• Larger cells do not function as efficiently– The surface is the only way cells interact with the

environment– Surface-area-to-volume ratio• As cell size increases, volume grows much more rapidly

Why are cells so tiny?

Cell radius (r) Surface area (4πr2) Volume ((4/3)πr3)

1 units 12.57 units2 4.189 units3

10 units 1,257 units2 4,189 units3

Cell Theory• Schleiden and Schwann• Three principles– All living things are composed of cells– Cells are the smallest living things (Functional units of the body)– Cells come from pre-existing cells

• Prokaryotes – Lack a nucleus and

membrane bound organelles

– MUCH smaller than eukaryotes

– Bacteria

• Eukaryotes – Have a nucleus and

organelles– Much bigger than

prokaryotes

Cell Types

• Cell membrane– Semi-permeable

• Cytoplasm— “cell blood”– Fluid matrix surrounding

nucleus– Surrounded by a cell

membrane• Nucleus— “cell brain”– Contains chromatin (loosely

coiled DNA)

Cell Organelles

• Interconnected membranes forming canals and flattened sac-like spaces

• Functions:– Communications system– Rough ER: studded with

ribosomes • Involved in protein synthesis

– Smooth ER: has no ribosomes• Involved in synthesizing lipid

Endoplasmic reticulum

• Composed of protein and RNA

• May be free in the cytoplasm or attached to ER

• Function:– Involved in protein

synthesis

Ribosomes

• Stack of flattened membranes

• Function:– Package and transports

proteins from the cell

Golgi apparatus

• “Cell powerhouse”• Contains its own DNA– Capable of self-reproduction

• Composed of 2 membranes• Contains enzymes used in cell

respiration• Function:– Produce ATP for cellular energy

(cell respiration)

Mitochondria

• Small sacs from the Golgi apparatus

• Contains enzymes capable of breaking down breaking down nutrients or toxins

• Function:– Digestion

Lysosomes

• Twin hollow cylinders (centrioles)

• Function:– Involved in cell division

Centriole

• Tiny sacs formed by the cell membrane folding in and pinching off

• Function:– Intake or excretion of

large materials (endocytosis and exocytosis)

Vesicles

• Tiny rods usually arranged in meshes or bundles

• Function:– Involved in cell

movement– Provides structure to

the cell

Microfilaments and

Microtubules

• Fine, long, threadlike organelles protruding from the cell surface

• Function:– Cell movement

Cillia and Flagella

nucleus

smooth ER

lysosomeGolgi

apparatus vesicles

centrosome

mitochondria

flagella

rough ER

• Selectively permeable (semi-permeable)– Allows some substances in, excludes others

• Composed of phospholipid bilayer (containing cholesterol) and protein inclusions– Fat soluble molecules pass through the lipid part– Water soluble molecules must move through

protein component • Pores, channels or receptors

Cell Membrane

Passive Transport

• Movement of a material into or out of a cell without the use of energy.– Diffusion– Osmosis– Facilitated diffusion

– *** NO ENERGY REQUIRED***

• The process by which molecules move down a concentration gradient– Move from area where there is more

concentration to areas that are less concentrated

– Rate limited by concentration

Diffusion

• Diffusion using special carrier molecules to allow usually non-permeable molecules to pass through a selectively permeable membrane– Example: Insulin facilitates glucose movement

• Rate of passage is limited by the number of carrier molecules and concentration

Facilitated Diffusion

• The diffusion of water through a selectively permeable membrane which may not allow dissolved substances to pass

• May result in changing volumes on either side of the membrane

• Osmotic pressure– The amount of pressure needed to stop osmosis

Osmosis

• Hypertonic– A solution which has a greater concentration

of solute particles than a given cell or solution

• Hypotonic– A solution which has a lesser concentration

solute particles than a given cell or solution

• Isotonic– A solution which has an identical concentration

of solute particles to a given cell or solution

Concentration Types

• The forcing of permeable molecules through a membrane by hydrostatic pressure– Example: Blood pressure

Filtration

• The movement of molecules against a concentration gradient using cellular energy and carrier molecules– Proton pump– Sodium-potassium pump

Active Transport

***ENERGY REQUIRED***

• Endocytosis– The inward movement of

molecules through a membrane by infolding and pinching off vesicles• Pinocytosis: taking in tiny

droplets of liquid• Phagocytosis: taking in solid

material• Receptor Mediated:

molecule bonds with receptor protein

• Exocytosis

Bulk Passage

• Prokaryotes– Binary fision• DNA replicated in parent • Parent divides• Fast

• Eukaryotes– Mitosis• Complicated• Lots of DNA

– Form chromosomes (compact structures, composed of DNA and histone proteins, that can be manipulated easily during cell division

Cell division

• Interphase– Period

“Inbetween” cell division

– Majority of cell’s life• Cell growth• Protein synthesis

Cell cycle

• Cell division that Is Mighty Common

• Makes all cells EXCEPT gametes (reproductive cells)

• DNA is doubled then– Cells divide once

Mitosis

• Cells Prepares to divide

• Chromatin condenses into chromosomes

• Nuclear membrane disappears

Prophase

• Chromosomes line up in the Middle

• Spindle Apparatus stretches from pole to pole

Metaphase

• Sister chromatids move Away to opposite poles

Anaphase

• Cell “Tears” in two• Nuclear membrane reforms• Chromosomes disperse into

chromatin• Cytokinesis (cytoplasmic

division) (separate phase?) – Produces 2 identical “daughter

cells”

Telophase

• Process by which cells develop different characteristics in structure and function

• Differences in outcome– Directed by cell’s DNA– Determined by cell’s

position in the body and its chemical environment

Cell differentiati

on