Introduction to the Study of the Cell and Molecular Biology

Cell biology is reductionist

theory that studying the parts can explain the character of the whole

Robert Hooke

first to use a double lens microscope

Antonie van Leeuwenhoek

-first to observe living cells (microorganisms)

-used a single lens microscope to examine pond water

Cell theory

-articulated in the mid 1800s by Matthias Schleiden, Theodor Schwann, & Rudolf Virchow

1. all organisms are composed of one or more cells

2. cell is structural unit of life

3. cells arise only by division from pre-existing cell (Virchow’s theory)

4. cells contain genetic information (DNA) passed to next cell generation

HeLa cells

-cultured tumor cells isolated from Henrietta Lacks (cancer patient)

-cells continue to undergo mitosis; essential tool for cell biologists

In vitro

done in a test tube, petri dish, cell content dish, etc.

In vivo

inside the organisms; done within organism context

Similarity in cells

-cells from different species share similar structure, composition, and metabolic features

-conserved throughout evolution

-ex: enzymes; villi/microvilli; ATP synthase in mitochondria and bacteria

Genes

-store information and instructions for:

1. constructing cellular structures

2. running cellular activities

3. making more of themselves

Cells acquire and utilize energy

-photosynthesis provides fuel for all living organisms

-animal cells derive energy from the products of photosynthesis (glucose)

-cells can store glucose bond energy in ATP

Metabolism

sum of chemical reactions in a cell

Cells engage in mechanical activities

-cells are active: transport materials, assemble/disassemble, self-transport

-activities based on mechanical changes initiated by motor proteins

Cells respond to stimuli

-cells have receptors that interact with the environment

-ex: hormones, growth factor, extracellular material, surface substance on other cells

-cells respond to stimuli by altering their metabolism, movement, or by dying

Cell self-regulation

-cells are protected from dangerous fluctuations in composition and behavior

-feedback circuits: returns cell to appropriate state

-maintaining order requires constant regulation

Cells evolve

-cells share many features- common genetic code, plasma membrane, ribosomes

-single ancestral cells evolved over 3 billion years to create all living organisms

Prokaryotes

-bacteria

-genetic material in nucleoid region

-small amount of DNA: 600-8000 mb

-arose 3.7 BYA

-cellular reproduction: simple binary fission; some are capable of conjugation

-locomotion: simple; stiff and rigid flagellum that rotates and propels the cell through the medium

-no extensive cytoskeleton

-contain 1 copy of their single circular chromosome

• adept at picking up and incorporating foreign DNA from environment

• plasmids: small circular piece of DNA → antibiotic resistance

Eukaryotes

-animal, plants, protists, fungi

-genetic material in membrane bound nucleus

-simple yeast have 12 mb DNA (most euk. cells have more)

-cytoplasm: crowded with membrane bound organelles and complex cytoskeletal proteins (ribosomes)

-locomotion: cytoplasmic movement, cilia, flagella (made of 9 + 2 microtubule arrangement; ex: sperm)

-cellular reproduction: mitosis- duplicated chromosomes condense into compact structures segregated by mitotic spindles (allow each daughter cell to receive equal genetic material)

Similarities between eukaryotes and prokaryotes

-same genetic language, common set of metabolic pathways, and common structural features

-bounded by plasma membrane as a selectively permeable barrier

-rigid cell wall for protection

-ribosomes (differ in size)

-flagella (differ in form and mechanism)

Evolution of life

-life began ~3-4 BYA; 1st cells were primitive, prokaryotic cells

-cyanobacteria: cells that do photosynthesis —> release oxygen —> changing life; ~2-3 BYA

-eukaryotes: 1-2 BYA

-complex life: ~600 million years ago

Bacteria conjugation

-recipient bacterium

-donor bacterium

-F pilus: connects the two bacteria; transfers plasmids in prokaryotes or tunneling microtubules in eukaryotes

Arachaea

evolutionarily related species that live in extremely inhospitable environments, often referred to as “extremophiles”

Methanogens

convert CO2 and H2 gases into methane

Halophiles

live in extremely salty environments like the Dead Sea or deep sea brine pools with salinity equivalent to 5 M MgCl2

Acidophiles

acid loving prokaryotes that thrive at a pH as low as 0

Thermophiles

live at very high temperatures

Hyperthermophiles

live in hydrothermal vents of the ocean floor up to a temperature of 121 C, the temperature used to sterilize surgical instruments in an autoclave