Cell Structure and Organisation

Cell - basic unit of biological organisation (has been conserved through evolution with mods)

Allows for controlled shape/growth of tissues and organisms.

Characteristics:

• Generates any protein products in genome
• Selective gene expression - reflectes specialisation
• Cell division and mitosis
• Metabolise and stay alive
• Apoptosis - die when required
• Communicate with external environment

Membrane is impermeable to water - isolates cell components from external environment and cell can regulate own composition (stability)

Membrane - phospholipid bilayer

• Phospholipid - outer hydrophilic globular head (glycerol) and inner hydrophobic fatty acid chains (organic):
  • Choline - phosphatidylcholine
  • Serine - phosphatidylserine 
  • Ethanolamine - phosphatidylethanolamine
  • Inositol - phosphatidylinositol
• Sphinomylein - glycerol replced by amino alcohol (sphingosine)
• Chloestrol - steroid = rigidity
• Glycolipid - carbohydrate-linked fatty acids

Fluid Mosaic Model - shows fluidity of membrane lipids - laterally mobile and can exchange places with neighbour 10M times/second - rarely move across 2 bilayers

• Integral proteins - through entire membrane
• Peripheral - through one side

Proteins thethered to membrane cytoskeleton and integral have hydrophobic amino acids to anchor

Functions of membrane proteins:

• Cell adehesion - tissue formation
• Recpetors - recieve external signals or endocytosis
• Transport proteins - control entry/exit of mols/ions

Protein transporter types:

• Uniporter - 1 molecule along conc gradient
• Symporter - 2 molecules in same direction, one against one along conc gradient
• Antiporter - 2 molecules in diff directions, one against one along conc gradient

Asymmetric cells - distinct apical, lateral and basal plasma membrane domains = POLAR

Connect via lateral membranes = epithelial sheets

Tight junctions - formed of adhesion molecules (actin) - bring cells together and seal in space 

Specialised membrane w/ septum before divsion

No membrane bound organelles

DNA coiled in central nucleoid - not membrane bound

Cytosol w/ ribosomes - not compartmental

Mesosomes - invaginations of plasma membrane - secretion/DNA synthesis here

DNA forms chromatin in nucleus

Nuclear membrane continuous w/ endoplasmic reticulum

Histones - proteins forming associations w/ DNA = nucleosomes

Lamins - filamentous mesh on inner surface of nucleus = structure and transcriptional reg

Nuclear pores - act as filters for passage of biomolecules between nucleus/cytoplasm

• Ions/small mols - diffuse across
• Large mol active transport
• mRNA w/ proteins (mRNPs) through pore by uncoiling then associated w/ ribosomes for translation
• RNPs leave nucleus have nuclear exprt sequence (NES)
• Transcription factors enter nucleus have nuclear localisation signal (NLS)
• NES and NLS bind to shuttle proteins that control passage
• Nuclear basket - regulates size of molecules passing in nucleus

Polarised epithelial cells w/ biosynthetic pathway - interconnected route from rough ER -> golgi -> secretory vesicle

Secretory substance secreted at apical domain

Smooth ER can be involved in synthesis of fatty acids/phospholipids

Modifies proteins

cis region - vesicles from ER fuse

medial region - proteins pass through = maturation

trans region - packaged to secretory vesicles

Acidic organelles w/ several hydrolytic enzymes (acid hydrolases) for protein degredation and re-use of amino acids

Phagocytosis - digest bacteria

Autophagy - organelle digestion

Endocytosis - engulf things outside cell

Acidic state - H+ ion ATPase punmp and Cl- ion channel

Main ATP production site - aerobic respiration

Double membrane

Outer membrane - porin channel proteins = permeable

Inner membrane - cristae rich in complexes where ATP production occurs

Central matrix - mitochondrial DNA coding for specific enzymes for respiration

Mitochondria evolved from cyanobacterial endosymbiosis

Site of photosynthesis 

Thylakoid membrane system w/ grana (disc-shaped membrane stacks w/ chlorophyl)

Stroma matrix w/ starch granules

One in each plant cell

<80% of cell volume 

Store for ions, nutrients, water, waste products

pH acidic - membrane protein pmps and Cl- ion channels

Structural role - osmotic pressure = hydrostatic pressure and plant rigidity