Gene Expression_Overview_SP25_ed9e277057f68abfbe8afbef25473784

Organism's Genotype and Phenotype

The genotype of an organism refers to its genetic makeup, which directly influences its phenotype, the observable characteristics. The genotype comprises the specific alleles that an organism possesses, impacting traits such as height, eye color, and susceptibility to certain diseases.

Essential Characteristics of the Hereditary Molecule

Replication & Transmission

DNA must be accurately replicated and transmitted to offspring for inheritance. This process is critical for ensuring that genetic information is maintained across generations, and involves multiple enzymes and checkpoints to reduce errors.

Information Storage

DNA stores genetic information that is crucial for the functioning of organisms. This information is encoded in sequences of nucleotides, which form the basis for genes – the units of heredity.

Genetic Variation

Variations in genes are responsible for differences between individuals. These variations can arise from mutations, gene flow, and sexual reproduction, contributing to the diversity of traits within a population.

Phenotypic Expression

Gene expression translates genetic information into phenotypic traits. This involves transcription (where DNA is converted to mRNA) and translation (where mRNA is used to synthesize proteins), leading to the visible traits that define an organism.

Learning Objectives

• Understand how gene expression results in the observable traits of an organism (phenotype).

• Compare and contrast prokaryotic and eukaryotic gene structures.

Genes and Protein Structures

Components of gene expression in eukaryotic cells includes:

• Nucleus: Location of DNA where transcription occurs.

• Types of RNA:

  • Nuclear noncoding RNA (e.g., Gomafu, Xist) plays roles in gene regulation and chromosome structure.

  • Messenger RNA (mRNA) carries the genetic information from DNA to the ribosome for protein synthesis.

• Cytoplasm: Site of protein synthesis, where ribosomes translate mRNA into proteins.

• Outcome: Production of proteins or RNA molecules that are crucial for various cellular functions and traits.

Proteins' Roles in Cell Physiology

• Gene Example: Specific genes encode proteins associated with particular traits (e.g., green eyes).

• Process: Genes contain information on how proteins are synthesized. The resultant proteins contribute to specific traits, such as eye color, or perform vital functions like enzymatic activity and structural roles in cells.

Types of Noncoding RNAs (ncRNAs)

Housekeeping ncRNAs:

• Include ribosomal RNA (rRNA), transfer RNA (tRNA), small nuclear RNA (snRNA), and small nucleolar RNA (snoRNA), which are essential for basic cellular functions and protein synthesis.

Regulatory ncRNAs:

• Short noncoding RNAs (< 200 nucleotides):

  • microRNA (miRNA) regulates gene expression post-transcriptionally by binding to mRNA.

  • small interfering RNA (siRNA) can silence gene expression.

• Long noncoding RNAs (> 200 nucleotides):

  • large intergenic noncoding RNA (lincRNA), circular RNA (circRNA), and other types (e.g., piRNA, scaRNA, eRNA, NAT) involved in gene regulation, chromatin remodeling, and cellular signaling.

Impact of ncRNAs on Cell Physiology

Reference to a study discussing the role of long noncoding RNAs in cancer and their potential use in translational medicine, highlighting their significance in diagnosis and treatment strategies.

Definition of a Gene

A gene is defined as a segment of DNA that encodes a functional product, which can be RNA or protein.

Features:

• Prokaryotic and eukaryotic genes have structural differences. Common features include:

  • Regulatory sequences that control gene expression levels.

  • Coding regions that contain the actual coding sequence for proteins.

Basic Prokaryotic Gene Structure

Key Components:

• Regulatory gene: Controls the expression of other genes, often organized in operons.

• Operon: Includes a promoter, operator, and structural genes that are co-regulated.

• Promoter, Operator, Terminator: These are critical for transcription initiation and termination.

• Open Reading Frame (ORF): Responsible for gene activation or repression, defining the boundaries of coding regions.

Basic Eukaryotic Gene Structure

Structure includes:

• Upstream regulatory sequences: Enhancers and silencer elements that manipulate transcription efficiency.

• Open Reading Frame (ORF): Contains exons (coding regions) and introns (non-coding regions that are spliced out).

• Poly-A signal sequence is critical for mRNA stability and translation.

Gene Orientation on DNA Strands

Genes are found on both strands of DNA; one acts as the template for RNA synthesis. The orientation of the promoter defines the direction of transcription, which is essential for proper gene expression.

Key Concepts

Gene expression is vital for multicellular organism development, influencing cell differentiation and overall cellular functions. Genes store essential information for the synthesis of ncRNAs and the proteins necessary for the organism's survival and function.