Genomes and Genes Flashcards

Page 1: Introduction to the Genome

The genome encompasses all genes that encode proteins within a cell, functioning as the biological blueprint for the organism. Example of base pairs illustrated as follows:

• DNA Sequence: ATCCGATTATTATATGG

• Complementary Base Pair: TAGGCTAATAATATACC

Page 2: Overview of the Human Genome

The human genome represents an extensive array of genes and chromosomes, encompassing around 3 billion DNA base pairs. It includes a total of 22 pairs of autosomal chromosomes and one pair of sex chromosomes (X, Y). Collectively, these elements dictate the biological characteristics of an individual through their hereditary information.

Page 3: Definition of Genome

The genome refers to the complete sequence of genetic material found within an organism, including both nuclear DNA and the DNA located in organelles such as mitochondria and plastids. It acts as a genetic catalog that stores vital information regarding hereditary traits, including but not limited to physical characteristics, susceptibility to diseases, and metabolic pathways.

Page 4: Genetic Makeup Defined

• Genotype: The set of genes (alleles) present in an organism which determine potential traits.

• Phenotype: The expression of these genes, which manifests as physical traits such as height, hair color, and the presence of certain diseases. It is noteworthy that the phenotype can be influenced by environmental factors, showing the complex interaction between genotype and environment.

Page 5: Structure of Genes

Genes are the fundamental units of inheritance and are composed of:

• DNA: Made up of deoxyribonucleotides, forming a double helix structure.

• RNA: Composed of ribonucleotides and plays a critical role in translating genetic information into functional proteins.

• Proteins: Made up of amino acids, act as the workhorses of the cell, performing a myriad of functions from catalyzing metabolic reactions to providing structural support.

Page 6: Central Dogma of Molecular Biology

The key processes as established by Francis Crick in 1958 include:

• DNA Replication: The process by which a cell duplicates its DNA prior to division, ensuring each daughter cell receives an identical copy.

• Transcription: The synthesis of RNA from a DNA template, which is a critical step in gene expression.

• Translation: The process by which a ribosome synthesizes proteins by decoding mRNA, forming the functional products of genes.

Page 7: Gene Organization - Basic Features

Key structural elements of a gene include:

• Promoter: A regulatory region that initiates transcription by providing a binding site for RNA polymerase.

• Terminator: A sequence that signals the end of transcription, ensuring that RNA synthesis stops at the correct endpoint.

• Transcribed Region: The segment of DNA that is copied into RNA during transcription.

• Coding Region and Untranslated Regions (UTRs): Critical parts of the RNA transcript, where coding regions translate into proteins and UTRs influence the stability and translation efficiency of the mRNA.

Page 8: Gene Organization in Prokaryotes

Prokaryotic genes possess distinct characteristics:

• Co-linearity: The sequence of nucleotides in mRNA is directly related to the DNA sequence, without any interruptions.

• Absence of Introns: Prokaryotic genes are typically uninterrupted by non-coding sequences, simplifying gene expression.

• Monocistronic and Polycistronic mRNA: mRNA can either code for one protein (monocistronic) or multiple proteins (polycistronic), enhancing efficiency in gene expression.

• Promoter and Transcription Region: These are less complex compared to eukaryotic systems, allowing for more rapid responses to environmental changes.

Page 9: Gene Organization in Eukaryotes

Eukaryotic genes are typically more complex:

• Introns: Non-coding sequences that are removed during RNA processing, allowing for alternative splicing, which can generate multiple protein products from a single gene.

• Exons: Coding sequences that remain in the mature mRNA, crucial for the final encoded protein.

• Monocistronic Structure: Eukaryotic mRNAs generally represent a single coding sequence, reflecting a more intricate regulation of gene expression.

Page 10: Alleles and Gene Variants

A single gene may produce numerous alleles, which represent different versions of the same gene:

• Allele: Variants at a specific gene locus that can lead to differences in phenotype.

• Gene Locus: The specific location of a gene on a chromosome, critical in understanding inheritance patterns.

• Types of alleles include:

  • Wild Type: The normal or most common phenotype expressed by a gene.

  • Mutant Allele: A variant that may result in a dysfunctional protein or altered function.

  • Null Allele: A variant gene that leads to no protein production at all, often causing a loss of function phenotype.

Page 11: Example of Gene Variability

The white (w) gene in Drosophila melanogaster serves as a classic example:

• Demonstrates the variability between wild type and various mutant alleles, showcasing the principles of Mendelian genetics and their application in model organisms.

Page 12: Changes in DNA Sequences

Variations in DNA can lead to phenotypic changes due to:

• Base Substitutions: The replacement of one nucleotide with another, potentially affecting protein function.

• Base Deletions: Removing nucleotides, which can lead to frameshift mutations.

• Base Insertions: Addition of nucleotides, which can also induce frameshifts and result in different protein products.

• Copy Number Variation (CNV): Changes in the number of copies of a particular gene, affecting gene dosage and organismal traits.

• It is essential to note that not all changes impact phenotype; some may be neutral mutations that do not affect fitness or function.

Page 13: Key Terms in Gene Function

Important terminology includes:

• Promoter: The site for RNA polymerase binding that initiates transcription.

• Transcribed Region: The part of DNA that is transcribed into RNA during gene expression.

• Start Codon: The codon that marks the beginning of translation (AUG).

• Stop Codon: The codon that signals the termination of translation (UAA, UAG, UGA).

• 5’ UTR and 3’ UTR: Untranslated regions that play roles in mRNA stability and regulation of translation.

• Terminator: A sequence that signals the end of transcription by RNA polymerase.

• Open Reading Frame (ORF): The region of DNA that can be translated into a functional protein.

Page 14: Gene Expression Process

The expression of genes follows the central pathway: DNA > RNA > Protein, involving transcription (DNA to RNA) and translation (RNA to protein) processes that are crucial for cellular functions.

Page 15: RNA Characteristics

RNA transcribed from genes can vary in length and type:

• Coding Strand vs. Template Strand: One strand of DNA serves as the template to synthesize RNA, emphasizing the directionality (5’ to 3’ for RNA synthesis) and content differences between strands.

Page 16: Transcription Regulation

Gene transcription is finely regulated by:

• Trans-acting Proteins: Factors such as transcription factors that bind to specific elements in the promoter region, enhancing or inhibiting transcription.

• Cis-acting Sites: Specific DNA sequences located near the promoter that modulate gene expression and are critical for proper regulation of transcription.

Page 17: Summary of Key Points

The genome consists of complete genetic information critical for the development and functioning of living organisms. It contains genes that encode proteins, with variations existing between species, particularly between prokaryotes and eukaryotes. Genes can have multiple forms (alleles) and mutations can significantly affect gene function, manifesting in various phenotypes. Gene expression is tightly regulated by various factors, especially at the promoter level, which is crucial for cellular differentiation and response to environmental cues.

Page 18: Further Reading

For more in-depth information, refer to Lewin's Essential Genes, Chapters 1 & 44, accessible via the University of Kent link, which provides a comprehensive understanding of genetics and molecular biology.