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Biology > 2.1.5 Biological Membranes > Flashcards

2.1.5 Biological Membranes Flashcards

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1
Q

Where are membranes found?

A
  • Around prokaryotic and eukaryotic cells
  • Around organelles
  • Double membranes around some organelles
  • Ingestion and secretion from cell
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2
Q

Functions of biological membranes at the surface of the cell

A
  • Keep cell contents together and separate from other cells
  • Communication between cells by protein receptors for hormones and other signalling molecules
  • allows body to determine foreign bodies (antigens)
  • Control the movement of substances
  • Active transport
  • Phagocytosis
  • Cell attachment
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3
Q

Functions of biological membranes within the cell

A
  • To isolate the nucleus
  • To separate organelle components from cell
  • Prevent disruptions of pathways and reactions
  • Allows attachment of ribosomes
  • Internal transport
  • Increase the SA
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4
Q

What is compartmentalisation and why is it important?

A
  • Containing reactions within cell
  • Vital as metabolism includes many different and often incompatible reactions
  • allows specific conditions needed for reactions to be contained
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5
Q

What makes up the majority of the cell surface membrane

A

Phospholipid molecules

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6
Q

How thick is a phospholipid bilayer

A

7-10 nm

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7
Q

What three formations can the phospholipid membrane form in

A
  • Micelle - individual units are wedge shaped
  • Bilayer - Individual units are cylindrical
  • Liposome - aqueous cavity inside
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8
Q

Why does a phospholipid membrane form in a bilayer

A
  • Phosphate group is charged and therefore interacts with water
  • Fatty acid tail is not charged and is hydrophobic
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9
Q

Structure of a phospholipid molecule

A

One molecule of glycerol, 2 fatty acid chains and one phosphate group

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10
Q

How do Carbon Carbon double bonds in the fatty acid chains affect the Phospholipid bilayer

A

Forms a kink in the fatty acid chain which therefore means molecules can pack less tightly and membrane is more fluid

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11
Q

What are intrinsic proteins

A

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

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12
Q

Channel Proteins

A
  • Intrinsic Protein
  • hydrophilic channel allows for passive movement of polar molecules and ion down a concentration gradient through membranes
  • held in place by the interactions with hydrophobic core
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13
Q

Carrier proteins

A
  • Intrinsic protein
  • Both passive transport and active transport into cells
  • often involves the shape of the protein changing
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14
Q

Glycoproteins

A
  • intrinsic protein
  • Embedded in the cell surface membrane with attached carbohydrate chains
  • They play a role in cell adhesion and receptors for chemical signals
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15
Q

Cell signalling

A

When the chemical binds to the receptor it elicits a response from the cell which may cause a response

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16
Q

Receptors for neurotransmitters

A

Binding to neurotransmitters triggers or prevents and impulse in the next neurone

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17
Q

Receptors for peptide hormones

A

Affect uptake and storage of glucose molecules

18
Q

Glycolipid

A
  • Intrinsic protein
  • Lipids attached to carbohydrate chains
  • Called cell markers / antigens
  • recognised by the immune system
19
Q

Extrinsic proteins

A
  • Present on one side of the bilayer
  • Often have hydrophilic R groups on their outer surfaces and interact with the polar heads of the phospholipids or the intrinsic proteins.
  • Can be present in either layer or some move between layers
20
Q

Cholesterol

A
  • Extrinsic protein
  • One hydrophilic and one hydrophobic end
    Regulates fluidity of membrane
  • Positioned between phospholipid molecules in bilayer
  • Prevent membranes becoming too fluid by adding stability
  • Prevent membranes becoming too solid by stopping phospholipid molecules grouping too closely and crystallising
21
Q

Factors affecting membrane structure

A
  • Temp - higher temp, higher ke, more fluid, permeability increases
  • Solvents - Organic solvents will dissolve membranes
22
Q

Definition of Diffusion

A

The net movement of particles from a region of higher concentration to lower concentration down a concentration gradient until equilibrium is reached

23
Q

Why is diffusion faster when the diffusion distance is smaller

A
  • particles move at high speeds and are constantly colliding which slows overall movement, shorter diffusion distance means less collisions take place
24
Q

What is the link between cells being microscopic and diffusion

A
  • much larger cell would slow rates of diffusion, reactions would not get to substrates they need or ATP quick enough for energy requiring processes
25
Q

factors affecting diffusion

A
  • Temp - higher temp = greater rate of diffusion
  • Concentration difference - greater difference = greater rate of diffusion
  • Thickness of membrane
  • SA of membrane
  • Size and type of membrane
26
Q

Why can’t hydrophilic molecules diffuse across membranes?
What’s an exception to this?

A
  • hydrophilic molecules such as ions and polar molecules due to the hydrophobic centre (hydrophobic molecules can diffuse rapidly across membrane)
  • Water is the exception to this as it is very small
27
Q

Facilitated diffusion

A

Diffusion across membranes of hydrophilic molecules via protein molecules - no interruption of Hydrophobic centre

28
Q

Carrier Proteins

A
  • Have a binding site for a specific chemical
  • When chemical binds, tertiary structure of protein changes bringing chemical across membrane where it is released
29
Q

Protein channels

A
  • Protein with a central pore lined with hydrophilic amino acids and contains water
  • Hydrophilic substances can pass through
30
Q

Why can protein channels not let all substances through?

A
  • Selective to only some substances
  • Need a trigger in order to open (chemical binding to protein channel or change in voltage)
31
Q

What is active transport

A

The movement of molecules/ ions in or out of a cell from a region of lower concentration to an e area of higher concentration
- Requires energy supplied by ATP and carrier proteins

32
Q

Process of Active Transport

A
  • On the inside of the cell, ATP binds to the carrier protein whilst the molecule / ion binds to the receptors in the channel of carrier protein on the outside
  • ATP is hydrolysed into ADP and Phosphate
  • Binding of the phosphate molecule opens up the inside of the cell releasing the molecule/ ion
  • Phosphate molecule recombines with ADP to form ATP and carrier protein returns to original shape
33
Q

Bulk transport

A
  • Form of active transport for large molecules too big for channel proteins
34
Q

Bulk transport examples

A
  • Endocytosis - bulk transport into the cell - Pinocytosis - bulk transport of liquids into cell
  • Exocytosis - bulk transport out of cell
35
Q

Endocytosis

A

Membrane bends inwards and pinches off to form a vesicle which can then travel through cytoplasm

36
Q

Exocytosis

A

Vesicle from eg: Golgi body moves and fuses with cell surface membrane which is then released outside of cell

37
Q

What is Osmosis

A

The net diffusion of water through a partially permeable membrane from a lower concentration of solutes and higher water potential to an area with a higher concentration of solutes and lower water potential passively

38
Q

What is water pressure

A

The pressure exerted by water molecules as they collide with a membrane or container - measured in Pa or kPa

39
Q

Water pressure of pure water

A

0kPa - this is the highest possible value and all solutions have a negative water potential

40
Q

Relation of kinetic energy to water potential

A

The more pure the water and so the higher the water pressure, the higher the kinetic energy in the water

41
Q

Effects of osmosis in Animal cells

A

haemolysis - When water moves into cell by osmosis: cell swells and bursts
Crenation - when water moves out of cell by osmosis: cell shrinks and shrivels

42
Q

Effects of osmosis in plant cells

A

Turgid: When water flows into a plant cell by osmosis: Hydrostatic pressure increases pushing cell surface membrane up to cell wall
Plasmolysis: When water moves out of a plant cell by osmosis: Reduction in the volume of the cytoplasm pulling cell surface membrane away from plant cell wall

Biology (8 decks)

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