AP BIO EXAM REVIEW: CELLS

CELL THEORY The cell is the basic unit of life All living things are composed of cells Cells can ONLY come from pre-existing cells

TYPES OF CELLS Prokaryotic Eukaryotic Cells are limited in their size Prokaryotic cells, in general, are smaller and considered more primitive. Genomic DNA is smaller with no histone proteins and forms a circle of DNA. These cells are found in the domains Archaea and Bacteria.

WHAT’S THE DIFFERENCE? PROKARYOTES EUKARYOTES No membrane bound organelles DNA in nucleoid Rod shape Bacteria & Archaea EUKARYOTES Membrane bound organelles DNA in nuclear membrane Plants, animals, fungi larger Multiple but key points They both have mitochondria

ORGANELLES smooth ER mitochondria rough ER chloroplast cytoskeleton cell wall large central vacuole microtubules nucleous mitochondria chloroplast ribosome lysosome nucleus golgi complex cell membrane mito-breaks down food molecules to make energy available (ATP) chlor- capture energy from the sunlight and use it to produce food for the cell Rib- where proteins are made Lys- digests food particles, wastes, cell parts, and foreign invaders Nuc- the control center of the cell; it contains the nucleolus Golgi-processes and transports proteins and other materials out of the cell Cell memb- thin, flexible barrier around a cell, it regulates what enters and leaves the cell Smooth- Synthesis of lipids, metabolism of carbs, Ca2+storage, and detoxification of drugs and poisons Rough- Aids in synthesis of secretory and other proteins from bound ribosomes, adds carbs to glycoproteins , and produces new membrane Cyto- Structural support and mobility and signal transmission for the cell Cell wall- prevent cells from bursting Vac- Digestion, storage, waste disposal, water balance, cell growth, and protection Microtub- Are used to move organelles (like a monorail) and chromosomes. nucleo-The nucleolus is dark staining object in the nucleus. It contains DNA which codes for the production of ribosomal RNA.

CELL MEMBRANES

WHAT IS IT? The cell membrane is a dynamic and intricate structure that regulates material transported across the membrane It is semi-permeable The cell membrane is a dynamic and intricate structure that regulates material transported across the membrane. The membrane is selectively permeable (or semi-permeable) meaning that certain molecules can cross the membrane and others cannot.

Phospholipids have hydrophilic heads and hydrophobic tails Two layers WHAT IS IT MADE OF? Phospholipid bilayer Phospholipids have hydrophilic heads and hydrophobic tails Two layers All cells have plasma membranes and many of their organelles also have membranes. All membranes are made from a bilayer of phospholipids. Hydrophilic head is attracted to water and the hydrophobic tails are attracted to one another as the tails are hydrocarbons and nonpolar so they do not mix with water. The cell membrane has two layers of phospholipids. The hydrophilic heads are facing an aqueous environment and the hydrophobic tails are facing one another.

CHOLESTEROL It is found in the cell membranes of animals but not plants. It affects the fluidity of the membrane Cholesterol functions in the following ways: It can weakly bind to hydrocarbon tails making it more difficult for smaller molecules to cross membrane. If the phospholipids are saturated, it prevents them from being packed too closely, making the membrane more fluid. However - if the phospholipids are unsaturated there are kinks in the tails where the cholesterol molecules can fill in and anchor them making the membrane less fluid.

PROTEINS IN THE MEMBRANE Transport Proteins Aquaporins Enzyme Receptor Site Cell to Cell Recognition Intercellular Joining Attachment to the cytoskeleton and extracellular matrix (ECM only in animal cells) Transport proteins, or permeases, transport molecules across the membrane. Aquaporins are special protein channels used to move water across the membrane.

PLASMA MEMBRANE SYNTHESIS The size of the plasma membrane is increased and decreased with the interaction of vesicles The size of the plasma membrane is increased and decreased with the interaction of vesicles. Vesicles bringing material to the membrane to be secreted increase the surface area of the plasma membrane; and through the process of endocytosis, the surface area of the cell membrane decreases.

CELL TRANSPORT

PASSIVE DIFFUSION The red molecules are initially more concentrated on side B. These molecules have more free energy. The net movement of the red molecules is from side B to side A, or from a higher concentration to a lower concentration. The water molecules (blue) are equally distributed and will move across at the same rate. Passive diffusion- the membrane is permeable to the molecules involved (CO2, O2, etc). Predicting the net movement is as if there was no membrane at all. The molecules move from high to low concentration.

FACILITATED DIFFUSION The molecule is impermeable to the membrane. The transport of the molecule requires a carrier protein or channel protein It requires no ATP. The driving force is an increase in entropy. The molecules are moving from an area of higher concentration to lower concentration or from higher free energy to lower free energy Facilitated diffusion- the membrane is not permeable to the smaller molecules involved (glucose, amino acids etc.). These molecules need a transport protein to transport the molecule across the membrane. Predicting the net movement of the molecules is like predicting the movement of molecules during passive diffusion. The net movement of the molecules is from an area of higher concentration to an area of lower concentration. The protein carriers (permeases) may take the form of a channel that allows certain molecules with a certain shape to enter the cytoplasm and others may take the form of a carrier protein that changes conformational shape to move the molecules across. Facilitated diffusion and passive diffusion are also called passive transport since no energy in the form of ATP is needed.

ACTIVE TRANSPORT Membrane is impermeable to the molecule Molecules are moving against a concentration gradient (from low to high) or from low free energy to high free energy Transport protein and ATP are both needed

SODIUM POTASSIUM PUMP This is the sodium-potassium pump which is vital to the nervous system. Starts with three Na+ attaching to the permease (transport protein) The permease is phosphorylated by ATP The permease becomes unstable which causes it to change its shape or conformation This allows the three Na+ to be released but on the other side of the membrane. This second conformation favors the attachment of two K+ ions and the release of the phosphate group. This change favors the proteins to return to its original conformation and the two K+ ions are released to the inside of the cell.

ELECTROGENIC PUMP Pumps ions against a concentration gradient AND a charge gradient Create a separation of charge across the membrane Sometimes an electrogenic pump is combined with another protein carrier involved in facilitated diffusion. The driving force moving the H+ ions is the concentration gradient (high concentration to low concentration) and the attraction of the positive H+ ions to the negative charges on the other side of the membrane.

OSMOSIS Osmosis is a special case of diffusion involving the movement of water. When the membrane is impermeable to certain molecules and they are not in equilibrium, water will move across the membrane “to help reach equilibrium.” Water is moving from high free energy to low free energy. "Water likes to dilute".

OSMOSIS IN PLANTS & ANIMAL CELLS Concentration refers to the amount of solute molecules dissolved in a given amount of solvent. Cell submerged in a hypotonic solution-The solution outside the cell is less concentrated than the solution inside the cell and therefore the solution outside the cell is said to be a hypotonic solution. If cells are submerged in a hypotonic solution like pure water, the net movement of water is into the cells. Animal cells may not be able to accommodate the water and subsequently burst. Plant cells become turgid because of a back pressure from the cell wall. Then the rate of the movement of water will be equal in both directions. (Point out that relative to the solution outside the cell, the solution inside the cell is hypertonic). Isotonic- Two solutions found inside the cell and outside the cell have equal amounts of solutes on both sides of the membrane. Water moves across the membrane at the same rate. The cells are at equilibrium. Cells submerged in a hypertonic solution-The solution outside the cells is more concentrated than the solution inside the cells and therefore the solution outside the cell is called a hypertonic solution. If cells are submerged cells in a hypertonic solution like syrup, the net movement of water is out of the cells. Both types of cells will decrease in volume. The plasma membrane of plant cells will pull away from the cell wall or plasmolysis will occur. Then the rate of the movement of water will be equal in both directions. (Point out that relative to the solution outside the cell, the solution inside the cell is hypertonic).

ENDOCYTOSIS The movement of larger particles into the cell by use of membrane vesicles Three types Phagocytosis Pinocytosis Receptor Mediated Endocytosis

PHAGOCYTOSIS “Cell Eating” Larger molecules or particles are brought into the cell by engulfing them into a plasma membrane vesicle Ex. White blood cells engulfing bacteria

PINOCYTOSIS “Cell Drinking” Dissolved molecules are brought into the cell by engulfing them into a plasma membrane vesicle

RECEPTOR MEDIATED ENDOCYTOSIS Receptors on the outside of cell membrane allow for the attachment of a particular molecule When a certain number of receptor sites are filled, endocytosis occurs

EXOCYTOSIS Opposite of endocytosis Material that needs to be secreted moves through Golgi apparatus where it may be modified The material is then surrounded by membrane forming a vesicle

QUESTIONS?

ANSWERS TO HANDOUT