Epigenetics
54 flashcards covering Epigenetics for the MCAT Biology & Biochemistry section.
Epigenetics is the study of changes in how genes are expressed without altering the actual DNA sequence. Think of it as adding or removing chemical tags on DNA or its packaging proteins, which can turn genes on or off. This process helps explain how identical twins can develop different traits or how environmental factors, like diet or stress, influence health over time. It's crucial for understanding development, disease, and inheritance beyond just genetics.
On the MCAT, epigenetics appears in biology and biochemistry questions that test mechanisms like DNA methylation and histone modification, often in the context of gene regulation or environmental interactions. You'll encounter multiple-choice questions asking about processes, examples such as genomic imprinting, or experimental evidence. Common traps include confusing epigenetic changes with permanent mutations or overlooking their reversibility. Focus on how these mechanisms affect cellular function and disease, as questions may require applying concepts to scenarios like cancer development.
Practice sketching epigenetic pathways to solidify your understanding.
Terms (54)
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Epigenetics
Epigenetics refers to the study of heritable changes in gene expression that do not involve alterations to the underlying DNA sequence, such as modifications that affect how genes are turned on or off.
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Epigenome
The epigenome consists of all the chemical modifications to DNA and histone proteins in a cell that regulate gene expression without changing the DNA sequence, varying between cell types and influencing development.
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DNA Methylation
DNA methylation is the process of adding a methyl group to DNA, usually on cytosine bases in CpG islands, which typically represses gene expression by preventing transcription factors from binding.
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Histone Modification
Histone modification involves chemical changes to histone proteins, such as acetylation or methylation, that alter chromatin structure and affect gene accessibility for transcription.
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Chromatin Remodeling
Chromatin remodeling is the dynamic process by which the structure of chromatin is altered, making DNA more or less accessible for transcription through the action of protein complexes.
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Gene Silencing
Gene silencing is an epigenetic mechanism that permanently or temporarily turns off gene expression, often through DNA methylation or histone modifications that compact chromatin.
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Gene Activation
Gene activation is the process by which epigenetic marks, like histone acetylation, loosen chromatin structure to allow transcription factors to access and express specific genes.
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CpG Islands
CpG islands are regions of DNA with a high frequency of cytosine-guanine dinucleotides that are often located near gene promoters and can be methylated to regulate gene expression.
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Histone Acetylation
Histone acetylation is the addition of acetyl groups to lysine residues on histone proteins, which generally promotes gene expression by reducing the affinity between histones and DNA.
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Histone Methylation
Histone methylation involves adding methyl groups to histone tails, which can either activate or repress gene expression depending on the specific lysine or arginine residue modified.
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Histone Phosphorylation
Histone phosphorylation is the addition of phosphate groups to histone proteins, often associated with chromatin relaxation during processes like DNA repair or transcription.
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Histone Ubiquitination
Histone ubiquitination is the attachment of ubiquitin molecules to histones, which can lead to gene repression or activation by signaling for further chromatin modifications.
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Euchromatin
Euchromatin is a loosely packed form of chromatin that is accessible for transcription, characterized by histone modifications that promote gene expression.
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Heterochromatin
Heterochromatin is a tightly packed form of chromatin that is generally transcriptionally inactive, maintained by epigenetic marks like DNA methylation.
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Genomic Imprinting
Genomic imprinting is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner, often through differential methylation of alleles.
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X-Chromosome Inactivation
X-chromosome inactivation is the epigenetic process in females that silences one of the two X chromosomes to prevent gene dosage imbalance, mediated by the Xist RNA.
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Epigenetic Inheritance
Epigenetic inheritance is the transmission of gene expression patterns from one generation to the next without changes to the DNA sequence, such as through modified histones or DNA methylation.
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Transgenerational Epigenetic Effects
Transgenerational epigenetic effects occur when environmental influences cause epigenetic changes that persist and affect subsequent generations beyond the directly exposed one.
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Epigenetic Regulation of Development
Epigenetic regulation of development involves modifications that control the timing and pattern of gene expression during embryogenesis, ensuring proper cell differentiation.
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Epigenetics in Cancer
Epigenetics in cancer refers to abnormal DNA methylation and histone modifications that lead to inappropriate gene silencing or activation, contributing to uncontrolled cell growth.
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DNA Methyltransferases
DNA methyltransferases are enzymes that add methyl groups to DNA, maintaining and establishing methylation patterns that regulate gene expression.
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Histone Deacetylases
Histone deacetylases are enzymes that remove acetyl groups from histones, leading to chromatin condensation and gene repression.
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Histone Acetyltransferases
Histone acetyltransferases are enzymes that add acetyl groups to histones, promoting an open chromatin structure and facilitating gene transcription.
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Bromodomain Proteins
Bromodomain proteins recognize and bind to acetylated lysine residues on histones, playing a role in recruiting other proteins to activate gene expression.
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Chromatin Remodeling Complexes
Chromatin remodeling complexes are multi-protein assemblies that use ATP to reposition nucleosomes, altering DNA accessibility for transcription.
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MicroRNAs in Epigenetics
MicroRNAs are small non-coding RNAs that can influence epigenetic modifications by targeting messenger RNAs or directly affecting chromatin structure.
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SiRNAs and Epigenetics
Small interfering RNAs guide the formation of heterochromatin and DNA methylation in some organisms, silencing repetitive elements and transposons.
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Environmental Influences on Epigenetics
Environmental influences on epigenetics include factors like diet and toxins that can alter DNA methylation patterns, affecting gene expression and health outcomes.
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Epigenetic Markers
Epigenetic markers are chemical tags on DNA or histones that indicate the epigenetic state of a gene, such as methyl groups that signal repression.
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Bisulfite Sequencing
Bisulfite sequencing is a technique used to detect DNA methylation by converting unmethylated cytosines to uracil, allowing identification of methylated regions.
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ChIP-seq
ChIP-seq is a method that combines chromatin immunoprecipitation with sequencing to map histone modifications or transcription factor binding sites across the genome.
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Epigenetic Reprogramming
Epigenetic reprogramming is the process during gamete formation and early embryonic development that resets epigenetic marks to establish new patterns.
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Epigenetic Changes in Aging
Epigenetic changes in aging involve progressive alterations in DNA methylation and histone modifications that contribute to cellular senescence and age-related diseases.
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Prader-Willi Syndrome
Prader-Willi syndrome is a genetic disorder caused by the loss of paternal epigenetic imprinting on chromosome 15, leading to symptoms like hyperphagia and intellectual disability.
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Angelman Syndrome
Angelman syndrome results from the loss of maternal epigenetic imprinting on chromosome 15, causing severe developmental delay and neurological issues.
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Epigenetics and Stem Cells
Epigenetics and stem cells involve dynamic modifications that maintain pluripotency by keeping genes for self-renewal active and differentiation genes repressed.
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Polycomb Group Proteins
Polycomb group proteins are epigenetic regulators that maintain gene silencing through histone modifications, crucial for development and cell identity.
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Trithorax Group Proteins
Trithorax group proteins counteract Polycomb proteins by promoting histone methylation that activates gene expression, especially in homeotic genes.
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Enhancer Elements
Enhancer elements are DNA sequences that increase transcription of genes through epigenetic modifications like histone acetylation, often located far from the gene.
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Silencer Elements
Silencer elements are DNA regions that repress gene expression via epigenetic mechanisms such as DNA methylation, binding repressor proteins.
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Locus Control Regions
Locus control regions are regulatory DNA sequences that ensure proper epigenetic activation of gene clusters, like in the beta-globin locus during development.
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Epigenetic Memory
Epigenetic memory is the ability of cells to retain gene expression patterns after cell division, maintained by stable epigenetic marks on chromatin.
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Reversible Nature of Epigenetic Marks
The reversible nature of epigenetic marks means that modifications like methylation can be added or removed in response to signals, allowing dynamic gene regulation.
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Epigenetics in the Immune System
Epigenetics in the immune system controls the expression of genes involved in immune responses, such as through histone modifications that enable rapid activation of defense genes.
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Epigenetics and Metabolism
Epigenetics and metabolism involve modifications that link environmental nutrients to gene expression, influencing metabolic pathways and disease risk.
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Common Trap: Epigenetics vs. Genetics
A common trap is confusing epigenetics, which involves changes in gene expression without altering DNA sequence, with genetics, which deals with DNA sequence variations themselves.
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Example of DNA Methylation in Action
In cancer cells, hypermethylation of tumor suppressor gene promoters leads to their silencing, allowing uncontrolled proliferation, as seen in many carcinomas.
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Histone Code Hypothesis
The histone code hypothesis proposes that specific combinations of histone modifications form a code that dictates chromatin states and gene expression outcomes.
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Epigenetic Drugs
Epigenetic drugs, such as HDAC inhibitors, target enzymes that modify histones or DNA to reverse abnormal epigenetic states in diseases like cancer.
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RNA-Directed DNA Methylation
RNA-directed DNA methylation is a process where small RNAs guide the addition of methyl groups to DNA, silencing transposons and maintaining genome stability.
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Epigenetic Clocks
Epigenetic clocks are patterns of DNA methylation that correlate with biological age, used to measure aging processes and predict health outcomes.
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Paramutation
Paramutation is an epigenetic phenomenon where one allele induces a heritable change in another allele at the same locus, observed in plants and some animals.
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Bivalent Chromatin
Bivalent chromatin contains both activating and repressing histone marks, keeping genes poised for expression in stem cells during development.
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Epigenetics in Neurological Disorders
Epigenetics in neurological disorders involves aberrant modifications that alter gene expression in the brain, contributing to conditions like Alzheimer's disease.