Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane...

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Membranes

Transcript of Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane...

Page 1: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Membranes

Page 2: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Assumed Knowledge

• Membrane components• Membrane structure• Membrane properties• Membrane functions• Membrane-bound organelles

Page 3: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Membrane components

• Composed of a phospholipid bilayerPhosphate ‘head’- hydrophilicLipid ‘tail’ – hydrophobic

• Arrangement prevents contact between the lipid core and water in the extracellular/intracellular environment

Page 4: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.
Page 5: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

• Carbohydrates – mainly glycoproteins (glyco- meaning sugar)

• Proteins Mainly transmembrane proteins – these span the

entire phospholipid bilayer e.g. ion channels, G-protein coupled receptors

• Cholesterol

Page 6: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.
Page 7: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Membrane structure

• The phospholipid bilayer gives the membrane fluidity

• This fluidity means proteins and other components e.g. cholesterol can move across the bilayer

• Cholesterol makes the membrane rigid – more cholesterol, more rigid

• Proteins and other molecules in the membrane give it an mosaic effect

• The fluid mosaic model

Page 8: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Membrane Properties

• Semi permeability: this means the membrane is permeable to some molecules but not all:

Permeable to Not permeable to

- Hydrophobic molecules e.g. O2 - Large molecules e.g. glucose

- Small uncharged molecules - Ions e.g. K+, H+, Cl-

Page 9: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

• Asymmetry: the extracellular side and the intracellular side of the membrane differ in their composition – this allows for recognition between the inside and outside environment

Page 10: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Membrane Functions

• Separation of the extracellular and intracellular environments

• Anchorage of the cytoskeleton maintaining the shape of the cell (the cytoskeleton is an intracellular network of proteins that act like a scaffolding)

• Attachment of the extracellular matrix for grouping of cells together to form tissues

• Selective permeability• Endocytosis (absorption of molecules by engulfing them)

• Exocytosis (removal of membrane bound molecules by fusion with the plasma membrane)

• Transport via proteins in the plasma membrane

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Endocytosis

Exocytosis

Page 12: Membranes. Assumed Knowledge Membrane components Membrane structure Membrane properties Membrane functions Membrane-bound organelles.

Membrane bound organelles

Within the cell there are numerous membrane bound organelles Organelles are structures within the cell with a unique function

- Endoplasmic reticulum: synthesis of proteins and lipids - Golgi apparatus: protein modification, packaging of

molecules for exocytosis or use in the cell- Lysosome: break down of cellular waste and debris - Nucleus: storage and replication of DNA- Mitochondria: ATP synthesis