Unit II: The Cell All organisms are made of cells, the organism’s basic unit of structure and function.

Size range of cells

How We Study Cells Microscopes - light microscope - electron microscope (TEM/SEM)

A Panoramic View of the Cell Prokaryotic Eukaryotic +only in bacteria/archaebacteria Protists, Fungi, Plantae, Animalia +no true nucleus/nuclear envelope true membrane-bound nucleus +genetic material in nucleoid region genetic material in nucleus +no organelles many organelles

Animal vs. Plant Cell Unique to Plant Cells: - cell wall - large central vacuole Chloroplasts Plasmodesmata Unique to Animal Cells: Centrioles Lysosomes - flagella and/or cilia

How organelles are fractionated (isolated)

The Nucleus and Ribosomes - enclosed by nuclear envelope - contains most of the genes that control the entire cell + DNA organized with proteins into chromatin - nucleolus Nuclear lamina – protein filaments that give structure to the inner nuclear membrane

The Nucleus and Ribosomes (con’t) - build proteins - RNA/protein complexes - free/bound

The Endomembrane System Includes: nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane*

Endomembrane System (con’t) Endoplasmic reticulum manufactures membranes two distinct regions + smooth ER - synthesis of lipids - carbohydrate metabolism - detoxify drugs/poisons - stores calcium ions + rough ER - manufacture proteins for secretion - membrane production

Endomembrane System (con’t) Golgi apparatus finishes, sorts, and ships cell products two poles + cis face + trans face Enzymes in the Golgi modify products of the ER in stages as they move through the Golgi stack from cis to trans face.

Endomembrane System (con’t) Lysosomes – contain hydrolytic enzymes digestive compartments + intracellular digestion + recycle cell material + program cell destruction (apoptosis)

Apoptosis – programmed cell death

Endomembrane System (con’t) Vacuoles function in cell maintenance + food vacuole + contractile vacuole + central vacuole (pictured) - tonoplast

Endomembrane System Summary

Other Membranous Organelles Peroxisomes consume oxygen for metabolism + contain specialized teams of enzymes - peroxide-producing oxidases and catalase RH2 + O2 -oxidase-> R + H2O2 2H2O2 -catalase-> 2H2O + O2

Mitochondria and Chloroplasts energy transformers of cells + double membranes + contain ribosomes/DNA Mitochondrial DNA is only passed on by mom

The Cytoskeleton Cytoskeleton provides structural support for motility and regulation + network of fibers - microtubules - microfilaments - intermediate filaments

Cytoskeleton (con’t)

Centrosomes Found in animal & plant cells Produce microtubules during cell reproduction Animal cells contain centrioles which contain 9 sets of 3 microtubules

F L A G E C I L I A

Flagellum Structure

Cell Surfaces and Junctions Cell Walls (1° & 2°) cellulose fibers Plasmodesmata Middle lamella Made of pectin (sticky polysaccharide) Pectin holds cell walls together like concrete

Cell Surfaces and Junctions ECM (Extra Cellular Matrix) meshwork of macromolecules outside plasma membrane + mostly glycoproteins (Collagen & proteoglycan) + support/anchorage (Fibronectin & integrin)

Cell Surfaces and Junctions Tight junctions – prevent fluid from moving between cell layers in a tissue Desmosomes – anchor adjacent cells Gap junctions – allows the movement of cytoplasm, ions, sugars, amino acids from one cell to the next

Tight Junctions

Desmosomes

Gap junctions

Membrane Structure and Function Collagen proteoglycan Fibronectin

Membrane Structure and Function (con’t) Plasma Membrane boundary that separates living cell from its non-living surroundings + 8 nm thick + selectively permeable + unique structure relates to function

Phospholipid Glycerol Fatty Acid Chains Amphipathic molecule – has hydrophilic & hydrophobic regions

Hydrophilic vs Hydrophobic

Membrane Structure and Function (con’t) Fluid Mosaic Model The Fluid Quality of Membranes + held together by hydrophobic interactions - lipids/proteins drift about laterally + unsaturated hydrocarbon tails - maintain fluidity at low temperatures + cholesterol - stabilizes the membrane restrains movement at high temp. hinders close packing at low temp.

Membrane Structure and Function (con’t) Fluid Mosaic Model Membranes as Mosaics + membrane is collage of proteins - integral proteins transmembrane - peripheral proteins appendages

Plasma membrane synthesis

Membrane Structure and Function (con’t) Functions of Membrane Proteins Transport Enzymatic Activity Signal Transduction Intercellular joining Cell-cell recognition Attachment to the cytoskeleton and ECM

Signal Transduction with G proteins

Types of Membrane Proteins

Voltage Gated Ion Channels

Glycoprotein

Glycolipid

Cholesterol Reduces membrane fluidity by reducing phospholipid movement Hinders solidification at low temperatures

Cholesterol is a steroid

Traffic Across Membranes Selective Permeability hydrophobic, small, lipid molecules pass easily across the membrane hydrophilic, large, charged (polar) molecules cannot pass easily How do cells get the materials they need inside?

Traffic Across Membranes (con’t) Passive Transport Diffusion + the tendency for molecules of any substance to spread out into the available space - concentration gradient

Passive Transport Requires no energy Occurs due to natural concentration gradient Molecules move from high concentration to low concentration (DOWN the gradient) 3 Types Diffusion Osmosis Facilitated Diffusion

Diffusion

Diffusion A.K.A. simple diffusion Movement of small molecules across a selectively permeable membrane from an area of HIGH concentration to an area of LOW concentration w/o the use of energy (DOWN the concentration gradient) e.g. O2, CO2, urea, & alcohol

Traffic Across Membranes (con’t) Passive Transport Osmosis + the diffusion of water - hypotonic,hypertonic, isotonic Tonicity – the ability of a solution to cause a cell to gain or lose water Osmoregulation – the control of water balance e.g. contractile vacuole in paramecium

Osmosis The diffusion of WATER across a selectively permeable membrane OSMOTIC PRESSURE The pressure exerted on plasma membranes in solution Isotonic solution Hypertonic solution Hypotonic solution

Water Potential The physical property predicting the direction in which water will flow, controlled by the solute concentration

Water potential (ψ) = pressure potential (ψp ) + solute potential (ψs )

(ψ) = Greek letter psi Water potentials (ψ) are a way of measuring the free-energy of water. Water will flow spontaneously from a high potential to a low potential, like a ball rolling down a hill.

Physical pressure due to air & the container

Water Potential “Water potential" (Ψ) is a measure of the free energy of water;  pure water  (which has a high amount of free energy) is arbitrarily assigned a water potential of zero; units pressure: MPa; can be positive or negative Factors that determine plant water potential:  1) amount of solutes- increasing concentrations will lower  the free energy (water potential); termed osmotic potential (ψs) 2)  turgor pressure (ψp) in plant cell- positive pressure inside plant cells; increases free energy; loss of turgor = wilting

Cells in Isotonic Solution If the concentration of solute (salt) is = on both sides, there will be no net movement of water "ISO" means the same

Cells in Hypertonic Solution

Hypertonic Solutions More solute (salt) molecules outside the cell, which causes water to be sucked out of the cell. In plant cells, the central vacuole loses water and the cells shrink, causing plasmolysis resulting in the plant wilting. In animal cells, the cells also shrink. In both cases, the cell may die. This is why it is dangerous to drink sea water

Plasmolysis A phenomenon in plant cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment.

Cells in Hypotonic Solution

Hypotonic Solutions There are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell. The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting In animal cells, the cell may be in danger of bursting, organelles called CONTRACTILE VACUOLES will pump water out of the cell to prevent this.

Osmotic Potential The tendency of water to move across a selectively permeable membrane into a solution Determined by measuring the pressure required to stop the osmotic movement of water into the solution.

Osmosis Review

Traffic Across Membranes (con’t) Passive Transport Facilitated Diffusion + diffusion with the help of transport proteins - gated channels

Facilitated Diffusion Protein Channel or Pore

Facilitated Diffusion Protein Carrier

Traffic Across Membranes (con’t) Active Transport energy-requiring process + ATP pumps molecules against concentration gradient + Na+/K+ pump

Active Transport Requires cell energy (ATP) to move molecules AGAINST the concentration gradient; from an area of LOW concentration to an area of HIGH concentration Sodium–Potassium pump (Exchange 3 sodium ions for 2 potassium ions) Hydrogen ion, or proton pump (Pump hydrogen ion against the concentration gradient)

Phosphorylation The addition of a phosphate (PO4) group (From ATP) to a protein or a small molecule This changes the protein shape

Active Transport (Uniport)

Active Transport Na-K Pump

Na-K Pump Antiport

Glucose-Sodium Symport

Traffic Across Membranes (con’t) Membrane Potential electrogenic pump + proton pumps (H+) electrochemical gradient + cotransport

Traffic Across Membranes (con’t)

Bulk Media Transport Endocytosis – Vesicle is created from the invagination of the plasma membrane, which pinches off, bringing large molecules into the cell Pinocytosis – Cell drinking (endocytosis) Phagocytosis – Cell eating (endocytosis) Receptor Mediated Endocytosis – Substrate binds to receptor found on the plasma membrane to be brought into the cell Exocytosis – Vesicle binds to the plasma membrane releasing the contents outside of the cell

Endocytosis

Pinocytosis

Phagocytosis

Receptor Mediated Endocytosis Ligand – molecule that binds specifically to a receptor site of another molecule LDL uses receptors to enter cells (hypercholesterolemia is due to receptor defect)

Exocytosis

Traffic Across Membranes (con’t) Transport of Large Molecules Exocytosis + the cell exports macromolecules using vesicles from Golgi apparatus Endocytosis + the cell takes in macromolecules by forming new vesicles from membrane - phagocytosis (“cellular eating”) - pinocytosis (“cellular drinking”) - receptor-mediated endocytosis + ligands