cells advanced biology. organization of the cell cells are dramatic examples of the underlying unity...

Cells

Advanced Biology

Organization of the Cell• Cells are dramatic examples of the underlying unity of all living things.• Idea first expressed by Matthias Schleiden and Theodor Schwann in

1839. They concluded that plants & animals are made of cells.• Rudolf Virchow saw cells dividing and making daughter cells in 1855.

Proposed cells only come from other cells.• August Weismann added to Virchows theory that the cell can be

traced from ancient cells.• CELL THEORY: • 1. Cells are the basic living units of organization & function in all

organisms.• 2. Cells come from other cells.

Cell Organization

• A cell is the smallest unit that can carry out all activities associated with life.

• But no part of an isolated cell can survive.

• A cell hardly gets NRG in the form it needs it to be in. It must be converted.Advances in technology helps us to better understand cells, their function & structure.

Cell Organization and Size• Cell organization & size helps them maintain

HOMEOSTASIS, stable internal environment.• A.) The organization of all cells is basically similar.• The plasma membrane, which is a membrane that surrounds

all cells, helps keep cells separate from their external environment.

• Plasma menbrane also serves as a SELECTIVE barrier of what enters & exist the cell.

• Cells have ORGANELLS which carry out specialized functions.

Cell Size

• B.) Cell size is limited.• Most cells are too microscopic to see with the naked eye.• The small micrometer is too small to see & count the

organelles of the cell, a nanometer is used instead.• A human egg can be seen with the naked eye, as big as a

period in a sentence.• A cell is small because it is much easier to maintain

homeostasis and do daily functions.• When a cell gets bigger, the volume increases faster than

the surface area also putting a restriction on size.

Cell Size

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Cell Shape & Function• Not all cells are spherical or cuboid.• Fingerlike projections from the plasma membrane are

called Microvilli, increase the surface area for absorption.• Some cells can change shape to accommodate a function. • Also small because molecules inside must travel distances.• This distance is smaller when the cell is small.

• C.) Cell size & shape are related to function• Size & shape are related to the function of a cell.• Examples: sperm, epithelial cells, nerve cells.

Methods for Studying Cells• One of the most important tools is the

microscope.• In 1665, Robert Hook discovered cells when he

observed dead cork and said they reminded him of the rooms monks lived in.

• Anton von Leeuwenhoek designed a good lens for microscopes a few years later and improved microscopy.



Cork cells

A.) Light microscopes are used to study stained cells

• Light microscope has a tube with glass lenses at each end, also called a compound microscope.

• Magnification is the ratio of size of image to actual size, usually no more than 1000X.

• Resolution is the capacity to distinguish detail.• Minimum space where two individual points can be seen, not blurry.• Bright-field uses light.• Dark-field has scattered light.• Phase contrast & differential interference contrast uses density.• Fluorescence looks at molecular structure of cells.

B.) Electron Microscope

• Ultra-structure is fine detail.• Electron microscopes magnify up to 1/4 million times.• Transmission Electron Microscope (TEM) requires

that the specimen is enbeded in plastic & cut into very thin strips to produce layered images.

• Scanning Electron Microscope (SEM) requires that the specimen is coated in metal and an indirect beam of electrons creates a 3-D image of the surface.

Microscopes



C.) Cell Fractionation enables study of cell organelles

• Cell fractionation is purifying organelles.• Centrifuge spins broken cells to form a pellet.• Pellet forms at bottom and supernatant is at the top

of solution.• The supernatant is spun again in differential

centrifugation, at higher speeds.• Pellets are further purified in density gradient

centrifugation.

Cell Fractionation



Prokaryotic & Eukaryotic cells• Prokaryotes do not have DNA in a nucleus but in a nuclear area

or Nucleoid, no membrane.• Prokaryote means before the nucleus.• Many prokaryotes have cell walls and flagella & have ribosomes.• Eukaryotes are highly organized, advanced cells.• Eukaryote means true nucleus.• Cells are filled with a jelly-like substance called protoplasm.• Outside nucleus is called cytosol.• Inside nucleus is called nucleoplasm. • Organelles in cytosol = cytoplasm.

Cell Membrane

• Lets things in & out of cell, keeps certain things away from other parts of the cell.

• Membranes are work surfaces that store energy.

• Endomembrane systems are all internal membranes.

• Some materials travel in vesicles.

Anatomy of a Cell Membrane

• A bi-phospholipid layer with integral proteins throughout.• Is Amphipathic due to hydrophobic & hydrophilic

regions.• 2-D fluid, cannot move without channel.• Lots of saturated fatty tails, become more solid.• Unsaturated, bends where double bonds exist.• Cholesterol acts as a buffer, either keeps tails apart or

brings them closer together. • Cholesterol makes the membrane more fluid at lower

temperature.

Types of membrane Proteins

• Receptor- recieves materials• Channel-lets things travel from one protein to another.• Enzymes- breaks down unwanted materials• Carrier- allows specific materials& ions to pass in & out• Recognition- identifies • Signal- gives signal for what is needed.• Aquaporins- gated water channels

Anatomy of a Cell Membrane



Methods of Movement across Membranes with no NRG

• Passive Transport- no NRG needed• Diffusion- particles randomly move from high

concentrations to low concentrations• Osmosis- diffusion of water through a membrane• Facilitated Diffusion- carrier protein facilitates the

movement of certain ions or other polar molecules from high concentration to low.

• A Concentration Gradient is created when there is different concentration of a substance on each side of a membrane.

Diffusion & Osmosis





Isotonic, Hypertonic, & Hypotonic Solutions

• Isotonic- same concentration of solutes on both sides of membrane, Equal movement of water.

• Hypertonic- more solute on outside of cell membrane. Movement of water is out of cell.

• Hypotonic- less solute on outside of cell. Movement of water is into cell



Plasmolysis

• Loss of turgor pressure• Water potential is from

inside cell to outside• Caused by putting cells in a

hypertonic solution.• Causes plant to wilt



Facilitated Diffusion



Methods of Movement across Membranes with NRG required

• Active Transport- ATP energy required• Sodium-Potassium Pump- a carrier mediated active transport system that

imports 2 potassium cations into the cell and exports 3 sodium cations.• This creates an unequal charge (Electrical gradient) due to more positive

charge on outside cell membrane.• This also creates a Membrane Potential because of the concentration

difference and charge difference.• Important in nerve impulses.• Endocytosis- taking in large particles by fusion to the cell memnbrane to

create a vacuole. (phago & pinocytosis)• Exocytosis- ridding large particles by fusion of a vesicle to the cell

membrane.

Sodium-Potassium Pump



Types of Endocytosis

• Phagocytosis- cell eating (WBC & bacteria)• Once inside, the large substance is digested by

lysosome enzymes.• Pinocytosis- cell drinking• Tiny droplets are taken in by folds in the membrane

that trap & pinch off inside.• Receptor- mediated endocytosis- special receptor

molecule called ligands combind with specific molecules on a coated pit & forms a coating around it before it pinches off inside the cell.

Exocytosis, Phagocytosis, & Pinocytosis







Receptor-Mediated Endocytosis



Cell Signaling• Mechanisms by which cells communicate with one another.• Most often use chemicals.• Signaling molecule from one cell will combine with a

receptor on another cell.• Example: cAMP,&neurotransmitters are signaling

molecules, GTP is a receptor molecule.• Enzymes are also used to catalyze the production on

secondary messenger molecules. See fig. 5-21• Signal Transduction is a process where cells convert and

amplify an extracellular signal into an intracellular signal

Cell Junctions

• Special intercellular connections

• Allow neighboring cells to do one or more of the following:

• form strong connections

• prevent passage of materials

• communicate with each other.

Types of Cell Junctions

• 1.) Anchoring Junctions• Tightly bound to each other. • Example: epithelial cells in the outer skin.• Cadherins are transmembrane proteins that play an important

role in these junctions.• Two types of anchoring junctions: Desmosomes & Adhering

junctions.• Adhering junctions cement cells together.• Cadherins form a continuous adhesion belt around each cell

connecting the microfilaments of the cytoplasm• Create a path for signaling from outside to inside cell.

Desmosomes

• Form points of attachment between cells like rivets.

• Substances still pass freely through the space between the membranes.

• Anchor to intermediate filaments inside the cell.



Cell Junctions cont.

• 2.) Tight Junctions• Seal off intercellular spaces between some

animal cells.• No space remains between cells.• Substances cannot leak between them.• Seal off body cavities.• Example: lining of intestine, blood-brain

barriers

Cell Junctions cont.• 3.) Gap Junctions• Bridges the space between cell but leaves very narrow spaces.• Are communicating junctions.• Contain channels that connect the cytoplasms of adjacent cells.• Composed of connexin, an integral membrane protein.• Groups of 6 connexin molecules cluster to form a cylinder that

spans the plasma membrane.• Small organic molecules, ions, and cAMP pass through the

channels.• Allow for rapid chemical & electrical communication.

Tight junctions & Gap Junctions


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Gap Junction Tight Junction

Cell Junctions cont.

• 4.) Plasmodesmata• Formed between plant cells.• Form between cell walls.• Connect the cytoplams.• Form cylindrical membranous

structures called desmotubule that connect the ER of ajacent cells.

• Allow molecule & ions to pass, not organelles.

• Can dilate their diameters.



cells advanced biology. organization of the cell cells are dramatic examples of the underlying unity...

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