chapter 24
Hormones
- Definition: Chemical signals produced by cells in certain organs and tissues.
- Mechanism: Hormones are released into the bloodstream and transmitted throughout the body.
- Function: They bind to specific receptors on the surface of various cells, which triggers changes in gene expression.
Gene Expression Control
- Processes involved in regulating gene expression:
- Transcription: The process by which mRNA is synthesized from DNA.
- Translation: The conversion of mRNA information into polypeptides.
- Post-translational modification: The processes that modify polypeptides after translation, including:
- Trimming (removing certain parts).
- Addition of functional groups.
- Protein folding (to form functional proteins).
mRNA Features
- mRNA modifications:
- Addition of a 5’ cap and 3’ poly-A tail, aiding in nuclear export and translation.
- Splicing: Removal of non-coding sequences (introns) from mRNA before translation.
Ribosomes and Protein Synthesis
- Ribosomes: The organelles responsible for synthesizing polypeptides.
- Rough Endoplasmic Reticulum (ER): Ribosomes attached to the rough ER assist in synthesizing secretory proteins.
- Golgi Apparatus: Processes, modifies, and packages proteins synthesized in the rough ER.
Protein Modification and Immune System
- Post-translational modifications occur in:
- Importance in immune response: Immunological proteins, such as antibodies, are synthesized and modified in these organelles.
Bone Marrow Stem Cells and Differentiation
- Bone marrow stem cells can differentiate into various blood cell types:
- Signals received by these cells determine gene activation and cell differentiation.
- Example: Some stem cells receive signals to differentiate into B cells, while others become T cells.
Cancer and Gene Expression
- Overview: Cancer is characterized by uncontrolled cell division resulting from mutations affecting oncogenes and tumor suppressor genes.
- Oncogenes: Mutated proto-oncogenes that promote cell division when they should not.
- Tumor suppressor genes: Normal genes that limit cell growth and division; loss of function due to mutations can lead to cancer.
- Example: BRCA1 and BRCA2 genes associated with breast and ovarian cancer.
Role of Signals in Gene Expression
- The activation of oncogenes and the inactivation of tumor suppressors contribute to cancer progression.
- Growth factors stimulate cells through receptor engagement, impacting mitosis regulation.
Immune System Overview
- Two major subdivisions:
- Innate Immune System: Rapid, non-specific response
- Involves immediate responses such as inflammation and phagocytosis by macrophages.
- Adaptive Immune System: Slower, specific response that involves B and T cells.
- Generates immunological memory following an infection.
Inflammatory Response
- Mechanism: Initiated by macrophages or mast cells detecting pathogens.
- Steps involved:
- Release of signals to call for immune support.
- Increased blood flow to the area, allowing more immune cells to arrive.
- Phagocytosis: Immune cells like macrophages engulf pathogens and debris.
T Cells and B Cells
- T Cells:
- Helper T Cells: Activate other immune cells.
- Cytotoxic T Cells: Destroy infected or cancerous cells.
- B Cells:
- Develop into plasma cells that secrete antibodies against specific antigens.
- Generate memory cells for long-term immunity.
Antigen Recognition
- Antigens: Molecules that trigger an immune response (e.g., components of pathogens).
- Specific to pathogen surface proteins, enabling immune targeting.
Vaccination Mechanisms
- Vaccines work by simulating an infection, training the immune system without causing disease.
- Types of vaccines:
- Live attenuated vaccines: Weakened forms of the pathogen.
- Inactivated vaccines: Killed pathogens.
- Subunit vaccines: Only specific antigens are included, not the entire pathogen (e.g., mRNA vaccines).
Effect of HIV on Immune System
- HIV targets helper T cells, leading to their depletion and resulting in AIDS (acquired immune deficiency syndrome).