Unit #4 Cells_2024-25 (1)

Cell Size and Scale

  • Human Height:

    • Approximately 10 m (average height of humans).

  • Cell Length:

    • Varies widely among organisms, from bacteria (about 0.1 m) to chicken nerve and egg muscle cells (0.1 m).

  • Relative Sizes on a Logarithmic Scale:

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      Frog egg: 1 mm, bacteria egg: 0.1 mm, and viruses range from 10 nm to 100 nm.

  • Micron Measurement:

    • Most plant and animal cells are around 10-100 um in size; some bacteria are about 1 um.

    • Mitochondria: 1 um, sperm cells: 100 nm, ribosomes: 10 nm, and proteins/lipids are about 1 nm;

  • Atoms:

    • The smallest unit of matter, around 0.1 nm.

About the ACT

  • Overview:

    • The ACT is an entrance exam widely used by colleges and universities for admissions.

  • Structure:

    • Multiple-choice format administered by ACT, Inc.

  • Purpose:

    • Measures high school students' readiness for college and provides a standardized metric for college admissions officers.

  • Components Reviewed:

    • Tests scores, high school GPA, course selection, letters of recommendation, extracurricular activities, interviews, and personal essays.

  • Importance:

    • Varies by institution.

ACT Exam Details

  • Timing and Questions:

    • English: 45 min, 75 questions.

    • Math: 60 min, 60 questions.

    • Reading: 35 min, 40 questions.

    • Science: 35 min, 40 questions.

    • Writing (Optional): 40 min, 1 essay.

    • Total Time: 175 minutes; 215 minutes if including Writing.

Indicators and Tests

  • Test Indicators and Responses:

    • Lugol's Iodine: Start amber, turns bluish/black to indicate starch presence.

    • Benedict’s Test: Start aqua-blue, changes to orange after heating to indicate simple sugars.

    • Biuret Reagent: Start cobalt-blue, turns purple for the presence of proteins.

    • Brown Paper Test: Opaque to translucent indicates lipids.

Overview of Viruses

  • General Characteristics:

    • Viruses are mobile genetic elements, non-cellular and likely of cellular origin.

    • They function as obligate intracellular parasites.

  • Main Function:

    • Deliver genetic material (DNA/RNA) to host cells to produce new viruses.

    • Depend on host cells for reproduction and essential biochemical processes.

Viral Structure and Function

  • Basic Composition:

    • Typically characterized by viral genome, capsid, and possibly an enveloping membrane.

  • Virus Examples:

    • Tobacco Mosaic Virus (TMV), Adenoviruses, Influenza viruses, and Bacteriophage T4.

Tobacco Mosaic Virus (TMV)

  • Structure:

    • Positive-sense single-stranded RNA virus.

    • Helical rod-shaped virion, notably infecting a variety of plant species.

    • Historical significance as the first virus discovered.

HIV Overview

  • Structure:

    • Key components: gp120, gp41, RNA genome, reverse transcriptase.

  • Difficulty in Cure:

    • The complex structure and rapid mutation make HIV challenging to treat effectively.

Gram Staining and Bacterial Classification

  • Gram Positive and Negative:

    • Gram-positive bacteria appear purple due to a thick peptidoglycan layer.

    • Gram-negative bacteria appear pink due to a thinner peptidoglycan layer and outer membrane.

  • Bacterial Morphology:

    • Cocci (spheres), Bacilli (rods), and Spirilla (spirals) classifications.

Endosymbiotic Theory

  • Concept:

    • Evolutionary theory suggesting that mitochondria and chloroplasts originated from free-living prokaryotes taken up by larger cells.

  • Implications:

    • Present results in complex eukaryotic cells characterized by compartmentalization.

Nobel Prize in Medicine**

  • Significant Discovery:

    • Details not provided; however, it is noted that the profound impact of viral studies has led to advanced understanding in biological sciences.