Carbohydrates, Lipids, Proteins, and Nucleic Acids

Monosaccharides

Simple sugar in which C, H, and O occur in the ratio of CH₂O

Major nutrients for cells; glucose is most common

Store energy in chemical bonds which is harvested by cellular respiration

Their carbon skeletons are raw material for other organic molecules

Can be incorporated as monomers into disaccharides and polysaccharides

Disaccharides

A double sugar that consists of two monosaccharides joined by a glycosidic linkage

Glycosidic linkage

Covalent bond formed by a condensation reactions between two sugar monomers

Polysaccharides

Macromolecules that are polymers of a few hundred or thousand monosaccharides, are formed by linking monomers in enzyme-mediated dehydration synthesis reactions, have two important biological functions: energy storage and structural support

Starch

Glucose polymer that is a storage polysaccharide in plants

Helical glucose polymer with a 1-4 linkages

Most animals have digestive enzymes to hydrolyze starch

Glycogen

Glucose polymer that is a storage polysaccharide in animals

Stored in the muscle and liver of humans and other vertebrates

Cellulose

Linear unbranched polymer of glucose in B 1-4 linkages

A major structural component of plant cell walls

Differs from starch in its glycosidic linkages

Cellulose and starch have different three-dimensional shapes and properties as a result of differences in glycosidic linkages

Cellulose reinforces plant cell walls. Hydrogen bonds hold together parallel cellulose molecules in bundles of microfibrils

Cellulose cannot be digested by most organisms, including humans

Chitin

A structural polysaccharide that is a polymer of an amino sugar

Forms exoskeletons of arthropods

Found as a building material in the cell walls of fungi

Lipids

Diverse group of organic compounds that are hydrophobic

Fats, Phospholipids, and Steroids

Fats

Constructed by Glycerol and Fatty Acids

Insoluble in water

Saturated Fat

No double bonds between carbons in the fatty acid tail

Carbon skeleton is bonded to the maximum number of hydrogens

Carbon skeleton is straight and pack tightly together

Solid at room temp

Animal fats

Unsaturated Fat

One or more double bonds between carbons in the fatty acid tail

Carbon skeleton is not bonded to the maximum number of hydrogens

Carbon skeleton kinks at each C=C prevents tight packing of the fatty acid chains

Liquid at room temp

Plaint oils

Phospholipids

Compounds with molecular building blocks of glycerol, two fatty acids, a phosphate group, and usually an additional small chemical group attached to the phosphate

Shows ambivalent behavior towards water. Hydrocarbon tails are hydrophobic and the polar head is hydrophillic

Cluster in water as their hydrophobic portions turn away from water, the hydrophobic tails turn toward the water-free interior and the hydrophilic phosphate heads arrange facing outward in contact with water

Are major constituents of cell membranes. At the cell surface, phospholipids form a bilayer held together by hydrophobic interactions among the hydrocarbon tails.

Steroids

Lipids which have four fused carbon rings with various functional groups attached. Cholesterol is an important steroid

Is the precursor to many other steroids including vertebrate sex hormones and bile acids

Is a common component of animal cell membranes

Can contribute to atherosclerosis

Polypeptide chains

Polymers of amino acids that are arranged in a specific linear sequence and are linked by peptide bonds

Protein

A macromolecule that consists of one or more polypeptide chains folded and coiled into specific conformations

Structural support

Storage

Transport

Coordination of an organism’s activities

Cellular response to chemical stimuli

Movement

Defense against foreign substances

Catalysis of biochemical reactions

Amino acid

Building block molecule of a protein; most consist of an asymmetric carbon, termed the alpha carbon, which is covalently bonded to a(n):

Hydrogen atom

Carboxyl group

Amino group

Variable group (R) - side chain specific to each amino acid, physical and chemical properties of the side chain determine the uniqueness of each amino acid

Peptide bond

Covalent bond formed by dehydration synthesis that links the carboxyl group of one amino acid to the amino group of another

Has a backbone of the repeating sequence N-C-C-N-C-C

Primary structure

Unique sequence of amino acids in the protein.

stabilized by the peptide bonds between the amino acids

Secondary structure

Regular, repeated coiling and folding of a protein’s polypeptide backbone

Stabilized by hydrogen bonds between peptide linkages in the protein’s backbone

Tertiary structure

The three-dimensional shape of a protein. The irregular contortions of a protein are due to bonding between and among side chains and to interaction between R groups and the aqueous environment. Types of bonds contributing to tertiary structure are weak interactions and covalent linkage

Quarternary structure

Structure that results from the interactions between and among several polypeptide chains

Denaturation

A process that alters a protein’s native conformation and biological activity

Proteins can be denatured by:

Transfer to an organic solvent. Hydrophobic side chains, normally inside the protein’s core, move towards the outside. Hydrophilic side chains turn away from the solvent towards the molecule’s interior.

Chemical agents that disrupt hydrogen bonds, ionic bonds, and disulfide bridges

Excessive heat

Deoxyribonucleic acid (DNA)

Contains coded information that programs all cell activity

Contains directions for its own replication

Is coped and passed from one generation of cells to another

In eukaryotic cells, is found primarily in the nucleus

Makes up genes that contain instructions for protein synthesis. Genes do not directly make proteins, but directs the synthesis of mRNA

Ribonucleic Acid (RNA)

Functions in the actual synthesis of proteins coded for by DNA

Sites of protein synthesis are on ribosomes in the cytoplasm

Messengry RNA carries encoded genetic message from the nucleus to the cytoplasm

The flow of genetic information goes from DNA → RNA → Protein

Nucleic Acid

Polymer of nucleotides linked together by dehydration synthesis.

Nucleotide

Building block molecule of a nucleic acid; made of a five-carbon sugar covalently bonded to a phosphate group and nitrogenous base

Pyrimidine

Nitrogenous base characterized by a six-membered ring made up of carbon and nitrogen atoms

Cytosine

Thymine

Uracil

Purine

Nitrogenous base characterized by a five-membered ring fused to a six-membered ring.

Adenine

Guanine