Notes, summaries, assignments, exams, and problems for Biology

Meselson-Stahl Experiment and DNA Replication

The Meselson-Stahl experiment tested the hypotheses of DNA replication. They cultured bacteria in a ¹⁵N medium. ¹⁵N is a heavy isotope of nitrogen, so the synthesized DNA is of heavy density. They then shifted the bacteria to a ¹⁴N medium, and DNA was isolated at different times corresponding to replication cycles 0, 1, and 2.

Results of the Experiment

After one replication cycle, the DNA was all of intermediate density. This rules out the conservative replication model, which predicts that both heavy density DNA and light density DNA will be present, but none of intermediate density will be present. This result is consistent with the semi-conservative replication model, which predicts that all DNA... Continue reading "Meselson-Stahl Experiment: Unraveling DNA Replication" »

The end of the 20th century brought constant changes and noticeable evolution, especially in science and technology. Every day, technologies that previously seemed remote and unattainable are announced. Thereby, nanotechnology was born—a technology dedicated to the design and manipulation of matter at the atomic or molecular level, for industrial or medical purposes. As a result, nanorobots arose, which are machines, or robots, of nanometric dimensions—an ultra-small measure compared to that of an atom—making their debut in 1949. From then on, literature and cinema have included these tiny robots, making people fantasize about the future of living with them. Furthermore, they are considered the fountain of youth, as they will help us... Continue reading "How Nanorobots Will Revolutionize Healthcare and Extend Lifespans" »

Translation

Translation refers to the process of polymerization of amino acids to form a polypeptide. The order and sequence of amino acids are defined by the sequence of bases in the mRNA. The amino acids are joined by a bond known as a peptide bond. Formation of a peptide bond requires energy. Therefore, in the first phase itself amino acids are activated in the presence of ATP and linked to their cognate tRNA–a process commonly called as charging of tRNA or aminoacylation of tRNA to be more specific. If two such charged tRNAs are brought close enough, the formation of peptide bond between them would be favored energetically. The presence of a catalyst would enhance the rate of peptide bond formation.

DNA Fingerprinting

As stated in the preceding... Continue reading "Biotechnological Applications in Medicine and Agriculture" »

Levels of Organization

From Atoms to Organisms

Atom, molecule, organelle, cell, tissue, organ, organ system

Inorganic Biomolecules

• Water
• Mineral salts

Organic Molecules

• Carbohydrates
  • Monosaccharides: one molecule; examples: glucose, fructose
  • Disaccharides: two monosaccharides; examples: sucrose, maltose
  • Polysaccharides: many monosaccharides; examples: glycogen, cellulose
• Proteins: macromolecules composed of small molecules called amino acids; examples: collagen, hemoglobin, antibodies
• Lipids: examples: fats, phospholipids, cholesterol. Fats break down into fatty acids and glycerol.
• Nucleic acids: macromolecules composed of nucleotides, two types: DNA and RNA; examples: genes

Cells

Simplest living unit. Living things can be unicellular organisms or multicellular... Continue reading "Levels of Organization in Biology: From Atoms to Organisms" »

Ecological Concepts

Biomagnification and Bioaccumulation

Biomagnification is the process in which chemical substances become more concentrated at each trophic level. This occurs because organisms at higher trophic levels must consume more biomass to meet their requirements.

Bioaccumulation refers to the build-up of a chemical substance in the tissues of a single organism.

Indicator Species and Biotic Index

Indicator species are sensitive to specific environmental conditions and consequently have a limited range of tolerance.

A high biotic index indicates the presence of many pollution-sensitive organisms, denoting an unpolluted environment.

A low biotic index indicates a polluted environment, due to a relative abundance of pollution-tolerant organisms.... Continue reading "Ecological Concepts: Biomagnification, Biodiversity, and Population Dynamics" »

Cellular and Tissue Organization

Organelles

• Mitochondria: Produces energy
• Vesicles: Transport and digestion of substances
• Endoplasmic Reticulum:
  • Rough: Synthesis and modification of proteins
  • Smooth: No attached ribosomes, synthesis of lipids
• Golgi Body or Apparatus: Processing and packaging of substances, secretory vesicles
• Ribosomes: Protein synthesis
• Centrosomes: Involved in cell division
• Cilia and Flagella: Movement
• Cytoskeleton: Maintains cell shape, movement of cell structures

Human Tissue

• Epithelia:
  • Covering Epithelia: Epidermis, mucous membrane, endothelia
  • Glandular Epithelia: Salivary glands, pancreas, thyroid
• Connective: Bone, adipose, cartilage, dense connective, blood
• Muscle: Smooth muscle, skeletal muscle, cardiac muscle
• Nervous: Neurons, glial cells

Organs

Group... Continue reading "Cellular and Tissue Organization: From Organelles to Organ Systems" »

What is the primary waste product in urine?

Ammonia

Identify the body functions that the urinary system helps regulate and maintain.

• Eliminate waste
• Primarily Ammonia
• Conserve nutrients
• Prevent excretion
• Regulate and maintain:

• Blood volume
• Blood pressure
• Conserve ions (sodium, potassium, calcium)
• Assist liver in detoxifying poisons

Briefly, in an essay, list and explain the three steps in urine production that occurs in the nephron. Terms like tubular reabsorption will not be given in question!

1. Glomerular filtration
2. Movement of protein-free solution and solutes from glomerulus into capsule space
3. Tubular reabsorption
4. Return of most of the fluid and solutes back into the capillaries
5. Tubular secretion
6. Addition of some solutes from the capillaries into the tubule

What

Healthy Eating Plate

• Oils:

  Olive oil for cooking, on salad, and at the table. Limit butter, avoid trans fat.

• Water:

  Drink water, tea, or coffee with little or no sugar. Limit milk (1-2 servings a day) and juice (1 small glass a day). Avoid sugary drinks.

• Vegetables:

  The more veggies and variety, the better. Potatoes and French fries don't count.

• Whole Grains:

  Eat a variety of whole grains like whole-wheat bread, whole-grain pasta, and brown rice. Limit refined grains like white rice and white bread.

• Fruits:

  Eat plenty of fruits of all colors.

• Healthy Protein:

  Choose fish, poultry, beans, and nuts; limit red meat and cheese; avoid bacon, cold cuts, and other processed meats.

Foods and Nutrients

The difference between food and nutrients is that nutrients... Continue reading "Guide to Healthy Eating: Nutrients, Functions, and Tips" »

Diffusion

Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration. This is a passive cell movement, meaning cells do not need to use energy for it.

Concentration Gradient

The concentration gradient is the difference in the concentration of molecules between two places.

Factors Affecting Diffusion

• Distance molecules travel (shorter distances enhance diffusion)

• Concentration gradient (a steeper gradient increases the rate)

• Surface area (larger areas facilitate more diffusion)

• Temperature (higher temperatures increase kinetic energy, speeding up diffusion)

• Size of molecule (smaller molecules diffuse more rapidly)

Osmosis

Osmosis is a special type of diffusion, specifically the passage of water molecules... Continue reading "Cell Transport & Plant Nutrition: Essential Biological Processes" »

Characteristics of a Balanced Diet

To maintain a balanced diet, consider the following:

• Eat five moderately sized meals a day to aid digestion.
• Consume a variety of foods from all food groups, following the recommended amounts in the food pyramid or food wheel.
• Incorporate fruits and fresh vegetables daily for essential vitamins.
• Choose fiber-rich foods to promote healthy bowel movements.
• Include unsaturated fats and limit saturated fats and cholesterol to reduce the risk of cardiovascular diseases.
• Consume carbohydrate-rich foods like bread, pasta, rice, and legumes regularly.
• Minimize sugar intake.
• Moderate salt consumption to prevent high blood pressure.
• Reduce the intake of processed and sugary foods (cakes, sweets, etc.).
• Drink 1.5 to 2 liters of