ap bio unit 4 cheat sheet

Lemon

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02-02-2025

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This cheat sheet covers the key concepts in AP Biology Unit 4, focusing on gene expression and regulation. Remember, this is a supplement to your textbook and class notes – not a replacement!

I. Gene Expression: From DNA to Protein

A. Central Dogma: The flow of genetic information: DNA → RNA → Protein.

B. Transcription: The synthesis of RNA from a DNA template. * Initiation: RNA polymerase binds to the promoter region of DNA. * Elongation: RNA polymerase adds nucleotides to the growing RNA molecule. * Termination: RNA polymerase reaches a termination signal and releases the RNA molecule.

C. RNA Processing (Eukaryotes only): * 5' capping: Addition of a modified guanine nucleotide to the 5' end for protection and ribosome binding. * Splicing: Removal of introns (non-coding sequences) and joining of exons (coding sequences). * 3' polyadenylation: Addition of a poly(A) tail to the 3' end for protection and stability.

D. Translation: The synthesis of a polypeptide chain from an mRNA template. * Initiation: Ribosome binds to the mRNA and initiator tRNA. * Elongation: Ribosome moves along the mRNA, adding amino acids to the growing polypeptide chain. * Termination: Ribosome reaches a stop codon and releases the polypeptide chain.

E. The Genetic Code: The correspondence between mRNA codons (three-nucleotide sequences) and amino acids. Remember the start codon (AUG) and the stop codons (UAA, UAG, UGA).

II. Gene Regulation: Controlling Gene Expression

A. Prokaryotic Gene Regulation (e.g., the lac operon): * Operon: A cluster of genes transcribed together as a single mRNA molecule. * Promoter: The region where RNA polymerase binds. * Operator: The region where a repressor protein can bind to block transcription. * Repressor: A protein that binds to the operator and prevents transcription. * Inducer: A molecule that binds to the repressor, causing it to change shape and release from the operator, allowing transcription. (e.g., Lactose in the Lac Operon)

B. Eukaryotic Gene Regulation: This is far more complex than prokaryotic regulation and involves many levels of control:

* **Transcriptional Regulation:**  Control of the rate of transcription.  This involves:
    * **Transcription factors:** Proteins that bind to DNA and regulate transcription.  Activators *increase* transcription, while repressors *decrease* it.
    * **Enhancers:** DNA sequences that increase transcription when bound by activators.
    * **Silencers:** DNA sequences that decrease transcription when bound by repressors.
    * **Epigenetics:** Changes in gene expression that do not involve changes to the DNA sequence itself (e.g., DNA methylation, histone modification).

* **Post-Transcriptional Regulation:** Control of RNA processing, transport, and stability. This includes RNA splicing, RNA interference (RNAi), and mRNA degradation.

* **Translational Regulation:** Control of the rate of translation.  This includes initiation factors, mRNA stability, and microRNAs (miRNAs).

* **Post-Translational Regulation:** Control of protein activity after translation.  This includes protein folding, modification, and degradation.

III. Mutations and their Effects

A. Types of Mutations: * Point mutations: Changes in a single nucleotide. These can be: * Substitution: One nucleotide is replaced with another. * Insertion: One or more nucleotides are added. * Deletion: One or more nucleotides are removed. * Frameshift mutations: Insertions or deletions that shift the reading frame of the mRNA, leading to a completely different amino acid sequence downstream.

B. Effects of Mutations: * Silent mutations: Do not change the amino acid sequence. * Missense mutations: Change one amino acid to another. The effect can range from negligible to severe, depending on the amino acid change and its location in the protein. * Nonsense mutations: Change an amino acid codon to a stop codon, resulting in a truncated protein. Usually deleterious.

IV. Techniques Used to Study Gene Expression

• Gel electrophoresis: Separates DNA, RNA, or proteins based on size and charge.
• PCR (Polymerase Chain Reaction): Amplifies specific DNA sequences.
• DNA sequencing: Determines the nucleotide sequence of DNA.
• Microarrays: Analyze the expression levels of thousands of genes simultaneously.
• CRISPR-Cas9: A gene editing technology that allows for precise modification of DNA sequences.

This cheat sheet provides a concise overview. Consult your textbook and class materials for a more complete understanding. Good luck with your AP Biology studies!