chapter
1
Genetics: The Study of Biological
Information
Synopsis
Chapter 1 is an introduction to the study of modern-day genetics. Genetics is the study of genes:
how genes are segments of DNA molecules; how genes are inherited; and how genes direct an
organism’s characteristics. The most important insight from this chapter is that the basic
function of most (but not all) genes is to direct the synthesis of (to encode) a particular type of
protein.
Key terms
DNA – the macromolecular polymer that constitutes genes
nucleotides – the chemical building blocks of DNA
bases – components of nucleotides that are of four different types in DNA;
abbreviated as A, G, C, and T
base pair – DNA is double-stranded; two nucleotide polymers are held together by
hydrogen bonds between A-T and G-C base pairs.
genes –segments of DNA that, in most cases, encode proteins
chromosomes – large DNA molecules that can contain hundreds or thousands of
genes
genome – all of the DNA, and thus all the genes, in a particular organism
metabolism – the chemical reactions by which organisms use energy and matter to
construct their bodies
genetic code – the way that genes are “read” by the molecular machines that use genes
to make proteins
RNA – a polymer structurally similar to DNA that serves as a chemical intermediate in
the pathway from genes to proteins
proteins – linear polymers of amino acids that fold into complex three dimensional
shapes. Proteins constitute the structures of cells, and also carry out the chemical
reactions of metabolism.
amino acids – the chemical subunits of proteins. Twenty different common amino
acids exist in proteins.
mutation – a heritable chemical change in the base sequence of DNA that enables
evolution to take place
1-‐
1
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
, chapter 1
evolution – the change in characteristics
of populations of organisms over time due to
the accumulation of mutations in genes
convergent evolution – the evolution of similar structures independently in the
lineages leading to different species
model organisms – species used commonly for genetic analysis by scientists
gene family – two or more genes with similar DNA sequences and similar functions
that most likely arose from a single ancestral gene by a series of duplication and
divergence events. A multigene family is a large gene family; a gene superfamily
is a group of gene families and multigene families that share a common ancestral
gene.
exons and introns – the portions of genes that are used to make proteins (exons) and
the regions of DNA that separate them (introns)
prokaryotic cells – single-cell organisms like bacteria whose genomes are not enclosed
within a membrane (not inside a nucleus)
eukaryotic cells – cells such as human cells whose genomes are within a nucleus, a
membrane-enclosed organelle
Human Genome Project – the effort to determine the DNA base sequence of every
human chromosome and to analyze the genes making up the human genome
Problem Solving
The first chapter of this book provides a broad overview of genetics. Chapter 1 covers a lot
of ground, but only superficially. Don’t worry if at this point you don’t understand all of the
information given at a deep level – you will later on. However, you are likely familiar already
(from introductory biology classes) with some of the fundamentals of what a gene is and how
genes are used to make proteins. The problems in this chapter are meant to get you started in
the habit of thinking like a geneticist – quantitatively, analytically, carefully, and logically.
Vocabulary
1.
a. complementarity 4. G-C and A-T base pairing in DNA through hydrogen
bonds
b. nucleotide 11. subunit of the DNA macromolecule
c. chromosomes 7. DNA/protein structures that contain genes
d. protein 1. a linear polymer of amino acids that folds into a
particular shape
e. genome 9. the entirety of an organism’s hereditary information
1-‐
2
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
, chapter 1
f. gene 8. DNA information for a single function, such as a
protein
g. uracil 12. the one of the four bases in RNA that is not in DNA
h. exon 6. part of a gene that contains protein coding
information
i. intron 2. part of a gene that does not contain protein coding
information
j. DNA 10. a double-stranded polymer of nucleotides that stores
the inherited blueprint of an organism
k. RNA 3. a polymer of nucleotides that is an intermediary in
the synthesis of proteins from DNA
l. mutation 5. alteration of DNA sequence
Section 1.1
2. The complementary strand of a DNA molecule is simply the strand with which the
original DNA molecule forms base pairs. Remember two things: (1) The two strands of
a double-stranded DNA molecule are oriented in the opposite direction with respect to
each other (their 5’ and 3’ ends run in opposite directions), and (2) the base pairs are
A-T and G-C. Therefore, the DNA strand complementary to the one shown is:
5’ AGCTTAATGCT 3’
3. a. If the 3 billion (3,000,000,000) base pairs of the human genome is divided into 23
chromosomes, the average size of a human chromosome is 3,000,000,000 base
pairs/23 chromosomes ≈ 135,435,000 base pairs per chromosome.
b. The human genome contains about 25,000 genes, and assuming that they are spread
evenly over the 23 chromosomes, on average there are 25,000 genes/23
chromosomes ≈ 1087 genes per chromosome.
c. About half the DNA of the human genome contains genes, meaning that all the
genes are found within 1.5 billion (1,500,000,000) base pairs. Therefore, on average
there are 1,500,000,000 base pairs / 25,000 genes ≈ 60,000 base pairs per gene.
Section 1.2
4. a. Both. Each protein is composed of a “string” of amino acids, and DNA is a
“string” of nucleotides.
b. DNA. DNA is double-stranded through complementary base pairing of single
strands in opposite orientations. A protein is a single strand of linked amino acids,
and the strand folds into a particular shape.
1-‐
3
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
, chapter 1
c. DNA. Four different kinds of nucleotides – A, G, C, and T – are present in the
DNA polymer. Twenty different common amino acids are present in almost all
proteins.
d. Protein. Twenty distinct amino acid subunits are the building blocks of almost all
proteins. DNA is made up of only four different types of nucleotides.
e. Protein. Proteins are polymers of amino acids; DNA is a polymer of nucleotides.
f. DNA. DNA is a polymer of nucleotides; proteins are polymers of amino acids.
g. DNA. Genes are segments of DNA; by using the genetic code, most genes encode
proteins.
h. Protein. Some proteins (enzymes) perform chemical reactions.
5. a. Each base in a single strand of a DNA molecule can be either an A, G, C or T.
Therefore, a specific 100-nucleotide DNA strand could start with any one of the
four nucleotides, the second nucleotide could be any one of the four nucleotides,
etc. The number of different possible sequences increases by a factor of 4 at each
successive step in the addition of a base (see the following figure). Thus, the
number of different possible sequences of a 100-nucleotide DNA strand is
4100 = ~1.6 × 1060. We need not consider the second, complementary strand of
DNA, as its base sequence is determined by the sequence of the first strand.
b. Because each amino acid can be 1 of 20 different amino acids, by the same logic as
in part (a), the number of different 100-amino acid proteins is 20100 = ~1.3 ×
10130.
1-‐
4
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
1
Genetics: The Study of Biological
Information
Synopsis
Chapter 1 is an introduction to the study of modern-day genetics. Genetics is the study of genes:
how genes are segments of DNA molecules; how genes are inherited; and how genes direct an
organism’s characteristics. The most important insight from this chapter is that the basic
function of most (but not all) genes is to direct the synthesis of (to encode) a particular type of
protein.
Key terms
DNA – the macromolecular polymer that constitutes genes
nucleotides – the chemical building blocks of DNA
bases – components of nucleotides that are of four different types in DNA;
abbreviated as A, G, C, and T
base pair – DNA is double-stranded; two nucleotide polymers are held together by
hydrogen bonds between A-T and G-C base pairs.
genes –segments of DNA that, in most cases, encode proteins
chromosomes – large DNA molecules that can contain hundreds or thousands of
genes
genome – all of the DNA, and thus all the genes, in a particular organism
metabolism – the chemical reactions by which organisms use energy and matter to
construct their bodies
genetic code – the way that genes are “read” by the molecular machines that use genes
to make proteins
RNA – a polymer structurally similar to DNA that serves as a chemical intermediate in
the pathway from genes to proteins
proteins – linear polymers of amino acids that fold into complex three dimensional
shapes. Proteins constitute the structures of cells, and also carry out the chemical
reactions of metabolism.
amino acids – the chemical subunits of proteins. Twenty different common amino
acids exist in proteins.
mutation – a heritable chemical change in the base sequence of DNA that enables
evolution to take place
1-‐
1
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
, chapter 1
evolution – the change in characteristics
of populations of organisms over time due to
the accumulation of mutations in genes
convergent evolution – the evolution of similar structures independently in the
lineages leading to different species
model organisms – species used commonly for genetic analysis by scientists
gene family – two or more genes with similar DNA sequences and similar functions
that most likely arose from a single ancestral gene by a series of duplication and
divergence events. A multigene family is a large gene family; a gene superfamily
is a group of gene families and multigene families that share a common ancestral
gene.
exons and introns – the portions of genes that are used to make proteins (exons) and
the regions of DNA that separate them (introns)
prokaryotic cells – single-cell organisms like bacteria whose genomes are not enclosed
within a membrane (not inside a nucleus)
eukaryotic cells – cells such as human cells whose genomes are within a nucleus, a
membrane-enclosed organelle
Human Genome Project – the effort to determine the DNA base sequence of every
human chromosome and to analyze the genes making up the human genome
Problem Solving
The first chapter of this book provides a broad overview of genetics. Chapter 1 covers a lot
of ground, but only superficially. Don’t worry if at this point you don’t understand all of the
information given at a deep level – you will later on. However, you are likely familiar already
(from introductory biology classes) with some of the fundamentals of what a gene is and how
genes are used to make proteins. The problems in this chapter are meant to get you started in
the habit of thinking like a geneticist – quantitatively, analytically, carefully, and logically.
Vocabulary
1.
a. complementarity 4. G-C and A-T base pairing in DNA through hydrogen
bonds
b. nucleotide 11. subunit of the DNA macromolecule
c. chromosomes 7. DNA/protein structures that contain genes
d. protein 1. a linear polymer of amino acids that folds into a
particular shape
e. genome 9. the entirety of an organism’s hereditary information
1-‐
2
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
, chapter 1
f. gene 8. DNA information for a single function, such as a
protein
g. uracil 12. the one of the four bases in RNA that is not in DNA
h. exon 6. part of a gene that contains protein coding
information
i. intron 2. part of a gene that does not contain protein coding
information
j. DNA 10. a double-stranded polymer of nucleotides that stores
the inherited blueprint of an organism
k. RNA 3. a polymer of nucleotides that is an intermediary in
the synthesis of proteins from DNA
l. mutation 5. alteration of DNA sequence
Section 1.1
2. The complementary strand of a DNA molecule is simply the strand with which the
original DNA molecule forms base pairs. Remember two things: (1) The two strands of
a double-stranded DNA molecule are oriented in the opposite direction with respect to
each other (their 5’ and 3’ ends run in opposite directions), and (2) the base pairs are
A-T and G-C. Therefore, the DNA strand complementary to the one shown is:
5’ AGCTTAATGCT 3’
3. a. If the 3 billion (3,000,000,000) base pairs of the human genome is divided into 23
chromosomes, the average size of a human chromosome is 3,000,000,000 base
pairs/23 chromosomes ≈ 135,435,000 base pairs per chromosome.
b. The human genome contains about 25,000 genes, and assuming that they are spread
evenly over the 23 chromosomes, on average there are 25,000 genes/23
chromosomes ≈ 1087 genes per chromosome.
c. About half the DNA of the human genome contains genes, meaning that all the
genes are found within 1.5 billion (1,500,000,000) base pairs. Therefore, on average
there are 1,500,000,000 base pairs / 25,000 genes ≈ 60,000 base pairs per gene.
Section 1.2
4. a. Both. Each protein is composed of a “string” of amino acids, and DNA is a
“string” of nucleotides.
b. DNA. DNA is double-stranded through complementary base pairing of single
strands in opposite orientations. A protein is a single strand of linked amino acids,
and the strand folds into a particular shape.
1-‐
3
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
, chapter 1
c. DNA. Four different kinds of nucleotides – A, G, C, and T – are present in the
DNA polymer. Twenty different common amino acids are present in almost all
proteins.
d. Protein. Twenty distinct amino acid subunits are the building blocks of almost all
proteins. DNA is made up of only four different types of nucleotides.
e. Protein. Proteins are polymers of amino acids; DNA is a polymer of nucleotides.
f. DNA. DNA is a polymer of nucleotides; proteins are polymers of amino acids.
g. DNA. Genes are segments of DNA; by using the genetic code, most genes encode
proteins.
h. Protein. Some proteins (enzymes) perform chemical reactions.
5. a. Each base in a single strand of a DNA molecule can be either an A, G, C or T.
Therefore, a specific 100-nucleotide DNA strand could start with any one of the
four nucleotides, the second nucleotide could be any one of the four nucleotides,
etc. The number of different possible sequences increases by a factor of 4 at each
successive step in the addition of a base (see the following figure). Thus, the
number of different possible sequences of a 100-nucleotide DNA strand is
4100 = ~1.6 × 1060. We need not consider the second, complementary strand of
DNA, as its base sequence is determined by the sequence of the first strand.
b. Because each amino acid can be 1 of 20 different amino acids, by the same logic as
in part (a), the number of different 100-amino acid proteins is 20100 = ~1.3 ×
10130.
1-‐
4
Copyright © 2015 McGraw-Hill Education. All rights reserved.
No reproduction or distribution without the prior written consent of McGraw-Hill Education.
