DNA Structure and Replication Quiz

DNA Structure Discovery

• Nucleotides are the building blocks of DNA, each consisting of a phosphate group, deoxyribose sugar, and one of four nitrogenous bases (adenine, cytosine, guanine, thymine).
• Chargaff's rule states that adenine pairs with thymine, and guanine pairs with cytosine, in equal amounts.
• Rosalind Franklin used X-ray diffraction to produce the first images of DNA, revealing its helical structure.
• James Watson and Francis Crick used existing data to construct the first model of DNA (1953), demonstrating that adenine pairs with thymine and guanine pairs with cytosine, forming hydrogen bonds across the helix center.

DNA Replication

• DNA replication is a semiconservative process.
• Helicase unwinds the DNA double helix, separating the strands, exposing the bases.
• DNA polymerase pairs free nucleotides with the exposed bases, creating new complementary strands.
• DNA ligase joins the fragments in the lagging strand, completing DNA replication.

RNA

• RNA differs from DNA in having a single strand, uracil instead of thymine, and ribose sugar instead of deoxyribose.
• Three main types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
  • mRNA carries the genetic code from DNA to ribosomes.
  • rRNA is a component of ribosomes, the protein synthesis machinery.
  • tRNA brings amino acids to ribosomes to synthesize proteins.

Protein Synthesis

• Transcription involves rewriting the DNA code onto mRNA.
  • Non-coding portions (introns) are removed, leaving coding portions (exons) that are joined to create a finished mRNA product.
• Translation converts the mRNA code into a chain of amino acids, forming proteins.
  • Codons (three-base sequences) on mRNA specify particular amino acids.
• Protein assembly requires tRNA to deliver amino acids to the ribosome, where they are linked together according to the mRNA sequence.

Mutations

• Mutations are changes in DNA sequences, such as a base substitution or a frameshift mutation.
• Mutations can alter the shape and/or structure of a protein and affect protein function or cause other undesired effects.

Recombinant DNA Technology

• Recombinant DNA technology involves combining DNA fragments from different sources. This creates genetically modified organisms (GMOs).
• Restriction enzymes cut DNA at specific sequences to isolate target fragments.
• DNA ligases join the fragments, creating a new DNA sequence.
• Techniques like gel electrophoresis, PCR, and nuclear transfer can be used to analyze and manipulate DNA.

Genetically Modified Organisms (GMOs)

• Genetically modified organisms (GMOs) are created by introducing foreign genes to create desirable traits.
• GMOs can be plants, animals or other organisms
• Modification methods are often focused on agricultural application (e.g., pest and drought resistance) but also include modifying for food production.

CRISPR Gene Editing

• CRISPR is a gene-editing technique enabling the deletion, insertion or substitution of specific target genes.
• CRISPR can modify genomes at the cellular level, even after developmental changes.

Stem Cells and Cloning

• Stem cells are cells with the potential to differentiate into various cell types.
• Embryonic stem cells are pluripotent, capable of differentiating into all cell types in the body.
• Cloning involves creating a genetically identical copy of an organism. One approach involves nuclear transfer.