CELLS

The Fundamental Units of Life

Cell Theory

1. All organisms are composed of 1 or more cells.

2. The cell is the basic living unit, providing organization for all organisms.

3. All cells arise from preexisting cells.

Cells Are Small• Most are too small to be

seen with the unaided eye…so Microscopes are used.

• A Light Microscope uses visible light shone through glass lenses.

• A “thin section” of specimen is required.

• van Leeuwenhoek

Principles of Microscopy

• LIGHT

• REFRACTION

• MAGNIFICATION

• RESOLUTION

RESOLUTION

Cells!

CELLS

• Eukaryotic Cells (animals, plants, fungi, protists)

– Complex & relatively large.– Membrane-bound nucleus & organelles.– 80-S Ribosomes.

• Prokaryotic Cells (archaea, bacteria)

– Simple & relatively small.– NO Membrane-bound nucleus & organelles.– 70-S Ribosomes.

CELLS

PROKARYOTIC EUKARYOTIC

EUKARYOTIC CELLS

Organelles = “little organs” (not really)

Membrane-bound

ORGANELLES

• Nucleus– Isolates the DNA & provides access to its

hereditary information.– The “control center” of the cell (Transcription).

Nucleus

1. Nuclear Envelope (a double membrane) with Pores.

2. Nucleolus• rRNA• Proteins• Ribosomes

3. Nucleoplasm with Chromatin/Chromosomes.

Ribosomes

• Not true organelles, more “structures”.

• Protein factories.

• 2 sub-units.

• Free (in cytoplasm), more for intracellular activities.

• Bound (on E.R.), often for extracellular activities (secretion) & packaging within certain organelles.

Endomembrane System

• Synthesis of Proteins & their transport.

• Packaging of Proteins for transport out of the cell (secretion) or to other areas of the cell.

• Modification of Proteins.

• Transport of lipids, lipoproteins, glycoproteins, etc.

Endomembrane System

1. Endoplasmic Reticulum (E.R.)– Rough E.R.– Smooth E.R.

2. Golgi Apparatus

3. Vesicles– Lysosomes

(also, nuclear envelope, vacuoles, and plasma membrane)

Endoplasmic Reticulum• Network of interconnected membranes

(continuous with the nuclear envelope).

• Flattened or tubular.

Rough E.R.

• The site of protein manufacture & initial modification, particularly of secretory proteins.

• Formation (budding) of Transport Vesicles.

Smooth E.R.

• Modification of proteins & formation of Lipids.– Lipid-derived hormones (steroids) are

synthesized, including sex hormones (testosterone, etc.) in certain glands.

– Detoxification (drugs, alcohol, caffeine, etc. ) in liver cells.

Golgi Apparatus

• Major modification, sorting, & shipping of ER-produced items (esp. for secretion).

• Addition of non-protein portions to protein molecules.

Lysosomes• Vesicles carrying digestive enzymes –

hydrolytic (proteolytic) enzymes.

• Animal Cells.

• Digestion of food brought in by phagocytosis.

Lysosomes

• Digestion and recycling of old & damaged organelles within the cell: Autophagy.

Endomembrane System

Vacuoles• Large vesicles with particular functions.

– Food Vacuoles.– Contractile Vacuoles.– Central Vacuole w/ tonoplast in Plant Cells.

•Storage.

•Dissolved Solutes.

•Dumping Ground.

•Protection.

•Shape.

Mitochondrion

• Site of cellular respiration = energy production.

Carbohydrates ATP

• Not part of endomembrane system.

• Have their own DNA, RNA, Proteins, and Ribosomes (70-S).

• Grow and reproduce independently.

• Animals, Plants, Fungi, Protists.

Mitochondrion

• Surrounded by a double membrane – an envelope.

Outer Membrane

Inner membrane (Cristae)

Matrix

Chloroplast

• Site of Photosynthesis = acquisition of chemical energy from sunlight.

Sunlight + CO2 Carbohydrates• A plastid (not part of endomembrane

system).• Have their own DNA, RNA, Proteins, and

Ribosomes (70-S).• Grow and reproduce independently.• Plants, Protists.

Chloroplast

• Surrounded by a double membrane – an envelope.

Inner Membrane (Grana composed of stacked Thylakoids) Stroma

Outer Membrane

Cytoskeleton

• Fiber-like structures that lend organization.• Support (providing a scaffolding onto which

organelles & vesicles can be organized).• Shape (maintain particular shape depending

on the cell’s location and/or function).• Transport of materials around or out of the

cell.• Motility of the whole cell from one location to

another.

Cytoskeleton

Microtubules Microfilaments Intermediate Filaments

Keratin Subunits

Tubulin Actin Keratin

Cytoskeleton

• Permanent– Flagella– Cilia– Muscle Contraction– Scaffolding & Shape

Maintenance

Cytoskeleton

• Transient– Spindle Fibers– Transport filaments

Cell Wall

• OUTSIDE the Cell Membrane (technically, outside the cell!)

• Various proteins & glycoproteins in Prokaryotes.

• Cellulose in Plants.

• Chitin in Fungi.

Eukaryotic Cell

Endosymbiont Theory

Onion Cells