Summary
Summary C3 ENZYMES 9700 AS LEVEL
- Module
- Institution
- Book
SUMMARIZED NOTES BY A-STUDENT
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
More summaries for
-
PHOTOSYNTHESIS
-
Biology AS Best summary notes
-
Cell structure_ A level
Seller
Follow
bhipeshs
Content preview
Chapter 4: Cell Membrane and TransportMonday, 25 April 2022 9:30 PM
FLUID MOSAIC MODEL OF MEMBRANE
• Cell surface membranes create an enclosed space separating internal cell environment from external cell environment,
controls the exchange of material across them (partially permeable) and acts as interface for communication
• Cell membranes are formed from phospholipid bilayer (7 nm wide)
PHOSPHOLIPIDS
• Contains 2 regions: polar head and non-polar tails
• Phosphate head is polar (hydrophilic) and soluble in water
• Fatty acid tail is non-polar (hydrophobic) and insoluble in water
• Form phospholipid monolayers on surface of water
• When shaken with water, they form spheres with hydrophilic phosphate heads outside and hydrophobic fatty acid tails
inside. This is called a micelle.
• Two-layered structures may form in sheet - phospholipid bilayer (basic structure of cell membrane)
• Phospholipid bilayers can form compartments – the bilayer forming the cell surface membrane establishing the boundary
each cell
STRUCTURE OF MEMBRANE
• Bilayers making the membrane also contain proteins which can be either intrinsic (integral) or extrinsic (peripheral)
• Intrinsic proteins are embedded in the membrane with their arrangement determined by their hydrophilic and hydrophob
regions
• Extrinsic proteins are found on the outer or inner surface of the membrane
• FLUID - Phospholipids and proteins can move around via diffusion
MOSAIC - Scattered pattern produced by the proteins within the bilayer
AS BIOLOGY NOTES Page 1
, COMPONENTS OF CELL SURFACE MEMBRANE
1. Phospholipid
Forms a bilayer with hydrophobic tails pointing inwards and hydrophilic head pointing outwards
Tails form a hydrophobic core, acting as a barrier to water-soluble substances
Individual phospholipid molecules can move around within their own monolayer by diffusion
Can be chemically modified to act as signalling molecule
2. Cholesterol
Hydrophobic tails and hydrophilic head
Fits between phospholipid molecules; oriented in same way
Increases fluidity of membrane, by stopping membrane from becoming too rigid at low temperatures
Interaction between cholesterol and phospholipid tails also stabilises the cell membrane at higher temperatures by
stopping the membrane from becoming too fluid
Cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack
more closely together
They also contribute to the impermeabilty of the membrane to ions
Increase mechanical strength and stability of membrane
Absent in prokaryote membrane
3. Glycolipids
Lipids with carbohydrate chains - enabling them to act as receptor molecules
Carbohydrate chains project into fluid surrounding the cell
Some act as antigens for cell-to-cell recognition
4. Glycoproteins
Proteins with carbohydrate chains - enabling them to act as receptor molecules
Carbohydrate chains project into fluid surrounding the cell
Some act as antigens for cell-to-cell recognition
5. Proteins
Intrinsic proteins- proteins embedded within the membrane
Transmembrane proteins - proteins that span the entire membrane (eg transport proteins)
Extrinsic proteins (peripheral proteins) - proteins found on inner or outer surface of membrane
Transport proteins create hydrophilic channels to allow ions and polar molecules to travel through the membrane
(including channel protein and carrier protein)
Each transport protein is specific to a particular ion or molecule
Transport protein allow the cell to control which substances enter or leave
AS BIOLOGY NOTES Page 2
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller bhipeshs. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £4.76. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
67474 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now