Unit 2: Genes Flashcards
Cystic fibrosis dilemma
It is the most common genetic disorder affecting 9,500 people in the UK and 100,000 people. 1 in 25 carry the CF faulty allele. On average 5 children are born with CF everyday and 2 young people die with CF due to lung damage. In the 1960s, the average life expectancy was 5 years old. 2000 the life expectancy was 31 and today it is 41 years old.
Symptoms of cystic fibrosis
It is a concern for the sticky mucus layer that lays on many tubes and ducts in the gas exchange, digestive systems and reproductive systems. It is inherited. Symptoms involve: recurring chest infections, wheezing, coughing, shortness of breathe, difficulty on putting on weight, difficulty growing, yellowing skin and eyes, diarrhoea, constipation, diabetes, weak bones, infertility (males), and liver problems.
How does the gas exchange happen in the lungs?
The lungs allow rapid gas exchange between the atmosphere and the blood. Air in pulled into the lungs by the trachea due to low pressure in the lungs, created by an increase in the volume of the thorax as the ribs move up and the diaphragm move down. When the diaphragm muscles and the muscles relax, volume deceases, pressure rises and air is forced out through the trachea. The trachea divides into two bronchi which carry air to and from each lung. With each lung there is a tree-like system where the bronchi divide into smaller tube, bronchioles, which are attached to balloon-shaped structures which are the alveoli. Alveoli is the site of gas exchange.
How does gas exchange and mucus differ for someone with and without CF?
There is nothing unusual about having a layer of mucus in the tubes of the gas exchange system. Everyone usually has a thin coasting of mucus in these tubes that is produced continuously from goblet cells in the walls of the airways. Any dust, debris or microorganism that entre the airways become trapped in the mucus. It is moved continuously by the wave like beating of cilia that cover the epithelia cells lining the tubes of the gas exchange system.
However people with CF have mucus that contains less water than usual resulting in a sticky mucus layer that the cilia find difficult to move. This sticky mucus in the lungs has major health effects. It increases the chance of a chest infection and make gas exchange less efficient, particularly in later stages of the disease
what is diffusion?
Diffusion is the net movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration. Molecules diffuse both ways, but the net movement will always be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas. The concentration gradient is the path from the an area of higher concentration to an area of lower concentration. The particles diffuse down the concentration gradient. Passive process- so no energy is needed.
Gas exchange surfaces are adapted for efficient diffusion
They give gas exchange organs (like lungs) a large surface area to volume ratio. Larger objects have a smaller surface area to volume ratio than small objects. The smaller the surface area to volume ratio the slower the gas exchange. They’re thin (often only one epithelia cell thick), this provides a short diffusion pathway across the exchange surface.
How are the lungs adapted for efficient gaseous exchange
Oxygen diffuses out of the alveoli, across the alveolar epithelium (a layer of thin flat cells) and the capillary epithelium (a type of epithelium that forms on the capillary wall) and into the blood.
Carbon dioxide diffuses into the alveoli from the blood and is breathed out.
Having lots of alveoli means that there is a larger surface area for diffusion to occur across.
The alveolar epithelium and capillary epithelium are each only one cell thick, giving a short diffusion pathway.
All alveoli have a good blood supply from capillaries as the constantly take away oxygen and bring more carbon dioxide maintaining the concentration gradient.
Breathing in and out refreshes the air in the alveoli, keeping the concentration gradients high.
How Fick’s Law describes the rate of diffusion
The rate of diffusion is proportional to the area of diffusion surface x difference in concentration / thickness of diffusion surface.
If the rate of diffusion was to double, the surface area or the difference in concentration will double or the thickness of the surfaces will halves.
Equation:
Rate = P x A x (C1 - C2)/T
P=permeability constant
A= surface area
(C1-C2)= difference in concentration
T= thickness of the exchange surface
Describe how cell membranes have a fluid ‘mosaic structure’
Phospholipid molecules form a continuous, double layer (bilayer), which is fluid because the phospholipids are constantly moving.
They contain a head and a tail. The head contains a phosphate group and is hydrophilic so it attracts water. While the tail is made of two fatty acids which are hydrophobic, so it repels water. Automatically arrange itself to form a bilayer, with the hydrophilic heads facing out towards the water, while the hydrophobic tails face the outside. This means that it doesn’t allow water soluble substance like ions through it.
Some proteins have a polysaccharide (carbohydrate) chain attached (glycoproteins)
Some lipids have a polysaccharide chain attached to them (glycolipids)
Cholesterol (a type of lipid) is also present in the membrane. It fits in between the phospholipids, forming bonds between them. This makes the membrane more rigid.
What is osmosis?
Osmosis is the diffusion of free water molecules across a semi permeable membrane from an area of high concentration to an area of low concentration of water molecules. Water molecules will diffuse both ways through the membrane, but the net movement will be to the side with lower concentration.
What is facilitated diffusion?
Some larger molecules (like amino acids and glucose) and charged particles (like ions) don’t diffuse directly to through the phospholipid bilayer of the cell membrane. Instead the diffuse using carrier proteins and channel proteins in the cell membrane (facilitated diffusion). Like diffusion, it moves down the concentration gradient, from higher concentration to lower concentration. It is a passive process, so it doesn’t require energy.
How does carrier proteins help with facilitated diffusion?
Carrier proteins move larger molecules into or out of the cell, down the concentration gradient. Different carrier proteins facilitated diffusion for different molecules.
1) First the larger molecules attaches to a carrier protein in the membrane (binding site)
2)Then the protein changes shape
3) This releases the molecule on the opposite side
How does channel proteins help with facilitated diffusion?
They form pores in the membrane for charged particles to diffuse through (down their concentration gradient). Diffusion channel proteins facilitate the diffusion of different charged particles.
What is active transport?
Active transport moves a substance against the concentration gradient. It uses energy to to move molecules and ions across plasma membranes, against a concentration gradient. This process involves carrier proteins.
This process is similar to facilitated diffusion where a molecule will attaches to a carrier protein and changes and this moves the molecule across the membrane, releasing it on the other side. The only difference is that energy is used (ATP) . It is produced by respiration. It acts as an immediate source of energy in the cell. When ATP is hydrolysed (broken down) in the cell, energy is released. This energy is used to move the molecule against the concentration gradient.
How can substances be taken in?
They can be taken in by endocytosis.
1) Some molecules are way too large to be taken into a cell by carrier proteins e.g. proteins, lipids and some carbohydrates.
2) Instead a cell surrounds the substance with a section of cell membrane.
3) The membrane then pinches off to form vesicle inside the cell containing the ingested substance (endocytosis)
4) Some cells also take in much larger objects by endocytosis like white blood cells as they are use endocytosis to take in things like microorganisms and dead cells so that they can destroy them.
5) Also uses ATP (Adenosine triphosphate) energy
How can substance be taken out (and the stages)?
Cells can secrete substance by exocytosis.
1) Some substances produce by the cell (like digestive enzymes, hormones and lipids) need to be released from the cell.
2) Vesicles containing the substance pinch off sacs of the Golgi apparatus (a structure that processes new proteins and lipids) and move towards the cell membrane.
3) The vesicle fuse with the cell membrane and release the to contents to the outside.
4) Some substances (like membrane proteins) aren’t released to the outside of the cell but instead inserted into the cell membrane.
5) uses ATP (Adenosine triphosphate)
What is the practical that is involved in soaking beetroot in concentrations ready to observe membrane permeability?
1) Use a scalpel to carefully cut 5 equal sizes of beetroot (1cmx1cm) on a cutting board and rinse to get out pigment released from cutting.
2) Using a measuring cylinder measure out different alcohol concentrations (20%,40%,60%,80%,100%) and a control with 0%.
3) Leave for 5 mins
4) Then take out the beetroot so you are just left with the coloured liquid.
Using the colorimeter to measure absorbed coloured liquid
1) Switch on the colorimeter and all 5 mins to stabilise. Use a blue filter and use pure water to calibrate the colorimeter to zero.
2) Use a clean pipette to transfer a sample of the liquid from your first beetroot tube to a clean cuvette- 3/4 full.
3) Put the cuvette into the colorimeter and record the absorbance and coloured solution.
4) Repeat steps 2 and 3 for all test tubes
5) Read results- high the absorbance reading, less light passing through the solution, more pigment has been released, so higher permeability of the membrane.
What effect does temperature have on permeability (different temperatures)?
1) Below 0 degrees C- phospholipids don’t have much energy, don’t move much. Packed closely together and membrane become rigid. Channel proteins and carrier proteins in the membrane deform, increasing permeability. Ice crystals may appear and pierce the membrane, increasing permeability.
2) 0-45 degrees C- phospholipids can move around and aren’t packed together tightly (membrane is partially permeable) Temp increases, more phospholipids can move because they have more energy- increase permeability.
3) Above 45 degrees C- phospholipid bilayer starts to melt and the membrane becomes more permeable, water inside the cell expands, putting pressure on the membrane. Channel and carrier proteins deform so they can’t control what enters and leaves the cell- increases permeability.
Increasing alcohol concentration, increase permeability, how?
Permeability of cell increases with alcohol concentration. This is because the alcohol dissolves the lipids in the cell membrane, so the membrane loses its structure.
What are the different types amino acids?
The monomers of proteins are amino acids. Dipeptide is formed when two amino acids are joined together. Polypeptide is formed when more than two amino acids are joined together. Proteins are made up of one or more polypeptide.
What is the general structure of amino acids?
Carboxyl group (-COOH), amine/amino group (-NH2) and a carbon containing R group (variable side group). Bank of only 20 amino acids. Only different is the R group
How are polypeptides formed?
By condensation reaction (amino acids are linked). Water molecule is released. Bonds formed between the amino acids is called peptide bonds. Reverse reaction happens during digestion.
What are the proteins structural levels?
Primary- sequence of amino acids in a polypeptide chain- help together by peptide bonds.
Secondary- Hydrogen bonds form between the amino acids. Coil into an alpha helix or fold beta pleated sheet.
Tertiary- Coiled and folded more. More bonds between different parts of the polypeptide chain (hydrogen bonds, ionic bonds (attraction between positive and negative), or disulphide bond/bridges (amino acid cytosine come close together- sulphur atom)), final 3D structure for single polypeptide chains. Also have hydrophobic (close together in the protein) /hydrophilic (push to the outside) interactions
Quaternary- made of several different polypeptide chains held together by bonds. Final 3D structure for proteins. Influenced by all bonds.
What determine the 3D structure and properties
Primary structure. Determines what bonds will form and how the protein will fold up. 3D structure determines its properties- function.
