Study guide: Cell Membrane and Organelles

📋 Course Outline

1. Human Cell Types and Sizes
2. Cell Membrane Structure and Roles
3. Membrane Fluidity and Transport
4. Nucleus and Cytoplasm
5. Endoplasmic Reticulum and Golgi Body
6. Lysosomes and Storage Disease
7. Mitochondria and Apoptosis

📖 1. Human Cell Types and Sizes

📝 Essential Points

• The listed human cell types and sizes are:
  • neurine cells: 300–400 μm
  • ova: 100 μm
  • fat cells: 50–150 μm
  • muscle cells: 15–200 μm
  • red blood cells: 7.5 μm
  • white blood cells: 15 μm
  • sperm cells: 5 μm

📖 2. Cell Membrane Structure and Roles

🔑 Key Concepts & Definitions

• Membrane Asymmetry: means that the compositions of the two membrane layers of a living cell are different

★ Must-know

• The cell membrane separates cytosol from extracellular fluid, encloses individual organelles, and prevents different biomolecules from mixing.

📌 Integral membrane proteins include channel proteins, whereas peripheral proteins can flip to the opposite side and can cause apoptosis.

Further detail

• Phospholipids in the cell membrane are relatively negatively charged, and cholesterol contains 27 carbon atoms.

💡 Memory Hook

The membrane separates the cell from its surroundings while selectively allowing substances through.

📖 3. Membrane Fluidity and Transport

🔑 Key Concepts & Definitions

• Fluid Mosaic Model: states that membrane lipids and proteins are able to move laterally

★ Must-know

• Membrane carbohydrates are located on the outer face of the outer membrane layer and form glycolipids and glycomolecules such as blood type antigens.

📌 Membrane fluidity increases when temperature increases or when the number of carbon–carbon double bonds increases, and it decreases when cholesterol increases.

• Membrane receptor proteins allow cells to respond to hormones and neurotransmitters, such as the insulin receptor on skeletal muscle cells responding to insulin from the pancreas.

📌 The membrane is permeable to gas molecules and small uncharged molecules but impermeable to ions and large uncharged molecules, especially when they are water soluble; carrier or channel proteins may transport the otherwise impermeable substances.

Further detail

• Membrane adhesion molecules connect neighboring cells and provide mechanical strength and support.

💡 Memory Hook

Higher temperature and more carbon–carbon double bonds increase fluidity, whereas more cholesterol decreases it.

📖 4. Nucleus and Cytoplasm

🔑 Key Concepts & Definitions

• Nucleus: stores genetic material as deoxyribonucleic acid (DNA), in which DNA forms genes and genes are organized into chromosomes

★ Must-know

• The nuclear envelope consists of two membrane layers and contains nuclear pores for material exchange.

📌 The cytoplasm includes all materials inside a living cell except the nucleus, whereas the cytosol is the jelly-like fluid filling the cell.

• The membrane-bound organelles are:
  • endoplasmic reticulum
  • Golgi body
  • lysosome
  • mitochondria

Further detail

• The nucleolus synthesizes ribosomes, and the nucleoplasm contains 23 pairs of chromosomes.

💡 Memory Hook

The nucleus stores DNA, whereas the cytoplasm contains the cell’s non-nuclear material.

📖 5. Endoplasmic Reticulum and Golgi Body

★ Must-know

📌 Smooth endoplasmic reticulum lacks surface ribosomes, whereas rough endoplasmic reticulum has ribosomes on its surface.

• Smooth endoplasmic reticulum synthesizes lipids in liver cells, detoxifies drugs in liver cells, and stores intracellular calcium in muscle cells.

• Rough endoplasmic reticulum synthesizes proteins, modifies newly synthesized proteins, and performs glycosylation to make glycoproteins.

• The Golgi body receives newly synthesized proteins from rough ER, matures and targets them, and releases vesicles toward the cell membrane for secretion.

Further detail

• The rough endoplasmic reticulum is continuous with the outer membrane of the nuclear envelope.

💡 Memory Hook

Rough ER synthesizes and modifies proteins, then the Golgi receives, matures, targets, and releases them.

📖 6. Lysosomes and Storage Disease

🔑 Key Concepts & Definitions

• Lysosome: contains lysozyme to catalyze the breakdown of unwanted intracellular substances and hydrogen ion pumps that deliver hydrogen ions into the lysosome
• Lysosomal Storage Disease: is a genetic disorder causing accumulation of unwanted intracellular molecules and swelling of cells

★ Must-know

📌 Lysosomal enzymes are activated in an acidic environment with a pH of 4.5–5.5.

Further detail

• Tay-Sachs disease is a lysosomal storage disease in which infants aged 3–6 months can lose motor skills and later develop seizures, vision and hearing loss, paralysis, and a cherry-red spot on the retina.

💡 Memory Hook

Acidic lysosomal activation enables breakdown, whereas enzyme defects cause intracellular accumulation and cell swelling.

📖 7. Mitochondria and Apoptosis

🔑 Key Concepts & Definitions

• Mitochondria: generate adenosine triphosphate as the energy-carrying molecule in cells
• Apoptosis: is programmed cell death that eliminates unwanted cells, including old erythrocytes during their 120-day turnover

★ Must-know

• Mitochondria have a double membrane, and their inner membrane contains many proteins responsible for ATP production.

Further detail

• The mitochondrial matrix is responsible for fatty acid oxidation and protein metabolism, including the urea cycle.

• Mitochondria contain circular DNA that encodes proteins responsible for ATP production.

• Abnormal interdigital apoptosis during embryonic development can cause fusion of fingers or toes.

💡 Memory Hook

Mitochondrial metabolism produces ATP, while apoptosis removes unwanted cells.

📊 Synthesis Tables

Membrane Protein Functions

Protein type	Main role	Example or consequence
Receptor	Enables responses to hormones and neurotransmitters	Insulin receptor on skeletal muscle cells
Adhesion molecule	Connects neighboring cells and provides mechanical support	Mechanical strength
Enzyme	Facilitates biochemical reactions or pathways	Mitochondrial ATP synthase
Channel or carrier protein	Transports substances that cannot cross directly	Transport of ions or large uncharged molecules