NYS Biology Regents Exhaustive Study Guide

Rearranging Matter for Life

• Conceptual Overview: In biological systems, organisms do not just consume food for energy; they use the atoms contained within food to build their physical structures. A classic model used in biology is the silkworm consuming a mulberry leaf.

• The Power of Glucose: Glucose is the primary subunit resulting from the digestion of plant carbohydrates. It consists of three essential elements:     * Carbon ($C$)     * Hydrogen ($H$)     * Oxygen ($O$)

• Functions of Glucose in the Silkworm:     1. ATP Production: Glucose is broken down during the process of cellular respiration to release chemical energy (ATP).     2. Lipid Synthesis: The atoms of $C$, $H$, and $O$ are rearranged to synthesize worm-specific fats (lipids).     3. Carbon Skeleton: Glucose serves as the structural "frame" or backbone for constructing other complex organic molecules.

• The Protein Secret: To synthesize proteins, an organism requires more than the components found in glucose. While glucose provides $C$, $H$, and $O$, proteins specifically require Nitrogen ($N$). To build worm-specific proteins, the silkworm must take the atoms from glucose and combine them with Nitrogen obtained from its diet.

• Vocabulary for Metabolism and Biosynthesis:     * Biosynthesis: The biological process where living organisms assemble complex molecules (such as lipids or proteins) from simpler precursor molecules.     * Subunits: Small molecules, such as glucose or amino acids, that serve as the fundamental building blocks for larger polymers.     * Metabolism: The sum total of all chemical reactions occurring within an organism, encompassing both the breakdown of nutrients and the construction of body structures.     * Rearrangement of Atoms: The process of breaking existing chemical bonds in food molecules and forming new bonds to create different molecular structures.

Evolution: Mechanisms and Evidence

• Natural Selection and Adaptation: Natural selection is the primary non-random mechanism of evolution, driven by the environment acting as a Selective Agent.     * Overproduction: Species tend to produce more offspring than the environment can support, resulting in competition for limited resources.     * Variation: Differences between individuals arise from Mutations (random changes in $DNA$) and sexual reproduction (shuffling of genes).     * Competition: The struggle between individuals for food, water, shelter, and potential mates.     * Survival of the Fittest: Individuals possessing favorable adaptations are more likely to survive, reproduce, and transmit their genetic information to the subsequent generation.

• Evidence for Common Ancestry:     * Comparative Anatomy: The study of Homologous Structures—body parts with similar underlying bone structures but different functions (e.g., a whale's flipper and a human's arm)—indicates a shared evolutionary history.     * Molecular Sequencing: This is the most reliable form of evidence. It involves comparing $DNA$ or amino acid sequences. Higher degrees of similarity in $DNA$ correlate to a closer evolutionary relationship.     * Fossil Record: Provides a chronological account of how organisms have changed over millions of years and documents extinct species.

• Extinction and Environmental Dynamics:     * Adaptive Radiation: A process wherein a single ancestral species evolves into various different forms to occupy different environmental niches (e.g., Darwin's Finches).     * Rapid Environmental Change: If an environment changes faster than a population can adapt, and the population lacks individuals with necessary variations, the species will face extinction.     * Phylogenetic Trees: Diagrams representing evolutionary relationships. For example, in a tree showing Lineage A and Lineage B branching from a Common Ancestor, species closer on the branches (like Species 1 and 2) are more closely related to each other than to more distant branches (like Species 4).

• Identifying the Selective Agent:     * The Selective Agent is the specific environmental factor that determines which individuals survive.     * Example: If pesticides kill insects, the pesticide is the selective agent.     * Example: If birds eat light-colored moths, the birds (predators) are the selective agent.     * Example: If a drought kills plants with small roots, the drought (lack of water) is the selective agent.

Transcription and Translation (Gene Expression)

• Core Concepts: Molecular biology focuses on how genes (nucleic acids) code for proteins. Gene expression occurs in two primary stages:     * Transcription: Copying information from a $DNA$ sequence (a gene) into a complementary $RNA$ sequence.     * Translation: Converting the $RNA$ sequence into the specific amino acid sequence of a polypeptide.

• Types of RNA:     1. Messenger RNA (mRNAs): Carries copies of $DNA$ sequences from the nucleus to the ribosome (the site of protein synthesis).     2. Ribosomal RNA (rRNAs): Acts as a catalyst to form peptide bonds between amino acids during translation.     3. Transfer RNA (tRNAs): Acts as a mediator by carrying specific amino acids to the ribosome for assembly into a polypeptide.

• Base Pairing Rules and Molecular Composition:     * DNA to DNA: Adenine ($A$) pairs with Thymine ($T$); Cytosine ($C$) pairs with Guanine ($G$).     * DNA to mRNA: Adenine ($A$) pairs with Uracil ($U$); Thymine ($T$) pairs with Adenine ($A$); Guanine ($G$) pairs with Cytosine ($C$); Cytosine ($C$) pairs with Guanine ($G$).     * RNA to RNA: $A$ pairs with $U$; $G$ pairs with $C$.     * Purines (Double-ring): Adenine ($A$) and Guanine ($G$).     * Pyrimidines (Single-ring): Cytosine ($C$), Thymine ($T$) (in $DNA$ only), and Uracil ($U$) (in $RNA$ only).

Reproduction and Development

• Asexual Reproduction:     * Involves one parent dividing into two or more offspring.     * Offspring are genetically identical clones of the parent.     * Mitosis: The type of cell division used for asexual reproduction and growth.     * Examples:         * Unicellular: Amoeba and Bacteria.         * Multicellular (budding/regeneration): Hydra, Flatworms, and Starfish.     * Steps in Mitosis:         1. Chromosomes and genes are replicated ($DNA$ Replication).         2. Each copy is distributed into a new cell.         3. Every resulting cell has the identical chromosome set as the original.     * Implication: There is no genetic variation. If the environment changes, the population may not survive. However, high adaptive value traits (e.g., antibiotic resistance) are passed directly to all offspring.

• Sexual Reproduction:     * Involves two organisms contributing $50\%$ of their genetic material.     * Meiosis: Cell division that produces gametes (sex cells: sperm and egg) with half the number of chromosomes.     * Fertilization: The fusion of two gametes to form a zygote, restoring the full chromosome count.

Genetics and Biotechnology

• DNA Characteristics:     * Located in the nucleus; carries instructions for protein assembly.     * Structure: Double-stranded, sugar-phosphate backbone, with base pairs ($A-T$ and $C-G$).     * Replication: Before cell division, $DNA$ untwists and unzips to copy each strand.     * Genetic Code: Instructions are written in three-base codes representing one of $20$ different amino acids.

• Gene Expression and Differentiation:     * Genes: Specific sequences of $DNA$ bases that code for proteins. Chromosomes contain thousands of genes.     * Regulation: Genes can be "turned on" (expressed) or "turned off" (not expressed) based on the cell's environment, such as the presence of hormones.     * Differentiation: Cells specialize because different sets of genes are active or inactive within them.

• Mutations:     * Errors in the $DNA$ sequence (e.g., insertions or deletions of bases) result in a wrong amino acid sequence, causing proteins to have the wrong shape and fail to function.     * Causes: Chemicals, radiation, $UV$ light, and X-rays.     * Inheritance: Mutations are only passed to the next generation if they occur in the gametes (sperm/egg).     * Outcomes: Genetic variation, potential for cancer (uncontrolled cell division), and beneficial or harmful traits.

• Biotechnology:     * Selective Breeding: Humans mate specific organisms to achieve desired traits in offspring.     * Recombinant DNA: Using restriction enzymes to cut $DNA$ and insert genes from one organism into another.     * Case Study (Insulin): A human insulin gene is cut from a human cell and spliced into bacterial $DNA$. The bacteria then divide rapidly and produce human insulin, which can be harvested for medical use.