Comprehensive Biology: Cell Structure, Molecular Biology, and Scientific Methods

Biology

The scientific study of life.

Observation

Data gathered.

Question

What you want to know.

Hypothesis

Testable explanation.

Controlled Experiment

Compares an experimental group with a control group.

Independent Variable

The factor manipulated by the researcher.

Dependent Variable

The factor measured, expected to change.

Controlled Variable

Factors kept constant.

Prediction

Expected outcome if the hypothesis is correct.

Conclusion

Summary of results, supports or refutes the hypothesis.

Randomized Controlled Trial (RCT)

Where subjects are randomly assigned to a treatment group or a control group.

Double-Blind Experiment

An RCT where neither the subjects nor the researchers know who is receiving the treatment and who is receiving the placebo.

Scientific Theory

A broad, well-substantiated explanation supported by a large body of evidence from many experiments and observations.

Matter

Anything that takes up space and has mass.

Element

A substance that cannot be broken down to other substances by chemical reactions.

Atom

The smallest unit of matter that retains the properties of an element.

Compound

A substance consisting of two or more different elements combined in a fixed ratio.

Protons

Positive (+) subatomic particles in the nucleus.

Neutrons

Neutral particles in the nucleus.

Electrons

Negative (-) particles orbiting the nucleus.

Atomic Number

The number of protons.

Atomic Mass

The total mass of an atom.

Mass Number

The sum of protons and neutrons.

Isotopes

Atoms of the same element with different numbers of neutrons.

Ion

An atom or molecule with a net electrical charge (due to losing or gaining electrons).

Four Most Common Elements in Human Body

Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).

Covalent Bond

Electrons are shared between atoms.

Ionic Bond

Electrons are transferred from one atom to another, forming ions that are attracted to each other.

Hydrogen Bond

A weak attraction between a hydrogen atom in one molecule and an electronegative atom (like O or N) in another molecule.

Unique Properties of Water

Cohesion, adhesion, high specific heat, lower density as a solid, and being a versatile solvent.

Radioactive decay

The process where an unstable isotope (radioisotope) spontaneously loses energy by emitting radiation.

Radiometric dating

Uses the predictable, fixed rate of decay (half-life) of radioactive isotopes in fossils or rocks to calculate their age.

Covalent bonds of Carbon

A Carbon atom can form four covalent bonds.

Monomer of Carbohydrates

Monosaccharide (e.g., glucose).

Polymer of Carbohydrates

Polysaccharide (e.g., starch).

Monomer of Proteins

Amino Acid.

Polymer of Proteins

Polypeptide/Protein.

Monomer of Nucleic Acids

Nucleotide.

Polymer of Nucleic Acids

DNA/RNA.

Lipids discussed

Fats (triglycerides), phospholipids, and steroids.

Dehydration Reaction

Removes a water molecule to join two monomers together, forming a polymer.

Hydrolysis Reaction

Adds a water molecule to break a polymer apart into monomers.

Saturated fats

Have the maximum number of hydrogen atoms possible and no double bonds between carbon atoms in the fatty acid tails, making them solid at room temperature.

Unsaturated fats

Have one or more double bonds in the fatty acid tails, causing kinks that prevent them from packing tightly, making them liquid at room temperature.

Primary structure of protein

The unique, linear sequence of amino acids.

Secondary structure of protein

Coils (α-helix) or folds (β-pleated sheet) in the polypeptide chain stabilized by hydrogen bonds.

Tertiary structure of protein

The overall, three-dimensional shape of a single polypeptide chain, resulting from interactions among the R groups of the amino acids.

Protein function and shape

A protein's specific 3D shape (conformation) determines its function.

Nucleotide structure

A nucleotide consists of three parts: a five-carbon sugar (ribose or deoxyribose), a phosphate group, and a nitrogenous base.

DNA

Double helix; sugar is deoxyribose; bases are A, T, C, G; stores genetic instructions; generally longer.

RNA

Single-stranded; sugar is ribose; bases are A, U, C, G (Uracil replaces Thymine); involved in protein synthesis (transcribing and translating instructions); generally shorter.

Cell theory

1. All living things are composed of one or more cells. 2. The cell is the basic structural and functional unit of life. 3. All cells come from pre-existing cells.

Prokaryotic cells

Smaller, lack a nucleus and membrane-bound organelles (e.g., bacteria).

Eukaryotic cells

Larger, have a nucleus that houses the DNA, and have many membrane-bound organelles (e.g., animal, plant, fungal cells).

Plasma Membrane

Selective barrier surrounding the cell.

Ribosomes

Sites of protein synthesis.

Nucleus

Contains the cell's DNA (chromosomes).

Cytoplasm

Jelly-like fluid filling the cell, where organelles are suspended.

Cytoskeleton

Network of protein fibers (microtubules, microfilaments, intermediate filaments) providing structure and movement.

Mitochondrion

Site of cellular respiration (produces ATP/energy).

Rough ER

ER studded with ribosomes; involved in protein synthesis and modification.

Smooth ER

Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium storage.

Golgi apparatus

Modifies, sorts, and packages molecules from the ER.

Lysosome

Sac of digestive enzymes that breaks down waste, food, and old parts.

Fluid mosaic model

Describes the plasma membrane as a fluid structure with various proteins 'floating' in a mosaic of a phospholipid bilayer.

Phospholipid orientation

The phospholipids are arranged with their hydrophilic heads facing the outside and inside of the cell, and their hydrophobic tails facing each other in the interior of the membrane.

Nucleus structure

Enclosed by a nuclear envelope (double membrane with pores); contains chromatin (DNA and proteins) and a nucleolus.

Nucleus function

Houses the cell's DNA (genetic control center) and directs protein synthesis via mRNA; the nucleolus is where ribosomes are made.

Ribosome structure

Composed of ribosomal RNA (rRNA) and protein; consists of a large and small subunit; can be free in the cytoplasm or bound to the rough ER.

Ribosome function

The site of protein synthesis (translation of mRNA into polypeptide chains).

DNA function in protein production

DNA contains the instructions (genes) to build a protein, transcribed into mRNA in the nucleus, which travels to a ribosome for translation into amino acids.

Endomembrane system

Includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and the plasma membrane.

Rough ER function

Protein folding/modification.

Smooth ER function

Lipid synthesis/detoxification.

Golgi function

Modification/sorting/packaging of molecules.

Lysosome function

Digestion/recycling.

Vacuole function

Storage (e.g., water, food, waste).

Plant cell features

Have a cell wall, chloroplasts (for photosynthesis), and a large central vacuole.

Animal cell features

Lack cell walls and chloroplasts but typically have lysosomes and centrioles (in the centrosome).

Mitochondria function

Site of cellular respiration (converts food energy to ATP).

Chloroplast function

Site of photosynthesis (converts light energy to sugar).

Mitochondria structure

Have a double membrane, their own DNA, and ribosomes; internal folds called cristae.

Chloroplast structure

Have a double membrane, their own DNA, and ribosomes; internal stacks of flattened sacs called grana, surrounded by a fluid called the stroma.

Cytoskeleton functions

1. Mechanical support/shape maintenance for the cell. 2. Plays a role in cell movement and the movement of organelles/vesicles within the cell.

Microtubules

The thickest component of the cytoskeleton; hollow tubes made of the protein tubulin; help maintain cell shape and act as tracks for organelle movement.

Cilia and flagella similarities

Both are locomotor appendages and contain a core of microtubules arranged in a 9+2 pattern.

Cilia and flagella differences

Cilia are generally short and numerous; they move in a coordinated, oar-like motion. Flagella are usually longer and few; they move in an undulating, whip-like motion.

Functions of cilia and flagella

Both move the entire cell (e.g., sperm flagellum) or move fluid/particles past the cell (e.g., respiratory tract cilia).