Bis 24

Introduction

• The teacher recaps the weekend and shares personal experiences such as working on the exam and grading notebooks.

• Announces the upcoming final mid-term assessment on Friday.

  • Format: 25 questions, 24 questions worth 9 points, and 1 question worth 5 points.

  • Informing students about revisiting two questions from the previous midterm.

Gene Regulation Overview

• Discussion on regulating gene expression at different levels:

  • Transcriptional Regulation: Control of whether a gene is transcribed.

  • Importance of controlling gene expression to save resources.

Mechanisms of Transcriptional Regulation

• Positive Influence on Gene Expression:

  • Positive regulators bind near a promoter to enhance transcription.

  • Examples of positive regulators discussed.

• Negative Influence on Gene Expression:

  • Negative regulators bind to DNA to turn off transcription.

  • Example: The lac repressor in E. Coli and its role in lactose utilization.

E. Coli and Lactose Utilization

• Lactose Utilization Mechanism:

  • Genes ZYA encode enzymes for lactose metabolism (lactose is a disaccharide of glucose and galactose).

  • Operator: A binding site for transcription factors.

  • Promoter (P lac): The site for regulator binding, upstream of ZYA.

  • Repressor (I gene): Encodes a transcriptional repressor that negatively regulates transcription when lactose is absent.

• Lactose Absent:

  • Lac repressor binds operator, blocking RNA polymerase.

  • Prevents transcription and conserves resources.

• Lactose Present:

  • Allolactose (isomer of lactose) binds to the lac repressor at the allosteric site.

  • Positive regulation occurs: repressor releases from operator; RNA polymerase can then transcribe ZYA genes.

Dual Regulation by Glucose and Lactose

• Experiment Observations: E. Coli uses glucose first, even when lactose is present.

• Cyclic AMP and CRP:

  • CRP (Cyclic AMP Receptor Protein) binds low glucose levels represented by high cyclic AMP.

  • This binding activates transcription of lactose genes when glucose levels are low.

  • The presence of glucose inhibits the activation of lactose utilization genes via low cyclic AMP levels.

Transcriptional Regulation Summary

• Importance of understanding positive and negative regulation mechanisms.

• Need to be able to reason through the logic behind gene regulation based on environmental signals.

• A cohesive understanding rather than memorization of truth tables for situations like the lac operon.

Concepts of Genotype and Phenotype

• Genotype: Sequence of nucleotides (As, Gs, Cs, Ts) in an organism's genome.

• Phenotype: Any measurable characteristic other than the genotype, e.g., height, color, enzyme production.

• Mutant genotypes represent different variants from the wild type.

Mutation Effects on Protein Production

• Types of Mutations:

  • Point mutations, frameshift mutations, and mutations in promoters.

  • Mutations can either disrupt transcription or alter the function of resultant proteins.

• Promoter Mutations: Can result in loss or decrease of transcription efficiency.

Genetic Diversity

• Discussion on different chromosome copy numbers (haploid, diploid, etc.) and significance in genetics.

  • Haploid: One copy of chromosomes.

  • Diploid: Two copies (one from each parent).

  • Terms: Wild type (most common variant) and alleles (variations of genes).

Regulation in Yeast Life Cycle

• Example of two yeast versions (Mating types): haploid and diploid conditions.

• Exploration of how mating leads to genetic diversity and study of phenotypic expression.

• Conclusion: Reproduction strategies are chosen based on environmental stability or variability.

Metabolic Pathway Implications

• Brief overview of pathways leading to nucleotide synthesis.

• Example of Gene Function: ADD2 gene's role in synthesizing a compound related to phenotypic expression.

• Effects of mutations: Knockout of ADD2 leads to accumulation of red pigment due to oxidative reactions.