Download Cells

Why are cells so tiny?
• 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
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
Cell Types
– Lack a nucleus and
membrane bound
organelles
– MUCH smaller than
eukaryotes
– Bacteria
• Eukaryotes
– Have a nucleus and
organelles
– Much bigger than
prokaryotes
Cell Organelles
• Cell membrane
– Semi-permeable
• Cytoplasm— “cell blood”
– Fluid matrix surrounding
nucleus
– Surrounded by a cell
membrane
• Nucleus— “cell brain”
– Contains chromatin (loosely
coiled DNA)
Endoplasmic reticulum
• 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
Ribosomes
• Composed of protein
and RNA
• May be free in the
cytoplasm or
attached to ER
• Function:
– Involved in protein
synthesis
Golgi apparatus
• Stack of flattened
membranes
• Function:
– Package and transports
proteins from the cell
Mitochondria
• “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)
Lysosomes
• Small sacs from the Golgi
apparatus
• Contains enzymes capable
of breaking down
breaking down nutrients
or toxins
• Function:
– Digestion
Centriole
• Twin hollow cylinders
(centrioles)
• Function:
– Involved in cell division
Vesicles
• Tiny sacs formed by the
cell membrane folding in
and pinching off
• Function:
– Intake or excretion of
large materials
(endocytosis and
exocytosis)
Microfilaments and Microtubules
• Tiny rods usually
arranged in meshes
or bundles
• Function:
– Involved in cell
movement
– Provides structure to
the cell
Cillia and Flagella
• Fine, long, threadlike
organelles protruding from
the cell surface
• Function:
– Cell movement
centrosome
Golgi
lysosome apparatus vesicles
nucleus
mitochondria
flagella
smooth ER
rough ER
Cell Membrane
• 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
Passive Transport
• Movement of a material into or out of a cell
without the use of energy.
– Diffusion
– Osmosis
– Facilitated diffusion
– *** NO ENERGY REQUIRED***
Diffusion
• 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
Facilitated 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
Osmosis
• 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
Concentration Types
• 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
Filtration
• The forcing of permeable
molecules through a
membrane by hydrostatic
pressure
– Example: Blood pressure
Active Transport
• The movement of molecules against a
concentration gradient using cellular energy
and carrier molecules
– Proton pump
– Sodium-potassium pump
***ENERGY
REQUIRED***
Bulk Passage
• 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
Cell division
• 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 cycle
• Interphase
– Period
“Inbetween” cell
division
– Majority of cell’s
life
• Cell growth
• Protein synthesis
Mitosis
• Cell division that Is Mighty
Common
• Makes all cells EXCEPT
gametes (reproductive cells)
• DNA is doubled then
– Cells divide once
Prophase
• Cells Prepares to
divide
• Chromatin condenses
into chromosomes
• Nuclear membrane
disappears
Metaphase
• Chromosomes line
up in the Middle
• Spindle Apparatus
stretches from pole
to pole
Anaphase
• Sister chromatids move
Away to opposite poles
Telophase
• Cell “Tears” in two
• Nuclear membrane reforms
• Chromosomes disperse into
chromatin
• Cytokinesis (cytoplasmic
division) (separate phase?)
– Produces 2 identical “daughter
cells”
Cell differentiation
• 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