1. Metabolism
Ch 5

2. Cellular Transport
Cellular Transport: movement of substances across a membrane [in or out] and within the cell
Includes substances needed for reactions in the cell, and substances created by reactions in the cell
Passive Transport: does not require energy input
Diffusion, facilitated diffusion, osmosis
Active Transport: requires the input of energy [ATP!!]
Protein pumps, endocytosis, exocytosis

3. Diffusion and Membranes
Diffusion: spontaneous spreading of molecules or atoms from an area of high concentration to low concentration
Concentration: the amount of particles in a given amount of space
Facilitated Diffusion: solute binds to a transport protein and moves across membrane [transport proteins are specific to certain solutes]

4. Diffusion and Membranes
The following factors all effect the rate of diffusion
Bigger concentration difference will increase rate of diffusion
Higher temps increases rate of diffusion
Small ions/molecules diffuse more quickly
Ions will flow towards the opposite charge
Higher pressure increases rate of diffusion
Dynamic Equilibrium: equal concentrations are reached, the particles will still move, but no overall change

5. Osmosis
Because lipid bilayers [cell membrane] are selectively permeable, only some substances can diffuse across them
water, hydrophobic molecules, and gases CAN cross, but ions and most large polar molecules [sugar] cannot

6. Osmosis Osmosis: diffusion of water across a semi-permeable membrane
Occurs in response to differences in solute concentration
The direction and rate of this diffusion is described in terms of tonicity
Hypotonic, isotonic, hypertonic

7. Tonicity Isotonic: equal solute concentrations, no osmosis
HypOtonic: fluid with low solute concentration compared to another
Hypertonic: fluid with high solute concentration compared to another

8. Osmosis
If a cell is hypotOnic, water will diffuse into the cell [swell]
If it is hypertonic, water will diffuse out [shrink]
Diffusion will continue until the fluids are isotonic
**Water is moving in both directions, but there is a net movement in one direction**

9. Turgor
An inflow of water causes pressure to build, in plant cells the cell wall counteracts the increase to control the amount of expansion
Turgor: pressure that a fluid exerts against a structure
Osmotic Pressure: amount of turgor that prevents osmosis into cytoplasm or other hypertonic fluid

10. Membrane Trafficking
Some substances are too large to move through the membrane by diffusion or transport proteins
Exocytosis: cell expels a vesicle’s contents to extracellular fluid
Endocytosis: cell takes in a small amount of extracellular fluid (and its contents) by the ballooning inward of the plasma membrane
Both require energy, both continually replace and withdraw patches of the membrane

11. Membrane Trafficking
Phagocytosis: “cell eating,” a cell engulfs a large solid particle like another cell
The object is digested by lysosomal enzymes
Some white blood cells engulf viruses and bacteria this way

12. Cellular Energy Remember chapter 3?
ATP [adenosine triphosphate] is a nucleic acid that serves an important role as an energy carrier in cells
ATP is composed of adenine, ribose [sugar], and three phosphate groups
Bonds between phosphate groups hold A LOT of energy which can be transferred when the bonds are broken

13. Cellular Energy
When a phosphate group is transferred from ATP to another molecule, ADP is formed [adenosine diphosphate]
Phosphate groups are then added back onto the ADP to create ATP and so on  ATP/ADP cycle
These reactions release energy that allows the cell to do work and perform necessary functions

14. Energy Energy: the capacity to do work
The energy that fuels most life on Earth comes from the sun, however, the dispersal of energy is resisted by chemical bonds
During a chemical reaction, one or more reactants become one or more products
Some reactions require energy, some release it
The energy in chemical bonds of a reaction contributes to a molecule’s free energy [energy available for work]

15. Energy Work occurs as a result of energy transfers
Energy lost from a transfer is usually in the form of heat, which is not useful for doing work
Due to this loss, energy in the universe must be replenished for life to continue
ENERGY ONLY FLOWS IN ONE DIRECTION

16. Energy
Metabolism: chemical reactions by which cells acquire and use energy
All living things are “chemical factories”  driven by chemical reactions!
Cells store energy by running reactions that build organic molecules [endergonic]
Cells use energy by running reactions that break down organic compounds [exergonic]

17. Energy
However, chemical bonds do not break without at least a small input of energy
Activation Energy: minimum amount of energy required to start a chemical reaction
At this state, the reaction can run without any additional energy input
Sometimes the amount of energy needed for a reaction to occur is so high, that the reactions would occur incredibly slow if allowed to occur on their own

18. Enzymes Metabolism requires the use of enzymes
Enzyme: organic molecule [PROTEIN] that speeds up a reaction without being changed by it
In a process called catalysis, an enzyme makes a reaction run much faster than it would on its own by lowering the activation energy
An enzyme recognizes only a specific substrate (reactants), and they fit together like a LOCK AND KEY

20. Enzymes
Active Site: pocket in an enzyme where substrates bind and a reaction occurs
An enzyme is does not change the amount of product that is made, it only SPEEDS UP THE REACTION

21. Enzymes
When the enzyme and substrate bind, subtle changes occur in the active site occur, known as an induced fit.
Induced fit enhances catalysis as the enzyme converts substrate to product.
When the products are released, the enzyme is restored to its original form and can repeat the reaction over and over

22. Enzymes
Environmental factors (pH, temperature, salt) influence an enzyme’s shape and function
Enzymes functions best in a particular range of conditions that reflect the environment in which it evolved

23. Metabolic Pathways
Building, rearranging, or breaking down organic molecules often occurs in steps
Metabolic Pathway: series of enzyme- controlled reactions by which cells build, remodel, or break down an organic molecule
Linear pathway: reactions run straight from reactant to product
Cyclic pathway: the last step regenerates a reactant for the first step

24. Electron Transfers
Metabolic pathways that capture or release energy can be dangerous for cells to run because the bonds of organic molecules hold enough energy to be harmful if released all at once [explosive]
Instead, cells break the bonds one by one so energy is released in small, manageable amounts
Most are oxidation–reduction reactions [REDOX]
In a typical redox reaction an electron is transferred from one molecule (oxidized) to another molecule (reduced)

25. Electron Transfers
Electron Transfer Chain: array of enzymes and other molecules that accept and give up electrons in sequence
The energy of the electrons is released with each step of the sequence
Important for photosynthesis and aerobic respiration