UNIT 2 - Genes and health Flashcards
(89 cards)
What do gas exchange surfaces in living things tend to have?
Large SA:Vol ratio
Thin surface
A steep concentration gradient maintained
State Fick’s Law
Rate of diffusion =proportional to= (S.A x conc. gradient) / Thickness of gas exchange surface
It Is porportional, to calculate it, you would need a diffusion coefficient (depends on the substance, temperature and pressure)
Following Fick’s law, which are the three factors that affect the rate of diffusion?
Big surface area
Big concentration gradient
Thin exchange surface
How are alveoli adapted to enable a fast diffusion rate?
Thin surface - 1 epithelial cell thick
Large surface area - bronchioles divide into lots of alveoli
Which biological molecules are present in the cell membrane?
Lipids (phospholipids and cholesterol)
Proteins (inc. enzymes)
Carbohydrates (in the from of glycoproteins and glycolipids)
What are the properties of cell membranes?
Flexible
Fluid
Selectively permeable
Which two techniques helped develop models of the cell membrane?
Electron microscopy
Use of radioactive isotopes
Describe the fluid mosaic model
Has a fluid phospholipid bilayer. Phospholipids heads (polar=hydrophilic) face the outside while the tails (non-polar=hydrophobic) face each other.
Cholesterol and proteins (protein channels and peripheral) float around the mosaic.
Some have carbohydrate groups on the outer surface of the membrane (glycoproteins and glycolipids), which are useful for cell signaling.
What facts and evidence is there for the fluid mosaic model? (6)
Phsopholipids have hydrophilic (polar) heads and hydrophobic (non-polar) tails so from bilayer in aqueous environments.
A monolayer of phospholipids is twice as large as the cell S.A.
Microscope images show proteins sticking out.
When lectins (react with carbohydrates) are added, there are found only on the outside.
Some small water soluble substances pass in and out of cells.
Ionic and polar molecules do not pass easily, but lipid-soluble substances do.
What three types of passive transport are there?
Diffusion, facilitated diffusion and osmosis.
What is diffusion?
Diffusion is the net movement of particles down a concentration gradient (from high conc. to low conc.)
Under what circumstances would diffusion not occur, even though there’s a concentration gradient? (3)
The membrane is not permeable enough (molecules don’t fit through pores).
The particle is charged.
The particle isn’t soluble.
What happens, in terms of movement of particles, when the concentration gradient is zero?
Particles still move across in all directions but the net movement is zero.
How does facilitated diffusion happen?
Big, non-polar molecules or polar molecules can’t pass across the phospholipid bilayer so they move across a channel protein (like a pore) to enter and exit the cell. They can also be aided by a carrier protein for the specific molecule, which changes shape, ‘pushing’ the molecule into/outside the cell.
What is osmosis?
Osmosis is the net movement of water molecules down a water potential gradient (from areas of high W.P. to areas of low W.P.) through a partially permeable membrane.
How does active transport work?
The specific molecule gets into the carrier protein. The carrier protein the changes shape (using energy from ATP) , therefore pushing the molecule to move against the concentration gradient.
What is the structure of adenosine triphosphate (ATP)?
An adenine nitrogenous base bonded to a ribose sugar, which is bonded to a chain of three phosphate groups.
How is energy harvested from ATP?
The bond between the second and the third is broken by hydrolysis, so energy is released:
Then energy is required to add the third phosphate to re-build the phosphate bond to adenosine diphosphate to create ATP again.
What happens during endocytosis?
A cell or a molecule becomes surrounded by the cell membrane and, due to the fluid nature of the cell membrane, a vesicle is created around it when it enters the cell, without destroying the cell membrane.
E.g. phagocytosis (solids)
e.g. pinocytosis (liquids)
What happens during exocytosis?
A particle is inside the cell, engulfed by a vesicle. The vesicle then fuses with the membrane (due to its fluid nature), releasing the contents out of the cell.
e.g. how insulin moves out.
How does temperature affect the permeability of cell membranes?
As temperature increases, phospholipids become more fluid, allowing more molecules to leak out of the cell (higher permeability).
Describe an experiment you would carry out in order to investigate how temperature affects membrane permeability. (Core Practical)
- Cut equal sized pieces of beetroot. (CV)
- Rinse under water to remove the betalain released by cutting.
- Place pieces in equal volumes of distilled water (CV) at a range of different temperatures (IV) and leave them for equal time (CV).
- Carefully remove pieces and shake solution gently.
- Asses the amount of pigment lost by using a colorimeter and measuring the % absorbance, which gives a quantitative representation of how permeable the membrane was. (DV)
- Plot values on graph to allow the relationship to be seen: temp = x axis; absorbance = y-axis.
Nucleic acids are polynucleotides. What is the general structure of a mononucleotide?
Phosphate added by condensation reaction to the C5 in the pentose sugar, which has the C1 bonded to a nitrogenous base, also formed by condensation reaction.
Both DNA and RNA are polynucleotides. How do nucleotides join together to form a polynucleotide?
They join by a condensation reaction, which forms a phosphodiester bond between the C3 of the pentose in one nucleotide and the phosphate of ANOTHER nucleotide.
