types with their descriptions:
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Study Notes
Nucleic Acids
- Nucleic acids are composed of nucleotides.
- Each nucleotide is composed of:
- A phosphate group
- A pentose sugar (deoxyribose in DNA or ribose in RNA)
- Nitrogenous bases (purines and pyrimidines)
- Purines are larger and double-ringed (adenine and guanine)
- Pyrimidines are smaller and single-ringed (cytosine, thymine, and uracil)
DNA Structure
- DNA is a double helix, with two strands of nucleotides connected and twisted.
- Hydrogen bonds connect complementary bases (adenine and thymine, or guanine and cytosine).
The Search for the Genetic Material
- Frederick Griffith (1928) demonstrated transformation, changing the genotype and phenotype of a cell by assimilation of genetic material from an outside source.
- Oswald Avery, Maclyn McCarty, and Colin MacLeod (1944) repeated Griffith's experiment, showing that DNA is the transforming agent.
The Search for the Structure of DNA
- Erwin Chargaff (1947) discovered that the amount of adenine in a DNA molecule is equal to the amount of thymine, and the amount of guanine is equal to the amount of cytosine (Chargaff's Rule).
- Maurice Wilkins and Rosalind Franklin (1952) used X-ray crystallography to determine the shape of DNA, showing that it is a three-dimensional double helix.
- James Watson and Francis Crick (1953) determined the true structure of DNA, winning the Nobel Prize.
Biological Properties of DNA
- DNA carries information from generation to generation.
- DNA must be copied accurately.
- DNA sometimes mutates, and mutations are copied accurately.
- DNA must be translated and its information put into action.
DNA Replication
- Occurs during the S period of interphase.
- Takes place within the nucleus of a eukaryotic cell.
- Involves the production of new DNA from existing DNA templates.
- The original parent strands separate, and new complementary daughter strands are synthesized.
- Helicase untwists and unzips the DNA helix, breaking the hydrogen bonds.
- DNA polymerase builds new DNA nucleotides using a single strand DNA template.
- One strand (3' to 5') is replicated continuously, while the other strand is antiparallel (5' to 3') and replicated discontinuously.
DNA Repair
- Nuclease enzymes remove damaged DNA.
- DNA polymerase builds new DNA to repair the mistake.
- DNA ligase pieces together the repaired region to the existing correct region.
The Central Dogma
- The flow of genetic material in a eukaryotic cell: DNA → RNA → Protein.
- Transcription: the production of RNA from a single strand DNA template.
- Translation: the production of protein from a messenger RNA strand.
Transcription
- Helicase untwists and unzips the DNA helix, breaking the hydrogen bonds.
- RNA polymerase produces new RNA nucleotides from a single strand DNA template.
- RNA codons are built from DNA codons.
- Transcription occurs in the nucleus.
RNA
- A single strand of nucleotides.
- RNA base nucleotides are complementary to DNA base nucleotides.
- If a DNA single strand base sequence reads…., then RNA polymerase would build the complementary RNA sequence.
Types of RNA
- mRNA (messenger RNA): RNA that is ultimately translated and results in the production of protein.
- tRNA (transfer RNA): RNA that carries an amino acid to be used in the building of protein.
- rRNA (ribosomal RNA): a structural RNA that comprises the ribosome.
Translation
- RNA → Protein.
- mRNA leaves the nucleus and goes to a ribosome.
- Each mRNA codon codes for the production of an amino acid.
- tRNA molecules each carry an amino acid and an anticodon that is complimentary to the mRNA codon.
- Amino acids are linked by peptide bonds.
Ribosome Structure
- Consists of a large and a small subunit.
- mRNA enters the ribosome between the two subunits to be read.
- The A site accepts a new tRNA molecule, which delivers a new amino acid.
- The P site holds a tRNA molecule that has a growing chain of amino acids.
- The E site is the exit site that releases previously used tRNA molecules.
Genetic Code
- A dictionary that indicates which amino acids result from each mRNA codon.
- It is a triplet code, non-overlapping, universal, and degenerate code.
- Uses a table to determine the amino acid coded for by each mRNA codon.
Point Mutations
- A point mutation is a mutation involving a base substitution.
- If the altered codon does not change the amino acid, it has no effect.
- If the altered codon codes for a different amino acid, a different protein results (missense mutation).
- If the altered codon codes for STOP, no protein results (nonsense mutation).
Frame Shift Mutations
- Alter the complete base sequence that follows the mutation.
- A base addition shifts the reading frame to the right, while a base deletion shifts the reading frame to the left.
- Can lead to missense or nonsense mutations.
- More harmful than point mutations.
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Description
Understand the components of nucleotides, including phosphate groups, pentose sugars, and nitrogenous bases, and how they form DNA and RNA molecules.