DNA Structure, Replication, and Scientist Contributions

DNA Structure

• Nucleotide: Composed of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (A, T, C, G)
• Chargaff's Rule: A = T and C = G, signifying complementary base pairing
• Antiparallel: The two strands of DNA run in opposite directions (5' to 3' vs 3' to 5')

Scientist Contributions

• Watson and Crick discovered the double-helix structure
• Rosalind Franklin contributed X-ray diffraction images to determine the structure
• Erwin Chargaff defined the base pairing rules (A = T, C = G)

DNA Replication

• Helicase unwinds the DNA helix
• DNA Polymerase adds complementary nucleotides to the growing strand
• Ligase seals the gaps between the Okazaki fragments
• Primase creates RNA primers to start replication
• Leading Strand is continuously synthesized in the 5' to 3' direction
• Lagging Strand is discontinuously synthesized in fragments (Okazaki fragments)
• Okazaki Fragments are short segments of DNA synthesized on the lagging strand

Transcription

• Occurs in the nucleus of eukaryotes
• RNA Polymerase binds to DNA at the promoter region
• RNA polymerase creates an mRNA strand using the DNA template
• mRNA is synthesized from 5' to 3'
• RNA Processing involves splicing the mRNA, and adding a cap and tail in eukaryotes

Translation

• Occurs in the ribosome (in the cytoplasm)
• mRNA is read in sets of three bases (codons)
• tRNA brings the corresponding amino acids to the ribosome
• The ribosome forms peptide bonds between amino acids to form a polypeptide chain
• Codon Chart/Wheel is used to match mRNA codons to amino acids
• START Codon: AUG, signals the beginning of translation
• STOP Codons: UAA, UAG, and UGA signal the end of translation

Gene Expression

• Gene expression regulation is vital for controlling which proteins are made, when, and in what amounts

Transcription Factors

• Positive Transcription Factors activate or enhance gene expression
• Negative Transcription Factors repress gene expression
• Binding Sites: Transcription factors bind to specific regions on the promoter of a gene to regulate its transcription

Interfering RNA

• Types: miRNA (microRNA) and siRNA (small interfering RNA)
• Function: Regulates gene expression by binding to mRNA and preventing translation or promoting mRNA degradation

Operons

• Definition: a group of genes regulated together under a single promoter
• Lac Operon is an operon in bacteria, regulated by the presence or absence of lactose

Epigenetics

• Definition: the study of changes in gene expression not caused by changes in DNA sequence

Examples of Epigenetic Markers

• DNA Methylation: The addition of methyl groups to DNA, typically represses gene expression
• Histone Modification: Histone proteins can be modified to either condense or relax chromatin, affecting gene accessibility

Mutations

• Frameshift Mutations are caused by insertions or deletions, which shift the reading frame of the codons and lead to a completely different protein

Point Mutations

• It is a change in a single nucleotide base
• Substitution occurs when one base is replaced by another (may or may not change the protein)
• Silent Mutation results in no change in the protein sequence
• Missense Mutation changes one amino acid in the protein sequence
• Nonsense Mutation changes a codon to a stop codon, leading to a truncated protein
• Mutations cause variations that are either beneficial, harmful, or neutral for an individual's survival and reproduction

Chromosomal Mutations

• Deletions: part of a chromosome is lost
• Duplications: part of a chromosome is repeated
• Inversions: part of a chromosome is reversed
• Translocations: parts of chromosomes are swapped
• Mutations contribute to genetic diversity within a population, which can lead to natural selection (positive, negative, or neutral effects)

Root Words

• Pro-: Before, in front of
• Poly-: Many, multiple
• Hist-: Tissue
• Anti-: Against
• Mut-: Change, alter
• Non-: Not
• Mis-: Wrong, incorrect
• Sub-: Under, below
• Trans-: Across, beyond
• -scribe, -script: Write, record
• Ex-: Out, away from
• -gen, -gene: Produce, create, origin

Explore DNA structure, including nucleotides, Chargaff's rule, and the antiparallel nature of strands. Learn about the key scientists Watson, Crick, Franklin, and Chargaff, and their contributions. Understand DNA replication: helicase, DNA polymerase, ligase, primase, leading/lagging strands, and Okazaki fragments.