Chapter 5 - Plasma Membranes Flashcards

1
Q

Characteristics of cell surface membrane

A

Made up of phospholipids
That have hydrophilic heads and hydrophobic tails
That allow non polar molecules through and some small polar molecules ( water)

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2
Q

What is the fluid mosaic model

A

Idea that phospholipids are free to move like a fluid

The proteins embedded in the bilayer vary in shape size and position like tiles in a mosaic

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3
Q

What is the structure of glycoprotein

A

Protein with a branching carbohydrate portion of a protein which acts as a recognition site for chemicals

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4
Q

Structure of glycolipid

A

Carbohydrate chain attached to the membrane, not a protein recognition site

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5
Q

What is an intrinsic protein (examples)

A

Transmembrane proteins that are embedded through both layers of a membrane
Amino acids have hydrophobic r groups that interact with hydrophobic core

Channel protein
Carrier protein
Glycoprotein

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6
Q

Extrinsic proteins

A

Peripheral proteins that are only present on either side of the bilayer

Have hydrophilic r groups that interact with the polar heads

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7
Q

What is the role of cholesterol

A

Regulates the fluidity of the membrane

Adds stability - doesn’t let them touch and crystallise, pulls them together

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8
Q

How does temperature affect the membrane structure?

A

Phospholipids are always moving
Increases kinetic energy
Moves faster - loses structure - increases fluidity
Loss of structure increases permeability - easier for particles to cross

At high temperatures carrier and channel proteins will denature - involved in transport of proteins

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9
Q

How does solvents affect membrane structure

A

Organic substances that are less polar than water or non polar will dissolve membranes

Non polar alcohol can enter membrane and disrupt the structure of phospholipids - making the membrane more fluid and permeable

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10
Q

A practical to investigate the permeability of membranes

A

Beetroot

Put equal amounts of beetroot in tube and increase the water bath at intervals of ten - measure absorbance of each sample 5 minutes after temperature is reached
Using colorimeter with blue filter
Pigment is releases from cell

More pigment molecules absorb more light, light transmitted decreases

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11
Q

What is diffusion

A

The net movement of particles from a region of high concentration to a region of low concentration

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12
Q

Factors affecting the rate of diffusion

A

Temperature
- more kinetic energy - move at faster speeds

Concentration difference
- overall movement from high to low is larger

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13
Q

Practicals to find the rate of diffusion and surface area

A

Distance travelled / time

Volume filled / time

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14
Q

Factors that affect rate of diffusion across membranes

A

Surface area
- larger the area of a exchange surface

Thickness of membrane
- when particles move over a long distance, collisions are more likely, which will slow the rate of reaction

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15
Q

What is facilitated diffusion

A

Diffusion across a membrane through a protein channel

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16
Q

What is the rate of facilitated diffusion dependent on

A
Temperature 
Concentration gradient 
Surface area 
Cell membrane thickness 
Number of channel proteins present
17
Q

Practical to investigate the factors affecting diffusion rates in model cells

A

Placed in different concentrations/ temperatures

Using dialysis tubing with pores

  • water can pass through
  • glucose can - use Benedict’s solution to test
  • starch can’t - iodine test
18
Q

What is active transport

A

The movement of molecules from a region of low concentration to a region of high concentration
Requires energy and carrier proteins - atp

19
Q

How does active transport happen with Carrier proteins

A
  • molecule binds to receptors on channel / carrier protein ( outside of cell)
  • (inside of cell) atp binds to carrier protein and is hydrolysed into Adp and a phosphate
  • when phosphate binds to carrier protein the protein changes shape, opening up to the inside of the cell
  • molecule is released into the cell
  • phosphate is released and recombined to adp to make atp
  • Carrier protein returns
20
Q

What is bulk transport

A

Another form of transport where large molecules or cells are moved into or out of a cell by enocytosis and exocytosis

Enzymes , hormones , bacteria

21
Q

What is endocytosis

A

Bulk transport of material into cells

  • phagocytosis - solids
  • pinocytosis - liquids
  • the cell surface membrane invaginate, bends inwards when it comes into contact with material
  • membrane enfolds material until fuses and forms a vesicle
  • vesicles pinches off and moves into the cytoplasm to transfer material
22
Q

What is exocytosis

A

Vesicles formed by the Golgi apparatus moves towards and fuses with the cell surface membrane - contents of vesicles are released

  • energy atp is required to move the vesicles along the cytoskeleton, changing the shape of cells to engulf and fusion of membrane
23
Q

What is water potential

A

The pressure exerted by water molecules as they collide with a membrane or container

Pure water = 0 water potential
The more concentrated the more negative the water potential

24
Q

What are the effects of osmosis on plants and animals cells

A

The increase of volume into a cell results in the increase in hydrostatic pressure

25
Cytolysis
Animal cells swell with water - increases hydrostatic pressure - the cell surface membrane can't stretch to withstand the pressure
26
Crenation
Reduction in the volume of the cell | Shrivel
27
What do animal cells have to prevent cytolysis and crenation
Have control mechanisms - blood plasma Makes sure they are surrounded by isotonic solutions
28
Why do plant cells have cell walls
They can't control the water potential around them | Need strong cellulose walls
29
Turgid
Plant cells swell Increased hydrostatic pressure pushes the membrane against the rigid walls
30
Plasmolysed
Plant cells shrivel Reduction in volume of cytoplasm Pulls the plasma membrane away from cell wall
31
What do channel proteins do
Hydrophilic channel Allows passive movement of polar molecules and ions Down a concentration gradient Held in position by interactions between hydrophobic r groups on outside of protein and hydrophobic core of membrane
32
Carrier proteins
Passive and active transport Involved changing of shape
33
Glycoproteins
Have receptors That elicits response from the cell Cell communication/signalling - responds to its environment Cell adhesion - when cells join to form tight junctions in tissues
34
Insulin glucagon example for glycoproteins
Receptor for hormones insulin and glucagon Affect uptake and storage of glucose by cells
35
Glycolipid
Cell markers/ antigens Can be recognised by the immune system as self or non self
36
What can pass through a phospholipid bilayer
Non polar molécules - oxygen Small Polar molecules - water / glucose Only Not ions
37
Partially permeable Selectively permeable
Only allows certain types of molecules through but not all Plasma membranes with protein channels that only allow specific substances to cross