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allows substances to pass through
"water fearing" molecules - usually non-polar molecules which have lower free energy when clustered together than when exposed to aqueous environments
"water loving" molecules - water soluable - usually polar or charged
integral proteins
membrane proteins that penetrate the phospholipid bilayer
peripheral proteins
membrane proteins that associate only with surfaces of membranes
random kinetic movement of molecules that results in net movement of particle from areas of high concentration to areas of low concentration
movement of water across semi-permeable membranes, from areas of low-osmotic concentration to areas of high osmotic concentration
solution with lower osmotic concentration relative to another solution
solution with higher osmotic concentration relative to another solution
solutions with same osmotic concentration
describes a molecule that has both hydrophillic and hydrophobic regions
electrochemical gradient
Diffusion gradient resulting from the combined effects of membrane potential and concentration gradient
membrane potential
the charge difference between the cytoplasm and fluid outside of the cell due to a differential distribution of ions
the coupling of the facilitated diffusion of one substance to
the transport by active process of another substance against the
concentration gradient
Fatty acids with carbons joined by a single bond.
Fatty acids with some carbons joined by double bonds.
List the function(s) of "integral proteins"
communication between extracellular and intracellular

examples :
1) ion channels
2) nuclear pores
3) transport proteins
4) gap junctions
List the function(s) of "phospholipid portion of the membrane"
1) provide structural integrity 2) serve as barrier between cell and environment
List the function(s) of "membrane carbohydrates"
important in cell recognition events
List the differences of plasma membranes between prokaryotes and eukaryotes
1) Prokaryotic membranes do not contain cholesterol
2) Types of membrane proteins differ between eukaryotic and prokaryotic cell
What are 3 ways of getting substances across membranes in both eukaryotic and prokaryotic cells?
1) exocytosis / endocytosis
2) simple diffusion
3) facilitated diffusion
4) active transport
How can you tell the difference between simple and facilitated diffusion?
the rate of diffusion is directly proportional to concentration

the rate of diffusion will eventually reach a maximal rate, dictated by membrane protein concentration.
What do endocytosis, receptor-mediated endocytosis, pinocytosis, phagocytosis, and exocytosis have in common?
Are all membrane mediated events - involving encapsulation of particles within membrane bound vesicle, fusion of membranes
Match appropriate letters.

Lipid Bilayer
Membrane Proteins

A) Cellular communication
B) Permeability barrier
C) Membrane transport
D) Accelerate reactions
E) Molecule reco
Lipid Bilayer - B
Membrane Proteins - A,C,D,E
Glycolipids - A
Glycoproteins - A
What will happen to a animal if immersed in the solutions:
Hypotonic - burst (lyse)
Isotonic - shrivel
Isotonic - normal
What will happen to a plant if immersed in the solutions:
Hypotonic - stable (turgid)
Isotonic - shrivel (plasmolysis)
Isotonic - wilt (flaccid)
What will happen to a bacterium if immersed in the solutions:
Hypotonic - stable (turgid)
Isotonic - shrivel (plasmolysis)
Isotonic - wilt (flaccid)
What will happen to a fungi if immersed in the solutions:
Hypotonic - stable (turgid)
Isotonic - shrivel (plasmolysis)
Isotonic - wilt (flaccid)
Compare and contrast the role of the plasma membrane of a cell with the skin of an animal
Both serve as protective barrier, Both allow nonspecific passage of lipid soluble molecules

Skin (outer dead layer) does not have active transport mechanisms
What are some of the major ways in which a cell membrane controls interactions with the environment?
1) Regulates traffic of molecules into and out of cell
2) Mediates cell-cell recognition events
3) Receives and transduces environmental stimuli via receptors
Compare and contrast facilitated diffusion and active transport
Involve transmembrane (integral) carrier proteins / require specific
recognition phenomenon

Facilitated is passive, substances move down concentration gradient
Active requires energy, moves substances against concentration gradient
What role does the Na-K pump play in transport?
1) Serves to maintain elevated extracellular [Na+] and low intracellular [K+]
2) Sets up Na+ gradient that can be used to do work (like move glucose into cell
against gradient)
A particular membrane is said to be permeable to water and sodium, but impermeable to sucrose. How can you explain this difference?
Most membranes are permeable to water, Na+ passes thru ion channels, no transport protein available for sucrose and sucrose too large (also polar) to cross lipid bilayer via simple diffusion.
What is the cross sectional width of a typical plasma membrane
8 nanometers
8 * 10^9
What is the chemical formula for Glucose
How does an enzyme function to facilitate chemical reactions? (2 answers)
a) couples endergonic and exergonic reactions
b) decreases activation energy
What do Km and Vmax mean to an enzyme reaction?
Km = affinity between enzyme and substrate
Vmax = maximum velocity of enzyme-catalyzed reaction (velocity at enzyme saturation)
How do temperature, pH, amount of enzyme and substrate concentration affect enzyme reactions?
Temperature and pH:
affect enzyme activity levels

Amount of enzyme:
affects Vmax (as amount of enzyme, ( Vmax)

Substrate concentration: affects rate of reaction (as ( [S], ( rate of reaction til
reach enzyme saturation
What is feedback inhibition in allosteric reactions? Give examples.
Feedback inhibition refers to a form of metabolic regulation in which the end products of a metabolic pathway inhibit an enzyme that catalyzes one of the steps in the pathway, thus turning down the rate at which that pathway produces
(Figure 6.16)
chemical substance that accelerates the rate at which a reaction occurs without itself being consumed during the reaction. Catalysts act by lowering the activation energy.
activation energy
energy barrier that must be overcome before reactions can proceed (the energy that must be put in to get the reaction to go)
biological catalyst, typically a protein (although there are examples of RNA enzymes, called ribozymes)
reactant molecule recognized (bound by) an enzyme
active site
region (site) within the enzyme molecule where the substrate binds and where catalysis occurs
allosteric site
region (site) separate and distinct from the active site where allosteric effector (or
egulator) molecules bind to the enzyme
molecule that binds to the enzyme and in so doing, reduces its catalytic activity
(decreases the rate of the reaction)
all the chemical reactions that take place within a living organism
catabolic pathways
degradative processes in which complex molecules are broken down into simpler molecules to release energy
(example: polymers are broken down to monomers
via hydrolysis reactions)
potential energy
energy with the potential to be released
kinetic energy
the energy of motion, which is directly related to the speed of that motion. Moving matter does work by transferring some of its kinetic energy to other
matter that it interacts with.
the capacity to do work
1st and 2nd laws of thermodynamics
the laws that govern energy transformations in organisms and other collections of

1st law of thermodynamics states that "energy can be transformed and
transferred, but it can be neither created nor destroyed".

2nd law of
thermodynamics states that "every energy transfer or transformation increases the
entropy of the universe", usually in the form of heat.
free energy
the portion of a system's energy that is available to do work
with respect to a chemical reaction, the point when there is no further change in
the concentration of products and reactants;

also refers to the point in a reaction when the free energy is lowest (as move towards equilibrium, free energy decreases; as move away from equilibrium, the free energy increases).
a mechanism for increasing enzyme activity that is observed only in enzymes
comprised of 2 or more subunits, each of which has an active site: binding of one
substrate molecule alters the conformation of the enzyme so that it more readily
binds additional substrate molecule
(FIGURE 6.15)
What is the role of enzymes in biochemical reactions?
a) increase the rate of exergonic reactions
b) to couple exergonic reactions and endergonic reactions
List factors that may alter the activity of an enzyme.
pH, temperature, [substrate], [enzyme], presence/absence of inhibitors, allosteric effectors
Explain the induced fit theory of enzyme activity
The binding of substrate to the active site of the enzyme induces a slight change in
the conformation (shape) of the enzyme such that there is a better fit between the
substrate and the enzyme
Distiniguish between a competitive and non-competitive inhibitor. (in regard to rate of reaction, Km, Vmax)
binds to the active site, Km increases; at low [substrate], inhibitor ↓
reaction rate; however, this inhibition can be overcome at high [substrate], Vmax is
the same

binds to enzyme at site other than the active site inducing a
change in the conformation of the enzyme molecule. In most cases Km remains the same. The rate is decreased at low [substrate]. There is a lower Vmax;
inhibition cannot be overcome by high [substrate],
Explain how feedback inhibition works. Why is allosteric regulation important?
Feedback inhibition refers to a form of metabolic regulation in which the endproducts of a metabolic pathway inhibit an enzyme that catalyzes one of the steps in the pathway, thus turning down the rate at which that pathway produces
product. (see figure 6.16 in your text for an example). Allosteric regulation is
important because it prevents the cell from wasting resources (prevents cell from
making products it has sufficient quantities of); also prevents the potentially toxic
buildup of products in the cell.
The 1st law tells us that energy can be incoverted but not destroyed, while the 2nd law says there is always a price to pay in conversion.

What is the that price and how does it relate to biological processes?
The price to pay is energy lost in every chemical reaction in the form of heat (entropy). This is relevant to biological systems because it means that chemical
reactions in cells are not 100% efficient, and that energy must be continually put into an organism to replace the energy lost in the form of heat.
Discuss this statement, "Life is an endergonic process." If this is true where do most ibological organisms get their energy?
Ultimately all energy used in by biological organisms comes from light (via
photosynthesis); living organisms must also obtain energy from potential energy
stored in chemical bonds.
Light energy → chemical energy → work

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