General Biology: Foundations, Chemistry, and Biomolecules Study Guide

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Characteristics of Life and Viruses

Defining Life and Viruses

Biologists use several criteria to define living organisms, including reproduction, metabolism, and locomotion. Viruses challenge these definitions because they share some, but not all, characteristics of life.

Reproduction: Viruses can reproduce, but only inside host cells, unlike living organisms that reproduce independently.
Metabolism: Living organisms carry out metabolic processes; viruses do not have metabolism outside a host.
Locomotion: Some living organisms move actively; viruses rely on passive movement.
Key Point: Not all characteristics of life are present in viruses, but reproduction is a shared trait.
Example: Bacteria reproduce by binary fission; viruses replicate by hijacking host machinery.

Shared and Unique Characteristics of Living Organisms

Universal and Specialized Traits

Living organisms share certain fundamental characteristics, but some traits are unique to specific groups.

Reproduction: All living things reproduce, either sexually or asexually.
Metabolism: All living organisms perform metabolic activities to sustain life.
Homeostasis: Maintenance of internal stability is universal among living things.
Photosynthesis: Only plants, algae, and some bacteria perform photosynthesis; it is not universal.
Key Point: Photosynthesis is not shared among all living organisms.

Levels of Biological Organization

Molecular Level and Chargaff's Rule

Biological study occurs at various levels, from atomic to tissue. Chargaff's rule, which describes the ratios of DNA bases, is best understood at the molecular level.

Chargaff's Rule: In DNA, the amount of adenine (A) equals thymine (T), and guanine (G) equals cytosine (C).
Molecular Level: This rule reflects the molecular structure of DNA.
Example: DNA base pairing: ,

Natural Selection and Adaptation

Survival and Reproduction

Natural selection favors organisms that are best adapted to their environment, increasing their chances of survival and reproduction.

Adaptation: Traits that improve survival and reproduction are favored.
Key Point: Organisms more adapted to their environment are more likely to survive and reproduce.
Example: Peppered moths in polluted environments developed darker coloration for camouflage.

Common Ancestry and Evolution

Phylogenetic Relationships

Evolutionary biology studies the relationships between organisms and their common ancestors.

Common Ancestor: Most organisms share a common ancestor, but some pairs are more distantly related.
Key Point: Whales and sharks do not share a recent common ancestor; whales are mammals, sharks are fish.
Example: Humans and apes share a common ancestor; chickens and dinosaurs are evolutionarily linked.

Experimental Design in Biology

Variables in Controlled Experiments

Controlled experiments are essential for testing hypotheses in biology. All variables except the independent variable are held constant.

Independent Variable: The factor that is changed or manipulated.
Dependent Variable: The factor that is measured.
Control Variable: Factors kept constant to ensure a fair test.
Example: Testing plant growth under different light conditions; light is the independent variable.

Atoms, Elements, and Chemical Reactivity

Noble Gases vs. Halogens

Elements are classified by their electron configurations, which determine their chemical reactivity.

Noble Gases: Have full valence electron shells, making them stable and unreactive.
Halogens: Have one electron less than a full shell, making them highly reactive.
Key Point: Halogens are more reactive than noble gases.
Example: Chlorine (halogen) reacts readily; neon (noble gas) does not.

Radioactive Isotopes in Biology

Applications of Radioisotopes

Radioactive isotopes are widely used in biological science for diagnosis, treatment, and research.

Imaging: Diagnosing diseases using radioactive tracers.
Treatment: Treating thyroid disorders with radioactive iodine.
Labeling: Studying genetic processes by labeling DNA.
Key Point: All of the above are common uses.

Chemical Bonding

Types and Formation of Bonds

Atoms form chemical bonds based on their electronegativity differences, resulting in ionic, covalent, or polar covalent bonds.

Ionic Bonds: Formed between atoms with large electronegativity differences (e.g., NaCl).
Covalent Bonds: Formed by sharing electrons between atoms with similar electronegativities.
Key Point: The type of chemical bonding depends on the difference in electronegativities between bonding atoms.
Equation:

Electronegativity Table and Non-Polar Covalent Bonds

Non-polar covalent bonds form between atoms with similar electronegativities.

Element	Electronegativity
Sodium	0.9
Cesium	0.8
Hydrogen	2
Fluorine	4
Oxygen	3.5
Chlorine	3

Key Point: Chlorine and Chlorine will form a non-polar covalent bond.

Covalent vs. Non-Covalent Interactions

Covalent bonds involve sharing electrons, while non-covalent interactions (e.g., hydrogen bonds) do not.

Peptide, Disulfide, Glycosidic Bonds: All are covalent.
Hydrogen Bond: Is a non-covalent interaction.

Ionic Bond Formation

Ionic bonds form by electron transfer from a metal to a nonmetal.

Example: Sodium (Na) donates an electron to chlorine (Cl) to form NaCl.
Key Point: The metal atom (M) loses an electron; the nonmetal atom (N) gains it.

Hydrogen Bond Formation

Hydrogen bonds form between a hydrogen atom and an atom with high electronegativity (e.g., oxygen, nitrogen).

Key Point: High electronegativity is required for hydrogen bond formation.
Example: Water molecules form hydrogen bonds between H and O.

Extremophiles and Halophiles

Adaptations to Extreme Environments

Halophiles are microorganisms that thrive in environments with high salt concentrations.

Key Point: Halophiles grow optimally at high salt concentrations.
Example: Halobacterium species in salt lakes.

Properties of Water

Surface Tension and Water Droplets

Water's surface tension allows droplets to form on leaves after rain.

Surface Tension: Caused by hydrogen bonding between water molecules.
Example: Water beads on plant leaves.

Density and Floating Ice

Ice floats on water because it is less dense than liquid water.

Key Point: Ice has a lower density due to its crystalline structure.
Equation:

Hydration Shells Around Ions

When ionic compounds dissolve in water, hydration shells form around the ions.

Example: Sodium ions (Na+) are surrounded by water molecules with oxygen atoms facing the ion; chloride ions (Cl-) are surrounded by water molecules with hydrogen atoms facing the ion.
Key Point: Hydration shells stabilize ions in solution.

Acids, Bases, and pH Regulation

Strong Acids and Bases

Strong acids and bases dissociate completely in water, affecting pH levels.

Key Point: Complete dissociation leads to high conductivity and strong pH changes.
Equation:

pH Regulation in the Human Body

The human body maintains specific pH levels to prevent infection and support physiological functions.

Example: The vagina maintains a slightly acidic pH to prevent the growth of harmful yeast and bacteria.
Key Point: pH regulation is crucial for health and disease prevention.

Organic Molecules and Functional Groups

Definition of Organic Molecules

Organic molecules contain carbon and hydrogen atoms covalently bonded to other atoms.

Key Point: Organic molecules are the basis of life and include carbohydrates, proteins, lipids, and nucleic acids.

Functional Groups and Alcohols

Attachment of a hydroxyl group (-OH) to a carbon backbone forms an alcohol.

Key Point: Alcohols are important in metabolism and biochemistry.
Example: Ethanol (C2H5OH)

Biomolecules: Carbohydrates and Polysaccharides

Carbohydrases and Carbohydrates

Carbohydrases are enzymes that break down carbohydrates.

Key Point: Carbohydrases belong to the carbohydrate class of biomolecules.

Starch vs. Chitin

Starch and chitin are polysaccharides with different structures and functions.

Starch: Polysaccharide of alpha glucose; storage molecule in plants.
Chitin: Polymer of N-acetylglucosamine; structural molecule in fungi and arthropods.
Bond Types: Starch contains glycosidic bonds; chitin contains linkages.
Key Point: Starch is for energy storage; chitin is for structure.

Protein Structure Hierarchy

Levels of Protein Structure

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

Primary Structure: Amino acid sequence.
Secondary Structure: Alpha helices and beta-pleated sheets.
Tertiary Structure: 3-dimensional shape formed by folding.
Quaternary Structure: Multiple polypeptide chains assembled together.

Level	Description
Primary	Amino acid sequence
Secondary	Alpha helix, beta sheet
Tertiary	3D folding of a single chain
Quaternary	Assembly of multiple chains