Exam 3 Review Notes

Exam 3 Review: Genetics & Molecular Biology

Genetics (Questions 1-15)

• Focus on pedigree charts and concepts not heavily tested previously.
• Key Concepts:
  • Sex-linked traits: Traits inherited via sex chromosomes (X and Y).
  • Codominance: Both alleles are expressed equally in the phenotype.
  • Incomplete dominance: The phenotype is a blend of both alleles.
  • Epistasis: One gene influences the expression of another gene.
  • Polygenic effects: Multiple genes influence a single trait.
  • Environmental effects: Environmental factors influence trait expression.
    • Examples: Height affected by nutrition, skin color affected by sun exposure.
  • Probability rules related to DNA traits (Chapter 15).

DNA Replication and Protein Synthesis (Questions 16-30)

• Focus on DNA replication and protein synthesis, including key terminology.
• Key Terms:
  • Genome: The complete set of genetic material in an organism.
  • Gene: A segment of DNA that codes for a specific protein or RNA molecule.
  • Promoter: A DNA sequence where RNA polymerase binds to initiate transcription.
  • Codon: A sequence of three nucleotides (triplet) in mRNA that codes for a specific amino acid.
  • Anticodon: A sequence of three nucleotides in tRNA that is complementary to a codon in mRNA.
  • Triplet: A sequence of three DNA or RNA nucleotides.
    • Essential for understanding how genetic information is read and translated.
• Protein Synthesis:
  • Review materials covered in class; study guides should be available.

Comprehensive Questions (Questions 31-60)

• Covers material from Chapter 1 up to genetics (Chapters 1-10).
• Focus on basic, comprehensive, and thought-provoking questions.

Exam Details

• Time Allotment: 1 hour and 20 minutes for 60 questions.
• Students with accommodations (OBSS) will receive extra time.
• Point Value: Exam will be worth 120 points.

DNA to Protein: The Central Dogma of Biology

Overview:

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

Transcription:

• The first step in gene expression, where DNA is transcribed into RNA.
• Double-stranded DNA is transcribed into single-stranded RNA.
• Enzyme: RNA polymerase copies a DNA template to make RNA.
• RNA has ribose sugar (with two OH groups: 2’ and 3’).
• Base Differences: RNA contains uracil (U) instead of thymine (T).

Translation:

• The second step, where RNA is translated into protein.
• Location: Ribosomes.
• Ribosomes are made of ribosomal RNA (rRNA).

Types of RNA Produced by Transcription:

• Messenger RNA (mRNA): Carries the genetic code for protein synthesis.
• Transfer RNA (tRNA): Brings amino acids to the ribosome during translation.
• Ribosomal RNA (rRNA): Forms ribosomes, the site of protein synthesis.

Messenger RNA Synthesis

Promoter:

• A DNA sequence signaling the start of transcription.
• RNA polymerase binds to the promoter to initiate transcription.

Termination Point:

• A sequence that signals the end of transcription.

RNA Polymerase:

• Synthesizes RNA in the 5' to 3' direction, similar to DNA polymerase.

Sense and Antisense Strands:

• Antisense Strand: The template strand used by RNA polymerase.
• Sense Strand: Has the same sequence as the mRNA, except T is replaced by U.
• mRNA sequence matches the sense strand (with U instead of T).
• The antisense strand (3’ to 5’) is used as a template to create the mRNA (5’ to 3’).

Translation and Ribosomes

Ribosome Structure:

• Ribosomes have three sites: E (Exit), P (Peptidyl), and A (Aminoacyl).
• Ribosomes attach to mRNA and read it in groups of three nucleotides called triplets or codons.

Codons and Anticodons:

• Codon: A group of three nucleotides on mRNA.
• Anticodon: A complementary sequence on tRNA that matches the codon.
• tRNA brings specific amino acids to the ribosome.

Translation Sites:

• A Site (Arrival): Where new tRNA molecules arrive with amino acids.
• P Site (Peptidyl): Where peptide bonds form between amino acids.
• E Site (Exit): Where empty tRNA molecules leave the ribosome.

Start and Stop Codons:

• Start Codon: AUG (methionine) signals the beginning of translation.
• Stop Codons: UAA, UAG, UGA signal the end of translation.
  • They recruit a release factor, causing the ribosome to detach and release the polypeptide.

Universal Genetic Code:

• Codons are conserved across species.
• Some amino acids have multiple codons (redundancy).
• Example: CUU, CUC, CUA, and CUG all code for leucine.

Third Position Wobble:

• The third nucleotide position in a codon can vary without changing the amino acid.
• Provides a buffer against mutations (synonymous mutations).
• Mutations in the first or second position usually result in a different amino acid (non-synonymous mutations).

Reading the Code:

• Start reading mRNA at the 5' end.
• Identify the start codon (AUG).
• Read each subsequent codon and determine the corresponding amino acid using the universal genetic code.
• Continue until a stop codon is reached.

Gene Expression & Cellular Differentiation

Cellular Differences:

• All cells in an organism have the same DNA.
• Different cell types (e.g., brain vs. liver) express different genes.
• Differentiation: The process by which cells become specialized.
• Different genes are turned on or off in different cell types.

Development:

• Starts with a single diploid cell (fertilized egg).
• Cells divide and differentiate into different tissue layers.
• Developmental Biology: The study of how organisms develop and differentiate.

Chickenosaurus example:

• All the DNA information to make a dinosaur is still alive in a chicken because chickens evolved from dinosaurs.
• Scientists can manipulate chicken embryos to express ancestral traits like scales, teeth, and forelimbs (instead of wings) by altering gene expression during development.