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

DNA Replication: The Biological Mechanism

DNA replication is the essential process by which a cell creates an exact copy of its DNA prior to cell division (mitosis or meiosis). This critical event occurs during the S phase of the cell cycle.

Initiation: Unwinding the DNA

• Helicase: An enzyme that unwinds and separates the double helix by breaking the hydrogen bonds between nitrogenous bases, creating a "replication fork."
• Single-strand binding proteins (SSBs): Bind to single strands of DNA to keep them separated and prevent the helix from re-forming.
• Primase: Adds short RNA primers to the single-stranded DNA template. These primers are necessary for DNA polymerase to begin adding nucleotides.

Elongation and Synthesis

• DNA Polymerase III: Adds complementary

Perineum Anatomy

Perineum Structures

The perineum is a diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and coccygeus).

It is divided transversely into two triangles:

• The anterior is the urogenital triangle, which includes the external genitals.
• The posterior is the anal triangle, which contains the anus.

The perineum is also divided into superficial and deep layers, with some muscles common to men and women.

Muscles of the Perineum and Pelvic Floor

Muscles making up the Urogenital and Anal (Pelvic) triangles/diaphragms include:

• Urogenital diaphragm: Superficial and intermediate planes
• Sphincters: Internal and external

Mitosis and Meiosis Comparison

Similarities Between Mitosis and Meiosis

• The sequence of changes in the nucleus and cytoplasm.
• The presence of the stages of prophase, metaphase, anaphase, and telophase.
• The spindle formation and the cycle of condensation of chromosomes.

Key Differences Between Mitosis and Meiosis

• Mitosis occurs in somatic cells, while meiosis is restricted to germ cells.
• In mitosis, each cycle of DNA replication is followed by one division. The resulting daughter cells are diploid (2n) and have the same amount of DNA as the parent cell.
• In meiosis, one DNA replication cycle is followed by two divisions, resulting in four haploid (n) daughter cells, which contain half the DNA of the parent cell.
• In mitosis, each chromosome behaves independently.

The Human Digestive System: An Introduction

The digestive system transfers organic nutrients, vitamins, minerals, and water from the foods we eat to the internal environment. Upon entering the body, food moves through the gastrointestinal (GI) tract, and the nutrients are absorbed and transported to the circulatory system where they are utilized.

Net Gain to the Body

Food and air are the primary sources of net gain to the body.

Distribution within the Body

Nutrients and substances are distributed throughout the body via the GI tract, lungs, storage deposits, and metabolism.

Net Loss from the Body

Excretion from the body occurs via the lungs, GI tract, kidneys, and skin.

Epithelial Cells

Epithelial cells separate compartments and are crucial in the digestive... Continue reading "Human Digestion and Metabolic Regulation" »

Introduction to Biomolecules

Living organisms are made up of thousands of biomolecules—molecules produced by living systems with distinct properties and functions favored through evolution. Small, simple molecules called micromolecules (or monomers), such as water, minerals, simple sugars, and nucleotides, serve as building blocks for larger macromolecules (or polymers) like proteins, lipids, carbohydrates, and nucleic acids. Biomolecules are classified into inorganic types (e.g., water, minerals, gases) and organic types (e.g., lipids, carbohydrates, proteins, nucleic acids). While biomolecules alone do not exhibit life, they organize into cells and are continuously synthesized and broken down to maintain and perpetuate life.

Water: The Essential

c) Antigen Processing and Presentation

• Engulf protein antigens, partially digest them, and display polypeptide fragments on the surface for T cells to "see."
• Fragments are associated on the surface with Major Histocompatibility Antigens (MHC II), which are necessary to activate T cells.

d) Dendritic Cell Migration

To increase the chance of interacting with the correct T cells, dendritic cells migrate to secondary lymphoid organs (chemokines are secreted to attract T cells).

VII. Extracellular Killing by the Immune System

A. Natural Killer (NK) Cells

NK cells lyse virus-infected cells, tumor cells, and parasites. They kill cells that do not express MHC class I antigens.

B. Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

1. In ADCC, NK cells and macrophages

Circulatory System

Blood is a viscous, red, and saline liquid (approximately 5 liters). It is composed of:

• Plasma (55%): A yellowish liquid made of water and substances such as nutrients and hormones.
• Blood Cells: Produced in the bone marrow, there are three types:
  • Red blood cells (erythrocytes): Transport oxygen from the lungs to the cells using a red protein called hemoglobin.
  • White blood cells (leukocytes): Essential components of the immune system.
  • Platelets: Fragments of cells that function to stop bleeding.

Blood Functions

• Transport nutrients
• Transport oxygen and carbon dioxide
• Transport waste products
• Regulate body temperature
• Participate in the immune system
• Prevent hemorrhages

Blood Vessels

• Arteries: Transport blood from the heart to the organs.

Cancer Stem Cells vs. Normal Stem Cells

Both normal stem cells and cancer stem cells (CSCs) share the ability to self-renew through asymmetric division, allowing one daughter cell to remain a stem cell while the other differentiates. They both generate heterogeneous populations of mature cells: normal stem cells produce tissue-specific cell types, while CSCs produce diverse tumor cells. Both rely on similar regulatory signaling pathways such as Wnt, Notch, and Hedgehog, but these pathways are tightly controlled in normal stem cells and dysregulated in CSCs, promoting tumor formation. Both exist as rare subpopulations within tissues, depend on signals from their niche, and can remain quiescent for long periods. CSCs, however, show enhanced resistance... Continue reading "Cancer Stem Cells: Signaling Pathways and Therapeutic Potential" »

Animal Development and Embryology

• Which best describes the blastula development stage? - A hollow ball of cells with a blastocoel.
• In early stages of development through the gastrula stage: Cells divide to increase the number of cells but they don’t increase in size.
• A fertilized egg cell is: Diploid.
• Which best describes the zygote development stage? - A fertilized egg cell.
• Which of the following correctly displays the sequence of developmental stages? - Cleavage-blastula-gastrula.
• The first cavity in an embryo formed during frog development is the: Blastocoel.
• The archenteron of the developing sea urchin eventually develops into the: Digestive tract or gut.
• _____ has determinate cleavage and will not have identical twins: Protostome.
• ____ has the

Lab 8: Temperature and Microbial Growth

Key Concepts

• Psychrophiles grow best between 0–20°C. Often found in cold environments like glaciers.
• Mesophiles prefer 20–45°C. These include human pathogens like E. coli.
• Thermophiles thrive at 55°C or higher. They are often found in hot springs.

Materials and Their Functions

• Tryptic Soy Broth (TSB): A nutrient-rich medium that supports bacterial growth.
• Incubators set to different temperatures (4°C, 25°C, 37°C, 55°C): Used to simulate environmental conditions.
• Spectrophotometer (OD600): Measures turbidity (cloudiness) of a culture to estimate cell density.
• Classification by growth: “+++” indicates heavy growth; “0” means no growth.

In this lab, students investigated how temperature affects... Continue reading "Microbiology Lab Fundamentals: Growth, Metabolism, Genetics" »