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Biological molecules Flashcards

1
Q

What is the role of membranes within cells?

A

To separate the different areas within cells (organelles) from each other and the cytosol. COMPARTMENTALISATION.

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2
Q

what are the roles of membranes at the

surface of cells?

A

1) Creating a partially permeable membrane between the contents of the cell from their environment.
2) A site for chemical reactions.
3) A site for cell signaling.

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3
Q

Define Compartmentalisation.

A

The formation of separate membrane -bound areas in a cell.

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4
Q

What makes up plasma membranes?

A

A phospholipid bilayer made of two layers of phospholipids.

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5
Q

What makes up a phospholipid?

A

A hydrophilic phosphate head made up of phosphorous and oxygen and 2 hydrophobic tails made up of long fatty acid chains.

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6
Q

Why are hydrophobic tails and hydrophilic heads important in the phospholipid bilayer?

A

Cells normally exist in aqueous environments with the inside and outside of cells usually being aqueous. The hydrophilic heads will then make up the outer layer of the membrane with the hydrophobic tails gathered in the centre.

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7
Q

Who proposed the Fluid Mosaic Model (FMM)?

A

American Scientist and singer Nicolson built upon an earlier bilayer model.

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8
Q

Whys is the model called the FMM?

A

The phospholipids are free to move relative to each other (fluid), with proteins embedded throughout in different shapes, sizes and positions like the tiles of a mosaic.

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9
Q

What are the two types of membrane proteins in the cell surface membrane.

A

Intrinsic and extrinsic proteins.

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10
Q

What are intrinsic proteins also known as?

A

Integral proteins or transmembrane proteins.

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11
Q

What keeps intrinsic proteins in place?

A

They have amino acids with hydrophobic R groups on their surface which interact with the hydrophobic core of the membrane ( made of fatty acids) to keep them in place.

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12
Q

Give 2 examples of intrinsic proteins involved in transport across the membrane.

A

Channel proteins and carrier proteins.

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13
Q

How do channel proteins work?

A

They provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient to the other side of the membrane.

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14
Q

How do carrier proteins work?

A

They alter their shape to transport substances down a concentration gradient (passive transport) and against a concentration gradient (active transport).

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15
Q

What are glycoproteins?

A

Intrinsic proteins that are embedded on the cell surface with carbohydrate chains of different lengths attached to their surface. They also play a role in cell adhesion.

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16
Q

What is cell adhesion?

A

When cells join together to form tight junctions in certain tissues.

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17
Q

How do glycoproteins work as cell receptors?

A

When a chemical binds to the glycoprotein it elicits a response from the cell (a direct response or the triggering of a cascade of events).

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18
Q

What is cell signalling or cell communication?

A

A response or cascade of events caused by the binding of a chemical ( neurotransmitters, drugs or hormones) to a receptor on the cells surface (glycoprotein).

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19
Q

Give two examples of cell signalling or cell communication in Module 5?

A

1) Receptors for neurotransmitters in a cholinergic synapse.

2) Receptors for peptide hormones (including insulin or glucagon).

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20
Q

What are glycolipids?

A

Lipids with a carbohydrate (sugar) chain known as cell markers or antigens used in the immune system to recognise cells as self or foreign.

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21
Q

What are extrinsic proteins also know as?

A

Peripheral proteins

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22
Q

Where are extrinsic protein located?

A

They are found in one side of the bilayer usually having hydrophilic R groups on their outer surface that will interact with polar heads of the phospholipids or intrinsic proteins. They can be found within either layer of the bilayer and some oven move across he 2 layers.

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23
Q

What is cholesterol

A

A lipid with a hydrophobic and as well as a hydrophilic end.

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24
Q

What is the function of cholesterol?

A

It regulates the fluidity of membranes by adding stability to membranes without making them too rigid. Cholesterol stops the membrane becoming rigid by not allowing the phospholipids to cluster together and form crystals.

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25
Where are cholesterol molecules located?
Positioned between phospholipids in the bilayer, the hydrophilic end interacts with the ends and the hydrophobic end with the tails pulling them together.
26
If temperature is increased what happens to the phospholipids in the bilayer?
The phospholipids will gain more kinetic energy ad begin to move more. This will cause the membrane to become fluid and loose its structure, if temperature continues to increase the membrane will break down completely.
27
How does loss of structure affect the permeability of the membrane?
It increases permeability making it easier for molecules to cross the membrane to enter and leave the cell.
28
Why are solvents and polarity important in the formation of the bilayer?
Water is a polar solvent and the bilayer is formed by keeping the hydrophobic tails away from the water, the polar phosphate heads interact with the water instead.
29
What do organic solvents do to the phospholipid bilayer and why?
As many organic solvents are less polar than water (like alcohols) or no polar at all (like benzene) they will dissolve the bilayer disrupting the cells.
30
Why are alcohols used in antiseptic wipes?
An alcohol will dissolve the membrane of the bacteria killing it and reducing the risk of an infection.
31
What is the difference between the affects that strong and pure alcohols have on membranes vs less concentrated solutions of alcohols?
Strong and pure alcohol will dissolve the membrane disrupting the woe structure whereas less concentrated solution of alcohol will enter the cell and between the phospholipids in the bilayer disrupting the fluidity of the membrane.
32
Give an example of where it can be important to have an intact cell membrane.
The transmission of nerve impulses via neurones. When nerve membranes are distorted nerve impulses take longer to be transmitted or are not transmitted at all.
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36
What is diffusion?
The net or overall movement of particles from a region g high concentration to a region of lower concentration.
37
When does diffusion stop?
As it is a passive process it will continue until there's is equilibrium between the two regions (no difference in concentrations).
38
How is diffusion an example of passive transport?
Diffusion uses the energy from the natural motion of particles (kinetic energy) rather than energy from another source.
39
Why does diffusion occur?
Diffusion happens because the particles in gasses and liquids are moving causing an uneven distribution of particles to become more even. When equilibrium is reached the movement does not stop but the distribution and direction of movement is equal.
40
Why is diffusion faster over shorter distances?
The collisions that particles have when moving slows down the rate of diffusion, a smaller number of collisions will take place when crossing a shorter diffusion distance.
41
What does diffusion distance have to do with the size of a cell?
Cells are microscopic as a larger cell would lead to slower rates of diffusion no allowing reactions to gain their substrates in time and not allowing ATP to energise the necessary functions of the cell.
42
How does temperature affect the rate of diffusion?
The higher the temperature the faster the rate of diffusion, this is because particles will gain more Kinetic Energy as the temperature increases allowing them to move faster.
43
what determines the steepness of a concentration gradient?
The concentration difference between the region of high concentration and the region of low concentration.
44
How does the steepness of the concentration gradient affect the rate of diffusion?
the steeper the concentration gradient greater (the difference in concentration between the two regions) the faster the rate of diffusion. This is because the overall movement from region of high concentration to region of low concentration will be greater.
45
What is simple diffusion?
Diffusion in the absence of a barrier.
46
What types of molecules can pass through the phospholipid bilayer easily?
Non polar molecules can move freely down a concentration gradient through the bilayer. Polar molecules can also pass through the membrane but only at a very small rate, smaller polar molecules move faster than larger ones.
47
What types of molecules cannot pass through the phospholipid bilayer easily?
Polar molecules can also pass through the membrane but only at a very small rate, smaller polar molecules move faster than larger ones. Ions cannot pass through the bilayer easily as the hydrophobic core of the membrane repels charged substances (ions).
48
Why are membranes described as partially permeable?
Different substances can pass through the bilayer with different levels of difficulty, some cannot pass through at all.
49
What are the 2 factors that affect the rate of diffusion across a membrane?
1) Surface area | 2) Thickness of membrane
50
How does surface area affect the rate of diffusion across a membrane?
The larger the area of an exchange surface the higher the rate of diffusion.
51
How does membrane thickness affect the rate of diffusion across a membrane?
The thinner the exchange surface the higher the rate of diffusion.
52
What is facilitated diffusion?
Diffusion across a membrane through protein channels.
53
Why are membranes with protein channels selectively permeable?
The protein channels are specific to one molecule or ion only.
54
What is a limiting factor that is specific to facilitated diffusion?
The number of channel proteins present, the more proteins available the higher the rate of diffusion.
55
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration.
56
What are the two things required for active transport?
1) Energy - Energy from metabolism supplied by ATP | 2) Carrier proteins
57
Describe the process of active transport via a carrier protein?
1) The molecule or ions outside the cell bind to receptors in he cannel of the protein. 2) ATP binds carrier protein from inside the cell, it is hydrolysed into ADP and a phosphate. 3) The binding of the phosphate with the carrier protein causes it to change its shape opening up the inside of the cell. 4) The molecule or ion enters the cell. 5) the phosphate is released from the protein and recombines with ADP to form ATP. 6) The carrier protein returns to its original shape
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59
What is bulk transport?
A form of active transport, large molecules such as enzymes, hormones, bacteria and other cells are too large to move through proteins so are transported across the membrane in bulk.
60
What is endocytosis?
The bulk transport of material into a cell.
61
What are the 2 types of endocytosis?
1) Phagocytosis for solids | 2) Pinocytosis for liquids
62
Describes the process for endocytosis?
1) The cell surface membrane invaginates (bends inwards) when contact is made with the material. 2) The membrane enfolds the material until the membrane fuses making a vesicle. 3) The vesicle pinches off and moves further into the cytoplasm to where the material is needed within the cell.
63
What is exocytosis?
The bulk transport of material out of a cell.
64
Describe the process for exocytosis?
1) A vesicle (usually formed by the Golgi apparatus) containing the material to be take out moves towards the cell surface membrane. 2) The vesicle fuses with the cell surface membrane and the material is released outside the cell.
65
When during endocytosis and exocytosis is energy from ATP required?
1) The movement of vesicles. 2) Changing the shape of cells to engulf materials. 3) Fusing the cell surface membrane and vesicles.
66
What is osmosis?
The diffusion of water particles across a partially permeable membrane. OR The movement of water particles from an area of high water potential to an area of low water potential across a partially permeable membrane.
67
Use solute, solvent and solution correctly in a statement.
A solute is a substance dissolved in a solvent forming a solution.
68
What is water potential (WP) ?
The pressure exerted by particles as they collide with a membrane or container.
69
What is the water potential of pure water.
0 Pascals. This is the highest value possible for WP, adding a solute decreases WP below zero therefore all solutions have a negative WP.
70
How does osmosis affect the volume of a solution?
It will lead to an increase in the volume of the solution,, if the solution is in a closed system it will also lead to an increase in hydrostatic pressure.
71
What is cytosis?
The breaking of the cell surface membrane and the bursting of the cell.
72
What causes cytosis?
An increase in hydrostatic pressure that the cell surface membrane cannot withstand.
73
What is crenation?
The 'puckering' of the cell surface membrane caused by a reduction in the volume of the cell.
74
What causes crenation?
Water molecules moving out of a cell via osmosis after being placed in a solution with a lower water potential than he cytoplasm.
75
What is turgor?
The pressure against the cell wall from the cell surface membrane.
76
What causes turgor?
Water entering a plant cell and increasing hydrostatic pressure on the cell surface membrane due to the plants inability to regulate the conditions around its cells.
77
What is a plasmolysed plant cell?
A plant cell whose cell surface membrane is pulled away from the cell wall due to water leaving the cell via osmosis.

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