Topic 2 - Genes And Health Flashcards
(237 cards)
1
Q
How does air move into and out of the lungs?
A
Air is drawn into the lungs via 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 diaphragm moves down. When the diaphragm muscles and those between the ribs relax, volume decreases, pressure rises and air forced out of the trachea.
2
Q
Describe how the trachea separates as it moves into the lungs.
A
The trachea divides into the bronchi which carry air to and from each lung. Within each lung there is a tree like system of tubes ending in narrow tubes, bronchioles, attached to a tiny balloon like alveoli. The alveoli are the sites of gas exchange.
3
Q
How is mucus made?
A
It is produced constantly by goblet cells.
4
Q
What is mucus?
A
A thick slimy fluid secreted by the cells lining many organs. Mucus is produced, for example, by cells in the gas-exchange system, the digestive system and the reproductive system. Apart from water, its main component is a protein called mucin. Mucus acts as a lubricant and as a protective layer.
5
Q
What does mucus do in the walls of the airways?
A
Any dust, debris or microorganisms that enter the airways become trapped in the mucus.
6
Q
What happens to the mucus in the airways?
A
It is continuously removed by the wave-like beating cilia that cover the epithelial cells lining the tubes of the gas exchange system.
7
Q
What is the difference in the mucus of CF sufferers? What problems does it cause?
A
People who have CF have mucus that contains less water than usual resulting in a sticky mucus that the cilia find difficult to move. This sticky mucus in the lungs has two major effects on health. It increases the chance of lung infection and makes gas exchange less efficient.
8
Q
Describe the structure of a part of the lung e.g a part of the bronchi
A
- Basement membrane holds the cell in position
- ciliated epithelial cells lining the airway attached to the basement membrane
- goblet cells in epithelial cells produces mucus which is released into the airway
- Cilia, hair like structures, beat and move mucus up and down out of the lungs.
9
Q
What is the epithelium?
A
Tissue which forms the outer surface of many animals. Epithelial cells also line the cavities of organs such as the gut and lungs. The epithelium consists of one or more layers of cells sitting on a basement membrane. These cells may be flat (squamous or pavement epithelium) or tall in shape (columnar epithelium).
10
Q
What are the different types of epithelia?
A
- Squamous /pavement
- columnar epithelium
- ciliated epithelial cells
11
Q
Where are ciliated epithelial cells found and what are there properties?
A
In the trachea, bronchi and bronchioles there are ciliated epithelial cells with cilia on the apical surface. These cilia beat in a coordinated way like a Mexican wave and move substances along the tube they line.
12
Q
How does sticky mucus increase the chance of lung infections?
A
Microorganisms become trapped in the lungs and some of these microorganisms cause illness (pathogens). The mucus is normally moved by the cilia into the back of the mouth cavity where it is either coughed out or swallowed and then killed in the stomach but in CF sufferers the layer of mucus is so sticky that the cilia cannot move it. Mucus production continues and the layers of thickened mucus build up in the airways. With low levels of oxygen in the thick mucus, harmful bacteria are able to thrive in these anaerobic conditions.
13
Q
What causes mucus to become even thicker and stickier?
A
White blood cells fight the infections within the mucus but they die break down and release DNA that makes the mucus even stickier.
14
Q
What is the problem with having repeated lung infections?
A
Repeated lung infections can eventually weaken the body’s ability to fight the pathogen and cause damage to the structures of the gas exchange system.
15
Q
Living organisms have to exchange substances with their surroundings. Give examples
A
They take in oxygen and nutrients and get rid of waste materials such as carbon dioxide.
16
Q
What is the difference between unicellular and multicellular organisms regarding the exchange of gases?
A
In unicellular organisms the whole surface membrane is the exchange surface. Larger multicellular organisms have more problems absorbing substances because of their size of the organisms surface area to volume ratio. If larger organisms relied only on their general body surface for exchange of substances they could not survive because the distance to the innermost tissue is too far for diffusion to supply oxygen quickly enough; change would be too slow.
17
Q
What happens to the surface area to volume ratio as organisms get larger?
A
The surface area per unit of volume gets less.
18
Q
What is diffusion?
A
The net movement of particles from a high concentration to a low concentration until equilibrium has been reached.
19
Q
How do you work out total surface area to volume ratio?
A
Organisms total surface area / volume
20
Q
What are the key features for efficient gas exchange?
A
- Large surface area of the alveoli
- Numerous capillaries around the alveoli
- Thin walls of the alveoli and the capillaries meaning a short distance between the alveolar air and blood in the capillaries
- Steep concentration gradient
21
Q
What does the rate of gaseous exchange depend on?
A
- Surface area - Rate of of diffusion is directly proportional to the surface area. As the surface area increases the rate of diffusion increases.
- Concentration gradient - Rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface. The greater the concentration gradient the faster the diffusion.
- Thickness of the gas exchange surface - rate of diffusion is inversely proportional to the thickness of the gas exchange surface. The thicker the surface the slower the diffusion.
22
Q
What is the calculation for rate of diffusion?
A
Surface area x Difference in concentration / thickness of the gas exchange surface
23
Q
What is Fick’s law?
A
The relationship between the properties that affect the rate of diffusion (surface area, concentration gradient, thickness of gas exchange surface)
24
Q
What are the properties of the alveoli that make them so good at the exchange of gases?
A
The large surface area of the alveoli, the steep concentration gradient between the alveolar air and the blood (maintained by ventilation of the alveoli and continuous flow of blood through the lungs) and the thin walls of the alveoli and the capillaries, combine to ensure rapid diffusion across the gas exchange surface.
25
How does the sticky mucus layer affect gas exchange?
- The sticky mucus layer in the bronchioles of a person with cystic fibrosis tends to block these narrow airways, preventing movement of air into the alveoli beyond the blockage. This reduces the number of alveoli providing surface area for gas exchange. Blockages are more likely at the narrow end of the airways. The se blockages will often allow air to pass when the breaths in but not when they breath out, resulting in the over inflation of the lung tissue beyond the blockage. This can damage the elasticity of the lung.
- People with CF also struggle when does physical exercise as the gas exchange system can not deliver enough oxygen to the muscle cells which is needed for aerobic respiration to provide energy.
26
Why is mucus so sticky (CF)?
It contains less water than normal. The reduced water level is due to abnormal salt (sodium chloride) and water transport across the cell surface membranes caused by a faulty transport protein channel in the membrane.
27
What are the functions of proteins in our body?
- Antibodies
- Enzymes
- Hormones
- Structural proteins (hair, nails, muscle, ligaments, tendon, hair)
- Components of cell membranes and have important functions in membranes
28
What make up proteins?
Amino acids
29
How many different types of amino acids are there?
20
30
Plants can make all 20 amino acids but animals can only make some. The amino acids that animals have to obtain are known as?
Essential amino acids
31
Describe the general structure of an amino acid.
In every amino acid a central carbon atom is bonded to an amine group (-NH2), a carboxylic acid group (-COOH), a hydrogen (-H) and a residual group (-R). Each different amino acid has a different acid group.
32
What is a condensation reaction?
A type of chemical reaction in which small molecules are joined together with the removal of a molecule of water. Condensation is involved in forming biologically important polymers. The reactions in which amino acids join to form proteins, and glucose molecules join to form starch and cellulose are examples of condensation reactions.
33
What do two amino acids form?
A dipeptide
34
What is a dipeptide?
A molecule that is made up of two amino acids joined by a peptide bond.
35
What is a peptide bond?
The bond joining two amino acids in a protein. Amino acids join together by condensation. When a protein is digested, the peptide bonds are broken down by hydrolysis.
36
What is a a primary structure?
The sequence of amino acids in a protein or polypeptide is known as the primary structure. The primary structure will determine how the polypeptide will fold. There are twenty different amino acids and they can be combined in different ways to produce many different proteins.
37
The peptide bond forms between...
The carbon and nitrogen
38
What is the secondary structure?
Chain of amino acids my twist to form an alpha helix or come together in beta pleated sheets due to hydrogen bonds between the amine and acid group.
39
What is an alpha helix?
- They have the shape of extended springs
- Held together by hydrogen bonds
- N-H donates a hydrogen atom to the C=O group
40
What are belated pleated sheets?
Amino acid chains fold back on themselves or several lengths of chain may link with hydrogen bonds holding the parallel chains in an arrangement known as a beta pleated sheet.
41
In a beta pleated sheet are the hydrogen bonds strong or weak?
Each hydrogen bond is weak but multiple keep it stable.
42
Does a protein only contain an alpha helix or a beta pleated sheet?
No, a protein can contain sections of alpha helixes and sections of beta pleated sheets.
43
What is a tertiary structure?
Entire 3D protein held together by bonds between R groups.
44
What types of bonds hold the tertiary structure together?
Ionic and covalent
45
What maintains the tertiary structure?
Chemical bonds and hydrophobic reactions between R groups maintain the tertiary structure of the protein.
46
When is an R group polar?
When the sharing of electrons is uneven.
47
Where are non-polar R groups faced in a protein?
Non-polar R groups (hydrophobic) face the inside of the protein, excluding water from the centre of the molecule.
48
In a folded structure what can happen to the R groups?
Chemical bonds can form between R groups that are close to each other in a folded structure.
49
When is a molecule described as a protein?
When the 3D structure is functional. Meaning the molecule is able to perform a specific function.
50
What is the quaternary structure?
Proteins made up with multiple polypeptide chains held together.
51
What are conjugated proteins?
Proteins with another chemical group associated with their polypeptide chains.
52
Give an example of a conjugated protein
Myoglobin and haemoglobin because they are an iron containing group.
53
What are the two types of proteins?
Globular and fibrous
54
What is the shape of fibrous and globular proteins?
Fibrous - Long and narrow
| Globular - Rounded / spherical
55
What is the role of fibrous and globular proteins?
Fibrous - Structural (strength and support)
| Globular - Functional (catalytic, transport)
56
What is the solubility of fibrous and globular proteins?
Fibrous - Insoluble in water
| Globular - soluble in water
57
What is the sequence like in fibrous and globular proteins?
Fibrous - Repetitive amino acid sequence
| Globular - Irregular amino acid sequence
58
What is the stability of fibrous and globular proteins?
Fibrous - Less sensitive to changes in heat, pH, etc
| Globular - More sensitive
59
Give examples of fibrous proteins
- Collagen
- Myosin
- Fibrin
- Actin
- Keratin
- Elastin
60
Why are globular proteins soluble and fibrous are not?
In globular proteins the hydrophobic R groups are folded into the core of the molecule, away from the surrounding water molecule, making them soluble. In fibrous proteins the hydrophilic R groups are exposed and therefore the molecule is insoluble.
61
What is a phospholipid? Describe its properties.
A phospholipid molecule is a lipid with two distinct sections. It has a head region consisting of glycerol and a phosphate group. This part of the molecule is attracted to water. The other end consists of two fatty acid tails. This end of the molecule repels water. Phospholipids are important components of cell membranes where they are arranged in a bilayer with the heads pointing outwards and the tails pointing towards each other.
62
Which part of the phospholipid bilayer is polar?
The head is polar as one end is slightly positive and the rest is slightly negative. The phosphate head is hydrophilic and attracts to other polar molecules.
63
Which part of the phospholipid bilayer is non-polar?
The fatty acid tails are non-polar, therefore are hydrophobic.
64
What happens when phospholipids are place on water?
The hydrophobic tails stand up vertically out of the water while the hydrophilic heads stay in the water.
65
What happens when the phospholipids are placed in water?
They may become arranged into a spherical cluster called a Michelle or form a bilayer. They tend to form bilayer because the tow fatty acids are too bulky to fit into the centre of the micelle.
66
Describe the formation of a phospholipid bilayer.
A lipid bilayer will tend to close in on itself so that there are no ends with exposed hydrocarbon chains, thus forming compartments as happens around and within cells. Hydrophobic fatty acid tails have no contact with water on either side (cytoplasm in the cell or aqueous tissue fluid) of the membrane and the hydrophilic phosphate heads remain in contact with the aqueous environment.
67
What do membranes contain?
- Glycolipid - lipid molecules with polysaccharides (no branches)
- Channel protein
- Glycoprotein - Protein molecules with polysaccharides (like a tree)
- Proteins - some are fixed others are free to move
- Cholesterol - inside the phospholipid bilayer
- Carrier proteins
- Enzymes
68
What are peripheral proteins?
Loosely attached proteins on the outside of the surface of the membrane.
69
What are integral proteins?
Fully embedded proteins within phospholipids, some even spanning both layers.
70
What are most integral proteins like?
Regions at their ends have polar hydrophilic amino-acids with the middle portion being mainly composed of non-polar hydrophobic amino acids.
71
When is the membrane more fluid? Why?
The more unsaturated a phospholipid the more fluid it is. The greater the ratio of phospholipids that contain unsaturated fatty acids to saturated fatty acids, the more fluid the membrane will be. The is because unsaturated phospholipid tails have 'kinks' preventing them from packing closely together, this allows more movement to take place.
72
How do substances pass through cell membranes?
- Diffusion
- Osmosis
- Active transport
- Exocytosis
- Endocytosis
73
When does diffusion occur?
Occurs when there is a concentration gradient
74
What types of molecules pass through cell membranes by diffusion?
Small molecules diffuse directly across the cell membrane (e.g oxygen/carbon dioxide) and hydrophobic substances.
75
What type of process is diffusion?
It is passive
76
Diffusion occurs across a ... (membrane)
Phospholipid bilayer
77
What is facilitated diffusion?
Diffusion is the movement of a substance from where it is in a high concentration to where it is in a lower concentration. Large molecules and ions can only cross cell membranes with the aid of carrier proteins. This form of diffusion is called facilitated diffusion.
78
What molecules pass through a cell membrane by facilitated diffusion?
Large olecules or hydrophilic (polar) molecules - they cannot simply diffuse through a phospholipid bilayer.
79
What type of process if facilitated diffusion?
Passive -> no metabolic energy is needed for diffusion to occur.
80
What are the proteins that aid facilitated diffusion?
- Channel proteins
| - Carrier proteins
81
What are channel proteins?
A protein that spans a membrane and is involved in the transport of molecules across the membrane.
82
How do channel proteins work?
They allow polar molecules to diffuse through a membrane. Different channel proteins with different shapes for different proteins.
83
What is a type of channel protein?
A gated channel which is a channel protein that opens and closes.
84
What is a gas exchange surface?
The layer across which oxygen and carbon dioxide are exchanged.
85
What is a carrier protein?
A protein that binds with a specific ion or molecule and helps it cross a membrane.
86
How does a carrier protein work?
The protein changes shape allowing the molecule to be transported across the membrane.
87
What is osmosis?
The net movement of water molecules from a solution of high concentration of solute to a low concentration of solute across a partially permeable membrane.
88
What molecules pass across a cell membrane by osmosis?
It is the movement of free water molecules
89
What is the type of process of osmosis?
It is a passive process through a phospholipid bilayer.
90
What is active transport?
Movement of molecules across a membrane against a concentration gradient (from low to high) and energy is required.
91
How does active transport work?
Carrier proteins move the molecule along with ATP (Adenosine Triphosphate) to provide the needed energy.
92
What is ATP? How is it formed?
Adenosine Triphosphate provides the immediate source of energy for all biological processes. It is formed during respiration, when fats and carbohydrates are broken down.
93
How does active transport occur?
ADP forms from the hydrolysis of ATP between the third and second phosphate group. Once removed the phosphate group becomes hydrated and a lot of energy is released as bonds form between water and phosphate. The energy released changes the shape of the carrier protein allowing the movement against the concentration gradient across a membrane.
94
What is exocytosis?
A process which involves the transport of substances out of cells. The vesicles move through the cytoplasm and fuse with the cell surface membrane, releasing the protein from the cell.
95
What is endocytosis?
A process which involves the transport of large particles or fluids into cells. Substances are taken into the cell by the creation of vesicles from the cell surface membrane.
96
What are exocytosis and endocytosis?
The bulk transport of very large molecules or particles, or very large quantities of a particular molecule across cell surface membranes.
97
In exocytosis what is normally released?
Usually proteins or polysaccharides
98
What are vesicles?
Small membrane - bound faces containing the substance
99
Give an example of exocytosis
Insulin is released from the cell surface membrane into the blood.
100
Give an example of endocytosis
White blood cells ingest bacteria
101
How is viscosity of mucus maintained?
The regulation of the water content of the mucus is achieved by the transportation of sodium ions and chloride ions across the epithelial cells. Water then follows by osmosis.
102
What causes cystic fibrosis?
A mutation in cystic fibrosis transmembrane regulatory protein.
103
What does the CFTR protein do?
It helps control the viscosity of mucus that lines the epithelial cells of the airways, digestive and reproductive system.
104
What happens if the mucus is too sticky?
The cilia cannot beat and remove the mucus, which clogs up airways.
105
What happens if the mucus is too runny?
The mucus can flood the airways
106
When there is excess water in the mucus what happens? (Process)
Detected by epithelial cells.
1) Salt is actively pumped out across the basal membrane (Na+) by carrier proteins.
2) Concentration of sodium in the epithelial cell falls and the concentration gradient increases between the mucus and the cell. This causes salt to diffuse through the sodium channels in the apical membrane (Na+) by facilitated diffusion through epithelial sodium ion channels (ENaCs).
3) Raised concentration of Na+ in the tissue fluid of the basal membrane side of the epithelial cell creates a potential difference. The tissue fluid now contains more positively charges ions than the mucus. Chloride, which is negatively charged, diffuses down electrical gradient (Cl-) it moves around in the gap of the cell.
4) This process increases the amount of sodium and chloride in the tissue fluid causing the water to be drawn out of the cells by osmosis due to the high salt concentration.
5) Water is drawn out of the mucus by osmosis into the epithelial cell.
107
What happens where there is too little water in the mucus? (Process)
1) Chloride is pumped into the cell across the basal membrane.
2) Increased concentration gradient of chlorine ions in the epithelial cell causes chloride to diffuse through the open CFTR channels (Cl-)
3) Sodium diffuses down the electrical gradient into the mucus, it moves around the gap in the cell.
4) Elevated salt concentration in the mucus draws water out of the cell by osmosis.
5) Water is drawn into the cell by osmosis.
108
Why is the mucus in cystic fibrosis sufferers so thick? (Process)
1) CFTR channel is absent or not functional
2) Sodium channel is permanently open
3) Water is continually removed from mucus by osmosis
109
What is an example of a gated channel protein?
The Cystic Fibrosis Transmembrane regulatory protein which opens to allow chloride to pass through when there is too little water and closes when there is too much water not letting the sodium pass through.
110
Describe the enzymes used in digestion and where are the located?
Most of the chemical breakdown of food molecules and the subsequent absorption of soluble products into the bloodstream occurs in the small intestine. Glands secrete digestive enzymes into the lumen of the gut, where they act as catalyst to speed up the extracellular breakdown of food molecules. Exocrine glands outside the gut, (salivary glands, liver and pancreas) a wide range of enzymes are produced. Enzymes are also built into the membranes of the gut wall. Groups of pancreatic cells produce enzymes that help breakdown proteins, carbohydrates and lipids. The digestive enzymes are delivered to the gut in the pancreatic juice released through the pancreatic duct. The pancreas is also a endocrine gland. Different groups of pancreatic cells release hormones, including insulin which is involved in regulating blood sugar levels.
111
How does cystic fibrosis affect the digestive system?
The pancreatic duct becomes blocked by sticky mucus, impairing the release of digestive enzymes. The lower concentration of enzymes within the small intestine reduces the rate of digestion. Food is not fully digested, so not all the nutrients can be absorbed. As a consequence the faeces contain a higher proportion of partially digested and undigested food, so energy is lost (malabsorption syndrome). Additional complications occur when the pancreatic enzymes become trapped behind the mucus blocking the pancreatic duct. These enzymes then damage the pancreas itself. Another complication occurs if damage occurs to cells within the pancreas that produce the hormone insulin, which is involved in the control of blood sugar levels. This can lead to a form of diabetes.
112
What is a exocrine gland?
A gland that secretes substances into a duct is called an exocrine gland. The salivary glands and the pancreas are examples of exocrine glands.
113
What is an endocrine gland?
A gland that secretes hormones directly into the blood is called an endocrine gland. Glands are organs which secrete particular substances. The pancreas is an endocrine gland because it secretes the hormone insulin into the blood. It is also an exocrine gland because it secretes digestive enzymes into a duct, which takes them into the intestine.
114
What type of protein is an enzyme?
A globular protein
115
What is a catalyst?
A substance that increases the rate of a chemical reaction but remains unchanged at the end of the reaction.
116
What is an active site?
The part of an enzyme molecule into which a substrate molecule fits during a chemical reaction. It a depression on the surface of the enzyme and it has a specific shape. Only a substrate molecule with the complementary shape will be able to fit into this active site.
117
What are the two theory's on how the active site has a catalytic effect?
- Lock and Key theory
| - Induced fit
118
What is a substrate?
In biochemical reactions, a substrate is the molecule on which an enzyme acts. The substrate of the enzyme amylase, for example, is starch while that of maltase is maltose. Enzymes are very specific in their actions. Only a substrate molecule with a particular shape will fit the active site of a particular enzyme.
119
What is an enzyme substrate complex?
In a chemical reaction controlled by an enzyme, one or more substrate molecules fit into the active site of the enzyme to form an enzyme–substrate complex. The substrate molecules are held in such a way that a reaction takes place. Product molecules are produced and released while the enzyme is unchanged.
120
What happens in the lock and key theory?
The enzyme holds the substrate molecule in such a way the react more easily. When the reaction has taken place the products are released, leaving the enzyme unchanged. The substrate is often linked to a 'key' which fits into the enzymes 'lock'.
121
Each enzyme will only catalyse one specific reaction, why?
Only one shape of substrate will fit into its precisely shaped active site.
122
What happens in the induced fit theory?
When the substrate enters the active site, the enzyme changes shape, fitting more closely around the substrate and speeding up the rate of reaction. Only a specifically shaped substrate will induce the correct change in shape of an enzymes active site. The slight shape change of the active site enables the substrate to react.
123
What is the activation energy?
Before a chemical reaction can take place, bonds must be broken. This requires energy. This activation energy is normally provided by heating the substances involved in the reaction. Enzymes reduce the amount of activation energy necessary, so reactions in living organisms can take place at relatively low temperatures.
124
Why is it important that enzymes lower the activation energy?
In cells, enzymes reduce the amount of energy needed to bring about a reaction; this allows reactions to occur without raising the temperature of the cell.
125
How do enzymes reduce the activation energy?
The specific shape of an enzymes active site and its complementary substrate is such that electrically charged groups on their surfaces interact. The attraction of oppositely charged groups may distort the shape of the substrate and assist in the breaking of bonds or in the formation of new bonds. In some cases the active site may contain amino acids with acidic side chains and the acidic environment created within the active site may provide conditions favourable for the reaction.
126
What do you call enzymes that work inside cells?
Intracellular
127
What do you call enzymes that work outside cells?
Extracellular
128
What are catabolic reactions?
A reaction that breaks down larger molecules into smaller molecules.
129
What is an anabolic reaction?
A reaction where molecules are build up into larger molecules.
130
What are the properties of enzymes?
- They are globular proteins
- They have an active site that allows binding with a specific substrate
- Catalyse reactions
- Reduce the activation energy required for a chemical reaction to take place
- do not alter the end product or nature of the reaction
- do not get used up and remain unchanged at the end of a reaction and able to bind with another substrate molecule
131
How is the rate of a reaction measured?
By determining the quantity of substrate used or the quantity of product formed in a given time.
132
Why does the reaction of reaction occur fast at the start and then level off?
If a mix of a fixed quantity of enzyme to substrate was used, at the start, the reaction would proceed quickly. However as the substrate is used up, there are fewer substrate molecules to collide with and bind to the enzyme so the reaction slows down and eventually stops and no further increase in the product occurs.
133
What is the slope of the rapid phase of a reaction known as?
The initial rate of a reaction
134
If you compare to initial rates of reaction, how do you which had a higher initial rate of reaction?
The graph that has the steeper slope has the higher initial rate of reaction.
135
How do you calculate the initial rate of a reaction?
Dividing the change in the y axis by the change in the x axis values.
136
How do enzyme and substrate concentrations affect the rate of reactions?
The higher the concentration of enzymes, the greater the number of active sites available to form enzyme-substrate collisions forming enzyme-substrate complexes so increases the rate of the reaction.
137
With a high substrate concentration, what limits the reaction?
The enzyme concentration as every active site becomes occupied and substrate molecules cannot enter an active site until one becomes free again.
138
What problems does CF have on the reproductive system?
- Females have a reduced chance of becoming pregnant because a mucus plug develops in the cervix. This stops the sperm from reaching the egg.
- Males with CF commonly lack the vas deferens (sperm duct) on both sides, which means that sperm cannot leave the testes. Where the vas deferens is present it can become partially blocked by a thick sticky mucus layer. This means fewer sperm are present in each ejaculate.
139
What is the effect of CF on sweat?
Sweat glands are exocrine glands that initially secrete into their lumen a solution of salt and water that is isotonic to the blood. In an individual without CF, CFTR and ENaC proteins allow the reabsorption of sodium chloride from the sweat as it moves up the duct towards the skin surface. The sweat that is released on to the skin and evaporates is therefore hypotonic.
140
What is cystic fibrosis caused by?
The mutation in the DNA that carries the instructions for making the CFTR protein.
141
What is a mutation?
A change in the genetic material in a cell. Some mutations are concerned with very small changes to an organism’s DNA. These are known as gene mutations. Mutations happen by chance, but certain environmental factors called mutagens can increase the rate of mutation. Mutations play an important part in breeding plants with desirable characteristics.
142
What evidence was used to discover DNA?
X-ray diffraction patterns
143
What is DNA?
The molecule which forms the genetic material of all living organisms. DNA is built up of nucleotides. In an animal or plant cell, DNA is found in the chromosomes in the nucleus. There are also small amounts of DNA in the mitochondria and chloroplasts. Genes are sections of DNA which code for particular proteins.
144
What is a gene?
A piece of DNA which has a specific sequence of nucleotic bases. These code for a sequence of amino acids in a polypeptide chain. An individual gene may have more than one form. These forms or alleles differ from each other in the sequences of their nucleotide bases and, as a result, produce slightly different proteins.
145
What does a genetic code dictate?
All the inherited characteristics of an organism.
146
What is a genome?
All the DNA inside a cell. The genome contains a full set of all the genes controlling the growth and development of the organism of which the cell is a part.
147
What is deoxyribose?
A five-carbon sugar. Deoxyribose is an important component of DNA. DNA is built up of nucleotides. Each nucleotide is formed from deoxyribose, a phosphate group, and a nucleotide base linked together by condensation.
148
What is a nucleotide?
Nucleic acids are polymers made up from a number of nucleotides joined to each other by condensation. Each nucleotide has three components: a five-carbon or pentose sugar ribose in RNA and deoxyribose in DNA; a phosphate group; a nucleotide base.
149
What is a nuclei base?
The nucleic acids DNA and RNA are polymers. They are built up of a large number of nucleotides. Each nucleotide contains a five-carbon or pentose sugar, phosphate and a nucleotide base. Four different nucleotide bases are found in the nucleotides which make up a DNA molecule. These are adenine, thymine, cytosine and guanine. In RNA, thymine is replaced by another base, uracil. It is the sequence of nucleotide bases in nucleic acids which forms the basis of the genetic code.
150
What is an organic base?
In DNA, each nucleotide contains one of the following four organic bases: adenine, cytosine, guanine and thymine.
151
When mononucleotides join together in a condensation reaction what forms?
A polynucleotide
152
What is the bond called that forms between two nucleotides?
Phosphodiester bond
153
What is the shape of DNA?
A double helix
154
What holds the bases together in DNA?
Hydrogen bonds
155
What are two nucleotides strands described as?
Antiparallel because they run in opposite directions.
156
In DNA what bases pair together? Why?
Ademine pairs with Thymine
Cytosine pairs with guanine
Bases A and G have a two ring structure whereas C and T only have one ring. The bases pair so there effectively three rings forming each 'rung' of the DNA molecule, making the molecule a uniform width along its whole length.
157
What is a complementary base pair?
The nucleotide bases in nucleic acids always pair in a particular way. Adenine always pairs with thymine in DNA and with uracil in RNA. Cytosine always pairs with guanine. Complementary base pairing allows exact copies of DNA to be made in DNA replication. Transcription and translation also rely on complementary base pairing.
158
How does DNA code for proteins?
Every gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain. The polypeptide chain then twists and folds into a functional protein.
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What is protein synthesis?
Transcription takes place in the nucleus. A molecule that is a copy of the gene, coding for the required protein is made. This copy is not made from DNA but from another type of nuclei acid called ribonucleic acid. This RNA molecule can leave the nucleus, carrying the information to the cytoplasm where it is used in the manufacture of the protein. The original gene of the DNA stays in the nucleus.
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What is transcription?
The process in which the genetic information contained in a DNA molecule is copied to produce messenger RNA. This is the first stage in protein synthesis. A molecule of DNA unwinds. The sequence of nucleotides on one of the strands, called the template strand, is used to produce a mRNA molecule by complementary base-pairing.
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What is the difference between DNA and RNA?
An RNA molecule is a single stranded polynucleotide made of ribonucleic acid nucleotides. RNA nucleotides are very similar in structure to DNA nucleotides, containing a phosphate, sugar and base, except that they contain ribose sugar and not deoxyribose. Another difference is that in RNA nucleotides, the base Uracil replaces thymine, so RNA never contains thymine.
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What is RNA made in the nucleus during transcription known as?
Messenger RNA
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What is a messenger RNA?
A type of RNA which acts as a messenger molecule. Genes are sections of DNA which code for particular proteins. DNA is too large to pass through the nuclear pore, so mRNA takes a copy of the genetic code. RNA passes out into the cytoplasm, where it enables amino acids to be assembled in the correct sequence to make a protein.
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What is translation?
The biological process of translation means turning the sequence of bases in the genetic code (the language of nucleotides) into a sequence of amino acids (the language of proteins).
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Describe the process of transcription (protein synthesis)?
At the start of transcription, an enzyme called RNA polymerase attaches to the DNA. The hydrogen bonds between paired bases break, and the DNA molecule unwinds. The sequence on one of the strands, the template strand, is transcribed to make and mRNA molecule with the same base sequence as DNA coding strand. The complimentary RNA nucleotides align themselves into position and then phosphodiester bonds form to produce an mRNA molecule. Because of the complementary base pairing, the order of the bases on the DNA exactly determines the order of the bases on the mRNA. Only the section of DNA that codes for the protein being made is transcribed. When transcription is complete, the mRNA molecule leaves the nucleus through a pore in the nucleus envelope and the DNA molecule 'zips up'.
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What is a nucleic acid?
Nucleic acids are polymers made up from a number of nucleotides joined to each other by condensation. There are two sorts of nucleic acid: DNA and RNA.
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What is a nuclear envelope?
A layer which surrounds the nucleus of a cell. It is called an envelope because it is really composed of two membranes perforated by tiny pores. mRNA leaves the nucleus through these nuclear pores during the process of protein synthesis.
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The code carried by the DNA is... Why?
A three base or triplet code. This is because there are only four bases and so only four different amino acids would be made, instead of the 20. There are overall 64 possible three letter combinations if the four DNA bases are grouped in triplets.
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What are the properties of the genetic code?
- Triplet code - each adjacent group of three bases codes for an amino acid.
- The code is Non-overlapping - each triplet code is adjacent
- 64 possible three letter combinations
- one triplet sequence is the start code and three are the stop code (chain terminators)
- This leaves on average three different triplet codes for each of the 20 naturally occurring amino acids in a protein molecule.
- Degenerate - several triplets can code for the same amino acid
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What does it mean when the code is described as degenerate?
Several triplets can code for the same amino acid
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What is a codon?
A sequence of three nucleotide bases on a messenger RNA molecule that codes for a particular amino acid. For example, the messenger RNA codon CCA codes for the amino acid proline.
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What is the coding strand also known as?
DNA sense strand
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What is the template strand also known as?
DNA antisense strand
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Starting with DNA sense strand (coding strand) how do you get to a protein?
- DNA sense strand
- DNA antisense strand
- Transcription of antisense strand
- mRNA
- Translation of mRNA
- Protein
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What can a mutation do in the sequence of bases in DNA?
Could change a triplet that makes up a gene. The could then change the amino acid sequence of the primary structure which may substantially alter the proteins three dimensional structure and properties.
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What are the types of mutation that occur in DNA?
- Substitutions
- Insertions
- Deletions
- Inversions
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What do insertions and deletions cause?
Insertions and deletions of a number of bases where the number cannot be divided by three causes a 'frame shift'. All the subsequent triplets from that point onwards are affected.
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What are ribosomes?
Ribosomes are small organelles (structures within the cell) made of ribosomal RNA and protein. Ribosomes are found free in the cytoplasm or attached to endoplasmic reticulum, a system of flattened, membrane bound sacs. Ribosomes are composed of two subunits, a smaller and a larger subunit. The larger subunit contains two tRNA binding sites. The mRNA attaches to the smaller subunit, so that two mRNA codons face the two binding sites of the larger subunit.
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What are transfer RNA molecules and why are they key to translation?
Each amino acid has its own tRNA molecule that transfers amino acid present in the cytoplasm to the ribosome. They are key to translation because of their properties.
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What are the properties of transfer RNA?
- They are single stranded RNA
- They can fold back on themselves
- Complementary base pairing makes them a clover leaf shape
- At one end they have a three base sequence known as a anticodon
- At the opposite end of the tRNA is a binding site for an amino acid.
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What is an anticodon?
A sequence of three nucleotide bases on a transfer RNA molecule, which is complementary to the corresponding messenger RNA codon. For example, CCA is one of the messenger RNA codons for the amino acid proline. The sequence of nucleotide bases from the corresponding anticodon is GGU.
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What is the process of DNA replication?
The entire DNA double helix unwinds from one end and the two single strands split apart as the hydrogen bonds the bases break. Free DNA nucleotides line up alongside each single DNA strand and hydrogen bonds form between the complementary bases. The enzyme DNA polymerase links the adjacent nucleotides with phosphodiester bonds in condensation reactions to form new complementary strands. Hydrogen bonding links the two strands together. In this way each original strand of DNA acts as a template on which a new strand is built and overall, two complete DNA molecules are complete.
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What are semi-conservative replications?
In DNA replication, each of the two resulting DNA molecules contains one ‘old’ (conserved) strand and one ‘new’ strand.
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What is fragmentary replication?
All DNA strands are made up of a mixture of original parent DNA nucleotides and new nucleotides.
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What is conservative replication?
One DNA has two original parent DNA strands, the other molecule has two 'new' strands.
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When does DNA replication need to occur?
When a cell divides during growth and repair of an organism, an exact copy of DNA must be produced so that each of the new daughter cells receives a copy.
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Which type of replication is correct?
The semi-conservative because of the presence of both medium and light DNA bands.
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What is a gene mutation?
When a new strand of DNA is being built, inaccuracies with complementary base pairs can occur when an incorrect base may slip into place.
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What could cause a genetic disorder?
If a mutation occurs within a gene and a new base triplet is created that codes for a stop signal or a different amino acid, the protein formed may be faulty.
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What causes single cell anaemia?
In the disease sickle cell anaemia, there is a mutation in the gene that codes for one of the polypeptide chains in haemoglobin. The base adenine replaces thymine at one position along the chain. The mRNA produced from this DNA contains the triplet code GUA rather than GAA. As a result the protein produced contains the non-polar amino acid valine rather than the polar glutamic acid. The small change has a devastating effect on the functioning of the molecule.
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what is the problem with having sickle cell anaemia?
The haemoglobin is less soluble. When oxygen levels are low, the molecules form long fibres that stick together inside the red blood cell, distorting its shape. The resulting half moon (sickle) shaped cells carry less oxygen and can block blood vessels.
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What chromosome is the CF gene?
7 as it carries the code to make the CFTR protein.
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What is locus?
The position of a gene on a chromosome. For example, a person with the gene disease thalassaemia has two copies of the recessive allele that causes the disease. Each allele will be at the same position or locus on one of the copies of chromosome 11.
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What is a chromosome?
One of the thread-like structures in the nucleus into which DNA is organised. A chromosome consists of DNA, a small amount of RNA, and various proteins, some of which are involved in packaging the DNA.
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How many pairs of chromosomes do humans have?
23 pairs
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What are the chromosomes in each pair known as?
Homologous chromosomes
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What is an allele?
One of the different forms of a particular gene.
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What are the possible outcomes for having CF?
1) FF - A person with two identical copies of the normal allele does not have cystic fibrosis.
2) ff - A person with two copies of the mutated allele has cystic fibrosis.
3) Ff - A person with one normal allele and one mutated allele does not have cystic fibrosis but is a carrier and could have children who have the disease.
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What are the properties of cell membranes?
- Flexible
- Fluid
- Selectively permeable
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What is the evidence for the fluid mosaic model?
- Phospholipids are both hydrophilic and hydrophobic so form bilayer in an aqueous environment.
- A monolayer film of phospholipids is twice as large as the cell surface area.
- Microscope images of cell surfaces show proteins sticking out.
- When lectins, which react with carbohydrates, are added to a membrane they are only found on the outside.
- Some water-soluble substances pass into and out of cells.
- Ionic and polar molecules do not pass easily through membranes, but lipid-soluble substances do.
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what are the three types of passive movement?
- Diffusion
- Facilitated diffusion
- Osmosis
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There will only be diffusion when?
- The membrane is permeable (pores big enough)
- The particle and/or pore is not charged
- The particle is soluble
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Name one similarity and one difference active transport and facilitated diffusion.
Both processes can use carrier proteins. Active transport requires energy whereas facilitated diffusion does not.
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What is the sugar-phosphate backbone?
The joining of nucleotides by phosphodiester bonds between the sugar of one nucleotide and the phosphate of another creates a chain of alternating sugar and phosphate groups. This is the structural framework of polynucleotides such as DNA and RNA.
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Describe the characteristics of mRNA.
- Formed in the nucleus from DNA antisense (template) strand
- Single stranded
- Not usually folded
- Carries codons
- Attaches to tRNA
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Describe the characteristics of tRNA.
- Single stranded
- Folded into specific pattern
- Carries anticodons complementary to the condones on mRNA and hence DNA sense strand
- Attaches to mRNA and amino acids
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What does degenerate mean?
There are 64 possible three letter combinations if four DNA bases are used as triplets. As there are only 20 amino acids in nature, this means that most amino acids are coded for by more than one triplet.
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Regarding the secondary structure, why do hydrogen bonds form between parts of the chain?
Chains of polypeptides fold up to form proteins. Amino and carboxylic acid groups in the amino acid chain carry small amounts of charge. The charge is negative on the CO of the carboxyl group and positive and on the NH of the amino group.
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What is cooperative binding?
When a molecule binds to another it changes the tertiary structure making easier for more binding.
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Describe Meselson's and Stahl's classic experiment, which demonstrates semi-conservative DNA replication.
1) Bacteria cultured in a medium containing 15N transferred into a normal (14N) medium. This makes medium DNA which spins down to centre in centrifuge.
2) The DNA extracted and centrifuged after two rounds of replication gave two bands; one medium and one light. The presence of both medium and light bands of DNA confirmed the semi-conservative model and ruled out the fragmentary model which would only produce one type of DNA containing a mixture of heavy and light nucleotides.
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When can mutations occur?
- DNA replication creates new cells. In gametes, mutations can be passed to offspring and lead to genetic disorders, such as cystic fibrosis.
- Transcription creates new mRNA. In body cells, mutations can lead to cancer.
- Translation creates proteins. Not all mutations of proteins are harmful; many are neutral and do not affect the function of the protein and some can even confer advantages on an organism, leading to evolution.
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What is a recessive allele?
An allele which is not expressed when a dominant allele is present; in peas, 'dwarf' is recessive.
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What is a dominant allele?
An allele which is always expressed; in peas 'tall' is dominant.
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What is incomplete dominance?
Neither allele is dominant and the resultant phenotype is a mix; e.g crossing a white snapdragon with a red one, will give pink.
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What does heterozygous mean?
One of each allele.
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What decisions need to be made on whether to have genetic screening?
- risks of miscarriage or harm to foetus from the testes
- religious beliefs - right to life of the foetus
- potential abortion in the event of a possible diagnosis
- the cost of bringing up a baby that is 'disabled'
- mental and emotional issues surrounding the birth of a 'disabled' baby
- choosing not to become a parent
- dealing with the risks/consequences of false negatives and false positives.
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What is preimplantation genetic diagnosis (PGD)?
Embryos created through in vitro fertilisation (IVF) are tested to see if they carry the faulty allele. Only those which have a normal allele are implanted into the woman.
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What is genetic screening?
Procedure that allows the identification of cells or individuals with a particular DNA sequence.
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What is genetic testing?
Procedure that allows the identification of cells or individuals with a particular DNA sequence.
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Genetic testing can be performed on any...
DNA
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How can genetic screening be used?
- To confirm a diagnosis
- To identify carriers
- For testing embryos
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How can you identify carriers using genetic screening?
A sample of blood or cells taken from inside the mouth can be used to detect abnormal alleles in people without the disease who are heterozygous.
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What are the two well established forms of parental genetic testing?
- Amniocentesis
| - Chronic Villus sampling
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Describe the process of amniocentesis
A way of obtaining cells from a developing fetus. A developing fetus is wrapped in a membrane called the amnion. The space between the amnion and the fetus is filled with a fluid called amniotic fluid. Amniotic fluid contains some fetal cells. These cells can be extracted by a needle and their chromosomes can be observed or the DNA that they contain may be investigated.
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When is amniocentesis carried out?
Around 15-17 weeks of pregnancy
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Describe the process of chronic villus sampling
Procedure in which a small sample of placental tissue (which includes cells of the fetus) is removed either through the wall of the abdomen or through the vagina.
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When is chronic villus sampling carried out?
8-12 weeks of pregnancy
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After the process of amniocentesis how long does it take before karyotyping DNA analysis?
2-3 weeks later because the foetal cells have to separated and grown in a culture.
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After the process of chronic villus sampling, how long is it until karyotyping DNA analysis?
Next day
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Which procedure, amniocentesis or chronic villus sampling, has a higher risk of miscarriage?
Chronic villus sampling which has a 2% chance of miscarried compared to amniocentesis which has only a 1% chance of miscarriage.
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What is the third form of prenatal genetic testing that is in the early stage of development?
Non-invasive prenatal diagnosis (NIPD)
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Describe the process of non-invasive prenatal diagnosis.
DNA fragments in the mother's blood plasma during pregnancy are analysed.
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How does non-invasive prenatal diagnosis work?
Whilst most of this 'cell-free DNA' is from the mother's blood palms herself, about 10-20% is from the embryo.
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When in the blood sample taken from a mother for non-invasive prenatal diagnosis?
7-9 weeks of pregnancy
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What are the four main ethical frameworks?
1) Rights and duties (right to life)
2) Maximising the amount of good in the world
3) Making decisions for yourself
4) Leading a virtuous life
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If a couple are at risk of having a child with a genetic disorder who can they talk to?
A genetic counsellor
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Why is regular physiotherapy important for CF sufferers?
Rhythmical tapping of the walls of the chest cavity (percussion therapy) and use of a flutter device can help to loosen the mucus and improve the flow of air into and out of the lungs. Physiotherapy should occur twice a day.
