Chapter 4

Schwann, Schleiden and Virchow are credited with coming up with the basics of the cell theory

3 components:◦ 1.All living organisms are made up of cells◦ 2.Cells are the basic units of structure and

function in living organisms.◦ 3.All cells come from cells that existed before

them by cellular reproduction. http://www.youtube.com/watch?v=AeygTtDx2W8

Every cell has the following main characteristics:◦ Cell membrane◦ Cytoplasm◦ DNA◦ Ribosomes

Antone von Leeuwenhoek assembled the first microscope that was useful for scientific research.

Compound light microscopes reflect light through a set of lenses and the specimen to magnify the specimen.

See handout for the parts of the microscope – you must know it. http://www.youtube.com/watch?v=3emmlXcV-MU&feature=related

Two important characteristics that determine the quality of a light microscope:◦ Magnification – an increase in the apparent size of

an object. We calculate magnification by the following:

Magnification of eyepiece x magnification of objective lens = total magnifying power

• Resolution – the measure of clarity of an image. As the magnification increases, the resolution of the image decreases.

Some microscopes use beams of electrons for magnification instead of light – electron microscopes

Scanning electron microscope (SEM) – used to study the detailed architecture of the surface of the object. Forms a 3D image, but does not show the inside of the object.

Transmission electron microscope (TEM) – used to provide a detailed 2D image of the inside structure of the object that is viewed.

http://www.cellsalive.com/howbig.htm

Cells are microscopic, they are visible only with light microscopes.

Most of their size ranges from 1-100 µm. Cells are small, because they have to be

able to carry materials from one side of the cell to the next in a short period of time.

Cells must have a large enough surface area to be able to take in nutrients and oxygen and release waste quickly.

Prokaryotic cells – ◦ small cells (about 1-10 µm) that do not have a

nucleus and membrane-bound organelles◦ Found in bacteria and archaebacteria

Prokaryotic Cell Organelles:◦ Nucleoid region – part of the prokaryotic cell

where the DNA is found◦ Cell membrane – innermost covering of the cell◦ Cell wall – outside of cell membrane, made up of

a special mix of polysaccharides and proteins (antibiotics break it down)

◦ Capsule – outside of the cell wall, protective covering (not all bacteria have it)

◦ Flagella (sing. Flagellum) – long, whiplike structure that moves bacteria

◦ Pili – short, hair-like projection used to stick to other surfaces and for conjugation (exchange of genetic materials between bacteria)

◦ Cytoplasm – jelly-like fluid that dissolves substances and holds organelles

◦ Ribosomes – organelles that make proteins in the cytoplasm

http://www.ted.com/talks/lang/eng/bonnie_bassler_on_how_bacteria_communicate.html

Protists, Fungi, Plants, and Animals Have nucleus and membrane-bound

organelles Much larger and more complex than

prokaryotic cells. Reproduce sexually and asexually

Nucleus◦ Control center of cell; contains most of the cell’s

DNA Nucleolus

◦ Location where ribosomes are synthesized Nuclear pore

◦ Allows RNA to move in and out of nucleus

Ribosomes◦ Protein synthesis

Rough ER◦ Comprised of a network of tubes and flattened

sacs.◦ Continuous with plasma membrane and nuclear

membrane◦ Site of protein synthesis (consists of ribosomes)

Smooth ER◦ Site of lipid and carbohydrate metabolism◦ No ribosomes

Golgi Apparatus◦ Connected with ER; flattened disc-shaped sacs,

stacked one on top of the other◦ Modification, storage, and packaging of proteins.◦ “tags” proteins so they go to the correct

destination.

Lysosomes (in animal cells and some protists)◦ Digestion of nutrients, bacteria, and damaged

organelles; destruction of certain cells during embryonic development

Peroxisomes◦ Diverse metabolic processes with breakdown of

H2O2 by-product Vacuoles

◦ Digestion (like lysosomes); storage of chemicals, cell enlargement; water balance

Chloroplasts◦ Conversion of light energy to chemical energy of

sugars (site of photosynthesis) Mitochondria

◦ Conversion of chemical energy of food to chemical energy of ATP

◦ “Power House” of cell◦ Bound by double membrane

Mitochondria

Cytoskeleton (including cilia, flagella, and centrioles in animal cells)◦ Maintenance of cell shape; anchorage for

organelles; movement of organelles within cells; cell movement; mechanical transmission of signals from exterior of cell to interior.

Cell walls (in plants, fungi, and protists)◦ Maintenance of cell shape and skeletal support;

surface protection; binding of cells in tissues

We will be looking at:◦ Cell Membranes◦ Selective permeability of cell membranes◦ The phospholipid bilayer that makes up cell

membranes◦ The model that describes cell membrane, the Fluid

Mosaic Model◦ Cell Transport Processes

Membranes provide the structural basis for metabolic order and surround the cell.

Most organelle’s are made from membranes Semipermiability- Regulate the transport

of molecules in and out of the cell Immune response Attaches cells to other cells or surfaces.

Cell membranes control what goes in and out of the cell

It allows some substances to cross more easily than others

Cell membrane is amazingly thin

Lipids, mainly phopholipids, are the main structural components of membranes

Phospolipid has a phosphate group and only two fatty acids◦ Head, with a charged phosphate group, is

hydrophillic◦ Fatty acid tails are nonpolar and hydrophobic◦ Thus, the tail end is pushed away by water, while

the head is attracted to water

Hydrophobic interior of the bilayer is one reason membranes are selectively permeable.

Nonpolar, hydrophobic molecules are lipid-soluble can easily pass through membranes

Polar molecules and ions are not lipid-soluble ◦ Ability to pass through membrane depends on

protein molecules in the phospholipid bilayer.

Phospholipid

Phospholipids form a two-layer sheet called a phospholipid bilayer. ◦ Hydrophillic heads face outward, exposed to

the water on both sides of a membrane◦ Hydrophobic tails point inward, mingling

together and shielded from water.

Hydrophobic interior of the bilayer is one reason membranes are selectively permeable.

Nonpolar, hydrophobic molecules are lipid-soluble can easily pass through membranes

Polar molecules and ions are not lipid-soluble ◦ Ability to pass through membrane depends on

protein molecules in the phospholipid bilayer.

Plasma membrane is described as a “Fluid Mosaic”

Mosaic denotes a surface made of small fragments, like pieces of colored tile◦ A membrane is considered “mosaic” because it

has diverse protein molecules embedded in a framework of phospholipids.

◦ A membrane mosaic is “fluid” in that most of the individual proteins and phospholipids can can drift literally in the membrane

Tails of phospholipids are kinked.◦ Kinks make the membrane more fluid by keeping

adjacent phospholipids from packing tightly together.

In animal cells, the steroid cholesterol stabilize the phospholipids at body temperature and also keep the membrane fluid at lower temperatures. ◦ In a cell, phospholipid bilayer remains about as

fluid as salad oil at room temperature.

◦ Cell Membrane Proteins: Integral proteins – act as ion channels or molecular

channels Peripheral proteins – act as receptors

Cell membrane carbohydrates bonded to proteins and lipids in the membrane: A protein with attached sugars is called a

glycoprotein whereas a lipid with sugars is called a glycolipid.

Function as cell identification tags that are recognized by other cells.

Significant for cells in an embryo to sort themselves to tissues and organs.

Also functions in the immune system to recognize and reject foreign cells.

Transport means the movement of molecules from one side of the cell membrane to the other

Transport is influenced by:◦ The size of substances ◦ The polarity of substances◦ The concentration of substances◦ The permeability of the cell membrane

Passive◦ Diffusion◦ Osmosis◦ Facilitated diffusion

Active Bulk

◦ Endocytosis◦ Exocytosis

Diffusion of a substance across a biological membrane

Diffusion is the movement of particles from high concentration to low concentration.

Moves with a concentration gradient No energy input required Eventually reaches equilibrium

◦ Molecules continue to move back and forth, but no net change in concentration will occur

Small, nonpolar molecules that easily diffuse across plasma membranes, such as O2 and CO2

Simple Diffusion

Osmosis◦ the diffusion of water across the cell membrane.

Especially important when the solute cannot move through the membrane.

◦ Tonicity: Describes the tendency of a cell in a given solution

to lose or gain water. Isotonic, hypertonic, and hypotoni

Osmosis (continued):◦ Isotonic solution

Equal concentration of solvent inside and outside of cell; water goes in and out

Cell’s volume remains the same; equilibrium◦ Hypertonic solution

Solute concentration is lower inside cell (solvent concentration is higher inside cell) ;Water goes out

Cell shrivels Causes plasmolysis in plant cells

Osmosis (continued):◦ Hypotonic solution

Solute concentration is greater inside the cell (solvent concentration is lower inside the cell); water goes in

Cell swells and may lyse Causes cytolysis in animal cells Refer to figure 5.17

Osmosis

Osmotic Pressure◦ The pressure exerted by the flow of water through

a semipermeable membrane separating two solutions with different concentrations of solute.

◦ Higher concentration of dissolved substances will result in lower osmotic pressure and in the movement of water into the area with more dissolved substances.

Facilitated diffusion◦ Many substances can’t diffuse freely across

membrane because of their size, polarity, or charge

◦ Need the help of specific transport proteins in the membrane to move across the membrane

Transport processes that can move substances from the lower concentration area to the higher by using energy.

Energy is gained by using ATP molecules

A type of active transport is the Na-K ion pump◦ 3 sodium ions move out of the cell with the help

of a transport protein, while 2 potassium ions move into the cell.

◦ This process requires energy in the form of ATP.

Type of active transport that involves movement of large particles.

Endocytosis – a process by which large particles can move into the cell by using membrane vesicles

Types of endocytosis:◦ Phagocytosis – engulfing solid particles◦ Pinocytosis – engulfing liquids, solutions◦ Receptor-mediated endocytosis – moving into

the cell by first binding with receptor molecules on the cell’s surface.

Receptor-mediated endocytosis

Exocytosis – the process by which the cell releases large molecules via vesicles through its cell membrane