Protein Synthesis, Cell Division, and Homeostasis
Protein Synthesis
Describe protein synthesis, detailing how so many things can be generated from so few (i.e., 4 organic bases, 20 amino acids, protein formation).
Protein structure:
- 1º Primary: Linear sequence of amino acids
- 2º Secondary: Twisting of the polypeptide chain (e.g., alpha-helices and beta-sheets)
- 3º Tertiary: Three-dimensional folding of the polypeptide chain
- Quaternary: Arrangement of multiple polypeptide chains into a functional protein complex
Cell Division: Mitosis and Meiosis
Detail what occurs in each phase of mitosis and meiosis. What is genetic burden? What is the difference between interphase and interkinesis?
Meiosis is a specialized type of cell division that reduces the chromosome number by half. This process occurs in all sexually reproducing eukaryotes (both single-celled and multicellular), including animals, plants, and fungi.
Phases of Cell Division:
- Prophase: Chromosomes become visible, the nuclear envelope breaks down, and centrioles separate.
- Metaphase: Chromosomes align in the middle of the cell.
- Anaphase: Sister chromatids (or homologous chromosomes in meiosis I) separate.
- Telophase: A cleavage furrow forms, and chromosomes decondense.
- Mitosis is a form of asexual reproduction.
Interphase: Is the longest phase of the cell cycle, typically lasting around 16 hours in a growing mammalian cell. It consists of three stages:
- G1 (Gap-1) phase: Pre-synthesis stage, in which the cell prepares for DNA replication (about 5 hours).
- S (Synthesis) phase: DNA replication occurs (about 7 hours).
- G2 (Gap-2) phase: Post-synthesis stage, where the cell prepares for cell division (about 3 hours).
Interkinesis: Also known as interphase II, occurs during meiosis between meiosis I and meiosis II. No DNA replication takes place during this phase (lacks an S-phase).
Cell Membrane Structure
Describe the structure of the cell membrane and explain why it is called the Fluid Mosaic Model.
The fluid mosaic model describes the cell membrane’s structure. It indicates that the cell membrane is not solid; it is flexible and has a consistency similar to vegetable oil. All the individual molecules are floating in a fluid medium and are capable of moving sideways within the cell membrane. “Mosaic” refers to something that contains many different parts. The plasma membrane is a mosaic of phospholipids, cholesterol molecules, proteins, and carbohydrates.
Membrane Permeability
What characteristics make it semi- or selectively permeable?
- Intrinsic: Channels and carriers
- Extrinsic: Enzymes and receptors
Factors Influencing Diffusion/Osmosis
What factors can influence the rate of diffusion/osmosis?
- Temperature
- Size of molecules
- Concentration gradient
- Distance
Tonicity
- Isotonic: Same solute concentration; nothing happens to the cell.
- Hypotonic: Less water in solution; cell implodes (crenation).
- Hypertonic: More water in solution; cell explodes (lysis).
Homeostasis and Feedback
Define and provide examples
- Negative feedback: Brings a system back to its set point (normal).
- Positive feedback: Moves a system away from its set point.
Examples of Feedback
Give an example of negative and positive feedback.
- Negative feedback example: Overheating, then sweating; sweating, then drinking.
- Positive feedback example: Blood clotting, labor contractions.
Intrinsic and Extrinsic Controls
Define intrinsic and extrinsic controls as related to homeostasis.
- Autoregulation (Intrinsic regulation): Occurs when the activities of a cell, tissue, organ, or organ system adjust automatically in response to some environmental change. Example: When oxygen levels decline in a tissue, the cells release chemicals that dilate local blood vessels, increasing blood flow and providing more oxygen.
- Extrinsic regulation: Results from the activities of the nervous system or endocrine system. Example: During exercise, the nervous system increases heart rate to circulate blood faster and reduces blood flow to less-active organs, such as the digestive tract, conserving oxygen for active muscles.