Biology Study Guide: DNA, Genetics, and Cellular Processes
DNA Structure and Function
DNA Structure
Deoxyribonucleic acid (DNA) is the primary genetic material of living organisms. It consists of two long strands of nucleotides wound together in a double helix shape. The strands are made of sugar-phosphate groups, with paired nitrogenous bases forming the rungs of the ladder.
- Purines (adenine and guanine) always pair with pyrimidines (thymine and cytosine) through hydrogen bonds.
- The strands are complementary and run in an antiparallel direction (5′ to 3′ and 3′ to 5′).
DNA Replication
DNA replication involves three stages:
- Strand Separation (Initiation)
- Building Complementary Strands (Elongation)
- Error Repair
DNA Packaging
- Eukaryotes: DNA wraps around histone proteins to form nucleosomes.
- Prokaryotes: DNA is circular and floats freely in the cytoplasm.
Gene Expression and Protein Synthesis
One Gene-One Polypeptide Hypothesis
Each gene codes for a specific polypeptide (protein or part of a protein).
Central Dogma
The process of gene expression involves two steps:
- Transcription: Synthesis of RNA from DNA.
- Translation: Conversion of RNA information into an amino acid sequence to synthesize a protein.
Genetic Code
- Codons: Three-nucleotide sequences that code for specific amino acids.
- 64 codons code for 20 amino acids, with some redundancy.
- The genetic code is nearly universal across all organisms.
Transcription
RNA is synthesized from DNA in three steps: initiation, elongation, and termination.
Translation
- tRNA molecules link codons on mRNA to specific amino acids.
- Ribosomes facilitate the process of translation.
Genetic Engineering and Biotechnology
Genetic Engineering
The intentional manipulation of genes and genomes.
Techniques
- Restriction enzymes: Cut DNA at specific sequences.
- PCR: Amplifies DNA.
- Gel electrophoresis: Separates DNA fragments by size.
- DNA sequencing: Determines the order of nucleotides in DNA.
Transgenic Organisms
Organisms that have been genetically modified to contain genes from other organisms.
Cellular Respiration
Overview
Aerobic process that converts glucose into ATP, releasing carbon dioxide and water as byproducts.
Stages
- Glycolysis
- Pyruvate Oxidation
- Krebs Cycle
- Electron Transport Chain
ATP Production
Cellular respiration produces a net gain of 36 ATP molecules per glucose molecule.
Photosynthesis
Overview
Process by which plants and other organisms convert light energy into chemical energy stored in glucose.
Stages
- Photo Reactions (Light-Dependent)
- Synthesis Reactions (Light-Independent/Calvin Cycle)
Calvin Cycle
Converts carbon dioxide into glyceraldehyde 3-phosphate, which can be used to synthesize glucose and other molecules.
Enzyme Activity and Regulation
Enzyme Inhibition
- Competitive Inhibition: Inhibitor competes with substrate for the active site.
- Non-Competitive Inhibition: Inhibitor binds to an allosteric site, changing the enzyme’s shape and preventing substrate binding.
- Feedback Inhibition: End product of a pathway inhibits the first enzyme in the pathway.
Homeostasis
Definition
Maintaining a stable internal environment within a range suitable for life processes.
Mechanisms
- Negative Feedback Loop: Counteracts a stimulus to maintain a set point.
- Positive Feedback Loop: Amplifies a stimulus.
Examples
- Thermoregulation: Regulation of body temperature.
- Osmoregulation: Regulation of water and solute balance.
Endocrine System
Overview
Controls the release of hormones that regulate various bodily functions.
Glands
- Endocrine Glands: Release hormones into the bloodstream.
- Exocrine Glands: Release secretions through ducts.
Hormones
- Chemical messengers that bind to specific cells and trigger effects.
- Types: Steroid hormones and protein hormones.
Hypothalamus and Pituitary Gland
The hypothalamus regulates the pituitary gland, which releases hormones that control other endocrine glands.
Blood Sugar Regulation
- Insulin: Lowers blood sugar levels.
- Glucagon: Raises blood sugar levels.
Diabetes
- Type I: Inability to produce insulin.
- Type II: Insulin resistance.
Reproductive System
Sex Hormones
- Gonads (testes and ovaries) produce sex hormones.
- Types: Androgens, estrogens, and progestins.
Menstrual Cycle
Changes in the uterine lining over the course of an ovarian cycle.
Nervous System
Neurons
The structural and functional units of the nervous system.
Structure
- Cell body: Contains the nucleus and organelles.
- Dendrites: Receive signals from other neurons.
- Axon: Transmits signals to other neurons or effector cells.
Types of Neurons
- Afferent Neurons: Sensory neurons.
- Interneurons: Integrate information.
- Efferent Neurons: Motor neurons.
Divisions of the Nervous System
- Central Nervous System (CNS): Brain and spinal cord.
- Peripheral Nervous System (PNS): Nerves outside the CNS.
Nerve Impulses
- Action Potential: Electrical signal that travels along an axon.
- All-or-None Principle: An action potential either occurs or it doesn’t.
Synaptic Transmission
Communication between neurons or between neurons and effector cells.