1.1 Living Systems Require a Limited Number of Atoms and Molecules
Learning goal: Know that 98% of the atoms in a living organism are carbon, oxygen, and hydrogen.
Answer: Living organisms are primarily composed of three elements: oxygen, hydrogen, and carbon, which together make up 98% of the
atoms in a typical organism. This contrasts with the Earth's crust, where these elements are not as abundant. These elements are essential to life
largely because of their roles in forming water and organic compounds, which are crucial to biological processes.
Learning goal: Understand that all known forms of life require water.
Answer: Water is fundamental for life, earning its description as the "matrix of life." Biochemist Albert Szent-Györgyi highlighted its importance
in supporting biochemical processes. Because water is essential for life, scientists prioritize the search for water on other planets, such as Mars,
when searching for signs of life. Water's unique properties make it indispensable to life by supporting chemical reactions and maintaining stable
conditions for living organisms.
Learning goal: Describe the composition of fuel molecules and their products after oxidation.
Answer: Fuel molecules in biology are typically made of carbon, hydrogen, and oxygen. When these molecules are metabolized (oxidized) in
living organisms, they react with oxygen to produce carbon dioxide and water. This oxidation, or combustion, of biological fuels releases
energy, which is then used to power cellular functions. The production of carbon dioxide and water as byproducts mirrors the combustion
process seen in machinery, underscoring the universal nature of these chemical reactions in energy release.
Learning goal: Explain the advantage of carbon over silicon as a major constituent of living cells.
Answer: Although silicon is abundant in Earth’s crust and shares similar bonding properties with carbon (both can form four covalent bonds),
carbon is preferred in biological systems for two main reasons:
• Stronger carbon–carbon bonds: Carbon bonds create stable structures, allowing for the formation of complex, resilient organic molecules
that serve as the building blocks of life.
• Higher energy release during combustion: Carbon-based molecules release more energy when they react with oxygen than silicon-based
ones do. This makes carbon compounds more efficient energy sources.
Additionally, the combustion product of carbon, carbon dioxide (CO₂), is water-soluble and can circulate in the environment, allowing for
recycling in biochemical processes. In contrast, silicon dioxide (SiO₂), once formed, is insoluble and remains "out of circulation," typically as
solid quartz, making it unsuitable for biochemical recycling.
Learning goal: Know that nitrogen, phosphorus, and sulfur also play important roles in organisms.
Answer: Fuel molecules in biology are typically made of carbon, hydrogen, and oxygen. When these molecules are metabolized (oxidized) in
living organisms, they react with oxygen to produce carbon dioxide and water. This oxidation, or combustion, of biological fuels releases
energy, which is then used to power cellular functions. The production of carbon dioxide and water as byproducts mirrors the combustion
process seen in machinery, underscoring the universal nature of these chemical reactions in energy release.
Question 1: Ninety naturally occurring elements have been identified, yet only three make up 98% of the atoms in an organism. Which are these
elements? Name them in order of appearance in a human being:
Answer: These elements are hydrogen (63%), oxygen (25.5%) and carbon (9.5%).
Question 2: Next to the elements that are most abundant in life there are also elements that are essential to life. Which element has an essential
role for life?
a. Boron
b. Aluminium
c. Sulfur
d. Helium
e. Silicon
Answer: Sulfur.
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,1.2 There Are Four Major Classes of Biomolecules
Learning goal: Describe and differentiate between the key classes of biomolecules.
Answer: Living organisms contain four primary classes of biomolecules: proteins, nucleic acids, lipids, and carbohydrates.
• Proteins are versatile polymers that perform a range of functions, including catalysis, structure, signalling, and defence.
• Nucleic acids (DNA and RNA) are primarily information storage molecules that direct all cellular functions.
• Lipids are smaller molecules that serve as energy stores, structural barriers, and signalling agents.
• Carbohydrates act as a primary fuel source and play roles in cell recognition and structural integrity.
Learning goal: Explain the various uses of proteins in the cell.
Answer: Proteins are involved in nearly every cellular process:
• They act as signal molecules (like insulin) and receptors to convey signals into the cell.
• Proteins are known as catalysts; enzymes, which are protein catalysts, accelerate biochemical reactions essential for life.
• They serve structural roles (providing support and shape), allow mobility (as in muscle proteins), and offer defences (such as antibodies).
Learning goal: Describe the building blocks and structure of proteins.
Answer: Proteins are polymers made of 20 types of amino acids. These
amino acids link via peptide bonds to form long, unbranched chains. The
sequence of amino acids determines how these chains fold into precise three-
dimensional structures that are crucial to their function.
Learning goal: Know the two main kinds of nucleic acids in the cell and that they are
mainly used for storing information.
Answer: The two primary nucleic acids in cells are DNA (deoxyribonucleic acid) and
RNA (ribonucleic acid). DNA stores the cell's genetic information and is often called the
"parts list" for cellular components. RNA, particularly messenger RNA (mRNA), helps
transfer and utilize that information by serving as a template for protein synthesis.
Learning goal: Describe the building blocks and structure of nucleic acids.
Answer: Nucleic acids are linear polymers made from nucleotides, which consist of:
• A five-carbon sugar (deoxyribose in DNA and ribose in RNA),
• A nitrogenous base (A, C, G, T in DNA; U replaces T in RNA),
• And at least one phosphoryl group.
DNA is double-stranded and forms a double helix in which base pairs (A–T and C–G)
interact across the strands. RNA is generally single-stranded and is like DNA in
structure, except for the base thymine being replaced by uracil and an additional
hydroxyl (-OH) group on its sugar component.
Learning goal: Know the names and structures of the four “bases” used in DNA.
Answer: DNA is composed of four bases:
• Adenine (A): a double-ring structure without a C=O
• Cytosine (C): a single ring structure with a NH2-group
• Guanine (G): a double-ring structure with a C=O
• Thymine (T): a single ring structure with a CH3-group
These bases form pairs, with adenine pairing with thymine (2) and cytosine pairing
with guanine (3) through hydrogen bonds, which stabilizes the DNA double-helix
structure.
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, Learning goal: Understand the uses of lipids in the cell.
Answer: Lipids serve several essential roles:
• They function as energy stores, providing energy through the combustion of their
hydrophobic components.
• Lipids are structural components in cell membranes, creating a hydrophobic
barrier that separates the cell's interior from the environment and organizes
cellular compartments.
• They also act as signalling molecules, helping cells communicate and regulate internal processes.
Learning goal: Explain which classes of biomolecules are used as fuel
Answer: Both lipids and carbohydrates serve as primary fuel sources in living organisms. Carbohydrates like glucose are used for immediate
energy needs, while lipids are often stored for long-term energy reserves and provide a higher energy yield when metabolized.
Learning goal: Define what carbohydrates are and what the building blocks are for macromolecules such as starch and glycogen.
Answer: Carbohydrates are organic molecules composed primarily of carbon,
hydrogen, and oxygen, and they serve as a major energy source. The basic building
block of carbohydrates is glucose.
• Glycogen is the storage form of glucose in animals, consisting of glucose
molecules linked together with occasional branches.
• In plants, starch serves as the storage form of glucose and is like glycogen in
structure.
Carbohydrates can form complex, branched chains that contribute to cell recognition
and communication, as well as energy storage.
Question 1: Most large biomolecules are generally linear and unbranched. Which large biomolecules are likely to be
highly branched?
a. RNA
b. DNA
c. Lipids
d. Oligosaccharides (or carbohydrates or sugars)
e. Proteins
Answer: Although proteins are strictly linear, they can be covalently cross-linked, so two chains can become
attached. Glycogen and certain other carbohydrates are branched!
SUMMARY: Chapter 1
1.1 Living Systems Require a Limited Variety of Atoms and Molecules
Oxygen, hydrogen, and carbon make up 98% of the atoms in living organisms. Hydrogen and oxygen are prevalent because of the abundance of
water, and carbon is the most common atom in all biomolecules.
1.2 There Are Four Major Classes of Biomolecules
Proteins, nucleic acids, lipids, and carbohydrates constitute the four major classes of biomolecules. Proteins are the most versatile with an
especially prominent role as enzymes. Nucleic acids are primarily information molecules: DNA is the genetic information in most organisms,
whereas RNA plays a variety of roles, including serving as a link between DNA and proteins. Lipids serve as fuels and as membranes.
Carbohydrates are key fuel molecules that also play a role in cell-to-cell interactions
Quick quiz: Name the four classes of biomolecules and state an important function of each class.
Answer: Proteins: catalysts. Nucleic acids: information transfer. Lipids: fuel and structure. Carbohydrates: fuel and cell-to-cell communication
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Learning goal: Know that 98% of the atoms in a living organism are carbon, oxygen, and hydrogen.
Answer: Living organisms are primarily composed of three elements: oxygen, hydrogen, and carbon, which together make up 98% of the
atoms in a typical organism. This contrasts with the Earth's crust, where these elements are not as abundant. These elements are essential to life
largely because of their roles in forming water and organic compounds, which are crucial to biological processes.
Learning goal: Understand that all known forms of life require water.
Answer: Water is fundamental for life, earning its description as the "matrix of life." Biochemist Albert Szent-Györgyi highlighted its importance
in supporting biochemical processes. Because water is essential for life, scientists prioritize the search for water on other planets, such as Mars,
when searching for signs of life. Water's unique properties make it indispensable to life by supporting chemical reactions and maintaining stable
conditions for living organisms.
Learning goal: Describe the composition of fuel molecules and their products after oxidation.
Answer: Fuel molecules in biology are typically made of carbon, hydrogen, and oxygen. When these molecules are metabolized (oxidized) in
living organisms, they react with oxygen to produce carbon dioxide and water. This oxidation, or combustion, of biological fuels releases
energy, which is then used to power cellular functions. The production of carbon dioxide and water as byproducts mirrors the combustion
process seen in machinery, underscoring the universal nature of these chemical reactions in energy release.
Learning goal: Explain the advantage of carbon over silicon as a major constituent of living cells.
Answer: Although silicon is abundant in Earth’s crust and shares similar bonding properties with carbon (both can form four covalent bonds),
carbon is preferred in biological systems for two main reasons:
• Stronger carbon–carbon bonds: Carbon bonds create stable structures, allowing for the formation of complex, resilient organic molecules
that serve as the building blocks of life.
• Higher energy release during combustion: Carbon-based molecules release more energy when they react with oxygen than silicon-based
ones do. This makes carbon compounds more efficient energy sources.
Additionally, the combustion product of carbon, carbon dioxide (CO₂), is water-soluble and can circulate in the environment, allowing for
recycling in biochemical processes. In contrast, silicon dioxide (SiO₂), once formed, is insoluble and remains "out of circulation," typically as
solid quartz, making it unsuitable for biochemical recycling.
Learning goal: Know that nitrogen, phosphorus, and sulfur also play important roles in organisms.
Answer: Fuel molecules in biology are typically made of carbon, hydrogen, and oxygen. When these molecules are metabolized (oxidized) in
living organisms, they react with oxygen to produce carbon dioxide and water. This oxidation, or combustion, of biological fuels releases
energy, which is then used to power cellular functions. The production of carbon dioxide and water as byproducts mirrors the combustion
process seen in machinery, underscoring the universal nature of these chemical reactions in energy release.
Question 1: Ninety naturally occurring elements have been identified, yet only three make up 98% of the atoms in an organism. Which are these
elements? Name them in order of appearance in a human being:
Answer: These elements are hydrogen (63%), oxygen (25.5%) and carbon (9.5%).
Question 2: Next to the elements that are most abundant in life there are also elements that are essential to life. Which element has an essential
role for life?
a. Boron
b. Aluminium
c. Sulfur
d. Helium
e. Silicon
Answer: Sulfur.
1|P a g e
,1.2 There Are Four Major Classes of Biomolecules
Learning goal: Describe and differentiate between the key classes of biomolecules.
Answer: Living organisms contain four primary classes of biomolecules: proteins, nucleic acids, lipids, and carbohydrates.
• Proteins are versatile polymers that perform a range of functions, including catalysis, structure, signalling, and defence.
• Nucleic acids (DNA and RNA) are primarily information storage molecules that direct all cellular functions.
• Lipids are smaller molecules that serve as energy stores, structural barriers, and signalling agents.
• Carbohydrates act as a primary fuel source and play roles in cell recognition and structural integrity.
Learning goal: Explain the various uses of proteins in the cell.
Answer: Proteins are involved in nearly every cellular process:
• They act as signal molecules (like insulin) and receptors to convey signals into the cell.
• Proteins are known as catalysts; enzymes, which are protein catalysts, accelerate biochemical reactions essential for life.
• They serve structural roles (providing support and shape), allow mobility (as in muscle proteins), and offer defences (such as antibodies).
Learning goal: Describe the building blocks and structure of proteins.
Answer: Proteins are polymers made of 20 types of amino acids. These
amino acids link via peptide bonds to form long, unbranched chains. The
sequence of amino acids determines how these chains fold into precise three-
dimensional structures that are crucial to their function.
Learning goal: Know the two main kinds of nucleic acids in the cell and that they are
mainly used for storing information.
Answer: The two primary nucleic acids in cells are DNA (deoxyribonucleic acid) and
RNA (ribonucleic acid). DNA stores the cell's genetic information and is often called the
"parts list" for cellular components. RNA, particularly messenger RNA (mRNA), helps
transfer and utilize that information by serving as a template for protein synthesis.
Learning goal: Describe the building blocks and structure of nucleic acids.
Answer: Nucleic acids are linear polymers made from nucleotides, which consist of:
• A five-carbon sugar (deoxyribose in DNA and ribose in RNA),
• A nitrogenous base (A, C, G, T in DNA; U replaces T in RNA),
• And at least one phosphoryl group.
DNA is double-stranded and forms a double helix in which base pairs (A–T and C–G)
interact across the strands. RNA is generally single-stranded and is like DNA in
structure, except for the base thymine being replaced by uracil and an additional
hydroxyl (-OH) group on its sugar component.
Learning goal: Know the names and structures of the four “bases” used in DNA.
Answer: DNA is composed of four bases:
• Adenine (A): a double-ring structure without a C=O
• Cytosine (C): a single ring structure with a NH2-group
• Guanine (G): a double-ring structure with a C=O
• Thymine (T): a single ring structure with a CH3-group
These bases form pairs, with adenine pairing with thymine (2) and cytosine pairing
with guanine (3) through hydrogen bonds, which stabilizes the DNA double-helix
structure.
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, Learning goal: Understand the uses of lipids in the cell.
Answer: Lipids serve several essential roles:
• They function as energy stores, providing energy through the combustion of their
hydrophobic components.
• Lipids are structural components in cell membranes, creating a hydrophobic
barrier that separates the cell's interior from the environment and organizes
cellular compartments.
• They also act as signalling molecules, helping cells communicate and regulate internal processes.
Learning goal: Explain which classes of biomolecules are used as fuel
Answer: Both lipids and carbohydrates serve as primary fuel sources in living organisms. Carbohydrates like glucose are used for immediate
energy needs, while lipids are often stored for long-term energy reserves and provide a higher energy yield when metabolized.
Learning goal: Define what carbohydrates are and what the building blocks are for macromolecules such as starch and glycogen.
Answer: Carbohydrates are organic molecules composed primarily of carbon,
hydrogen, and oxygen, and they serve as a major energy source. The basic building
block of carbohydrates is glucose.
• Glycogen is the storage form of glucose in animals, consisting of glucose
molecules linked together with occasional branches.
• In plants, starch serves as the storage form of glucose and is like glycogen in
structure.
Carbohydrates can form complex, branched chains that contribute to cell recognition
and communication, as well as energy storage.
Question 1: Most large biomolecules are generally linear and unbranched. Which large biomolecules are likely to be
highly branched?
a. RNA
b. DNA
c. Lipids
d. Oligosaccharides (or carbohydrates or sugars)
e. Proteins
Answer: Although proteins are strictly linear, they can be covalently cross-linked, so two chains can become
attached. Glycogen and certain other carbohydrates are branched!
SUMMARY: Chapter 1
1.1 Living Systems Require a Limited Variety of Atoms and Molecules
Oxygen, hydrogen, and carbon make up 98% of the atoms in living organisms. Hydrogen and oxygen are prevalent because of the abundance of
water, and carbon is the most common atom in all biomolecules.
1.2 There Are Four Major Classes of Biomolecules
Proteins, nucleic acids, lipids, and carbohydrates constitute the four major classes of biomolecules. Proteins are the most versatile with an
especially prominent role as enzymes. Nucleic acids are primarily information molecules: DNA is the genetic information in most organisms,
whereas RNA plays a variety of roles, including serving as a link between DNA and proteins. Lipids serve as fuels and as membranes.
Carbohydrates are key fuel molecules that also play a role in cell-to-cell interactions
Quick quiz: Name the four classes of biomolecules and state an important function of each class.
Answer: Proteins: catalysts. Nucleic acids: information transfer. Lipids: fuel and structure. Carbohydrates: fuel and cell-to-cell communication
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