This cheat sheet covers the key concepts of AP Biology Unit 5, focusing on genetics and molecular biology. Remember to consult your textbook and class notes for a more comprehensive understanding. This is designed as a quick reference and review tool.
I. Molecular Genetics: The Central Dogma
A. DNA Replication:
- Semi-conservative: Each new DNA molecule consists of one original strand and one newly synthesized strand.
- Enzymes:
- Helicase: Unwinds the DNA double helix.
- Topoisomerase: Relieves strain ahead of the replication fork.
- Primase: Synthesizes RNA primers.
- DNA Polymerase III: Adds nucleotides to the 3' end of the growing strand (leading strand continuous, lagging strand discontinuous with Okazaki fragments).
- DNA Polymerase I: Removes RNA primers and replaces them with DNA.
- Ligase: Joins Okazaki fragments.
- Leading vs. Lagging Strand: Understand the difference and why Okazaki fragments are necessary.
- Replication Fork: The point where the DNA strands separate and replication occurs.
B. Transcription:
- RNA Polymerase: Synthesizes RNA from a DNA template.
- Promoter: Region of DNA where RNA polymerase binds to initiate transcription.
- Transcription Factors: Proteins that regulate the binding of RNA polymerase.
- RNA Processing (Eukaryotes):
- 5' Cap: Added to the 5' end for protection and ribosome binding.
- Poly-A Tail: Added to the 3' end for stability and export from the nucleus.
- Splicing: Removal of introns and joining of exons.
- Types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal).
C. Translation:
- Ribosomes: Sites of protein synthesis.
- mRNA: Carries the genetic code from DNA to the ribosome.
- tRNA: Carries specific amino acids to the ribosome based on the codon in mRNA.
- Codons: Three-nucleotide sequences on mRNA that specify amino acids.
- Anticodons: Three-nucleotide sequences on tRNA that are complementary to codons.
- Start Codon (AUG): Initiates translation.
- Stop Codons (UAA, UAG, UGA): Terminate translation.
- Amino Acids: Building blocks of proteins.
- Peptide Bonds: Link amino acids together.
II. Gene Regulation
A. Prokaryotes (Operons):
- Operon: A cluster of genes transcribed together.
- Lac Operon: Model system for understanding gene regulation in prokaryotes (understand inducible vs. repressible).
- Repressor Protein: Binds to the operator to prevent transcription.
- Inducer: Molecule that binds to the repressor, causing it to change shape and preventing it from binding to the operator.
B. Eukaryotes:
- Transcriptional Regulation: Control of gene expression at the level of transcription.
- Epigenetic Regulation: Changes in gene expression that do not involve changes to the underlying DNA sequence (DNA methylation, histone modification).
- Post-transcriptional Regulation: Control of gene expression after transcription (mRNA processing, mRNA stability, translation).
- Post-translational Regulation: Control of gene expression after translation (protein modification, protein degradation).
III. Mutations
A. Types of Mutations:
- Point Mutations: Changes in a single nucleotide.
- Substitution: One nucleotide is replaced with another.
- Insertion: A nucleotide is added.
- Deletion: A nucleotide is removed.
- Frameshift Mutations: Insertions or deletions that shift the reading frame.
- Chromosomal Mutations: Changes in the structure or number of chromosomes.
B. Causes of Mutations:
- Spontaneous Mutations: Occur naturally during DNA replication.
- Induced Mutations: Caused by mutagens (e.g., radiation, chemicals).
C. Effects of Mutations:
- Harmful: Can lead to genetic disorders or cell death.
- Beneficial: Can provide new variations that are advantageous for evolution.
- Neutral: Have no effect on the phenotype.
IV. Genetic Engineering & Biotechnology
- Recombinant DNA Technology: Combining DNA from different sources.
- Restriction Enzymes: Cut DNA at specific sequences.
- Plasmids: Circular DNA molecules used as vectors to transfer DNA into cells.
- PCR (Polymerase Chain Reaction): Amplifies DNA sequences.
- Gel Electrophoresis: Separates DNA fragments by size.
- Gene Therapy: Introducing genes into cells to treat genetic disorders.
- Cloning: Creating genetically identical copies of an organism or gene.
This cheat sheet provides a general overview. Thorough review of your course materials is essential for success on the AP Biology exam. Remember to practice with past AP Biology exams and utilize practice questions to solidify your understanding of these concepts.
