2.3: Carbon in Biological Molecules

What unique property of carbon makes it central to biological molecules?

Carbon has four valence electrons, allowing it to form covalent bonds with oxygen, hydrogen, and nitrogen.

What types of structures can carbon and hydrogen form?

Carbon and hydrogen can form hydrocarbon chains or rings.

What are functional groups and give two examples?

Functional groups are groups of atoms that impart specific properties to molecules. Examples include -CH3 (methyl) and -COOH (carboxyl).

How does the presence of a carboxyl group (-COOH) affect a molecule?

It makes the molecule more acidic.

What effect does the presence of an amine group (NH2) have on a molecule?

It makes the molecule more basic.

What are isomers?

Isomers are molecules with the same molecular formula but different structures, leading to different properties or functions.

What is the difference between isomers and isotopes?

Isomers have the same molecular formula but different structures, while isotopes are variants of the same element with different numbers of neutrons.

What is the focus of Big Idea 2 in the AP Biology Curriculum Framework?

Biological systems utilize free energy and molecular building blocks to grow, reproduce, and maintain dynamic homeostasis.

What does Essential Knowledge 2.A.3 state?

Organisms must exchange matter with the environment to grow, reproduce, and maintain organization.

What is the role of macromolecules in cells?

Macromolecules, such as proteins, nucleic acids, carbohydrates, and lipids, are complex molecules that make up cells and are essential for life.

What is the fundamental component of all macromolecules?

Carbon.

How many covalent bonds can a carbon atom form?

Up to four covalent bonds.

What is the atomic number of carbon and how does it relate to its electron configuration?

Carbon has an atomic number of 6, with two electrons in the inner shell and four in the outer shell.

What is the chemical formula for methane?

CH4.

How do the covalent bonds in hydrocarbons relate to energy?

The covalent bonds store a significant amount of energy, which is released when hydrocarbons are burned.

What are hydrocarbons?

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen.

What are some common uses of hydrocarbons in daily life?

Hydrocarbons are used as fuels, such as propane in gas grills and butane in lighters.

What is the significance of the octet rule in relation to carbon?

The octet rule states that atoms tend to bond in a way that gives them eight electrons in their outer shell, which carbon achieves by forming four covalent bonds.

What is the relationship between carbon's electron configuration and its ability to form macromolecules?

Carbon's four valence electrons allow it to form stable covalent bonds with various elements, making it versatile for building macromolecules.

What is the result of carbon forming covalent bonds in methane?

The result is a filled outermost electron shell, satisfying the octet rule.

What is the process called when hydrocarbons are burned?

Oxidation.

Why are hydrocarbons considered a significant energy source?

They store a large amount of energy in their covalent bonds, which is released during combustion.

What is the simplest hydrocarbon molecule?

Methane.

What is the geometry of the methane molecule?

Tetrahedral geometry.

How many hydrogen atoms are bonded to the central carbon atom in methane?

Four hydrogen atoms.

What shape do the hydrogen atoms form around the central carbon in methane?

A tetrahedron.

What is the bond angle between the hydrogen atoms in methane?

109.5° apart.

What types of carbon-to-carbon bonds exist in hydrocarbons?

Single, double, and triple covalent bonds.

How do single, double, and triple bonds affect molecular geometry?

Single bonds allow rotation, double bonds lead to a planar configuration, and triple bonds result in a linear shape.

What are the examples of hydrocarbons mentioned that illustrate different carbon-to-carbon bonds?

Ethane, ethene, and ethyne.

What prefix is used for two carbon hydrocarbons?

Eth-.

What suffixes indicate the type of carbon-carbon bond in hydrocarbons?

-ane for single bonds, -ene for double bonds, and -yne for triple bonds.

What is the shape of ethane?

Tetrahedral.

How many hydrogen atoms are connected to each carbon in ethane?

Three hydrogen atoms.

What is the shape of ethene, and why?

Planar, due to the double bond between the two carbon atoms.

How many bonds does each carbon have in ethene?

Three bonds (two with hydrogen and one with another carbon).

What happens to the atoms around a carbon atom when it forms a double bond?

They are locked in place and cannot rotate.

What is the significance of the three-dimensional shape of macromolecules?

It is critical to how they function.

What is the overall geometry of a molecule with single bonds?

Tetrahedral.

What happens to the shape of a molecule when it has a double bond?

It becomes planar.

What is the difference in rotation between single and double bonds?

Single bonds allow rotation; double bonds do not.

What is the impact of different geometries of carbon bonds on hydrocarbons?

They significantly affect the shape a particular molecule can assume.

What is the general structure of hydrocarbons?

They can exist as linear carbon chains, carbon rings, or combinations of both.

What are aliphatic hydrocarbons?

Hydrocarbons that consist of linear chains of carbon atoms, which can sometimes form rings with all single bonds.

What are aromatic hydrocarbons?

Hydrocarbons that consist of closed rings of carbon atoms with alternating single and double bonds.

Give examples of aliphatic and aromatic hydrocarbons.

Cyclohexane is an example of an aliphatic hydrocarbon, while benzene is an example of an aromatic hydrocarbon.

What is the structure of cyclohexane?

A ring consisting of six carbon atoms, each with two hydrogens attached.

What is the significance of the benzene ring in biological molecules?

The benzene ring is found in some amino acids, cholesterol, and hormones like estrogen and testosterone.

What is beta-carotene?

A hydrocarbon that contains both aliphatic and aromatic portions.

What is the molecular structure of benzene?

A six-carbon ring with alternating double bonds, where each carbon has one hydrogen attached.

How does pyridine differ from benzene?

Pyridine has a nitrogen atom substituted for one of the carbons in the benzene ring, with no hydrogens attached to the nitrogen.

What are structural isomers?

Isomers that differ in the placement of their covalent bonds, leading to different arrangements of atoms.

Provide an example of structural isomers.

Butane and isobutane are structural isomers with the same formula (C4H10) but different arrangements.

What are geometric isomers?

Isomers that have similar placements of their covalent bonds but differ in how these bonds are made to surrounding atoms.

How do cis and trans configurations differ in butene?

In cis-2-butene, the two methyl groups are on the same side of the double bond, while in trans-2-butene, they are on opposite sides.

What is the effect of the cis configuration on the carbon backbone?

The cis configuration causes a bend in the carbon backbone.

What is the effect of the trans configuration on the carbon backbone?

The trans configuration results in a more linear structure.

What distinguishes butane from isobutane in terms of structure?

Butane has a single chain of carbons, while isobutane has a branched chain.

Describe the shape of cis-2-butene and trans-2-butene.

Both consist of a four-carbon chain with a planar shape; cis has both CH3 groups on the same side, while trans has them on opposite sides.

What is the chemical formula for butane and isobutane?

Both have the chemical formula C4H10.

What is the role of the nitrogen atom in pyridine?

The nitrogen atom replaces one of the carbons in the benzene structure, affecting its properties.

What is a characteristic of benzene as a chemical compound?

Benzene is classified as a carcinogen and is a natural component of crude oil.

What is the significance of the alternating bonds in aromatic hydrocarbons?

The alternating single and double bonds contribute to the stability and unique properties of aromatic compounds.

What does a cis configuration represent in molecular structure?

A cis configuration has substituents on the same side of a double bond or central atom, exemplified by cis-butene where terminal CH3 groups are on the same side.

What does a trans configuration represent in molecular structure?

A trans configuration has substituents on opposite sides of a double bond or central atom, illustrated by a person with a glove on one hand and a sock on the opposite foot.

What are enantiomers?

Enantiomers are molecules that are mirror images of each other, differing in the three-dimensional arrangement of atoms.

How do the R and S forms of thalidomide differ in terms of configuration?

The R form is trans and the S form is cis.

How does the melting point of the R form of thalidomide compare to the S form?

The R form has a higher melting point and is absorbed less efficiently than the S form.

What effect do the R and S forms of thalidomide have on cholesterol?

The S form competes with cholesterol and disrupts cellular membrane structure, causing adverse side effects.

What are unsaturated fats?

Unsaturated fats contain at least one double bond between carbon atoms.

What is the effect of cis double bonds on triglycerides?

Cis double bonds create a bend in the carbon chain, preventing tight packing and keeping triglycerides liquid at room temperature.

What are trans fats?

Trans fats have double bonds that result in relatively linear fatty acids, allowing them to pack tightly and form solid fats at room temperature.

What health risks are associated with trans fats?

Trans fats are linked to an increased risk of cardiovascular disease.

What are saturated fats?

Saturated fats have no double bonds between carbon atoms and contain all available hydrogen atoms, typically being solid at room temperature.

How do oleic acid and eliadic acid differ?

Oleic acid has a kinked chain due to a double bond, while eliadic acid has a straight chain.

What is the significance of L-forms of amino acids in nature?

Only L-forms of amino acids are used to make proteins in nature.

Where are D forms of amino acids found?

D forms of amino acids are found in the cell walls of bacteria, but not in their proteins.

What is the relationship between the structure of triglycerides and their physical state at room temperature?

Triglycerides with cis double bonds remain liquid (oils) at room temperature, while those with trans double bonds are solid.

What visual representation is used to illustrate the R and S forms of thalidomide?

A dark triangle represents a bond coming toward you, and a dashed triangle represents a bond going away from you.

What happens when a mixture of enantiomers is used instead of a pure form?

A mixture of enantiomers can be less effective or even harmful, as the two forms may react differently.

What does the bend in the molecule caused by the cis configuration indicate?

The bend prevents tight packing of triglyceride molecules, affecting their physical state.

What is the impact of double bonds in fatty acids on their classification?

Fatty acids with double bonds are classified as unsaturated, while those without are classified as saturated.

What is the main product of photosynthesis in terms of glucose forms?

The D-form of glucose is the main product, while the L-form is rarely seen in nature.

What are D-alanine and L-alanine examples of?

They are examples of enantiomers or mirror images.

Which form of amino acids is used to make proteins?

Only the L-forms of amino acids are used to make proteins.

What are functional groups in the context of macromolecules?

Functional groups are groups of atoms that confer specific chemical properties to molecules and are found along the carbon backbone.

What is the carbon backbone of macromolecules composed of?

Chains and/or rings of carbon atoms, sometimes substituted with elements like nitrogen or oxygen.

What are substituted hydrocarbons?

Molecules with other elements in their carbon backbone.

How do functional groups affect macromolecules?

They contribute to the differing chemical properties and functions of the four types of macromolecules: proteins, lipids, carbohydrates, and nucleic acids.

What are some important functional groups in biological molecules?

Hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl.

How are functional groups classified?

They are classified as hydrophobic or hydrophilic based on their charge or polarity characteristics.

What is an example of a hydrophobic functional group?

The non-polar methyl group.

What is a characteristic of the carboxyl group?

It can ionize to release hydrogen ions (H+), contributing to the hydrophilic nature of the molecule.

What is the structure of a hydroxyl group?

A hydroxyl group consists of OH attached to a carbon chain.

What is the polarity of methyl groups?

Methyl groups are nonpolar.

What defines a carbonyl group?

A carbonyl group consists of an oxygen double bonded to a carbon in the middle of a hydrocarbon chain.

What is the acidic property of carboxyl groups?

Carboxyl groups can ionize, releasing H+ ions into solution.

What is the basic property of amino groups?

Amino groups can accept H+ ions from solution, forming H3+.

What is the structure of phosphate groups?

Phosphate groups consist of a phosphorus atom with one double bonded oxygen and two OH groups.

How do phosphate groups behave in solution?

Both OH groups in phosphate can lose a H+ ion, making them acidic.