Chapter 6 A Tour of the Cell

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

Microscopes as Windows to Cells The first light microscope was developed around 1600. 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”

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

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

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

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

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

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

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

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.

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.

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

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

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.

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.

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

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

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

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

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

Ribosomes Make proteins from DNA Made in the nucleolus

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

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

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

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

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

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