#Cell structure

#Outline basic cell structure

Cell membrane

• 10nm thick
• semipermeable structure made from phospholipid bilayer keeps internal composition relatively constant in presence of ECF changes due to impermeability to some compounds
• contains membrane proteins and channels which allow interaction with other cells or messenger systems
• bound to microtubular filaments (e.g. actin) which anchor and support the cytoskeleton
• more detail here

Cytoplasm

• internal part of the cell that contains cytosol and proteins that form cytoskeleton
• organelles are housed here
• some important processes occur here e.g. glycolysis

Golgi apparatus

• complex of vesicles and folded membranes
• modify and package proteins into vesicles for exocytosis
• create lysosomes that break down various cell components such as DNA, proteins and polysaccharides

Mitochondria

• consists of outer membrane, inner membrane, and intermembrane space
• produce ATP via aerobic metabolism
  • involved in citric acid cycle, fatty acid metabolism, and urea cycling
  • the electron transport chain occurs across the inner membrane
• more detail on mitochondria here

Endoplasmic reticulum (ER)

• network of tubular systems, consisting of rough and smooth ER
• rough ER synthesises proteins
• smooth ER lacks ribosomes and produces fat and steroid hormones

Nucleus

• contains DNA
• regulates gene expression to modulate organelle activity
• the nucleolus (part of the nucleus) contains mRNA
• RBC is anuclear, skeletal muscle is multinuclear, almost all other cells are mononuclear

#Outline cell membrane structure and function

#Proteins

Randomly distributed across the cell membrane.

Integral proteins (aka transmembrane proteins)

• so called because they are integrated into the cell membrane
• span the width of the cell membrane
• examples
  • many receptors, including all ion channels and G-protein coupled receptors
  • transmembrane pumps, e.g. Na-K ATPase
  • some carrier proteins and cell-bound enzymes

Peripheral proteins

• inner surface proteins
  • bound to the inner surface of the cell
  • includes many receptors
  • are often bound to the cytoskeleton to provide cell structure
  • e.g. cytochrome C
• outer surface proteins
  • bound to the outer surface of the cell
  • includes many receptors
  • may be involved in cell-cell signalling and adhesion
  • examples
    • ABO antigens
    • MHC-I and MHC-II, used for immune signalling

Glycoproteins and glycolipids

• proteins/lipids that communicate with the outer surface may have carbohydrate moieties
• allow interaction with other structures
• examples
  • ABO antigens (which are both glycolipids and glycoproteins)
  • MHC proteins (glycoproteins)

#Lipids

Phospholipid bilayer

• hydrophilic (polar) heads face outward
• hydrophobic (non-polar) tails face inward
• forms a flexible, fluid-like structure

Cholesterol

• interacts with phospholipid tails, preventing the membrane from being either too rigid or too fluid
• strengthens the cell membrane
• decreases its permeability to water, essential for maintaining concentration gradients across the cell membrane
• involved in endocytosis

Glycolipids

• see above