Module 1 Origin of Cells

First life

Estimated to have emerged ~3.8 billion years ago.

Origin of first cell

Speculated to have arisen from RNA inside a phospholipid bilayer, separating internal and external environments.

RNA world hypothesis

RNA could act as both genetic material and catalyst, able to self-replicate and direct protein synthesis.

Transition to DNA

DNA replaced RNA as the main genetic material because it is more stable.

ATP

Universal source of metabolic energy used by all cells.

Major energy processes

Glycolysis, photosynthesis, oxidative metabolism.

ATP yield

Oxidative metabolism generates 36–38 ATP.

Importance of ATP

Drives cellular processes and energy-dependent reactions.

Prokaryotic cells

Found in Bacteria and Archaea; small, simple, circular DNA, no nucleus(nucleoid) instead, no membrane-bound organelles.

Eukaryotic cells

Found in all other organisms; larger, complex, linear DNA (chromatin), a true nucleus, and contains membrane-bound organelles.

Archaea adaptations

Capable of living in extreme environments such as volcanoes and hot springs. This branched to form the first eukarya.

Endosymbiosis theory

Eukaryotes evolved by engulfing aerobic bacteria (→ mitochondria) and photosynthetic bacteria (→ chloroplasts).

Unique plant cell features

Cell wall, chloroplasts, large central vacuole(break down garbage) and they have acid enzymes

Animal cell features

Lack cell wall, typically smaller vacuoles, contain lysosomes.

Lysosomes

Membrane-bound organelles containing hydrolytic enzymes that break down waste.

Red blood cells (epithelial cells)

No nucleus, no organelles, specialized to carry oxygen only.

Fibroblasts (epithelial)

Cells that secrete extracellular matrix and collagen; important in tissue repair.

Epithelial cells

Form protective sheets lining organs and body surfaces.

Lymphocytes (blood cells)

White blood cells that function in immune defense.

Why use model organisms?

Ethical considerations, easier to handle, short lifespan, faster reproduction, sequenced genomes, conserved pathways.

Ex: mouse

Model organisms

Bacteria (E. coli), yeast (S. cerevisiae), worms (C. elegans), flies (Drosophila), mice, zebrafish, plants (Arabidopsis).

Advantages of E. coli

Divides rapidly, easy to manipulate, useful in gene regulation and transfer studies.

Experimental organisms

Like chickens or frogs. These have genetic variation across all. Some are eukaryotic and some aren’t. Some can be bacteria and some can be viruses

Why is bacteria a good experimental model?

divide rapidly, utilize gene regulation, ideal for gene transfer, E. coli

Viruses in research

Can introduce foreign DNA into host cells, important in molecular biology and potential gene therapy.

Downside of using mice and r.m monkeys for models

They don't suffer from some diseases like humans. Not the best for studying heart disease, for example, so dogs sometimes tend to be better

Rats are better than mice in psychological conditions like PTSD.

Advanced model systems

ideal for research, and they also establish disease models by mimicking human gene defects

In vivo

Studies performed in living organisms.

In vitro

Studies performed outside living organisms, in lab conditions ("in glass").

HeLa cells

First immortal human cancer cell line from Henrietta Lacks in 1951, widely used in research without her consent.

Contributions of HeLa cells

Enabled advances in cancer research, vaccines, genetics, and cell biology.

Nobel Prizes and models

Yeast (2001), C. elegans (2002, 2006), Tetrahymena (2009) for major biological discoveries.

Light microscopy

Uses visible light to pass through specimens; resolution ~0.2 µm.

Resolution

ability to separate structures

Limitations of light microscopy

Resolution decreases as magnification increases.

Fluorescence microscopy

Uses fluorescent dyes to label molecules, absorbs one wavelength and emits another.

Confocal microscopy

Produces sharper images by combining slices at different depths (optical sectioning). Give sharper image

Transmission electron microscopy (TEM)

Electrons pass through thin slices; 2D image; resolution can see as small as~1 nm.

Scanning electron microscopy (SEM)

Electron beam bounces off specimen surface; 3D image; resolution shows as small as 3–20 nm.