Bio exam

Lipids, Cells, and Cell Structures

1. Types of Lipids

Lipids are a diverse group of organic molecules characterized by their hydrophobic nature. They can be classified into three main types:

 * Glycerides: These are esters of glycerol and fatty acids. They include triglycerides, which are the primary storage form of energy in animals, and phospholipids, which form the bilayer structure of cell membranes.

 * Steroids: These are lipids with a four-ring structure. Cholesterol is a well-known steroid that is a component of cell membranes and a precursor for many hormones.

 * Waxes: These are esters of fatty acids and long-chain alcohols. They are primarily found in plants, where they serve as a protective coating on leaves and stems.

2. Prokaryotic vs. Eukaryotic Cells

Prokaryotic cells are simpler and smaller than eukaryotic cells. They lack membrane-bound organelles and have a single, circular chromosome. Bacteria and archaea are examples of prokaryotic organisms.

Eukaryotic cells are more complex and larger, with membrane-bound organelles that perform specific functions. They have multiple, linear chromosomes. Animals, plants, fungi, and protists are examples of eukaryotic organisms.

3. Eukaryotic Cell Structure

 * Plasma membrane: A phospholipid bilayer that surrounds the cell and controls the movement of substances into and out of the cell.

 * Cell walls (of plants): A rigid structure outside the plasma membrane that provides support and protection.

 * Nucleus: The control center of the cell, containing the cell's DNA.

 * Nuclear envelope: A double membrane that surrounds the nucleus and separates it from the cytoplasm.

 * Chromatin: The DNA and proteins that make up the chromosomes.

 * Nucleolus: A region within the nucleus where ribosomes are assembled.

 * Ribosomes: Cellular machines that carry out protein synthesis. They can be free-floating in the cytoplasm or bound to the endoplasmic reticulum.

 * Endoplasmic reticulum (ER): A network of membrane-bound sacs and tubules involved in protein synthesis, lipid synthesis, and calcium storage.

   * Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification.

   * Rough ER: Studded with ribosomes and is involved in protein synthesis.

 * Golgi apparatus: Modifies, sorts, and packages proteins and lipids for transport within or outside the cell.

 * Vacuoles: Membrane-bound sacs that store water, waste products, and other substances.

 * Mitochondria: The "powerhouses" of the cell, responsible for cellular respiration and ATP production.

 * Chloroplasts (in plants): The sites of photosynthesis, where plants convert sunlight into energy.

 * Centrosome: A region of the cytoplasm that organizes microtubules during cell division.

 * Cilia: Short, hair-like structures that move fluid or particles across the cell surface.

 * Flagella: Longer, whip-like structures that propel the cell.

4. Plant vs. Animal Cells

Plant cells have cell walls, chloroplasts, and a large central vacuole, while animal cells lack these structures. Animal cells have centrioles, which are absent in plant cells.

5. Prokaryotic vs. Eukaryotic Cell Structure (continued)

Prokaryotic cells lack membrane-bound organelles, while eukaryotic cells have many such organelles. Prokaryotic cells have a single, circular chromosome, while eukaryotic cells have multiple, linear chromosomes.

6. Fluid Mosaic Model

The fluid mosaic model describes the structure of the plasma membrane as a fluid phospholipid bilayer with proteins embedded in it. The phospholipids are arranged in a double layer, with the hydrophilic heads facing outward and the hydrophobic tails facing inward. Proteins can be integral or peripheral, and they serve various functions, including transport, signaling, and cell recognition.

7. Membrane Proteins and Carbohydrates

Membrane proteins play essential roles in cell function, including:

 * Transport: Facilitating the movement of substances across the membrane.

 * Signaling: Receiving and transmitting signals from the environment.

 * Cell recognition: Identifying and interacting with other cells.

 * Enzymatic activity: Catalyzing chemical reactions.

Membrane carbohydrates are attached to proteins or lipids and play a role in cell recognition and adhesion.

8. Movement of Substances Across Cell Membranes

The movement of substances across cell membranes depends on their size, charge, and polarity. Small, uncharged molecules can diffuse directly across the lipid bilayer. Larger or charged molecules require transport proteins to cross the membrane.

9. Diffusion, Osmosis, Facilitated Diffusion, and Active Transport

 * Diffusion: The net movement of molecules from a region of higher concentration to a region of lower concentration.

 * Osmosis: The diffusion of water across a selectively permeable membrane.

 * Facilitated diffusion: The transport of molecules down their concentration gradient with the aid of a transport protein.

 * Active transport: The transport of molecules against their concentration gradient, requiring energy (ATP).

10. Osmosis in Cells

 * Hypotonic environment: The concentration of solutes outside the cell is lower than inside the cell. Water will move into the cell, causing it to swell and possibly burst.

 * Hypertonic environment: The concentration of solutes outside the cell is higher than inside the cell. Water will move out of the cell, causing it to shrink.

 * Isotonic environment: The concentration of solutes outside the cell is equal to the concentration inside the cell. There will be no net movement of water.

12. Functions of Mitosis

Mitosis is essential for the growth, development, repair, and reproduction of multicellular organisms. It ensures that each new cell receives a complete copy of the genetic material.

13. Phases of the Cell Cycle

The cell cycle consists of two major phases: interphase and mitosis.

 * Interphase: The cell grows and prepares for division. It consists of three stages:

   * G1 phase: The cell grows in size and synthesizes proteins.

   * S phase: The DNA is replicated.

   * G2 phase: The cell continues to grow and prepares for mitosis.

 * Mitosis: The chromosomes are separated and distributed to the daughter cells. It consists of four stages:

   * Prophase: The chromosomes condense and become visible. The nuclear envelope breaks down.

   * Metaphase: The chromosomes line up at the equator of the cell.

   * Anaphase: The sister chromatids are separated and move to opposite poles of the cell.

   * Telophase: The nuclear envelope reforms around the chromosomes at each pole. The chromosomes begin to decondense.

14. Mitotic Spindle

The mitotic spindle is a network of microtubules that forms during mitosis. It is responsible for separating the chromosomes and distributing them to the daughter cells.

15. Roles of Interphase, Mitosis, and Cytokinesis

 * Interphase: Prepares the cell for division by replicating DNA and synthesizing proteins.

 * Mitosis: Separates the replicated chromosomes and distributes them equally to the daughter cells.

 * Cytokinesis: Divides the cytoplasm and organelles between the daughter cells, completing the process of cell division.