Bio Chap. 4 | 4.1-4.3

Learning Outcome 1

Outline the four main stages that are hypothesized to have led to the origin of living cells.

Learning Outcome 2

Explain the experiments of Miller and Urey.

Learning Outcome 3

Explain the concept of an RNA world and describe how it could have evolved into a DNA/RNA/protein world.

Miller-Urey Experiment Setup

The experiment used a mixture of gases (methane, ammonia, hydrogen, water vapor) with electrical sparks to simulate early Earth's atmosphere and lightning.

Miller-Urey Experiment Results

The experiment produced amino acids and other organic compounds, demonstrating that organic molecules could form spontaneously under early Earth conditions.

RNA World Hypothesis

The hypothesis that RNA molecules were the first self-replicating molecules and that they could both store genetic information and catalyze chemical reactions.

Four Main Stages - Origin of Life

1) Formation of organic molecules, 2) Formation of polymers, 3) Formation of protocells with membranes, 4) Development of self-replicating systems

Reducing Atmosphere Hypothesis

Early Earth had an atmosphere with little oxygen (reducing conditions) that favored the formation of organic molecules from inorganic precursors.

What conditions did the Miller-Urey experiment simulate?

Early Earth's reducing atmosphere with methane, ammonia, hydrogen, and water vapor, plus electrical discharge to simulate lightning.

Why was the Miller-Urey experiment significant?

It showed that organic compounds (amino acids) could form spontaneously from inorganic materials under early Earth conditions, supporting abiogenesis.

What is abiogenesis?

The process by which living organisms arise naturally from non-living matter, such as simple organic compounds.

What makes RNA special in the RNA World hypothesis?

RNA can both store genetic information (like DNA) and catalyze chemical reactions (like proteins), making it a candidate for the first self-replicating molecule.

What are protocells?

Early cell-like structures with membranes that could maintain different internal conditions from their environment, a step toward true living cells.

Why was Earth's early atmosphere important for life's origin?

The reducing atmosphere (lacking oxygen) prevented the breakdown of organic molecules and allowed complex chemistry to occur.

What is the significance of self-replicating systems?

They represent the transition from non-living chemical reactions to true life, as they can reproduce and evolve through natural selection.

Learning Outcome 1

Calculate the linear magnification in microscopy using the magnification formula and scale bars.

Learning Outcome 2

Compare and contrast the different types of light and electron microscopes and their uses.

What is magnification?

The degree to which the size of an image is larger than the object itself. It is the ratio between the size of the image and the actual size of the object.

What is resolution?

A measure of the clarity of an image; it is the ability to observe two adjacent objects as distinct from one another.

Light microscope magnification range

Up to 1500x magnification

Electron microscope magnification range

Up to 500,000x magnification

What limits the resolution of light microscopes?

The wavelength of light - shorter wavelengths give better resolution. The theoretical limit is about 0.2 micrometers.

What are the two main types of electron microscopes?

Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM)

TEM (Transmission Electron Microscope)

Uses a beam of electrons transmitted through ultra-thin specimens to create detailed internal images. Provides high magnification and resolution of internal structures.

SEM (Scanning Electron Microscope)

Uses a beam of electrons to scan the surface of specimens, creating detailed 3D-like images of surfaces and external structures.

Advantages of light microscopy

Can observe living specimens, relatively inexpensive, easy to use, can use various stains and techniques, specimens don't need special preparation.

Disadvantages of light microscopy

Limited magnification (up to 1500x), limited resolution due to wavelength of light, less detail than electron microscopy.

Advantages of electron microscopy

Very high magnification (up to 500,000x), excellent resolution, detailed internal and surface structures visible.

Disadvantages of electron microscopy

Specimens must be dead, expensive equipment, complex sample preparation, cannot observe living processes, specimens must be in a vacuum.

What is the formula for calculating magnification?

Magnification = Image size ÷ Actual size, or M = I ÷ A

How do you calculate actual size?

Actual size = Image size ÷ Magnification, or A = I ÷ M

How do you calculate image size?

Image size = Actual size × Magnification, or I = A × M

What are scale bars used for?

Scale bars are used to determine the actual size of structures in microscope images by providing a reference measurement.

What is the difference between magnification and resolution?

Magnification is how much larger an image appears, while resolution is the ability to distinguish between two separate points or structures.

Why can't light microscopes achieve the same resolution as electron microscopes?

Because electron microscopes use electrons with much shorter wavelengths than visible light, allowing them to resolve much smaller details.

What type of specimens can be viewed with light microscopy?

Living or dead specimens, including cells, tissues, and organisms that are transparent or can be stained.

What type of specimens can be viewed with electron microscopy?

Only dead specimens that have been specially prepared, dehydrated, and coated with metal for SEM or cut into ultra-thin sections for TEM.

What is fluorescence microscopy?

A type of light microscopy that uses fluorescent dyes or proteins to label specific structures, allowing them to be viewed with enhanced contrast and specificity.

What factors affect image quality in microscopy?

Magnification, resolution, contrast, and the quality of specimen preparation.

Learning Outcome 1

Compare and contrast the general features of prokaryotic and eukaryotic cells.

Learning Outcome 2

Explain how the proteome underlines the structure and function of a cell.

Learning Outcome 3

Analyze how cell size and shape affect the surface area/volume ratio.

What are the two main categories of cells?

Prokaryotic cells (bacteria and archaea) and eukaryotic cells (plants, animals, fungi, protists).

Key difference between prokaryotic and eukaryotic cells

Prokaryotic cells lack a membrane-bound nucleus and organelles, while eukaryotic cells have a membrane-bound nucleus and specialized organelles.

What is the proteome?

The complete set of proteins that a cell is currently making or an organism can make. It determines the structure and function of cells.

How does the proteome relate to cell characteristics?

The proteome determines cell structure, function, and capabilities. Different cell types have different proteomes even with the same genome.

What is the plasma membrane?

The boundary that separates the living cell from its surroundings. It controls what enters and exits the cell.

What is cytoplasm?

The region of the cell that is outside the nucleus (in eukaryotes) or nucleoid region (in prokaryotes). It contains the cytosol and organelles.

What is the nucleoid region?

In prokaryotic cells, the area where the genetic material (DNA) is located, but it's not enclosed by a membrane.

What is the nucleus?

In eukaryotic cells, the membrane-bound organelle that contains the cell's genetic material (DNA) and controls cell activities.

What are ribosomes?

Small structures found in all cells that synthesize proteins by translating messenger RNA.

Where are ribosomes found in prokaryotic cells?

Free-floating in the cytoplasm, attached to the plasma membrane.

Where are ribosomes found in eukaryotic cells?

Free in the cytoplasm, attached to the endoplasmic reticulum, and inside organelles like mitochondria and chloroplasts.

What are organelles?

Membrane-bound structures found in eukaryotic cells that perform specific functions (mitochondria, chloroplasts, ER, Golgi apparatus, etc.).

Surface area to volume ratio formula

SA:V = Surface Area ÷ Volume

Why is surface area to volume ratio important for cells?

It affects the cell's ability to exchange materials with its environment. As cells get larger, the ratio decreases, limiting efficient exchange.

How does cell shape affect surface area to volume ratio?

Elongated or flattened shapes increase surface area relative to volume, improving material exchange efficiency.

What happens to SA:V ratio as cell size increases?

The surface area to volume ratio decreases, making it harder for the cell to exchange materials efficiently with its environment.

Why do cells remain relatively small?

To maintain an efficient surface area to volume ratio for adequate exchange of nutrients, gases, and waste products.

What is a bacterial cell wall made of?

Peptidoglycan, a polymer that provides structural support and protection.

What is compartmentalization in eukaryotic cells?

The organization of cellular functions into membrane-bound organelles, allowing for specialized environments and efficient cellular processes.

What are the main components of all cells?

Plasma membrane, genetic material (DNA), ribosomes, and cytoplasm.

How do prokaryotic cells organize their genetic material?

DNA is located in the nucleoid region, not enclosed by a membrane, and may also be found in plasmids.

How do eukaryotic cells organize their genetic material?

DNA is enclosed within a membrane-bound nucleus, organized into chromosomes.

What is the significance of membrane-bound organelles?

They allow for compartmentalization, creating specialized environments for different cellular processes and increasing cellular efficiency.

What determines cell function?

The specific proteins produced (proteome), which are determined by gene expression patterns and cellular needs.

Example of how cell shape affects function

Red blood cells are biconcave discs to maximize surface area for oxygen exchange while maintaining flexibility to move through capillaries.