Slide 1: Genetics and Evolution - Molecular Basis of Inheritance

• Inheritance refers to the transfer of genetic information from parent to offspring
• Molecular basis of inheritance involves the study of DNA, RNA, and protein synthesis
• Transcription is the process of synthesizing RNA from a DNA template
• The substrates for transcription are:
  • DNA template strand
  • RNA nucleotides
  • Enzymes like RNA polymerase ++++

Slide 2: Substrates for Transcription - DNA Template Strand

• During transcription, one of the DNA strands acts as a template for RNA synthesis
• This template strand is usually the antisense or non-coding strand
• It provides the genetic information necessary for RNA synthesis
• The DNA template strand has complementary base pairs to the RNA strand being synthesized
• Example: If the DNA template strand is 5’-ATTGCCTA-3’, the RNA strand synthesized would be 3’-UAACGGAU-5' ++++

Slide 3: Substrates for Transcription - RNA Nucleotides

• RNA nucleotides are the building blocks of RNA molecules
• They consist of three components:
  • A nitrogenous base (adenine, guanine, cytosine, or uracil)
  • A ribose sugar
  • A phosphate group
• RNA nucleotides are added sequentially to the growing RNA chain during transcription
• Example: RNA nucleotide with adenine as the base: A-C-G-U | Ribose sugar - phosphate group ++++

Slide 4: Substrates for Transcription - RNA Polymerase

• RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template
• It catalyzes the formation of phosphodiester bonds between RNA nucleotides
• RNA polymerase recognizes specific DNA sequences called promoters to initiate transcription
• It unwinds the DNA double helix to expose the template strand
• Example: RNA polymerase in E. coli is a multi-subunit enzyme called RNA polymerase holoenzyme ++++

Slide 5: The Process of Transcription

• Transcription occurs in three stages: initiation, elongation, and termination
• Initiation:
  • RNA polymerase binds to the promoter sequence on DNA
  • It separates the DNA strands to form a transcription bubble
  • The template strand is exposed for RNA synthesis
• Elongation:
  • RNA polymerase adds complementary RNA nucleotides to the growing RNA chain
  • It uses the DNA template strand as a guide for base pairing
• Termination:
  • RNA polymerase reaches a termination sequence on DNA
  • It releases the RNA transcript and detaches from the DNA ++++

Slide 6: Transcription Example - mRNA Synthesis

• Let’s consider an example of mRNA synthesis from a DNA template:
• DNA template strand: 5’-ATGCGACTTCCA-3'
• RNA nucleotides added sequentially: UACGCUGAAGGU
• The resulting mRNA strand: 5’-UACGCUGAAGGU-3'
• This mRNA molecule can be translated into a protein during protein synthesis ++++

Slide 7: Transcription Example - tRNA Synthesis

• Another type of RNA synthesized during transcription is transfer RNA (tRNA)
• tRNA carries amino acids to the ribosome during protein synthesis
• Example tRNA gene sequence: DNA template strand: 5’-GCTGTAACGG-3'
• RNA nucleotides added sequentially: CGACAUUGCC
• The resulting tRNA molecule: 5’-CGACAUUGCC-3'
• The anticodon region of tRNA base-pairs with codons on mRNA ++++

Slide 8: Transcription Example - rRNA Synthesis

• Ribosomal RNA (rRNA) is another type of RNA synthesized during transcription
• rRNA forms the structural and catalytic components of the ribosome
• Example rRNA gene sequence: DNA template strand: 5’-ATCGTAACTAGG-3'
• RNA nucleotides added sequentially: UAGCAAUUGACC
• The resulting rRNA molecule: 5’-UAGCAAUUGACC-3'
• rRNA combines with proteins to form ribosomes for protein synthesis ++++

Slide 9: Regulation of Transcription

• Transcription is regulated in cells to control gene expression
• Regulatory proteins bind to DNA and either enhance or inhibit transcription
• Transcription factors are proteins that control the initiation of transcription
• Gene expression can be affected by various factors like hormones, signaling molecules, and environmental conditions ++++

Slide 10: Importance of Transcription

• Transcription is a crucial step in gene expression
• It is responsible for the synthesis of different types of RNA molecules
• mRNA carries genetic information for protein synthesis
• tRNA transports amino acids to the ribosome
• rRNA forms the structural components of the ribosome
• Understanding transcription is essential to unravel the molecular basis of inheritance

11. Substrates for Transcription:

• DNA template strand
  • Provides the genetic information for RNA synthesis
  • Usually the antisense or non-coding strand
• RNA nucleotides
  • Composed of a nitrogenous base, ribose sugar, and phosphate group
  • Added sequentially to the growing RNA chain
• RNA polymerase
  • Enzyme responsible for synthesizing RNA from DNA template
  • Binds to promoter sequence and separates DNA strands
  • Catalyzes the formation of phosphodiester bonds between RNA nucleotides
• Promoter sequence
  • DNA sequence where RNA polymerase binds to initiate transcription
  • Recognized by specific transcription factors

12. The Process of Transcription:

• Initiation
  • RNA polymerase binds to the promoter sequence on DNA
  • DNA strands separate to form a transcription bubble
  • Template strand is exposed for RNA synthesis
• Elongation
  • RNA polymerase adds complementary RNA nucleotides to the growing RNA chain
  • Utilizes the DNA template strand as a guide for base pairing
• Termination
  • RNA polymerase reaches a termination sequence on DNA
  • Released RNA transcript and detachment of RNA polymerase
  • Completion of transcription

13. Transcription Example - mRNA Synthesis:

• DNA template strand: 5’-ATGCGACTTCCA-3'
• RNA nucleotides added sequentially: UACGCUGAAGGU
• Resulting mRNA strand: 5’-UACGCUGAAGGU-3'
• This mRNA molecule can be translated into a protein during protein synthesis

14. Transcription Example - tRNA Synthesis:

• Transfer RNA (tRNA)
• Carries amino acids to the ribosome during protein synthesis
• Example tRNA gene sequence:
  • DNA template strand: 5’-GCTGTAACGG-3'
  • RNA nucleotides added sequentially: CGACAUUGCC
  • Resulting tRNA molecule: 5’-CGACAUUGCC-3'
• Anticodon region of tRNA base-pairs with codons on mRNA

15. Transcription Example - rRNA Synthesis:

• Ribosomal RNA (rRNA)
• Forms the structural and catalytic components of the ribosome
• Example rRNA gene sequence:
  • DNA template strand: 5’-ATCGTAACTAGG-3'
  • RNA nucleotides added sequentially: UAGCAAUUGACC
  • Resulting rRNA molecule: 5’-UAGCAAUUGACC-3'
• rRNA combines with proteins to form ribosomes for protein synthesis

16. Regulation of Transcription:

• Transcription is regulated to control gene expression
• Regulatory proteins bind to DNA and enhance or inhibit transcription
• Transcription factors control the initiation of transcription
• Gene expression is influenced by hormones, signaling molecules, and environmental conditions
• Regulation allows cells to respond to varying internal and external stimuli

17. Importance of Transcription:

• Transcription is a crucial step in gene expression
• It is responsible for the synthesis of different types of RNA molecules
• mRNA carries genetic information for protein synthesis
• tRNA transports amino acids to the ribosome
• rRNA forms the structural components of the ribosome
• Understanding transcription is essential to unravel the molecular basis of inheritance

18. Protein Synthesis:

• Protein synthesis involves two main steps: transcription and translation
• In transcription, DNA is transcribed into mRNA
• In translation, mRNA is decoded by ribosomes to synthesize proteins
• Transcription occurs in the nucleus, while translation occurs in the cytoplasm
• The central dogma of molecular biology describes the flow of genetic information from DNA to RNA to protein

19. Genetic Code:

• The genetic code is a set of rules that determine how nucleotide sequences in mRNA are translated into amino acid sequences in proteins
• It is read in codons, which are groups of three nucleotides
• There are 64 possible codons, representing different amino acids and stop signals
• Multiple codons can code for the same amino acid, except for methionine and tryptophan which have unique start codons
• The genetic code is universal, meaning that it is shared by all organisms

20. Transcription vs. Replication:

• Transcription and replication are two processes involving DNA
• Transcription produces RNA from a DNA template, while replication produces an identical copy of the DNA molecule
• In transcription, only a specific region of DNA is transcribed, whereas in replication, the entire DNA molecule is copied
• Transcription uses RNA polymerase, while replication uses DNA polymerase
• Transcription results in a single-stranded RNA molecule, while replication yields a double-stranded DNA molecule

21. Genetic Mutations:

• Genetic mutations are changes in the DNA sequence
• Point mutations involve the substitution, insertion, or deletion of a single nucleotide
• Frameshift mutations occur when the reading frame of the gene is altered by insertions or deletions
• Mutations can have different effects, ranging from no effect to causing genetic disorders
• Examples of genetic disorders caused by mutations: cystic fibrosis, sickle cell anemia

22. Regulation of Transcription:

• Transcription is tightly regulated to control gene expression
• Transcription factors bind to specific DNA sequences to either enhance or inhibit transcription
• Enhancers are DNA sequences that enhance transcription when bound by activator proteins
• Silencers are DNA sequences that inhibit transcription when bound by repressor proteins
• Epigenetic modifications can also regulate transcription by altering the accessibility of DNA to transcription machinery

23. Transcriptional Regulation in Prokaryotes:

• In prokaryotes, gene expression is primarily regulated at the level of transcription
• The lac operon is a classic example of transcriptional regulation in prokaryotes
• It consists of three genes involved in lactose metabolism: lacZ, lacY, and lacA
• Gene expression is controlled by the lac repressor protein and the presence of lactose as an inducer
• When lactose is present, it binds to the lac repressor, causing it to detach from the operator region and allowing transcription to occur

24. Transcriptional Regulation in Eukaryotes:

• In eukaryotes, transcriptional regulation is complex and involves multiple levels of control
• Transcription factors play a key role in regulating gene expression
• Enhancers and silencers can be located far away from the gene they regulate and interact with the promoter through DNA looping
• Chromatin remodeling and histone modifications also regulate gene expression by altering the accessibility of DNA to transcription machinery
• Transcriptional regulation in eukaryotes allows for cell-specific gene expression and developmental processes

25. RNA Processing:

• After transcription, RNA undergoes processing before it can be translated into a protein
• In eukaryotes, RNA processing includes capping, splicing, and polyadenylation
• Capping involves the addition of a modified guanine nucleotide to the 5’ end of the mRNA molecule
• Splicing removes introns and joins exons to generate a mature mRNA molecule
• Polyadenylation adds a poly-A tail to the 3’ end of the mRNA molecule
• RNA processing ensures the stability and functionality of mRNA

26. Genetic Code: Start and Stop Codons:

• The start codon initiates translation and specifies the amino acid methionine
• In most organisms, the start codon is AUG
• Stop codons signal the termination of translation
• There are three stop codons: UAA, UAG, and UGA
• Stop codons do not specify any amino acid, but instead, they signal the release of the nascent polypeptide chain

27. Genetic Code: Decoding Codons:

• The genetic code is read by ribosomes during translation
• tRNA molecules, with anticodons complementary to the mRNA codons, bring amino acids to the ribosome
• The ribosome reads the codons in a sequential manner, forming peptide bonds between the amino acids
• Examples:
  • Codon AUG codes for the amino acid methionine
  • Codon UUU codes for the amino acid phenylalanine
  • Codon GCG codes for the amino acid alanine
  • The decoding of codons is essential for protein synthesis

28. Post-Translational Modifications:

• After translation, proteins may undergo further modifications to become fully functional
• Examples of post-translational modifications include phosphorylation, glycosylation, acetylation, and ubiquitination
• Phosphorylation adds phosphate groups to proteins, altering their activity
• Glycosylation adds carbohydrates to proteins, affecting their stability and function
• Acetylation adds acetyl groups to proteins, regulating their interaction with other molecules
• Post-translational modifications enhance the diversity and functionality of proteins

29. Central Dogma of Molecular Biology:

• The central dogma of molecular biology describes the flow of genetic information in cells
• It states that DNA is transcribed into RNA, and RNA is translated into protein
• DNA replication occurs before transcription, ensuring the faithful transmission of genetic information
• The central dogma provides a framework for understanding the molecular basis of inheritance and gene expression

30. Applications of Transcription:

• Understanding transcription has significant implications in various fields of biology
• Medical research: studying how mutations in transcription factors or regulatory regions contribute to genetic disorders
• Biotechnology: using transcription factors to manipulate gene expression for the production of desired products
• Drug development: targeting transcription factors involved in disease processes for therapeutic interventions
• Transcriptional regulation is a fundamental process with implications in many areas of biological research and application