Biological membranes parrt 2

Question 1

What is active transport

Answer 1

the movement of substances against their concentration gradient, from a low to high concentration across a cell membrane using carrier proteins and ATP

Question 2

What is endocytosis

Answer 2

bulk transport of molecules too large to pass through a cell membrane even via a channel or carrier proteins into a cell

Question 3

what is exocytosis

Answer 3

bulk transport of molecules too large to pass through a cell membrane, even via a channel or carrier proteins out of a cell

Question 4

describe how active transport works

Answer 4

• goes against the concentration gradient
• this is energy is provided by the hydrolysis of ATP, ATP is often described as the universal energy currency as all cells make use of it to supply their energy needs
• cells or organelles may need to accumulate more of a particular ion than they could do by simple or facilitated diffusion alone

Question 5

What do carrier proteins do

Answer 5

• have specific regions or sites that combine reversibly with only certain solute molecules or ions
• have a region that binds to and allows the hydrolysis of a molecule of ATP, to release energy and in this way they act as enzymes
• the energy helps the carrier protein changes its conformation shape and in doing so it carries the ion from one side of the cell membrane to another

Question 6

Describe bulk transport

Answer 6

• some cell need to transport large molecules and particles that are too large pass through the plasma membrane in or out
• they do this by bulk transport a process that requires energy form ATP

Question 7

What does endocytosis do

Answer 7

• this is how large particles may be brought into a cell
• they do not pass through the plasma membrane
• instead a segment of the plasma membrane surrounds and encloses the particle and brings it into the cell this is enclosed in a vesicle

Question 8

Name type of endocytosis

Answer 8

• phagocytosis - this involves the intake of solid matter

- pino(endo)cytosis - this is if the cells ingest liquids by endocytosis

Question 9

What is ATP used for endocytosis

Answer 9

• ATP is needed to provide energy to form the vesicles, and move them using molecular motor protein along cytoskeleton threads into the cell interior

Question 10

What is exocytosis

Answer 10

• how large molecules may be exported out the cells, they do not pass through the plasma membrane, instead a vesicle containing them is moved towards and then fuses with the plasma membrane

Question 11

How does exocytosis work

Answer 11

1. a membrane bound vesicle containing the substance to be secreted is moved towards the cell surface membrane
2. the cell surface membrane and the membrane of the vesicles fuse together
3. the fused site opens releasing the contents of the secretory vesicles
   - ATP is needed to fuse the membranes together as well as for moving the vesicles, a molecule of ATP is hydrolysed for every step that a motor protein takes along the cytoskeleton thread as it drags the vesicle

Question 12

what happens to the phospholipid bilayer when the temperature drops

Answer 12

• saturated fatty acids become compressed
• however there are many unsaturated fatty acids, making up the cell membrane phospholipid bilayer and as they become compressed the kinks in their tails push adjacent phospholipid molecules away, this maintains the membrane fluidity
• therefore proportions of unsaturated and saturated fatty acids within a cell membrane determine the membranes fluidity at cold temperatures
• cholesterol in the membrane also buffers the effect of lowered temperature to prevent a reduction in the membranes fluidity - this prevents the phospholipid molecules from packing together to closely because cholesterol molecules are in between groups of phospholipid molecules

Question 13

What happens to the phospholipid bilayer when temperature increases

Answer 13

• the phospholipids acquire more kinetic energy and move around more in a random way, this increases the membrane fluidity
• permeability increases
• effects the way that membrane-embedded proteisn are positioned and may function if some of the proteins that act as enzymes in a membrane drift sideways, this could alter the rate of reactions they catalyse
• as increase in a membrane fluidity may affect he infolding of the plasma membrane during phagocytosis
• an increase in membrane fluidity may also change the ability, of cells to signal to other cells by releasing chemicals often by exocytosis
• the presence of cholesterol molecules buffer the effects of increasing heat as it reduces the increase in membrane fluidity

Question 14

what happens to high temperature in proteins

Answer 14

high temperature cause the atoms within their large molecules to vibrate and this breaks the hydrogen bonds and ionic bonds that hold their structure together and they unfold
- their tertiary structure changes and cannot change back again when they cool, they are denatured

Question 15

what is underneath the plasma membrane

Answer 15

underneath the plasma membrane there are cytoskeleton threads these are made of proteins
- if membrane and cytoskeleton threads become denatured then the plasma membrane will begin to fall apart this will become more permeable as holes appear in it

Question 16

What will happen if membrane embedded enzymes cease to function

Answer 16

• they become denatured, if the shape of their active site changes slightly or enzymes move within the membrane the rate of reactions that they catalyse will be slowed

Question 17

What are the effects of solvents on phospholipids

Answer 17

• organic solvents such as acetone and ethanol will damage cell membranes as they dissolve lipids