Cells (4) Transport Across Cell Membranes Flashcards
The cell surface membrane surrounds cells and forms what?
The boundary between the cell cytoplasm and the environment.
Phospholipids form what?
Phospholipid bilayers
The heads are hydrophillic or hydrophobic?
Hydrophillic
The tails of the phospholipid are what?
Hydrophobic
The ____________ tails point towards the ______ of the cell membrane, _________ by the water on both sides.
Hydrophobic, centre, repelled
A function of the phospholipid in the membrane is to allow lipid-soluble substances to do what?
Enter and leave the cell
A function of the phospholipid in the membrane is to ______ water-soluble substances entering and leaving the cell.
Prevent
A function of the phospholipid in the membrane is to make the membrane what?
Flexible and self-sealing
Some proteins occur in the surface of the bilayer and never completely move across it, they act to either give mechanical support to the membrane or, (in conjuction with glycolipids) what?
Cell receptors for molecules such as hormones.
Protein channels form what?
Water-filled tubes to allow water-soluble ions to diffuse across the membrane
Carrier proteins that bind to ions or molecules like glucose or amino acids, do what?
Change shape in order to move these molecules across the membrane
Proteins provide what?
Structural support
Proteins act as channels transporting what?
Water-soluble substances across the membrane
Proteins allow active transport across the membrane through what?
Carrier proteins
Protein form cell surface receptors, why?
For identifying cells
Proteins help cells do what?
Adhere together (stick together?)
Proteins act as receptors. For example, what? (relates to moods)
Hormones
Cholesterol molecules occur within the what?
The phospholipid bilayer of the cell surface membrane
Cholesterol adds what to the membranes?
Strength
Cholesterol molecules are very what to prevent water loss and dissolved ions from the cell?
Hydrophobic
Cholesterol pill together the fatty acid tails of the phospholipid molecules, limiting their what?
Movement and that of other molecules but without making the membrane as a whole too rigid.
Cholesterol reduces lateral movement of molecules including??
Phospholipids
Cholesterol make the membrane less…
Fluid at high temperatures
Cholesterol prevents _______ of water and dissolved ions from the cell.
Leakage
What are glycolipids?
Glycolipids are made up of a carbohydrate covalently bonded with a lipid
The carbohydrate portion extends from the phospholipid bilayer into what?
The watery environment outside the cell where it acts a a cell surface receptors for specific chemicals
Glycolipids act as recognition sites. True or false
True
Glycolipids help maintain what?
Stability of the membrane
Glycolipid help cells to attach to one another and form?
Tissues
What are glycoproteins?
Carbohydrates chains that attached to many extrinsic proteins on the outer surface of the cell membrane.
Glycoproteins acts a recognition site. True or false
True
Glycoproteins help cells to attatch cells to one another and and so forms?
Tissues
Glycoproteins allows cells to recognise one another, for example, lymphocytes can do what?
Can recognise an organisms own cells
Generally molecules cannot freely diffuse across the cell surface membrane as they are not soluble in lipids and therefore what?
Cannot pass through the phospholipid bilayer
Generally molecules cannot freely diffuse across the cell surface membrane as they too large to pass through what of the membrane?
Channels
Generally molecules cannot freely diffuse across the cell surface membrane as they are of the same charge a the charge on the what?
Protein channels and even if they are small enough to pass through, they are repelled.
Generally molecules cannot freely diffuse across the cell surface membrane as they are polar and can have a difficulty doing what?
The non-polar hydrophobic tails in the phospholipid bilayer
Why is the cell surface membrane fluid?
The individual phospholipid molecules can move relative to another, giving it a flexible structure that is contally changing shape.
Why is the cell surface membrane mosaic?
The proteins embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as the stones oflr tiles of a mosaic
what is diffusion?
The net movement of molecules or ions from a region of high concentration to one where the concentration is lower until evenly distributed
What is facilitated diffusion?
a passive process which relies on the inbuilt motion of diffusing molecules where protein channels or carrier proteins are involved.
Protein channels allow specific water-soluble ions to do what?
Pass through the membrane
Protein channels are selective, each opening in the presence of a specific ion. True or False
True
What happens the protein channel if the specific ion is not present?
Will remain closed
Ions bind to the protein to change its shape in a way that close to one side and opens it to the other side. True or False
True
What do carrier proteins do?
When a molecule like glucose binds to a carrier protein causing it to change shape in such a way that the molecule released to the inside of the membrane.
What is osmosis?
Osmosis is the passage of water molecules from a region of high water potential to a region of lower water potential through a selectively permeable membrane
What is a solute?
Any substance that is dissolved in a solvent like water
What is water potential units?
kPa (kilopascals)
If you add a solute to pure water, what happens to the water potential
it will be lowered
The water potential of a solution (water and solute) must always be less than 0, that is, a negative value. True or False
True
Water will move by osmosis from a region of higher (less negative) water potential to one of lower (more negative) water potential. True or False
True
If a red blood cell is placed in pure water, it will what?
Absorb water by osmosis because it has a lower water potential.
If a red blood cell is placed in a solution with a water potential lower than its own, what will happen?
Water leaves by osmosis and the cell shrinks and becomes shrivelled
If the protoplast is pushed against the cell wall what does this mean?
It is turgid
If the protoplast is beginning to pull away from the cell wall, what does this mean?
incipient plasmolyisis is occuring
If the protoplast is completely pulled way from the cell wall, what does this mean?
It is fully plasymolysed
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
In active transport, ATP is used for two things what are they?
1) directly moving molecules
2) individually moving molecules using a concentration gradient
In active transport, a molecule or ion binds to what of the carrier protein?
Receptor sites
On the inside of a cell/organelle, ATP binds to the protein causing it to what?
Split into ADP and inorganic phosphate molecule, resulting the protein molecule to change shape and opens to the opposite side of the membrane
In active transport, As the molecule is releases to the other side of the membrane, the phosphate molecule is released from the protein (protein - orginal shape) and what happens next?
The phosphate molecules then recombines with the ADP to form ATP during respiration
In active transport, Occasionally, the molecule or ion is moved into a cell/organelle at the same time as a different onr is being removed from it. What is an example of this
Sodium potassium pump
The epithelial cells lining the ileum posses what?
microvilli
What are microvilli?
Finger like projections of the cell surface membrane.
What does microvilli provide?
A large surface area for the insertion of carrier proteins which diffusion, facilitated diffusion and active transport can take place
What is another way in increasing the rate of movement across membranes instead of microvilli?
an increase in the number of protein channels and carrier proteins in any given area of the membrane
In a human, there is normally a greater concentration of what within the ileum than in the blood?
Glucose and amino acids
If there is a greater concentration of glucose within the ileum, it will move down the concentration gradient into the blood by what process?
Facilitated diffusion
What helps to maintain the concentration gradient between the inside of the ileum and the blood?
when glucose is being absorbed, it is being removed by cells as they use it up during respiration.
What is co-transport?
The transport of one substance coupled with the transport of another substance across a plasma membrane in the same direction through the same protein carrier
In the sodium potassium pump, explain the co transport process on 4 main steps.
1) sodium potassium pump
2) concentration gradient of sodium ions
3) sodium ions diffuse into the cell through a cotransport protein. Glucose move in now through the same protein
4) glucose passes out the cell into the blood by facilitated diffusion through a carrier protein. Also the same for amino acids!
Why do diarrhoea disease lead to excessive loss of fluid from the body?
There is damage to the epithelial cells lining the intestine causing a loss in micro villi due to the toxins and an excessive secretion of water due to toxins (cholera)
Why is just drinking water insufficient to treat cholera symptoms?
It does not replace the electrolytes or ions that are being lost from the intestinal cells
Why is glucose used in oral rehydration mixture?
Glucose stimulates the uptake of sodium ions from the intestine and provides energy as it is a respiratiory substrate
Why is sodium chloride used in a oral rehydration mixture?
Sodium ions replace those lost from the body and encourage the use of the sodium-glucose transporter proteins to absorb more sodium ions
Why must the water be boiled before being used to dissolve the powder?
Boiling the water will kill any diarrhoeal pathogens that would make the patients condition worse
Why might adding mashed bananas to the mixture help?
Potassium from the banana will replace the lost potassium ions and stimulates appetite and aids recovery
Why is it important not to add too much glucose to the mixture?
Too much glucose might lower the water potential in the intestine; lower in epithelial cell. Water can leave the cell by osmosis and lead to dehydration.
Why might starch be better than glucose in the mixture?
It’s large and insoluble so will not leave the cell by osmosis
Rice flour can be used as a source of starch (viscous) how do you reduce the viscosity?
Digest with amylase to turn into smaller soluble molecules
