DNA Structure and Genetic Material

• Viruses played a key role in discovering that DNA contains genetic material, as shown in the Hershey-Chase experiment.
• Griffith's experiments demonstrated that DNA is transferred between bacteria, allowing them to take on new traits.

DNA Structure

• DNA's monomer is a nucleotide.
• A DNA nucleotide comprises a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).
• Nitrogenous base pairs (A-T, C-G) form the rungs of DNA, connected by hydrogen bonds.
• Covalent bonds between a nucleotide's sugar and the next nucleotide's phosphate group form the sugar-phosphate backbone.
• DNA strands run antiparallel (5' to 3' and 3' to 5').
• DNA strands are complementary because base pairing rules dictate their sequence.
• DNA contains deoxyribose, the bases adenine, guanine, cytosine, and thymine, and exists as a double helix.
• RNA contains ribose, the bases adenine, guanine, cytosine, and uracil, and exists as a single strand.
• DNA is primarily in the nucleus, while RNA is in the nucleus, cytoplasm, and ribosome.

DNA Replication

• DNA synthesis begins at the replication origin.
• DNA Helicase unwinds the DNA, forming a replication fork.
• RNA Primase creates RNA primers, which are short starter sequences.
• DNA Polymerase adds nucleotides to the growing DNA strand, using the original strand as a template.
• DNA Polymerase adds nucleotides only in the 5' to 3' direction.
• Ligase connects Okazaki fragments on the lagging strand during termination.
• The leading strand is synthesized continuously in the 5' to 3' direction, moving towards the replication fork.
• The lagging strand is synthesized discontinuously in fragments (Okazaki fragments) away from the replication fork, requiring multiple primers.
• Both DNA and RNA are built in the 5' to 3' direction.
• Replication bubbles allow simultaneous DNA replication at multiple points, accelerating the process.

Transcription

• Transcription occurs inside the nucleus.
• RNA polymerase binds to the promoter region (containing a TATA box) on the DNA during initiation.
• Transcription factors facilitate RNA polymerase binding to the promoter to initiate transcription.
• RNA polymerase synthesizes a complementary mRNA molecule in the 5' to 3' direction, moving along the DNA template strand during elongation.
• RNA polymerase detaches from the DNA at a termination sequence, and the mRNA molecule is released.
• The promoter site is a specific DNA sequence, including the TATA box, where RNA polymerase binds to start transcription.
• Transcription factors are proteins that bind to the promoter region, regulating RNA polymerase binding.
• RNA Polymerase synthesizes mRNA from a DNA template.
• Transcription begins at a start site of the gene on the DNA.
• RNA polymerase moves along the DNA template in the 3' to 5' direction, synthesizing mRNA in the 5' to 3' direction.
• Introns (non-coding regions) are removed from the pre-mRNA, and exons (coding regions) are joined to form mature mRNA during RNA splicing.
• The end goal of transcription is a mature mRNA molecule for translation into a protein.

Translation

• Translation occurs in the cytoplasm on ribosomes.
• During initiation, the small ribosomal subunit binds to the mRNA.
• The initiator tRNA (carrying methionine) binds to the start codon (AUG) on the mRNA
• The large ribosomal subunit joins the complex.
• tRNAs bring amino acids to the ribosome, matching their anticodons to mRNA codons, during elongation.
• Peptide bonds form between the amino acids, creating a polypeptide chain, and the ribosome moves along the mRNA codon by codon.
• The ribosome reaches a stop codon (UAA, UAG, or UGA) on the mRNA during termination.
• A release factor binds to the stop codon, causing the polypeptide chain to be released, and the ribosome disassembles.
• Ribosomes consist of small and large subunits that combine during translation.
• mRNA carries the genetic code from DNA to the ribosome.
• The A and P sites are where tRNAs bind on the ribosome during translation.
• The A site is for incoming tRNA, and the P site holds the tRNA with the growing polypeptide chain.
• AUG is the start codon that signals the beginning of translation and codes for methionine.
• The catalytic site is the part of the ribosome where peptide bonds form.
• UAA, UAG, and UGA are stop codons that signal the end of translation.

Gene Expression

• The lac operon regulates genes for lactose metabolism in bacteria.
• A repressor protein binds to the operator region in the absence of lactose, preventing RNA polymerase from transcribing lac operon genes.
• Lactose binds to the repressor protein in the presence of lactose, detaching it from the operator, allowing RNA polymerase to transcribe lac operon genes, enabling lactose utilization.
• Promoters are DNA sequences where RNA polymerase binds to start transcription.
• Operators are DNA sequences where repressor proteins bind to regulate transcription.
• RNA transcription is the process of synthesizing RNA from a DNA template, regulated by promoters, operators, and transcription factors.
• Transcription factors are proteins that bind to promoters and other regulatory sequences to control gene expression.
• Hox genes control the body plan of an embryo along the head-tail axis, determining body segment identity during development.
• Mutations in Hox genes can cause dramatic changes in body structure.
• Epigenetics involves changes in gene expression not caused by changes to the DNA sequence.
• Epigenetic mechanisms include DNA methylation and histone modification.
• Epigenetic modifications affect the accessibility of DNA to transcription factors and RNA polymerase, influencing gene expression.
• Environmental factors can influence epigenetic changes, which can be passed down to future generations.

Mutations

• Point mutations involve changes in a single nucleotide base.
• Missense mutations cause a base substitution that results in a different amino acid.
• A nonsense mutation occurs when a base substitution results in a premature stop codon.
• Silent mutations are base substitutions that do not change the amino acid sequence due to genetic code redundancy.
• Frameshift mutations are insertions or deletions of nucleotides that alter the reading frame.
• Insertion adds one or more nucleotide bases.
• Deletion removes one or more nucleotide bases.
• Chromosomal mutations are large-scale changes in chromosome structure.
• Inversion reverses a segment of a chromosome end-to-end.
• Translocation occurs when a segment of a chromosome breaks off and attaches to another chromosome.
• Mutations range from no noticeable change to significant alterations in phenotype.
• Harmful mutations can disrupt protein function and cause disease.
• Beneficial mutations can provide a selective advantage and drive evolution.
• Neutral mutations have no significant effect on the organism.

Explore DNA structure, including nucleotides, base pairing, and the sugar-phosphate backbone. Learn about the roles of viruses and bacteria in discovering DNA's genetic function. Understand the differences between DNA and RNA.