Cell Theory

2014-15

History• Cells were unknown

until the invention of light microscopes in the 1650’s

• two scientists working independently built the first microscopes

– Anton von Leeuwenhoek in Holland

– Robert Hooke in England

Anton von Leeuwenhoek

• Studied pondwater, sour milk, and semen

• named moving organisms “animalcules”

Anton von Leeuwenhoek

People thought human sperm cells contained tiny human beings called a homunculus

Robert Hooke• Studied cork - a

kind of tree bark

• named the structures he saw “cells” because they reminded him of the small rooms monks slept in.

Matthias Schleiden (1804-1881)

–German lawyer-turned-botanist

–Studied plants, preferring to study plant structure under the microscope

–Determined that all plants are made of cells

Theodor Schwann: 1810-1882

• German physiologist

• Studied animal tissues, particularly nerve and muscle tissues

• Determined that all animals are made of cells

Rudolph Virchow (1821-1902)

Omnis cellula e cellula ("All cells come from cells")

The Cell Theory

• The cell theory has three parts:–All living things contain at least one

cell–Cells are the smallest living units of

matter–Cells can only come from pre-existing

cells

Modern light microscopes

Scanning electron microscopes

• 3-D images of outside of objects

• 25-50 million times magnification

Pollen grains:

Transmitting electron microscope

• Looks at VERY thin slices of substances

• Sees the inner workings of the items

Disadvantages of electron microscopes

• Expensive

• Non-portable

• Can only look at dead things

All living things contain at least one cell

• Many scientists have observed many types of living things

• Each of them noted that no matter what they observed, ALL LIVING THINGS contain cells

Cells are the smallest living units of matter

–scientists realized that when cells were dissected or broken open they died (still happens despite our fancy technology)

–This meant that whatever “life” is, it is something that happens inside cells

Cells can only come from pre-existing cells

–Except the first cell

–has not been disproved yet- no scientist has ever built a living cell from nonliving molecules

Spontaneous Generation

• Until 1850, most people believed that living things could spontaneously appear from non-living material

Spontaneous generation

• People believed that mice could be “created” spontaneously by

putting grain in dark, quiet place and leaving it for a few weeks.

• Scientists sought to disprove it

Francesco Redi

• First to challenge spontaneous generation

• Did not accept that flies appeared from rotting meat

Redi’s Experiment

– IV= cover

– DV= presence of flies

– Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies

Redi’s Conclusions

–Flies lay eggs, grow into maggots, grow into flies

–If flies can’t lay eggs, then no new flies

Objections to Redi

–“sealing the jar closed kept a magical essence from entering the rotting meat and bringing it to life”

–“Scientists seek only to challenge belief systems and stir things up”

Lazzaro Spallanzani

• microbes that spoil food come from the air and can be killed by boiling

• IV= air, DV= food spoilage

• Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil

Spallanzani’s Experiment

• Flask 1: boiled broth, open

• Flask 2: boiled broth, sealed shut

• Results–Flask 1 spoiled

–Flask 2 did not spoil

Objections to Spallanzani

• Sealing the flask blocked the magical life force in the air from getting to the broth.

Louis Pasteur• 1822. France• Supported that

spontaneous generation is a myth

• Invented pasteurization (sterilization by heat)

Pasteur’s Experiment

• Used special “swan-neck flasks” that allowed air in but kept bacteria out

Pasteur’s Experiment

• IV= bacteria, DV= spoiling broth

• Hypothesis; If boiled broth is kept free of bacteria, then it will not spoil even if air can reach it.

Spontaneous generation is dead!

• Redi didn’t believe in it, and did an experiment using flies

• Spallanzani didn’t believe in it, and experimented with broth

• Pasteur disproved it conclusively with his open-air yet spoilage free flasks.

Pasteur is the father of modern microbiology

• supported the last part of the cell theory: cells only come from pre-existing cells

• showed that heat can be used to sterilize foods and preserve them

As a result…

• in the late 1870’s, doctors start to wash their hands and instruments before operating...some even start wearing gloves

Organelles are membrane-bound cell

parts•Mini “organs” that have unique functions

•Located in cytoplasm (everything inside the cell membrane)

Cells have evolved two different architectures:

• Prokaryote

• Eukaryote

Prokaryote cells are smaller and simpler

• Commonly known as bacteria

• Single-celled (unicellular) or

• Filamentous (strings of single cells)

Prokaryote cells

•Very small •These are prokaryote

•E. coli bacteria on the head of a steel pin.

Prokaryote Cells

• cytoplasm: inner liquid filling

• DNA in one big loop called the NUCLEOID

Prokaryote Cells

• ribosomes: for building proteins

• Reproduce using BINARY FISSION

Endosymbiont theory:

•a prokaryote ancestor “eats” a smaller prokaryote

•They join forces and become more complex

•

Eukaryotes

• Bigger and more complex• Have membrane-bound

organelles including NUCLEUS• Have chromosomes• can be multicellular• include animal, plant, fungal, and

protist cells

•Cell membrane–delicate phospholipid and protein skin around cytoplasm

–found in all cells

Cell Structures

•Nucleus–a membrane-bound sac evolved to store the cell’s chromosomes-DNA wrapped around histones

–has nuclear pores: holes to let substances in and out

Parts of a nucleus:

ribosomes

•Nucleolus–inside nucleus

–location of ribosome factory

–made of RNA

nucleoplasm

• a highly viscous liquid that includes the chromosomes and nucleoli.

Chromatin

• Unraveled DNA (not involved in cell division, so not in our familiar chromosomes- looks like tangled yarn)

•mitochondrion– makes the cell’s energy (ATP) via cellular respiration–the more energy the cell needs, the more mitochondria it has

Parts of a mitochondrion:

•Ribosomes–Very small; build proteins from amino acids in cytoplasm

–may be free-floating, or

–may be attached to ER

–made of rRNA

•Endoplasmic reticulum–may be smooth: builds lipids and carbohydrates

–may be rough: stores proteins made by attached ribosomes

Endoplasmic reticulum

• Part of intracellular transport system; always near nucleus

•Golgi Complex–takes in sacs called vesicles of raw proteins from ER–sends out vesicles containing finished cell products–Smaller than ER and closer to cell membrane

Golgi Complex

Golgi Complex

• Proteins in the Golgi Complex can be stored for later use, chemically changed, or exported to outside of cell

•Lysosomes–sacs filled with digestive enzymes

–digest worn out cell parts

–digest food absorbed by cell

Lysosomes

• Can also be used to reabsorb body parts that are no longer needed– This is how you lost your tail <3

•Centrioles–pair of bundled tubes (microtubules)

–organize cell division

Centriole

• Also called centrosome

• Made of protein filaments

• Part of cytoskeleton

Cytoskeleton

•found throughout cytoplasm

•gives shape to cell & moves organelles around.

Structures found in plant cells•Cell wall–very strong–made of cellulose (in plants)–protects cell from rupturing

Cell wall

• Also find cell walls in fungi (chitin), bacteria (peptidoglycans), and protists (cellulose)

•Vacuole–huge water-filled sac–keeps cell pressurized–stores starch, signaling molecules, etc.

•Chloroplasts (also in some protists)–filled with chlorophyll–turn solar energy into food energy

Chloroplasts:

Eukaryote cells can be multicellular

•The whole cell can be specialized for one job•cells can work together as tissues•Tissues can work together as organs

Label the cells