DIMS Lectures Molecular Biology PDF
What is Molecular Biology?
Molecular biology is a branch of biology that deals with the molecular basis of biological activity. It involves the study of DNA, RNA, and protein synthesis, as well as the regulation of these processes. Understanding molecular biology is crucial for advancements in genetics, medicine, and biotechnology.
Key Concepts
1. Gene Structure: The Blueprint of Life
A gene is the smallest unit of heredity responsible for the formation of mRNA, which in turn codes for proteins. Genes are composed of 4,000 to 15,000 nucleotides and have specific regions that play crucial roles in gene expression.
Components of a Gene
Coding Strand (Sense Strand): The strand of DNA that contains the genetic code for protein synthesis.
Template Strand (Antisense Strand): The complementary strand used as a template for RNA synthesis.
Untranslated Regions (UTRs): Regions at the 5' and 3' ends of the mRNA that are not translated into proteins but play roles in regulating gene expression.
Promoter Region
The promoter region is a sequence of DNA that initiates transcription. It typically includes the TATA box at the -10 position and the TTGACA sequence at the -35 position.
The promoter region is where RNA polymerase binds to start transcription.
2. Transcription: From DNA to RNA
Transcription is the process by which RNA is synthesized from a DNA template. This process is carried out by the enzyme RNA polymerase, which reads the DNA template strand and synthesizes a complementary RNA strand.
Steps of Transcription
Initiation: RNA polymerase binds to the promoter region of the gene with the help of a sigma factor (in bacteria) or transcription factors (in humans).
Elongation: RNA polymerase moves along the DNA template strand, synthesizing RNA in the 5' to 3' direction.
Termination: Transcription ends when RNA polymerase reaches a termination signal. There are two types of termination:
Rho-dependent termination: Involves the Rho factor, which helps release RNA polymerase from the DNA.
Rho-independent termination: Involves the formation of a hairpin loop in the RNA, causing RNA polymerase to detach.
3. Post-Transcriptional Modifications: Preparing RNA for Translation
After transcription, the newly synthesized RNA undergoes several modifications before it can be translated into protein. These modifications ensure the stability and functionality of the RNA.
Key Modifications
5' Capping: A modified guanine nucleotide is added to the 5' end of the mRNA. This cap protects the RNA from degradation and is involved in the initiation of translation.
3' Polyadenylation: A poly-A tail (a sequence of adenine nucleotides) is added to the 3' end of the mRNA. This tail also protects the RNA and aids in its export from the nucleus.
Splicing: Introns (non-coding regions) are removed from the pre-mRNA, and exons (coding regions) are joined together. This process is carried out by the spliceosome.
4. Translation: From RNA to Protein
Translation is the process by which ribosomes synthesize proteins using the information encoded in mRNA. This process involves several key components:
mRNA: Carries the genetic code from DNA to the ribosome.
tRNA: Transfers amino acids to the ribosome based on the codons on the mRNA.
Ribosomes: The cellular machinery that synthesizes proteins.
Polyribosomes (Polysomes)
Multiple ribosomes can attach to a single mRNA molecule, forming a polysome. This allows for the simultaneous synthesis of multiple copies of a protein, increasing the efficiency of translation.
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