AP Biology Ultimate Guide Complete
Unit 1: Chemistry of Life
Elements
Elements: are substances that cannot be broken down into simpler substances by
chemical means.
Oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).
These four elements are used to build biological molecules, such as carbohydrates,
proteins, lipids, and nucleic acids. They are also used to form storage compounds
and cells in all organisms.
Some elements are known as trace elements because they are required by an
organism only in very small quantities. They include iron (Fe), iodine (I), and
copper (Cu).
Other elements are present but in smaller quantities.
Subatomic Particles
Atoms are the unit of life and are the building blocks of the physical world.
o Protons are positively charged (+) particles
o Neutrons are uncharged particles.
o Electrons are negatively charged (–) particles
Some atoms have the same number of protons but differ in the number of
neutrons in the nucleus. These are called isotopes.
Compounds
Consists of two or more elements
The atoms of a compound are held together by chemical bonds, which may be ionic
bonds, covalent bonds, or hydrogen bonds.
An ionic bond is formed between two atoms when one or more electrons are
transferred from one atom to the other.
The charged forms of the atoms are called ions.
A covalent bond is formed when electrons are shared between atoms. If the
electrons are shared equally between the atoms, the bond is called non-polar
covalent. If the electrons are shared unequally, the bond is called polar covalent.
Water: The Versatile Molecule
Hydrogen bonds are weak chemical bonds that form when a hydrogen atom
that is covalently bonded to one
, The hydrogen bonds that hold water molecules together contribute to a number of
special properties, including cohesion, adhesion, surface tension, high heat
capacity, and expansion on freezing.
Water molecules have a strong tendency to stick together. This exhibits cohesive
forces.
Water molecules also like to stick to other substances—This makes them adhesive
These two forces taken together—cohesion and adhesion—account for the ability of
water to rise up the roots, trunks, and branches of trees. This is capillary action.
The cohesion of water molecules contributes to another property of water known
as surface tension. The surface of the water has tension to it. The water molecules
are stuck together, and light things like leaves and water striders can sit atop the
surface without sinking.
Acids and bases
Reactions are also influenced by whether the solution in which they occur is acidic,
basic, or neutral.
A solution is acidic if it contains a lot of hydrogen ions (H+). If you dissolve an acid
in water, it will release a lot of hydrogen ions.
Bases do not release hydrogen ions when added to water. They release a lot of
hydroxide ions (OH–).
The acidity or alkalinity of a solution can be measured using a pH scale. The pH
scale is numbered from 1 to 14. The midpoint, 7, is considered neutral pH.
The concentration of hydrogen ions in a solution will indicate whether it is acidic,
basic, or neutral.
o pH = –log [H+]
The pH scale is logarithmic and represents a tenfold change in hydrogen ion
concentration.
Organic molecules
Molecules with carbon are organic molecules and molecules that do not contain
carbon atoms are called inorganic compounds.
Carbon is important for life because it is a versatile atom, meaning that it has
the ability to bind not only with other carbons but also with a number of
other elements including nitrogen, oxygen, and hydrogen
Polymers are chains of building blocks in macromolecules
Monomers are the individual building blocks of a polymer
Polymers are formed through dehydration synthesis (or condensation) reactions. A
water molecule is lost in the reaction, and a larger compound is formed.
Hydrolysis is when polymers can also be broken down into monomers.
The water breaks the bond between the two monomers.
Four classes of organic compounds central to life on Earth:
1. carbohydrates
2. proteins
3. lipids
, 4. nucleic acids
Carbohydrates
Carbohydrates are organic compounds that contain carbon, hydrogen, and oxygen.
They are in a ratio of approximately 1:2:1
Most carbohydrates are categorised as either monosaccharides, disaccharides, or
polysaccharides. The term saccharides means “sugar.” The prefixes refer to the
number of sugars in the molecule.
Monosaccharides:
It is an energy source for cells.
The two most common sugars are glucose and fructose. Their chemical formula is
C6H12O6
Glucose is an important part of the food we eat, and it is the product made by
plants during photosynthesis.
Glucose and fructose can be depicted as either “straight” or “rings.” They have OHs
and Hs attached to them.
Disaccharides
When two monosaccharides are joined, the bond is called a glycosidic linkage,
and the resulting sugar is called a disaccharide. The disaccharide formed from two
glucose molecules is maltose.
To break up the disaccharide and form two monosaccharides - Just add water.
Polysaccharides
Polysaccharides are made up of many repeated units of monosaccharides.
They can consist of branched or unbranched chains of monosaccharides. Need to
know for the test : starch, cellulose, and glycogen.
Glycogen and starch are sugar storage molecules. Glycogen stores sugar in animals
and starch stores sugar in plants.
Cellulose, on the other hand, is made up of β-glucose and is a major part of the cell
walls in plants. Its function is to lend structural support.
Chitin, a polymer of β-glucose molecules, serves as a structural molecule in the
walls of fungus and in the exoskeletons of arthropods.
Proteins
Proteins are important for structure, function, and regulation of your tissues and
organs.
Amino acids are building blocks of proteins. They contain carbon, hydrogen,
oxygen, and nitrogen atoms. There are 20 different amino acids.
Proteins have four important parts around a central carbon:
, o An amino group (–NH2), a carboxyl group (–COOH), a hydrogen, and an
R-group.
Amino acids differ only in the R-group, which is also called the side chain.
When it comes to spotting an amino acid, look for the amino group (NH2), then
look for the carboxyl molecule (COOH).
Side chain polarity affects whether an amino acid is more hydrophobic or more
hydrophilic.
The AP Exam divides them into 3 broad categories: hydrophobic (non-polar and
uncharged), hydrophilic (polar and uncharged), and ionic (polar and charged).
Of the common amino acids:
o Two (glutamic acid and aspartic acid) donate a proton, making them
negatively charged.
o Two (lysine and arginine) accept a proton at physiological pH, which
makes them positively charged.
Two contain the atom sulphur: methionine and cysteine.
Polypeptides
When two amino acids join, they form a dipeptide. The carboxyl group of one
amino acid combines with the amino group of another amino acid.
The bond between two amino acids is peptide bond.
If a group of amino acids is joined together in a “string,” the resulting organic
compound is called a polypeptide. Once a polypeptide chain twists and folds on
itself, it forms a 3D structure called a protein.
The linear sequence of the amino acids is the primary structure of a protein.
When the polypeptide begins to twist it begins forming either a coil (known as an
alpha helix) or zigzagging pattern (known as beta-pleated sheets). These are
secondary structures.
When the secondary structure reshapes the polypeptide, amino acids that were far
away in the primary structure arrangement can now also interact with each other.
This is called the tertiary structure.
When different polypeptide chains sometimes interact with each other, they form a
quaternary structure. Haemoglobin is a molecule in the blood that helps distribute
oxygen to the tissues in the body. It is formed when four separate polypeptide
chains interact with each other and is a quaternary structure.
Liplids
This consists of carbon, hydrogen, and oxygen atoms.
The most common examples of lipids are triglycerides, phospholipids, and steroids.
Lipids are important due to their non-polar structures, they function as structural
components of cell membranes, sources of insulation, signalling molecules, and a
means of energy storage.
Our bodies store fat in tissue called, adipose, which is made of cells called
adipocytes; these cells are filled with lipids called triglycerides.
Unit 1: Chemistry of Life
Elements
Elements: are substances that cannot be broken down into simpler substances by
chemical means.
Oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).
These four elements are used to build biological molecules, such as carbohydrates,
proteins, lipids, and nucleic acids. They are also used to form storage compounds
and cells in all organisms.
Some elements are known as trace elements because they are required by an
organism only in very small quantities. They include iron (Fe), iodine (I), and
copper (Cu).
Other elements are present but in smaller quantities.
Subatomic Particles
Atoms are the unit of life and are the building blocks of the physical world.
o Protons are positively charged (+) particles
o Neutrons are uncharged particles.
o Electrons are negatively charged (–) particles
Some atoms have the same number of protons but differ in the number of
neutrons in the nucleus. These are called isotopes.
Compounds
Consists of two or more elements
The atoms of a compound are held together by chemical bonds, which may be ionic
bonds, covalent bonds, or hydrogen bonds.
An ionic bond is formed between two atoms when one or more electrons are
transferred from one atom to the other.
The charged forms of the atoms are called ions.
A covalent bond is formed when electrons are shared between atoms. If the
electrons are shared equally between the atoms, the bond is called non-polar
covalent. If the electrons are shared unequally, the bond is called polar covalent.
Water: The Versatile Molecule
Hydrogen bonds are weak chemical bonds that form when a hydrogen atom
that is covalently bonded to one
, The hydrogen bonds that hold water molecules together contribute to a number of
special properties, including cohesion, adhesion, surface tension, high heat
capacity, and expansion on freezing.
Water molecules have a strong tendency to stick together. This exhibits cohesive
forces.
Water molecules also like to stick to other substances—This makes them adhesive
These two forces taken together—cohesion and adhesion—account for the ability of
water to rise up the roots, trunks, and branches of trees. This is capillary action.
The cohesion of water molecules contributes to another property of water known
as surface tension. The surface of the water has tension to it. The water molecules
are stuck together, and light things like leaves and water striders can sit atop the
surface without sinking.
Acids and bases
Reactions are also influenced by whether the solution in which they occur is acidic,
basic, or neutral.
A solution is acidic if it contains a lot of hydrogen ions (H+). If you dissolve an acid
in water, it will release a lot of hydrogen ions.
Bases do not release hydrogen ions when added to water. They release a lot of
hydroxide ions (OH–).
The acidity or alkalinity of a solution can be measured using a pH scale. The pH
scale is numbered from 1 to 14. The midpoint, 7, is considered neutral pH.
The concentration of hydrogen ions in a solution will indicate whether it is acidic,
basic, or neutral.
o pH = –log [H+]
The pH scale is logarithmic and represents a tenfold change in hydrogen ion
concentration.
Organic molecules
Molecules with carbon are organic molecules and molecules that do not contain
carbon atoms are called inorganic compounds.
Carbon is important for life because it is a versatile atom, meaning that it has
the ability to bind not only with other carbons but also with a number of
other elements including nitrogen, oxygen, and hydrogen
Polymers are chains of building blocks in macromolecules
Monomers are the individual building blocks of a polymer
Polymers are formed through dehydration synthesis (or condensation) reactions. A
water molecule is lost in the reaction, and a larger compound is formed.
Hydrolysis is when polymers can also be broken down into monomers.
The water breaks the bond between the two monomers.
Four classes of organic compounds central to life on Earth:
1. carbohydrates
2. proteins
3. lipids
, 4. nucleic acids
Carbohydrates
Carbohydrates are organic compounds that contain carbon, hydrogen, and oxygen.
They are in a ratio of approximately 1:2:1
Most carbohydrates are categorised as either monosaccharides, disaccharides, or
polysaccharides. The term saccharides means “sugar.” The prefixes refer to the
number of sugars in the molecule.
Monosaccharides:
It is an energy source for cells.
The two most common sugars are glucose and fructose. Their chemical formula is
C6H12O6
Glucose is an important part of the food we eat, and it is the product made by
plants during photosynthesis.
Glucose and fructose can be depicted as either “straight” or “rings.” They have OHs
and Hs attached to them.
Disaccharides
When two monosaccharides are joined, the bond is called a glycosidic linkage,
and the resulting sugar is called a disaccharide. The disaccharide formed from two
glucose molecules is maltose.
To break up the disaccharide and form two monosaccharides - Just add water.
Polysaccharides
Polysaccharides are made up of many repeated units of monosaccharides.
They can consist of branched or unbranched chains of monosaccharides. Need to
know for the test : starch, cellulose, and glycogen.
Glycogen and starch are sugar storage molecules. Glycogen stores sugar in animals
and starch stores sugar in plants.
Cellulose, on the other hand, is made up of β-glucose and is a major part of the cell
walls in plants. Its function is to lend structural support.
Chitin, a polymer of β-glucose molecules, serves as a structural molecule in the
walls of fungus and in the exoskeletons of arthropods.
Proteins
Proteins are important for structure, function, and regulation of your tissues and
organs.
Amino acids are building blocks of proteins. They contain carbon, hydrogen,
oxygen, and nitrogen atoms. There are 20 different amino acids.
Proteins have four important parts around a central carbon:
, o An amino group (–NH2), a carboxyl group (–COOH), a hydrogen, and an
R-group.
Amino acids differ only in the R-group, which is also called the side chain.
When it comes to spotting an amino acid, look for the amino group (NH2), then
look for the carboxyl molecule (COOH).
Side chain polarity affects whether an amino acid is more hydrophobic or more
hydrophilic.
The AP Exam divides them into 3 broad categories: hydrophobic (non-polar and
uncharged), hydrophilic (polar and uncharged), and ionic (polar and charged).
Of the common amino acids:
o Two (glutamic acid and aspartic acid) donate a proton, making them
negatively charged.
o Two (lysine and arginine) accept a proton at physiological pH, which
makes them positively charged.
Two contain the atom sulphur: methionine and cysteine.
Polypeptides
When two amino acids join, they form a dipeptide. The carboxyl group of one
amino acid combines with the amino group of another amino acid.
The bond between two amino acids is peptide bond.
If a group of amino acids is joined together in a “string,” the resulting organic
compound is called a polypeptide. Once a polypeptide chain twists and folds on
itself, it forms a 3D structure called a protein.
The linear sequence of the amino acids is the primary structure of a protein.
When the polypeptide begins to twist it begins forming either a coil (known as an
alpha helix) or zigzagging pattern (known as beta-pleated sheets). These are
secondary structures.
When the secondary structure reshapes the polypeptide, amino acids that were far
away in the primary structure arrangement can now also interact with each other.
This is called the tertiary structure.
When different polypeptide chains sometimes interact with each other, they form a
quaternary structure. Haemoglobin is a molecule in the blood that helps distribute
oxygen to the tissues in the body. It is formed when four separate polypeptide
chains interact with each other and is a quaternary structure.
Liplids
This consists of carbon, hydrogen, and oxygen atoms.
The most common examples of lipids are triglycerides, phospholipids, and steroids.
Lipids are important due to their non-polar structures, they function as structural
components of cell membranes, sources of insulation, signalling molecules, and a
means of energy storage.
Our bodies store fat in tissue called, adipose, which is made of cells called
adipocytes; these cells are filled with lipids called triglycerides.
