Basic Cell Structure

Into the Cell The Cell Theory “Cell Doctrine”

1. All organisms are constructed of one or more cells. 2. The cell is the basic unit of life. ¸ Minimum level of complexity that exhibits all characteristics of life. 3. All cells derive from previous cells.

What does a cell need? Isolated activity compartments

n Selective isolation from environment (plasma membrane) n Energy (ATP) n Instructions (DNA) n Machinery to carry out instructions and regulate processes (proteins) n Compartmentalization of incompatible or specialized activities (organelles) •Cell membrane •Plasmalemma •Organelle membranes

Cell & Organelle Membranes: Cell Size Varies More than just a phospholipid bilayer with Function

n Human nerve cell: > 1 meter n Frog egg: 2 mm n Average animal cell: 50 µm n Human red blood cell: ~8 um n Bacteria: 1–2 µm n Organelle: 1 µm n Virus: 50 nm

Heyer 1 Basic Cell Structure

Why Must Cells Smaller cells have more total surface area

Be Small? n Increased surface area makes it easier for gasses, nutrients, etc. to enter a cell

‹ Same volume fi

Why Must Cells So, Why Can’t Cells Be Small? Be Even Smaller? Upper limits on cell vThey must be big size are set by enough to hold all diffusion distance. their parts! Molecules must vMacromolecules diffuse through cell. cannot be shrunk.

v Volume controlled by nucleus.

Early views of cells Modern views of cells

n Plasma membrane n Better microscopes and stains n “Nucleus” ( “center”) unstained – Electron microscope. 50µm – filled with “chromatin” human cheek cell n “Cytoplasm” and stained (“colored stuff”) “chromatin” much more n “Cytoplasm” (“cell fluid”) complicated, structured, and dynamic than previously appreciated. 5 µm

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Two major types of cells Cell-Type EUKARYOTIC CELL PROKARYOTIC CELL Systematics DNA Five-Kingdom Model Membrane (no nucleus) Membrane Cytoplasm

Contrasting eukaryotic and I. Prokaryotic — Bacteria prokaryotic cells in • No membranous organelles II. Eukaryotic — Protists size and complexity • Single celled or simple colonial III. Eukaryotic / multicellular— Plant • Organelles present, including chloroplasts • Cellulose cell wall around plasma membrane IV. Eukaryotic / multicellular—Fungi • No chloroplasts • Chitinous cell wall Organelles V. Eukaryotic / multicellular— Animal 1 µm Nucleus (contains DNA) • No chloroplasts nor cell wall • Varied cell morphology

Prokaryotes lack a true Prokaryotic Cell Structure endomembrane system

n Single-celled organisms n No nucleus v The plasma nor other membrane is membranous organelles the only n No cytoskeleton membrane. n Most with cell wall outside plasma membrane Photosynthetic prokaryote n Some with capsule outside cell wall

Eukaryotic Cell Structure Cytoplasm —organelles & cytoskeleton n Fills cell; contains – cytosol • fluids and more • gel & sol state – membrane-bound organelles • concentrate specific enzymatic activities • isolate incompatible reactions or toxic products – cytoskeleton • maintain and alter cell shape • hold and move organelles, etc.

Heyer 3 Basic Cell Structure

Organelles & Cytosol Cellular Organelles

n Nucleus – Nuclear envelope – Nucleolus • Nucleus of nucleus • Transcribes rRNA for ribosomes – Chromatin/ chromosomes – Nuclear lamina • Protein scaffolding underlying the envelope and n Cytosol: Dense, semisolid aqueous gel containing a supporting the tremendous variety of solutes and macromolecular machines chromatin

Nuclear envelope: 2 membranes Nucleus

Nuclear n Double-membrane envelope with pores surface n Contains DNA of chromosomes n Controls cell Pore – structure complexes – function n Blueprints for new cells Nuclear lamina

Nuclear envelope: 2 membranes Cellular Organelles

n Endoplasmic Reticulum Smooth E.R. – New membrane synthesis – Lipid synthesis & processing – Steroid synthesis – Lipophilic detoxification – Intra-cellular Ca++ store – Usually tubular appearance

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Cellular Organelles Cellular Organelles

n Endoplasmic n Ribosomes Reticulum – Free and RER-bound Rough E.R. – Ribosome attachment sites – Synthesis of membrane proteins – Synthesis of proteins for secretion or intra-organelle storage – Flattened beaded stacks; Membrane often continuous with nuclear envelope

Cellular Organelles RER to Golgi n Golgi Complex Transporting proteins in vesicles – Further processing and trafficking of proteins from RER – Receives vesicles from ER; buds off vesicles to plasma membrane for export

Progression of membrane & proteins Cellular Organelles

n Vesicles – Shuttle between organelles and plasma membrane

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Lysosomes are digestive compartments Cellular Organelles

n Lysosome – Contains hydrolytic enzymes – Digest food, bacteria, old cell parts – Apoptosis (cellular self-destruct)?

Lysosomes are digestive compartments Vacuoles

Lysosomes Large storage vessels Central vacuole in a plant cell

Fat vacuoles in adipose cells m µ 150

Contractile vacuole Endomembrane System n Continuous exchange of membrane and membranous contents Paramecium lives in fresh water — takes on water by osmosis. Pumps out water with the contractile vacuole.

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Endomembrane System Peroxisomes n May form from ER or autonomously n Both produces and removes hydrogen peroxide – Detoxifies organic compounds, e.g. ethanol w Nuclear envelope – Destroy bacteria w Endoplasmic reticulum n ß-oxidation of Chloroplast fatty acids Peroxisome Mitochondrion w Golgi apparatus n Phospholipid synthesis w Lysosomes — esp. myelin w Vacuoles & vesicles

Figure 6.19 1 µm

Cellular Organelles: bioenergetics Cellular Organelles: bioenergetics

n Mitochondria n Chloroplast – Double-membrane – Triple-membrane – Aerobic respiration – Photosynthesis • uses sunlight to construct organic molecules (CO2Æ sugar) • Powerhouse of cell – Also have some of their own DNA • Converts chemical energy from – Plants catabolism into ATP & some protists – Have some of own DNA to maintain activity when nucleus is unavailable

Cytoskeleton Cytoskeleton protein framework that extends throughout the cytoplasm

Organizing the organelles

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Cell Support Structures Cytoskeletal structures

n Cytoskeleton

micro- micro- intermediate tubules filaments filaments structural Tubulin Actin Keratin protein (dimer) (and others) motor Dynein Myosin protein (and others) ∅

Cytoskeleton Cytoskeleton

Tensegrity: A balance of tension & compression

Cytoskeleton Cellular Structure: Centrioles

Microtubule organizing centers

Heyer 8 Basic Cell Structure

Vesicle transport along The nucleus & the cytoskeleton microtubule “rails”

ATP energy is used to pull vesicles along microtubules.

n Intermediate filaments penetrate envelope to connect with nuclear lamina

n Microtubule organizing center adjacent to nucleus

Cell Mobility Structures flagella & cilia Eukaryotic versions

n Flagella

n Cilia

HOWHOW DODO CILIACILIA ANDAND FLAGELLAFLAGELLA MOVEMOVE ?? Molecular motors: structure of n Dynein arms cause microtubules to bend cilia & flagella

Fig. 4.19

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Myosin cross-bridges pull Cytoskeletal support of actin filaments along cell membrane

Crowded network of cross-linked microfilaments (red) underlying the plasma membrane (blue) .

“cytoplasmic cortex”

Cytoplasmic Streaming Cytoskeleton and pseudopodia

n Selective growth of the n Motor proteins pull microfilament cytoplasmic meshwork macromolecular produces a bulge (pseudopodium) complexes and in cell membrane organelles along the for amoeboid microfilament movement or meshwork phagocytosis.

The Cell: A Living Unit greater than the sum of Its parts n Cells rely on the integration of structures and organelles Many Variations in Theme in order to function m µ 5

Figure 6.32

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