UNIT 2 - B 2.1 - Cell Membranes Flashcards
What are two ways scientists gathered evidence to find the model of a cell membrane?
Through using electron microscopes and studying cell/their actions in various environments
What is the model of the cell membrane called?
The fluid mosaic model
What is the “backbone” of the membrane?
the phospholipid bilayer
What is each phospholipid composed of?
1 glycerol (3 carbons) 2 fatty acids and a highly polar alcohol attached to a phosphate group
Why are fatty acids not soluble in water?
Because they are non-polar
Why are phospholipids amphipathic?
Because their fatty acid tails are hydrophobic but the alcohol with the phosphate group is hydrophilic
Why is the membrane typically fluid/flexible?
Because the fatty acid tails don’t attract each other strongly
What maintains the overall structure of the membrane?
The relationship between the membrane’s chemical makeup and the chemical properties of water
Why would hydrophilic molecules, even small ones, find it hard to move through the membrane?
Because of the hydrophobic region in the middle of the bilayer
What is diffusion?
A type of transportation where particles move from a region of higher concentration to a region of lower concentration
What is an example of diffusion through cell membranes?
Oxygen has a higher concentration on the outside so it diffuses into the cell while carbon dioxide has a higher concentration inside the cell so it diffuses to the outside (respiration)
Where are proteins embedded in the membrane?
in the fluid matrix of the phospholipid bilayer
What are the two main types of proteins in the membrane?
integral proteins and peripheral porteins
Which type of membrane proteins shows an amphipathic character?
integral proteins
Where are peripheral proteins located?
on the surface of the membrane, both inner and outer
What are peripheral proteins often anchored to?
integral proteins
What are the types of proteins typically present in a cell membrane?
Hormone-binding, enzymatic, cell adhesion, cell-to-cell communication, channel forming, and pumps for active transport
What are hormone-binding proteins used for?
They have specific shapes to fit specific hormones which attach to the protein, then the protein changes shape resulting in a message being sent into the cell
What are enzymatic proteins used for?
they are grouped together so that a sequence of metabolic reactions (metabolic pathway) is catalysed
What are cell adhesion proteins used for?
They allow temporary or permanent connections (junctions) between cells
What are the two types of junctions?
gap junctions and tight junctions
What allows cell-to-cell communication proteins to distinguish between self and non-self material?
They have carbohydrate molecules attached which provides an identification label allowing for organisms to make these distinguishments
What do channel forming proteins do?
they span the membrane, providing passageways for substances to be transported through
What is involved in proteins acting as pumps for active transport?
the proteins shuttle a substance from one side of the membrane to the other by changing shape and they use energy in the form of ATP
What are the two general types of cellular transport?
passive transport and active transport
What is the main difference between active transport and passive transport?
active transport requires energy in the form of ATP but passive transport does not
When is passive transport taking place?
when a substance moves from a high concentration to a low concentration (down the concentration gradient)
Where does the source of energy for passive transport come from?
the kinetic energy of the molecules
Why must energy be used in active transport?
Because the substance is usually moving against the concentration gradient
What is an example of passive transport other than diffusion?
osmosis
What does osmosis involve the movement of?
Water across a partially permeable membrane
What is the concentration gradient allowing for osmosis a result of?
a difference in solute concentrations on either side of the membrane
A hypotonic solution has a lower concentration than what kind of solution?
hypertonic solution
Which direction does water move from?
Hypotonic to hypertonic
Why wouldn’t osmosis occur?
if isotonic solutions occur on either side of a partially permeable membrane
What are aquaporins?
protein channels which allow water molecules to pass through them
What is facilited diffusion?
a type of diffusion involving integral proteins
Which two types of proteins are involved in facilitated diffusion?
carrier proteins and channel proteins
How do carrier proteins transport substances from one side of the membrane to the other?
by changing shape
Which direction(s) can carrier proteins transport substances?
with the concentration gradient (facilitated diffusion) or against the concentration gradient (active transport)
What kinds of molecules can carrier proteins carry?
both water-soluble and insoluble molecules
How are channel proteins different from carrier proteins?
they have pores through which molecules of the right size and charge can pass
What allows channel proteins’ gates to open and close?
chemical or mechanical signals
What molecules can channel proteins carry?
Only water-soluble molecules
What allows cell membranes to be selectively permeable?
the presence of channel proteins and carrier proteins
What do the factors which facilitate diffusion depend on?
the concentration difference across the membrane, the number of carrier proteins actively involved in transport, and the number of channel proteins open
What does the transportation of molecules against a concentration gradient allow the cell to do?
to maintain interior concentrations of molecules that are different from exterior concentrations
How can active transport take place?
because of the highly selective proteins in the membrane that bind with the substance to be transported
What is an example of an active transport?
the sodium-potassium pump
What are sodium-potassium pumps especially important for?
neurons so that animals can respond to stimuli
What are the two major factors in how easily a substance can move passively across a membrane?
size and charge
What sort of substances will move across a membrane easily?
small and non-polar substances
What sort of substances do not move across a membrane easily?
polar or large or substances that are both
What are examples of substances that move easily across a membrane?
oxygen, carbon dioxide and nitrogen
What are examples of substances that have a hard time moving across a membrane?
chloride ions, potassium ions, sodium ions (due to charges), glucose, and sucrose (due to large size)
Why is the cell membrane selectively permeable to large, charged molecules?
Because they must travel through integral proteins
What are glycolipids in the cell membrane?
when a membrane phospholipids has a carbohydrate chain attached to it
What are glycoproteins in the cell membrane?
cell membrane proteins that have carbogydrate chains attached to them
Which side of the cell are carbohydrate chains found only?
the exterior, extracellular side
What are glycolipids and glycoproteins important for?
cell identification and cell adhesion
What are blood types A, B and O a result of?
carbohydrate chains
What do carbohydrate chains allow the body to do?
work out which cell belong to the body (self) and which cells are from the outside (non-self)
What would happen if the carbohydrate chains of a transplanted tissue or organ are not compatible?
rejection will occur- the reciever’s immune system will attack the foreign cells resulting in the transplant’s failure
What is glycocalyx?
a thin sugar layer made up of carbohydrate chains attached to proteins that can cover a cell
What are the functions of glycocalyx in animal cells?
cell to cell adhesion, cell to cell recognition and reception of various signalling chemicals
What are the functions of glycocalyx in bacterial and fungal cells?
adhesion and protection
What is the function of glycocalyx in plant cells?
to help anchor the plant’s cell membrane to the cell wall
What may the membrane’s consistancy be compared to?
the consistancy of olive oil
Where may cholesterol be found in animal cells’ membranes?
in the hydrophobic regions
What does cholesterol have a role in with the membrane?
determining the membrane’s fluidity
What would happen if cholesterol was not in the cell membrane?
The membrane wouldn’t be able to function at such a wide temperature range
How do cholesterol molecules help the membrane’s fluidity?
by interacting with the tails in the phospholipid bilayer
Since plant cells do not have cholesterol molecules, what do they depend on to have a proper membrane fluidity?
saturated or unsaturated fatty acids
What allows fluidity for the cell membrane?
because the heads of the phospholipids are the only things that can create hydrogen bonds with water and because hydrogen bonds are relatively weak, individual phospholipids and unanchored proteins are relatively free to move around
What do the double bonds within the fatty acid tails cause the molecules to become?
bent and less tightly packed and lower melting points
When do the cell membrane fatty acids have mostly saturated bonds?
when the surrounding temperatures are higher
What allows a denser arrangement of the phospholipid layer?
higher temps= more saturated bonds= straighter shape= denser arrangement of phospholipid layer
What does the membrane’s increased density allow for?
a stronger membrane and more able to be effective at higher temperatures
What types of organisms are more vulnerable to temperature changes?
single-celled organisms like bacteria
What are fatty acid desaturases?
a type of enzyme in bacterial membranes
What do fatty acid desaturases do?
speed up reactions that result in an increase in double bonds within the fatty acid tails
What does cholesterol in the membrane act to do at high temperatures vs low temperatures?
at high temperatures: stabilize membranes
at low temperatures: maintain membrane flexibility
Why is there more cholesterol in the plasma membrane than the endoplasmic reticulum membrane?
Because the plasma membrane is subjected to more extreme temperatures
How may large molecules and large amounts of material move across the plasma membrane?
through endocytosis and exocytosis
What’s the difference between endocytosis and exocytosis?
endocytosis allows macromolecules to enter the cell while exocytosis allows them to leave
What is the process of endocytosis?
When a portion of the plasma membrane is pinched off to enclose the material within a vesicle in the cell
Why do the ends of the membrane reattach after endocytosis?
Because of the hydrophobic and hydrophilic properties of phospholipids and the presence of water
What is exocytosis?
The process of endocytosis, but backwards
What is the first step of protein exocytosis?
protein produced by the ribosomes of the rough ER enters the lumen of the ER and is packed into a vesicle
What is the lumen?
The inner space of the ER
What is the second step of protein exocytosis?
the vesicle carrying the protein fuses with the cis side of the golgi apparatus
What is the third step of protein exocytosis?
The protein is modified as it moves through the golgi apparatus and exits on the trans face inside another vesicle
What is the fourth step of protein exocytosis?
the vesicle with the modified protein moves towards and fuses with the plasma membrane resulting in the secretion of the contents from the cell
What are gated channels?
channels which allow ions to pass through the cell membrane which open and close in response to chemical and electrical stimuli
What does movement of ions through channels control?
The electrical potential across the membranes
What types of cells especially have their electrical potentials controled by ions movement through channels?
nerve cells and muscle cells
What is an example of a neurotransmitter-gated ion channel?
nicotinic acetylcholine receptors
What are neurotransmitters?
chemicals that allow signals to pass between two nerves at junctions
What are the junctions called where signals pass between two nerves?
synapses
Where do neurotransmitters also function?
At the junctions between nerves and muscles
When do neurotransmitter-gated ion channels open?
When acetylcholine attaches to a nicotinic acetylcholine receptor
What are some of the positive ions that can pass through the neurotransmitter-gated ion channels when they are opened?
Na, K, and Ca
What do the positive ions passing through the neurotransmitter-gated ion channel cause?
the membrane potential to change so that an impulse is generated
How are our bodies’ responses possible?
nerve impulses carried along multiple connected neurons within the body
What can cause muscle movement?
When the neurotransmitter is released at the junction between a nerve and a muscle, the receptor opens and positive ions move allowing for muscle movement
What produces antibodies to nicotinic acetylcholine receptors?
The autoimmune disorder known as mysathenia gravis
What do the antibodies produced by mysathenia gravis do which makes incomplete muscle movement more common?
They bind to the receptors which reduces the person’s response to the neurotransmitter, acetylcholine
What are voltage-gated channel proteins opened by?
changes in membrane polarity
What are examples of voltage-gated protein carriers?
Positive sodium and potassium channels
Which channel in sodium and potassium channels opens first?
the sodium channel
What depolarizes the membrane of a neuron?
When the sodium channel opens and sodium ions move from the outside of the neuron to the inside
What happens after the potassium channels opens (slowly) and potassium ions move from the inside of the cell to the outside?
The membrane returns to its normal potential
What is the process of re-establishing membrane potential after depolarization?
Repolarization
What is the sodium-potassium pump an important example of?
Active transport
Where do animal cells have a higher concentration of potassium ions?
Inside the cells
Where do animal cells have a higher concentration of sodium ions?
Outside the cells
What does the higher concentration of positive sodium ions outside the cells than positive potssium ions inside the cell create?
A difference in charge across the membrane
What is a difference in charge across a membrane also called?
the membrane potential
What kind of cells is the membrane potential especially important to?
nerve cells
What does a nerve impulse take place as a result of?
sodium ions diffusing into the cell through specialized channels creating a change in charge
What is depolarization?
a change in charge
What repolarizes the cell?
potassium ions diffusing out of the cell
What does the sodium-potassium pumps maintain?
the membrane potential
What is the first stage of the sodium-potassium pump?
The pump protein with an attached ATP molcule binds to three sodium ions in the cell
What is the second stage of the sodium-potassium pump?
ATP is split after the binding of sodium ions which provides energy and leaves a phosphate attached to the carrier
What is the addition of phosphate called?
phosphorylation
When does ATP become adenosine diphosphate (ADP)?
When ATP carries out phosphorylation of the sodium-potassium pump and loses a phosphate
What is the third stage of the sodium-potassium pump?
The protein changes shape due to the phosphorylation and expells sodium ions out of the cell
What is the fourth stage of the sodium-potassium pump?
Two potassium ions from outside the cells bind to different regions of the protein which causes the release of the phosphate group
What is the fifth stage of the sodium-potassium pump?
The protein’s original shape is restored after it loses the phosphate group and the potassium ions are released inside the cell
How many of each ion enter/exit the cell during each cycle of the sodium-potassium pump?
three sodium ions leave, two potassium ions enter
What is indirect active transport?
it uses the energy produced by the movement of a molecule moving down a concentration gradient to transport another molecule against a concentration gradient
What is an example of indirect active transport?
the transportation of glucose into the cells lining the intestines of animals
Where is thier often a higher concentration of glucose?
inside the cell
What are also being transported while glucose is being moved?
sodium and potassium ions
What are the main steps in coupled transport such as the transportation of glucose with potassium and sodium ions?
- more sodium ions outside the cell than inside the intestinal cell
- sodium ions and glucose molecules bind to a specific transport protein on the extracellular surface
- sodium ions pass through the carrier to the inside of the cell down a concentration gradient with the carrier capturing the energy released by this movement
- the captured energy is used to transport the glucose through the same protein into the cell
What is the protein carrier that moves glucose and sodium into intestenal cells called?
sodium-dependent glucose transporter or sodium-glucose linked transporter
Where does the sodium-dependent glucose transporter also occur?
in the functional units of the kidney, nephrons
What is the sodium-dependent glucose transporter 2 responsible for?
most of the glucose reabsorption in the kidney
How does the SGLT1 decrease glucose in the urine?
In the kidney, it allows the uptake of glucose from the kidney filtrate
What allows for cell to cell adhesion interactions?
the plasma membrane
How do skin and muscle cells perform their function effectively?
by binding tightly to one another through adhesion
What is cell adhesion molecules involved in usually?
Cell connections
What do cell connections allow?
coordinated behavior and they have important structural functions
What do desmosomes do?
help form sturdy but flexible sheets of cells in certain organs
What are examples of organs where desmosomes create their sheets of cells?
heart, stomach, bladder
What do other types of cell connections involve?
channels formed between adjacent cells that allow small molecules and ions to pass between them
What do the channels involved in cell connections allow?
cells to join together and to communicate
What are plasmodesmata?
tubes connecting cytoplasm of adjacent cells
What prodcues plasmodesmata?
plant cells
What do plasmodesmata allow?
the exchange of materials especially water and smalle solutes between connected cells
