The cell is the smallest unit of life. All organisms are composed one or more cells. New cells arise from previously existing cells.

• The cell is the smallest unit of life.

• All organisms are composed one or more cells.

• New cells arise from previously existing cells.

Basic Cell Structure

Each cell has four common components:1. Plasma membrane2. Region containing DNA3. Cytoplasm 4. Biochemical molecules & biochemical

pathways

Fluid mosaic model:

• Working model of the membrane

• Protein molecules bobbing in phospholipid sea

• Proteins determine membrane’s specific functions

Phospholipids

• Most abundant lipid

• Polar/hydrophilic head(attracted to water)

• Pair of nonpolar/hydrophobic tails(repelled by water)

Hydrophilic head

Hydrophobic tails

Polar heads, outside & inside

Nonpolar tails in the interior cell membranes

Hydrophilic head

phospholipid

Hydrophilic head

Hydrophobic tail

outside

inside

Microvilli- intestinal cells

Membrane Junctions

Tight junctions Desmosomes Gap junctions

Selectively permeable- allows certain substances to pass through

By 2 ways: active or passive transport

Passive- downhill

Active- uphill (needs energy)

Passive: downhill reaction• Simple diffusion• Osmosis• Facilitated diffusion• Filtration

Active: uphill reaction, needs ATP• Exocytosis• Endocytosis

- Pinocytosis- Phagosytosis

No Barrier:

• Substances “spread out”

• High concentration to low concentration

e.g.: Red dye placed in glass of water

• Substances diffuse

• High concentration to low concentration

• Pores in membrane must be large

• “Down the concentration gradient”

• Dynamic equilibrium, equal rates in both directions

Biological membrane:

Carrier proteins:

• Bind specific molecule & change shape

• Pass molecule through middle of protein

Osmosis- diffusion of a water through a semi-permeable membrane

• Moves down concentration gradient

e.g., Two sugar solutions of different concentrations separated by porous membrane which lets water through but not sugar

What will happen?

• More concentrated to less concentrated

• Until concentration same on both sides: isotonic

Concentration of solute less: solution is hypotonic.

Concentration of solute greater: solution is hypertonic.

Animal cells No cell walls

Isotonic environment: Influx of water equals the efflux of water No change in cell shape

Hypotonic solution: Water enters cell Bursts, or lyses

Hypertonic solution: Water leaves cell Shriveled, or crenate

Glomerular filtration

Passive transport & facilitated diffusion do NOT require

ATP

DOES require the input of

ATP

Transport proteins AGAINST concentration

gradient

outside cell

inside cell

ATP ATP ADP + P ADP + Pii + Energy + Energy

mucus

http://www.1lecture.com/Physiology/Endocytosis%20and%20Exocytosis/index.html

Goblet cell

Nerve Axon at Rest

Na+/K+ Pumphttp://www.1lecture.com/Biochemistry/cotransport/

H+ Pump in a Plant

• Ion channels - Voltage gated- Chemically gated- Mechanically gated

• Porins - Larger - Less specific

• Aquaporins - water

Channel Proteins

Channel Proteins:Ion Channels

Channel Proteins:Porins

• MAC• Barrel shaped protein

Channel Proteins:Aquaporins

H2O

Membrane Permeability

Cell membrane:

selectively permeable

4 factors that determine permeability lipid solubility

molecular size

polarity

charge

1

2

3

4

Lipid solubility Most important factor

Hydrophobic molecules Passively diffuse Hydrocarbons, carbon dioxide, & oxygen

Molecular Size and Polarity

Larger molecules, less permeable Lower kinetic energy Small pore sizes in the membrane

Polar molecules hydrophilic, less permeable Very small, polar uncharged (water) molecules can diffuse

-+

Molecular Size

Polarity

Charge

Charged molecules hydrophilic, less permeable Surrounded by coat of water (hydration shell), increases the size

Rough and Smooth ER

• Digest food• Autophagy• Autolysis

• Rid body of toxic substances• Contains enzymes that can oxidize

various organic substances

Liver cell

• Centriole pair• Assemble

microtubules• Assist in cell

division• 9 clusters of

microtubule triplets

Figure 3.23c

(c) MicrotubulesHollow tubes of spherical protein

subunits called tubulins

25 nm

Tubulin subunits

Microtubules appear as gold networkssurrounding the cells’ pink nuclei inthis photo.

Cillia & Flagella- 9x2 arrangement

0.1 micrometer

Cillia & Flagella- 9x2 arrangement

Flagellum

Flagellar Movement

Ciliated Epithelium

ciliated surface

nuclei

mucus

Ciliary Movement

Ameboid Movement

Ex. WBC

INQUIRY

1. Define isotonic, hypotonic, and hypertonic. 2. What % saline is a cell?3. Distinguish between active and passive

transport.4. What is the function of:

• Mitochondria• Nucleus• Golgi apparatus• Lysozome• Ribosomes• Smooth and rough ER

Cellular Visions: The inner life of a cell (video)http://www.studiodaily.com/main/searchlist/6850.html