Genetics and Cellular Function

Overview

This section introduces the molecular basis of genetics and cellular function, focusing on the structure and roles of DNA and RNA, gene action, DNA replication, and heredity. Understanding these concepts is fundamental for Anatomy & Physiology students, as genetic mechanisms underlie cellular processes and inheritance.

• DNA and RNA – the nucleic acids: These molecules store and transmit genetic information.

• Genes and their action: Genes direct the synthesis of proteins, which determine cell structure and function.

• DNA replication and the cell cycle: Accurate duplication of DNA is essential for cell division and tissue growth.

• Chromosomes and heredity: Chromosomes carry genes that are inherited from parent to offspring.

DNA Molecular Structure

DNA: Deoxyribonucleic Acid

DNA is a threadlike molecule found in the nucleus of most human cells. It has a uniform diameter but varied length, with 46 DNA molecules present in the nucleus of most human cells. The total length of DNA in a cell is about 2 meters, though each molecule averages about 2 inches long.

• Polymer of nucleotides: DNA and other nucleic acids are composed of repeating units called nucleotides.

• Nucleotide structure: Each nucleotide consists of:

  • One sugar – deoxyribose

  • One phosphate group

  • One nitrogenous base

• Nitrogenous bases: Can be either pyrimidines (single carbon-nitrogen ring) or purines (double ring).

Nitrogenous Bases of DNA

Classification and Structure

Nitrogenous bases are the fundamental units that encode genetic information in DNA. They are classified as purines or pyrimidines based on their chemical structure.

• Purines (double ring):

  • Adenine (A)

  • Guanine (G)

• Pyrimidines (single ring):

  • Cytosine (C)

  • Thymine (T)

• DNA bases: A, T, C, G

Example: The sequence of bases (e.g., ATCG) determines the genetic code for protein synthesis.

DNA Structure

Double Helix Model

The molecular shape of DNA is a double helix, resembling a spiral staircase. This structure is essential for the stability and replication of genetic material.

• Backbone: Each sidepiece of the helix is a backbone composed of alternating phosphate groups and the sugar deoxyribose.

• Base pairs: Steplike connections between the backbones are pairs of nitrogen bases, which form the rungs of the helix.

Additional info: The double helix structure allows for complementary base pairing, where Adenine pairs with Thymine and Guanine pairs with Cytosine, stabilized by hydrogen bonds.

Summary Table: Nitrogenous Bases

Key Equations

• Complementary Base Pairing:

(Adenine pairs with Thymine) (Guanine pairs with Cytosine)

Applications

• Genetic information: The sequence of DNA bases encodes instructions for protein synthesis, which determines cell structure and function.

• Medical relevance: Mutations in DNA can lead to genetic disorders and are important in the study of heredity and disease.