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The Cellular Basis of Life

• Historical contributions

• Modern Cell Theory

• Types of Microscopes

• Micrographs

•Cell membranes

• Membrane transport

• Nucleus

•Organelles

Contributors to Our Knowledge of Cells

Anton

von LeeuwenhoekAssembled the first microscope

Robert Hooke Observed and named “cells”

Robert Brown Discovered the nucleus.

Schleiden and Schwann

Determined that all plants and animals are made of cells.

Rudolf Virchow Cells come only from pre-existing cells.

Modern Cell Theory

1. All living things are made of cells.2. Cells are the basic structural unit (ie,

building blocks) of life (plant, animal, bacterial, etc.)

3. All cells come from other (pre-existing) cells.

4. The way a cell is made is determined by its function (ie, what it has to do) = principle of complementarity

Visualizing Cells

• Done using microscopes.

• Different types– Compound light microscopeCompound light microscope: most common.

Passes beam of light through specimen. Contains more than one lens and magnifies up to 1000 times. Can be used to view living organisms.

EYEPIECE

OCULAR LENS (inside)

REVOLVING NOSEPIECE

COARSE ADJUSTMENT KNOB

FINE ADJUSTMENT KNOB

STAGE

DIAPHRAGM

LIGHT SOURCE

“Compound” lenses…

• COMPOUND MAGNIFICATION!!

• Which combination would show the largest AREA?• Which combination would you use to examine details?

Eyepiece LensObjective

LensTotal

Magnification

15x 15x

10x 10x

20x 40x

Compound Micrographs

Electron Microscopes

• TRANSMITTING = TEM• Specimen is thinly sliced.• Electrons pass through and

image forms on fluorescent screen.

• SCANNING = SEM• Specimen is coated

with metal (Os,Pb,Au)• Electrons bounce off

surface to form image.

Concentrates a beam of electrons within a vacuum; magnifies up to 1,000,000 times. Used to view much smaller organisms.

Sample Electron Micrographs

Types of Cells

• PROKARYOTE• Smaller, more

primitive• Bacteria• Fewer organelles• No nucleus; instead

has nucleoid region

• EUKARYOTE• Larger (~10 x)• Complex inner

membrane system• More organelles• Contains a true

nucleus

*Nucleus

*Endomembrane system

*Mitochondria

*Chloroplasts

Key features of Eukaryotic Cells:

What molecule is this?

The Fluid Mosaic Model of theCell Membrane

.

AMPHIPATHIC:having both hydrophilic and hydrophobic areas

Cell Wall

• Found outside the cell membrane in PLANTS, FUNGI, and BACTERIA.

• Plants use pressure against the cell wall (called turgor pressure) to help support it.

The Nucleus

• “Control center” of the cell

• Contains DNA which determines cell activity through the manufacture of proteins

The rest of the cell …

• Cytoplasm - semi-liquid material which fills the space between the membrane and the nucleus.

• Contains structural fibers called microfilaments.

• Contains “little organs” (organelles) which each have a specific job to do.

Organelles

Ribosomes Not bound by a membrane

Assemble proteins

Endoplasmic reticulum

May be rough or smooth

Process and transport proteins

Golgi apparatus Modify proteins and ship to new site

Contain special enzymes to attach carbohydrates or lipids to proteins delivered by the ER

Vacuoles Sites for storage of materials

Animals store proteins, fats or carbohydrates; plants store water or salts.

Organelles, continuedLysosomes Sacs filled with chemicals

and enzymes.Attach target, release enzymes which recycles components.

Mitochondria Powerhouse of the cell; double membrane allows maximum surface area.

Produces energy (ATP) for cellular activities using a carbohydrate source.

Nucleolus Dark area found inside the nucleus of eukaryotic cells.

Produces ribosomes.

Plastids Storage sacs. Contain starch, pigments,

Chloroplasts Contain chlorophyll Important in photosynthesis. Found only in plants, algae.

Cell Permeability

Membrane Transport Mechanisms

• PASSIVE TRANSPORT• Powered by the concentration

gradient• Must move down the gradient

from [high] to [low]• Examples: diffusion• At equilibrium, concentration is

equal on both sides.• Osmosis = diffusion of water• Facilitated diffusion = uses

carrier molecule (ex: membrane protein)

• ACTIVE TRANSPORT• Requires the use of ATP• Can move up the gradient• Examples: ion pumping• Bulk transport

– EXOcytosis moves material OUT of the cell

– ENDOcytosis moves material INTO the cell

» Water in = pinocytosis

» Food in = phagocytosis

Vesicle-Mediated Transport

What process is this?

Tonicity

Solution is HYPOTONIC

Solution is HYPERTONIC

Complexity of Organisms

• Single-celled organisms are unicellular.• Other organisms are multicellular.• In order to maintain complexity, there must

be a hierarchy of structure.• Cells form tissues which form organs;• Organs are arranged into organ systems

which all combine to form the organism.