Transport Across Cell Membranes Flashcards
What is a brush border?
A collection of microvilli on the surface of epithelial cells
How are the epithelial cells of the small intestine adapted for absorption of digested food?
Many microvilli
Increase SA= more carrier + channel proteins = more facilitated diffusion at once.
Many protein channels and carrier proteins = more facilitated diffusion at once.
Define diffusion
Net movement of molecules or ions from an area of high to an area of low concentration
What is the ileum and lumen?
The space inside the small intestine = lumen
Ileum = small intestine
How is the glucose concentration gradient maintained between the epithelial cells and the blood?
The blood is constantly circulated to remove glucose next to cells
Maintain conc. gradient
What role do K+/Na+ pumps play in glucose absorption?
Pumps remove Na+ from cell into blood.
Maintains low conc. of Na+ in cell so Na+ move into cell via facilitated diffusion (carrier proteins)
Glucose moves along with Na+
By what processes does glucose move from the ileum to the blood?
Co-transport with Na+
Facilitated diffusion
What would occur if active transport didn’t happen in the small intestine?
Glucose and amino acids would pass out unabsorbed
Only absorb 50% of digestive products (equilibrium reached with diffusion)
What two main substances are absorbed into the blood that require active transport?
Glucose and amino acids
What is co-transported with sodium ions into the epithelial cells from the ileum?
Glucose or amino acids
Describe how starch is digested and absorbed
Starch broken down by amylase and then Maltase into glucose
Sodium ions are actively transported out of epithelial cell via K+/Na+ pump to set up conc. gradient of Na+
Na+ enter epithelial cells with glucose via co-transport proteins.
High glucose concentration in cell, low in blood. Move via facilitated diffusion (carrier protein)
What is the function of the cell surface membrane?
separate cytoplasm from environment
Allow and control transport of molecules and ions
Allow small, lipid soluble, non-polar molecules to diffuse across
Cell recognition and signalling
What is the function of the phospholipids in the cell surface membrane ?
Allow membrane to be flexible and self sealing
Allow lipid soluble substance across
Form phospholipid bilayer
What is the function of extrinsic proteins in the cell surface membrane ?
Structural support
Help cells stick together
Bind with carbohydrates to form glycoproteins for cell recognition
Act as hormone receptors
Enzymes
What is the function of cholesterol in the cell surface membrane ?
Make membrane less flexible (stronger)
Prevent leakage of water and dissolved ions
Prevent membrane becoming too fluid at high temps
Prevent lateral movement
What are the function of intrinsic proteins in the cell surface membrane ?
Transport water soluble molecules and ions
Allow active transport
What is the function of the glycoproteins in the cell surface membrane ?
Allow cells to adhere
Recognition site (hormone and neurotransmitters)
What is the function of the glycolipids in the cell surface membrane ?
Maintain stability of cell membrane
Recognition site (cholera toxins)
Allow cells to adhere
What is the function of a membrane within a cell?
Seperate organelles (seperate conditions and metabolic reactions)
Allow transport of substances (ER
Separate harmful enzymes (hydrolytic) in lysosomes
Why might a substance be unable to enter a cell?
Too large to fit through channels or bilayer
Same charge as channels (repelled)
Water not lipid soluble
How is the cell membrane described and why?
Fluid mosaic
Fluid = able to move
Mosaic = proteins of different sizes and shapes like mosaic
Why are the phospholipids able to move?
Weak forces of attraction between them
What are channel proteins also called?
Why
Aquaporins
Filled with water and lined with hydrophillic amino acids
Define simple diffusion
Net movement of molecules or ions from an area of high concentration to an area of low concentration untill an equilibrium is reached
Why and how is simple diffusion passive?
No ATP required
Powered by kinetic energy of particles
Give an example of simple diffusion within cells
CO2 O2 urea enzymes hormones
What factors affect the rate of simple diffusion?
Temperature
Surface area
Diffusion pathway
Concentration gradient
How and why does SA affect simple diffusion?
Larger = more
More area for diffusion to occur at once
What law links diffusion and the factors affecting it?
Ficks law
What is ficks law?
Rate of diffusion is proportional to
SA X Conc. gradient
———————————
Length of diffusion pathway
How can you tell facilitated diffusion is occurring rather than just simple diffusion?
Diffusion occurs faster than concentration gradient should allow
Is facilitated diffusion active or passive ?
Passive
What factors affects the rate of facilitated but not simple diffusion?
Intrinsic Proteins
Describe how carrier proteins work
Have complementary shape to specific molecule or ion
Molecule binds to protein causing change in shape.
Causes molecules to be deposited on other side
Describe how channel proteins work
Channel specific to certain ions or molecules
Opens in presence of specific substance allowing it to cross (large and water soluble)
Define osmosis
Net movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane
What is meant by a selectively permeable membrane?
Only allows H2O and small molecules through via simple diffusion
What is water potential?
The force exerted by free water molecules on a membrane
Why does water potential get more negative when more solute is added?
Water molecules adhere to solute molecules and so are no longer free
Less free water molecules to exert pressure
What occurs to plant cells and body cells when the solution surrounding it has a higher water potential?
Water moves in vía osmosis down water concentration gradient
Plant cell goes turgid (protoplast pushes against cell wall)
Animal cell swells and bursts
What is the protoplast?
The cell membrane and it’s contents
What does isotonic mean?
Same water potential
What occurs to plant cells and body cells when the solution surrounding it is isotonic ?
No net movement of water molecules
Plant= incipient plasmolysis
Animal = no change
What occurs to plant cells and body cells when the solution surrounding it has a lower water potential?
Water moves out vía osmosis down water concentration gradient
Plant = plasmolysed
Animal= shrivelled (red blood cell will appear dark due to higher haemoglobin conc)
Why do plant cells require cell walls in terms of swelling?
Plant cells surrounded by almost pure water
Can’t control water potential surrounding cells
Water constantly moves in via osmosis
Turgid = pressure on cell wall = no more water enters
Define active transport
The movement of molecules or ions from an area of low concentration to an area of high concentration using energy released from hydrolysis of ATP and a carrier protein
Explain how active transport works
Complementary molecule binds to carrier protein.
ATP and ATP hydrolase bind to protein.
Energy released from ATP hydrolysis changes shape of carrier protein depositing molecule on other side.
Pi is released cause protein to revert back to original shape
ADP +Pi =ATP in mitochondrion during aerobic respiration
How many sodium ions and potassium ions are moved in the sodium/potassium pump?
3x sodium
2x potassium
What is the sodium/potassium pump an example of?
Active transport
What determines whether a molecule is transported by active transport or facilitated diffusion using a carrier protein?
Depends on the concentration gradient and where the molecule is moving to.
If moving out of cell but concentrations are higher out of cell then must move via active transport
How is the sodium/potassium pump complementary to two molecules?
Originally complementary to sodium ions inside of cell
Change to tertiary structure causes sodium ions to be deposited on outside. Change causes new shape which is complementary to potassium
What substances can move via facilitated diffusion and active transport?
Molecules or ions
Define bulk transport
The movement of a large group of molecules or ions via a vesicle
Describe exocytosis
When a vesicle membrane fuses with the cell membrane releasing contents to external environment
Describe endocytosis
When a large molecule or group of molecules is engulfed.
The cell membrane forms pseudopods around the substance and pinches off around it to form a vesicle which is inside the cell
How is the villi adapted for maximum absorption?
Good blood supply
Thin surface layer of cells
Large surface area
What is a lacteal and where is it found?
Found in villi
Lymphatic capillary that absorbs dietary lipids
What’s the difference between microvilli and villi?
Villi is a finger like projection made of many cells
Microvilli and small projections of cell membrane on epithelial cells
How does a large surface area maximise nutrient uptake?
More space for carrier and channel proteins so more area which molecules or ions can cross
How is active transport used in the uptake of glucose into epithelial cells?
Active transport moves sodium ions out of (and potassium ions in to) cell into blood.
Creates and maintains a lower conc. of Na in cell than ileum so Na moves into cell along with glucose
What is co-transported from the ileum to epithelial cells?
Sodium and glucose or amino acids
Describe how starch is digested and absorbed from the ileum
Starch is broken down by amylase into maltose then by maltase into glucose. (enzymes = extrinsic proteins in membrane)
Glucose uptake by facilitated diffusion untill equilibrium occurs
Sodium ions are transported out cell into blood via active transport by sodium/potassium pump
Sodium ion concentration gradient set up (lower in cell than ileum)
Sodium moves down concentration gradient via co-transport with glucose which moves against concentration gradient.
Glucose concentration higher in cell so moves via facilitated diffusion out into blood
What is an osmometer?
A device used to experiment with Osmosis
Selectively permeable bag
Name the method used to make solutions of different concentrations using a concentrated solution
Dilution series
Why is more pigment released at higher temps?
Membrane more fluid and proteins denature
