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Flashcards in Membranes Structure and Function Deck (25)
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State 5 roles of membranes within cells and at the surface of cells.

- Membranes around organelles divide the cells into different compartments, acting as a barrier between the organelle and the cytoplasm.
- Membranes can form vesicles to transport substances between different areas of the cell.
- Membranes within cells are also partially permeable so they can control which substances enter and leave the organelle.
- Membranes within organelles act as barriers between the membrane contents and the rest of the organelle.
- Membranes within cells can be the site of chemical reactions, the membranes of some organelles are folded increasing their surface area and making chemical reactions more efficient.


Define the term “compartmentalisation” and explain why it is useful to the cells.

The formation of separate membrane bound areas in a cell is called compartmentalisation. It is vital to a cell as metabolism includes many different and often incompatible reactions. Containing reactions in separate parts of the cell allows the specific conditions required for cellular reactions.


Define the term “partially permeable”.

Membranes that allow some substances to cross but not others.


Define the term “cell signalling”.

A complex system of intercellular communication.


Define the term “phospholipid bilayer”.

It is an arrangement of phospholipids found in cell membranes, the hydrophilic phosphate heads form both the inner and outer surface of a membrane, sandwiching the fatty acid to form a hydrophobic core.


Explain what is meant by “fluid” and “mosaic” in the “fluid mosaic model of membrane structure”.

Fluid: all phospholipids and membrane proteins can move around because they are not bonded to eachother.
Mosaic: the phospholipids and the proteins form a pattern when viewed from above.
Fluid Mosaic model: model of the structure of a cell membrane in which phospholipids within in the phospholipid bi-layer are free to move and proteins of various shapes and sizes are embedded in various positions.


Define the term“glycoprotein”.

Extrinsic membrane proteins with attached carbohydrate molecules varying in lengths and shapes


Define the term “phospholipid”.

It is a modified triglyceride where one fatty is replaced by a phosphate group.


Define the term “cholesterol”.

A lipid containing a hydrocarbon tail attached to a hydrocarbon ring and a hydroxly group.


Define the term “glycolipid”.

Cell surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes.


Define the term “channel protein”.

Intrinsic Membrane proteins that provide a hydrophilic channel through a membrane that allows passive movement of polar molecules and ions down the concentration gradient.


Define the term ''carrier protein''.

Membrane proteins that actively play a part in the transport of substances through a membrane using energy from ATP.


Define the term ''intrinsic proteins''.

Transmembrane proteins that are embedded through both layers of a membrane e.g. channel proteins or carrier proteins. They have amino acids with hydrophobic R-groups on their external surfaces which interact with the hydrophobic core of the membrane keeping them in place.


Define the term ''extrinsic proteins''.

Peripheral proteins that are present one side of the bi-layer only e.g. enzymes, proteins that bind cytoskeleto to membrane. They normaly have hydrophilic R-groups on their outer surfaces which interact with the polar heads of the phospholipids or with the intrinsic proteins.


Define the term ''receptor protein''.

Usually glycoproteins, they detect the presence of an extra cellular chemical and cause a response in the cell.


Draw a diagram of a phospholipid, label its components and annotate with their properties.

- Two hydrophobic fatty acid tails
- One hydrophilic (polar) phosphate head


State the role of phospholipids.

Form the phospholipid bi-layer. Phospholipids bi-layers are perfectly suited as membranes because the outer surface of the hydrophilic phosphate heads can interact with water.


State the role of cholesterol.

Regulates the fluditity of membranes, they are positioned between the phosopholipids in a membrane bi-layer with hydrophilic end with the heads and the hydrophobic end interacting with the tails, pulling them together.


State the role of glycoproteins.

Intrinsic proteins. They play a role in cell adhesion and work as receptors for chemical signals. When chemicals bind to the receptor it elicits a response from the cell. This may cause a direct response or set off a cascade of events inside the cell. This is cell communication or signalling.


State the role of glycolipids.

They are cell markers or antigens and can be recognised by the cells of the immune system as self- or non-self.


Define the term “cell adhesion”.

Glycoproteins play a role in cell adhesion when cells join together to form tight junction in certain tissues.


Explain the importance of membrane bound proteins in chemical reactions.

They have to be particular positions for chemical reactions to take place.


Describe the effect of changing temperature on the permeability of cell membranes.

Higher temp = more permeable. When a cell is heated up the phospholipids have more kinetic energy so they move further apart. This makes the membrane more fluid and lose its structure. This makes it easier for particles to cross. If temperature continues to increase the cell will break down completely.
Channel and carrier proteins will be denatured at higher temps - as they denature membrane permeability will be affected,


Describe the effect of solvent (e.g. ethanol) concentration on the permeability of cell membranes.

A higher solvent concentration = more permeable cell.
Non-polar alcohol molecules can enter the cell membrane and the presence of these molecules between the phospholipids disrupts the membrane. When the membrane is disrupted it becomes more fluid and more permeable.


Describe a method using a colorimeter to investigate the effect of temperature (or ethanol concentration) on the permeability of cell membranes.

1. Place five equally sized pieces of beetroot into a 100ml water bath of distilled water.
2. Increase the temperature of the bath by 10oc intervals.
3. Take samples of the water containing the beetroot five minutes after each temperature is reached.
4. Measure the absorbance of each sample using a colorimeter with a blue filter.
5. Repeat with fresh beetroot pieces and calculate a mean.