Chapter 7 A Tour of the Cell

Cell TheoryMicroscope – Developed during the 1500’s by eyeglass makers• Made cell research possible• Robert Hook – observed compartments in a thin slice of cork (1665)

• He named these compartments cells• He was actually viewing the walls of dead cells (plant cells)

Cell TheoryAnton van Leeuwenhoek (1675): was the first person to observe living cells.

Cell TheoryCell Theory – All living things are composed of cells, AND that cells are the basic unit of structure and function in all living things• Added to the theory later is that all cells come from cells

Cell TheoryWho developed the cell theory?

• Matthias Schleiden (1838): concluded that all plants are composed of cells

• Theodor Schwann (1839): concluded that all animals are composed of cells

• Rudolph Virchow (1855): determined that cells come only from other cells

Microscopes1. Light Microscope• Magnifies Objects up to 1000 times actual

size

Appendix B- A14

MicroscopesMagnification: refers to the microscope’s power to increase an object’s apparent size

Resolution: refers to the microscope’s power to show detail clearly

Microscopes2. Electron Microscope• Can magnify up to 1,000,000 times• Enough to see details inside the cellScanning Electron Microscope (SEM)• Used to study the surface structures of cells.

Microscopes

Transmission Electron Microscope (TEM)• Used to study internal cell structures

Microscopes• Specimens for the electron microscope must be killed and preserved before viewing.• This is why the light microscope is useful for observing living cells.Micrograph – a photograph of the view through a microscope.

Cell Diversity- Size

Ostrich Egg

Biggest Cells:

6 inches long, 5 inches wide, 3 pounds

Plant and Animal Cell – Similarities

Organelle – Part of a cell with a specific function

Similarities Plants and AnimalsPlasma Membrane – defines the boundary of the cell and regulates the traffic of chemicals between the cells and it surrounding.

Plant and Animal Cell

Nucleus – Houses cells genetic material (DNA)Cytoplasm – the entire region of the cell between the nucleus and the plasma membrane• Consists of various organelles suspended in a fluid• Most organelles each have their own membranes; meant to help keep their own environments separate.

Plant and Animal Cell - Differences

Chloroplast – found in some plant cells; responsible for photosynthesis• Converts light energy to chemical energyCell Wall – A strong cell wall outside the plant cell and maintains its shape.

Plant and Animal Cell - Differences

• Cells differ widely in shape.• Most cells are roughly cuboidal or spherical.

Multi-cellular organisms show emergent properties

• Emergent properties arise from the interaction of the component parts; the whole is greater than the sum of the parts'.

Cell DifferentiationDifferentiation: Cells within a multi cellular organism specialize their function.

Stem Cells• a stem cell that has the potential to differentiate into any of the three germ layers:

• endoderm (interior stomach lining, gastrointestinal tract, the lungs)

• mesoderm (muscle, bone, blood, urogenital), • ectoderm (epidermal tissues and nervous system). 

•Pluripotent stem cells can give rise to any fetal or adult cell type. However, alone they cannot develop into a fetal or adult organism because they lack the potential to contribute to extraembryonic tissue, such as the placenta.

Two Classes of Cells1. Prokaryotic Cells – Lack a nucleus and most other organellesNucleoid Region – area in a prokaryotic cells where DNA is concentrated • Includes: Bacteria, Archaea• Appeared earliest in Earth’s fossil records.

Binary Fission

Two Classes of Cells2. Eukaryotic Cells – has a nucleus surrounded by its own membrane and has internal organelles bounded by membranes.Includes: protist, fungi, plants, plants, and animals • Fossil records has them appear after prokaryotic cells

Prokaryotes Eukaryotes

nucleus? NO (nucleoid) YES

membrane-bound organelles?

NO YES (Many)

size 1 - 10 m 10 - 50 m

when evolved? 3.5 billion years ago 1.5 billion years ago

cytoplasm? YES YES

cell membrane? YES YES

cell wall? Some Do Plants

ribosomes? YES YES

DNA? CircularFree Floating

Chromosomes in Nucleus

examples Bacteria Plants, Animals, Fungi, and Protists

Membranes

• This is what made life possible• Membranes keep Eukaryotic cells organized• Membranes regulate transport of substances across the boundary – allow certain substances to pass.• Maintains a specific and unique environment within each compartment it encloses.

Plasma Membranes• Composed mostly of proteins and a type of lipid called phospholipids• Phospholipids are structured like fats:

• Has two fatty acids instead of 3

Hydrophilic – water lovingHydrophobic – water fearing

Plasma Membranes• Phospholipid structure enables them to form boundaries or membranes• A cells environment is aqueous; inside (cytoplasm) and out

• This requires that a cell forms two structures inside and out, like a sandwich

Phospholipid Bilayer - the two layer sandwich of molecules that surrounds a cell.It surrounds the cell and some organelles.

Phospholipid Bilayer

This creates a selected barrier.

• Non-polar molecules like oxygen and carbon dioxide• Polar molecules like sugars and other ions do not.

Plasma Membranes• Together with proteins; membranes are dynamic; fluid like……• Proteins move in a sea of phospholipids.

• Like an iceberg

Function of Membrane Protein• Many types of proteins are embedded in the

membranes phospholipid bi-layer• Carbohydrates may be attached to the

membrane as well

Function of Membrane Protein1. Protein perform, in some if not most cell’s

functions• Enzymes catalyze reactions near the cell

2. Help cells communicate with each other• Chemicals release signals that can be

“picked up” by proteins embedded in the membrane of another cell

3. Transport Proteins – Help move certain substances across the membrane.

Polar molecules need help to get through a cells membrane

MembranesDiffusion• the net movement of the particles of a substance from where they are more concentrated to where they are less concentrated.

• Molecules and fluid are in constant motion, colliding and bouncing as they spread out into available space.

MembranesEquilibrium• Molecules moving across a membrane is equal to the number moving in the other direction

Passive TransportCellular membranes are barriers to the diffusion

of some substancesSelectively Permeable Membrane – allows substances to cross the membrane more easily than others and blocks the passage of some substances all together.• In a typical cell a few molecules (mainly O₂ & CO₂) diffuse freely through the membrane.• Water also diffuses through the protein molecules (channels)

Passive TransportDiffusion across a membrane uses no energy is

expended by the cell.• Only the random motion of molecules are required to move them across the membrane • Most small molecules still have restricted access.

Facilitated Diffusion

Transport proteins provide a pathway for certain molecules to pass.

• Specific proteins allow the passive transport of different substances.

• This allows for specific proteins to allow the passive transport of different substances

• This helps substances including some ions and smaller polar molecules, like water and sugar, to diffuse in and out of the cell.

Facilitated Diffusion

Both diffusion and facilitated diffusion are forms of passive

transport = NO ENERGY

OsmosisThe passive transport of water across a

selectively permeable membraneHypertonic – a solution with higher concentration of solute.Hypotonic – a solution with lower solute concentration Water will go from Hypotonic (hypo = below) to Hypertonic (hyper = above)Isotonic – solution in which the concentration of solute are equal.• Iso = equal

Animal Cells vs. Plants Cells• Animal cells need to maintain a isotonic environment to maintain balance – be HAPPY

• A plant cell to maintain firmness needs to be hypotonic

• Animal cells can burst with too much water• In a plant cell; the cell wall prevents too much

water from entering the cell, preventing bursting.

Isotonic = limp stem cell death

Active TransportWhen a cell expends energy to move molecules or ions across a membrane

• Protein “pumps” a solute across a membrane, usually in the opposite direction to the way it travels in diffusion

• Requires chemical energy supplied by the mitochondria

• Active Transport play a vital role in maintaining the cells chemical environment.

Transport of Large MoleculesVesicles – small membrane sacs that specialize in moving products into, out of and within a cell.• Protein made in the cell then moved out Exocytosis – the fusion of a particle (in vesicle) to the inner wall of a cell membrane and spilling its contents out of the cell.

Transport of Large MoleculesEndocytosis – takes in material into the cell within vesicles that bud inward from the plasma membrane.

The Cell Products - NucleusNucleus• Nucleus contains DNA• DNA directs the activities of the cell• DNA is attached to certain proteins, forming long fibers called Chromatin.

• Normally chromatin looks like a plate of spaghetti• During reproduction they organize.

Nuclear EnvelopeSurrounds the nucleus.

• Substances made in the nucleus move into the cells cytoplasm through tiny holes, or pores, in the nuclear envelope.

Nucleolus – a ball like mass of fibers and granules; these parts make up organelles called ribosome.

RibosomeWhere proteins are constructed.

• DNA has the information, ribosomes make the protein. • Function like “assembly lines” making protein.

• Ribosomes are actually clusters of protein and nucleic acids – formed in the nucleus.

• Some ribosomes are bound to membranes in the cytoplasm; make proteins found in the membrane and exported by the cell.• Some ribosomes are suspended in the cytoplasm

• They make enzymes and other proteins that remain in the cytoplasm

Endoplasmic ReticulumAn extensive network of membranes

• Main transportation and manufacturer of the cell

• It is a maze of membranes arranged as tubes and sacs that separates the inside of the endoplasmic reticulum (ER) from the cytoplasm.

Endoplasmic ReticulumTwo Regions of ER

They are connected but different1.Rough ER – Named because of bound ribosomes outside the ER membrane. •These ribosomes produce proteins that are packaged in vesicles by the ER and later exported or secreted by the cell.•Specialized Cells – Salivary Glands are rich in ER because they secrete enzymes in your mouth

Endoplasmic Reticulum2. Smooth ER – lacks ribosomes, by using enzymes in ER membrane helps to build lipid molecules• Specialized Cells – cells in the ovaries and testes

produce sex hormones have a large amount of smooth ER.

Golgi ApparatusAn organelle that modifies, stores, and

routes proteins and other chemical products to their next destinations

• enzymes in the golgi apparatus refine and modify ER products by altering their chemical structure.•Some products of the golgi apparatus are used in the cell; some are secreted out by exocytosis, out of the cell.

Secretory PathwaySecretory Pathway

Vacuoles Large membrane-bound sacs

Store undigested nutrientsContractile Vacuole – found in some single-celled freshwater organisms• Pumps excess water out of the cell

VacuolesCentral Vacuole – found in plants; can be large

• Stores chemicals like salt• Helps with plant growth by causing the cells to expand• Flower Central Vacuoles have pigments that give color• Some contain poisons – for protection

LysosomesAnother membrane-bound sacs, contain enzymes that

break down macromolecules like:Proteins

Nucleic AcidsPolysaccharides

Function: • Fuse with incoming food vacuoles and help digest nutrients for the cell• Help destroy harmful bacteria

• White blood cells• Serve as recycling center for damaged organelles• It can engulf and digest another organelle

Chloroplast and MitochondriaChloroplast – are the photosynthetic organelles found in some cells of plants and algae.Photosynthesis – the conversion of light energy from the sun to the chemical energy stored in sugars and other organic compounds

Chloroplast and MitochondriaChloroplast have an envelope; made of two membrane

• Internal membranes divide the chloroplast into compartmentsChloroplast’s solar “power packs” – the structures that actually trap light energy and convert it to Chemical energy.

Chloroplast and MitochondriaMitochondria – in eukaryotic cells; are sites where cellular respiration occurs.Cellular Respiration – the process that releases energy from sugars and certain other organic molecules and then uses it to form ATP• ATP (adenosine triphosphate) is the main energy source that cells use for most of their work• Mitochondria is found in almost all kinds eukaryotic cells – including plants and algae.

MitochondriaStructure:• Like all organelles – structure = function• Like chloroplast two membranes surround mitochondria

• Inner membrane has numerous in foldings• Enzymes and molecules relate to cellular respiration are built into inner membrane.

• Folds increase surface area; the area in which cellular respiration takes place.

Mitochondria

Fold are like the lines of Disney World; increases the number of people in a small areas.

PeroxisomesStructure: spherical organelles that contain enzymes within single membranesFunction: Degrade hydrogen peroxide, a toxic compound that can be produced during metabolism.

CytoskeletonA network of fibers extending through out the

cytoplasm• These fibers are constantly breaking down

and rebuiltMicrotubules – straight, hollow tubes of proteins that give rigidity, shape, and organization to a cell.• Also provide “tracks” for organelles to move.

Cytoskeleton

CytoskeletonMicrofilaments – thinner solid rods of proteins; enable the cell to move or change shape when protein subunits slide past one another.• This processes are seen in the movements of amoeba and white blood cells.

Flagella(flagellum-singular) are long, thin, whip-like

structures, with a core of microtubules that

enable some cells to move• Usually waves with an S-shaped motion that propels the cell

Cilia

Are generally shorter and more numerous than flagella

• Contains bundles of microtubules, move in a back-and-forth motion – like oars

Flagella and Cilia• Cilia and flagella can also extend from stationary cells

• Not for motion, move fluid or trap debris

Organelles do not work together.Organelles do not work together.They work independent of each They work independent of each other. other.

Organelle Prokaryote Or Eukaryote

 

Plant or Animal Cell

Function

Nucleus 

Eukaryote Both Holds the DNA (genetic information) of cells – has a membrane that allows RNA to be transported in and out 

Ribosome Both Both Where proteins are made during translation

Mitochondria 

Eukaryote Both Cellular respiration occurs here to produce ATP this is the power house of the cell

Chloroplast Eukaryote Plant Photosynthesis occurs here in plant cells

Endoplasmic Reticulum(ER)

Eukaryote Both “highway of the cell” and site of protein and lipid synthesis

Golgi body Eukaryote Both Sorts and packages cellular products like the post office of the cell

Lysosome    

Eukaryote Both Breaks down waste products

Cell Wall Both Plant Protects plant and some prokaryotic cells; supports cell

Vacuole Eukaryote Plant Stores water and waste, supports cell to make it rigid

Cell Membrane Both Both Controls what enters and exits a cell. It is made up of a lipid bilayer that is selectively permeable (only small and non-polar molecules can pass through it). Large and/or charged molecules must go through transport proteins embedded in the membrane. Passive transport does not require energy (high concentration to low concentration). Active transport requires energy (low concentration to high concentration)

Cytoplasm Both Both The water-like substance that takes up most of a cell