Genetics and Cellular Function

Overview

This chapter introduces the molecular basis of genetics and cellular function, focusing on the structure and roles of DNA and RNA, gene action, DNA replication, the cell cycle, and heredity. These topics are foundational for understanding how cells store, transmit, and express genetic information in Anatomy & Physiology.

• DNA and RNA – the nucleic acids: Key molecules for genetic information storage and transfer.

• Genes and their action: How genetic instructions are used to synthesize proteins.

• DNA replication and the cell cycle: Mechanisms for copying genetic material and cell division.

• Chromosomes and heredity: Organization of genetic material and inheritance patterns.

DNA Molecular Structure

DNA: Deoxyribonucleic Acid

DNA is a long, threadlike molecule with a uniform diameter but varied length, found in the nucleus of most human cells. It serves as the hereditary material in humans and most organisms.

• Humans have 46 DNA molecules in the nucleus of most cells.

• Total length of DNA in a cell is about 2 meters; average DNA molecule is about 2 inches long.

• DNA and other nucleic acids are polymers of nucleotides.

Nucleotide Structure

• Each nucleotide consists of:

  • One sugar – deoxyribose

  • One phosphate group

  • One nitrogenous base

• Nitrogenous bases are either:

  • Pyrimidine (single carbon-nitrogen ring)

  • Purine (double ring)

Nitrogenous Bases of DNA

Classification and Structure

Nitrogenous bases are the components of nucleotides that encode genetic information. They are classified as purines or pyrimidines.

• Purines (double ring):

  • Adenine (A)

  • Guanine (G)

• Pyrimidines (single ring):

  • Cytosine (C)

  • Thymine (T)

• DNA bases: A, T, C, G

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.

• Each sidepiece is a backbone composed of phosphate groups alternating with the sugar deoxyribose.

• Steplike connections between the backbones are pairs of nitrogen bases.

Complementary Base Pairing

• Bases are united by hydrogen bonds:

  • Adenine (A) pairs with Thymine (T) (two hydrogen bonds)

  • Guanine (G) pairs with Cytosine (C) (three hydrogen bonds)

• This pairing allows for accurate DNA replication and transmission of genetic information.

Example: DNA Double Helix

The classic double helix model, as shown in Figure 4.2, demonstrates how the sugar-phosphate backbone and nitrogenous base pairs form the stable structure of DNA.

Additional info:

• The double helix structure was first described by Watson and Crick in 1953.

• DNA's structure allows for the storage of vast amounts of genetic information in a compact form.