Module 2.5 Biological Membranes Flashcards
How thick are membranes?
7-10nm
Describe the phospholipid bilayer
Hydrophilic phosphate heads make up outside
Hydrophobic fatty acid tails make up inside
2 layers of phospholipid make up the bilayer
Is the phosphate head evenly charged?
No
Intrinsic protein
Spans whole bilayer
Extrinsic protein
Partially embedded inside or outside
Glycolipids and glycoproteins
For cell signalling Allow self recognition Receptors for drugs + hormones Antigens Glycoproteins can bind cells in tissues
Channel proteins
Allow small ions/small water soluble molecules to diffuse through
Carrier proteins
Help large molecules to diffuse through
Used in active transport
Cholesterol
For stability and to regulate fluidity
Cells communicate w/hormones
Hormones bind to receptors (complimentary shape)
Response occurs in target cell e.g. gene/DNA activated
Insulin
Made in beta cells in the islets of langerhans in the pancreas
Released when glucose level of blood too high
Target cells are muscle tissue, adipose tissue + liver cells
Effect is glucose taken out of blood = blood glucose level lowered
Beta blockers
Stop heart muscle beating to fast which could cause a heart attack
Poisons
Bind w/receptors
Botox paralyses facial muscles
Hijacking receptors
Viruses can bind with receptors e.g. HIV and AIDS
HIV virus can bind with receptors on T-lymphocytes
Lowers immune system
HIV bursts WBCs
🌟Diffusion
Net movement
High to low conc.
Down conc. gradient
Passive process
🌟Osmosis
Net movement of water From high water pot. to lower water pot. Across partially permeable membrane Down water pot. gradient Passive process
🌟Active transport
Net movement of molecules/ions Low to high conc. Against conc. gradient Uses ATP Requires energy Across partially permeable membrane Needs carrier proteins/channel proteins
Channel proteins
Polar molecules/ions
Carrier proteins
Large molecules
Hypertonic
Lots of salts and sugars
Isotonic
The same water pot. in and out =no net movement
Hypotonic
High water pot.
Water pot. of pure water
0 kPa
More concentrated solution
Lower water pot. = more negative number
Water moves from a
Higher water potential (less neg. number) to a lower water potential (more neg. number)
Water potential
Solute potential + pressure potential
What happens when a cell is placed in a hypotonic solution?
Water moves into the cell (via osmosis)
Animal cells will burst (haemolysed)
Plant cells will become turgid (cytoplasm and vacuoles will push the membrane against the cellulose cell wall)
What happens when a cell is placed in a hypertonic solution?
Water moves out of the cell (via osmosis)
Animal cells shrink (crenated)
Plant cells become plasmolysed (cell membrane pulls away form cell wall)
🌟Basic structure of cell surface membranes
Phospholipids form bilayer
Hydrophobic tails pointing inwards
Hydrophilic heads pointing out
Role of phospholipids: to provide a barrier to large/polar molecules and ions
Carrier/channel proteins for active transport/facilitated diffusion
Cholesterol stabilises the membrane and regulates fluidity
Glycoproteins which act as receptors for cell communication
🌟Roles of cell surface membranes inside cells
Form edge of organelles within a cell
Isolation of contents of organelles from cytoplasm
Site of attachment of enzymes and ribosomes (on RER)
Provide selective permeability - controls what enters and leaves organelles
Separates areas of differing concentration to provide gradients
🌟Cell signalling - how receptors work
Release of signal molecules e.g. hormones by exocytosis into the blood
Proteins/glycoproteins/glycolipids act as receptors for hormones and drugs
The receptor is specific as the shape of the receptor and hormone are complementary in shape
The hormone binds to the receptor
Binding causes a change inside the cell which brings about a response
🌟Role of glycoproteins
Cell signalling - communication between cells to help them work together
Act as antigens for…
Cell recognition - self/non-self
Receptors found on target cells
For hormones/cytokines to trigger reactions/responses in cells
Cell adhesion in tissues
Form bonds with water molecules to stabilise the membrane
Receptors on transport proteins
🌟Small, non-polar substances
Diffuse through the phospholipid bilayer
🌟Larger substances
Use carrier proteins
Specific to certain molecules
The protein changes shape to allow the molecule through to the other side
Facilitated diffusion/active transport (uses ATP, against gradient, faster, one way)
Endocytosis/exocytosis
Bulk transport
🌟Polar substances
Through channel proteins
Facilitated diffusion
🌟Compare active transport and facilitated diffusion
Active transport:
- Carrier proteins
- Anything from low to high conc.
- Uses ATP
- Only goes in one direction
- Much quicker than diffusion
Facilitated diffusion:
- Carrier proteins
- Channel proteins
- Larger molecules e.g. glucose
- Ions/polar molecules e.g. K+ and Ca2+
- Needed when phospholipid bilayer won’t allow large/polar/water soluble molecules to cross
- No ATP needed
🌟Compare the roles of carrier proteins and channel proteins and how they work
Carrier proteins:
- Specific to molecule
- Molecule attaches on one side of the membrane
- Protein changes shape
- Releases molecule on the other side of the membrane
- Carries large molecules across the membrane in facilitated diffusion (doesn’t require energy)
- Carries all molecules across the membrane in active transport (requires energy)
Channel proteins:
- Specific to molecule
- Forms a pore through the centre of the protein
- Hydrophilic conditions inside the pore
- Allows charged and polar substances across the membrane in facilitated diffusion
🌟Facilitated diffusion
Net movement High conc. to lower conc. Down conc. grad. Through carrier proteins (large molecules) Channel proteins (ions) Passive process
🌟Stages of exocytosis
Vesicle moves towards cell surface membrane along microtubules
Vesicle fuses w cell surface membrane
Protein released out of cell by exocytosis
Movement of vesicles on microtubules and fusion of vesicles w membrane requires ATP
🌟Stages of endocytosis
Molecule binds w receptor
Cell surface membrane invaginates (ATP required)
Membrane fuses w itself
Vesicle formed
Vesicle moves through cytoplasm to destination organelle
