Honors Biology The molecules of Cells

Chapter 3

Life’s molecular diversity is based on the properties of carbon

 Most compounds in living organisms are organic – composed of carbon bonded to other elements. Functions of organic compounds:  Main structural components of cells and tissues  Participate in and regulate many chemical reactions  Provide energy

 By sharing electrons, carbon can bond to four other atoms.

 This allows for branching in up to four directions.

 A chain of carbon atoms is called a carbon skeleton.

 Carbon skeletons can be branched or unbranched.

 Therefore, different compounds with the same molecular formula but different properties can be produced.

 These structures are called ISOMERS.

 Carbon skeletons can vary in:  Length   Branching Double bonds  Rings

 An organic compound has unique properties that depend upon:   The size and shape of the molecule and The groups of atoms (functional groups) attached to it.

 A functional group affects a biological molecule’s function in a characteristic way.

 Compounds that contain functional groups are hydrophilic (water-loving)

Cells make a huge number of large molecules from a small set of small molecules

Four classes of biological molecules: Carbohydrates Lipids Proteins Nucleic Acids

 The four classes of biological molecules contain very large molecules  They are often called macromolecules because of their large size  They may also be called polymers when they are made from identical building blocks strung together  The building blocks of polymers are called monomers.

 Dehydration synthesis (condensation) is the linking of monomers by the removal of water. This reaction builds polymers.

 Hydrolysis (“to break, with water”) breaks down polymers to monomers by adding water.

 A good example of hydrolysis is when you digest your food!

Carbohydrates

 Serve as fuel and structural components for cells  General structure: contain carbon, hydrogen and oxygen in a ratio of about 1:2:1

Classification of Carbohydrates

 Monosaccharides: contain one type of sugar unit  Disaccharides: contain two types of sugar units  Polysaccharides: contain many sugar units

Monosaccharides

  Also known as simple sugars Example: glucose is an important fuel molecule in living cells  Monosaccharides are also used as raw materials to manufacture other organic molecules  Monosaccharides are the monomers for disaccharides and polysaccharides.

Polysaccharides

 Composed of repeating monosaccharide units  They can function in the cell as a storage molecule or as a structural compound

Storage Polysaccharides

  Starch – storage polysaccharide of plants Glycogen – storage polysaccharide of animals

Structural Polysaccharides

 Cellulose is a polymer of glucose that forms plant cell walls.

 Chitin is a polysaccharide that is a structural component of the exoskeleton of insects and crustaceans. (also used in surgical thread for stitches that dissolve!)

Lipids (fats)

 Lipids are water insoluble (hydrophobic – “water fearing”) compounds that are made from glycerol and fatty acids.

 They contain twice as much energy as a polysaccharide, so their main function is long-term energy storage.

 Lipids differ from other organic compounds in that they are neither huge macromolecules nor polymers.

 Three types of lipids:   Fat Phospholipids  Steroids

Types of Fats:    Unsaturated – corn oil, olive oil, and other vegetable oils. Liquid at room temperature.

Saturated – have the maximum number of hydrogens. Examples include beef fat and butter. Solid at room temperature.

Trans fat – made by adding hydrogen to unsaturated fats. Associated with health risks.

 Phospholipids – a modified fat that is the main structural component of cell membranes.

 Steroids – cholesterol is a common component of cell membranes. Animal cells use it as a precursor for making other steroids, including hormones.

Proteins

 A protein is a polymer built from various combinations of 20 amino acid monomers.

Proteins are essential to the structures and functions of life



Structural

proteins provide associations between body parts.



Contractile

muscle.

proteins are found within 

Defensive

proteins include antibodies of the immune system.

   

Signal

proteins are best exemplified by the hormones

Receptor

proteins serve as ‘antenna’ for outside signals

Transport Enzymes

proteins carry oxygen.

regulate the chemical reactions within cells.

Proteins are made from amino acids linked by peptide bonds

 This is done by means of an enzyme mediated dehydration synthesis.

 A polypeptide chain contains hundreds or thousands of amino acids.

 The amino acid sequence causes the polypeptide to assume a particular shape  The shape of a protein determines its specific function.

Levels of protein organization



Primary structure

– unique sequence of amino acids  Correct amino acid sequence is determined by the cell’s genetic information  The slightest change in this sequence affects the protein’s ability to function.



Secondary

structure – coiling or folding of the peptide chain  Coiling results in a helical structure called an alpha helix  Folding may lead to a structure called a beta pleated sheet.



Tertiary

structure – overall 3-D shape



Quaternary

structure – how the polypeptides fit together in a molecule

Protein structure determines function

 Changes in protein structure can affect function  Mutations can disrupt the biological activity of a protein  Denaturation can cause the protein to become inactive

Nucleic acids are information rich polymers

 Two classes – RNA and DNA

 Nucleic acids store information that codes for proteins, which govern the structure and function of the organism

Composition of nucleic acids

  Monomers are nucleotides Each nucleotide is composed of:  Nitrogenous base   5-carbon sugar Phosphate group