Chapter 1- Cells- Membranes

Question 0

Draw structure of a phospholipid

Answer 0

Martha.

Question 1

Draw and label the structure of membranes

Answer 1

Do it

Question 2

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
-what is the structure of a phospholipid? And what is this called?

Answer 2

Consists of a polar head (hydrophilic) made from glycerol and phosphate and 2 non-polar fatty acid tails (hydrophobic)
2) called amphipathic

Question 3

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What does hydrophilic and hydrophobic mean?

Answer 3

Hydrophilic- substance is attracted to water

Hydrophobic- are not attracted to water

Question 4

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
- fatty acid ‘tails’ don’t strongly attach one another membranes what does this allow?

Answer 4

Fluid or flexible which allowed animal cells to have variable shapes and also allows process of endocytosis

Question 5

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
Why do phospholipids arrange in a double layer?

Answer 5

As when phospholipids are mixed with water the phosphate heads are attracted to the water but the tales are attracted to each other not the water

Question 6

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What is the primary function of membranes?

Answer 6

To form a barrier which ions and hydrophilic molecules cannot easily pass

Question 7

What does cholesterol do in phospholipids?

Answer 7

1) Role in determining membrane fluidity which changes the temp
2) disrupts the regular packaging of the hydrocarbon tails of phospholipid molecules so prevents them from crystallising and behaving as a solid
3) restricts fluidity of membrane
4) reduces permeability to hydrophilic particles such as sodium ions and hydrogen ions
5) due to shape can help membranes curve to become concave which helps formation of vesicles during endocytosis

Question 8

What does proteins create in phospholipids?

Answer 8

Creates extreme diversity in membrane function

Question 9

Wha role does intergralproteins have in phospholipids?

Answer 9

Are hydrophobic and are embedded in the hydrocarbon chains in the centre of the membrane- many are transmembrane- they extend across the membrane, with hydrophilic parts projecting through regions

Question 10

What does peripheral protein remain bound to in phospholipids?

Answer 10

Hydrophilic so remain on surface- some have a single hydrocarbon chain attached to them which is inserted into the membrane, anchoring the protein to the membrane surface

Question 11

What are the 6 functions of membrane proteins?

Answer 11

1) hormone binding site (hormone receptor)
2) immobilised enzymes with the active site on the outside
3) cell adhesion to form tight junctions between groups of cells in tissues and organs
4) cell to cell communication
5) channels for passive transport to allow hydrophilic particles across by facilitated diffusion
6) pumps for active transport which use ATP to move particles across the membrane

Question 12

What are the 2 transport mechanisms in regard to functions of membrane proteins?

Answer 12

Protein channels (facilitated) and protein pumps (active)

Question 13

definition of diffusion

Answer 13

Net movement of particles from a high region concentration to a low concentration

Question 14

Definition of osmosis

Answer 14

Net movement of water molecules across a semi-permeable mebrane from a high region of low solute concentration to a high concentration

Question 15

Definition of simple diffusion

Answer 15

Small, non-polar molecules can freely diffuse across the membrane - passive diffusion across semi-permeable membrane

Question 16

Definition of facilitied diffusion

Answer 16

Larger, polar substances (ions, macromolecules) can’t freely diffuse and require assistance of transport proteins (carrier proteins/channel proteins to help their movement)

Question 17

Explain the role of protein pumps and ATP in active transport across membranes:
- what is active transport?

Answer 17

Is the passage of materials against conc. gradients (low–>high)

Question 18

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What does active transport require?

Answer 18

Requires use of protein pump which uses ATP energy to translocate the molecules against the gradient

Question 19

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What does hydrolysis of ATP causes?

Answer 19

A conformational change in the protein pump takes place using the energy from ATP resulting in forced movement of substances

Question 20

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of
Protein pumps are what for given molecules? Which allows them to?

Answer 20

Are specific for given molecules allowing them to regulate movement

Question 21

(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
Draw protein channel, Carrier protein and protein pump

Answer 21

Lallalal

Question 22

(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
-how does a polypeptide get to the ER?

Answer 22

There designed for secretion and contain an initial target sequence which directs the ribosome to the ER

Question 23

(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
What happens when polypeptide reaches ER?

Answer 23

Continues to be synthesised by ribosomes into lumen of ER, where signal sequence is removed from Nascent chain

Question 24

(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
Where is polypeptide chain transferred to after ER and via what?

Answer 24

To the Golgi apparatus via a vesicle which forms from a budding membrane

Question 25

(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
Finally the polypeptide is transferred from the Golgi apparatus to what? Via what? And what happens to it?

Answer 25

Via a vesicle to the plasma membrane where it the protein is secreted

Question 26

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
- what is membrane principally held together by?

Answer 26

The relatively weak hydrophobic associations between phospholipids

Question 27

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
- what does the associations between weak Hydrogen bonds and phospholipids allow membranes to do?

Answer 27

Allows membranes to have fluidity/flexibility as the phospholipids can move to some extent–> allows for breaking/remaking of membranes allowing larger substances access in and out of cell

Question 28

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is endocytosis and what are in the vesicles?

Answer 28

1) Process in which large substances enter cell without travelling across the plasma membrane
2) contain water and solute a from outside the cells, or larger molecules needed by the cell which can’t pass through the plasma membrane

Question 29

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
How does it work? (Endocytosis)

Answer 29

1) Vesicles can be formed by pinching off a small piece of the plasma membrane of cells.
2) the vesicles is formed in the inside of the plasma membrane
3) it contains material that was outside the cell

Question 30

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What are the main 2 types of endocytosis?

Answer 30

Phagocytosis and pinocytosis

Question 31

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is the process of phagocytosis?

Answer 31

Process by which solid substances (eg food particles) are ingested

Question 32

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is pinocytosis?

Answer 32

Process by which liquids/solutions (eg dissolved substances) are ingested by cell

Question 33

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is exocytosis?

Answer 33

Process in which large substances exit without passing across plasmic membrane

Question 34

(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
How does exocytosis work

Answer 34

Vesicles fuse with plasma membrane expelling their contents into extracellular environment

Question 35

Explain full process of endocytosis through to protein syntheses to exocytosis

Answer 35

1) ENDOCYTOSIS–> part of plasma membrane is pulled inwards, a droplet of fluid becomes enclosed and vesicles is pinched off, vesicles then move through the cytoplasm carrying their contents
2) proteins are synthesised by ribosomes and enter rough endoplasmic reticulum
3) vesicles bud off from the rER and carry the proteins to the Golgi apparatus
4) Golgi apparatus modifies the proteins
5) vesicles bud off from the Golgi apparatus and carry the modified proteins to the plasma membrane
6) EXOCYTOSIS –> vesicles fuse with the plasma membrane, the contents of the vesicles are expelled, the membrane flattens out again

Question 35

What protein channels?

Answer 35

Channels are holes with a very narrow diameter. The walls of the channel consist of protein- the diameter and the chemical properties of the channel ensure that only one type of particle passes through