4.1 Structure and function of DNA

DNA, the blueprint of life, holds the key to genetic information and inheritance. Its double helix structure, composed of nucleotides, stores and transmits the code for all living organisms. Understanding DNA's structure is crucial for grasping its role in evolution.

DNA's functions extend beyond information storage. It directs protein synthesis, regulates gene expression, and drives genetic diversity through mutations. These processes form the basis for heredity, species identification, and the evolutionary changes that shape life on Earth.

DNA Structure and Function

Components of DNA structure

Top images from around the web for Components of DNA structure

• 

  File:DNA Structure+Key+Labelled.pn NoBB.png - Wikipedia, the free encyclopedia View original

  Is this image relevant?

• 

  DNA Structure and Sequencing | OpenStax Biology 2e View original

  Is this image relevant?

• 

  Storing Genetic Information | Biology for Majors I View original

  Is this image relevant?

• 

  File:DNA Structure+Key+Labelled.pn NoBB.png - Wikipedia, the free encyclopedia View original

  Is this image relevant?

• 

  DNA Structure and Sequencing | OpenStax Biology 2e View original

  Is this image relevant?

1 of 3

Top images from around the web for Components of DNA structure

• 

  File:DNA Structure+Key+Labelled.pn NoBB.png - Wikipedia, the free encyclopedia View original

  Is this image relevant?

• 

  DNA Structure and Sequencing | OpenStax Biology 2e View original

  Is this image relevant?

• 

  Storing Genetic Information | Biology for Majors I View original

  Is this image relevant?

• 

  File:DNA Structure+Key+Labelled.pn NoBB.png - Wikipedia, the free encyclopedia View original

  Is this image relevant?

• 

  DNA Structure and Sequencing | OpenStax Biology 2e View original

  Is this image relevant?

1 of 3

• Nucleotide composition forms basic DNA building blocks comprising deoxyribose sugar, phosphate group, and nitrogenous base
  • Nitrogenous bases divided into two categories: purines (adenine A, guanine G) and pyrimidines (thymine T, cytosine C)
• Double helix structure consists of two antiparallel strands with complementary base pairing (A-T, G-C) held together by hydrogen bonds
  • Sugar-phosphate backbone forms exterior of helix, bases oriented inward
• DNA dimensions: width 2 nanometers, complete turn 10.5 base pairs, length of one turn 3.4 nanometers

DNA as genetic material

• Genetic information storage accomplished through specific nucleotide sequences encoding genes that determine traits and characteristics
• Hereditary material passed from parents to offspring ensures continuity of genetic information across generations (sexual reproduction)
• Blueprint for cellular functions directs protein synthesis and regulates gene expression (enzyme production)
• Genetic diversity arises from mutations in DNA sequence leading to variations (eye color)
• Species identification facilitated by unique DNA sequences serving as molecular markers (DNA barcoding)

Processes of gene expression

1. DNA replication follows semiconservative model involving enzymes (DNA polymerase, helicase, primase)
   • Leading and lagging strand synthesis occurs, with Okazaki fragments on lagging strand
2. Transcription converts DNA to RNA using RNA polymerase enzyme
   • Promoter regions and transcription factors regulate process
   • Primary transcript undergoes RNA processing (splicing)
3. Translation synthesizes proteins from mRNA using ribosomes
   • tRNA incorporates amino acids based on codon sequence
   • Start and stop codons signal beginning and end of protein synthesis

• Gene expression regulation occurs through transcriptional control, post-transcriptional modifications, and epigenetic factors (DNA methylation)

DNA in evolution and inheritance

• Source of genetic variation through mutations (point, frameshift, chromosomal) and recombination during meiosis
• Natural selection acts on DNA-based traits, potentially increasing advantageous mutations and eliminating deleterious ones
• Molecular clock hypothesis uses DNA mutation rates to estimate species divergence times
• Comparative genomics reveals evolutionary relationships through DNA sequence similarities (human-chimpanzee genome)
• Horizontal gene transfer allows DNA exchange between different species (antibiotic resistance in bacteria)
• Adaptive evolution occurs as changes in DNA sequences lead to new traits and adaptations (beak shape in Galápagos finches)
• Speciation results from accumulation of genetic differences leading to reproductive isolation (Drosophila species)