Chapter7_DNA Function

Chapter 7: DNA Structure and Gene Function

Overview of DNA

• DNA (Deoxyribonucleic Acid): A molecule that stores the information necessary for the life and functioning of organisms.

  • Recognized as a cellular component since the late 19th century.

  • One of the two molecules (along with RNA) that can store genetic information.

  • Information in DNA is copied and passed on to the next generation.

Nucleic Acids

• Class of Macromolecules: Nucleic acids include two main types - DNA and RNA.

  • Composed of Nucleotides: Each nucleotide consists of:

    • A sugar (deoxyribose in DNA)

    • A phosphate group

    • A nitrogenous base

  • The structure formed by the sugar and phosphate group is called the sugar-phosphate backbone.

Types of Nucleotides

• Nucleotide Variants: Five different nucleotides exist based on their nitrogenous bases:

  • Common bases in both DNA and RNA: Cytosine (C), Adenine (A), Guanine (G).

  • Unique to DNA: Thymine (T).

  • Unique to RNA: Uracil (U) (replaces thymine in RNA).

Genetic Information Flow

• Genotype vs. Phenotype: The DNA of an organism determines its traits and functions.

  • Genotype: The genetic makeup.

  • Phenotype: Observable characteristics influenced by genotype.

  • Genetic information is inherited through generations.

Chromosome Structure

• Chromosomes: Comprised of DNA wrapped around histone proteins within the nucleus of a cell.

DNA as an Instructional Storage Device

• DNA issues instructions via transcription where RNA is produced to carry these instructions.

• Translation: The process of using these instructions to build proteins.

Transcription Process

• Definition: The process where a single gene's information is used to create one RNA molecule.

  • Enzyme: RNA polymerase which assists in the transcription process.

    • Identifies starting and stopping points of genes.

    • Attaches RNA nucleotides to form a growing RNA strand.

Phases of Transcription

1. Initiation:

   • RNA polymerase binds to a promoter sequence on the DNA.

   • Initiates RNA synthesis.

2. Elongation:

   • RNA nucleotides are sequentially added to the growing chain.

3. Termination:

   • RNA polymerase reaches a terminator sequence, halting transcription.

From Nucleotide Sequence to Protein

• One Gene: One Protein Hypothesis: Each gene generally corresponds to the production of a specific protein.

  • Not all proteins are required at all times; thus, DNA information is selectively issued.

Genetic Code Basics

• Genetic Code: Specifies how RNA sequences (codons) are translated into amino acids.

  • A codon consists of three RNA bases that correspond to one amino acid.

Translation Overview

• Translation: The conversion of the RNA sequence into an amino acid sequence, facilitated by:

  • mRNA: Carries genetic information from nucleus to the cytoplasm.

  • tRNA: Delivers specific amino acids to ribosomes based on mRNA codons.

  • Ribosomes: Sites for protein synthesis.

Phases of Translation

1. Initiation:

   • Assembly of ribosomal subunits and the setup of the translation machinery.

2. Elongation:

   • Continuation of amino acid chain formation by peptide bond connections.

   • Ribosome facilitates the attachment and movement along the mRNA.

3. Termination:

   • When the ribosome reads a stop codon, the process concludes resulting in a complete polypeptide chain.

Mutations in DNA

• Definition: Permanent changes in the nucleotide sequence that can affect protein production.

  • Types:

    • Base Substitution: Minor changes affecting one amino acid (missense mutation).

    • Insertions/Deletions: Can lead to significant alterations (frameshift mutations).

  • Mutations can introduce genetic diversity and are crucial for evolution.

DNA Replication Overview

• Process: During the cell cycle, DNA must be replicated to ensure daughter cells receive the correct genetic material.

  • Key Features:

    • Bidirectional replication from origin sites producing two daughter strands.

    • Semiconservative: Each daughter strand contains one original strand and one new strand.

Visual Aids

• Diagrams illustrating nucleotide structures, genetic code, translation process, and DNA replication processes run throughout the materials, helping to visualize complex concepts.