Unit 5 Study Guide

DNA Structure

• Nucleotides: Building blocks of DNA, composed of:

  • DNA Backbone: Made of alternating 5-carbon sugar (deoxyribose) and phosphate groups.

  • Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

• Complementary Base Pairing:

  • A pairs with T (2 hydrogen bonds)

  • C pairs with G (3 hydrogen bonds)

• Purines vs. Pyrimidines:

  • Purines: Adenine (A) and Guanine (G) (double-ringed structures)

  • Pyrimidines: Cytosine (C) and Thymine (T) (single-ringed structures)

• Phosphodiester Bonds: Covalent bonds linking nucleotides in the DNA backbone.

• Hydrogen Bonds: Hold complementary bases together.

• Gene: A segment of DNA that codes for a protein.

DNA Function

• Double Helix: Allows for compact storage and stable transmission of genetic information.

• Nitrogenous Bases: Provide the genetic code that determines protein synthesis.

• Phosphodiester Bonds: Maintain the integrity of the DNA strand.

• Hydrogen Bonds: Allow for easy separation during replication and transcription.

DNA vs. RNA

Transcription

• Purpose: To create an mRNA copy of a DNA sequence.

• Location: Nucleus

• Role of RNA Polymerase: Unzips DNA and synthesizes mRNA by pairing RNA bases with complementary DNA bases.

• Transcription Example:

  • DNA: TAC GGC TAA

  • mRNA: AUG CCG AUU

Translation

• Purpose: To convert mRNA into a protein.

• Location: Ribosome (in the cytoplasm or rough ER)

• Roles in Translation:

  • Ribosome: Reads mRNA and facilitates protein synthesis.

  • tRNA: Brings amino acids to the ribosome.

  • Anticodons: Found on tRNA, complementary to mRNA codons.

  • Amino Acids: Linked together to form proteins.

• Translation Example:

  • mRNA: AUG CCG AUU

  • Amino Acid Sequence: Met - Pro - Ile

Mutations

• Mutation: A change in DNA sequence.

• Types of Mutations:

  • Substitution Mutations: One nucleotide is replaced with another.

    • Silent Mutation: No change in amino acid sequence.

    • Missense Mutation: One amino acid changes, potentially altering protein function.

    • Nonsense Mutation: Creates a stop codon, leading to a shortened protein.

  • Frameshift Mutations: Insertion or deletion of a nucleotide shifts the reading frame.

    • Insertion: Extra nucleotide added, altering the sequence.

    • Deletion: A nucleotide is removed, changing the sequence.

Impact of Mutations:

• DNA Sequence: Changes base pairs.

• mRNA Sequence: Alters codons transcribed from DNA.

• Amino Acid Sequence: Could change protein structure and function.

• Protein Structure & Folding:

  • No Change in Function: If mutation does not affect folding or active sites.

  • Change in Function: If mutation disrupts protein shape or active sites, altering biological activity.

  •