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Biology > - Module 2.1.5 Biological Membranes > Flashcards

- Module 2.1.5 Biological Membranes Flashcards

1
Q

What are the 6 main membranes in a plant cell?

A

1- Plasma membrane
2- Tonoplast membrane
3- Outer Mitochondrial Membrane
4- Inner Mitochondrial Membrane
5- Outer Chloroplast membrane
6- Nuclear envelope
Membranes are flexible and able to break and fuse together easily.

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2
Q

What is compartmentalisation?

A

Formation of separate membrane-bound areas in a cell. Vital to a cell as metabolism includes many incompatible reactions. Eg a lysosome may carry digestive enzymes at pH 4.8 and the rest of the cell may be at 7.2.

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3
Q

Role of the plasma membrane

A

Separates the contents of the cell from the outside environment.
Partially permeable, only some substances can cross.
Site of cell communication (cell signalling).
Attachment to the cytoskeleton in some organisms - can help support the cell and maintaining it’s shape.
Site of some chemical reactions.

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4
Q

What is cell signalling?

A

Communication between cells and cell recognition. A molecule released by one cell, attaches to another and causes a response.

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5
Q

Structure of the plasma membrane.

A

Membranes are formed from a phospholipid bi-layer. Hydrophobic fatty acid tails point inwards and form a hydrophobic core, hydrophilic phosphate heads point outwards.
The phosphate group is negatively charged, making the head polar hydrophilic. The fatty acid tails are uncharged and non-polar and hydrophobic.

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6
Q

What happens when a phospholipid is submerged in water?

A

It forms a micelle.

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7
Q

How do phospholipids control movement of substances?

A

They act as a barrier to most substances.
Small, non-polar molecules like oxygen and carbon dioxide diffuse rapidly across the membrane.
Small, polar molecules such as water and urea struggle to diffuse across- it would be very slow.
Charged particles (ions) are unlikely to diffuse across a membrane at all.

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8
Q

What are the components of a cell membrane?

A

Various proteins and lipids particular to each cell type.
Phospholipid bi-layer.
Glycoprotein
Glycolipid
Cholesterol
Protein molecules (intrinsic and extrinsic)

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9
Q

What is cholesterol?

A

It is a lipid that stabilises the membrane. It binds to the fatty acid tails and makes them more compact, reducing the fluidity of the membrane.
It also reduces the permeability of the membrane to charged particles and prevents crystalisation of the phospholipids.

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10
Q

What are glycolipids and glycoproteins?

A

Glycoproteins - cell membrane proteins that have a carbohydrate chain attached on the extracellular side.
Glycolipids are lipids that have carbohydrate chains attached, also on the outer surface of the membrane.

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11
Q

What is the function of glycolipids and glycoproteins?

A

Carbohydrate chain allows them to act as receptor molecules - this allows them to bind with substances at the cell surface.
Some act as cell markers or antigens, for cell identification (allows immune system to determine self or non self)

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12
Q

What different receptor types are there?

A

Signalling receptors, bind to hormones and neurotransmitters.
Receptors in endocytosis
Receptors involved in cell adhesion and stabilisation.(cell adhesion allows cells to group and form tissues)

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13
Q

What are intrinsic proteins?

A

Span the width of the membrane (embedded through both layers)
Transport water soluble charged particles (carrier and channel proteins)

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14
Q

What are protein channels?

A

A hydrophilic passage-way for charged substances (and polar molecules) to passively diffuse down the concentration gradient.

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15
Q

What are carrier proteins?

A

Change shape to move substances from one side of the membrane to the other. This can be down the concentration gradient (passive) and against it (active).

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16
Q

What are extrinsic proteins?

A

Aka peripheral proteins,
Can be either side of the bilayer
Some can move between layers
Normally have hydrophilic R groups on their surface to interact with phospholipid heads

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17
Q

What is the relationship between increasing temperatures and membranes?

A

If you increase temperature the kinetic energy increases. The membrane becomes more fluid and breaks down/denatures at high temps. Loss of structure increases membrane permeability. Channel and carrier proteins can become denatured.

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18
Q

What happens to the permeability of membranes at low temperatures?

A

Membrane permeability decreases.
Phospholipids vibrate much less, pack together tightly and and rarely provide pathways for molecules to pass through.

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19
Q

What happens to membrane proteins at low temperatures?

A

Protein channels remain in place, but transporter proteins may not work as well bc low temps make it difficult for the cells to provide ATP for active transport. (respiration is controlled by enzymes)

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20
Q

What happens to the ions and molecules at a low temp that stops them from passing through the membrane as much?

A

Molecules and ions move around less, so fewer hit the membrane and pass through.

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21
Q

What can determine the membrane’s permeability at lower temps?

A

The proportions of saturated and unsaturated acids. Some organisms, like fish, plants and microorganisms can change the proportions to adjust.

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22
Q

What solvents are less polar than water, or non polar? What do they do?

A

Alcohol is less polar, benzene is non-polar.
Organic solvents dissolve the phospholipid bi-layer and the cholesterol which disrupts their function and causes them to become more permeable. This is why alcohol is used in antiseptic wipes, to dissolve the bacteria membranes.

23
Q

What are the factors affecting diffusion?

A

Membrane thickness
Surface area
Temperature
Concentration gradient.

24
Q

What is simple diffusion?

A

Diffusion where there is no membrane involved.

25
Q

What is diffusion across a membrane?

A

Diffusion when a membrane is involved.

26
Q

What are the factors affecting simple diffusion?

A

Temperature
Concentration gradient/difference

27
Q

What are the factors affecting diffusion across a membrane?

A

Temperature
Concentration gradient
Surface area
Membrane thickness

28
Q

What are the key three adaptations of alveoli?

A

Large surface area
Lining that is one cell thick
Very good blood supply

29
Q

What are villi?

A

Tiny structures that increase the surface area of the small intestine.

30
Q

What are the important features of the villi?

A

Wall is one cell thick, ensure only a short distance for absorption to happen by diffusion and active transport.
Network of blood capillaries
Internal structure called lacteal

31
Q

What is the lacteal in the villi?

A

Transports fatty acids and glycerol away from the small intestine in the lymph.

32
Q

What kind of flow do fish have over their gills?

A

Countercurrent flow, blood and water travel in opposite directions. To maintain the concentration gradient. Means that they can extract oxygen at almost 3x the rate of humans.

33
Q

Describe countercurrent flow.

A

As blood flows in the opposite direction to water it always has a lower oxygen concentration than the water. This ensures that diffusion happens at every point in the gills.

34
Q

What is facilitated diffusion?

A

Large or polar molecules pass through the membrane with the help of a protein.
Proteins are specific to the molecule that they carry.
It’s a passive process.
Either channel proteins or Carrier proteins.

35
Q

How are channel proteins used in facilitated diffusion?

A

Ions and small molecules.
Act like a pore
Often can be opened and closed.
Most common type in facilitated diffusion.

36
Q

How are carrier proteins used in facilitated diffusion

A

Larger molecules.
Molecules attach to the protein and it changes shape to transfer the molecule across the membrane.
Some are used in facilitated diffusion, some for active transport.

37
Q

What is partially permeable vs selectively permeable?

A

Partially permeable = membranes that allow some molecules through.
Selectively permeable = membranes that allow specific molecules through.

Generally membranes are partially permeable but membranes with proteins are selectively.

38
Q

Define active transport.

A

Movement against the concentration gradient.
Uses a carrier protein and ATP.
Each carrier protein is specific.

39
Q

What are the 6 steps of active transport?

A

1- Ion to be transported binds to the receptor on the carrier protein.
2- Inside the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
3- Phosphate binding to the protein causes it to change shape, opening up to the inside of the cell
4- Ion then released to the inside of the cell
5- Phosphate molecule is released from the protein and reforms ATP.
6- Carrier protein returns to it’s original shape.

40
Q

What is bulk transport?

A

Form of active transport.
Large molecules like enzymes, hormones and whole cells (bacteria) are too large to move through proteins so are moved in and out of cells by bulk transport.

41
Q

What types of bulk transport are there?

A

Exocytosis
Endocytosis (pinocytosis - liquids, phagocytosis - solids)

42
Q

What is the definition of osmosis?

A

The net movement of water molecules across a partially permeable membrane, from a region of high water potential to low water potential.

43
Q

What is water potential?

A

The tendency of water molecules in a system to move.

44
Q

What is the value of pure water’s water potential? What is this like compared to solutions?

A

Pure water has the highest water potential at 0kPa. Solutions have lower water potential and it has a negative value.

45
Q

What are the two things that water potential determines?

A

The direction and rate of movement of water.

46
Q

What are the units of hydrostatic pressure?

A

kPa

47
Q

What happens in animal cells when in a solution with higher water potential?

A

Cell surface membranes cannot stretch to withstand increased pressure. So the cell bursts, cytolysis.

48
Q

What happens in ANIMAL CELLS when in a solution with lower water potential?

A

They lose water and undergo crenation.

49
Q

What are hypertonic, isotonic and hypotonic solutions?

A

Hypertonic is one that has lower water potential than the cell, so there is net movement of water out of the cell.
Isotonic is when water potential in the solution and the cell are the same, there is no net movement of water.
Hypotonic is when the solution has a higher water potential than the cell, so there is net movement of water out of the cell.

50
Q

What is turgor?

A

Pressure against the cell walls.

51
Q

What happens when turgor pressure increases? (plant cell)

A

It resists further entry of water into the cell, the cell is turgid.

52
Q

What happens when a PLANT CELL is placed in a solution with a lower water potential than it’s own?

A

Water is lost by osmosis, the cell becomes plasmolysed.

53
Q

What are plasmolysed, flaccid and turgid cells?

A

Plasmolysed cells are cells that have lost water and shrunk.
Flaccid cells are cells with normal levels of water.
Turgid cells are cells that have had more water enter the cell so are swollen.

54
Q

How is the kidney and osmosis related?

A

In mammals, maintaining a constant blood solute potential is a major function of the kidney that relies on the process of osmosis.

Biology (20 decks)

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