Chapter 4: Cell Biology (DNA)

Question 1

describe DNA using the following terms: nucleotides, phosphate, sugar, base, adenine, guanine, thymine, cytosine

Answer 1

A DNA molecule is made up from a chain of nucleotides. Each nucleotide is made up from a complex of 3 subunits: phosphoric acid (phosphate), pentose sugar (deoxyribose), and a nitrogen-containing base. There are four possible bases. Two are purines with a double ring (adenine[A] and guanine[G]) and two are pyrimidines with a single ring (thymine[T] and cytosine[C]).

Question 2

describe DNA using the following terms: double helix, hydrogen bonding, complementary base pairing, antiparallel

Answer 2

A DNA polynucleotide strand has a backbone made of alternating phosphate and sugar molecules, bases attach to sugar and project to one side. DNA has two strands that twist about each other to form a double helix. The strands are held together by hydrogen bonding between bases: A always pairs with T forming 2 hydrogen bonds and G is always paired with C forming 3 hydrogen bonds. A purine is always paired with a pyrimidine to create complementary base pairing.

Two DNA strands are antiparallel, meaning they are oriented in opposite directions. The fifth carbon atom (5’) is the uppermost on one strand and the third carbon atom (3’) is the uppermost on the other strand.

Question 3

describe DNA replication with reference to three basic steps
1 - unzipping
2 - complementary base pairing
3 - joining of adjacent nucleotides
- don’t forget to reference different enzymes (3)

Answer 3

(1) DNA helicase enzyme unwinds and “unzips” double stranded DNA by breaking weak hydrogen bonds between paired bases
(2) New complementary DNA nucleotides, always present in nucleus, fit into place by process of complementary base pairing. Bases are positioned and joined by enzyme DNA polymerase. Because DNA polymerase may only add nucleotides to one end of the chain and of the antiparallel configuration of DNA, DNA synthesis occurs in opposite directions. The leading strand follows the helicase enzyme, while synthesis on the lagging strand results in formation of short segments of DNA called Okazaki fragments
(3) To complete replication, enzyme DNA ligase connects Okazaki fragments and seals any breaks in the sugar-phosphate backbone, essentially completing the joining of adjacent nucleotides. The two resulting double helix molecules are identical to each other and to the original DNA molecule

Question 4

define recombinant DNA

Answer 4

a molecule that contains DNA from 2 or more different sources

Question 5

describe three uses for recombinant DNA

Answer 5

(1) to produce substances such as insulin, tPA, hepatitis B vaccine, and human growth hormone
(2) to promote health of plants: for example, frost resistant strawberries are being developed
(3) to produce larger fishes, cows, etc

Question 6

compare and contrast the general structure composition of DNA and RNA

Answer 6

DNA
-deoxyribose sugar
-adenine, guanine, thymine, cytosine
-double stranded
-helix yes
RNA
-ribose sugar
-adenine, guanine, uracil, cytosine
-single stranded
-helix no