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Biology 12
Biological Molecules & the Chemistry of Life Key
A. Important Inorganic Molecules
Water
1.
Explain why water is considered a polar molecule.
Because it has charged atoms. Since the atoms are different sizes,
the O which is larger, holds the electrons in its orbit more
frequently than the hydrogen will, therefore giving it a negative
charge and the hydrogen a positive charge.
2.
What holds a water molecule together? What type of bond holds
several water molecules together? Where will this bond form? How
would you describe this type of bond?
Covalent bonds form between 1 O and 2 H. Hydrogen bonds form
between the H+ of one water molecule and the O- of a neighboring
molecule thereby holding them together weakly.
3.
List 4 functions of water in the body. Give an example of each
function.
i. Universal solvent and helps in chemical reactions, e.g. digestion
of starch into glucose molecules.
ii. Helps transport the dissolved and suspended substances since
it is cohesive and clings to the surfaces of vessels it will fill
blood vessels and move freely through them. e.g. the transport
of O2 into blood.
iii.  Temperature is slow  maintains temperature in living
systems at a constant level.
iv. High heat of vaporization keeps living systems from over
heating (water absorbs a lot of heat before it will evaporate so
it can be used to remove heat from a system through sweating
or panting).
Acids and Bases
4.
Give the major characteristics of an acid and relate acids to the pH
scale.
Molecules that dissociate in water and release H+ , they are sour
tasting. The greater the dissociation the stronger the acid and so
the lower the pH. (pH 1 –pH 7).
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5.
Give the major characteristic of a base and relate bases to the pH scale.
Molecules that can take up H+ or release OH-, they are bitter
tasting. The stronger the base the greater the dissociation of the
molecules  the more OH- in solution (less H+) and so the higher
on the pH scale it will be. (pH 7 – pH 14)
6.
How many more H+ would there be in a solution of pH3 than in a
solution of pH8?
100 000 X more, or (10 8-3 ) 105 X more
Buffers
Hemoglobin in red blood cells acts as a buffer by preventing a drop in pH
of the blood. It is a tertiary protein that bonds to iron, which gives it its
red hue when carrying oxygen.
7.
Which type of ion, H+ or OH-, is hemoglobin capable of loosely
bonding with?
It must bond to free H+ if it is to prevent a drop in pH since it is
the H+ that makes a solution acidic.
8.
a. Describe anemia i.e. what is it, what are the symptoms, and how do
you become anemic? (do not refer to pernicious anemia)
Anemia is a disease caused by low hemoglobin counts. A person
with anemia will feel tired, no energy, generally pale (especially
membranes of the eye lids). Poor diet (not enough sources of iron
in the diet and so not making enough hemoglobin) and excessive
bleeding can cause anemia.
b. Why would an anemic person be in greater danger of a blood pH
drop?
An anemic person has less iron therefore less hemoglobin can be
made and found in their blood and so there would be less ability to
buffer against a rise in H+.
B. Some Important Organic Molecules
Study Figure 2.17 page 32 carefully. It shows the formation of an organic
molecule (dehydration synthesis)
9. Look carefully at the bonds formed during synthesis of a large molecule.
Water is produced, where does it come from (be specific)?
When two organic monomers are joined one loses a H+ and the other
loses an OH- thus creating a water molecule.
10. When the reaction is reversed (hydrolysis) water is needed. What are the 2
roles water molecules play in this reaction?
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To break or disrupt the C-O bond that was formed (polarity of water
enables this) and the “lost H+ and OH-“ are replaced (reformed) from the
dissociated ions of water.
Proteins
11. Although many proteins are enzymes, there are many other types of proteins
in our bodies. Give 4 other types of proteins (HEATS: acronym to remember
types) and their role in living things.
Hormones, enzymes, antibodies, transporters (hemoglobin, albumin),
structural (keratin, collagen, collagen, actin, myosin).
12. Explain the derivation (origin) of the term "amino acid".
This molecule has two parts: the amino group (-NH2) and the acid group
(-COOH) thus its name amino acid.
13. Draw the structural formula of a typical amino acid. Circle the amino group,
acid group and remainder. Label them.
Amino group
Acid group (carboxyl)
14. Why are there twenty types of R groups?
Because there are twenty different amino acids
15. Clearly identify the difference between the amino acid cysteine and the amino
acid alanine.
Cysteine has an atom of sulphur in its R group that is absent in alanine.
16. Diagram the joining of 2 amino acids together through dehydration synthesis
to form a dipeptide with a peptide bond. (Figure 2.25 p. 38 - 11th Edition).
Highlight the peptide bond.
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17. a) When does a polypeptide become a protein?
Once it has been released from the ribosome, i.e. the stop codon has
been read (primary structure). Or when it takes on its 2, tertiary or
quaternary structure.
b) Where does this occur in a cell?
At the ribosomes in the cytoplasm or RER; or in the ER, and perhaps
Golgi apparatus, if it is being secreted.
18.
Describe the four structures proteins can assume in terms of what they are
made of and the bonds holding them together. Make a sketch (very
simple) for each labeling relevant bonds. Once the sequence of amino
acids is laid out then hydrogen bonds will form between different
polar molecules (certain amino acids) of the polypeptide chain to form
the secondary structure. The tertiary structure is formed when there
are covalent, ionic and/or hydrogen bonds formed between the R
groups of the chain twisting it into a particular 3D shape. The
quaternary structure forms when 2 or more chains link together
19. What is meant by protein denaturation and what is its significance in living
organisms (specifically enzymes).
The change in a protein's secondary, tertiary or quaternary bonds is due
to a change in pH or temp. It results in a shape change that makes the
protein nonfunctional.
Carbohydrates
20. By looking at a structural formula of a molecule, how would you know you
were looking at a carbohydrate?
It consists of H and O in a 2:1 ratio.
21. How is a monosaccharide converted to a disaccharide? Give examples.
What is the empirical formula for glucose?
Through a dehydration synthesis reaction bonding 2 monomers together.
E.g. glucose + glucose = maltose; or glucose + fructose = sucrose; or
glucose + galactose = lactose. The formula for glucose is C6H12O6
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22. How are monosaccharides converted to polysaccharides?
By the repeated dehydration synthesis reactions between monomers
(glucose) to make a chain 100’s of monomers long, e.g. starch, cellulose,
glycogen.
23. Distinguish between starch and glycogen and sugars (e.g. sucrose). Why is
glucose such an important molecule?
All are polymers made of glucose molecules, but starch is not as branched
as a glycogen macromolecule and sucrose is only 2 monomers long.
Starch is a storage form in plants, glycogen in animals while sucrose is
quickly digested and forms an immediate energy source. Glucose is
important because it can be easily transported from one place to another,
is a short-term storage form of chemical energy and can be readily used
in the production of ATP, it also is the building block for other
carbohydrates.
24. How would you distinguish a cellulose molecule from a starch molecule (2
ways)? Why is cellulose undigestible?
Cellulose is an unbranched chain of glucose molecules which are joined
by carbon oxygen bonds that reverse their orientation for each monomer
added to the chain. Because the bonds joining the O and H are different
and can’t be broken by the enzymes we have it is indigestible by us. Only
certain monerans (bacteria) have these enzymes and that is why bacteria
can be found in mammalian digestive tracts, to help us digest plant food.
Lipids
25. Explain how a neutral fat is synthesized.
. The union of 1 glycerol molecule with 3 fatty acid molecules. 3 H2O
molecules released in the process.
26. Explain how a neutral fat is hydrolyzed.
If 3 H2O molecules are added then the glycerol and fatty acids will break
apart.
27. Define what saturated and unsaturated fats mean. A C - H bond is
considered energy rich. How much more energy per gram do fats contain
than carbohydrates?
A saturated fat has all C bonds filled with H (no double bonds between C
atoms) while an unsaturated fat will still have some double bonds
between the C atoms.
Fats have 3X the energy than carbs.
28. Read the Health Focus on page 36 and compare trans fats to polyunsaturated
fats.
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Trans fats are oils that have been hydrogenated and therefore are solid
at room temperature and are considered saturated. Polyunsaturated
fats are oils and will have many double bonds.
Phospholipids
29. Differentiate between a lipid and a phospholipid.
A phospholipid has one less fatty acid than a lipid and in its place is a
phosphate group. This group can ionize and so carries a charge (polar).
The 2 fatty acids are non-polar and form the “tails” of the molecule.
Lipids in general are nonpolar.
30. Identify one significant use of phospholipids in living organisms.
They form the plasma membrane of all cells.
Steroids
31. a. What are steroids made of?
Steroids are lipids but they have a backbone of 4 carbon rings (the
monomers have folded back on themselves to form these rings) with
different functional groups attached distinguishes them. The basic
steroid is cholesterol all others are made from this.
b. Where are they made in the cell? In the body?
In the smooth ER… in the body?
Adrenal gland, ovaries and testes.
c. List 2 examples of steroids.
estrogen and testosterone
Nucleic Acids
Read the pages on DNA, RNA & nucleotides, we will be going into more detail with
these polymers in the future but you must know their basic structure and function now.
Answer the question on ATP below.
32. Sketch a molecule of ATP and describe its structure.
ATP is at first a nucleotide consisting of the base adenine bonded to
ribose (adenosine) and a phosphate group. However this nucleotide can
go on to form additional high energy bonds with 2 more phosphate
groups (triphosphate)
33. What process produces ATP? How many ATP molecules can be made from
a single glucose molecule?
The phosphate molecules are added on to the nucleotide in the
mitochondria of all cells thru the chemical reaction called cellular
respiration. Glucose bonds are broken; the energy released is used to
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bond a phosphate group to the nucleotide (adenosine
monophosphate). As the 3rd and final phosphate is added the
molecule is complete. The ‘burning’ of 1 glucose molecule will
produce 36 ATP molecules
34. Why is ATP the “energy currency” of the cell?
The energy released is equal to the amount needed to drive most
reactions therefore is more efficient form of chemical energy than
glucose.
35. Copy out the ATP cycle as given in Figure 6.3, page 101. Since this is a
cycle what does this tell you about this molecule?
The ATP molecule is recyclable; it can be used over and over again.