Lecture 13 BIOL225

Lecture 313 Overview

This lecture provides key information regarding exam structure, answering student questions, and essential scientific concepts, including microscopy, gene expression, and carbohydrates.

Office Hours and Exam Information

  • Following the lecture, the professor offers a half-hour in-office time for student questions.

  • The department door is closed due to heating issues; students are encouraged to wear sweaters.

  • Students can email the professor with questions at any time.

  • The exam opens at 6:00 a.m. and closes at 11:59 p.m., with a duration of 50 minutes unless accommodations are needed.

  • Allowed materials during the exam:

    • Notes

    • Textbooks

    • Brightspace content

  • Prohibited materials:

    • Search engines

    • AI assistance

  • Students are required to work alone.

  • Discussion about the exam day should be avoided until the exam is completed by all students.

Exam Format

  • The format for the exams consists entirely of multiple-choice questions. Short answer questions are omitted to facilitate quicker grading due to the professor's concurrent responsibilities in teaching two courses.

  • Sample questions and practice materials are available online, including old midterms and textbook problems.

Microscopy and Cryopreservation

Transmission Electron Microscopy (TEM)

  • TEM provides very high resolution but is unsuitable for live samples as it requires samples to be extremely thin and stained with heavy metals (e.g., uranyl acetate).

Cryopreservation

  • Essential for cells since water expands when frozen, which can rupture cell membranes.

  • Cryoprotectants and controlled temperature decrease prevent ice crystal formation during freezing, preserving cell integrity.

Exam Format Details

Multiple-Choice Questions

  • The exam includes about 28 questions, where results are typically returned quickly after grading.

  • Grading adjustments may occur if questions are found to be excessively difficult, shifting scoring to maintain fairness.

  • The exam contributes to 10% of the final course grade.

Gene Expression and Reporter Genes

Clonal Culture

  • Clonal culture results in genetically identical cells which are essential for consistent experimental results.

DNA Structure

  • DNA is structured as a right-handed helix with major and minor grooves. These grooves allow access for binding proteins to specific sequences.

  • The two strands of DNA are connected by hydrogen bonds and stabilized by stacking interactions, similar to a pile of plates.

Gene Expression Regulation

  • Gene expression is regulated by activators and repressors which bind to promoter regions and influence RNA polymerase activity.

  • The transcriptional start site (plus one site) indicates where RNA polymerase begins transcription.

  • Transcription can occur at basal levels in the absence of additional factors.

Reporter Genes

  • Reporter genes (e.g., GFP - Green Fluorescent Protein) indicate the activity of other genes by visual fluorescence. They do not alter the underlying gene's function but provide a method to observe gene expression indirectly.

Regulatory Elements in Gene Expression

  1. Activators: Increase transcription by recruiting RNA polymerase.

  2. Repressors: Decrease transcription by preventing RNA polymerase binding.

    • Example of GFP from the jellyfish Aequorea victoria that emits fluorescent green light when exposed to blue light.

    • GFP can be placed under the control of various promoters to visualize gene expression in different cellular contexts.

Carbohydrates: An Introduction

Definition and Formula

  • Carbohydrates are polyhydroxy aldehydes or ketones and follow the general formula C<em>nH</em>2nOnC<em>nH</em>{2n}O_n.

  • Notable types include:

    • Trioses (3 carbons)

    • Pentoses (5 carbons)

    • Hexoses (6 carbons), such as glucose.

Classification

  • Based on the presence of a carbonyl group:

    • Aldoses: Carbonyl group at the end of the molecule (e.g., glucose).

    • Ketoses: Carbonyl group within the molecule (e.g., ribulose).

Importance of Carbohydrates

  • Carbohydrates function as a source of energy, structural components, and play roles in molecular recognition.

  • Polysaccharides like starch are crucial for energy storage in plants, reducing osmotic pressure inside cells.

Glycosidic Bonds

  • The linkage between two sugar molecules is called a glycosidic bond.

  • In starch, glucose molecules are connected via these bonds: 1-4 linkage occurs between the alpha hydroxyl of one glucose and the hydroxyl of another.

Starch and Glycogen

  • Starch: Comprised of amylose and amylopectin; the latter has branching from 1-6 bonds every 30 residues.

  • Glycogen: Similar to amylopectin but more branched, allowing for more effective energy storage in animals.

Final Remarks

  • This lecture covers essential topics in preparation for the upcoming exam, emphasizing molecular biology and the role of carbohydrates in biological systems.

  • Good luck with your exams, and remember, understanding core concepts will serve you well for future assessments!