General Biology: Core Concepts and Processes Study Guide

I. DNA Structure & Function

DNA Basics

DNA (deoxyribonucleic acid) is the hereditary material in almost all living organisms. Its structure and properties are fundamental to genetics and molecular biology.

• Double helix: DNA consists of two antiparallel strands forming a helical structure.

• Base pairing rules: Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G).

• Hydrogen bonds: Hold complementary bases together.

• Strand directionality: DNA strands have 5' and 3' ends.

Nucleotides

Nucleotides are the building blocks of nucleic acids.

• Each nucleotide consists of:

  • Phosphate group

  • Deoxyribose sugar

  • Nitrogenous base (A, T, C, G)

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

• Pyrimidines: Cytosine (C) and Thymine (T)

Comparing DNA & RNA

DNA and RNA are both nucleic acids but differ in structure and function.

• Both contain nucleotides, phosphodiester bonds, phosphate groups, purines & pyrimidines, 5' → 3' ends.

• Key differences:

  • DNA has deoxyribose; RNA has ribose.

  • DNA has thymine; RNA has uracil.

  • DNA is double-stranded; RNA can be single-stranded.

Telomeres & Telomerase

Telomeres are repetitive DNA sequences at chromosome ends, protecting them from degradation.

• Telomeres shorten with age and correlate with cell senescence.

• Telomerase maintains chromosome ends to prevent shortening.

II. DNA Replication

Mechanism

DNA replication is the process by which DNA is copied before cell division.

• Semiconservative: Each new DNA molecule contains one old and one new strand.

• New nucleotides are always added to the 3' end.

• Replication begins at origins of replication, forming two replication forks.

Enzymes & Proteins to Know

• Helicase: Unwinds DNA.

• Topoisomerase: Relieves supercoiling.

• Single-stranded binding proteins: Stabilize unwound DNA.

• Primase: Makes RNA primers.

• DNA polymerase:

  • Synthesizes DNA.

  • Proofreads and removes RNA primers & fills gaps.

• Ligase: Joins DNA fragments (especially on the lagging strand).

Leading vs. Lagging Strand

• Leading: Continuous synthesis.

• Lagging: Discontinuous synthesis, forms Okazaki fragments, requires more primers.

III. Gene Expression (Transcription & Translation)

Transcription

Transcription is the synthesis of RNA from a DNA template.

• Produces mRNA from DNA template.

• Uses RNA polymerases (focus: RNA polymerase II in eukaryotes).

• mRNA processing involves:

  • 5' cap

  • Poly-A tail (stabilizes mRNA)

  • Splicing to remove introns and join exons.

Codons

• Triplets of nucleotides = 3 bases per codon.

• AUG is the usual start codon (methionine).

• Several codons may code for the same amino acid (redundancy).

Translation

Translation is the process of synthesizing proteins from mRNA at ribosomes.

• Occurs at ribosomes.

• Release factors recognize stop codons to terminate translation.

IV. Genome Organization

Genome organization refers to the arrangement of genes and non-coding regions within DNA.

• Eukaryotic genes contain introns and exons.

• After splicing, only exons remain in the final mRNA.

• Spliceosomes remove introns (test questions include identifying processed mRNA sequences).

V. Basic Chemistry Concepts

Atoms & Molecules

Atoms are the basic units of matter, forming molecules through chemical bonds.

• Molecules consist of atoms.

• Subatomic particles:

  • Protons (positive)

  • Neutrons (neutral)

  • Electrons (negative)

Isotopes

• Same element, different number of neutrons.

Bond Types

• Ionic bond: Electron transfer → cation & anion attraction.

• Covalent bond: Electron sharing.

  • Polar vs. nonpolar: Based on electron distribution.

• Hydrogen bonds: Weak interactions between polar molecules.

Chemical Reactions

• Endergonic: Require energy input (positive ΔG).

• Exergonic: Release energy.

• Spontaneous: Don't require outside energy to proceed.

VI. Cell Membranes & Transport

Tonicity

Tonicity describes the effect of solute concentration on water movement across cell membranes.

• Hypotonic: Water enters the cell (more turgid).

• Hypertonic: Water exits the cell.

• Isotonic: No net movement.

VII. Cellular Respiration & Photosynthesis

Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose.

• Glycolysis: Occurs with or without oxygen.

• Electron Transport Chain: Uses redox reactions; oxygen is final electron acceptor.

• Oxidative phosphorylation: Requires oxygen.

Photosynthesis

Photosynthesis is the process by which plants convert light energy into chemical energy.

• Occurs in thylakoid membranes.

• Purpose: Generate ATP and NADPH.

• Antenna pigment molecules:

  • Absorb light.

  • Transfer energy to reaction centers.

VIII. Enzymes & Proteins in DNA/Genetics

Enzymes and proteins play critical roles in DNA replication and gene expression.

Replication

• DNA polymerase

• Helicase

• Topoisomerase

• Ligase

• Primase

• Single-stranded binding proteins

Transcription

• RNA polymerase II (main enzyme for mRNA)

• Promoters, terminators, regulatory sequences

Translation

• tRNA, ribosomes, release factors

IX. Genetic Sequences & Restriction Concepts

Palindromes

Palindromic DNA sequences read the same on both strands in opposite directions.

• Important for restriction enzymes & molecular biology techniques.

X. What to Be Prepared To Do on the Exam

• Identify correct molecular structures (nucleotides, DNA vs. RNA).

• Recognize roles of replication enzymes.

• Apply base pairing rules.

• Distinguish introns from exons.

• Identify properties of codons, start/stop signals.

• Explain DNA replication direction and processes.

• Understand cell transport and tonicity.

• Identify chemical reaction types (endergonic, exergonic).

• Evaluate basic chemistry and bonding concepts.

• Recognize steps of photosynthesis and respiration.