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
Initiation:
RNA polymerase binds to a promoter sequence on the DNA.
Initiates RNA synthesis.
Elongation:
RNA nucleotides are sequentially added to the growing chain.
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
Initiation:
Assembly of ribosomal subunits and the setup of the translation machinery.
Elongation:
Continuation of amino acid chain formation by peptide bond connections.
Ribosome facilitates the attachment and movement along the mRNA.
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.