Movement of materials. An understanding of this phenomenon requires you to know what each of the following is:

Solution- is a mixture of the following
Solvent - material in which something is dissolved
Solute - the material dissolved in the above

Concentration – the amount of material per unit volume. Since two things cannot occupy the same volume the concentrations of solvent and solute in a solution are directly related. The more of one the less of the other.
Unless at absolute 0 temp molecules are in motion. The rate being temperature dependant. This movement is termed Brownian motion and is random. As a consequence of this movement materials have a tendency to move from high concentrations to low until an equilibrium is established. This is what is termed Diffusion. Since movement is work that requires energy, the energy for this movement is in the concentration gradient  (Principles of Thermodynamics). Osmosis is a specific case of Diffusion involving the movement of water.

 

When one is looking at concentration differences in solutions one compares the solute concentration outside the cell with that inside.

In an ISOTONIC solution the solute concentrations outside the cell are equal to inside (therefore the same is true for the solvent and no diffusion or osmosis can occur because there is no gradient and therefore energy available)

In Hypertonic solutions the solute concentrations outside the cell are greater than inside (therefore the opposite is true for the solvent and no diffusion of solutes in can occur but osmosis and loss of water will occur because there are gradient and therefore energy available.

In Hypotonic solutions the solute concentrations outside the cell are lower than inside (therefore the opposite is true for the solvent and therefore  no diffusion of solutes in can occur. Diffusion is outward but prevented by the membrane being selectively permeable) Osmosis and potential gain of water will occur because there is a gradient and therefore energy available. In this situation and Isotonic cells require cellular energy to move materials.

 

Movement processes

Membranes cannot be completely permeable otherwise things would move back and forth with no regulation.
Cannot be impermeable otherwise nothing could move  - Therefore selectively permeable

Two fundamentally different processes involved with movement
Active and passive processes

Passive processes

Diffusion,  diffusion through channels (proteins) and Facilitated diffusion
All similar in that driving force (energy ) – concentration gradient

Diffusion within cells  - simple

Diffusion across membranes-  Simple Diffusion  involves small non polar molecules –regarded as Passive
More lipid soluble more rapidly it moves.

When equilibrium established no net movement

Osmosis – diffusion of water controlled by concentration of solutes
High solute negative osmotic potential
Pure water  zero

Variations in Osmotic potential drive movement of water

Isotonic           (isosmotic)
Hypertonic      (Hyperosmotic)
Hypotonic       (Hypoosmotic)

Tugor Pressure

Hydrophilic molecules rejected
Hydrophobic not
Sometimes charged molecules or ions enter however – due to channel proteins (called membrane transport proteins)

Allow diffusion of small charged ions, the  diameter determine size of molecule allowed through.  (filled with water therefore simple diffusion)

Facilitated diffusion – interaction with the carrier protein

2 types  Uniport – single solute  in one direction

Coupled-  two or more solutes transported  requires the presence of all the solutes involved to function

            Symport  - move same direction
Antiport  - Opposite directions

Carrier proteins dictate the movement therefore many.  Irrespactive concentration gradients provide the energy.

 

Active transport

Similar to facilitate diffusion in that requires carrier proteins, but energy not a result of concentration but provided by the cell

Primary – Direct involvement of ATP ( by dephosphorylation)

Secondary – Movement coupled with the movement of something else moving along a concentration gradient. Remember Na moves out against a gradient using ATP. It combines with glucose to create Na glucose that now has a concentration gradient and thus moves in.

Endocytosis  Pinocytosis vs Phagocytosis
May require receptor sites for molecule to attach to – Receptor mediated

Exocytosis  movement out rather than in.

Cell Structure:

There are two major cell types Prokaryotic (simple with no organelles) and Eukaryotic with organelles.

All cells have a cell Envelope (a variable layered structure isolating the cell from it environment)

Inside the envelope is the cytoplasm? A solution called the cytosol + suspended materials (organelles in eukaryotes)

Prokaryote Cell organization>

Cell envelope – outermost layer is the glycocalyx (glycoprotein) – not required!!
Is common in pathogens because of its properties

1. Attachment to surfaces
2. Site of virulence factors
3. Protection against phagocytosis

Inside this is the Cell Wallμ- not required but protects against Osmotic Shock. The rigidity is function of a macromolecule called Peptidoglycan (only found in prokaryotes).
Gram Positive – 90% peptidoglycan
Gram negative—10%

Inner most layer and most important ,therefore absolutely required- Cell membrane (40% phospholipid and 60 % protein.

                Functions are 1. Regulation of flow of materials
2. Energy Transformations ( Respiration & Photosynthesis)
Associated with the membrane are inward extentions

1. Mesosome (DNA and cytoplasm separation during Binary Fission)
2. Chromatophore ( bag like structure containing photosynthetic Pigment)

 

Cytoplasm Suspended materials (macromolecules with unique functions):

  Genetic information DNA is stored in an area of the cell called a nucleoid.
1.DNA is organized as a single circular chromosome (approx 1000μ long.)
10%vol)

In addition  there is extra genetic information ( Multiple miniature chromosomes{DNA} independent of the chromosome and exchangeable)

2.  RNA – three types m, t and r

1. Ribosomes (70S)

Replication of DNA, Transcription and Translocation occur in the cytoplasm.

Polycistronic (multiple genes are expressed at the same time)
Polyribosomal (many ribosomes on a single m RNA)

 Both  of the above increase the rate of biochemical activity

 

Inclusion bodies: Three (polymers) are not membrane bound and are associated with storage of required nutrients.

1. Glycogen – storage of carbohydrates- a polymer of glucose
2. Poly beta hydroxyl butyrate – a polymer of butyric acid for formation of lipids
3. Volutin- a polymer of orthophosphate, a source of phosphate

1. Endospore – membrane bound concentrated inactive organism produced for survival in adverse conditions. Only Gram + bacilli of the genera Bacillus and Clostridium (pathogens) produce them.

 

Eukaryotic Cell Structure:
Cell Envelope usually has a maximum of two layers.
Outermost layer:
Cell wall – gives rigidity and cell shape , Not usually found in Animalia and Protista.
In Fungi made of Chitin and in Plantae Cellulose

Animalia sometimes possess an extracellular matrix made of glycoprotein.

Inner and most important layer:
Cell Membrane(40% phospholipid and 60 % protein.

                Function is the Regulation of flow of materials only.

In plants there are outward extensions that connect the cytoplasm of adjacent cells-Plasmodesmata.

In protista outward extensions are formed by the cytoskeleton for movement- Pseudopodia.

Cytoplasmic Contents(Organelles)

Nucleus- a double membrane bound structure for the storage of genetic information

1. Holes called nucleopores for exchange of material between the cytoplasm and nucleoplasm
2. Chromosomes- multiple linear  - made of Chromatin
1. DNA genetic information
2. Histone protein for organization of chromosomes
3. Nucleolus – site of Ribosome {80S} formation

Replication of DNA and Transcription occur in the nucleoplasm!!!
Therefore RNA and Ribosomes at least temporarily found in the Nucleus

Endoplasmic Reticulum: Connected to the nucleus (double membrane)
Two parts 1. Rough ER (has Ribosomes on the outer membrane- therefore the site    
of Translation.

1. Smooth ER- site of protein modification and biosyntheisis 

                                   (particularly Lipids)

Golgi apparatus: Independent of ER. Vesicles formed in the SER transport proteins to the Golgi apparatus for sorting and distribution. (subdivided into large folds called Cisternae)

Lysosomes- generated from the Golgi Apparatus to transport proteins to the desired location.

Phagosomes – generated from the cell membrane by endocytosis and contain materials to be degraded . Degradation accomplished by mixing enzymes in lysosome with material in phagosome. Fusion of the two to produce a Secondary lysosome required.

Energy Generating Organelles:
Mitochondria - Found in all respirers including plants.

1. Smooth outer membrane for isolation
2. Highly folded inner membrane (cristae) – the location of Oxidative phophorylation
3. Mitochondrial matrix – the site of the TCA (Tricarboxylic Acid) cycle
4. mDNA and ribosomes {70S}

Chloroplast (in plants) the site of Photosynthesis – are a type of Plastid
1. Smooth outer membrane for isolation
2. Highly folded inner membrane (large folds – grana , small folds – thylakoids – 
chlorophyll associated with these folds – site of Light Dependant Reactions
3. Stroma – site of the Light Independent Reactions
4. DNA and ribosomes {70S}

Other Plastids:

1. Chromoplast – pigmented  but not photosynthetic
2. Amyloplast  - storage of Amylose a polmer of Glucose synthesized in photosynthesis.

Remember not all plastids are found in all plant cells.

Central  Vacuole- found in Plant cells. There are two main function

1. Turgor Pressure to generate rigidity
2. Increase Surface Area to volume Ratios to increase cell size above theoretical maximum.

Contractile Vacuole- found in Animal cells. Used regulate water uptake and prevent Osmotic Shock

Cytoskeleton. Found in all Eukaryotic cells. Made of Protein fibers or tube like structures. Three main types made of thre different types of protein and each have unique functions.

1. Actin filaments – capable of expansion and contraction & associated with cell movement
2. Intermediate Filaments – rigid primarily maintain the location of organelles with in cells
3. Microtubules ( usually generated from microtubule organizing centers –MTOC’s  - some are permanent and act as rails along which materials can move within the cell. Others are assembled and disassembled to move specific materials within the cell.