MEMBRANE PERMEABILITY

•SELECTIVE PERMEABILITY - THE PERMEABILITY OF THE PLASMA MEMBRANE TO DIFFERENT SUBSTANCES VARIES. - PLASMA MEMBRANES PERMIT SOME SUBSTANCES TO PASS MORE READILY THAN OTHERS.

GRADIENTS ACROSS THE PLASMA MEMBRANE

• CONCENTRATION GRADIENT - A DIFFERENCE IN THE CONCENTRATION OF A CHEMICAL FROM ONE PLACE TO ANOTHER, SUCH AS FROM THE INSIDE TO THE OUTSIDE OF THE PLASMA MEMBRANE. - MANY IONS AND MOLECULES ARE MORE CONCENTRATED IN EITHER THE CYTOSOL OR THE EXTRACELLULAR FLUID

•MEMBRANE POTENTIAL (ELECTRICAL GRADIENT)

- A DIFFERENCE IN THE DISTRIBUTION OF POSITIVELY AND NEGATIVELY CHARGED IONS BETWEEN THE TWO SIDES OF THE PLASMA MEMBRANE. - TYPICALLY, THE INNER SURFACE OF THE PLASMA MEMBRANE IS MORE NEGATIVELY CHARGED AND THE OUTER SURFACE IS MORE POSITIVELY CHARGED

• ELECTROCHEMICAL GRADIENT - THE COMBINED INFLUENCE OF THE CONCENTRATION GRADIENT AND THE ELECTRICAL GRADIENT ON MOVEMENT OF A PARTICULAR ION - MOVEMENT OF SUBSTANCES: A. AREA OF MORE TO LESS CONCENTRATION B. POSITIVELY CHARGED SUBSTANCE TO A NEGATIVELY CHARGED AREA AND VICE VERSA

TRANSPORT ACROSS THE PLASMA MEMBRANE

•DIFFUSION - IS A PASSIVE PROCESS IN WHICH THE RANDOM MIXING OF PARTICLES IN A SOLUTION OCCURS BECAUSE OF THE PARTICLES’ KINETIC ENERGY - BOTH THE SOLUTES AND THE SOLVENT UNDERGO DIFFUSION.

- IF A PARTICULAR SOLUTE IS PRESENT IN HIGH CONCENTRATION IN ONE AREA OF A SOLUTION AND IN LOW CONCENTRATION IN ANOTHER AREA, SOLUTE MOLECULES WILL DIFFUSE TOWARD THE AREA OF LOWER CONCENTRATION UNTIL THE PARTICLES BECOME EVENLY DISTRIBUTED THROUGHOUT THE SOLUTION AND THE SOLUTION IS SAID TO BE AT EQUILIBRIUM

• FACTORS INFLUENCING DIFFUSION RATE ACROSS PLASMA MEMBRANES:

1. STEEPNESS OF THE CONCENTRATION GRADIENT2. TEMPERATURE3. MASS OF THE DIFFUSING SUBSTANCE*4. SURFACE AREA5. DIFFUSION DISTANCE*

• 3 TYPES OF DIFFUSION:A. SIMPLE DIFFUSION - A PASSIVE PROCESS IN WHICH SUBSTANCES MOVE FREELY THROUGH THE LIPID BILAYER OF THE PLASMA MEMBRANES OF CELLS WITHOUT THE HELP OF MEMBRANE TRANSPORT PROTEINS - NONPOLAR, HYDROPHOBIC MOLECULES AND SMALL, UNCHARGED POLAR MOLECULES PASS THROUGH THE LIPID BILAYER BY SIMPLE DIFFUSION

B. FACILITATED DIFFUSION - IN THIS PROCESS, AN INTEGRAL MEMBRANE PROTEIN ASSISTS A SPECIFIC SUBSTANCE ACROSS THE MEMBRANE. THE INTEGRAL MEMBRANE PROTEIN CAN BE EITHER A MEMBRANE CHANNEL OR A CARRIER. - SOLUTES THAT ARE TOO POLAR OR HIGHLY CHARGED

•OSMOSIS - A TYPE OF DIFFUSION IN WHICH THERE IS NET MOVEMENT OF A SOLVENT THROUGH A SELECTIVELY PERMEABLE MEMBRANE. - A PASSIVE PROCESS WHERE THE SOLVENT IS WATER, WHICH MOVES BY OSMOSIS ACROSS PLASMA MEMBRANES FROM AN AREA OF HIGHER WATER CONCENTRATION TO AN AREA OF LOWER WATER CONCENTRATION

- WATER MOVES THROUGH A SELECTIVELY PERMEABLE MEMBRANE FROM AN AREA OF LOWER SOLUTE CONCENTRATION TO AN AREA OF HIGHER SOLUTE CONCENTRATION*AQUAPORINS - INTEGRAL MEMBRANE PROTEINS THAT FUNCTION AS WATER CHANNELS.

•ACTIVE TRANSPORT - IS CONSIDERED AN ACTIVE PROCESS BECAUSE ENERGY IS REQUIRED FOR CARRIER PROTEINS TO MOVE SOLUTES ACROSS THE MEMBRANE AGAINST A CONCENTRATION GRADIENT.

A. PRIMARY ACTIVE TRANSPORT - ENERGY DERIVED FROM HYDROLYSIS OF ATP CHANGES THE SHAPE OF A CARRIER PROTEIN, WHICH “PUMPS” A SUBSTANCE ACROSS A PLASMA MEMBRANE AGAINST ITS CONCENTRATION GRADIENT

B. SECONDARY ACTIVE TRANSPORT - THE ENERGY STORED IN A NA OR H CONCENTRATION GRADIENT IS USED TO DRIVE OTHER SUBSTANCES ACROSS THE MEMBRANE AGAINST THEIR OWN CONCENTRATION GRADIENTS. - BECAUSE A NA OR H GRADIENT IS ESTABLISHED BY PRIMARY ACTIVE TRANSPORT, SECONDARY ACTIVE TRANSPORT INDIRECTLY USES ENERGY OBTAINED FROM THE HYDROLYSIS OF ATP

• SYMPORTERS - IF TRANSPORTERS MOVE TWO SUBSTANCES IN THE SAME DIRECTION • ANTIPORTERS - MOVE TWO SUBSTANCES IN OPPOSITE DIRECTIONS ACROSS THE MEMBRANE

CYTOPLASM-CONSISTS OF ALL THE CELLULAR CONTENTS BETWEEN THE PLASMA MEMBRANE AND THE NUCLEUS, AND HAS TWO COMPONENTS:I. THE CYTOSOL (INTRACELLULAR FLUID) - IS THE FLUID PORTION OF THE CYTOPLASM THAT SURROUNDS ORGANELLES AND CONSTITUTES ABOUT 55% OF TOTAL CELL VOLUME

- IS 75–90% WATER PLUS VARIOUS DISSOLVED AND SUSPENDED COMPONENTS

- THE CYTOSOL IS THE SITE OF MANY CHEMICAL REACTIONS REQUIRED FOR A CELL’S EXISTENCE.

•CYTOSKELETON - IS A NETWORK OF PROTEIN FILAMENTS THAT EXTENDS THROUGHOUT THE CYTOSOL

- THREE TYPES OF FILAMENTS CONTRIBUTE TO THE CYTOSKELETON’S STRUCTURE, AS WELL AS THE STRUCTURE OF OTHER ORGANELLES:

1. MICROFILAMENTS - ARE THE THINNEST ELEMENTS OF THE CYTOSKELETON. THEY ARE COMPOSED OF THE PROTEINS ACTIN AND MYOSIN AND ARE MOST PREVALENT AT THE EDGE OF A CELL - MICROFILAMENTS HAVE TWO GENERAL FUNCTIONS: A. THEY HELP GENERATE MOVEMENT (MUSCLE CONTRACTION, CELL DIVISION, AND CELL LOCOMOTION) B. PROVIDE MECHANICAL SUPPORT

•MICROVILLI - NONMOTILE, MICROSCOPIC FINGERLIKE PROJECTIONS OF THE PLASMA MEMBRANE. WITHIN EACH MICROVILLUS IS A CORE OF PARALLEL MICROFILAMENTS2. INTERMEDIATE FILAMENTS - THICKER THAN MICROFILAMENTS BUT THINNER THAN MICROTUBULES

- SEVERAL DIFFERENT PROTEINS CAN COMPOSE INTERMEDIATE FILAMENTS, WHICH ARE EXCEPTIONALLY STRONG - THEY ARE FOUND IN PARTS OF CELLS SUBJECT TO MECHANICAL STRESS3. MICROTUBULES - THE LARGEST OF THE CYTOSKELETAL COMPONENTS, ARE LONG, UNBRANCHED HOLLOW TUBES COMPOSED MAINLY OF THE PROTEIN TUBULIN

- HELP DETERMINE CELL SHAPE - THEY ALSO FUNCTION IN THE MOVEMENT OF ORGANELLES SUCH AS SECRETORY VESICLES, OF CHROMOSOMES DURING CELL DIVISION, AND OF SPECIALIZED CELL PROJECTIONS, SUCH AS CILIA AND FLAGELLA

II. ORGANELLES - SPECIALIZED STRUCTURES WITHIN THE CELL THAT HAVE CHARACTERISTIC SHAPES, AND THEY PERFORM SPECIFIC FUNCTIONS IN CELLULAR GROWTH, MAINTENANCE, AND REPRODUCTION1. RIBOSOMES - ARE THE SITES OF PROTEIN SYNTHESIS - THEY HAVE A HIGH CONTENT OF ONE TYPE OF RIBONUCLEIC ACID (RIBOSOMAL RNA, OR RRNA), BUT EACH ONE ALSO INCLUDES MORE THAN 50 PROTEINS

- SOME ARE ATTACHED TO THE OUTER SURFACE OF THE NUCLEAR MEMBRANE AND TO THE ENDOPLASMIC RETICULUM. THESE RIBOSOMES SYNTHESIZE PROTEINS DESTINED FOR SPECIFIC ORGANELLES, FOR INSERTION IN THE PLASMA MEMBRANE, OR FOR EXPORT FROM THE CELL. - SOME ARE “FREE” OR UNATTACHED TO OTHER CYTOPLASMIC STRUCTURES. FREE RIBOSOMES SYNTHESIZE PROTEINS USED IN THE CYTOSOL.

- RIBOSOMES ARE ALSO LOCATED WITHIN MITOCHONDRIA, WHERE THEY SYNTHESIZE MITOCHONDRIAL PROTEINS2.ENDOPLASMIC RETICULUM (ER) - IS A NETWORK OF MEMBRANES IN THE FORM OF FLATTENED SACS OR TUBULES THE ER EXTENDS FROM THE NUCLEAR ENVELOPE TO WHICH IT IS CONNECTED AND PROJECTS THROUGHOUT THE CYTOPLASM

•ROUGH ER - IS CONTINUOUS WITH THE NUCLEAR MEMBRANE AND USUALLY IS FOLDED INTO A SERIES OF FLATTENED SACS. THE OUTER SURFACE OF ROUGH ER IS STUDDED WITH RIBOSOMES, THE SITES OF PROTEIN SYNTHESIS. - PRODUCES SECRETORY PROTEINS, MEMBRANE PROTEINS, AND MANY ORGANELLAR PROTEINS.

•SMOOTH ER - EXTENDS FROM THE ROUGH ER TO FORM A NETWORK OF MEMBRANE TUBULES - DOES NOT HAVE RIBOSOMES ON THE OUTER SURFACES OF ITS MEMBRANE. - DOES NOT SYNTHESIZE PROTEINS, BUT IT DOES SYNTHESIZE FATTY ACIDS AND STEROIDS, SUCH AS ESTROGENS AND TESTOSTERONE

- IT INACTIVATES OR DETOXIFIES DRUGS AND OTHER POTENTIALLY HARMFUL SUBSTANCES; REMOVES THE PHOSPHATE GROUP FROM GLUCOSE-6-PHOSPHATE; AND STORES AND RELEASES CALCIUM IONS THAT TRIGGER CONTRACTION IN MUSCLE CELLS.

3. GOLGI COMPLEX - SOME PROTEINS SYNTHESIZED BY RIBOSOMES ATTACHED TO ROUGH ER ARE ULTIMATELY TRANSPORTED TO OTHER REGIONS OF THE CELL INITIALLY THROUGH THE GOLGI COMPLEX - CONSISTS OF 3 TO 20 CISTERNAE, SMALL, FLATTENED MEMBRANOUS SACS WITH BULGING EDGES

• FUNCTIONS OF THE GOLGI COMPLEX:

A. MODIFIES, SORTS, PACKAGES, AND TRANSPORTS PROTEINS RECEIVED FROM THE ROUGH ER.B. FORMS SECRETORY VESICLES THAT DISCHARGE PROCESSED PROTEINS VIA EXOCYTOSIS INTO EXTRACELLULAR FLUID; FORMS MEMBRANE VESICLES THAT FERRY NEW MOLECULES TO THE PLASMA MEMBRANE; FORMS TRANSPORT VESICLES THAT CARRY MOLECULES TO OTHER ORGANELLES, SUCH AS LYSOSOMES.

4. LYSOSOMES - MEMBRANE-ENCLOSED VESICLES THAT FORM FROM THE GOLGI COMPLEX - THEY CAN CONTAIN AS MANY AS 60 KINDS OF POWERFUL DIGESTIVE AND HYDROLYTIC ENZYMES THAT CAN BREAK DOWN A WIDE VARIETY OF MOLECULES ONCE LYSOSOMES FUSE WITH VESICLES FORMED DURING ENDOCYTOSIS.

FUNCTIONS OF THE LYSOSOME:A.DIGEST SUBSTANCES THAT ENTER A CELL VIA ENDOCYTOSIS AND TRANSPORT FINAL PRODUCTS OF DIGESTION INTO CYTOSOL.B. CARRY OUT AUTOPHAGY, THE DIGESTION OF WORN-OUT ORGANELLESC.IMPLEMENT AUTOLYSIS, THE DIGESTION OF AN ENTIRE CELL.D. ACCOMPLISH EXTRACELLULAR DIGESTION

5. MITOCHONDRIA-REFERRED TO AS THE “POWERHOUSES” OF THE CELL BECAUSE THEY GENERATE MOST OF THE ATP THROUGH AEROBIC RESPIRATIONFUNCTIONS: - GENERATE ATP THROUGH REACTIONS OF AEROBIC CELLULAR RESPIRATION. - PLAY AN IMPORTANT EARLY ROLE IN APOPTOSIS.

6. CILIA AND FLAGELLA - MOTILE CELL SURFACE PROJECTIONS THAT CONTAIN 20 MICROTUBULES AND A BASAL BODY.FUNCTIONS:• CILIA: MOVE FLUIDS OVER CELL’S SURFACE; • FLAGELLA: MOVE ENTIRE CELL.

7. PROTEASOME - TINY BARREL-SHAPED STRUCTURE THAT CONTAINS PROTEASES (PROTEOLYTIC ENZYMES). - DEGRADES UNNEEDED, DAMAGED, OR FAULTY PROTEINS BY CUTTING THEM INTO SMALL PEPTIDES.

8. PEROXISOME - VESICLE CONTAINING OXIDASES (OXIDATIVE ENZYMES) AND CATALASE (DECOMPOSES HYDROGEN PEROXIDE); NEW PEROXISOMES BUD FROM PREEXISTING ONES.- OXIDIZES AMINO ACIDS AND FATTY ACIDS; DETOXIFIES HARMFUL SUBSTANCES, SUCH AS HYDROGEN PEROXIDE AND ASSOCIATED FREE RADICALS

NUCLEUS

- THE NUCLEUS IS A SPHERICAL OR OVAL-SHAPED STRUCTURE THAT USUALLY IS THE MOST PROMINENT FEATURE OF A CELL - FUNCTIONS: 1. CONTROLS CELLULAR STRUCTURE. 2. DIRECTS CELLULAR ACTIVITIES. 3. PRODUCES RIBOSOMES IN NUCLEOLI.

- WITHIN THE NUCLEUS ARE MOST OF THE CELL’S HEREDITARY UNITS, CALLED GENES, WHICH CONTROL CELLULAR STRUCTURE AND DIRECT CELLULAR ACTIVITIES. - GENES ARE ARRANGED ALONG CHROMOSOMES. - EACH CHROMOSOME IS A LONG MOLECULE OF DNA THAT IS COILED TOGETHER WITH SEVERAL PROTEINS. THIS COMPLEX OF DNA, PROTEINS, AND SOME RNA IS CALLED CHROMATIN - THE TOTAL GENETIC INFORMATION CARRIED IN A CELL OR AN ORGANISM IS ITS GENOME

• NUCLEOLI - SPHERICAL BODIES INSIDE THE NUCLEUS THAT FUNCTION IN PRODUCING RIBOSOMES. - EACH NUCLEOLUS IS SIMPLY A CLUSTER OF PROTEIN,DNA, AND RNA; IT IS NOT ENCLOSED BY A MEMBRANE - NUCLEOLI ARE THE SITES OF SYNTHESIS OF RRNA AND ASSEMBLY OF RRNA AND PROTEINS INTO RIBOSOMAL SUBUNITS