Comparing DNA and RNA
Table 2.1
Feature
DNA
RNA
Nitrogen bases
A denine (A), Cytosine (C), G uanine (G),
Thym ine (T)*
A denine (A), Cytosine (C), G uanine (G),
Uracil (U)
S u ga r in nucleotides
Deoxyribose
Ribose
Num ber of strands
Two (double-helix, like a tw isted ladder)
One
Nitrogen base pairing (num ber of hydro-
gen bonds)
A with T (2), G with C (3)
A with U (2), G with C (3)
How is it copied?
Self-replicating
Made by using D N A as a blueprint
Function
Encodes inform ation for m aking proteins
Carries the genetic code and assists in m ak-
ing proteins
Types
Nuclear, m itochondrial**
M essenger R N A (m RN A), transfer R N A
(tRN A), ribosom al R N A (rRNA)***
* Letters and words in red emphasize the differences between DNA and RNA.
**The nucleus and mitochondria are cell organelles, which will be discussed in Chapter 3.
***These RNAs participate in the process of protein synthesis, which will be discussed in Chapter 3.
cell’s synthesis of proteins from amino acids.
Table 2.1
shows the characteristics of the nucleic acids.
DNA has a double-helix structure. Prior to cell divi-
sion, the DNA copies itself as shown in Figure 2.14b. The
double-helix structure allows DNA to copy itself easily
prior to cell division. We will discuss cell division in more
detail in Chapter 3.
In its sequence of nucleotides, DNA encodes informa-
tion on how to make proteins. (See Chapter 3 for more
details.) It takes about 1,000 nucleotides to make a gene,
which codes for one protein. In 2003, the Human Genome
Project originally estimated that humans have about
30,000 genes but reduced this estimate to 20,000 to 25,000
in 2008. Genes determine which traits each individual
inherits (your mother’s brown eyes or your father’s blue
ones, for example) and control all the activities that take
place in a person’s cells throughout a lifetime. Any change
that occurs in the sequence of nitrogenous bases of a gene
CONCEPT CHECK
1.
Why
is water referred to as the universal solvent?
2.
What
is the difference in hydrogen ion concen-
tration between a solution of pH 8.5 and one of
pH 5.5?
3.
How
do sucrose and glucose differ from one
another?
is called a
mutation,
which can re-
sult in the death of a cell, cause
cancer, or produce genetic defects
in future generations.
One other important nucleo-
tide compound vital to cell func-
tions is
adenosine triphosphate
(ATP)
. ATP is the chemical that
stores
and
releases
energy
for
chemical reactions within cells. It
consists of the nitrogenous base adenine bound to the sugar
ribose and three phosphate groups (
Figure 2.15a
). When
the cell needs energy for a chemical reaction or some oth-
er type of work, ATP gets split into ADP and a phosphate
group by an enzyme called ATPase via a hydrolysis reaction
(
Figure 2.15b
). When the cell absorbs energy, ADP com-
bines with a phosphate to make ATP by an enzyme called
ATP synthetase in a dehydration synthesis reaction.
adenosine tri-
phosphate (ATP)
(a-DEN-o-sen trT-FOS-
fat) The main energy
currency in living cells;
used to transfer the
chemical energy
needed for metabolic
reactions.
4.
What
do phospholipids do?
5.
What
types of bonds are important for the fold-
ing and twisting of polypeptides?
6.
What
is the importance of an enzyme?
7.
What
is the structure of DNA?
42 CHAPTER 2
Introductory Chemistry
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