Biology Chapter 5: Biological Molecules

Chapter 5: The Structure and Function of Large Biological Molecules

• Living organisms are composed of four main types of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids.
• Small organic molecules combine to form larger molecules within cells.
• Macromolecules are large molecules formed from thousands of covalently linked atoms.
• Molecular structure and function are interdependent.

Concept 5.1: Macromolecules are Polymers, Built from Monomers

• A polymer is a long molecule made up of similar building blocks.
• Monomers are the small building-block molecules that form polymers.
• Carbohydrates, proteins, and nucleic acids are examples of polymers.

The Synthesis and Breakdown of Polymers

• Dehydration reactions join monomers together; a water molecule is removed.
• Enzymes facilitate dehydration reactions.
• Polymers are broken down into monomers through hydrolysis, which is the reverse of dehydration.

The Diversity of Polymers

• Cells contain thousands of diverse macromolecules.
• Macromolecules vary among cells within the same species and even more between species.
• A diverse range of polymers can be made using a limited number of monomers.

Concept 5.5: Nucleic Acids Store and Transmit Hereditary Information

• The amino acid sequence of a polypeptide is determined by a gene, a unit of inheritance.
• Genes are made of DNA, a nucleic acid.

The Roles of Nucleic Acids

• Two types of nucleic acids: DNA and RNA.
• DNA directs its own replication and the synthesis of mRNA.
• mRNA guides protein synthesis, which occurs in ribosomes.

The Structure of Nucleic Acids

• Nucleic acids are polymers called polynucleotides.
• Polynucleotides are formed from monomers called nucleotides.
• Each nucleotide comprises a nitrogenous base, a pentose sugar, and a phosphate group.
• A nucleoside is a nucleotide without the phosphate group.

Nucleotide Monomers

• A nucleoside is a nitrogenous base plus a sugar.
• Two families of nitrogenous bases: pyrimidines (single ring) and purines (double ring).
• DNA has deoxyribose; RNA has ribose.
• Nucleotide = nucleoside + phosphate group

Nucleotide Polymers

• Nucleotides are linked to form polynucleotides.
• Adjacent nucleotides are joined by covalent bonds between the 3' carbon of one nucleotide and the 5' carbon of the next.
• This creates a sugar-phosphate backbone with nitrogenous bases as appendages.
• The sequence of bases is unique to each gene.

The DNA Double Helix

• DNA consists of two polynucleotide strands that spiral around a central axis to form a double helix.
• The two strands run in opposite directions (antiparallel).
• Nitrogenous bases pair up via hydrogen bonds (A with T, and G with C).