Molecular Basis of Inheritance
- Production of mature mRNA
- Importance of RNA processing
- Pre-mRNA splicing
- Addition of a 5’ cap
- Addition of a poly-A tail
Production of mature mRNA
- Synthesis of primary transcript
- RNA processing steps
- Removal of introns
- Addition of a cap and tail
- Formation of mature mRNA
Importance of RNA processing
- Ensures stability of mRNA
- Facilitates transport from nucleus to cytoplasm
- Allows for translation of mRNA into protein
- Controls gene expression
- Influences alternative splicing
Pre-mRNA splicing
- Removal of introns
- Conserved splice donor and acceptor sites
- Formation of spliceosome complex
- Recognition of intron/exon boundaries
- Cleavage and ligation reactions
Addition of a 5’ cap
- Facilitates mRNA stability
- Protects mRNA from degradation
- Aids in translation initiation
- Modification at the 5’ end of pre-mRNA
- Consists of a methylated guanine nucleotide
Addition of a poly-A tail
- Enhances mRNA stability
- Protects mRNA from degradation
- Facilitates nuclear export of mRNA
- Increases translational efficiency
- Consists of a string of adenine nucleotides
Synthesis of primary transcript
- Initiation of transcription at the promoter site
- RNA polymerase binding to DNA template strand
- Elongation of RNA molecule
- Termination of transcription at the terminator site
- Formation of pre-mRNA molecule
Removal of introns
- Recognition of intron/exon boundaries
- Splicing out of introns by spliceosome
- Formation of mature mRNA molecule
- Retention of exons for protein coding
- Alternative splicing possibilities
- Consists of snRNPs (small nuclear ribonucleoproteins)
- Recognition of intron/exon boundaries
- Assembly of spliceosome at the splice sites
- Catalyzes the splicing reaction
- Allows for removal of introns and ligation of exons
Recognition of intron/exon boundaries
- Conserved nucleotide sequences at splice sites
- 5’ splice site (splice donor site)
- 3’ splice site (splice acceptor site)
- Intronic branch point sequence
- Consensus sequences that guide splicing process
Addition of a 5’ cap
- Facilitates mRNA stability
- Protects mRNA from degradation
- Aids in translation initiation
- Modification at the 5’ end of pre-mRNA
- Consists of a methylated guanine nucleotide (7-methylguanosine)
Addition of a poly-A tail
- Enhances mRNA stability
- Protects mRNA from degradation
- Facilitates nuclear export of mRNA
- Increases translational efficiency
- Consists of a string of adenine nucleotides (generally 100-200 nucleotides long)
Synthesis of primary transcript
- Initiation of transcription at the promoter site
- RNA polymerase binding to DNA template strand
- Elongation of RNA molecule by adding nucleotides
- Termination of transcription at the terminator site
- Formation of pre-mRNA molecule after completion of transcription
Removal of introns
- Recognition of intron/exon boundaries by spliceosome
- Splicing out of introns by spliceosome
- Formation of mature mRNA molecule consisting of exons
- Retention of exons for protein coding
- Possibility of alternative splicing leading to different mRNA isoforms
- Consists of snRNPs (small nuclear ribonucleoproteins)
- snRNPs recognize conserved sequences at splice sites
- Assembly of spliceosome at the splice sites
- Catalyzes the splicing reaction
- Allows for removal of introns and ligation of exons
Recognition of intron/exon boundaries
- Conserved nucleotide sequences at splice sites
- 5’ splice site (splice donor site) - GU
- 3’ splice site (splice acceptor site) - AG
- Intronic branch point sequence - A near the 3’ end of intron
- Consensus sequences guide the splicing process and provide specificity
Importance of RNA processing
- Ensures stability of mRNA
- Facilitates transport from nucleus to cytoplasm
- Allows for translation of mRNA into protein
- Controls gene expression by regulating splicing patterns
- Influences alternative splicing leading to multiple protein isoforms
Pre-mRNA splicing
- Pre-mRNA undergoes alternative splicing to generate different splice variants
- Spliced genes can code for different protein products
- Example: Fibronectin gene, which can generate over 20 different mRNA variants
- Alternative splicing contributes to proteome diversity
Production of mature mRNA
- The primary transcript undergoes various processing steps before becoming mature mRNA
- This includes splicing, capping, and polyadenylation
- The mature mRNA is exported from the nucleus to the cytoplasm
- It can then be translated into a protein by the ribosomes
- Mature mRNA is more stable and functional compared to the primary transcript
Regulation of RNA processing
- RNA processing can be regulated at various levels
- Transcription factors and chromatin modifications can influence splicing patterns
- RNA-binding proteins can enhance or inhibit splicing efficiency
- Alternative splicing can be regulated by signaling pathways and cellular conditions
- Dysregulation of RNA processing can lead to genetic disorders and diseases
Regulation of gene expression
- Transcriptional regulation
- Promoters and enhancers
- Transcription factors
- Chromatin remodeling
- Post-transcriptional regulation
- mRNA stability
- Translation initiation
- RNA interference (miRNA, siRNA)
- Epigenetic regulation
- DNA methylation
- Histone modification
- Non-coding RNAs
Transcriptional regulation
- Promoters and enhancers control transcription initiation
- Transcription factors bind to specific DNA sequences
- Activators enhance transcription, repressors inhibit it
- Chromatin remodeling influences DNA accessibility
- Coactivators and corepressors modulate transcriptional activity
Post-transcriptional regulation
- mRNA stability determines its abundance
- Regulatory proteins and RNA-binding proteins control stability
- AU-rich elements (AREs) promote mRNA degradation
- Translation initiation is regulated by various factors
- RNA interference (RNAi) involves small non-coding RNAs (miRNA, siRNA)
Epigenetic regulation
- DNA methylation adds methyl groups to cytosine residues
- Methylated DNA reduces gene expression
- Histone modification alters chromatin structure
- Acetylation, methylation, phosphorylation, etc.
- Non-coding RNAs regulate gene expression at the transcriptional level
Examples of gene regulation
- Lac operon in bacteria
- Promoter sequence and the role of lactose and glucose
- Transcriptional activator (CAP) and repressor (LacI)
- Regulation of p53 tumor suppressor gene
- Feedback loops and cell cycle regulation
- X-chromosome inactivation in females
Gene expression and development
- Differential gene expression leads to cell specialization
- Homeobox genes and body plan development
- Hox genes and segmental patterning in animals
- Induction and cell signaling during embryogenesis
- Environmental factors and gene expression
Molecular basis of genetic diseases
- Mutations can disrupt gene function
- Single gene disorders and inherited traits
- Cystic fibrosis, sickle cell anemia, Huntington’s disease, etc.
- Polygenic disorders and complex traits
- Diabetes, Alzheimer’s disease, heart disease, etc.
- Genetic testing and counseling
Gene therapy and genetic engineering
- Gene therapy for genetic disorders
- Introduction of functional genes into affected cells
- Viral vectors and non-viral delivery systems
- Ethical considerations and safety concerns
- Genetic engineering and biotechnology applications
- GMOs, gene editing (CRISPR), cloning, etc.
Population genetics and evolution
- Genetic variation and allele frequencies
- Hardy-Weinberg equilibrium and genetic drift
- Natural selection and adaptation
- Genetic flow and migration
- Speciation and reproductive isolation
Human evolution
- Shared ancestry with other primates
- Fossil record and hominid species
- Homo habilis, Homo erectus, Homo neanderthalensis, etc.
- Out-of-Africa hypothesis and modern human origins
- Major milestones in human evolution