Cellular Anatomy and Physiology

Cell Membrane

• A lipid bilayer with embedded proteins about 7.5 nm thick
• A barrier between cell contents and interstitial space
• Embedded protein and lipids can move laterally
• Lipid bilayer with hydrophilic ends pointing out and hydrophobic pushing in

Contains

• Ion channels
• Transmembrane transport proteins

Adhesion Molecules: They are divided into 3 families

Selectins

• These molecules are induced by the cytokine interleukin-1 (IL-1) and tumour necrosis factor (TNF).
• L-Selectins are expressed on neutrophils and bind to endothelial mucin-like molecules (GlyCam-1).
• E-Selectins-family adhesion proteins. -Examples are leucocyte LFA-1, MAC-1 and VLA-4

Cell Regeneration

• For example, the majority of cells within the body can be categorized by their ability to regenerate themselves fully or not. The three categories are
• Labile (renewing) cells - continue to divide throughout life, and any damage is completely repaired by regeneration, eg, skin, mucous membranes, lymphoid tissues.
• Stable cells - do not divide after growth ceases, but can regenerate in response to injury, eg, CT, liver, pancreas.
• Permanent cells - as the name suggests, these cannot replicate, and are often replaced by fibrous tissue, eg, neurones, cardiac tissues.

Cell Cycle

• The cell cycle is the basis of much of the current research in the treatment of cancer.
• In many cancers the cell's quality control mechanism is overridden due to a genetic defect and faulty DNA replication is allowed to progress
• Cancer is usually due to more than one mutation - the "double hit hypothesis" such that both copies of the gene are affected
• It's a fascinating field and will likely have clinical outcomes so it is vital to know about it.

Cell cycle is as follows

• G0 Quiescent phase for certain cells
• G1 First gap phase ? S ( Synthesis) phase (DNA synthesis) ?
• G2 Time for some error correction ? M (Mitosis) phase

Control

• Cyclins - at least 15 proteins involved in the cell cycle whose levels change through the cell cycle
• Cyclin dependent kinases - at least 9 serine/threonine kinases. They require the presence of cyclins.
• Kinase inhibitory proteins (KIPs) bind to and inhibit CDKs

Checkpoints

• The G1 checkpoint ensures that conditions are appropriate for cell proliferation and that DNA is intact
• The G2 checkpoint ensures that cells do not enter mitosis without repair to damaged DNA and DNA replication is complete
• Maturation (aka Mitosis) promoting factor is a complex of a B cyclin and the cyclin-dependent kinase (Cdc2) that stimulated mitotic and meiotic cycles
• Progression through restriction point is required for the cell to move from G1 to S where DNA synthesis occurs.
• It depends on whether internal and external factors are suitable or else the cell can enter the G0 phase.

Cancer drugs and the cell cycle

Cytoplasm

• Gluconeogenesis
• Fatty acid synthesis
• Hexose monophosphate shunt
• Glycolysis
• Protein synthesis
• Steroid synthesis

Mitochondria: aerobic cell respiration

• Fatty acid Beta Oxidation
• Acetyl CoA production
• Krebs's cycle

Mitochondria and Cytoplasm

• Haem synthesis
• Gluconeogenesis
• Urea cycle

Golgi bodies

• Responsible for transporting products synthesised in the smooth endoplasmic reticulum.

Smooth endoplasmic reticulum

• A site of lipid synthesis within the cell.

Lysosomes (lysis- breakage, soma- body)

• Contain digestive enzymes which break down expendable cell organelles, engulfed viruses and other intracellular detritus.
• They carry hydrolases that degrade nucleotides, proteins, lipids, phospholipids, and also remove carbohydrate, sulfate, or phosphate groups from molecules.

Peroxisomes

• Peroxisomes are responsible for the metabolism of fatty acids within cells.

Ribosomes

• Intimately associated with the rough endoplasmic reticulum and are responsible for protein translation.