Review questions for Carbon Compounds in cells:
Your best bet here is to try can answer these questions from memory. If you can, great!
If not, study, and try again. Next best thing: use this as a work sheet while you study – filling in as you find
the answers I would not recommend: getting the answers and just memorizing the questions/answers. They
will not be the same on the exam!
1. Draw out the following functional groups:
Methyl
Carboxyl
Hydroxyl
Carbonyl
Amino
Phosphate
See pg 3.5. Have you drawn them correctly?
The “stick” that appears not to be bound to anything is actually what is bound to “the rest of the structure.”
For example: the hydroxyl group (-OH) is in ethanol, is on the end of a short carbon chain. Ethanol is usually
written as CH3CH2OH, could also be drawn to show the bond to each carbon, as shown below. (In lab
shorthand, we often write ethanol as EtOH – emphasizing the functional group and telling us that it is on
ethane.
H H
H - C - C - OH
H H
Note the difference between an aldehyde and a ketone – both have the C = O (double bond, sharing two
electron pairs) but in and aldehyde, the C is also bound to an H and “the rest” of whatever the molecule is,
whereas in the ketone, its between to groups of “other atoms””
Note also the one I did not ask you for, a sulfhydryl group. This is an important group because in proteins ,
two cysteines, each with a -SH group, can undergo a reaction in which they become covalently linked in a
“disulfide bond” - S-S- which can hold two strands together more strongly than any non-covalent interaction .
2. Explain how condensation reactions and hydrolysis reactions are related.
In a condensation reaction, two molecules are joined together, and an H from one + an OH from the other
join also to form water. Condensation reactions are involved in making polymers of smaller units (such as
forming polysaccharides from simple sugars, or proteins (polypeptides) from amino acids
Hydrolysis means “water-breaking” – in many cleavage reactions (such as the breakdown of polymers into
monomer units), an OH is added on one side, and an H to the other – the reverse of condensation. (We say
that “water is added back across the bond”
3. What are the four main groups of organic compounds?
Carbohydrates: monosaccharides (simple sugars), disaccharides, oligosaccharides and polysaccharides
Lipids – fats (and oils) phospholipids (membranes) sterols and waxes
Proteins – amino acids and polypeptides (protein is a polypeptide, suggests that it has some function)
Nucleic Acids - including nucleotides such as ATP, NAD etc, as well as DNA and RNA
4. What is the relationship between:
Glucose and cellulose?
Cellulose a polymer made up many glucose units.
Between cellulose and starch?
Starch and cellulose are both polymers of glucose, but they are attached to each other differently
(see below) and that difference shows up as a difference in their properties. See below for more
information on this!
Between glucose and ribose?
Both are simple (single ) sugars, but glucose has 6 carbons and ribose has 5 carbons. (Both have
one oxygen in their ring and one carbon out of the ring, so the rings are 6 member and 5 member
rings respectively)
Between glucose and sucrose?
Glucose is a monosaccharide, a simple sugar or single 6-carbon compound. Sucrose is a
disaccharide, made up of two units (glucose and fructose).
Here is a bit more information that you really need, but which you might find helpful:
Note that fructose, which is a 6-carbon sugar, had a 5member ring: four of the Cs and one O are in the ring,
and the other two Cs hang off. In figure below, you are told something about the bond between these two
sugars. The numbers indicate that the bond is between the number 1 carbon on the glucose, and the
number 2 carbon on the fructose. The  (alpha) indicates the orientation in space of the O group between
eh two sugars (atoms are either “up” or “down relative to the flat plane of the ring, and in alpha bonds (a)
they the link in both is from the same side. In a beta () bond, one is from the up side and one is from the
down side . Lactose has a  bond between galactose and glucose
This is a key part of the difference between starch
(amylose) and cellulose, as shown below:
5. Why are fats “hydrophobic” (what does it mean, and what is it about the structure of fats that makes
them so?)
The fatty acids are long chains of CH groups (hydrocarbon chains) , and the bond C-H and C-C are not
polar. Non-polar groups tend to want to stay together, away from water (hydrophobic)
6. How are fats and phospholipids related?
Both have fatty acids covalently linked to a glycerol. Glycerol is a 3-carbon compound with an –OH group
on each carbon In fats, or triglycerides, all three –OHs are replaced with a fatty acid chain. In
phospholipids, two of the –OHs have fatty acid chains, and the third has a phosphate group, and usually
other things attached to that.
7. What is the difference in structure and in behavior of saturated vs. unsaturated fatty acids
Unsaturated fatty acids have one or more double bonds between some of the carbons. Saturated fatty
acids have no double bonds – they are “saturated” with Hs. The double bonds introduce “kinks” that
have more movement around the bond than is possible with single bonds; the hydrocarbon chains with
double bonds in them (unsaturated) can move more. This is why unsaturated lipids are oils (liquid at
room temp) and saturated ones (lard, butter, and partially hydrogenated vegetable oil!) are solid.
8. Why are lipids biologically important?
Phospholipids make up cellular membranes. Since every cell has a plasma membrane, and eukaryotic
cells have many internal membranes, phospholipids are very important in cell structure and function
Fats are an important form of energy storage for animals – excess glucose can be stored as a
polysaccharide (glycogen) but there is a limit to how much glycogen cells can have. (Also glycogen is
quite polar, and has a lot of water associated with it). Fats are more compact storage (hydrophobic, so
they exclude water) and fat cells can carry large stores of them. In a later chapter we will see how those
fats are used to give us usable energy
9. Draw the structure of an amino acid (try to do this from memory)
See figure in text to check
10. What is the nature of the “R” group?
It can be any number of different things – there are 20 different R groups, some acidic, some basic,
some rings, some that are non-polar, some that are polar ….. Some of the structures are shown in the
text.
11. What type of reaction creates the peptide bond between two amino acids?
It is a condensation reaction.
12. What is meant by “primary protein structure”. What is tertiary protein structure?
Primary protein structure refers to the sequence of amino acids – the order they are in the “string”
Tertiary refers to the folded structure of the protein.
13. How can one wrong amino acid render the protein non-functional?
It can be a key amino acid in the interaction of the protein with some other molecule – if, for example, a
(+) amino acid generally interacts with a (-) charged molecule, and this (+) amino acid is changed to a
non-polar one, the reaction will not occur
Or, It can be important in holding the protein in its conformation (again, if an amino acids properties are
important for correct folding, and it is changed, the protein may not fold properly
14. What happens when a protein is denatured?
The non-covalent bonds that hold it in its three-dimensional conformation come apart (example, heating
breaks hydrogen bonds), and it is no longer folded properly. Denatured proteins seldom do what they are
supposed to.
15. What are the three parts of a nucleotide?
See fig 3.23.
There is a ribose ring. On one side (the #1 carbon) is covalently attached a ring structure, on the other
side (to the #5 carbon, which is not in the ring) is attached one or more phosphate groups.
16. What are the three kinds of RNA, and what role does each one play in protein synthesis?
mRNA is a copy of the section of the DNA that has the code for a protein. (Note: DNA is very long
strands of nucleotides, and the messages are interspersed among other “non-coding” stretches of DNA.
The way they are selected to be made into mRNAs is really interesting, but you will learn about that
another time)
tRNAs are the molecules that do the translating. The tRNA molecules have a loop at one end that Hbonds with the matching (complementary) three nucleotides on the mRNA and on the other end has
attached to it the amino acid that corresponds to those three nucleotides, according to the genetic code.
rRNAs along with many different proteins, make up the ribosomes. Ribosomes are where the mRNAs
and tRNAs come together – two tRNAs can “dock” on consecutive mRNA sites (codons), and one of the
proteins in the ribosome facilitates the reaction between the two amino acids to make the peptide bond.
The chain moves down one position and the next one comes in, and this process continues so that the
whole RNA sequence is translated to make a polypeptide chain