ch5 - membranes

What are the two types of membranes

-cell surface/ plasma membrane which surround cells 

-internal membranes which surround organelles within a cell  

are the membranes partially permeable and what does this mean

they are both partially permeable means it only allows certain molecules to pass through 

What are the 3 key roles of plasma membranes

acts as partially permeable barrier keeping contents of a cell separate from its environment 

controls what substances leave and enter the cell 

allows cells to communicate with each via cell signaling  

What is the 2 key role of inner membranes

acts as a partially permeable barrier between organelles and the cytoplasm

divides cell into areas, compartments, where different processes = compartmentalisation

What is the fluid mosaic model and what does it suggest

suggests plasma membranes are made up of phospholipids: that are constantly moving & are arranged in a bilayer structure which lipids and proteins of different sizes are embedded in

What properties of phospholipids create the bilayer structure

hydrophilic heads are attracted to water therefore face outward 

hydrophobic fatty acid tails are repelled by water therefore face inward creating a hydrophobic centre 

Due to the hydrophobic centre which molecules can and can't pass through plasma membranes

small nonpolar molecules CAN pass through 

large polar molecules & ions CANNOT - they require transport proteins to pass through

Name the 5 lipid and protein components which are embedded in the phospholipid bilayer

Cholesterol 

Intrinsic/integral proteins 

Extrinsic/peripheral proteins 

Glycoproteins 

Glycolipids 

What does fluidity mean

The phospholipids ability to move and slide past each other, allowing cell membrane to be more flexible

what happens when permeability increases

molecules diffuse through phospholipid bilayer quicker  

Where is cholesterol found and describe its function

Location = between phospholipid tails 

Function = to regulate fluidity and maintain stability 

> High temps - restricts movement of phospholipids to prevent membrane becoming too fluid 

> Low temps - prevents phospholipids packing too close together to prevent membrane becoming too rigid

Where are intrinsic proteins found and describe its function

Location = embedded and span across the phospholipid bilayer 

Function = to transport molecules across the membrane 

What are the 2 types of intrinsic proteins

Carrier protein 

Channel protein

What are carrier and channel proteins also known as

Transport proteins

Describe how a carrier protein works

large polar molecules will bind to the protein causing a conformational/ shape change allowing the molecule to diffuse across the membrane: 

down (facilitated/passive diffusion) OR against (active transport) conc. gradient, involving more complex steps

> afterwards the carrier protein will change back to its original shape 

describe how a carrier protein works to transport a molecule AGAINST conc. gradient

large polar molecule and ATP bind to the protein 

> hydrolysis of ATP into ADP and Pi releases energy which causes a conformational/shape change

> allowing molecule to diffuse across membrane against the conc gradient

> Pi is released causing protein to return back to its original shape to be used again

Describe how a channel protein works

tubes that fill with water to allow ions to diffuse across the membrane: 

down (facilitated/passive diffusion) the conc gradient 

Where are extrinsic proteins found and describe its function

Location = on the surface of the phospholipid bilayer either on one side or the other

Function = to provide mechanical support as well as aid in making glycolipids and glycoproteins

What is a glycoprotein

protein with a carbohydrate chain attached 

What is a glycolipid

lipid with a carbohydrate chain attached

What are the 3 functions of glycoproteins and glycolipids

> Cell adhesion = when cells attach one to another 

> Cell recognition = allows cells to recognise one another

> Cell signalling = enables cells to communicate and coordinate activities in the organism