Summary
Summary 4 Cell Membranes and Transport
- Institution
- CIE
EVERYTHING you need to know about "Cell Membranes and Transport" for A-level Biology CIE
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
Seller
Follow
Content preview
Cell Surface Membranes Structure and Function10 April 2021 19:26
7.5 nm
• The globular proteins and glycoproteins float about in a 'lipid sea' with the polar carbohydrate
portions forming the glycocalyx on the outside
• This is named the fluid mosaic model
Features of the Fluid Mosaic Model
• The membrane is stabilised by hydrophobic interactions
• Globular proteins are either peripheral or integral
• There is relatively free lateral movement of components, but very little transverse mobility
• The structure is fluid and the fluidity is regulated by the numbers of double bonds in the fatty
acids (more double bonds, higher fluidity) and the proportion of cholesterol (more cholesterol,
less fluidity)
• Membrane fluidity needs to be controlled
• The more kinks in the tails, the more fluid the membrane
• Cholesterol reduces the fluidity (above 37°C)
• Cold temperatures reduce fluidity, to the point where it may actually solidify
• Some organisms vary the balance of saturated/unsaturated phospholipids and cholesterol when
ambient temperature varies, in order to keep the membrane fluid enough so the proteins within it
function efficiently
• The lipid bilayer represents a permeability barrier to polar solutes and ions, which can only cross if
transported by a membrane bound protein
• The fluid mosaic model assumes an asymmetrical structure, 2-10% of the membrane is
carbohydrate on the external surface. These are involved in recognition mechanisms
• Different types of membrane differ in thickness, but most are between 5 and 10nm
• The plasma membrane is 7.5nm wide
Cell Signalling
• Cells respond to their changing environment by receiving and processing signals from one another
• They also send out messages
• Most cell signals are in the form of chemical messengers, such as hormones or growth factors
which may have come from cells nearby, or from far away in the body
• An example is neurotransmitters across nerve synapses
How Do Cells Detect These Signals?:
• They have receptors on their cell surface membranes to which certain chemical messengers bind
• This then triggers an internal response
• Receptors are usually trans-membrane proteins which initiate signalling processes within the cell
on binding with the molecule on the outside of the cell surface membrane
Exceptions:
• In a few cases, the receptors are within the cell, sometimes even within the nucleus
• These are triggered by molecules which are able to diffuse through the membrane, usually steroid
hormones, such as oestrogen
• Nitrous oxide also binds to receptors within cells
• Again, this triggers the initiation of a chain of reactions within the cell (cascade reaction)
sometimes involving a second messenger. The response occurs within the cell
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 Zubaid. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £2.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
71184 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