Biology 2

• The central dogma is the flow of genetic information from DNA to RNA to protein.
• Components of Central Dogma of Molecular Biology:

  • DNA codes for RNA, and RNA codes for proteins
  • DNA is genetic material passed on from parents to offspring
  • DNA contains instructions necessary for the survival of every organism
• DNA Model:

  • Proposed by Biologists Francis Crick and James Watson in 1953
  • Double helix structure that twists spirally, similar to a twisted ladder or spiral staircase
  • Nucleotides are the building blocks of DNA
• Phosphate Group:

  • Composed of a phosphorus atom surrounded by oxygen atoms
  • When joining to a growing strand of DNA, two phosphates are lost
• Sugar:

  • For DNA, the sugar group is called deoxyribose
  • DNA has an absence of an oxygen atom in the second carbon, making it a stable molecule
• Nitrogenous Bases:

  • Classified into purines (Adenine and Guanine) and pyrimidines (Thymine, Cytosine, Uracil)
  • Adenine pairs with Thymine in DNA and with Uracil in RNA
• Ribonucleic Acid (RNA):

  • Single-stranded molecule composed of nucleotides
  • Copies information stored in DNA and can act as enzymes
• Proteins:

  • Final product in the central dogma of molecular biology
  • Serve as structural support and aid in transporting molecules
• DNA Replication:

  • Important for cell division and proper formation of gametes
  • Errors can lead to diseases, including cancer
  • Process by which DNA makes a copy of itself during cell division
• Initiation of DNA Replication:

  • DNA helicase unwinds and separates the DNA helix
  • Primase binds RNA nucleotide to the initiation point of the DNA strand
• Elongation of DNA Replication:

  • Leading Strand Elongation occurs in the same direction as the replication fork movement
  • Lagging Strand Elongation is synthesized in the opposite direction
• Termination of DNA Replication:

  • DNA polymerase III stops when it reaches a section of the DNA template that has already been replicated
  • DNA Ligase seals the gaps between Okazaki fragments
• DNA Transcription:

  • RNA is synthesized from DNA in the first stage of the central dogma of molecular biology
  • Happens when DNA is copied to form complementary mRNA sequence
• Initiation of DNA Transcription:

  • RNA polymerase binds to DNA and separates DNA strands
  • RNA polymerase binds at promoters, serving as initiation sites
• Elongation of DNA Transcription:

  • Nucleotides from the cytoplasm are added to the growing RNA chain
  • RNA is synthesized in the 5’-3’ direction
• Termination of DNA Transcription:

  • RNA polymerase reaches the terminator site, signaling the end of transcription
  • DNA double helix reforms
• mRNA Modification:

  • RNA Splicing cuts introns and splices exons back together
  • 5’ End Capping protects mRNA from degradation and regulates nuclear transport
• Poly-A Tail:

  • Allows addition of multiple adenosine monophosphates at the end of the mRNA molecule
  • Protects mRNA from degradation and aids in termination process
• Translation:

  • Decodes the message carried by mRNA
• Translation happens when the message carried by the mRNA is decoded into a protein subunit
• Initiation:

  • mRNA transcribed inside the nucleus is released into the cytoplasm
  • Ribosomal subunits bind to the mRNA strand until they encounter the start codon (AUG)
  • Each tRNA molecule in the cytoplasm has an anticodon
  • Anticodon is composed of a set of three nitrogenous bases in the tRNA molecule that is complementary to one of the mRNA codons
• Elongation:

  • Formation of the growing polypeptide chain by bringing in the proper tRNA to translate the mRNA into a protein
• Termination:

  • Continuous attachment of tRNA to the mRNA allows the polypeptide chain to elongate until it encounters a stop codon (UAA, UAG, or UGA)
  • Stop codon terminates and completes the process of translation
• Mutation is defined as any change in an organism's genome
• Mutations may result from:

  • Insertion or deletion of DNA sequences
  • Changes in chromosome number or content due to errors in meiosis and chromosome breaks leading to chromosome inversion
  • Several types of mutations occur independently during DNA replication
  • Mutations attracting the genes are responsible for repairing damaged DNA
  • Incorrect nucleotides might be inserted in one in every thousand bases
• Mendelian Concept of Hereditary:

  • Genetics is the study of the laws and processes of biological inheritance, concerned with the transfer of traits
  • Gregor Mendel derived the laws of inheritance stating that traits are inherited through units called genes
  • Genes are specific segments of DNA found in pairs at particular loci on chromosomes, responsible for the inheritance of traits (e.g., eye color, hair color, blood type)
  • Genes can exist in different variants known as alleles, responsible for genetic diversity and variations within a population
• • Heredity is the passing of traits from parents to offspring
• Mendel's Law of Heredity:

  • Law of Dominance and Recessive states that some alleles are dominant, while others are recessive
  • Law of Segregation states that copies of a gene separate when producing gametes
  • Law of Independent Assortment states that alleles segregate independently during the formation of gametes
• Monohybrid Cross:

  • Mendel's experiments in garden peas were monohybrid crosses
  • Punnett square is a technique for predicting genotype by considering dominant and recessive genes of male and female parents for one trait
• Mendel's Phenotypic and Genotypic Ratios:

  • Genotype and phenotype differentiate between the genetic makeup and the expression of genes
  • Genotype refers to the alleles carried in an organism's DNA, inherited from parents
  • Phenotype refers to the visible or observable expression of genes, usually showing the phenotype of the dominant allele
• Dihybrid Cross:

  • Mendel used dihybrid crosses to study the inheritance of two pairs of alleles through a number of generations
• Non-Mendelian Patterns of Inheritance:

  • Patterns of inheritance that do not follow Mendel's laws
• Incomplete Dominance:

  • Two alleles for a gene, but neither is dominant or recessive
  • Phenotype in the heterozygous condition is a blend of the two alleles
• Codominance:

  • Both alleles contribute to the phenotype of an organism
• Multiple Alleles:

  • Arise through mutation, and the same gene in different individuals may have different mutations, each producing new alleles
  • An individual can have at most two different alleles, while a species may have multiple alleles of many of its genes
  • Examples include eye color, hair color, and blood type
• Sex-Linked Traits:

  • The 23rd pair of chromosomes in humans determines the sex of the individual
  • X chromosome is larger and carries more genes than the Y chromosome
  • If a gene is found only on the X chromosome and not on the Y chromosome, it is a sex-linked trait
  • Males exhibit some traits more frequently than females
• Red-green colorblindness (X-linked Recessive)

  • Inability to differentiate between red and green
• Male Pattern Baldness (Autosomal Dominant)

  • Develops after being present in one chromosome, often in men
• Hemophilia (X-linked Recessive)

  • Causes the blood not to clot, leading to prolonged clotting time or internal bleeding
• Duchenne Muscular Dystrophy (X-linked Recessive)

  • Muscular weakness, progressive deterioration of muscle tissue, and loss of coordination