(10) the cell theory 9 19

The Cell Theory – a timeline

• Late 1500’s: -first lenses used in Europe

-used to determine cloth quality (weave

and precision)

-combos of lenses gave better view

• Early 1600’s: Leeuwenhoek uses microscope to

study nature

Early 1600’s

• Leeuwenhoek

• first to view pond water organisms

• First to see living microscopic orgs

• Made careful sketches

Early 1600’s

Robert Hooke ( 1665)

• Used light microscope to look at thin slices of plant tissues -- cork

• Looked empty, like monk’s chamber

• Called tiny chambers

“cells”

Matthias Schleiden 1838

• German Botanist (plants)

• All plants looked at were made of cells, so concluded:

“All plants are

made of cells.”

Theodore Schwann -- 1839

• German scientist who studied animals -- zoologist

• Saw that all animals he studied were cellular so concluded:

“All animals are made of cells.”

Rudolf Virchow -- 1855• German physician

who studied cell reproduction

• “Where a cell exists, there must have been a preexisting cell…..”

The Cell Theory

• All living things are composed of cells

• Cells are the basic units of structure and function in living things

• New cells are produced from existing cells

Prokaryotes vs. Eukaryotes

• Prokaryotes: *NO NUCLEUS *Small and Simple – few

organelles *Have cell membranes and cytoplasm

Ex. Bacteria • Eukaryotes: *Contain nuclei

*Contains organelles that perform specialized functions

*Uni-or multicellular

Figure 7.4 A prokaryotic cell

Basic Cell Structures

• Cell membrane – thin, flexible barrier around cell

• Nucleus – large, centralized structure that contains genetic material and controls cellular activities

• Cytoplasm – material inside membrane (but not inside the nucleus) that supports the internal cell shape and organelles

Basic cell parts: cell membrane and cytoplasm

• Cell membrane – *provides barrier between internal

and external environment of cell

*is semi-permeable (some things can go in, some cannot; some things can exit, some never can)

*made up of phospholipid bilayer with proteins embedded that allow for needed passage of large molecules

• Major job of cell membrane is to maintain the cell’s environment – establish homeostasis

Fluid Mosaic Model

• Cell membrane and embedded proteins are not locked into position – they flow against one another as the cytoplasm and the external liquid environment dictate (so, is fluid)

• There are MANY different components of the cell membrane – it is a mosaic of many parts

Figure 8.6 The detailed structure of an animal cell’s plasma membrane, in cross section

Nucleus

• Largest organelle• Enclosed by nuclear envelope or membrane,

which is a double membrane – each of which is a lipid bilayer!!!

• Nuclear membrane has pores in it• Contains inactive DNA – chromatin• When gets ready to divide, chromatin condenses

into chromosomes• Directs protein synthesis by synthesizing mRNA

and sending to ribosomes in the cytoplasm

Cytoplasm

• Entire region between the nucleus and the cell membrane

• The semifluid substance that fills this area is called CYTOSOL, and this is what the organelles are suspended in

Cell Wall

• Found in plant cells (another barrier in ADDITION to the cell membrane)

• Protects the cell

• Gives support to cell

• Made of polysaccharide called cellulose

• Is very porous and allows molecules to pass through, but is NOT SELECTIVELY PERMEABLE

Organelles• Control:

*Nucleus (plant and animal)

• Assembly, Transport, and Storage:*Endoplasmic reticulum (plant and animal)*Ribosomes (plant and animal)*Golgi apparatus (plant and animal)*Vacuoles (plant and animal)*Lysosomes (plant and animal)

• Energy transformations:*Chloroplasts (plant only)*mitochondria (plant and

animal)

Endoplasmic reticulum – “highway system”

• EXTENSIVE – accounts for more than half the total membrane system in eukaryotic cells

• Name means “little net within the cytoplasm”• Smooth and rough e.r. are actually connected, not

distinct, separate sections• Job is to transport materials quickly from one

place to another in cell

Figure 7.11 Endoplasmic reticulum (ER)

Smooth e.r.

• Functions in synthesis of lipids, metabolism of carbs, detoxification of drugs and poisons

*Lipids – oils, phospholipids, steroids(sex hormones and adrenal hormones)

*Liver cells – glycogen; gets converted to glucose phosphate which cannot leave cell, so e.r. makes enzyme that converts this to glucose

*Detox – liver; adds hydroxyl groups to drugs, makes them soluble and able to be

flushed out of body

Rough e.r.

• Makes secretory proteins

(ex. Insulin made by pancreatic cells)• Most are glycoproteins (proteins covalently bound

to carbs)• Rough e.r. is also a membrane factory – grows by

adding proteins and phospholipids; parts can be taken from here and added to other membrane systems using the vesicles for transport

Ribosomes“protein factories”

• Sites of protein synthesis• Are made of rRNA and protein• Cells with high rates of protein synthesis have MANY

ribosomes (human pancreas cell has MILLIONS of ribosomes)

• Are “free” ribosomes in cytosol that make proteins for the cell that they are INSIDE of

• Ribosomes that are attached to endoplasmic reticulum (bound) are making proteins for packaging and export OUTSIDE OF CELL

Figure 7.10 Ribosomes

Golgi apparatus“Gift wrapper/UPS system”

• Finishes, sorts, ships cell products• Golgi will modify products as needed –

gives more variety by removing some monomers and substituting others

Figure 7.12 The Golgi apparatus

Vacuoles“Bank Vaults” or “trash cans”

• Sites of storage in cells

*good things stored – water, minerals,

food etc.

*bad things stored – broken down cell parts, waste

Lysosomes“suicide bags”

• Membrane-bounded sac of hydrolytic enzymes• Different lysosomes break down each of the major

classes of macromolecules – proteins, polysaccharides, fats, nucleic acids

• Work best at pH of 5• Used in autophagy – recycle the cell’s own

organic material for use

Mitochondria and Chloroplasts“powerhouses”

• Mitochondria – carry on cellular respiration – sites of energy production in cell (glucose broken down to produce ATP)

• Chloroplasts – carry on photosynthesis

– sites where sunlight, CO2 and water are converted into glucose

Figure 7.17 The mitochondrion, site of cellular respiration

Figure 7.18 The chloroplast, site of photosynthesis

Cytoskeleton“hay in mud makes bricks”

• Network of fibers extending into cytoplasm of cell

• Provides structural support, and aids in cell motility and cell regulation

• Made up of microtubules (thickest), microtubules (thinnest), and intermediate filaments

Cilia and Flagella“hairs and tails”

• Cilia are short projections from cell body – hair-like

• flagella are much longer – whip-like• Movement may not be for entire organism;

may be part of a larger unit – ex. Cilia lining windpipe propel foreign substances out…

Organelles do not work alone…

• Cell is a dynamic interaction of ALL of its parts – literally, the basic unit of life….