Molecular Biology vs. Genetics

Chapter 1 History

• Molecular Biology is the study of gene structure and function at the molecular level
• It encompasses genetics and biochemistry disciplines
• Early knowledge on the molecular nature of genes was absent so it was known as transmission genetics
• Gregor Johann Mendel studied transmission genetics using pea plants
• Chromosomes were recognized as units carrying genes within the nucleus
• In 1910, Thomas Hunt Morgan studied Drosophila melanogaster to provide evidence for the chromosome theory of inheritance. This was simpler than working with plants
• Barbara McClintock and Harriet Creighton (1931) demonstrated recombination between easily identifiable features, establishing a chromosome-gene relationship

Early Foundations

• Friedrich Miescher (1869) discovered nuclein (DNA) in white blood cells, noting its phosphorus content
• Phoebus Levene (1909–1929) identified the DNA components: sugar (deoxyribose), phosphate group, and four nitrogenous bases (adenine, thymine, cytosine, guanine). He incorrectly proposed a simple tetranucleotide structure.
• Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944) showed that DNA, not protein, carries genetic information through transformation experiments.

Structural Studies of DNA

• Erwin Chargaff (1950) established the crucial rule that the amount of adenine equals thymine, and cytosine equals guanine in DNA. This aided a better understanding of DNA.
• Maurice Wilkins and Rosalind Franklin (1951-1953) used X-ray diffraction techniques to study the structure of DNA. Franklin's work, especially Photo 51, provided key data on DNA's helical structure and dimensions

Watson & Crick

• Chargaff's rules and Franklin's X-ray diffraction data guided Watson and Crick (1953) to propose the double-helical model for DNA structure.
• Their model showed two strands running in opposite directions, held together by A-T and C-G base pairs.

Chapter 2 DNA Nucleosome

• DNA is organized into giant molecules called chromosomes
• Each chromosome contains a single DNA molecule, housing multiple genes
• Each gene specifies the instructions to make a single protein. In humans each chromosome contains approximately 2000 genes and 46,000 genes.
• Chromatin fibers & chromosomes are two types of DNA that differ in condensation levels at different stages. Chromosomes are the tightly condensed form of DNA within the cell's nucleus.

Chromosomes and Chromatin: Higher Levels of Chromatin Structure

• The lowest level is the 10 nm nucleosome core (DNA wrapped around histone proteins).
• The next level is the 30-nm fiber (compacted nucleosomes).
• The next level is the 300-nm fiber, and finally chromosome structures (700-1400nm).
• Different levels of compaction allow chromosomes to fit within the cell's nucleus.
• Structural proteins and DNA-packing regulate gene expressing.

Chromatin

• Euchromatin is less condensed, actively expressed regions (lighter stained) - ~92% of DNA
• Heterochromatin is more condensed, less active regions (darker stained), contains fewer genes

Mosaisim

• Adult females are genetic mosaics because different cells will have inactivated X-chromosomes (Barr bodies) based on their parental origin. The calico-cat's fur colour is a good example.
• X-inactivation is important for preventing the excessive expression of gene transcripts (more commonly occurring in females).

Chapter 3 Vectors and oligonucleotides

• Restriction enzymes are endonucleases cutting DNA within specific sequences.
• Restriction enzymes are used to cut DNA at specific locations.
• Experiment Using Restriction Endonuclease: Restriction enzymes are used by Boyer and Cohen to create recombinant DNA vectors by ligating 2 separate DNA pieces together
• Restriction modification system • A group of enzymes prevent the host cells from being destroyed by their own restriction enzymes.
• DNA mapping is a practice used by scientists to locate genes in DNA
• Plasmid vectors –pBR 322 and pUC vectors • pBR 322 is a widely used E. coli cloning vector. • pUC is a more widely used plasmid vector.

Plasmids, Cosmids, M13 Phage vectors

• Plasmids are small, circular DNA molecules that replicate separately from the chromosome.
• Cosmids are hybrid plasmids, that contain cos sequences of bacteriophage lambda
• M13 Phage and its vectors are DNA from bacteriophage M13. These sequences are useful for site-directed mutagenesis studies and for sequencing processes

Chapter 4 Techniques in Molecular Biology

• Polymerase Chain Reaction (PCR) is a technique for creating multiple copies of a DNA fragment.
• RT-PCR (reverse transcriptase PCR) is a variation of PCR used to amplify only certain areas of DNA or RNA
• Real-Time PCR (quantitative PCR) is a technique for determining the amount of DNA or RNA, which is monitored in real time as it is being measured.
• Gel Electrophoresis is used to separate DNA or RNA fragments based on their size and charge.
• Other techniques like Southern Blotting, Northern blotting and Western blotting are used in identifying specific DNA or RNA sequences using tagged probes or antibodies.

Chapter 5 Transgenesis

• Transgenesis is the technique of introducing foreign genetic material into an organism allowing the organism to express new genetic traits.
• There are different methods of introducing new DNA into cells (physical & chemical).
• Physical methods include microinjection, biolistic, electroporation.
• Chemical methods include lipids, liposomes mediated, non-liposomal.
• Biological methods include conjugation, transformation, transduction, Agrobacterium mediated transfer.

Chapter 6 Recombinational Repair

• Homologous recombination occurs during meiosis.
• The process of homologous recombination allows for shuffling of genes among maternal and paternal chromosomes, generating diverse genetic combinations in offspring.
• Holliday model describes how homologous recombination occurs as a way of repairing DNA.

Chapter 7 Mobile Genetic Elements

• Transposable Elements (TEs) are DNA segments capable of moving from one genomic position to another
• TE's are significant features in diverse evolutionary processes and shaping the genome
• McClintock discovered elements Ac and Ds and described transposable elements
• Mechanisms of transposition include cut and paste & replicative transposition
• Transposable elements are involved in various cellular processes

Chapter 8 Regulation of Gene Activity

• Prokaryotes have operons, groups of genes transcribed together.
• The lac operon regulates lactose metabolism.
• Negative control: repressor proteins prevent transcription when a substrate is absent.
• Positive control: activator proteins enhance transcription when a substrate is present (example, cAMP and CAP controlling transcription).
• The trp operon regulates tryptophan production. It uses attenuation to regulate transcription, depending on substrate tryptophan, to ensure correct regulation.
• The ara operon is regulated by the presence of arabinose in the cell. The protein AraC controls this operon.

Chapter 9

• (No content provided in the OCR)

Chapter 10

• (No content provided in the OCR)