DNA and Genetic Material

Learning Outcomes

• Define a genome and a gene.

• Explain how genomes can differ in eukaryotic organisms.

• Define a chromosome and describe how it is packaged inside eukaryotic cells.

• Identify where in DNA genetic information can be found.

• Explain the central dogma and describe a few exceptions that can be found in cells.

• Explain what the processes of transcription and translation accomplish.

• Compare where transcription and translation occur in cells.

• Define the genetic code and its use.

• Define the relationship between genotype and phenotype.

Example Questions to Review

• What are the different parts of a nucleotide? (Review!)

• What are the different parts of a DNA helix? (Review!)

• How is the overall structure of DNA and RNA different? (Review!)

• What does it mean that the backbone structure of nucleic acids is directional? (Review!)

• What are the base pairs present in DNA and RNA? (Review!)

• Definitions to Know:

  • Chromosome

  • Gene

  • Genome

  • Central Dogma

  • Genetic Code

• How can the genomes of different eukaryotic organisms be organized differently?

• What is the relationship of transcription and translation to the central dogma?

• What is the relationship between genotype and phenotype?

• Where in DNA can we find genetic information?

• Are there exceptions to the central dogma that can be found in living organisms?

Major Historical Timepoints Describing DNA as Genetic Material

• Early 1900s: Scientists had a good understanding of heredity.

• Early 1900s: The units of heredity were called "genes."

• Early 1920s: The term "genome" was introduced, combining "gene" and "chromosome."

• Early 1940s: The proposal of the one-gene, one-enzyme hypothesis.

• Early 1950s: The description of the DNA double helix.

Structural Characteristics of DNA and RNA

DNA Structure

• Schematic Diagrams of DNA Structure:

  • Base Pairing:

  • Example Sequence: 5'-TGCCGTATACGACGGTG-3'

  • DNA Orientation:

  • 5' to 3' end notation.

• Double Helix Structure:

  • Length of one complete turn of helix: $(10 ext{ rungs per turn}) = 3.4 ext{ nm}$

  • Width of helix: $(2.0 ext{ nm})$

  • Distance between bases: $(0.34 ext{ nm})$

  • Presence of major and minor grooves.

RNA Structure

• Structure of mRNA:

  • Contains stem and loop formations with unpaired regions.

  • Complementary base pairing occurs between antiparallel regions.

Proteins and Amino Acids

• Peptide-Bonded Backbone Structure:

  • Amino acids joined by peptide bonds.

  • Structural Elements:

  • C-terminus and N-terminus indicated.

  • Example of Residue Numbering:

  • Gly, Pro, Ser, Asp, Phe, Val, Tyr, Cys (G-P-S-D-F-V-Y-C).

Genome Overview

Definition of Genome

• A genome is defined as a collection of an organism's DNA.

General Genomic Comparisons

Human vs Budding Yeast Genome Structure

Human Genome Structure

• Base Pairs: 3.2 billion

• Chromosomes: 23 pairs of linear chromosomes (½ from mother; ½ from father)

• Cell Type: Humans are diploids.

Budding Yeast Genome Structure

• Base Pairs: 12 million

• Chromosomes: 16 linear chromosomes in a haploid strain (used in laboratory settings)

• Cell Type: Yeast can exist as haploids or diploids.

Genes and Their Function

• Definition of a Gene:

  • Basic units of heredity that encode information for making proteins.

• Gene Count:

  • Approx. 20,000-25,000 genes in the human genome.

  • 6,275 genes in the budding yeast genome.

• Function of Genes:

  • Most genes code for proteins.

  • Some genes encode RNA that serve functions beyond coding for proteins.

Messenger RNA and Protein Synthesis

• Role of mRNA:

  • Carries information from the nucleus to the cytoplasm for ribosome interpretation.

  • Connects DNA to protein synthesis.

• Transcription and Translation: Locations

  • Transcription occurs in the nucleus.

  • Translation occurs in the cytoplasm.

Central Dogma of Molecular Biology

Definition

• The central dogma describes the flow of genetic information from DNA to RNA to protein.

• Processes Involved: Transcription and Translation

  • Transcription: Process where DNA is transcribed to mRNA.

  • Translation: Process where mRNA sequence is read by ribosomes to synthesize proteins.

The Flow of Information

• DNA $
  ightarrow$ mRNA $
  ightarrow$ Proteins.

• Involves RNA polymerase for transcription and ribosomes for translation.

Locating Genetic Information in DNA

• Genetic information is present within DNA base pairs and sequences.

• Ribosomes can read codons to determine the sequence of amino acids in proteins.

Connection Between DNA, Genotype, and Phenotype

• Flow of Information:

  • Genetic information flows from DNA to RNA to proteins.

• Genotype vs Phenotype:

  • Differences in genotype (DNA sequence) can lead to differences in phenotype (observable traits).

  • Example of Mice with Varying DNA Sequences:

  • Mainland mouse with a specific DNA sequence leading to dark coats.

  • Beach mouse with a different DNA sequence leading to light coats.

The Genetic Code

• Definition of the Genetic Code:

  • Refers to the system used by cells to translate three-letter codons into specific amino acids.

• Components of the Genetic Code:

  • Uses the four nucleotide bases found in DNA: Adenine (A), Cytosine (C), Guanine (G), and Thymine (T) (or Uracil (U) in RNA).

• Significance:

  • This code dictates protein synthesis based on the sequence of nucleotide bases.

Additional Notes on Coding for Proteins

• Not all genes actually code for proteins.

• Ribosomes are composed of proteins and ribosomal RNA (rRNA).

• Transfer RNA (tRNA) plays an integral role in the process of translation, bridging mRNA and the corresponding amino acids.