Molecular Biology: DNA Structure and Function

Upcoming Quizzes and Tests

• Upcoming quiz covers DNA structure, replication, transcription, and RNA processing
• Quiz is 10 multiple-choice questions
• Even-numbered day classes: quiz on the 17th, test on the 24th
• Odd-numbered day classes: quiz on the 21st, test on the 27th

Lab Feedback

• Fully explain the importance of each aspect of the lab work
• Avoid vague terms like "cobwebby" without a specific explanation of its significance to the process
• Question 2: Agarose drying pattern creates pores, which allow DNA fragments of varying sizes to migrate at different rates during electrophoresis
• Question 3: DNA's phosphate backbone carries a negative charge, causing it to be drawn toward the positive electrode in electrophoresis
• Question 5: Higher agarose concentrations create denser gels, slowing DNA migration, leading to shorter distances traveled during electrophoresis

Gene Regulation

• Gene regulation is more complex than Bio 1 topics
• Gene regulation examples:
  • Calico cat coat patterns arise from gene expression differences
  • Maternal care in the first three weeks of mouse pups' lives affects anxiety levels in adulthood
  • Touch and grooming during infancy correlates to four times higher morphine resistance in mice
  • Teenagers' alcohol use affects their DNA, impacting their children and grandchildren (epigenetics)

Epigenetics

• Epigenetics involves inheritable changes to gene expression without altering the DNA sequence
• "On/off switches" of gene expression change over a lifetime, affecting future generations

Histones

• Histones are special proteins that package DNA
• Histone roles:
  • Prevent DNA tangling
  • Regulate gene expression
• Tightly wound DNA around histones inhibits transcription (genes "off")
• DNA and histone complex creates a nucleosome
• DNA has a negative charge (phosphate groups)
• Histones have a positive charge (amino acids)
• The opposing charges facilitate DNA binding to histones

Visual Aid

• DNA wrapped around histones under a microscope appears like a "string of beads"

Histones and DNA

• Histones are positive, DNA is negative, this attraction allows DNA to wrap around histones.
• Tightly wound DNA inhibits transcription (genes are "off")
• Acetylation of histones neutralizes their positive charge allowing DNA to unwind and genes to be expressed (genes "on")

Epigenetics

• Epigenetic modifications alter gene expression without changing the DNA sequence
• These changes can be passed down across generations

DNA Methylation

• DNA methylation is a more stable epigenetic modification than histone acetylation
• Methyl groups (CH₃) added to DNA, frequently in gene promoter regions
• Methylated promoters inhibit RNA polymerase binding, reducing gene transcription and effectively "turning off" the gene
• Removing methyl groups allows for RNA polymerase binding, promoting gene transcription and effectively "turning on" the gene

Why Methylation Matters

• Methylation patterns impact gene expression
• X chromosome inactivation in females; one X chromosome (randomly selected) is silenced in each cell, preventing double gene expression – this inactivation leads to calico cat patterns, a result of X-linked genes in mammals.

Methylation and Life Experiences

• Methylation patterns are dynamic and can evolve in response to environmental factors and life experiences
• This plasticity allows adaptation to environmental changes

Maternal Care and Brain Chemistry

• Early childhood experiences imprint brain chemistry and behavior
• 2011 study: Intensive maternal care during infancy affects neuropeptide Y (NPY) production in the brain
• NPY regulates body weight, stress levels, and anxiety
• Nurturing mothers raise mice with higher NPY levels and lower anxiety in adulthood
• Methylation and its role in gene regulation was investigated
• Nurturing mothers reduce methylation on the Npy1 receptor gene resulting in increased gene expression and reduced anxiety in mice

Genetics and Epigenetics

• Environmental factors, especially in childhood, impact epigenetic patterns
• These patterns can be inherited across generations
• DNA methylation acts like a "dimmer switch" controlling gene activity
• Differences in methylation patterns are seen across different parenting/touching styles
• 2017 study noted that children with less physical contact have less developed molecular profiles – highlighting the impact of physical touch on gene expression

Behavioral Studies and Implications

• Early childhood experiences (maternal care, touch) impact brain development and behavior for a lifetime
• Early alcohol exposure in rats results in methyl pattern changes in offspring, suggesting transgenerational effects
• Binge drinking by either parent affects methylation patterns in offspring, emphasizing the importance of healthy lifestyles

IL-10 and Addiction

• Nurturing mothers increase IL-10 production (an immune molecule)
• IL-10 reduces cravings in morphine-dependent rats, implying that IL-10 plays an important role in addiction susceptibility
• High-touch mothers decrease morphine addiction risk in their offspring.

Conclusion

• Environmental and genetic factors shape behavior and health outcomes
• Understanding individual differences requires considering both nature and nurture

Twin Studies and Genetics

• Identical twins share 100% of their DNA, whereas fraternal twins share 50%
• Twin studies assess the influence of genetics and environment on traits
• Height, hair color, eye color are mostly genetic
• Mathematical ability has a larger environmental influence
• Autism is mostly genetic, but the reasons for higher male prevalence remain unclear
• Crohn's disease, breast cancer, and stroke show greater environmental influence

Epigenetics and Environmental Influences

• Epigenetics explores how environmental influences modify gene expression without altering the DNA
• Methylation tags affect gene activation/silencing
• Environments alter methyl tags that modify gene expression
• Specific exposures, such as space travel, can modify methylation patterns
• Factors like childhood experiences, societal influences, drug exposure, and alcohol exposure affect methylation patterns and long-term health outcomes
• Epigenetic changes can be inherited over several generations influencing the offspring

Angelman Syndrome

• Angelman syndrome is a neurodevelopmental disorder characterized by:
  • Severe intellectual disability
  • Lack of speech
  • Frequent laughter/smiling
  • Distinct gait, with arms and legs held forward
  • Frequent hand-flapping

Prader-Willi Syndrome (PWS)

• PWS is characterized by:
  • Low muscle tone
  • Increased body fat
  • Constant hunger
  • Food craving
  • Difficulty regulating food intake
  • Developmental delays
  • Cognitive difficulties

Chromosome 15 Deletion

• Angelman and PWS stem from a deletion on chromosome 15
• The syndrome depends on parental origin of the deletion
• Maternal deletion causes Angelman syndrome
• Paternal deletion causes Prader-Willi Syndrome
• This showcases how cells differentiate between maternal and paternal chromosomes (even when identical), regulating gene expression

Imprinting and Methylation

• Genomic imprinting involves differential methylation patterns between maternal and paternal chromosomes
• This differentially affects gene expression influencing development and health
• The mechanisms behind maternal/paternal chromosome distinctions and methylation control are still under research

This quiz consists of 10 multiple choice questions focusing on DNA structure, replication, transcription, and RNA processing. It is designed to test your understanding of these fundamental concepts in molecular biology. Be prepared for a mix of critical thinking and factual recall related to DNA processes.