cell membrane

characteristic of phospholipid bilayer

Hydrophilic and (-) charged phosphate head+Hydrophobic fatty acid tails 

• Presence of kinks (C=C), unsaturated

• Will ⬆ their fluidity 

In aq environment 

• The phospholipids will rearrange themselves to form a bilayer

• With the hydrophobic tails facing inwards to form the hydrophobic core

• The hydrophilic heads in contact with the aqueous environment

function of phospholipid bilayer

1. Regulates substances that move in and out of the cell by acting as a barrier to:

   • Ions (charged)

   • Polar (hydrophilic)

   • Large 

2. Creates a barrier between intracellular and extracellular environment 

3. Allows for compartmentalisation to occur

characteristic of cholesterol

1. 4 ring structure 

2. Slightly amphipathic 

Due to these groups present:

1. Hydrophilic

2. Hydrophobic

3. Polar

4. Hydroxy

function of cholesterol

1. Regulates movement of the phospholipid bilayer 

   a. At warmer temperature 

   • Phospholipid molecules may be overly fluid

   • cholesterol will restrict the moment of phospholipid molecules through the interaction with it

   b. At colder temperatures

   • Phospholipid molecules may be overly firm 

   • Cholesterol will prevent close packing between phospholipid molecules 

   
   2. Anchor proteins down into the membrane

characteristic of proteins- how does it interact with the phospholipid bilayer

Amphipathic 

• The hydrophobic and nonpolar phospholipid bilayer will interact with the nonpolar amino acids found on the exterior of the protein 

• The charges hydrophilic phosphate head will interact with the polar amino acid found on the exterior of the protein

function of protein

1. Function as protein channels/carriers to facilitate diffusion 

   a. channel

   • Has a hydrophilic core

   • Allow large, charged, polar molecules to pass through 

   b. carrier

   • Binding to 1 solute induces a conformational change 

     • Provides access to the opposite side of the membrane 

   a. Act as a pump

   • Uses ATP to move solutes up against the concentration gradient 

   • E.g: Na+/K+ pumps 

2. Function as enzyme/receptor proteins

   a. Hold ribosomes in position

   b. Allow entry of polypeptide synthesised on ribosomes at RER

3. Stabilises the membrane structure

characteristic of glycoproteins

Carbohydrate chains that are associated with the membrane protein

characteristic of glycolipid

Carbohydrate chains that are associated with the hydrophobic tails of the membrane

function of glycoprotein + glycolipid

1. Serve as recognition sites in cell-2-cell recognition and cell adhesion 

2. Serve as receptors

function of cell membrane

1. regulate movement in and out of cell by acting as a barrier

2. allow for compartmentalisation

3. serve as a surface for chemical reactions to occur

4. increased surface area for chemical reactions

5. enable communication between cell and surroundings

regulate movement in and out of cell by acting as a barrier:

what cannot pass through the barrier?

1. Ions (charged)

2. Polar (hydrophilic)

3. Large

allow for compartmentalisation:

why?

1. unique environment to form for highly specialised activities 

2. Spatial separation

3. Accumulation of ions to high concentrations

example for “⬆surface area for chemical reactions”

 mitochondrial membrane

how does the cell enable communication between cell and its surroundings

• Glycolipid + glycoprotein will enable

  a. cell-2-cell recognition 

  b. Cell adhesion 

• Recognise specific receptors for signal transduction to occur

what are the different types of transport?

1. simple diffusion

2. facilitated diffusion

3. active transport

4. bulk transport

5. osmosis

which transport requires ATP

active + bulk

what is the movement of concentrated gradient for all transport?

1. simple diffusion

   • down

2. facilitated diffusion

   • down

3. active transport

   • up

4. bulk transport

   • up

   • down

5. osmosis

   • down

which transport requires transport protein

facilitated + active

definition of simple diffusion

Net movement of water down the concentration gradient from a region of high concentration to a region of low concentration

definition of facilitated diffusion

Net movement of water down the concentration gradient from a region of high concentration to a region of low concentration through a protein channel/carrier

what are the types of transport protein?

1. Transmembrane hydrophilic channel protein 

2. Carrier protein 

definition of active transport

Energy-consuming process (ATP) that transports protein across the membrane through a pump, against a concentration gradient

• It is one directional 

• When the solute binds to the pump, the pump will undergo a conformational change

Allowing the solute to have access to the other side of the membrane

what are the types of bulk transport

1. exocytosis

2. endocytosis

definition for exocytosis

Secretion of macromolecules (e.g: waste materials) to the exterior of the cell by fusion of membrane vesicle and plasma membrane

definition for endocytosis + type of endocytosis

Infolding of membrane to form a vesicle to acquire the macromolecule 

1. Phagocytosis 

   • Engulfing a solid 

2. Pinocytosis 

   • Invagination of liquid 

   • receptor -mediated endocytosis 

3. Large volume of liquid is being taken up

definition of osmosis

Net movement of water down the concentration gradient from a region of high water potential to a region of low low potential through a selectively permeable membrane 

where can water travel?

• go directly through the membrane (small) 

• through a channel (aquaporin)