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Questions and Answers
What discovery did Griffith make in 1927?
What did Hershey and Chase's experiment demonstrate?
What is the role of tRNA during protein synthesis?
How many chromosomes are found in human somatic cells?
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What is the primary function of DNA helicase during DNA replication?
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Which of the following correctly describes the Watson and Crick model of DNA?
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What happens during the process of transcription?
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Which base pairs are connected by double hydrogen bonds in DNA?
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What is the function of ribosomal RNA (rRNA)?
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What is a key characteristic of semiconservative DNA replication?
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Which characteristic of RNA is true for messenger RNA (mRNA)?
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What is the function of DNA ligase in the DNA replication process?
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Which statement accurately describes the structure of DNA based on Watson and Crick's model?
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What is the primary role of the start codon in protein synthesis?
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What do Meselson and Stahl's findings about DNA replication suggest?
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Study Notes
Bacterial Transformation and Genetic Material
- Griffith (1927) identified bacterial transformation, where bacteria can change their genetic makeup by taking in foreign DNA from other bacteria.
- Avery's team provided experimental support that DNA is the genetic material.
DNA and Inheritance Studies
- Hershey and Chase (1952) demonstrated that DNA, not proteins, serves as the molecule of inheritance by tagging bacteriophages with radioactive isotopes 32P (DNA) and 35S (proteins).
- Rosalind Franklin utilized X-ray diffraction to show that DNA has a double helix structure.
- Meselson and Stahl (1953) confirmed that DNA replicates in a semiconservative manner, supporting Watson and Crick's model.
Types and Functions of RNA
- Messenger RNA (mRNA): synthesized from DNA during transcription, carries genetic information.
- Transfer RNA (tRNA): transports specific amino acids to the ribosome for polypeptide formation during translation.
- Ribosomal RNA (rRNA): structural component of ribosomes.
Chromosomes and Their Characteristics
- Chromosomes: Coiled DNA associated with histone proteins.
- Haploid (N): Contains one set of chromosomes found in sex cells (e.g., sperm and egg).
- Example: Sperm has 22 autosomes + X or Y chromosome; egg has 22 autosomes + X chromosome.
- Diploid (2N): Contains two sets of chromosomes in somatic (body) cells.
- Common examples: kidney, liver, brain, and skin cells.
- Humans have 46 chromosomes in somatic cells, arranged as follows:
- Females: 44 autosomes + XX sex chromosomes.
- Males: 44 autosomes + XY sex chromosomes.
- Karyotype: A visual representation of chromosomes arranged by size during metaphase.
Watson-Crick DNA Model
- DNA structure: Resembles a twisted ladder (double helix).
- Nitrogen bases pair through weak hydrogen bonds:
- Adenine (A) pairs with Thymine (T) through double hydrogen bonds.
- Cytosine (C) pairs with Guanine (G) through triple hydrogen bonds.
- The two DNA strands are complementary and anti-parallel.
DNA Replication
- Process of DNA duplication involves several enzymes:
- DNA Helicase: Unwinds DNA by breaking hydrogen bonds between strands.
- DNA Polymerase: Synthesizes new DNA strands by adding nucleotides in a 5' to 3' direction; also repairs DNA.
- DNA Ligase: Joins nucleotides together to form a continuous DNA strand.
Protein Synthesis
- Transcription: Process where DNA is transcribed into RNA.
- RNA polymerase binds to a promoter, assembling nucleotides to form mRNA.
- Codons: Three-nucleotide sequences in mRNA that code for specific amino acids; the start codon is AUG.
- Stop codons: UAA, UAG, UGA signal termination of protein synthesis.
- Splicing: Involves removing introns (non-coding regions) from pre-mRNA to produce mature mRNA.
Bacterial Transformation and Genetic Material
- Griffith (1927) identified bacterial transformation, where bacteria can change their genetic makeup by taking in foreign DNA from other bacteria.
- Avery's team provided experimental support that DNA is the genetic material.
DNA and Inheritance Studies
- Hershey and Chase (1952) demonstrated that DNA, not proteins, serves as the molecule of inheritance by tagging bacteriophages with radioactive isotopes 32P (DNA) and 35S (proteins).
- Rosalind Franklin utilized X-ray diffraction to show that DNA has a double helix structure.
- Meselson and Stahl (1953) confirmed that DNA replicates in a semiconservative manner, supporting Watson and Crick's model.
Types and Functions of RNA
- Messenger RNA (mRNA): synthesized from DNA during transcription, carries genetic information.
- Transfer RNA (tRNA): transports specific amino acids to the ribosome for polypeptide formation during translation.
- Ribosomal RNA (rRNA): structural component of ribosomes.
Chromosomes and Their Characteristics
- Chromosomes: Coiled DNA associated with histone proteins.
- Haploid (N): Contains one set of chromosomes found in sex cells (e.g., sperm and egg).
- Example: Sperm has 22 autosomes + X or Y chromosome; egg has 22 autosomes + X chromosome.
- Diploid (2N): Contains two sets of chromosomes in somatic (body) cells.
- Common examples: kidney, liver, brain, and skin cells.
- Humans have 46 chromosomes in somatic cells, arranged as follows:
- Females: 44 autosomes + XX sex chromosomes.
- Males: 44 autosomes + XY sex chromosomes.
- Karyotype: A visual representation of chromosomes arranged by size during metaphase.
Watson-Crick DNA Model
- DNA structure: Resembles a twisted ladder (double helix).
- Nitrogen bases pair through weak hydrogen bonds:
- Adenine (A) pairs with Thymine (T) through double hydrogen bonds.
- Cytosine (C) pairs with Guanine (G) through triple hydrogen bonds.
- The two DNA strands are complementary and anti-parallel.
DNA Replication
- Process of DNA duplication involves several enzymes:
- DNA Helicase: Unwinds DNA by breaking hydrogen bonds between strands.
- DNA Polymerase: Synthesizes new DNA strands by adding nucleotides in a 5' to 3' direction; also repairs DNA.
- DNA Ligase: Joins nucleotides together to form a continuous DNA strand.
Protein Synthesis
- Transcription: Process where DNA is transcribed into RNA.
- RNA polymerase binds to a promoter, assembling nucleotides to form mRNA.
- Codons: Three-nucleotide sequences in mRNA that code for specific amino acids; the start codon is AUG.
- Stop codons: UAA, UAG, UGA signal termination of protein synthesis.
- Splicing: Involves removing introns (non-coding regions) from pre-mRNA to produce mature mRNA.
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Description
Explore the pivotal discoveries in genetics from Griffith's bacterial transformation to Avery's evidence of DNA as the genetic material and Hershey and Chase's experiments determining DNA's role in inheritance. This quiz tests your knowledge of these foundational experiments in molecular biology.
