9 Cell Membrane & Steroid hormones

Overview of Cell Membrane Structure

• The cell membrane is primarily composed of a phospholipid bilayer.

  • The bilayer serves as the foundational structural component of the membrane.

Phospholipid Structure

• Composed of:

  • Hydrophilic heads: Polar phosphate groups that interact well with water.

  • Hydrophobic tails: Fatty acid chains (hydrocarbon) that do not interact well with water.

    • These tails are crucial for the bilayer's non-polar properties.

Lipid Composition

• The plasma membrane has a 1:1 weight ratio of proteins to lipids:

  • About 75% of membrane composition consists of lipids.

  • Major types of lipids include:

    • Phospholipids: Comprising glycerol and two fatty acids; they are amphipathic (having both hydrophobic and hydrophilic parts).

    • Cholesterol: Found within the fatty acid tails, providing structure and integrity to the membrane.

  • Glycolipids: Contain a sugar component (glucose) attached to lipids, contributing to the glycocalyx (the carbohydrate-rich structure on the cell surface).

Membrane Proteins

• Membrane proteins are categorized based on their positioning within the bilayer:

  • Integral proteins: Span the entire membrane (Transmembranal).

  • Peripheral proteins: Attach partially across the membrane.

  • Surface proteins: Reside on the outer or inner surface.

• Functions of these proteins include transport, signaling, and structural support.

Glycoproteins and Glycolipids

• Glycoproteins: Proteins that have carbohydrate chains attached, playing important roles in cell recognition and signaling.

• All sugars associated with the membrane will either be part of glycolipids or glycoproteins.

Cholesterol Function

• Cholesterol is crucial for maintaining membrane fluidity and structural integrity:

  • It is found embedded within the non-polar tails of phospholipids.

  • Functions include:

    • Precursor for steroid hormones such as estrogen, testosterone, cortisol, and aldosterone.

Hormones Derived from Cholesterol

• Steroid hormones produced from cholesterol include:

  • Testosterone: Produced by the testes, increases skeletal muscle mass.

  • Estrogen: Produced by the ovaries, builds the lining of the uterus (endometrium).

  • Progesterone: Regulates the menstrual cycle and maintains the uterine lining.

  • Cortisol: Anti-inflammatory hormone produced by the adrenal cortex, regulates metabolism and inflammatory responses.

  • Aldosterone: Increases sodium reabsorption in kidneys, important for fluid balance and blood pressure regulation.

Membrane Transport Processes

• Molecules that can freely cross the membrane include:

  • Water, small non-polar, and non-charged molecules (e.g., oxygen, carbon dioxide).

• Passive transport includes:

  • Simple diffusion: Movement of substances from high to low concentration across the membrane.

  • Osmosis: Specific to the movement of water.

Inflammation and Cortisol Effects

• Signs of Inflammation:

  • Redness, heat, swelling, pain, and loss of function due to increased blood flow and fluid accumulation.

• Cortisol: Reduces inflammation and acts to manage blood glucose levels by promoting gluconeogenesis (conversion of substrates to glucose).

Key Takeaways for Quiz

• Understand the structure and functions of cell membrane components: phospholipids, cholesterol, glycolipids, glycoproteins, and membrane proteins.

• Recognize the hormones derived from cholesterol and their roles in the body.

• Be familiar with the processes of membrane transport and how substances cross the cell membrane.