Medical Student Lecture Notes with Examples
1. Cell Structure
The cell is the basic unit of life. Human cells have different shapes and sizes but share common structures.
Major Parts of a Human Cell:
| Structure | Function | Example |
|---|---|---|
| Cell Membrane | Controls what enters/exits the cell (selectively permeable) | Like a security gate |
| Cytoplasm | Jelly-like fluid where reactions occur | "Work area" of the cell |
| Nucleus | Contains DNA, controls cell activities | "Control center" or "brain" of the cell |
| Mitochondria | Produces energy (ATP) | "Powerhouse" of the cell |
| Ribosomes | Make proteins | Found free or on the rough ER |
| Endoplasmic Reticulum (ER) | Transports substances | |
| — Rough ER (with ribosomes): makes proteins | ||
| — Smooth ER: makes lipids | Like a factory belt | |
| Golgi Apparatus | Packages and ships proteins | Like a post office |
| Lysosomes | Break down waste and old cell parts | "Clean-up crew" |
| Centrioles | Help in cell division | Found in animal cells |
2. Cellular Transport Mechanisms
Cells must move substances in and out to survive.
Types of Transport:
a) Passive Transport (no energy needed)
-
Diffusion: Movement of molecules from high to low concentration.
-
Example: Oxygen entering a cell.
-
-
Osmosis: Diffusion of water across a membrane.
-
Example: Water moving into red blood cells.
-
-
Facilitated diffusion: Uses a protein channel.
-
Example: Glucose entering cells via transport proteins.
-
b) Active Transport (requires energy - ATP)
-
Moves substances from low to high concentration.
-
Example: Sodium-potassium pump in nerve cells.
c) Endocytosis and Exocytosis
-
Endocytosis: A Cell takes in materials (e.g., white blood cells engulf bacteria).
-
Exocytosis: A Cell releases materials (e.g., nerve cells release neurotransmitters).
3. The Genetic Code and Protein Synthesis
a) DNA (Deoxyribonucleic Acid)
-
Found in the nucleus.
-
Carries the genetic code for making proteins.
b) RNA (Ribonucleic Acid)
-
Helps carry out the instructions from DNA.
Steps of Protein Synthesis:
-
Transcription (in nucleus)
-
DNA → mRNA (messenger RNA)
-
mRNA carries the code to ribosomes.
-
-
Translation (in the cytoplasm at the ribosome)
-
mRNA → Protein
-
tRNA (transfer RNA) brings amino acids to build the protein.
-
Example:
-
DNA: A-T-G-C
-
mRNA: U-A-C-G
-
Protein: Made of amino acids joined according to this code.
4. Cell Division
Cell division is necessary for growth, repair, and reproduction.
a) Mitosis (body cells)
-
One cell → two identical daughter cells.
-
Used in growth and tissue repair.
Phases of Mitosis:
-
Prophase – Chromosomes condense.
-
Metaphase – Chromosomes line up in the middle.
-
Anaphase – Chromosomes pulled apart.
-
Telophase – New nuclei form.
-
Cytokinesis – The Cell splits into two.
b) Meiosis (reproductive cells)
-
Makes sperm and egg cells.
-
One cell → four non-identical cells (with half the chromosomes).
5. Aging and Cells
What Happens as Cells Age?
-
DNA damage accumulates over time.
-
Cells divide more slowly.
-
Some cells die or enter a resting phase (senescence).
-
Telomeres (ends of chromosomes) shorten with each division, linked to aging.
Example:
-
Skin cells in older adults regenerate more slowly, leading to wrinkling and slower wound healing.
Post a Comment