Chapter 1 Practice Problems

Question 1

G-C and A-T base pairing in DNA through hydrogen bonds

Answer 1

complementarity

Question 2

subunit of the DNA macromolecule

Answer 2

nucleotide

Question 3

DNA/protein structures that contain genes

Answer 3

chromosomes

Question 4

a linera polymer of amino acids that folds into a particular shape

Answer 4

protein

Question 5

the entirety of an organism’s hereditary information

Answer 5

genome

Question 6

DNA information for a single function, such as production of a protein

Answer 6

gene

Question 7

the only one of the four bases in RNA not in DNA

Answer 7

uracil

Question 8

part of a gene that can contain protein coding information

Answer 8

exon

Question 9

part of a gene that does not contain protein coding information

Answer 9

intron

Question 10

a double-stranded polymer of nucleotides that stores the inherited blueprint of an organism

Answer 10

DNA

Question 11

a polymer of nucleotides that is an intermediary in the synthesis of proteins from instructions in DNA

Answer 11

RNA

Question 12

alteration of DNA sequence

Answer 12

mutation

Question 13

if one strand of a DNA molecule has the base sequence 5’-AGCATTAGCT-3’ what is the base sequence of the other complementary base

Answer 13

5’-AGCTTAATGCT-3’

Question 14

the size of one copy of the human genome is approximately 3 billion base pairs, and it contains about 27,000 genes organized into 23 chromosomes.

a. Human chromosomes vary in size. What would you predict is the size of the average chromosome?
b. assuming that genes are spread evenly among chromosomes, how many genes does an average human chromosome contain?
c. about half of the DNA in chromosomes contains genes. How large in base pairs is an average human gene?

Answer 14

a. 3 Billion/23 = 130,435,000 base pairs per chromosome
b. 27,000/23 =1174 genes per chromosome
c. 1,500,000,000 base pairs/27,000 genes = 55,555 base pairs per gene

Question 15

Indicate whether each of the following works or phrases applies to proteins, DNA, or both

a. a macromolecule composed of a string of subunits
b. double-stranded
c. four different subunits
d. 20 different subunits
e. composed of amino acids
f. composed of nucleotides
g. contains a code to generate other macromolecules
h. performs chemical reactions

Answer 15

a. both
b. DNA
c. DNA
d. proteins
e. proteins
f. DNA
g. DNA
h. proteins

Question 16

a. How many different DNA strands composed of a 100 nucleotides could possibly exist?
b. how many different proteins composed of 100 amino acids could possibly exist?

Answer 16

a. 4^100 = 1.6 x 10^60

b. 20^100 = 1.3 x 10^130

Question 17

RNA shares with proteins the ability to fold into complex 3-D shapes. As a result, RNA molecules can, like protein molecules, catalyze biochemical reactions. Why can some RNA molecules act as enzymes whereas DNA molecules cannot?

Answer 17

Because DNA molecules all have the same 3-D structure while RNA has different 3-D structures for different functions

Question 18

The human protein lactate dehydrogenase has 332 amino acid. What is the smallest possible combined size of the parts of the gene that specify this protein using the genetic code?

Answer 18

332 x 3 = 996 base pairs

Question 19

a. are the triplets in the genetic code table written as DNA or RNA?
b. amino acids are each specified only by a single triplet. Identify these two amino acids and the corresponding triplets.
c. If you know the sequence of amino acids in a protein, what does the genetic code table allow you to infer about the sequence of base pairs in the gene that specifies that protein?

Answer 19

a. RNA
b. AUG specifies Met, UGG specifies Trp
c. the amino acid sequence of a protein allows you to infer many of the nucleotides in the RNA sequence.

Question 20

why do scientists think that all forms of life on earth have a common origin?

Answer 20

because organisms as distant as humans and bacteria share the same genetic code and many of their proteins are similar in amino acid sequence and biochemical function

Question 21

How can a scientist tell if a protein present in bacteria and a fruit fly protein have a common origin? How can a scientist determine whether a protein with a common origin in bacteria and a fruit fly function in a common pathway?

Answer 21

scientists cannot perform experiments on humans, but researches can manipulate organisms like yeast, fruit flies, and mice in the laboratory in many ways useful. Universal principles of biology may be learned from these model organisms because of the common origin of all life

Question 22

why do scientists think that new genes arise by duplication of an original gene and divergence by mutation?

Answer 22

the genomes of all organisms have gene families and superfamilies

Question 23

explain how the exon/intro structure of genes contributes to the generation of new gene functions during evolution

Answer 23

Exons from different genes could be shuffled by chromosome rearrangements. Modules from different proteins could thus reassort to form new proteins with new functions.

Question 24

mutations in genes that change their pattern of expression are thought to be a major factor in the evolution of different organisms. would you expect the same protein to work in the same way in two different types of cells? Is it possible that the same protein might function in different biochemical pathways in eye cells and muscle cells even if the protein’s basic mechanism always remains the same?

Answer 24

a protein is likely to perform the same type of biochemical reaction in different cell types but it will not necessarily interact with the same molecules in all kinds of cells

Question 25

A single zebrafish gene function was inactivated completely by mutation and a zebrafish with this mutation had none of its normal horizontal stripes. For each of the following statements, indicate whether the statement is certainly true, certainly untrue, or if there is unsufficient info to decide

a. the normal gene function is required for the viability of the zebrafish
b. the normal gene function is required for the formation of stripes
c. the normal gene function is required to make the pigment deposited in the stripes
d. the gene is required in zebrafish only for stripe formation

Answer 25

a. untrue
b. true
c. insufficient info
d. insufficient info

Question 26

different mutations in the WDR62 gene that inactivate gene function were found in the genomes of many different people with microcephaly. This info provided strong support for the idea that the WDR62 gene mutation causes microcephaly.

a. The human genome sequence identified WDR62 as one of the approximately 27000 genes in the human genome. What info about the function of WDR62 do you think was learned originally from the DNA sequence of the normal human genome?
b. what additional info was provided by identification of WDR62 as the microcephaly disease gene
c. the mouse genome contains a gene similar to human WDR62. Experiments in mice have shown that the mouse WDR62 gene expressed in the brain. Technology is now available that allows scientists to generate mice in which the now normal copies of WDR62 gene are replaces with mutant copies of the gene that are nonfunctional. Why would a scientist want to generate such WDR62 mutant mice?

Answer 26

a.The DNA sequence of the WDR62 gene would have enabled scientists to predict the amino acid sequence of the protein it encodes. Conserved regions of amino acid sequence often reveal structural features indicative of the biochemical function of the protein.
b. Knowing that the WDR62 mutations cause microcephaly indicates that at the level of the organism, the gene and the protein it encodes are required for proper brain development.
c. If the mutant mice had a syndrome resembling that of people with microcephaly, then we would know for sure that WDR62 is the microcephaly disease gene. These mice could also be used in various experiments to study the biochemical pathways in which the WDR62 protein participates
d

Question 27

Researchers have successfully used gene therapy to ameliorate some human genetic diseases by adding a normal gene copy to cells whose genomes originally had only nonfunctional mutant copies of that gene.

a. the success of this gene therapy approach provides us with clues about the role of the RPE65 protein in the retina. Do you think that RPE65 is needed for the proper development of the human eye?
b. can you see a potential difficulty in applying this gene therapy approach for diseases like microcephaly?

Answer 27

a. RPE65 is needed for retinal function, but not for retinal development
b. Providing a missing gene product after an organ has already developed improperly because of its absence likely will have no therapeutic effect.