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Semester 3: CELL AND MOLECULAR BIOLOGY
Structure and function of cells and molecules
Structure and function of cells and molecules
Introduction to Cells
Cells are the basic units of life, responsible for all biological processes. They can be classified into prokaryotic and eukaryotic cells, with differing structures and functions.
Cell Structure
Key components of cells include the cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and ribosomes. Each organelle has a specific role in maintaining cell function.
Cell Membrane and Transport
The cell membrane is a lipid bilayer that regulates the movement of substances in and out of the cell. It is selectively permeable, utilizing processes such as diffusion, osmosis, and active transport.
Cell Division and Reproduction
Cells reproduce through processes of mitosis and meiosis. Mitosis results in two identical daughter cells, while meiosis produces gametes for sexual reproduction.
Biomolecules
Cells contain various biomolecules essential for life, including carbohydrates, proteins, lipids, and nucleic acids. Each type of biomolecule serves critical functions in cellular processes.
Protein Structure and Function
Proteins are composed of amino acids and perform a vast array of functions including catalyzing reactions (enzymes), providing structural support, and facilitating communication within and between cells.
Nucleic Acids
Nucleic acids, such as DNA and RNA, store and transmit genetic information. DNA consists of two strands forming a double helix, while RNA is typically single-stranded and involved in protein synthesis.
Cell Communication
Cells communicate through various signaling pathways and molecules. This includes hormonal signaling, neurotransmission, and paracrine signaling, essential for coordination of physiological functions.
Cellular Metabolism
Metabolism encompasses all the biochemical reactions occurring within a cell, including catabolic and anabolic pathways, to produce energy and synthesize necessary compounds.
Gene expression mechanisms
Gene expression mechanisms
Transcriptional Regulation
Transcriptional regulation involves the process by which the synthesis of RNA from DNA is controlled. This can occur through the binding of various transcription factors to promoter regions, enhancers, and silencers. The interaction between these proteins and the DNA influences the recruitment of RNA polymerase and the overall transcription rate.
Post-Transcriptional Modifications
Once RNA is synthesized, it undergoes several modifications before it becomes mature mRNA. These modifications include 5' capping, polyadenylation of the 3' end, and splicing, which removes introns from the pre-mRNA. These modifications are crucial for RNA stability, export from the nucleus, and translation efficiency.
Translation Regulation
Translation is the process of synthesizing proteins from mRNA. Regulation of translation can occur at various levels, including initiation, elongation, and termination. Factors influencing translation include the availability of ribosomes, tRNAs, and initiation factors. The presence of specific regulatory elements in the mRNA can also modulate translation rates.
Post-Translational Modifications
After proteins are synthesized, they often undergo various modifications that can affect their function, localization, and stability. Common post-translational modifications include phosphorylation, glycosylation, and ubiquitination. These modifications play a critical role in cellular signaling and function.
Gene Silencing and Epigenetics
Gene expression can also be regulated through epigenetic mechanisms, which involve modifications to DNA and histones that affect chromatin structure without altering the DNA sequence. Techniques such as RNA interference and the action of small non-coding RNAs contribute to gene silencing, impacting overall gene expression and cellular function.
Regulation of gene expression
Regulation of Gene Expression
Introduction to Gene Regulation
Gene regulation is the process by which the information encoded in a gene is turned on or off, influencing the production of proteins. This process is critical for cell differentiation and adaptation.
Types of Gene Regulation
Gene regulation can occur at multiple levels, including transcriptional, post-transcriptional, translational, and post-translational regulation.
Transcriptional Regulation
Transcriptional regulation involves the control of mRNA synthesis. Key elements include transcription factors, enhancers, silencers, and the promoter region.
Post-transcriptional Regulation
This level of regulation affects mRNA after it has been synthesized. It includes processes such as splicing, polyadenylation, and RNA interference.
Translational Regulation
Translational regulation determines the efficiency of translation of mRNA into proteins. Factors include ribosome binding, initiation factors, and availability of tRNAs.
Post-translational Regulation
Post-translational modifications such as phosphorylation, glycosylation, and ubiquitination can alter protein function and stability.
Examples of Gene Regulation in Plants
In plants, gene regulation is crucial for responses to environmental stimuli, developmental processes, and hormone signaling.
RNA processing and translation
RNA processing and translation
Introduction to RNA Processing
RNA processing is a crucial stage in gene expression where the initial RNA transcript or precursor RNA undergoes several modifications to become a mature messenger RNA (mRNA) ready for translation.
Types of RNA
In eukaryotic cells, there are several types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA), and small RNAs including small nuclear RNA (snRNA) and microRNA (miRNA). mRNA is the focus of processing and translation.
Steps in RNA Processing
RNA processing involves several key steps: 1. Capping - Addition of a 5' cap to the RNA. 2. Polyadenylation - Addition of a poly-A tail at the 3' end. 3. Splicing - Removal of non-coding sequences (introns) and joining of coding sequences (exons).
Importance of Splicing
Splicing is essential to generate mature mRNA that can be translated into proteins. Alternative splicing allows a single gene to code for multiple proteins, increasing the diversity of proteins.
Translation Overview
Translation is the process by which the mRNA sequence is decoded to produce a specific polypeptide or protein. It occurs in the ribosomes and involves tRNA, which brings the appropriate amino acids.
Translation Steps
Translation consists of three main stages: 1. Initiation - Assembly of the ribosome, mRNA, and the first tRNA. 2. Elongation - Sequential addition of amino acids as dictated by the mRNA code. 3. Termination - Release of the completed polypeptide once a stop codon is reached.
Regulation of Translation
Translation is tightly regulated by various factors, including availability of tRNA, initiation factors, and regulatory proteins. This ensures protein synthesis is efficient and responsive to cellular needs.
Conclusion
RNA processing and translation are integral to gene expression. Understanding these processes is essential for studying molecular biology, biotechnology, and genetic engineering.
Epigenetic mechanisms and RNA interference
Epigenetic mechanisms and RNA interference
Introduction to Epigenetics
Epigenetics refers to heritable changes in gene expression that do not involve changes to the underlying DNA sequence. It plays a crucial role in development, cellular differentiation, and response to environmental stimuli.
Types of Epigenetic Mechanisms
Key types include DNA methylation, histone modification, and non-coding RNA interactions. DNA methylation commonly silences gene expression, while histone modifications can either activate or repress genes.
Role of RNA Interference
RNA interference (RNAi) is a biological process where RNA molecules inhibit gene expression or translation. It is a critical mechanism for regulating gene function and maintaining genomic stability.
Molecular Players in RNA Interference
Key molecules include small interfering RNAs (siRNAs) and microRNAs (miRNAs), which guide the RNA-induced silencing complex (RISC) to target mRNAs for degradation or inhibition.
Interplay between Epigenetics and RNA Interference
RNAi can impact epigenetic modifications by influencing the expression of genes involved in the establishment and maintenance of epigenetic marks. Conversely, epigenetic changes can affect the efficiency of RNAi.
Applications in Research and Medicine
Understanding epigenetic mechanisms and RNAi has vast implications in fields such as cancer research, gene therapy, and the development of biotechnological applications.
Conclusion
Both epigenetic mechanisms and RNA interference are essential for the regulation of gene expression and offer promising avenues for therapeutic interventions in various diseases.
