AP+Biology+Unit+6+Gene+Expression+and+Regulation+Review

Study Guide: Gene Expression and Regulation

Topic 6.1: DNA and RNA Structure

• Key Concepts: Heritable information provides continuity of life and is essential for growth and reproduction.

• DNA and RNA:

  • Primary Sources: DNA and RNA are the main carriers of genetic information.

  • Structure Overview:

    • DNA: Double helix formed by complementary base pairing (A-T, C-G).

    • RNA: Single-stranded, uses uracil instead of thymine (A-U).

  • Genetic Transmission:

    • Genetic information is stored in the sequences of DNA and RNA.

    • Prokaryotic cells typically have circular chromosomes, while eukaryotic cells possess multiple linear chromosomes.

    • Some prokaryotes and eukaryotes may contain plasmids—small, extra-chromosomal, double-stranded, circular DNA that assists in gene cloning and transformation.

• Key Scientists:

  • Crick and Watson: Discovered the double helix structure of DNA, elucidating the mechanism of hereditary information.

  • Franklin and Wilkins: Provided critical X-ray diffraction images that demonstrated the helical structure of DNA.

• Memory Aids for Bases:

  • Purines: (Adenine, Guanine) - Have a double ring structure; remembered as "AG for double A's."

  • Pyrimidines: (Cytosine, Thymine, Uracil) - Have a single ring structure; remember "CUT is a single division."

Topic 6.2: Replication

• DNA Replication Process:

  • Ensures genetic continuity by copying DNA before cell division.

  • Direction of Synthesis: DNA is synthesized in the 5' to 3' direction.

  • Semiconservative Process: Each new DNA strand conserves one parent strand, ensuring accurate duplication.

  • Key Enzymes Involved:

    • Helicase: Unwinds the DNA double helix at the replication fork, separating the two strands.

    • Topoisomerase: Relieves torsional strain and supercoiling ahead of the replication fork.

    • DNA Polymerase: Synthesizes new DNA strands by adding nucleotides and requires an RNA primer to initiate synthesis.

    • Ligase: Joins Okazaki fragments on the lagging strand to create a continuous DNA molecule.

  • Strands: Continuous synthesis on the leading strand and discontinuous (in fragments) synthesis on the lagging strand due to antiparallel nature of the structure.

Topic 6.3: Transcription and RNA Processing

• Flow of Genetic Information:

  • The flow of genetic information follows the pathway from DNA to RNA to protein, crucial for cellular functions.

  • Functional Role of mRNA:

    • mRNA carries genetic instructions from DNA in the nucleus to ribosomes in the cytoplasm for protein synthesis.

  • Transcription Process:

    • RNA polymerase synthesizes mRNA by reading template DNA in the 3' to 5' direction and constructing the RNA strand in the 5' to 3' direction.

    • The template strand of DNA is also referred to as the antisense strand.

  • Eukaryotic mRNA Modifications involve:

    • Addition of a 5' GTP cap: Protects mRNA from degradation and assists in ribosome binding.

    • Addition of a poly-A tail: Enhances mRNA stability and facilitates export from the nucleus.

    • Splicing: Removal of non-coding regions (introns) and joining of coding regions (exons) to produce a mature mRNA molecule.

Topic 6.4: Translation

• Key Process of Translation:

  • Ribosomes translate mRNA sequences into polypeptides, dictating the structure and function of proteins in the cell.

  • Initiation: Translation begins at the start codon (AUG).

  • Reading Frame: Ribosomes read mRNA codons in triplets, each corresponding to specific amino acids during polypeptide synthesis.

  • Retroviruses: Unique viruses such as HIV can reverse transcribe their RNA genome into DNA, integrating into the host's genome and affecting gene expression.

Topic 6.5: Regulation of Gene Expression

• Gene Expression Controls:

  • The regulation of gene expression is pivotal for cellular differentiation and function.

  • DNA Regulatory Sequences: Interact with specific proteins (transcription factors) to enhance or suppress transcription processes.

  • Epigenetic Changes: Modifications to DNA/histones (e.g., methylation, acetylation) can affect chromatin structure and gene accessibility, influencing transcription without altering the DNA sequence itself.

Topic 6.6: Gene Expression and Cell Specialization

• Transcription Factors:

  • Proteins that influence the transcription of specific genes by binding to nearby DNA.

  • Promoters: Specific DNA sequences where RNA polymerase binds to initiate transcription, leading to the expression of genes responsible for various cell types and functions.

  • Differential Expression: Gene regulation results in diverse cell types and specialized functions within multicellular organisms.

Topic 6.7: Mutations

• Types of Mutations:

  • Mutations can be classified based on their effects on phenotype: beneficial (advantageous), detrimental (harmful), or neutral (no effect).

  • Causes of Mutations: Environmental factors (radiation, chemicals) and errors during DNA replication can induce mutations, leading to variations in DNA sequence.

Topic 6.8: Biotechnology

• Genetic Engineering Techniques:

  • Techniques in biotechnology include:

    • Electrophoresis: Used to separate DNA fragments based on size.

    • Polymerase Chain Reaction (PCR): Amplifies specific DNA sequences, making millions of copies for analysis.

    • Bacterial Transformation: Introducing plasmids into bacterial cells for cloning or protein expression.

    • DNA Sequencing: Determining the nucleotide order in DNA, essential for genomic studies and personalized medicine.