Biology Lecture Notes

Click below to find brief notes that may help you study for exams in biology. Review summaries, watch animations, and take unlimited practice exams. This animation demonstrates translation in protein synthesis.

Topic 1 Topic 2 Topic 3 Topic 4 Topic 5 Topic 6 Topic 7 Topic 8 Topic 9 Topic 10 Topic 11


Describe the photosynthetic process that allow organisms to capture and store energy. Leaves convert sunlight into usable energy in a complex pathway. Always on exams.

Cellular Respiration

Aerobic respiration is the process by which organisms use oxygen to turn fuel, such as fats and sugars, into chemical energy. In contrast, anaerobic respiration does not use oxygen. Respiration is used by all cells to turn fuel into energy that can be used to power cellular processes.

Introduction to the Cell

Cellular organelles explained, from ribosomes to mitochondria. The cell nucleus, where the DNA is located, is surrounded by a wealth of other protein structures in a substrate of protoplasm.

DNA Structure and Replication

DNA replication occurs through the help of several enzymes. These enzymes "unzip" DNA molecules by breaking the hydrogen bonds that hold the two strands together. Each strand then serves as a template for a new complementary strand to be created. Complementary bases attach to one another (A-T and C-G).

DNA Mutations and Biotechnology

Mutations is the process by which a gene or chromosome changes; structurally and the end result of that process. All mutations are not harmful' as beneficial mutations occur frequently among various viruses, and bacteria and also in higher organisms. CRISPR is a technology that can be used to edit genes. It's a way of targeting a specific bit of DNA inside a cell, editing precisely in order to alter that segment of DNA.

AP Biology
Energy and Transport
Sodium Potassium Pump
Cellular Structure
Introduction To Lipids
Cell Membranes
Homeostatic Disruptions
Cell Cycle, Mitosis And Meiosis
Viral Replication
Biological Molecules
Gibbs Free Energy
The Sensory System
Anatomy and Physiology
Cooperative Interactions
AP Biology Lab
Plant Pigments
Structural Biology
Bacteria And Antibiotics
Neuroscience Of Memory
The Physics Of Life: Water
Ecosystem Dynamics
Weather And Climate

Skull Tutorials
Spinal Cord
Neuron Structure
Parasympathetic Nerves
Muscle Anatomy
Head and Neck Muscles
Upper Limbs
Muscles Of The Upper Arm
Cardiovascular System
Heart Structure
Respiratory System
Reproductive System
Digestive System
Peritoneal Cavity
Lower Limbs
Femoral Triangle
Knee Joint
Lower Limb Arteries

Organelles Of A Human Cell
Virus Magnification
Immune System - Fighting Infection
Insulin Receptors - Diabetes
Brain Research
DNA Replication
Endoplasmic Reticulum
Clonal Selection Theory
Breast Stem Cells

Amphipod Movement
Baker's Yeast
Cheek Cells
Microorganism Size
Stentor Coeruleus
White Blood Cells
Microscopic World
Diatoms Made Visible
Life Without Oxygen: Anaerobic
Paramecium: Ciliates
Different Species

Diatom Algae Populations
Sensory Systems Of Snakes
Hurricane Forecasting
Nanotech - Water Purification
Harnessing Wave Energy
Changing Ecology
Solar Power
Giving Robots And Prostheses
Robobees: Design
How Did Life On Earth Begin?
Mobile Solar Power
Forecast Space Weather
Chemistry Pioneer
Genetic Path To Biodiversity
Tsunami Debris
Freshwater Mussels
Safer Drinking Water
Earth Worm Invasion
New Leaf Sensor Alerts
Hurricane Sleuth
Marshes And Sea Level Rise
Super Stars
Evolution In Action
Fascinating Flight
Ice And Its Frozen Secrets
Green Roofs

The Science Of Sex
How To Clone A Mammoth
DNA Damage
Stem Cells
Evolution Of Males And Females
Meiosis & Mitosis
R And K Selection
Classical Genetics
Molecular genetics

Walking Frogs
Deep-Sea Anglerfish Pair
Hummingbird Flight
Ultrafast Snapping Shrimp
Pigeons' Warning Call
Humpback Whales
Barn Owls' Hearing
Training Guide Dogs
Ravens Can Make Plans
Whale Size
Jaguar Cubs
Rare Birds
Starling Flocks
Blindfold Ants Navigation
Tadpoles Hatch Early
Lizards Have REM Sleep
Tiniest Chameleons
Sea Creatures
Chimps Destroy Drone
Monkeys Using Tools
Dog Breeding?

Dragonfly's Mouth
Bee Pollination
Turret Spiders
House Centipede
A Flea Jumping
Cricket Sounds
Tiny Spiders
It's a Bug Life
Dust Mites
Bed Bugs
Daddy Longlegs
Bombardier Beetle
Mantis Shrimp
Insect Wings
Giant Leaf Insects
Honey Bees
Jumping Insects


Enzymes are chemical catalysts that accelerate chemical reactions at physiological temperatures by lowering their activation energy. Enzymes are usually proteins consisting of one or more polypeptide chains. Enzymes have an active site that provides a unique chemical environment, comprised of certain amino acid R groups (residues). This unique environment is perfectly suited to convert particular chemical reactants for that enzyme, scientists call substrates, into unstable intermediates that they call transition states. Enzymes and substrates bind with an induced fit, which means that enzymes undergo slight conformational adjustments upon substrate contact, leading to full, optimal binding. Enzymes bind to substrates and catalyze reactions in four different ways: bringing substrates together in an optimal orientation, compromising the bond structures of substrates so that bonds can break down more easily, providing optimal environmental conditions for a reaction to occur, or participating directly in their chemical reaction by forming transient covalent bonds with the substrates.

Enzyme action must be regulated so that in a given cell at a given time, the desired reactions catalyze and the undesired reactions are not. Enzymes are regulated by cellular conditions, such as temperature and pH. They are also regulated through their location within a cell, sometimes compartmentalized so that they can only catalyze reactions under certain circumstances. Enzyme inhibition and activation via other molecules are other important ways that enzymes are regulated. Inhibitors can act competitively, noncompetitively, or allosterically. Noncompetitive inhibitors are usually allosteric. Activators can also enhance enzyme function allosterically. The most common method by which cells regulate the enzymes in metabolic pathways is through feedback inhibition. During feedback inhibition, metabolic pathway products serve as inhibitors (usually allosteric) of one or more of the enzymes (usually the first committed enzyme of the pathway) involved in the pathway that produces them.

Structure of DNA

DNA (deoxyribonucleic acid) consists of two biopolymer strands, coiled around each other to form a double helix. These two DNA strands are called polynucleotides since they are composed of several monomer proteins. Each nucleotide is made up of nitrogen-containing cytosine (C), guanine (G), adenine (A), or thymine (T), one deoxyribose sugar molecule, and a phosphate group. The nucleotides are joined to one another in a chain by covalent hydrogen bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone, according to base-pairing rules. The total amount of DNA in all living organisms is estimated to weigh 50 billion tons (Wikipedia). That's a lot of DNA, especially as protein molecules are microscopic and thus invisible to the naked eye.

The DNA backbone is resistant to cleavage, unless there is a mutation, and both pieces of the double-stranded structure store the same biological information. When a cell divides, it RNA transcription must replicate the DNA in its genome so that the two daughter cells are afforded an exact copy of the genetic information stored in the parent cells. The double-stranded structure of DNA provides a simple mechanism for DNA replication. The two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase. A large part of DNA (almost 99% in humans) is non-coding, meaning that these sections do not serve as patterns for protein sequences, but rather perform little-known functions.

Biology & Biotech Jobs

Microbiologists held about 23,200 jobs in 2017. The median annual wage for microbiologists was $66,850 in May 2017. The lowest 10 percent earned less than $39,480, and the highest 10 percent earned more than $128,190. Employment of microbiologists is projected to grow 8 percent from 2017 to 2026. More microbiologists will be needed to contribute to basic research and solve problems of industrial production, and develop new medicines, such as vaccines and antibiotics. In addition, pharmaceutical and biotechnology companies will need to hire experts in order to develop drugs that are produced with the aid of microorganisms.

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