Topic 2 - Cell membrane and phopholipids

Question 1

what is the structure of a phospholipids

Answer 1

1 glycerol,2 x fatty acids,1 phosphate group

Question 1

which part of a phospholipid is hydrophilic and which part is hydrophobic

Answer 1

head is hydrophilic - interacts with water
tail is hydrophobic - made up of hydrocarbons

Question 2

what happens when many phospholipids interact with water

Answer 2

they create spherical clusters with the tails facing inwards to shield themselves from water with their glycerol heads - forms a bilayer

Question 3

what does the phospholipid bilayer make up

Answer 3

cell surface membrane

Question 4

features of phospholipid bilayer

Answer 4

-it is selectively permeable, it allows small, unpolar molecules to cross
- It has a hydrophobic barrier, won’t allow large unpolar molecules to cross

Question 5

why is a fluid mosaic model named this way

Answer 5

membrane is fluid and has a mosaic like arrangement of proteins

Question 6

how much mass of a membrane is made by proteins

Answer 6

45% - varies between 25% and 75%

Question 7

what kind of proteins are in the membrane

Answer 7

integral and peripheral proteins

Question 8

where are integral proteins and what do they do

Answer 8

they span the width of the protein
They help transport substances that cannot diffuse across the membrane but are still vital to the cell’s functioning

Question 9

where are peripheral proteins and what do they do

Answer 9

confined to the inner or outer surface of the membrane
May be free or bound to an integral protein, peripheral proteins on the extracellular side of the membrane act as transmitters, or are involved in cell recognition

Question 10

what are glycoproteins

Answer 10

protein molecules with polysaccharides attached

Question 11

what factors affect membrane fluidity

Answer 11

cholesterol and temperature

Question 12

how does cholesterol affect membrane fluidity

Answer 12

• Vital in controlling membrane fluidity
• The more cholesterol, the less fluid - more rigid and the less membrane permeable
• Has a hydrophobic region so its able to create a further barrier to polar substances moving through its membrane
• Binds to the hydrophobic tail of a phospholipid, causing them to pack more closely together which restricts their movements
• Helps maintain shape of animal cells, eg RBCs

Question 13

how does temperature affect membrane fluidity

Answer 13

• Temp below 0 degrees - increases permeability, phospholipids are packed closely together and membrane is rigid, channel and carrier proteins denature, ice crystals form which could pierce the membrane
• Temps between 0 and 45 - phospholipids can move and aren’t as tightly packed, membrane = partially permeable, as temp increases phospholipids move more because they have more energy
• Temps above 45 - phospholipid bilayer starts to melt, water inside cell expands - putting more pressure on membrane, channel and carrier proteins denature

Question 14

what is the definition of facilitated diffusion

Answer 14

The overall net movement of molecules of molecules and ions from a region of high concentration to a region of low concentration down a concentration gradient

Question 15

what type are some proteins that involved in facilitated diffusion

Answer 15

carrier proteins

Question 16

what happens when an ion/molecule binds to a carrier protein

Answer 16

it changes shape and therefore the molecule is able to cross the molecule

Question 17

what is diffusion also called and why

Answer 17

passive transport - uses no energy

Question 18

what is the definition of active transport

Answer 18

movement of molecules/ions from an area of low concentration to an area of high concentration against a concentration gradient - uses energy

Question 19

where does active transport get its energy from

Answer 19

the energy transfer molecule ATP

Question 20

what is the full name of ATP

Answer 20

adenosine triphosphate

Question 21

how is ATP formed and how is it used

Answer 21

• It is formed during respiration, the breakdown of energy store molecules
• The substance to be transported across the membrane binds to the carrier protein
  One phosphate group is removed from ATP by hydrolysis and ADP forms
  A small amount of energy is required to break the bond holding the end phosphate in ATP
  Once removed, phosphate group becomes hydrated
  A lot of energy is released as bonds form between water and phosphate

Question 22

how is a phosphate group removed from ATP

Answer 22

hydrolysis

Question 23

what is the full name of ADP

Answer 23

adenosine diphosphate

Question 24

how much energy is required to break the bond holding the end phosphate

Answer 24

not much

Question 25

what happens to the phosphate group that is removed and how much energy is released

Answer 25

it is hydrolysed
a lot of energy is released

Question 26

what is active transport also referred as

Answer 26

pumps - the pumping of substances across membranes that occurs in every cell

Question 27

what is a glycolipid

Answer 27

Glycolipids are lipids with a carbohydrate attached by a glycosidic bond

Question 28

what processes are used when a large molecules/large quantities of molecules need to be transported across a membrane

Answer 28

the bulk transport is achieved by endocytosis or exocytosis

Question 29

what is exocytosis

Answer 29

Release of substances (usually proteins or polysaccharides) from the cell

Question 30

what is a vesicle

Answer 30

small membrane bound sacs containing substance

Question 31

what is the process of exocytosis

Answer 31

Vesicles fuse with the cell membrane and the contents are released.

Question 32

what is endocytosis

Answer 32

Is the reverse of exocytosis

Question 33

what is an example of exocytosis

Answer 33

insulin is released to blood by exocytosis

Question 34

what is the process of endocytosis

Answer 34

• Substances are taken into the cell by the creation of a vesicle from the cell surface membrane
• Part of the membrane engulfs the solid or liquid material to be transported
• In some cases, the substance which is to be absorbed, attaches itself to a receptor in the membrane and is then absorbed by endocytosis

Question 35

what is an example(s) of endocytosis

Answer 35

how cholesterol is taken in by cells
how white blood cells ingest bacteria