Cell Biology: Cell Membrane and Cytoplasm

Cell Membrane

• Also known as plasma membrane
• Thin, semi-permeable membrane that surrounds the cell
• Composed of:
  • Phospholipid bilayer (phospholipids with hydrophilic heads and hydrophobic tails)
  • Proteins (integral and peripheral)
  • Cholesterol (regulates fluidity and permeability)
• Functions:
  • Regulates what enters and leaves the cell
  • Maintains cell shape and structure
  • Provides mechanical support and protection

Cytoplasm

• Gel-like substance inside the cell membrane
• Composed of:
  • Water (about 70%)
  • Salts
  • Sugars
  • Amino acids
  • Organelles (e.g. mitochondria, lysosomes, ribosomes)
• Functions:
  • Provides mechanical support and shape to the cell
  • Site of many metabolic reactions (e.g. glycolysis, protein synthesis)
  • Helps to move organelles and molecules within the cell

Mitochondria

• Often referred to as the "powerhouses" of the cell
• Found in the cytoplasm
• Functions:
  • Generate energy for the cell through cellular respiration
  • Convert glucose into ATP (adenosine triphosphate)
  • Regulate cell growth and division
• Structure:
  • Outer membrane
  • Inner membrane (folded into cristae to increase surface area)
  • Matrix (where citric acid cycle and fatty acid oxidation occur)

Nucleus

• Control center of the cell
• Found in the cytoplasm
• Functions:
  • Stores genetic information (DNA)
  • Regulates gene expression
  • Coordinates cell growth and division
• Structure:
  • Nuclear envelope (double membrane with pores)
  • Nucleoplasm (gel-like substance inside the nuclear envelope)
  • Chromatin (DNA and proteins)

Lysosomes

• Membrane-bound organelles found in the cytoplasm
• Functions:
  • Contain digestive enzymes (acid hydrolases)
  • Break down and recycle cellular waste and foreign substances
  • Help to defend against pathogens and foreign substances
• Structure:
  • Single membrane
  • Acidic internal environment (pH 4.5-5.5)

Cell Membrane

• Composed of a phospholipid bilayer, proteins, and cholesterol
• Phospholipids have hydrophilic heads and hydrophobic tails
• Cholesterol regulates fluidity and permeability
• Regulates what enters and leaves the cell
• Maintains cell shape and structure
• Provides mechanical support and protection

Cytoplasm

• Gel-like substance inside the cell membrane
• Composed of 70% water, salts, sugars, amino acids, and organelles
• Organelles include mitochondria, lysosomes, and ribosomes
• Provides mechanical support and shape to the cell
• Site of many metabolic reactions, such as glycolysis and protein synthesis
• Helps to move organelles and molecules within the cell

Mitochondria

• Often referred to as the "powerhouses" of the cell
• Found in the cytoplasm
• Generate energy for the cell through cellular respiration
• Convert glucose into ATP (adenosine triphosphate)
• Regulate cell growth and division
• Have an outer membrane, inner membrane (folded into cristae), and matrix
• Citric acid cycle and fatty acid oxidation occur in the matrix

Nucleus

• Control center of the cell
• Found in the cytoplasm
• Stores genetic information (DNA)
• Regulates gene expression
• Coordinates cell growth and division
• Has a nuclear envelope with pores, nucleoplasm, and chromatin (DNA and proteins)

Lysosomes

• Membrane-bound organelles found in the cytoplasm
• Contain digestive enzymes (acid hydrolases)
• Break down and recycle cellular waste and foreign substances
• Help to defend against pathogens and foreign substances
• Have a single membrane and an acidic internal environment (pH 4.5-5.5)