The Four Major Groups of Organic Compounds: Carbohydrates, Lipids, Proteins, and Nucleic Acids; and Their Functions in Living Systems

Carbon a Most Versatile Atom

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— C —

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-The Carbon atom has •6 protons•6 neutrons•6 electrons-Carbon has 4 electrons in its outermost energy level, therefore it needs four electrons to complete its octet.-Carbon covalently shares electrons with up to four other atoms. This characteristic makes Carbon very versatile when it comes to chemical structures.

Carbon’s Chemical Properties and Molecular Diversity

Carbon Skeletons Vary

• Carbon chains– Vary in length– May be linear or branched– May contain only c-c single

bonds or may contain double and/or triple bonds at various locations

• Carbon rings– May contain only single c-c

bonds, or may contain double bonds

Functional Groups Confer Specific Properties to Carbon Compounds

• Carbon skeletons come in may shapes and forms. These are basically Hydrocarbons (molecules composed of only Carbon and Hydrogen atoms).

• Functional groups, have specific properties characteristic to their chemical structure and further add variety to the Hydrocarbon skeleton molecular structures.

Functional Groups and Their Functions

Hydroxyl Group — OH Alcohols

Carbonyl Group — C = O

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Aldehydes

Ketones

Carboxyl Group — COOH Organic Acids

Carboxylic Acid

Amino Group — NH2 Organic Bases

Amines

Phosphate Group

— OPO32- Organic

Phosphates

Monomers ↔ PolymersDehydration ↔ Hydrolysis

• Monomers are molecules that are chemically bonded through dehydration synthesis to make polymers, which are the functional macromolecules.

• Polymers can be broken down into their monomer components through hydrolysis.

Carbohydrates aka Saccharides Are Aldoses and Ketoses

• Carbohydrates have the atomic ratio C:H2O.

• They are composed of many monosaccharide (monomers) chemically combined through dehydration synthesis into polysaccharides (polymers).

• Glucose C6H12O6 is made by plants and is the most common monosaccharide.

• Serve as energy sources for plants, animals and other organisms. Converted into ATP energy.

• Serve as structural molecules in plants and other organisms.

• Dietary source: plant products.• Cellulose is bulk or fiber.

PolysaccharidesCellulose

Most abundant glucose

polymer, component

of plant cell walls

StarchPlants store glucose in starch polymers (grains, tubers). Serve as glucose source for animals.

GlycogenVery branched glucose polymer. Animals store glucose as glycogen.

AKA animal starch.

Lipids Are Hydrophobic

• Lipids include:fatty acids, steroids,phospholipids, and waxes.

• Because they are not soluble in water, they are good structural, insulation, transport, and storage macromolecules, such as:– Adipose tissue– cell membranes

components– hormones – triglycerides– oils and waxes

Saturated Fats

from animal sources

Unsaturated Fats

from plant sources

Fatty Acids Are Long Hydrocarbons with a Carboxylic Acid Functional Group

• Saturated fatty acids usually come from animal sources and are solid at room temperature, these are high in caloric value.

• Unsaturated fatty acids usually come from plant sources and are liquid at room temperature, these are lower in caloric value.

Triglycerides: Three Fatty Acids Dehydrated to One Glycerol

-The diagram to the left, depicts a glycerol being dehydrated with a fatty acid.

-This reaction occurs a total of three times to form a triglyceride, as seen on the diagram to the right

-Triglyceride molecules transport fats in the bloodstream and serve as building blocks for other lipids, such as phospholipids.

Steroids

. A steroid’s structure is composed of carbon rings.

. Steroids serve as the structural components of many hormones, such as

estrogen and testosterone.

. Steroids are essential for maintaining the fluidity of cell membranes.

. Diets rich in saturated fats promote accumulation of LDL “bad cholesterol” in the wall of arteries, reducing blood flow and promoting hypertension and the incidence of strokes.

Proteins

• Proteins are the structural components of living tissue. They also serve as enzymes, hormones, and immunoglobulins, among many other roles.

• Proteins are composed of amino acids (a.a.). We acquire a.a. by consuming meat, fowl, fish, dairy, eggs, legumes, and nuts

Proteins: Composed of Amino Acids• Amino acids are the

monomers that are dehydrated to form polypeptides or proteins.

• Humans have about 20 different amino acids from which proteins are synthesized. The difference between one protein and another has to do with the number of amino acids that a protein contains and the unique sequences in which the amino acids are arranged.

• Protein synthesis occurs in the ribosomes of cells and is controlled by genetic information.

Amino Acids (a.a.)Have both amino and carboxyl functional groups. The “R” group varies for each of the 20 a.a.

Protein Synthesis:

• Amino acids are chemically combined through dehydration synthesis by peptide bonds to form polypeptides (protein)

• The sequence of amino acids in a polypeptide is determined by genetic information

A Protein Structure Determines Its Function

Primary structure determined by a.a. sequence

Secondary structure determined by Hydrogen bonding:

α helix or β sheet

Tertiary structurepolypeptide folding due to covalent and ionic bonds

Quaternary structureTwo or more polypeptides chemically combined

Nucleic Acids Have Sugars, Nitrogenous Basesand Organic Phosphate Components

• Nucleic Acids serve as information macromolecules, such as DNA and RNA. (We will study these further in the future.)

• Another type of Nucleic Acid, ATP, serves as the energy currency of cells. (We will study ATP further in the future.)

• Nucleotides (picture at left) are the molecular components of Nucleic Acids.

DNA for Hereditary InformationNucleotides are chemically joined to form DNA, a double stranded helix. The bases, of each strand, hydrogen bond to each other.

The phosphates and sugars form the backbone of the double helix. The sequence of bases on the DNA determines the amino acid sequence of proteins.

Four types of bases:

Adenine (A), Guanine (G), Thymine (T), and Cytosine (C). These bases bind to each other. A always binds with T,

G always binds with C.

Structure Is Always Related to Function• Living organisms

require thousands of different types of molecules to maintain their structure and sustain their body’s functions.

• The ability of Carbon to bond with four other atoms is the basis for the vast variety of chemical structures found in organisms.