DNA as Genetic Material

Identifying DNA as the Genetic Material

• Smooth (S) strain bacteria are pathogenic, causing disease.
• Rough (R) strain bacteria are non-pathogenic.
• Transformation is the process where genetic material alters a cell's characteristics.
• Bacteriophages are viruses that infect bacteria.
• X-ray crystallography is a technique used to determine the structure of molecules.

Scientists and Their Experiments

• Griffith's experiment with mice demonstrated that genetic material from heat-killed S strain bacteria could transform R strain bacteria into a pathogenic form.
• Avery discovered that DNA stores and transmits genetic information.
• Hershey and Chase confirmed that DNA, not protein, is the genetic material using bacteriophages.
• Chargaff determined that the amount of adenine (A) is equal to thymine (T) and the amount of guanine (G) is equal to cytosine (C) in DNA.
• Franklin and Wilkins used X-ray crystallography to produce images of DNA, revealing its helical structure.
• Watson and Crick are credited with developing the accurate three-dimensional model of the DNA molecule as a double helix.

Structure of DNA

• Deoxyribonucleic acid (DNA) is the genetic material that contains the instructions for building and maintaining an organism
• It has a double helix shape
• A nucleotide is the monomer of DNA, consisting of a deoxyribose sugar, a phosphate group, and a nitrogenous base
• The nitrogenous bases of DNA are adenine (A), thymine (T), guanine (G), and cytosine (C)
• Adenine and guanine are purines; cytosine and thymine are pyrimidines
• Complementary base pairing dictates that adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C)
• The sugar-phosphate backbone forms the sides of the DNA ladder
• Hydrogen bonds hold the nitrogenous bases together
• In prokaryotic cells, DNA is located in the nucleoid region
• In eukaryotic cells, DNA is found in the nucleus.
• The functions of DNA include storing genetic information, replication, and passing on genetic information to daughter cells.
• The elements that make up DNA are carbon, hydrogen, oxygen, nitrogen, and phosphorus.
• Each deoxyribose sugar is attached to a phosphate group and a nitrogenous base
• Each phosphate group is attached to a deoxyribose sugar
• Each nitrogenous base is attached to a deoxyribose sugar

DNA Replication

• Replication is the process of copying DNA
• DNA replication occurs in the nucleus in eukaryotes
• DNA replication occurs in the S phase of cell division
• The goal of DNA replication is to produce two identical DNA molecules from one original DNA molecule
• DNA replication is semi-conservative because each new DNA molecule contains one original strand and one newly synthesized strand.
• The Meselson-Stahl experiment demonstrated that DNA replication is semi-conservative by using isotopes of nitrogen to track the original and new DNA strands.
• DNA helicase "unzips" the DNA molecule by breaking the hydrogen bonds between the nitrogenous bases, creating a replication fork.
• DNA polymerase adds complementary nucleotides to the template strand, synthesizing new DNA strands.
• DNA ligase joins the Okazaki fragments on the lagging strand, creating a continuous DNA strand.
• Primase synthesizes RNA primers, which provide a starting point for DNA polymerase to begin synthesis

Transcription & Translation

• Ribonucleic acid (RNA) is a nucleic acid that plays a role in protein synthesis
• Ribose sugar is the sugar found in RNA
• Uracil (U) is a nitrogenous base found in RNA, replacing thymine
• Messenger RNA (mRNA) carries genetic information from DNA to the ribosomes
• Transfer RNA (tRNA) brings amino acids to the ribosomes during translation
• Ribosomal RNA (rRNA) is a component of ribosomes
• A gene is a segment of DNA that encodes a protein or RNA molecule
• A protein is a complex molecule made of amino acids that performs various functions in the cell
• A trait is a characteristic or feature of an organism
• A ribosome is the site of protein synthesis
• The promoter region is a sequence of DNA where RNA polymerase binds to initiate transcription.
• RNA polymerase is an enzyme that synthesizes RNA from a DNA template
• Transcription is the process of synthesizing RNA from a DNA template
• Translation is the process of synthesizing a protein from an mRNA template
• A codon is a sequence of three nucleotides in mRNA that specifies an amino acid
• An anticodon is a sequence of three nucleotides in tRNA that is complementary to a codon in mRNA
• An amino acid is a monomer of a protein
• A peptide bond is a chemical bond that links amino acids together
• A polypeptide is a chain of amino acids linked by peptide bonds
• The start codon (AUG) signals the beginning of translation
• The stop codon (UAA, UAG, UGA) signals the end of translation
• The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA) is translated into proteins (amino acid sequences) by living cells.
• Transcription occurs in the nucleus, whereas translation occurs in the cytoplasm at the ribosomes.
• The central dogma of biology states that DNA is transcribed into RNA, which is then translated into protein

Mutations

• A point mutation is a change in a single nucleotide base
• A frameshift mutation is an insertion or deletion of nucleotides that alters the reading frame of the genetic code
• An insertion mutation is the addition of one or more nucleotide base pairs into a DNA sequence
• A deletion mutation is the removal of one or more nucleotide base pairs from a DNA sequence
• A substitution mutation is the replacement of one nucleotide base pair with another
• A nonsense mutation results in a premature stop codon, leading to a shortened and nonfunctional protein
• A missense mutation results in a different amino acid being incorporated into the protein
• A silent mutation does not change the amino acid sequence due to the redundancy of the genetic code
• A mutation can impact a protein's structure and function by altering the amino acid sequence, which affects the protein's folding and its ability to interact with other molecules.