Light microscope Magnification

The ratio of the size of an image to the real size of the object.

Resolution A measure of the clarity of an image and is

determined by the minimum distance two points must be separated to be seen as separate.

0.2 um limit of light microscopes Most membrane-enclosed organalles cannot be resolved

by light microscope.

Microscopy

Electron microscope Focuses a beam of electrons through a specimen

or onto its surface. Resolution= 2nm

100x greater than a light microscope. Transmission electron microscope

Beam of electrons is passed through a thin section of a specimen stained with atoms of heavy metals.

Electromagnets, acting as lenses, then focus the image onto a monitor.

Microscopy

Scanning electron microscope An electron beam scans the surface of a specimen

that is usually coated with a thin gold film. The beam excites electrons from the specimen,

which are detected and translated into an image on a video screen and appears three-dimensional.

What do cell biologist use a TEM to study? What does an SEM show best? What advantages does light microscopy have

over both TEM and SEM?

Microscopy

Compare and Contrast The small size of cells is influenced by

geometry Area is proportional to the square of linear

dimension. Volume is proportional to its cube. The plasma membrane surrounding every cell

must provide sufficient surface are for exchange of oxygen, nutrients, and wastes relative to the volume of the cell.

Prokaryotic vs. Eukaryotic

Membranes compartmentalize the eukaryotic cell, providing local environments for specific metabolic functions.

Questions Describe the molecular structure of the plasma

membrane. If a eukaryotic cell has a linear dimension that is 10

times that of a bacterial cell, proportionally how much more surface are would the eukaryotic cell have?

Proportionally how much more volume would it have?

Prokaryotic vs. Eukaryotic

Nuclear envelope Phospholipid bilayer Nuclear pores

Chromosomes Made of DNA and proteins (Histones)

DNA is the heredity information carrying the code that is used to make proteins.

Nucleolus Portion of the DNA that manufactures the

components of ribosomes. Ribosomes are shipped to the cytoplasm where

they assemble amino into proteins.

Nucleus-Information Central

Composed of protein and ribosomal RNA. Free ribosomes

Proteins produced are used within the cell. Attached or Bound ribosomes

Attached to the endoplasmic reticulum Usually make proteins that will be included in

the membranes, packaged into organelles, or exported from the cell.

Ribosome-Protein Factory

Consists of stacks of flattened membranes involved in the production of various materials.

Cross section, they appear as a series of mazelike channels.

Rough ER- ribosomes are attached ER serves to attach polysaccharide groups to

polypeptides as they are assembled by the ribosomes. Smooth ER- no ribosomes

Synthesis of lipids and steroid hormones Carbohydrate metabolism Breakdown of toxins, drugs, and toxic by-products.

Liver cells

Endoplasmic reticulum (ER)Regulates protein traffic and performs

metabolic functions in the cell

Flattened membrane sacs arranged like a stack of bowls.

Function to modify and package proteins and lipids into vesicles. Small round-shaped membrane sacs that bud

from the ends of a Golgi body. Vesicles often migrate to and merge with the

plasma membrane, releasing their contents outside the cell.

Golgi Complex (Apparatus)Shipping and Receiving Center

In animal cells: Are vesicles from Golgi bodies that contain

digestive (hydrolytic) enzymes that digest macromolecules.

They serve to break down food, cellular debris, and foreign invaders such as bacteria.

In protists: Lysosomes fuse with food vacuoles to digest

material ingested by phagocytosis. Macrophages (type of white blood cell)

Use lysosome to destroy bacteria. Recycle a cell’s own macromolecules.

LysosomesDigestive Compartments

Mitochondria and Chloroplast

Carry out aerobic respiration

A process of obtaining energy (ATP) from carbohydrates

Carry out photosynthesis.

The process of incorporating energy from light into carbohydrates

A network of fibers that organize structures and activities in the cell.

Network of protein fibers that give mechanical support and function in cell motility (of both internal structures and the cell as a whole).

Three main types of fibers found in the cytoskeleton Microtubules, microfilaments, and intermediate

filaments.

Cytoskeleton

Made of the protein tubulin Function to provide support and motility

for cellular activities. Found in spindle apparatus which guides

the movement of chromosomes during cell division.

Found in flagella and cilia, structures that project from the plasma membrane to provide motility for the cell.

Microtubules

Intermediate filaments and Microfilaments

Provide support for maintaining the shape of the cell

Made of the protein actin

Involved in cell motility

Found in muscle cells and in cells that move by changing shape, such as amoeba

Structures that protrude from the cell membrane and make wavelike movements

Cilia Numerous and short, like short hairs.

Flagella One or two to a cell and are long, like a tail.

Flagella and Cilia

Located outside the nuclear membrane. Gives rise to the microtubules that make up

the spindle apparatus used during cell division

Centrioles

Found in plants, fungi, protists, and bacteria Outside the plasma membrane Provide support for the cell Plants

Made of cellulose Primary cell wall; middle lamella (a thin layer of

polysaccharides called pectin, glue adjacent cells together); secondary cell wall; plasmodesmata

Fungi Made of cellulose or chitin

Cell Walls

Storage vesicle or Food vacuole Fluid-filled bodies Central vacuole in plants

Turgor pressure on the cell walls maintains rigidity in the cell

Without cell turgor, a plant cell will wilt

Vacuoles

Specialized metabolic compartment bounded by a single membrane.

Oxidative organelle filled with enzymes that function in a variety of metabolic pathways, such as: Enzymes transfer hydrogen atoms from certain

molecules to oxygen, producing hydrogen peroxide as a by-product; H2O2 is converted to water by another enzyme.

Breaking down fatty acids for energy. Detoxifying alcohol, hydrogen peroxide, and other

poisons or toxins.

Peroxisomes

Boundary that separates the living cell from its nonliving surroundings.

Is about 8 nm thick. Surrounds the cell and controls chemical

traffic into and out of the cell. Is selectively permeable

It allows some substances to cross more easily than others.

Has a unique structure which determines its function and solubility characteristics.

Membrane Structure

The fluid quality of membranes1. Held together by hydrophobic interactions,

which are weak attractions.2. Most membranes lipids and some proteins

can drift laterally within the membrane.3. Phopholipids move quickly along the

membrane’s plane, 2 um per second.

A membrane is a fluid mosaic of lipids, proteins, and

carbohydrates

4. Membrane proteins drift more slowly than lipids

5. Some membranes proteins are tethered to the cytoskeleton and cannot move far.

A membrane is a fluid mosaic of lipids, proteins, and

carbohydrates

Membranes must be fluid to work properly. Solidification may result in permeability changes and enzyme deactivation.

1. Unsaturated hydrocarbon tails enhance membrane fluidity, because kinks at the carbon-to-carbon double bond hinder close packing of phospholipids.

2. Membranes solidify if the temperature decreases to a critical point. Critical temperature is lower in membranes with a greater concentration of unsaturated phospholipids.

A membrane is a fluid mosaic of lipids, proteins, and

carbohydrates

3. Cholesterol modulates membrane fluidity by making the membrane:

*less fluid at warmer temperatures by restraining phospholipid movement.

*more fluid at lower temperatures by preventing close packing of phospholipids.

4. Cells may alter membrane lipid concentration in response to changes in temperature. Many cold tolerant plants (e.g. winter wheat) increase the unsaturated phospholipid concentration in autumn, which prevents the membranes from solidifying in winter.

A membrane is a fluid mosaic of lipids, proteins, and

carbohydrates

Different proteins embedded and dispersed in the phospholipid bilayer.1. Integral proteins- generally transmembrane protein with hydrophobic interior of the membrane.2. Peripheral proteins- which not embedded but attached to the membrane’s surface.

*may be attached to integral proteins or held by fibers of the ECM.

*on cytoplasmic side, may be held by filaments of the cytoskeleton.

Membrane as mosaics of sturcture and function

Membranes are bifacial. The membrane’s synthesis and

modification by the ER and Golgi determines the asymmetric distribution of lipids, proteins, and carbohydrates:

1. Two lipid layers may differ in lipid composition.

2. Membrane proteins have distinct directional orientation.

3. Carbohydrates are restricted to the membrane’s exterior.

Membrane as mosaics of sturcture and function

Cell-cell recogntion = the ability of a cell to determine if other cells it encounters are alike or different from itself.

Is crucial in the functioning of an organism. It is the basis for:1. Sorting of an animal embyro’s cell into tissues and organs.2. Rejection of foreign cells by the immune system.

Membrane carbohydrates and cell-cell recognition

The way cells recognize other cells is probably by keying on cell markers found on the external surface of the plasma membrane.

Because of their diversity and location, likely candidates for such cell markers membrane carbohydrates:

1.Usually branched oligosaccharides2.Some covalently bonded to lipids (glycolipids)3.Most covalently bonded to proteins (glycoproteins)4.Vary from species to species, between individuals

of the same species and among cells in the same individual.

Membrane carbohydrates and cell-cell recognition

Selective permeability = property of biological membranes which allows some substances to cross more easily than others.

Selective permeability depends upon: Membrane solubility characteristics of the

phospholipid bilayer. Presence of specific integral transport proteins.

Traffic Across Membranes

Permeability of the lipid bilayer Nonpolar (hydrophobic) molecules

Dissolve in the membrane and cross it with ease Hydrocarbons, Oxygen, Carbon Dioxide

Polars (hydrophilic) molecules Small, polar uncharged molecules that are small enough

to pass between membrane lipids, will easily pass through. Water, ethanol

Larger, polar uncharged molecules will not easily pass through Glucose

All ions have difficulty penetrating the hydrophobic layer. Na+, H+

Traffic Across Membranes

Transport proteins = integral membrane protein that transport specific molecules or ions across biological membrane. Provide a hydrophilic tunnel through the

membrane. Bind to a substance and physically move it

across the membrane. Are specific for the substance they translocate.

Traffic Across Membranes

Passive transport Concentration gradient (Down) Diffusion

Example: movement of O2 and CO2

Osmosis Hypertonic solution

Animal cell: lose water and shrivel Plant cell: lose water, plasma membrane pulls away

from the cell wall, and loses turgor pressure. Hypotonic solution

Animal cell: gain water and lysis (bursting) Plant cell: gain water and become turgid

Isotonic solution- no osmosis

Traffic Across Membranes

Facilitate diffusion An integral protein allows a solute to diffuse

down a concentration gradient The cell does not use energy. The rate of facilitated diffusion depends on the

number of specific integral proteins and the strength concentration gradient.

Traffic Across Membranes

Active transport Involves the aid of a transport protein. Moves a solute against a concentration gradient Energy expenditure in the form of ATP-mediated

phosphorylation is required to help the protein change its structure and thus move the solute molecule

Active transport proteins often couple the passage of two solutes in opposite directions across membranes. Sodium-potassium pump, which functions in nerve impulse

transmission.

Traffic Across Membranes

Traffic Across Membranes

Exocytosis Process of exporting

macromolecules from a cell by fusion of vesicles with the plasma membrane

Vesicles usually budded from the ER or Golgi and migrates to plasme membrane

Used by secretory cells to export products Insulin in pancreas Neuro-transmitter from

neuron

Endocytosis Process of importing

macromolecules into a cell by forming vesicles derived from the plasma membrane

Vesicles forms from a localized region of plasma membrane that sinks inward; pinches off into the cytoplasm

Used by cells to incorporate extracellular substances

Receptor-mediated endocytosis More discriminating process than pinocytosis A molecule that binds to a specific receptor

site of another molecule is called a ligand. Membrane-embedded proteins with specific

receptor sites exposed to the cell’s exterior’s, cluster in regions called coated pits.

Traffic Across Membranes

Progressive stages of receptor-mediated endocytosis

Extracellular ligand binds to receptorin a coated pit.

Causes inwardbudding of the

coated pit.

Forms a coatedvesicle inside aclathrin cage.

Ingested materialis liberated from

the vesicle

Protein receptorscan be recycled to

the plasma membrane

Example: cholesterol enters cells In the blood, cholesterol is bound to lipid and

protein complexes called low-density lipoproteins (LDLs)

These LDLs bind to LDL receptors on cell membranes, initiating endocytosis.

An inherited disease call familial hypercholesterolemia is characterized by high cholesterol levels in the blood. LDL receptors are defective, so cholesterol cannot enter

the cells by endocytosis and thus accumulates in the blood, contributing to the development of atherosclerosis.

Receptor-mediated endocytosis

Composed of glycoproteins and other carbohydrate-containing molecules. Collagen forms strong fibers that are embedded in a network of

proteoglycan complexes. These large complexes form when multiple proteoglycans, each consisting of a small core protein with many carbohydrates chains, link to a long polysaccharide.

Cells may be attached to the ECM by fibronectins and other glycoproteins that bind to integrins, proteins that span the plasma membrane and bind, via other protein, to microfilaments of the cytoskeleton.

Thus, information about changes outside the cell can be communicated through a mechanical signaling pathway involving fibronectins, integrins, and the microfilaments of the cytoskeleton. Signals from the ECM appear to influence the activity of genes in the nucleus.

Extracellular Matrix (ECM)Animal Cells

Plants- Plasmodesmata Channels in plant cell walls through the plasma membranes of

bordering cells connect, thus linking most cells of a plant into a living continuum.

Water, small solutes, and some proteins and RNA molecules can move through these channels.

Animals- Tight junction

Proteins hold adjacent cell membranes tightly together Desmosomes (anchoring junctions) Gap junctions (communicating junctions)

Are cytoplasmic connections that allow for the exchange of ion and small molecules between cells through protein-lined pores.

Cell Junctions