Biological membranes Flashcards
What is the function of Phospholipids
Hydrophilic, polar phosphate head on the outside
Hydrophobic, non-polar fatty acid tails on the inside
Form a bilayer.
Selectively permeable - allows non-polar molecules to pass through
Allows cell to maintain different concentrations either side
Membranes are able to form vesicles
Provides fluidity
Structure and function of Glycoprotein
Carbohydrate chain attached to protein
Important in cell recognition
So that the immune system can tell the difference between body cells & e.g. invading bacteria.
Structure and function of Glycolipid
Carbohydrate chain attached to phospholipid
For cell recognition and to provide energy.
Function of Extrinsic protein
Receptor sites for hormones. Detect chemicals released form other cells. For cell recognition.
Function of Cholesterol
Cholesterol increases fluidity/ rigidity by reducing movement of other molecules in the membrane.
Function of Transport Protein
Can be carrier proteins or channel proteins
The channel proteins create selective hydrophilic pores (for water + water soluble compounds).
Carrier proteins are involved in facilitated diffusion and active transport.
Channel proteins are only used for facilitated diffusion.
Why is the plasma membrane referred to as being fluid-mosaic?
Molecules within the membrane able to move (fluid)
Mixture of phospholipid and protein (mosaic)
How does the bilayer formed by phospholipids affect entry and exit of substances into and out of a cell?
allows movement of small, lipid soluble, non-polar molecules such as gases through the membrane
prevents movement of large, water soluble, polar molecules such as ions and amino acids
The membrane is selective and partially permeable
Define diffusion
Diffusion is a passive process.
It is the movement of substances from an area of high concentration, to an area of low concentration, down a concentration gradient.
Where can diffusion take place?
Diffusion can occur from one area to another or across a partially permeable membrane
Which substances can simply diffuse across the phospholipid bilayer?
Small, non-polar, non-charged, lipid soluble molecules can diffuse across the phospholipid bilayer
Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.
The hydrophobic fatty acid part of membrane is non-polar
Oxygen and carbon dioxide are small non-polar molecules;
Oxygen/carbon dioxide can diffuse through the fatty acid layer
Down a concentration gradient
Which factors increase the rate of diffusion and why?
High concentration gradient
Increase the temperature
Increase the surface area
Increase the pressure
Decrease the diffusion pathway (reduce membrane width)
Write the equation for Fick’s law:
Rate of diffusion ∝ concentration gradient x surface area
Diffusion pathway
Define the process of facilitated diffusion
The movement of substances from high concentration to a low concentration, down a concentration gradient, through a channel or carrier protein.
What sorts of substances are transported using facilitated diffusion? Why? Examples?
It is used for substances which are large, polar, charged or water-soluble
The fatty acid layer of the plasma membrane is hydrophobic and non polar it will not allow polar substances to diffuse though
Ions, amino acids
Is it channel proteins, carrier proteins or both that Selectively transports substances across a membrane (specific)
both
Is it channel proteins, carrier proteins or both that The protein forms a pore which does not change shape when a substance travels through it
channel
Is it channel proteins, carrier proteins or both that The substance to be transported binds to one side of the protein, this causes it to change shape, so the substance is released on the other side of the membrane
carrier
Is it channel proteins, carrier proteins or both that Is made of a polypeptide
both
Is it channel proteins, carrier proteins or both that Can be used for facilitated diffusion
both
Is it channel proteins, carrier proteins or both that Can be used for active transport
carrier
What could limit the rate of facilitated diffusion?
The number of transport proteins available in the membrane
the concentration gradient
the surface area
Define the process of active transport
Active transport is an active process, it requires energy (which comes from ATP)
It is the movement of a substance from a low concentration to a high concentration, against the concentration gradient
It requires ATP which binds to a carrier protein and enables it to change shape.
How does active transport move substances against their concentration gradient?
Substance binds to a carrier protein
ATP binds to carrier protein
ATP is converted to ADP and releases energy
This causes the carrier protein to change shape
The substance is released on the other side of the membrane
What could limit the rate of active transport?
The number of carrier proteins
The amount of oxygen available for respiration. (this affects the amount of ATP available)
Very High temperature – if the temperature is high it could denature enzymes involved in respiration so ATP cannot be produced.
If the temperature is moderately high 🡪increased rate of active transport 🡪 as molecules have more kinetic energy 🡪 increased rate of respiration 🡪 more ATP ALSO more collisions between carrier proteins and substance to be transported
Give two ways in which active transport differs from diffusion? (you can simply state the differences)
In active transport ATP is used;
and movement is against a concentration gradient
Contrast the processes of facilitated diffusion and active transport. (you must write comparisons here)
Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;
Facilitated diffusion does not use ATP whereas active transport uses ATP;
Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.
Since ‘contrast’, both sides of the differences needed
Write a definition of osmosis:
The net movement of water from an area of high water potential to an area of lower water potential through a partially permeable membrane
What is the water potential of pure water?
0
What happens to the water potential of a solution if more solute is added?
It decreases (becomes more negative)
What does it mean if 2 solutions are isotonic?
They have the same water potential
When investigating diffusion or osmosis, you might want to make solutions of different concentrations. What is this called?
A dilution series
Vegetables are made of different types of tissue, in an experiment where do you take a cutting from and why?
When taking a cutting you must ensure it’s through one tissue only in order for it to be a fair test. As different tissues may affect water potential differently.
Why are bungs are placed on test tubes when conducting an experiment overnight?
To stop water from evaporating and therefore changing the water potential of the solution.
When you need to find the concentration of the solution that has the SAME water potential as the vegetable/fruit you are investigating you:
Plot data on a graph (give titles of the x and y axis)
Draw a line of best fit
From the graph either: (depending on question)
Find when the ratio is 1 (there is no change in mass/length)
extrapolate the line of best fit and read off
Find where it crosses the x axis
Ratio’s or % change in mass are calculated to
allow a valid comparison when the initial length/mass is not the same.
Take additional readings/repeat experiments to
identify any anomalies and calculate a mean
A graph can be improved if you take additional readings because
your line of best fit will be more reliable
AND - depending on question - where the point crosses the x axis is more precise –
Join dot to dot when
you cannot predict intermediate values
Summarise how the products of carbohydrate digestion or the products of protein digestion are absorbed
Na+/K+ pump moves 3 Na+ ions out of the cell (into the blood) and 2K+ ions into the cell by active transport. This uses ATP.
This creates a lower concentration of Na+ in the epithelial cell than in the lumen of the intestine
Na+ ions move into the epithelial cell by facilitated diffusion. They travel through a symport protein and bring glucose with them. This is called co-transport.
The glucose is moving into the cell cell against its concentration gradient
The glucose concentration in the epithelial cell increases
Glucose moves into the blood from the epithelial cell through a carrier protein by facilitated diffusion.
Adaptations of the epithelial cell
Lots of mitochondria 🡪 Release energy in the form of ATP 🡪 ATP is needed for active transport
Lots of enzymes attached to their membrane 🡪 Breaks down maltose into glucose
Microvilli 🡪 provide a large surface area for maximum absorption
Carrier proteins for active transport
Channel/Carrier proteins for facilitated diffusion
Co-transport (or symport protein for the transport) of sodium ions and glucose or for sodium ions and amino acids
What is co-transport?
When a transport protein transports more than one substance at the same time
What is a symport protein?
A type of cotransport protein.
A symport protein transports two substances through the membrane in the same direction together (like the Na+/glucose symport protein
What is an anti-port protein?
A type of cotransport protein.
An antiport protein transports two substances through the membrane in the opposite directions (e.g. the Na+/K+ pump)