Microscopes provide windows to the world

of the cell

Cellular Diversity• The average adult has

nearly 100 trillion cells• There are about 200

different types of cells• Cells come in a variety

of shapes and sizes• Cellular diversity

permits organization of cells into more complex tissues and organs

History of the Microscope

• 1665, Robert Hooke described cells using a light microscope

• Magnification vs resolution• Highest magnification of l.m. = 1000x• 1950, Electron microscope allowed

researchers to clearly identify organelles• There are 2 types:

– Transmission– Scanning

Transmission Electron Microscope

(TEM)• e- transmitted through

specimen are focused

• image magnified by electromagnetic lenses to bend trajectories of charged e- – Used to study internal cell

structure – Image is focused onto a viewing

screen/film

Scanning Electron Microscope

(SEM)• e- beam scans surface of

specimen that is coated with a thin film of gold

• Beam excites secondary e- on sample’s surface

• Secondary e- are collected & focused on viewing screen– Useful for studying surface of

specimen– SEM has great depth of field &

produces 3D image

SEM images

Disadvantages of Electron microscopes

• Can usually only view dead cells because of the elaborate preparation required

• May introduce structural artifacts

Cell Fractionation

• Technique that enables researchers to isolate organelles without destroying their function– Disrupted cells are

centrifuged to isolate components of different sizes, densities, and shapes

Surface area: volume ratio

Place in order depending on which will dissolve fastest slowest•granulated sugar•Powdered sugar•Sugar cube•Fine sugar

Why do you cut up potatoes to boil them?

Cells

• Prokaryotic vs Eukaryotic

• Cell sizes (0.1-100um)– What limits a cell from being too large?– Too small?

• Eukaryotic cells have 1000x volume of prokaryotic cells, but only 100x the surface area. How can they compensate for the small surface area to volume ratio?

Prokaryote“before nucleus”

Eukaryote“true nucleus”

A Generalized CellCytoplasm

- all the cellular contents between the plasma membrane and the nucleus

- cytosol - the fluid portion, mostly water

*site of many chem. Rx.

- organelles - subcellular structures having characteristic shapes and specific functions

The cytoskeleton - network of protein filaments throughout the cytosol-provides structural support for the cell-three types according to increasing size: microfilaments (cables), intermediate filaments (cables), and microtubules (support beams)

Resist tension

Bearingtension

Resistcompression

Organelles• Centrosome -

located near the nucleus, consists of two centrioles

Cilia and Flagella

Cilia - short, hair-like projections from the cell surface, move fluids along a cell surface

Flagella - longer than cilia, move an entire cell; ex. sperm cell’s tail

Internal Membranes• Partitions cell into compartments

• Have unique lipid & protein compositions depending upon their specific fx.

• Participate in metabolic reactions (enzymes)

• 1. Nuclear envelope - a double membrane that separates the nucleus from the cytoplasm

– Nuclear pores - numerous openings in the nuclear envelope, control movement of substances between nucleus and cytoplasm

– Nucleolus - spherical body that produces ribosomes

Class I: membrane derived

2. Endoplasmic reticulum - network of membranes in the shape of flattened sacs or tubules

- Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins

-Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs

•3. Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae - modify, sort, and package proteins for transport to different destinations- proteins are transported by various vesicles

4. Vesicles

• Sacs made of membrane

• Transport substances throughout cell and to/fro membrane

5. Vacuoles

• Food vacuole formed by phagocytosis (protists & macrophages)

• Contractile vacuole pumps excess water from cell (protozoans)

• Central vacuole enclosed by membrane (tonoplast); stores organic compounds, ions, poisons, provides turgor pressure (plants)

6. Lysosomes• Sequesters destructive enzymes from cytosol• Maintains optimum acidic environment for enzyme

function

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Peroxisome

• Bound by a single membrane derived from lipids w/i cell

• Contains enzymes that transfer Hydrogen atoms from various substrates to oxygen (H2O2).

• Contains catalase that converts H2O2 to water.

• Breaks down fatty acids • Detoxification of alcohol &

other poisons (liver)

Class II: bacteria like organelles (energy production)

Mitochondria - the “powerhouses” of the cell– Generate ATP

– More prevalent in physiologically active cells: muscles, liver and kidneys

– Inner and outer mitochondrial membranes

– Cristae - the series of folds of the inner membrane

– Matrix - the large central fluid-filled cavity

– Self-replicate during times of increased cellular demand or before cell division

Class III: Involved in Gene Expression