Exam 4 Review Outline F 2017

Chapter 12 – Mendel and the Gene

Key Terms

  • Gene: Fundamental unit of heredity which carries information from parent to offspring.

  • Allele: Different versions of a gene that can exist at a specific locus on a chromosome.

  • Phenotype: The observable traits of an organism, which result from the expression of genes.

  • Genotype: The genetic constitution of an organism, represented by its alleles.

Mendel's Laws

  1. Law of Segregation: During gamete formation, the alleles for a trait separate so that each gamete receives only one allele.

  2. Law of Independent Assortment: The alleles of different genes assort independently of one another during gamete formation.

Genetic Calculations

  • Determine Gametes: Be able to derive gametes for any given parental genotype.

  • Monohybrid Crosses: Crosses that involve one trait (e.g. Aa x Aa).

  • Dihybrid Crosses: Crosses that involve two traits (e.g. AABB x aabb).

Testcross

  • Definition: A breeding experiment used to determine the genotype of an organism with a dominant phenotype by crossing it with a homozygous recessive individual.

Inheritance Patterns

  • Complete Dominance: The dominant allele completely masks the recessive allele in heterozygotes.

  • Incomplete Dominance: The phenotype of heterozygotes is a blend of the phenotypes of the two homozygotes.

  • Co-Dominance: Both alleles in a heterozygote express themselves without blending (e.g., AB blood type).

  • Epistasis: Interaction between genes where one gene masks or modifies the expression of another.

Traits Classification

  • Discrete Traits: Traits that fall into distinct categories (e.g., flower color).

  • Quantitative Traits: Traits that show continuous variation and are often polygenic (e.g., height).

  • Polygenic Traits: Traits controlled by more than one gene.

  • Environmental Effects: How the environment influences the expression of genes.

Linked Genes and Genetic Mapping

  • Linked Genes: Genes that are located close to each other on the same chromosome and tend to be inherited together.

  • Recombinant: Offspring whose phenotype differs from that of the parents, indicating that genetic recombination has occurred.

  • Linkage Map: A genetic map that shows the relative positions of genes on a chromosome based on recombination frequencies.

Sex-Linked Genes

  • Definition: Genes located on sex chromosomes (typically the X chromosome in humans).

  • Key Points:

    • A father cannot pass an X-linked trait to his son (son inherits Y from father).

    • Males cannot be carriers for X-linked traits; they either exhibit the trait or do not.

    • A female must have the trait from both parents to exhibit an X-linked trait.

    • Sex-influenced traits are dominant in one sex but recessive in the other.

Analyzing Pedigrees

  • Understand how to read pedigrees to ascertain the possible phenotypes/genotypes and determine if traits are dominant, recessive, autosomal, or sex-linked.

  • Key Hints:

    • If a trait skips generations, it is likely recessive.

    • If a child has a trait, at least one parent must also have it for dominant traits.

Chapter 13 - Nucleic Acid Structure and Replication

Fundamental Structure of Nucleotides

  1. DNA/RNA Composition: Comprised of a phosphate-sugar backbone.

  2. Knowledge of carbon counting in sugar moieties of nucleotides.

  3. DNA Replication Direction: Occurs in the 5’ to 3’ direction.

  4. Phosphodiester Bond: Links the phosphate group of one nucleotide to the hydroxyl group of the sugar of the next, forming a chain.

  5. Antiparallel Strands: The two strands of DNA run in opposite directions.

Key Experiments

  • Griffith Experiment: Demonstrated the principle of transformation in bacteria.

  • Avery & McLeod Experiment: Identified DNA as the transforming substance.

  • Hershey & Chase Experiment: Used bacteriophages to confirm that DNA is genetic material.

  • Chargaff's Rule: States that adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C).

  • Rosalind Franklin Experiment: Provided X-ray diffraction images leading to the discovery of DNA's double helix structure.

DNA Replication Mechanisms

  • Semi-Conservative Replication: Each strand of DNA serves as a template for the new strand; each new double helix contains one old and one new strand.

  • Enzymes Involved:

    • DNA Helicase: Unwinds the double helix.

    • Topoisomerase: Relieves the strain ahead of the replication fork.

    • SSB Proteins: Stabilize single strands during replication.

    • DNA Primase: Synthesizes RNA primers.

    • RNA Primers: Short RNA sequences that provide a starting point for DNA synthesis.

    • DNA Ligase: Joins Okazaki fragments on the lagging strand.

    • DNA Polymerase: Synthesizes new DNA strands.

    • Telomerase: Extends the ends of chromosomes (telomeres) during replication.

Replication Process

  • Origin of Replication: Different in prokaryotes (single origin) and eukaryotes (multiple origins).

  • Replication Fork: The area where the DNA is unwound.

  • Leading Strand: Synthesized continuously.

  • Lagging Strand: Synthesized in short fragments (Okazaki fragments).

  • Bidirectional Replication: DNA replication occurs in both directions from the origin.

  • Deoxyribose Nucleotide Triphosphates: The building blocks for DNA synthesis.

Proofreading and Repair Mechanisms

  • Eukaryotic Proofreading Mechanisms: Enzyme mechanisms to correct errors that arise during DNA replication.

  • DNA Repair Types:

    • Direct Repair: Fixes specific types of damage.

    • Nucleotide Excision Repair: Removes damaged sections of DNA (e.g., thymine dimer).

Chromosome End Dynamics

  • Telomere Function: Protects chromosome ends from deterioration.

  • Importance of Telomerase: Enables the replication of linear chromosomes, preventing loss of genetic information.

Base Pair Specificity

  • Chargaff's Rule: A=T and G=C; arises due to specific hydrogen bonding between bases.

    • Purines: Adenine (A) and Guanine (G).

    • Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U in RNA).

Chapter 14 - Gene Expression

Central Dogma of Molecular Biology

  • Processes: The flow of genetic information from DNA to RNA to proteins.

Transcription

  • Stages of Transcription:

    1. Initiation: RNA polymerase binds to the promoter and unwinds the DNA.

    2. Elongation: RNA polymerase synthesizes RNA in the 5’ to 3’ direction.

    3. Termination: The RNA synthesis stops, and the new mRNA strand is released.

RNA Processing in Eukaryotes

  • Modifications including capping, polyadenylation, and splicing to produce a mature mRNA.

  • Benefit: Increases mRNA stability and facilitates transport out of the nucleus.

Translation

  • Stages of Translation:

    1. Initiation: mRNA, initiator tRNA, and ribosomal subunits assemble.

    2. Elongation: tRNAs add amino acids to the growing polypeptide chain.

    3. Termination: The ribosome encounters a stop codon, releasing the newly synthesized polypeptide.

Components Required for Translation

  • mRNA: Template that carries the genetic code.

  • tRNA: Transfers amino acids to the ribosome according to codon sequences.

  • Ribosomes: The cellular machinery where translation occurs; composed of two subunits (large and small).

    • A, P, E Sites: Locations within the ribosome for tRNA binding and peptide bond formation.

  • Codons: Triplet sequences in mRNA that correspond to specific amino acids.

Important Translation Concepts

  • Reading Frame: The way codons are read in sets of three.

  • Degenerate Code: More than one codon can specify the same amino acid.

    • Special Codons:

    • Start codon (AUG): Initiates translation.

    • Stop codons (UAA, UAG, UGA): Terminate translation.

Chapter 15 – Mutations

Types of Mutations

  • Point Mutations: Alterations of a single nucleotide.

    • Silent Mutation: No change in amino acid sequence.

    • Missense Mutation: Changes one amino acid to another.

    • Nonsense Mutation: Creates a premature stop codon.

    • Substitution: Replacing one base with another.

    • Addition: Inserting an extra nucleotide.

    • Deletion: Removing a nucleotide.

    • Frameshift Mutation: Caused by insertions or deletions that shift the reading frame.

Mutation Classifications

  • Spontaneous vs. Induced: Spontaneous mutations arise naturally, while induced mutations occur due to environmental factors.

  • Germ Line vs. Somatic: Germ line mutations affect offspring, while somatic mutations affect the individual.

  • Loss of Function vs. Gain of Function: Loss of function mutations inactivate a gene, gain of function mutations enhance activity.

  • Reversion Mutation: A mutation that restores the original phenotype or function.

    • Example: Sickle Cell Anemia, where specific mutations affect hemoglobin synthesis.

Chromosomal Mutations

  • Types:

    • Deletion: Loss of a segment of DNA.

    • Duplication: A segment is copied twice.

    • Inversion: A segment is reversed within the chromosome.

    • Translocation: A segment is moved to a different chromosome.

Chapter 16 – Gene Regulation (Not on Exam 4)

Overview of Gene Regulation

  • Benefits: Allows cells to respond to environmental changes and control expression of genes.

  • Regulation in Prokaryotes vs Eukaryotes: Prokaryotes primarily regulate at the transcriptional level, while eukaryotes have additional regulation layers.

Operons

  • Repressible Operon: Example - Trp Operon: normally on and is turned off when the end product is abundant.

  • Inducible Operon: Example - Lac Operon: normally off and is turned on in the presence of a substrate (lactose).

Transcription Regulation of the Lac Operon

  • Situations:

    1. High Glucose, High Lactose: Operon off due to glucose presence.

    2. High Glucose, Low Lactose: Operon off due to lack of lactose.

    3. Low Glucose, Low Lactose: Operon off due to lack of both.

    4. Low Glucose, High Lactose: Operon on, promoting transcription.

  • Mechanisms: cAMP and CAP proteins function as activators.

Eukaryotic Transcriptional Regulation

  • Core Promoter Region: Contains TATA Box and initiation site.

  • Protein Complexes for Transcription: Enhancers and activators play important roles.

  • DNA Methylation/Acetylation: Chemical modifications influencing gene expression.