chapter 1: cells - the fundamental units of life

vary in size

range from a few micrometers (µm) to about 1 millimeter (mm)

vary in shape

many projections like neurons to submarine-like shape of paramecium

vary in chemical requirements

as simple as CO2, sunlight, and water to more complex macromolecules

vary in function

production of molecules needed by the organism or regulation of movement of the organism by mechanical or electrical forces

central dogma of molecular biology

DNA -> RNA -> protein

cell theory

new cells only come from existing cells

1.) All organisms are composed of cells

- german botanist Matthias Scleiden (1804-1881)

-german zoologist Theodor Schwann (1810-1882)

2.) Cells come only from preexisting cells because cells are self-reproducing

- german physician Rudolph Virchow (1821-1902)

3.) Cells are the basic units of structure and function in organisms

production of new cells...

requires duplication of genome and other cellular components

microscope

invented in the 17th century, allowed scientists to visualize cells

Robert Hooke

observed cork under a microscope and termed the chambers "cells" - actually observed cell walls and empty spaces where cells used to be

Antoni von Leeuwenhoek

visualized live cells from various sources - pond water, rainwater, humans

light microscopes

tissue can be fixed and embedded into a solid wax or resin, sectioned into thin slices, and stained

- can also visualize live cells

- scientists have developed assays that utilize fluorescent markers to visualize different cellular components

electron microscopy (EM)

- invented in the 1930s

- utilizes beams of electrons, rather than light, to visualize cellular detail down to a few nanometers

- tissue must be fixed and embedded in a solid wax or resin, sectioned into very thin slices, and stained

- cannot look at living cells

transmission electron microscopy (TEM)

images thin selections of tissues/cells typically stained with electron-dense heavy metals

scanning electron microscopy (SEM)

images the outside surface of tissues/cells/organisms after being coated with very thin film of a heavy metal

prokaryotes

most diverse and numerous cells on Earth; divided into two domains (bacteria and archaea) that are structurally similar, but biochemically different

bacteria

- cause diseases, but also environmentally important decomposers

- can be useful in manufacturing products and drugs

- cells can divide quickly (~20 mins)

- within a relatively short time, can produce more cells than humans alive

- most diverse and numerous; inhabit a wide range of habitats

- mostly single-celled organisms

archaea

- known to live everywhere, even in most extreme environments, and may be predominant form of life in soil and seawater

- only identified as a separate kingdom in 1977

- more closely related to eukaryotes

- still uncovering the characteristics of these species

eukaryotic cells

nucleus - stores genetic information

mitochondria - generate usable energy from food molecules

chloroplasts - capture energy from sunlight

internal membranes - create intracellular compartments with different functions

cytosol - concentrate aqueous gel of large and small molecules

cytoskeleton - responsible for directed cell movement

* might have originated as predators

nucleus

- generally, most prominent organelle

- enclosed within two concentric membranes (nuclear membrane)

- contains DNA; visible as chromosomes during cell division

mitochondria

- present in essentially all eukaryotic cells

- enclosed within two membranes

- inner membrane folds toward interior of the organelle

- carry out cellular respiration to produce ATP

- contain their own DNA

- can vary in size and shape

chloroplasts

- capture sunlight and use energy to synthesize energy-rich sugar molecules

- process called photosynthesis

- contain their own DNA

endoplasmic reticulum (ER)

network of interconnected spaces enclosed by a membrane and site of cell membrane component synthesis

golgi apparatus

stack of flattened membrane-enclosed sacs (look like flattened pancakes)

- materials are trafficked between organelles using transport vesicles

lysosomes

small, irregular organelles used for intracellular digestion, releasing nutrients from food particles, and breaking down other molecules

peroxisomes

small, membrane-enclosed vesicles that provide a sequestered environment for hydrogen peroxide to inactivate toxins

endocytosis

process by which cells import extracellular materials

exocytosis

process by which cells export materials into the extracellular space

cytosol

- aqueous part of cytoplasm that is left if you remove organelles from a cell

- contains many large and small molecules

- acts more like a gel than a liquid

- constantly in motion

cytoskeleton

systems of protein filaments in a cell, composed of:

actin filaments - abundant in all cells, but play a central part of machinery that regulates muscle contraction

microtubules - thickest filaments formed as hollow tubes that reorganize in dividing cells to segregate duplicated chromosomes

intermediate filaments - strengthen animal cells

"model" organisms

- all cells have similar basic properties; outer membrane, genome

- thought to have arisen from a common ancestor

- studying a subset can provide information about all cells

escherichia coli (E. coli)

- small, rod shaped cell

- inhabits guts of humans and other vertebrates

- rapid growth in culture

- used to determine fundamental mechanisms (DNA replication, decoding of genetic information to make proteins)

- prokaryote - limited use for understanding eukaryotic cells

saccharomyces cerevisiae (Brewer's yeast)

- single celled eukaryote (fungus)

- used for brewing beer and baking bread

- rapid reproduction when nutrients available

- contains mitochondria (though not chloroplasts)

- used to determine basic mechanisms of eukaryotic cells

arabidopsis thaliana (model plant)

- flowering plants share close evolutionary relationship

- multicellular organism

- small, common weed

- reproduce in large numbers (thousands of offspring in 8-10 weeks)

- used to study development and physiology of plants (including crop plants) and the evolution of plant species

drosophila melanogaster

- invertebrate, multicellular animal

- used to demonstrate chromosomes contain genes (units of heredity), and to understand the development of multicellular organisms

- contain genes similar to human genes

caenorhabditis elegans

- invertebrate, nematode worm

- hermaphrodite (produce both sperm and eggs)

- all adult worms contain the exact same number of body cells (959)

- used to understand cell division, development, and apoptosis

zebrafish (Danio rerio)

- vertebrate, multicellular animal

- transparent for the first few days of development (book says 2 weeks, but pigment starts to develop around day 3)

- contain genes similar to human genes

mouse (Mus musculus)

- vertebrate, multicellular animal

- mammal

- used to study mammalian genetics, development, and disease

- can manipulate genome to study how genes affects presentation