Cell membrane (1st year) Topic 2 Flashcards

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1
Q

What is the plasma membrane?

A

The plasma membrane of the cell separates the internal contents of the cell from its external environment. It only allows specific substances to enter or leave the cell.

It is differentially permeable

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2
Q

Mention some functions of the plasma membrane.

A

1) It separates the contents of the cell from its external environment.
2) Communicates with other cells.
3) Regulates the exchange of substances in and out of the cell between the cytoplasm and its external environment.
4) Chemical reactions occur on it.
5) It acts as a receptor site to recognize external stimuli.

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3
Q

What is the plasma membrane made up of?

A

Phospholipids

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4
Q

What are phospholipid molecules made up of ?

A

Hydrophilic polar phosphate heads and hydrophobic non-polar fatty acid tails.

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5
Q

How do phospholipid molecules arrange themselves within the cell?

A

In a single layer they arrange themselves.The hydrophilic phosphate head spread over the surface of the water, whilst the hydrophobic fatty acid tails arrange themselves away from the water,forming a bilayer.

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6
Q

What can we also find on the surface of the plasma membrane?

A

Glycolipids,glycoprotein,cholesterol, proteins

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7
Q

What is a glycolipid?

A

carbohydrate + lipid
contains polar and non-polar parts
Also contains carbohydrate side chains which is used for cell signalling.

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8
Q

What is a glycoprotein?

A

carbohydrate + protein
can be amphipathic (having both polar and non-polar regions). Also contains carbohydrate side chains used for cell signalling

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9
Q

What is cholesterol?

A

Slightly similar to lipids.
It is slightly polar at one end

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10
Q

What can we call the plasma membrane instead of a phospholipid bilayer?

A

The fluid mosaic model

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11
Q

What are micelles?

A

Micelles are spherical structures that form in water which has its hydrophilic phosphate head molecules pointing outward (water-loving),whilst its hydrophobic fatty acid tails pointing inward (water-hating). These structures are important for the absorption of fats in living organisms. They form if there are phospholipids present in large amounts.

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12
Q

What are polar molecules?

A

Electrons are unevenly distributed, due to the difference in electronegativity between the atoms. Polar molecules never mix with non-polar molecules.

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13
Q

What are non-polar molecules?

A

Electrons are evenly distributed. No electronegativity between the atoms,therefore there are no charges.

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14
Q

What is freeze-fracturing?

A

This technique has allowed us to better understand how proteins fit into the phospholipid bilayer. First cells are rapidly frozen ,then the surfaces are cut with a sharp metal blade, and this allows the insides to be examined.

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15
Q

Do phospholipid molecules stay still in the cell?

A

No,they are constantly moving which means they are fluid.

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16
Q

Differentiate between saturated and unsaturated fatty acid tails.

A

The fatty acid tails in the plasma membrane can be either saturated or unsaturated. When fatty acid tails are unsaturated,they are more fluid and they move more. The more unsaturated a fatty acid tail is,the more fluid it is. Unsaturation means that there is the presence of double bonds. If a fatty acid tail is bent,it is because it is unsaturated.If it is straight it means that it is saturated.

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17
Q

Mention the different proteins that can be found on the plasma membrane

A

Integral (intrinsic) proteins: embedded within the membrane)
Transmembrane proteins (proteins that span the width of the entire membrane
Extrinsic (peripheral) proteins: attached to the membrane’s surface

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18
Q

What is the main function of cholesterol in the plasma membrane?

A

To avoid the phosopholipids from sticking to eachother,therefore making them more fluid. Cholesterol also makes membranes flexible and stable.Also reduces the escape of polar molecules through the membrane.

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19
Q

Can the proteins within the membrane have hydrophilic and hydrophobic regions?

A

Yes,some parts of a protein can have hydrophilic regions and other parts can have hydrophobic regions within the same protein.

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20
Q

How can we further classify these types of proteins? Specifically the transmembrane.

A

Channel proteins and carrier proteins

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21
Q

What are carrier and channel proteins?

A

They are proteins which are responsible in the selective transport of polar molecules and ions across the membrane through facilitated diffusion or active transport.

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22
Q

Can you mention some functions of these proteins within the plasma membrane?

A

They can be used as receptor molecules to act as receptor sites for cell signalling between cells. For example hormones are chemical messengers which circulate in the blood and bind to specific target cells which have the correct antigens.
Proteins also take part in energy transfer systems in process like photosynthesis and respiration.

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23
Q

What is an antigen?

A

A cell identity marker. For example glycolipid or glycoprotein.

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24
Q

Draw a diagram of a phosopholipid bilayer,showing cholesterol,protein with labelling

A
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25
Q

Cells need essential substances like glucose,oxygen,amino acids etc and need to get rid of toxins like carbon dioxide. How do these material pass into and out of the cell through the plasma membrane? Mention 4 transport mechanisms.

A

Diffusion
Osmosis
Active transport
Bulk transport (endocytosis or exocytosis)

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26
Q

Which of these 4 transport mechanisms are passive and which ones use energy?

A

Passive: Diffusion
Osmosis
Energy needed: Active transport and Bulk transport

27
Q

What is an ion?

A

An ion is an atom which is losing or gaining an electron.Therefore it is a charged particle.

28
Q

Some molecules or ions are small enough to squeeze and pass through the cell membrane by simple diffusion such as water molecules,oxygen and carbon dioxde. Define Diffusion.

A

Diffusion is the movement of molecules from a region of high concentration to a region of low concentration until an equilibrium is reached. (Molecules are evenly spread out)

29
Q

What is a concentration gradient?

A

The difference between the 2 regions of diffusion. (The one which has the most particles and the one which has the less particles)

30
Q

What is a solution made up of ?

A

A solute and a solvent. The solvent dissolves the solute making the solution.

31
Q

Mention 3 factors which affect the rate of diffusion.

A

1) Rate of diffusion decreases rapidly with distance: diffusion is effective if short distances are present.
2)The greater the surface area,through which diffusion is taking place,the greater the rate of diffusion. (the larger the cell,the smaller the surface area,which means that diffusion wouldnt be as effective.This limits cell size.
3)The steepness of the diffusion gradient: the steeper the gradient,the faster is the rate of diffusion. This is ideal for efficiency.

32
Q

Some molecules and ions like glucose,amino acids,or glycerol,or sugars are too large and are repelled by the hydrophobic region of the membraneand need other methods of transport to enter the membrane.What is facilitated diffusion?

A

Facilitated diffusion is the movement of molecules from a region of high concentration to a region of low concentration across a membrane, with the help of a transport protein.

33
Q

Therefore which proteins do these substances make use of the cross the membrane?

A

Channel proteins and carrier proteins. These proteins have a hydrophilic environment which allows the entry of these substances to pass through the membrane by facilitated diffusion.

34
Q

What are the “gated ion channels” known as?

A

Channel proteins

35
Q

What is their main function? (Gated ion channels)

A

Transport proteins which have a fixed shape and allow the passage of ions are called ion channels.

The ion channels can exist in either an open or a closed state.

Allow the passage of ions.

36
Q

What is the main function of carrier proteins?

A

Exist in 2 states : “ping and pong” (the protein rapidly alternates between the 2 shapes ping and pong.
Change their shape often
The binding site faces outwards

Allow the passage of molecules

37
Q

What is osmosis?

A

Osmosis is a special kind of diffusion which only involves water molecules. Osmosis occurs through a barrier which is semi-permeable,which only allows small water molecules and not other big molecules like sugar molecules.

38
Q

Define osmosis

A

Osmosis is the movement of water molecules from a dilute solution to a concentrated solution through a semi-permeable membrane

39
Q

What is a dilute solution?

A

A solution which has a lot of water molecules.

40
Q

What is a concentrated solution?

A

A solution which has few water molecules.

41
Q

What happens when the dilute solution and the concentrated solution are separated by a semi-permeable membrane?

A

Water molecules will diffuse from the region where there is a lot of free water molecules to the region where there is a few water molecules.

42
Q

What do we call a membrane which allows all substances to pass through?

A

Permeable membrane

43
Q

What do we call a membrane which does not allow substances to pass through?

A

Non-permeable

44
Q

Define isotonic solution and explain what happens to a plant cell and an animal cell in this type of solution and describe the terms that we give them.

A

An isotonic solution is a solution in which the concentration of the solutes is the same both inside and outside of the cell.
(50 % solute 50% water) No net effect will be seen (normal)
Animal cell: Normal
Plant cell: Flaccid
Water will diffuse in and out of the cell normally and not net effect will be seen.

45
Q

Define hypertonic solution and explain what happens to a plant cell and an animal cell in this type of solution and describe the terms that we give them.

A

A hypertonic solution is a solution in which a higher concentration of solute is present than the inside of the cell. This will cause the water inside of the cell to move out,which will cause the cell to shrink,to decrease the higher concentration of solute in the enviroment.
Animal cell: shriveled/it shrinks
Plant cell: Plasmolysed
In plant cells,the water will move out from the vacuole by osmosis,and the cell membrane will detach from the cell wall.
Animal cell: for example in red blood cell Crenation happens. The water in the red blood cell will move out which will cause the volume to decrease and the cell membrane to shrink

46
Q

Define hypotonic solution and explain what happens to a plant cell and an animal in this type of solution and describe the terms that we give them.

A

A hypotonic solution is a solution in which the solution will have a lower concentration of solute in the outside environment that inside of the cell. This will cause water to move into the cell which causes the cell to swell.
Animal cell: burst/swells/lyses
Plant cell: Turgid
In plant cells water will continue to move into the vacuole but it will not burst due to strong cells walls.
In animal cells for example a red blood cell Haemolysis occurs. This is because water willenter the red blood cell by osmosis which will cause the volume to increase causing the cell to burst with the escape of haemoglobin

47
Q

Define active transport

A

In active transport,movement of molecules takes place from a region of low concentration to a region of high concentration against a concentration gradient,with the help of a carrier protein and energy from ATP.

48
Q

When does active transport happen?

A

It happens when a substance in higher concentration should enter the cell the membrane stops it because it is harmful

49
Q

Why is active transport beneficial?

A

This is because it gives the cell more control over which substances should enter the cell. If diffusion would be the only method by which materials could enter the cell,then the cell would have too many substances in it and would have no control of what the cell needs the most and even harmfoul substances could enter it,so active transport gives the cell more control on what the cell really needs.

50
Q

True or false, the plasma membrane has control on what enter or leaves the cell thanks to active transport even when the substances are present in high concentrations it can allow these substances to not enter (no entry of substances) It is going against the principles of diffusion,this is called active transport

A

True

51
Q

The cells that carry out active transport do not have a lot of mitochondria,true or false?

A

False

52
Q

What is the sodium potassium pump?

A

The sodium potassium pump is a carrier protein which spans the membrane from one side to another. This sodium pump is coupled with a potassium pump which actively moves potassium ions in the cell with the help of ATP. ATP changes into ADP which causes the carrier protein to change shape.

53
Q

How many sodium and potassium ions are exchanged between the inside and the outside of the cell?

A

3 sodium ions move out and 2 potassium ions move in

54
Q

Why is the sodium potassium pump important?

A

1) it keeps the electrical activity of nerve cells and muscle cells.
2) Controls the osmotic balance of animal cells
3) Drive active transport of substances like sugars and amino acids

55
Q

What are endocytosis and exocytosis?

A

These are active processes involving the bulk transport of materials through membranes either into cells (endocytosis) or out of cells (exocytosis)

55
Q

How does endocytosis happen?

A

Occurs by an infolding or extension of the cell surface membrane to form a vesicle or a vacuole

55
Q

What are the 2 types of endocytosis?

A

Phagocytosis and Pinocytosis

55
Q

Mention some characteristics of phagocytosis

A

Material is taken up in solid form.
Some phagocytes specialize in phagocytosis ex:some white blood cells engulf bacteria

56
Q

Mention some characteristics of pinocytosis

A

Material is taken up in liquid form
Vesicles formed are very small

56
Q

What is exocytosis?

A

The reverse process of endocytosis.
This is when waste materials are removed from cells and useful chemicals like enzymes are secreted

57
Q

Mention some examples where simple diffusion takes place.

A

Food is mostly absorbed by the intestine in this way,or when gases move in and out of red blood cells or in leaves

58
Q

Mention some examples where osmosis takes place.

A

Water moves into amoeba by osmosis or when water moves into or out of plant cells.

59
Q

Mention some examples where active transport takes place

A

Glucose is absorbed by active transport through the small intestines,and in plants root hair cells have protein carriers that pump substances into the hair cells by active transport.