Biochemistry Lecture 1: Cell Membrane Structure

Biochemistry Notes - Lecture 1

• Membranes are composed of phospholipids
• Phospholipids interact with each other and the aqueous compartments to form a bilayer membrane
• The fluid mosaic model describes the structure of cell membranes
• Cholesterol is a component of cell membranes that provides stability
• Diffusion within membranes affects lipids and proteins
• The lipid bilayer is a fragile barrier
• Interactions between membrane components maintain its integrity
• Components of the cell membranes include:
  • Phospholipids
  • Cholesterol
  • Proteins
  • Glycoproteins
  • Glycolipids
• Phospholipids have 2 fatty acid chains, glycerol, and a highly polar or charged group
• They are amphipathic
• Sterols, such as cholesterol, have 4 ring structures at the centre and saturated hydrocarbon tails
• Cholesterol is generated in the liver from acetyl-CoA
• Cholesterol is made in the smooth endoplasmic reticulum of hepatocytes
• Hepatocytes produce cholesterol→ bile→ large intestine→ reabsorbed
• Cholesterol is lipophilic
• Cholesterol is essential for the synthesis of bile acids, without bile acids there is no breakdown of fatty acids
• Bile acids are amphiphilic and enable the solubilization of dietary fats (emulsification)
• Emulsification is important for the uptake of dietary fats
• Bile acids increase the surface area for lipid digestion

Biochemistry Notes - Lecture 1, continued

• Lipid-soluble hormones include: cortisol, aldosterone, testosterone, T3, and T4
• Hormones bind to receptors and activate genes; this takes more time compared to activating a protein.
• Bile acids are synthesized from cholesterol
• Bile acids are essential for lipid digestion and increase the solubility of lipids
• Bile acids increase the surface area for lipid digestion
• Cholesterol is used to produce bile acids
• Bile acids enable digestion of lipids by solubilizing the fats into the small intestines
• Primary bile acids include: cholic acid, chenodeoxycholic acid, deoxycholic acid, and lithocholic acid
• Primary bile acids are produced by the liver, usually conjugated in the body, and modified in the gut by bacteria
• Secondary bile acids are less toxic, being modified by conjugation, often linking to molecules with waste or toxic products.
• Bile is crucial for lipid digestion, making the fats more water soluble

Biochemistry Notes - Lecture 1, continued

• Fatty acids are commonly found, trans fatty acids are obtained from diet
• Phospholipid tails can be saturated or unsaturated

Biochemistry Notes - Lecture 2

• Cholesterol is a component of lipoproteins, which transport lipids in the body
• Lipoproteins contain a hydrophobic core (triacylglycerol and cholesterol esters) and an amphipathic coat of phospholipids and apolipoproteins
• Chylomicrons, VLDL, IDL, and LDL are lipoproteins that carry lipids
• LDL returns to the liver to deliver cholesterol to other tissues that need it
• Apolipoproteins act as signals for cellular uptake and metabolism
• LDL recycles to the liver for metabolism and cholesterol use
• Cholesterol is stored in adipocytes and can be metabolized in cells

Biochemistry Notes - Lecture 2, continued

• Metabolized fatty acids are converted to acetyl CoA, which enters the Krebs cycle or can be stored if in excess
• Fatty acids can be converted into chylomicrons to travel through the body
• Phospholipids are amphipathic molecules that are involved in carrying lipids
• Lipoproteins are important for carrying lipids through the body

Biochemistry Notes - Lecture 3

• Signal transduction involves extracellular signals like hormones binding to receptors triggering intracellular changes (including changes in cell shape or activation of enzymes), allowing a cell-to-cell communication
• Signal molecules diffuse to receptors nearby
• Examples of signaling pathways include acetyl choline, glucose, insulin, and apoptosis

Biochemistry Notes - Lecture 4

• Lipids and proteins are the major membrane components
• Membrane asymmetry refers to the different compositions and orientations of lipids on each leaflet within the membrane
• Cholesterol, flippase, floppase, and scramblase are involved in maintaining membrane asymmetry and composition

Biochemistry Notes - Lecture 5

• Lipids can be hydrophobic (tails) or hydrophilic (heads)
• Lipids form a bilayer structure with the hydrophobic tails in the inside
• Protein is also an integral part of the membrane

Biochemistry Notes - Lecture 6

• Various factors have the potential to affect the rate of diffusion through a membrane
• The way in which lipid molecules are organized directly affects the proteins that are associated with the membrane

Biochemistry Notes - Lecture 7

• There are different types of membrane proteins that can be directly associated with the membrane (integrated into)
• Membrane proteins have several functions that depend on their types
• There are multiple pathways for molecules to enter a membrane
• Cholesterol, and other factors like temperature affect the fluidity of the membrane

Biochemistry Notes - Lecture 8

• Glycolysis is a metabolic pathway used to breakdown glucose
• The pentose phosphate pathway is a pathway used to produce NADPH and phosphorylated sugars
• NADPH is an important electron carrier in biosynthetic reactions

Biochemistry Notes - Lecture 9

• The Pentose Phosphate pathway plays an important role in cell reactions, and can be used for various purposes depending on the needs of the cell.

Biochemistry Notes - Lecture 10, continued

• NADPH and NADH are similar but play different roles.
• The structure and location within the cells can be different
• Different forms of glucose can be produced depending on the cellular need