biological membranes : the structure of cell membranes Flashcards
define fluid mosaic model
theory of cell membranes structure with proteins embedded in a sea of phospholipids
what does the cell-membrane form and what for ? (4 marks )
a barrier
- to separate the cell contents from the cell’s exterior environment
AND
- separate organelles from cytoplasm
AND
- they need to allow some molecules through in and out of the cell
what do some organelles have and what do they also form ?
cell membrane and a barrier
what does permeability refer to ?
the ability to let substances pass through
how does substances pass through the cell membrane ? (3 marks )
- some very small molecules simply diffuse through the cell membrane , in between its structural molecules
- some substances dissolve in the lipid layer and pass through
- other substances pass through special protein channels or are carried by carrier proteins
what are the cell-membranes described as and why ?
partially permeable because these membranes do not let all types of molecules pass through them
what does the component molecules of the cell membrane determine ?
- determines which molecules it allows through
what is the cell membrane referred to as ? (2)
plasma membrane / cell surface membrane
what is the external environment in terms of single-celled organisms ?
the environment is external surroundings
what is external environment in terms of multicellular organisms ?
each cell’s environment is the tissue fluid or cells surrounding it
what may the plasma membrane contain ?
enzymes involved in specific metabolic pathways
what does plasma membrane contain and why ? (A)
has antigens so that the organism’s immune system can recognise the cell as being ‘self’ and not attack it
what may the plasma membrane release and why ?
may release chemicals that signal to other cells
what may the plasma membrane contain and why ? (R)
contains receptors for such chemical signals
–> so is a site for cell communication OR signalling
- hormones and drugs may bind to membrane bound receptors
what may the plasma membrane be the site of ?
chemical reactions
why are there membranes around the organelles ?
so that organelles are able to perform its function
what happens in some organelles ?
metabolic processes occur on membranes
how does this occur in mitochondria ?
- the mitochondria has folded inner membranes called cristae
- this gives a large surface areas for some of the reactions of aerobic respiration + localise some of the enzymes needed for respiration to occur
how does this occur in chloroplasts ?
- the inner membrane is called thylakoid membranes - house chlorophyll
- on these membranes some of the reactions of photosynthesis occurs
how does this occur on epithelial cells ?
- some digestive enzymes on the plasma membrane of the epithelial cells - lines the small intestine
-these enzymes catalyse some of the final stages in the breakdown of certain types of sugars
who + when proposed the fluid mosaic model ?
in 1972-Singer + Nicolson
what did the model allow ?
the passage of molecules through the membrane
what did their structure explain ?
how cell membranes could be more dynamic and interact more with the cells environment
what did the fluid mosaic model propose ?
the fabric of the membrane consisted of a phopsholipid bilayer with proteins floating in it - making a mosaic pattern
what can the lipid molecules do and the proteins do ?
the lipid molecules can change places with each other + some of the proteins may move giving fluidity
what is the fabric of the membrane made up of ?
2 layers of phospholipid molecules
- their hydrophilic heads are in contact with the watery exterior or watery interior (cytoplasam)
- their hydrophobic tail regions are in the centre of the membrane away from water
draw and label the cell membrane
find in textbook :)
define glycolipid
lipid/phsopholipid with a chain of carbohydrate molecules attached
define gylcoprotein
protein with a chain of carbohydrate molecules attached
what are the types of protein channels within the membrane ?
channel , peripheral and carrier
what do some channel proteins act as ?
- have pores and acts as channels to allow ions , which have an electrical charge and are surrounded by water molecules to pass through
what do carrier proteins act as ?
- they are carriers and by changing the shape, carry specific molecules across the membrane
what do peripheral proteins acts as ?
- attached to the carrier proteins and function as enzymes antigens or receptor sites for complementary-shaped signalling chemicals such as hormones
why is cholesterol important for cell membranes ?
for helping regulate the fluidity of the membrane
- to maintain mechanical stability and resist the effects of temperature changes on the structure of the membrane
what is the total thickness of the cell membrane roughly ?
between 5 and 10nm
define glycocalyx
a sugary coating on the cell’s surface that protects the cell, helps it communicate, and allows it to be recognized by other cells
what does the protein channels and carrier of the neurons allow ?
entry and exit of ions to bring about the conduction of electrical impulse along their length
how is the myelin sheath formed ?
by flattened cells around them several times - giving several layers of cell membrane
what is the membrane formed of ?
20 % protein
76 % lipid
what does white blood cells contain and what does it enable them to do ?
contain special protein receptors that enable them to recognise antigens on foreign cells
-> usually from invading pathogens from tissue or organ plants
what does root hair cells in plants have and why ?
many carrier proteins
–> to actively transport nitrate ions from the soil into the cells
what is the inner membrane of the mitochondria formed and why ?
76 % protein
24 % lipid
–> their inner membrane contains many electron carriers that are made of protein , and hydrogen ion channels associated with ATP synthase enzymes
define intrinsic
that is located inside or is a natural, essential part of something
give an example of intrinsic in terms of bio ?
intrinsic proteins:
-are proteins that are embedded within the cell membrane
-span across the membrane or are firmly attached to it
define extrinsic
means something that is located outside or comes from outside a system or structure
give an example of extrinsic in terms of bio ?
extrinsic proteins:
- are proteins found on the outer or inner surface of the cell membrane but not embedded in it
- attach loosely to the membrane
