Biological Membranes

Question 1

What is the role of PLASMA/CELL SURFACE membranes?

Answer 1

Surrounding all cells, SEPARATING the CELLS CONTENTS from the OUTSIDE WORLD are membranes.

Question 2

What are membranes found around in eukaryotic cells?

Answer 2

In eukaryotic cells membranes are also found around many organelles.

Question 3

What are membranes made up of?

Answer 3

Membranes are made up of molecules called phospholipids

Question 4

What is the role of membranes at the surface of cells?

Answer 4

The plasma membrane has many roles at the surface of cells:
It separates the cell from environment - helps creates concentration gradient
It controls the exit and entry of molecules and ions - provide selective permeability
It’s involved in FACILITATED diffusion, active uptake and osmosis
It’s involved in cell recognition (glycoproteins)
It’s involved in cell to cell attachment (glycoproteins)
It acts as a receptor for hormones over neurotransmitters

Question 5

What is the role of membranes within cells?

Answer 5

The membrane around many organelles present in eukaryotic cells separate the organelles contents from the cells CYTOPLASM so each organelle is a discrete entity and is able to perform its function

It helps COMPARTMENTALISE/surround organelles e.g. Mitochondria/golgi
It is involved in the ISOLATION of contents e.g. Isolate DNA(nucleus)
It is a SITE for attachment of ribosomes (e.g. Nuclear envelope)
It provides selective permeability
It helps create concentration gradients

Question 6

What are the differences and similarities between phospholipids and triglycerides?

Answer 6

Differences:

• phosphate group
• 2 fatty acid tails
• 2 ester bonds

Similarity:
Both have glycerol
Both have fatty acid
Both have ester bond

Question 7

What is a phospholipid molecule made up of?

Answer 7

The phospholipid molecule is made up of :
A Phosphate Glycerol head
Bonded to 2 fatty acid tails

Question 8

What is hydrophilic and hydrophobic in phospholipid?

Answer 8

Phospholipid head is hydrophilic attracted to water

Phospholipid tail is hydrophobic not attracted to water

Question 9

What is a polar molecule ?

Answer 9

A polar molecule is any molecule with charge

Question 10

What is a non polar molecule ?

Answer 10

A non polar molecule is any molecule that DOES NOT have an overall charge

Question 11

What is the distribution of electrons like in non-polar molecules?

Answer 11

In non-polar molecules the electrons are distributed more SYMMETRICALLY
and thus does not have an abundance of CHARGES at the OPPOSITE sides.
The charges all CANCEL out.

Question 12

Is the phosphate head polar or non polar?

Answer 12

Polar

Negatively charged

Question 13

Is the fatty acid tail polar or non polar ?

Answer 13

Non poplar

Question 14

How is the phospholipid bilayer created?

Answer 14

The cytoplasm inside a cell contains a lot of water,
and so does the fluid outside cells.
Due to this the phospholipid molecules group in order to shield the hydrophobic tails from water
But keeping the hydrophilic heads drawn to water
This causes the phospholipids to arrange themselves in a double layer with the heads facing out toward the water and tails inside form water
This is called a phospholipid bilayer..

Question 15

What does ‘plasma membranes are partially permeable’ mean ?

Answer 15

Partially permeable means that some substances can pass through others cannot

Question 16

How thick are cell membranes?

Answer 16

7-10nm

Question 17

What is the phospholipid bilayer also made up of?

Answer 17

The phospholipid bilayer is also made up of many different types of molecules

Question 18

What did SINGER and NICHOLSON do in 1972?

Answer 18

In 1972 singer and Nicholson proposed a model of how all the compounds found in cell membranes might be arranges to form a biological membrane.

Question 19

What is the term fluid mosaic model used to describe?

Answer 19

The term fluid-mosaic is used to describe the molecular arrangements in membranes. The main features are:

1. Phospholipid bilayer
2. Intrinsic proteins - extend right across the bilayer
3. Extrinsic proteins - are partially embedded in the bilayer

Question 20

What do intrinsic proteins act as?q

Answer 20

Instrinsic proteins which are extend right across the bilayer act as CHANNEL proteins or CARRIER proteins to help move substances across the membrane

Question 21

What do extrinsic proteins act as?

Answer 21

Extrinsic proteins are partially embedded in the bilayer

These are involved in cell recognition

Question 22

What does fluid mosaic mean?

Answer 22

Fluid = molecules move around 
Mosaic = proteins floating amongst phospholipids so it's not just made of phospholipids

Question 23

Why is the arrangement the fluid mosaic model suggests ideal for cell membranes?

Answer 23

Such an arrangement is ideal for cell membranes as lipid bilayers tend to reseal themselves once disturbed or torn.

Question 24

There are additional chemical components that make up the membrane:

Answer 24

Glycolipids
Glycoproteins
Phospholipid
Cholesterol molecules

Question 25

What is the role of glycolipids?

Answer 25

Glycolipids play a part in COMMUNICATION BETWEEN CELLS and CELL TO CELL RECOGNITION

Question 26

What is the role of phospholipid?

Answer 26

Phospholipids act as a barrier to polar/charged particles

Phospholipids select what enters or leaves the cell

Question 27

What is the function of glycoproteins?

Answer 27

Glycoproteins have several functions:
- they act as surface antigens and are involved in cell recognition (enabling cells to distinguish self from non-self)
- cell to cell attachment - holds cells together in a TISSUE
They act as a receptor for HORMONES DRUGS TRANSPORT PROTEINS
- cell signalling

Question 28

What is the role of cholesterol molecules?

Answer 28

Cholesterol molecules are positioned within the bilayer

Cholesterol molecules help STABILISE the membrane by MAINTAINING FLUIDITY
Reducing permeability to polar/charged molecules e.g. After and ionic cannot pass easily

Question 29

What make up the GLYCOCALYX?

Answer 29

The glycoproteins and glycolipids make up the GLYCOCALYX

Question 30

What is the glycocalyx?

Answer 30

The glycocalyx is a carbohydrate base covering

that covers the outside of cells