REVIEW: Cellular Functions, Part 1
Cell structure
1. What is the difference between a prokaryote and a eukaryote?
Eukaryotes have membrane-bound organelles, and prokaryotes do not. Keep in mind that
prokaryotic is not synonymous with unicellular.
2.Briefly describe function and structure (if discussed) of the following components of
cell structure:
function
structure
a. nucleus
houses the cell’s genomic
DNA
b. cell membrane
See question (3)
c. cell wall
found only in plant cells; adds
rigidity to the cells and helps it
to withstand high osmotic
pressures
site of aerobic cellular
respiration and ATP
production
membrane-bound. The DNA
inside is in an uncoiled state,
unless the cell is dividing
phospholipid bilayer, with
other more minor constitutents
surrounds the cell membrane.
Composed mainly of
cellulose.
d. mitochondria
e. ribosomes
protein synthesis
f. endoplasmic reticulum –
rough and smooth
rough ER is site of protein
synthesis; smooth ER
synthesizes phospholipids, and
packages proteins destined for
secretion into vesicles
completes processing of
molecules for secretion
synthesizes/stores proteins and
lipids in plants.
g. Golgi apparatus
h. plastids (chloroplasts)
Cell membranes & Transport
3. What functions does the cell membrane serve?




Separate cell contents from outside
Receive signals from other cells (hormones)
Let in nutrients
Let out waste products and manufactured materials
double membrane. The inner
membrane has many
infoldings (cristae) to
maximize surface area for cell
resp.
two subunits; composed of
RNA and protein
rough ER is studded with
ribosomes
double membrane structure,
which further contains stacked
thylakoid membranes
4. According to the Fluid Mosaic Model, what are the three major components of a cell
membrane? How are they arranged in relation to each other? Draw a diagram to
illustrate this.
Phospholipids – arranged in a bilayer, with polar heads facing outwards, and hydrocarbon
tails facing inwards.
Proteins – integral proteins are embedded in the bilayer; peripheral proteins are
associated with the polar surface of the membrane.
Cholesterol - Hydrophilic portion interacts with phospholipid heads. Hydrophobic
portion embedded in membrane. Cholesterol alters the fluidity and permeability of the
membrane.
The phospholipid blayer forms the bulk of the membrane. None of the components are
rigidly bonded to one another, but are free to float around one another.
Draw your own diagram  I’m not that handy on the computer. Main aspects of your
diagram should be:
the orientation of the phospholipids within the bilayer
the presence of integral proteins, and
the configuration of the peripheral proteins and cholesterol.
5. What are the two classifications of protein found in cell membranes? How do they
differ in their functions?
Integral proteins – Function as channels/transporters to get molecules across the membrane.
Peripheral proteins – Temporarily associate with the surface of the membrane; can act as
signal receptors or to regulate ion channels (the latter function was not discussed).
6. What are the factors that determine a molecule’s ability to pass through the cell
membrane? List them, and describe the relationship between the factors and
permeability.
Size – Small molecules can pass through easily, but large molecules are blocked
Polarity – To an extent, polarity prevents molecules from passing through the hydrophobic
interior of the membrane. Very small polar molecules may be able to diffuse through.
Charge – Charged molecules will never be able to diffuse through the membrane, regardless
of size.
7. Describe the natural movement of a particle within a concentration gradient.
Particles will move from areas of high concentration to areas of low concentration. This is
referred to as movement “along” or “down” a concentration gradient.
8. Compare: (Read the list first – sometimes a very detailed explanation is not required)
a. simple diffusion, and facilitated diffusion
Both involve the passive movement of particles along their concentration gradients.
Facilitated diffusion occurs through a transmembrane (integral) protein, because for
whatever reason the membrane is not permeable to that particle.
b. facilitated diffusion through an ion channel, and through a transport protein
The ion channel is almost like a tunnel; it simply forms a pore through which the ion
can pass. Facilitated diffusion through a transport protein involves the substrate
binding to, and changing the conformation of, the protein.
c. simple diffusion, and osmosis
Osmosis is the simple diffusion of water.
d. passive transport, and active transport
Passive transport does not require an energy input, where active transport does.
Energy is required for active transport because it involves molecules being
transported against their concentration gradients, rather than along, as is the case
with passive transport.
e. direct active transport, and indirect active transport
Direct active transport is powered by the hydrolysis of the terminal phosphate bond
in ATP. Indirect active transport is powered by harnessing the free energy released
as ions move through transport proteins, along their electrochemical gradients.
f. symport, and antiport
Both are forms of indirect active transport, where the movement of an ion through a
protein powers the movement of another molecule across the membrane. They differ
in the direction of molecule transport, in relation to the driving ion – in symport, the
molecule and ion move across the membrane in the same direction; in antiport, they
move in opposite directions.
9. a. What does it mean if a solution is hypertonic to another one? Hypotonic?
When comparing two solutions, the solution with a higher solute concentration is hypertonic.
The solution with the lower solute concentration is hypotonic.
b. What does it mean if a solution has a lower osmotic pressure than another one?
Higher?
When comparing two solutions, one has a lower osmotic pressure if it has a lower
concentration of water as compared with solute (i.e. it is hypertonic). The solution with
higher osmotic pressure has a higher concentration of water as compared with solute.
c. Describe the direction of osmosis, using terms that refer to tonicity, and osmotic
pressure.
Direction of osmosis: hypotonic solution  hypertonic solution
high osmotic pressure  low osmotic pressure
10. List the two cellular components that help a plant cell maintain its structure in
hypertonic and hypotonic environments. Describe how they do this.
Cell wall – rigid, resists bursting when cell is placed in a hypotonic environment.
Central vacuole – very large; helps prevent shrivelling when cell is placed in a hypertonic
environment.
Thermodynamics/Cell energetics
11. All energy can be classified into one of two broad categories:
a. What are these categories?
Kinetic energy, and potential energy
b. What is chemical energy, and into which category can chemical energy be
placed?
The energy store din chemical bonds; it is a form of potential energy.
12. State the two laws of thermodynamics.
First law: Energy cannot be created or destroyed.
Second law: Every chemical or physical change in the universe causes an increase in
randomness and disorder (entropy).
13.
a. What is enthalpy? What is entropy?
Enthalpy – Heat content of a molecule. Denoted ΔH
Entropy – Randomness/disorder in the universe. Denoted ΔS.
b. Does the universe favour an increase or decrease in enthalpy? Entropy?
Decrease in enthalpy (ΔH < 0)
Increase in entropy (ΔS > 0)
14. Give two examples of situations that would constitute an increase in entropy.
Any catabolic process (macromolecules  monomers)
Diffusion of a substance
15. Contrast energy with Gibbs free energy. Which is a more useful quantity when
examining chemical reactions?
Gibbs free energy is the amount of energy in a system that is actually available to do
work. Gibbs free energy is more relevant for describing the inputs and outcomes of a
chemical reaction, since it is the energy that can actually be used.
16. Construct a comparison table for anabolism and catabolism. Include the following
points:
Anabolism
Catabolism
Definition
Cellular reactions that
build macromolecules
from their constituent
monomers
Cellular reactions that
break macromolecules
back down into their
constituent monomers
Example
Amino acids 
Proteins
Monosaccharides 
Polysaccharides
Proteins  Amino
acids
Polysaccharides 
Disaccharides 
Monosaccharides
Energy
Absorbed and stored
Released
17. Define oxidation. Define reduction.
Give (non-specific) examples of each.
Oxidation is the loss of electrons. It can also involve the loss of hydrogen atoms, or the
gain of an electronegative atom such as oxygen (oxidation by partial transfer – the
unequal sharing of electrons in a polar bond).
Reduction is the gain of electrons. It can also involve the gain of hydrogens, or the loss
of an electronegative atom (a regaining of the electrons that are unequally shared in a
polar bond).
18. Why are these two types of reactions always found coupled with one another?
Energy cannot be created or destroyed – the free energy lost in losing electrons must get
transferred to another molecule. Loss will always be accompanied by gain.
19. When redox reactions are found occurring in a series, is each successive electron
acceptor more, or less, electronegative than the one before it?
More electronegative. (If you have trouble with this remember that O is the final
acceptor in the electron transport chain – it is highly electronegative.)
20.
a. What are the two electron carriers (coenzymes) discussed in class?
NAD+ and FAD
b. Write out the chemical equations that show how they accept electrons.
NAD+ + 2e- + H+  NADH
FAD + 2e- + 2H+  FADH2
c. When they accept electrons, are they being oxidized, or reduced?
They are being reduced.
21. List the components of an ATP molecule. Draw a picture of
one.



adenine (the same purine you find in DNA and RNA)
ribose (a pentose)
three negatively-charged phosphate groups
22. Why and how can energy be released from a molecule of ATP?
The negative charges carried by the phosphate groups make the bond between the second
and the terminal phosphates very unstable. Hydrolyzing the bond releases the chemical
energy contained in the bond, which can be used to power endergonic reactions.
23. Compare substrate-level phosphorylation and oxidative phosphorylation.
Substrate-level – Direct transfer of a phosphate to ADP; involves both substrates binding
to an enzyme, which catalyzes the reaction.
Oxidative – Indirect; powered by the free energy released by a series of redox reactions.
Enzymes
24. What is the difference between an apoenzyme and a holoenzyme?
Apoenzyme – the inactive form of an enzyme that requires additional cofactors or
coenzymes in order to function.
Holoenzyme – the apoenzyme + its cofactors and/or coenzymes. This is the active form.
Not all enzymes exist in these 2 forms – some do not need cofactors or coenzymes.
25. Compare the Lock and Key model and the Induced Fit model of enzyme function.
Both explain the specificity of the enzyme-substrate bond.
The Lock and Key model depicts the enzyme`s active site as static and unchanging in
shape. The substrate`s shape fits that of the active site, and bonding occurs in a
straightforward manner.
In the Induced Fit model, the weak binding of the first substrate to the enzyme induces a
conformational change in the active site, which allows the active site to better fit the
shape of a second substrate. The second substrate can then form a strong bond, and the
enzyme catalyzes the appropriate reaction.
26. List the two factors we described that can affect enzyme function. Describe their
effects.
temperature – Initial increase in function with temperature. Too high a temperature can
inhibit enzyme function by denaturing the enzyme.
pH – any pH outside of the enzyme`s optimal range will cause a decrease in enzyme
function.
27. What is denaturation?
The breakdown of the 2° and 3° structure of a protein. This occurs as the result of an
external stress such as temperature or pH. Breakdown of these structures changes the
overall shape of the protein and renders it unable to perform its function.
28. Compare:
a. Allosteric activators and allosteric inhibitors
Both bind to the allosteric site of an enzyme (not the same as active site) in order to
stabilize an enzyme conformation. Activators stabilize a shape that exposes the active
site to substrates for binding. Inhibitors stabilize a shape that hides the active site, so that
it cannot bind.
b. Competitive and Non-competitive inhibition
Both involve the inhibition of an enzyme`s function. In competitive inhibition a
molecule that is shaped similarly to the substrate binds to the enzyme`s active site,
blocking any substrate from being able to bind. Non-competitive inhibition is any type of
inhibition that does not occur by this mechanism (includes allosteric inhibition).
29. What is feedback inhibition, and why is it such a good mechanism of regulating
enzyme function?
Feedback inhibition occurs when the product of a series of cellular reactions serves to
inhibit an enzyme that catalyzes a reaction found earlier on in the series. It is a good
mechanism because it prevents the cell from wasting energy and resources carrying out
reactions for which there is already a sufficient amount of product.
Cellular respiration
30. What is the overall chemical equation for cellular respiration?
C6H12O6 + 6O2  6CO2 + 6H2O + energy
31. In what stage of cellular respiration are the following molecules found/produced?
a. pyruvate – produced in glycolysis.
b. FADH2 – produced in the Krebs cycle
c. NADH – produced in glycolysis, pyruvate oxidation, and Krebs
d. glucose – starting product of glycolysis
e. oxaloacetate – 4 carbon starting product of Krebs cycle; regenerated at the end
f. acetyl-coA – produced by pyruvate oxidation
g. citrate –Krebs cycle
h. ATP – both taken in and produced in glycolysis; some produced in Krebs;
mostly produced by chemiosmosis (oxidative phosphorylation)
32. For each of the molecules in #31, briefly explain why they are important.
a. pyruvate – the branching point between aerobic cellular respiration, and
anaerobic fermentation
b. FADH2 – temporarily stores the electrons from glucose so that their free energy
can be transferred to the ETC
c. NADH – same as (b)
d. glucose – main energy source for the cell
e. oxaloacetate – starting substrate for the Krebs cycle
f. acetyl-coA – molecule that enters the Krebs cycle; is also produced by the
breakdown of fatty acids from lipid catabolism so that the energy contained in
lipids can be used as an alternative source for ATP production
g. citrate – first intermediate produced in the Krebs cycle by the bonding of
acetyl-coA to oxaloacetate; this is where the Krebs cycle gets its alternative name
of "citric acid cycle"
h. ATP – the primary source of free energy in a cell
33. a. In which two stages is ATP produced?
MY APOLOGIES – it`s actually three.
Glycolysis
Krebs
ETC/chemiosmosis
b. For each of the stages in (a), classify the ATP production as either substrate level, or
oxidative.
Glycolysis & Krebs – substrate-level
Chemiosmosis - Oxidative
34. What is the role of NADH and FADH2 in oxidative phosphorylation?
NADH and FADH2 hold onto the free energy contained in the original glucose molecule
by successively stripping the molecule of its electrons. They transfer this energy to the
electron transport chain by reducing the proteins in the chain. The energy that is released
with each following redox reaction in the chain is then used to pump H+ into the
intermembrane space. The accumulation of H+ builds up an electrochemical gradient
which can then be used to oxidative phosphorylation as the H+ rushes through an ATPase
complex, which harnesses the free energy that is released to catalyze the phosphorylation
of ADP to ATP.
35. How many molecules of ATP are produced per NADH? FADH2?
3 per NADH
2 per FADH2
36. Construct and complete a table comparing the stages of cellular respiration. It should
look like this:
Stage
Location
Glycolysis
cytopl
asm
matrix
Pyruvate
oxidation
Krebs cycle
ETC
matrix
# of
steps
10
Energy consumed
ATP NADH FADH2
2
Energy produced
ATP NADH FADH2
4
2
3
2
8
6
2
10
2
(used in
ETC)
(used in
ETC)
inner
membr
ane
8
32
(2 from
NADH)
2
Total
4
36
37. On page 108, look at the free energy diagram of electrons as they pass through the
stages of cellular respiration (Fig. 23). Why is the diagram shaped like a staircase, rather
than a straight line?
The energy of the glucose molecule is released in a stepwise manner, rather than all at once
(remember what would happen if it was – think of the poor gummi bear!!!)
Related metabolic pathways
38. Describe the process of protein catabolism.
Proteins  AAs
AAs are deaminated (amino group gets excreted as NH3)
Carbon skeletons are used to manufacture the substrates for aerobic respiration
pyruvate, acetyl co-A, or a Krebs intermediate
39. Describe the process of lipid catabolism.
triglycerides  glycerol + fatty acids
glycerol is converted to glucose, or to DHAP (glycolysis intermediate)
fatty acids undergo ß oxidation to generate acetyl co-A
40. What is the molecule that is the branching point between aerobic respiration and
anaerobic fermentation? What determines the path it will take?
Pyruvate. The path it takes is determined by the amount of oxygen available.
41. What is the electron acceptor and final product of ethanol fermentation? Lactate
fermentation?
Ethanol: Acetaldehyde is the electron acceptor that is reduced by NADH. It is produced
by the decarboxylation of pyruvate. The final product is ethanol.
Lactate: Pyruvate is the electron acceptor; lactic acid is the final product.
42. What does VO2 max measure?
VO2 max measures the maximum amount of oxygen that can be cleared by the
bloodstream by the body’s cells, during a bout of maximal physical exertion. It is a
measure of rate, expressed in mL of oxygen/kg of mass per minute of time. (mL/kg/min)