1. Chapter 6
A Tour of the Cell

2. 6.1 All organisms are made of cells
Cell theory
All living things are made up of cells
Cells are the basic unit of structure and function
All cells come from pre-existing cells

3. Microscopes as Windows to Cells
The first light microscope was developed around
Robert Hooke – 1665
Observed“compartments,” cells, in a thin slice of cork
Anton van Leeuwenhoek
1700 developed simple light microscopes with high- quality lenses to observe tiny living organisms “animalcules”

4. Microscopes
Light microscopes (LM) magnify objects up to 1000 times, bacteria or larger
Electron microscopes (1950’s) use a beam of electrons and can magnify up to 1 million times
Cells must be killed and preserved
Scanning Electron Microscope (SEM) to study the surface structures of cells
Transmission Electron Microscope (TEM) to explore their internal structure
micrograph: a photograph of the view through a microscope

5. Prokaryotic Cell
prokaryotic cell: lacks a nucleus and most other organelles
Bacteria and archaea; found in earliest fossil record
Much simpler in structure than a eukaryotic cell ~1 to 10 micrometers
The DNA is concentrated in the nucleoid region which is not separated by a membrane

6. Eukaryotic Cell
eukaryotic cell: has a nucleus surrounded by its own membrane
Protists, fungi, plants, and animals
Much larger than a prokaryotic cell ~ 10 to 100 micrometers

7. 6.2 Cell membranes Structure
Membranes regulate the transport of substances across the boundary
Composed mostly of proteins and phospholipids

8. Phospholipids Two fatty acids at one end
hydrophobic
Phosphate group(PO43-) at the other
Negatively charged and hydrophilic

9. Phospholipid Bilayer
phospholipid bilayer: the phospholipids form a two- layer “sandwich” of molecules that surrounds the organelle or cell
Phosphate ends face the outside
Fatty acids inside
Fluid mosaic
Proteins drift freely within the membrane

10. Membrane Proteins Enzyme activity Cell communication
carryout important chemical reactions
Cell communication
Chemical signals relayed to recognized cells
Transport proteins
Help move certain substances across the membrane
Ex. Water and sugar

11. 6.3 Regulation across the membrane
isos- means “equal”
hyper- means “over, above, excessive”
hypo- means “under, beneath”
tonos- means “tension” or “strength” (-tonic)
Cellular membranes function like gatekeepers, letting some molecules through but not others.

12. Diffusion
diffusion: the net movement of particles of a substance from where they are more concentrated to where they are less concentrated.
permeable: a membrane that allows molecules to pass through freely
equilibrium: a system is in balance; the number of molecules going one direction is equal to the number in the other direction.

13. Passive Transport
selectively permeable membrane: allows some substances to cross the membrane more easily than others and blocks the passage of some altogether.
normally only oxygen and carbon dioxide diffuse freely
passive transport: diffusion across a membrane that expends no energy
facilitated diffusion: transport proteins provide a pathway for certain molecules to pass.
Ex. sugars do not pass easily through the hydrophobic region so they need the proteins to help

14. Osmosis
osmosis: the passive transport of water across a selectively permeable membrane
hypertonic: solution with a higher concentration of solute (more sugar)
hypotonic: solution with a lower solute concentration (more water)
isotonic: solutions in which the concentrations of solute are equal

15. Water Balance Water balance in animal cells
if there is too much water moving in (hypotonic) the cell may burst
too much moving out (hypertonic), it may shrivel and die
animals in aquatic environments depend on isotonic conditions
Water balance in plant cells
a plant cell is healthiest in
hypotonic environments because
it remains firm but will not burst.
The cell wall is too strong.
in an isotonic situation, there is no net movement of water so it will wilt.

16. Active Transport
active transport: a cell expends energy to move molecules or ions across a membrane
maintains the cell’s chemical environment usually from low to high concentration
Ex. in animal cells, K and Na pump; K pumps in, Na out.

17. Transport of Large Molecules
vesicles: small membrane sacs that specialize in moving products into, out of , and within a cell
exocytosis: vesicle fuses with the plasma membrane and spills contents outside the cell
endocytosis: reverse; takes material into the cell within vesicles that bud inward

18. Animal and Plant Cells
organelle: each part of a cell with a specific job to do, “mini-organ”
many are enclosed by their own membranes to help maintain the chemical environment inside that is different then the rest of the cell
plasma membrane: a thin outer covering; the boundary of the cell and regulates the traffic of chemicals between the cell and its surroundings

19. Nucleus
nucleus: houses the cell’s genetic material in the form of DNA, largest organelle
chromosomes: wound up DNA
nucleolus: center of the nucleus; makes ribosomes

20. Cytoplasm
cytoplasm: the entire region of the cell between the nucleus and the plasma membrane, which consists of organelles and fluid
cytoskeleton: provides structure for a cell

21. Endoplasmic Reticulum(ER)
Rough: Works as a highway to move substances through the cell
Rough because of ribosomes on the surface
Smooth: produces lipids, like sex hormones

22. Ribosomes
Make proteins from DNA
Made in the nucleolus

23. Golgi Body Like a post office
Modifies, stores and routes proteins and other chemicals to its destination

24. Lysosomes Membrane-bound sacs that contain enzymes
Break down large molecules
Destroy harmful bacteria
Recycle old organelles

25. Vacuoles Large, membrane-bound sacs
Stores nutrients, pigments, salts, etc
Contractile vacuoles pump out excess water

26. Mitochondria Powerhouse of the cell
Produces energy
More active cells have more mitochondria
Folded membrane gives more surface are for more energy production

27. Centrioles Only in Animal Cells Used during cellular reproduction
Small, rod shaped; located near nucleus

28. Additions for Plant Cells
chloroplasts: organelle where photosynthesis occurs
cell wall: protects the plant cell and maintains its shape; consists of cellulose and is found outside the plasma membrane
vacuoles: large membrane bound sacs for storage
Main water storage in plants