Topic 2- Genes And Health Flashcards
(93 cards)
1
Q
What is the concentration gradient?
A
The difference in concentration between two areas.
A larger concentration gradient results in a faster rate of diffusion.
2
Q
How does temperature, surface area and membrane thickness affect rate of diffusion?
A
Higher temperatures increase the rate of diffusion because molecules move faster at higher temperatures, facilitating quicker movement.
Larger surface area results in a faster rate of diffusion as more area allows more molecules to pass through simultaneously.
Thicker membranes slow down the rate of diffusion as a thicker barrier requires more time for molecules to pass through.
3
Q
Describe these transport processes, what they’re used by and what effects their rate:
Active transport?
Diffusion?
Facilitated diffusion?
A
1.The movement of substances against the concentration gradient which requires energy. Energy from ATP is used to change the shape of the carrier protein and allow substances to be released on the other side.
- The surface area of a membrane and the number of carrier proteins
- The passive net movement of particles in fluids from a high to a low concentration.
Used by small (co2) or non-polar molecules (o2) to pass directly through the membrane.
- Temperature, Surface area and thickness of exchange surface. - A passive process where molecules diffuse through carrier or channel proteins across membrane down conc. gradient.
- Used by large molecules as they’re too big and polar molecules as they get repelled by hydrophobic fatty acid tails due to insolubility.
- The rate of facilitated diffusion increases with more proteins and a higher concentration gradient.
4
Q
What changes occur in carrier proteins during active transport?
A
Energy from ATP causes the carrier protein to change shape, releasing the substance on the other side.
5
Q
What was the original fluid mosaic model based on?
What were it’s issues? (2)
A
An electron micrograph called the ‘sandwich model’.
1. Didn’t allow hydrophilic phosphate heads to contact water
2. Didn’t keep hydrophobic, non-polar amino acids away from water.
6
Q
What is the evidence from reinterpretation of fluid mosaic model EM?
A
Re-interpretation showed phosphate heads were more electron dense so were the darker part and the fatty acid tails were lighter and on the inside
7
Q
What is the evidence for fluid mosaic model from removing proteins?
A
It showed 2 types of protein, some could be easily removed by increasing the ionic strength of a solution and some could only be removed with a strong detergent.
8
Q
Why does evidence from removing proteins support the FM model?
A
As there is loosely attached peripheral proteins and integral proteins which are fully embedded.
9
Q
What are the 3 steps for evidence from freeze fracture EM?
A
- Freeze the membrane then break between the layers
- Coat the inner fractured surface with a heavy metal.
- Use a scanning EM to get a 3D image
10
Q
FICKS LAW:
What 3 properties is the rate of diffusion dependant on?
A
- SA: Rate of diffusion = directly proportional to surface area
- Concentration gradient to rate of diffusion is directly proportional to difference in concentration
- Thickness of exchange surface to ROD is inversely proportional to thickness of surface
11
Q
What is Ficks Law equation?
A
ROD is directly proportional to SA X difference in concentration gradient divided by thickness of exchange surface
12
Q
What does the cell membrane include? (5)
A
- Phospholipid bilayer
- Integral proteins
- Peripheral proteins
- Cholesterol
- Carbohydrates
13
Q
• What is the structure of the phosphoripid bilayer? (3)
A
2 fatty acid hydrophobic tails, 1 hydrophilic negatively charged phosphate group, 1 glycerol group
14
Q
What happens to the phospholipids in a wet environment?
A
They form a bilayer, they could form a Micelle but favour bilayer as the fatty acid tails are too bulky
15
Q
Where is cholesterol found + what does it do?
A
- It is a lipid which sits in the core of the membrane but not in bacteria
- It makes it more rigid
16
Q
What increases the fluidity of the membrane?
A
High temperatures increase the fluidity which increase the permeability
17
Q
What is the permeability?
A
Semi permeable
18
Q
What do glycoproteins and lipids do? (2)
A
- They form hydrogen bonds with water outside the cell which stabilises it
- They act as signalling receptors with active binding sites for communication molecules like hormones and drugs
19
Q
What are saturated phospholipids? (2)
A
They have NO DOUBLE BOND and their tails are easier to compact
20
Q
What are unsaturated phospholipids? (3)
A
- Have a double bond
- Kinked tails
- Can’t fit together nicely
21
Q
Which type of saturation makes the cell membrane more fluid?
A
Unsaturated
22
Q
How did freeze fracture EM support Model?
A
It showed a smooth mosaic like structure interspersed with larger particles.
23
Q
What were the 3 steps of evidence from using labelled tracers?
A
- Lectin (molecules that bind to polysaccharides) were labelled with ferritin which can be seen under EM. 2. It was mixed with membrane samples. 3. The lectin only bound to the surface of the membrane.
24
Q
How did evidence from labelled tracers support the FMM?
A
They showed that the membrane is asymmetrical.
25
What were the 3 steps of evidence from mouse + human cells?
1. Label mouse membrane proteins green and humans red. 2. Fuse the cells. 3. Use microscope to view labelled protein movement.
26
What was observed from mouse and human cell FMM evidence and how does it support?
First, the coloured membranes stayed in their halves but after an hour at 37 degrees they completely mixed. This can only happen via diffusion so shows the membrane is fluid.
27
What are the 3 types of Channels?
Channel proteins, gated channels and carrier proteins.
28
What are channel proteins?
They are water filled channels that allow polar molecules and ions to pass through to avoid the hydrophobic layer of membrane.
29
What are gated channels?
A type of channel that requires a signal to open like a hormone or change in voltage.
30
What happens at a carrier protein?
1. An ion or molecule like sugar, amino acids or nucleotides bind to the proteins site. 2. The protein changes shape to allow them to pass through.
31
Which side of a carrier protein has more binding?
The side with more molecules as it carries them down the concentration gradient.
32
What is osmosis?
The net movement of water molecules from a dilute to a concentrated solution through a partially permeable membrane.
33
What does isotonic mean?
Equal water potential both sides of cell membrane.
34
What are the 2 types of active transport?
Endocytosis and exocytosis.
35
What is Exocytosis?
1. The bulk removal of substances from a cell using ATP. 2. Vesicles fuse with the membrane and release substances within to the surroundings like the release of insulin from the blood.
36
What is Endocytosis?
1. The bulk transport of substances into a cell using ATP. 2. Part of the membrane buds off to become a vesicle which engulfs the substance and releases it into the cell like cholesterol into cells.
37
How does ATP provide energy?
Very little energy is required to break the bond holding the third phosphate
The phosphate becomes hydrated
Lots of energy is released as the bonds form between water and the third phosphate
38
What is the point of regulating water content of mucus?
To maintain a consistent viscosity
39
What happens if mucus water content is:
Too runny?
Too thick?
1. It floods the airways
2. It cant get beaten out of the lungs by cilia.
40
What are the consequences of unregulated mucus water content for CF patients? (3)
Theyre mucus is too thick so cant be beaten out of the lungs, which causes lung infections as the bacteria are trapped.
Their white blood cells break down and their DNA makes the mucus stickier.
The inflammation leads to lung damage. This is an example of a positive feedback loop
41
How is mucus water content regulated?
By the transport of sodium and chloride ions across epithelial cells which causes water to follow them via osmosis
42
What does ENaC’s stand for?
What does CFTR stand for?
1. Epithelial sodium ion channels
2. Cystic fibrosis transmembrane conductance regulator which is a type of gated channel
43
What happens when there is excess water in the mucus?
1. Sodium ions are actively pumped across the basal membrane and then diffuse through open ENaC’s in apical membrane.
2. The chloride ions diffuse down the electrical gradient into tissue fluid and CFTR channels close.
3. Water is drawn out of cell via osmosis due to higher conc. of salts in tissue fluid
4. Water is drawn back into cell
44
What happens when too little water in the mucus?
1. Chloride ions are pumped across the membrane and diffuse out of the open CFTR channels at top of membrane.
2. Sodium ions diffuse down the electrical gradient into the mucus and the ENaCs close
3. The elevated salt concentration in the mucus draw water out of the cell by osmosis.
45
What is wrong with mucus water content regulation process in CF patients?
1. The CFTR protein is non functional or absent
2. The ENaC is constantly open so may let more sodium than normal in
3. So water is continuously removed from mucus and drawn into the cell.
46
What is a genome?
All of the DNA/genes that make up an individual.
47
What is a gene?
A gene is a specific section of DNA made up of a sequence of complementary base pairs which code for one or more proteins
48
What are the base pairing rules for organic bases?
A+G both have 2 rings
C+T both have one ring.
So A+T have 3 rings and 2 hydrogen bonds
And C+G have 3 rings and 3 hydrogen bonds
49
What did Watson and Crick do?
They proposed the structure of DNA model based on Rosa Franklin evidence from X-ray diffraction patterns of DNA.
50
What bonds hold together:
Organic bases?
Nucleotides?
Amino acids?
1. Hydrogen bonds
2. Phosphodiester bonds
3. Peptide bonds
51
What is the primary structure of a protein?
The sequence of amino acids in a polypeptide chain joined together in a condensation reaction held together by peptide bonds.
52
What is the primary structure determined by and what happens if there is a change in nucleotide sequence?
It is determined by the gene encoding the protein. If the nucleotide sequence changes, a different amino acid could be coded for meaning that primary sequence could be different, resulting in different structure and function.
53
What is the secondary structure?
The coiling or folding of a polypeptide chain due to hydrogen bonds forming between different amino acids. It included alpha helices and beta pleated sheets.
54
What creates alpha helices?
Hydrogen bonds forming between the slightly negative C=O of a carboxyl group and the slightly positive NH of an amine group. They stabilise the shape.
55
How are beta pleated sheets formed?
Around 15 amino acids in length fold back on themselves and then link together by hydrogen bonds including the parallel chains.
56
What strengthens weak hydrogen bonds?
Cumulative impact.
57
What is the tirtiary structure? What interactions does it have?
The 3D shape/structure of the protein. Maintained by bonds and hydrophobic (weakest) interactions between R groups.
Cysteines have sulfur containing R groups, if two of these meet they form disulphide bonds between them. Ionic bonds also form between 2 negatively charged R groups which is rare.
58
Which bonds are stronger in tirtiary structure?
Ionic and disulphide bonds are stronger than hydrogen but are more susceptible to changes in pH.
59
What is the quaternary structure?
Proteins made up of multiple polypeptide chains. E,g haemoglobin is made up of 4 polypeptide chains conjugated by an iron containing haem group. These include globular and fibrous proteins.
60
What is a globular protein and examples?
A globular protein is a spherical, compact protein. Its chains are coiled up so that the hydrophilic parts are on the outside and the hydrophobic parts are on the inside which makes it soluble and therefore easily transported. Examples include, haemoglobin, enzymes, antibodies and DNA polymerase.
61
What is a fibrous protein and examples?
Fibrous proteins are long insoluble polypeptide chains which are coiled tightly around each other and cross linked for extra support. Because they are strong, they are often found in supportive tissue. Examples include collagen (made up of 3 polypeptide chains and mainly glycine and proline), keratin and elastin.
62
Why does the primary structure of a protein determine its 3D shape?
Amino acids have different R groups which can interact in different ways. The primary structure is the sequence of amino acids so the sequence determines the folding and the chemical bonds being formed between the amino acids on the polypeptide chain.
63
What are the 5 compare and contrast points about globular and fibrous proteins?
1. Globular proteins have a spherical and compact shape whereas fibrous proteins are long twisted polypeptides.
2. Globular proteins are soluble due to their hydrophilic side chains whereas fibrous proteins are insoluble due to their hydrophobic parts on the outside.
3. Globular proteins are involved in enzyme catalysis reactions whereas fibrous proteins aren’t.
4. Fibrous proteins are involved in structural support within the body e.g keratin whereas globular proteins have a wide variety of functions such as hormones and transport proteins.
5. Globular proteins have an irregular amino acid sequence with alpha helices and beta pleated sheets interspersed throughout whereas fibrous proteins have a more regular structure with long chains of alpha helices and beta pleated sheets.
64
Draw the structure of an amino acid and the reaction between 2.
65
What 3 things are the genetic code and what do they mean?
1. Universal- The same 4 amino acids are used in every organism on the planet, the same codons code for the same amino acids, codons are transcribed into mRNA which is translated in amino acids in every organism.
2. Degenerate- some amino acids are coded for by more than one codon as there are 64 codons and only 20 amino acids.
3. Non-overlapping- the triple codes don’t overlap. Each triplet is separate from others on the chromosome.
66
What are the 2 similarities between DNA and RNA?
1. They both are made up of nucleotides joined together in a condensation reaction and held together by phosphodiester bonds.
2. They both have a sugar phosphate backbone.
67
What are the 5 differences between DNA and RNA?
1. DNA is composed of deoxyribose which is a 5C sugar whereas RNA is composed of a ribose sugar still 5C.
2. DNA is double stranded with a double helix structure whereas RNA is single stranded.
3. DNA uses A+T for its organic bases whereas RNA uses uracil instead of thymine.
4. DNA is a longer molecule whereas RNA is much shorter.
5. DNA is made up of DNA nucleotides whereas RNA is made up of RNA ribonucleotides.
68
What did Meselson and Stahl do?
They found that DNA replicated semi-conservatively which means that every new molecule of DNA produce, half of it belongs to the original DNA.
69
What was Meselson and Stahl’s 5 step experiment?
1. They grew E.coli in a growth medium containing a heavy isotope of nitrogen (N15) for several generations.
2. They moved the E.coli into a broth containing N14 and let it replicate for one generation.
3. They extracted the DNA and centrifuged it in a density-gradient solution.
4. They found that after 1 replication in N14, it showed a middle band.
5. They let it replicate for another generation in the N14 and found it showed a middle and top band.
70
Draw what the DNA from Meselson and Stahl’s experiment looked like in the test tubes.
71
What does transcription do and what are the 6 steps?
- It creates an exact copy of the DNA by converting it into mRNA.
1. DNA helicase unwinds the DNA double helix and the hydrogen bonds between the organic bases break.
2. RNA polymerase binds to the start codon (AUG).
3. Free RNA nucleotides line up alongside the DNA template strand in a complementary fashion e.g C+T, A+U.
4. RNA polymerase catalyses the condensation reaction between the RNA nucleotides and they form phosphodiester bonds which creates the sugar phosphate backbone.
5. RNA polymerase reaches the stop codon (UAG) and mRNA detaches from DNA template strand and leaves through the nuclear pore.
6. The DNA double helix zips back up and hydrogen bonds reform between the bases.
72
Where does translation take place and what are the 5 steps?
- Takes place in the ribosome.
1. MRNA binds to the ribosome and tRNA anticodon binds to start codon (AUG) and brings over the first amino acid.
2. The second tRNA brings over the second amino acid.
3. A condensation reaction takes place between the adjacent amino acids and a peptide bond is formed as they move away from the tRNA that transported them.
4. The ribosome moves along the mRNA and more tRNA bring over more amino acids and eventually a polypeptide chain forms.
5. TRNA reaches the stop codon (UAG) and polypeptide chain leaves the ribosome.
73
What are the 5 steps of DNA replication?
1. DNA helicase breaks the hydrogen bonds between the nitrogenous organic bases and the DNA double helix unwinds.
2. DNA polymerase binds to the start codon (AUG).
3. Free DNA nucleotides line up alongside the template strand as they are attracted to the exposed bases.
4. DNA polymerase catalyses the condensation reaction between the DNA nucleotides and they form phosphodiester bonds which forms the sugar phosphate backbone.
5. DNA polymerase reaches the stop codon (UAG) and hydrogen bonds form between the organic bases and the DNA double helix winds up containing one new strand and one old strand.
74
What are enzymes and how do they lower activation energy?
They are biological catalysts that speed up chemical reactions.
There are complementary charges on substrates and active sites. Attraction of opposite charges may distort the shape of the substrate to help make and break bonds more easily as the molecules are held more closely together.
75
What is required to make and break bonds?
Energy
76
What determines the shape of the active site of an enzyme?
The tirtiary structure.
77
What are the 5 steps of the lock and key theory?
1. One or more molecules form a complementary shape to fit the active site.
2. The substrate molecules form temporary bonds with the amino acids on the active site and form an enzyme-substrate complex.
3. They enzyme holds the substrate molecules in a way for them to react more easily.
4. The products are released and the enzyme remains unchanged.
5. Each enzyme can only catalyse one specific reaction.
78
What does the lock and key theory suggest about shape of enzyme and substrate?
They fit perfectly together
79
What are the 3 steps of induced fit model?
1. When the substrate enters the active site, the enzyme changes shape slightly to fit more tightly around the substrate.
2. Only a specifically shaped substrate can induce the correct changes in shape of the enzyme.
3. A slight change in shape of the active site allows the substrate to react and form an enzyme-substrate complex.
80
What is a mutation?
It is a change in the base sequence of DNA.
81
Where can mutations happen?
In individual genes or whole chromosome. If it occurs in an ovary or teste cell dividing to become a gamete, they can be passed on.
82
When do mutations happen?
They can happen in DNA replication when sometimes the wrong nucleotides are used which can alter the sequence of the bases and changes which amino acids are coded for.
83
What are the 5 types and what are they?
1. Deletion= when a nucleotide is missed out and the entire triplet sequence is altered so codes for an entirely different protein. Results in frame shift to the left
2. Duplication= When 2 of the same nucleotides are inserted which alters the entire triplet sequence so a different protein is coded for. Results in frame shift to the right.
3. Substitution= when a nucleotide is swapped for another. May change amino acid may not
4. Inversion= When the sequence of bases in a triplet are reversed so only changes one amino acid.
5. Insertion= When an extra nucleotide is inserted which changes the entire triplet sequence and causes a different amino acid to be coded for and results in frame shift to the right.
84
What can increase the rate of mutations?
Agents called mutagens
85
What are the 2 main causes of mutations?
1. Ionising radiation: x-rays, gamma rays and uv
2. Chemicals: tar, cigarette smoke and nitrous oxide.
86
What are the 3 consequences of mutations (2 bad, 1 good)?
1. If they are in body cells, they only impact the cells and if they are harmful the cell will just die.
2. If they dont die, the mutations can be passed on.
3. Some mutations can be advantageous so will increase in frequency in the subsequent generations and create more genetic variation.
87
What are the definitions for each of these?
Allele
Phenotype
Recessive
Dominant
Incomplete dominance
Homozygote
Heterozygous
1. A form of a gene that can code for different variations
2. The observable characteristics of a gene
3. An allele which cannot be expressed if a dominant allele is present.
4. An allele which is always expressed
5. Where neither are dominant so phenotype is a mix of both alleles.
6. Someone with 2 of the same alleles
7. Someone with one of each allele.
88
What are the 3 main uses for genetic screening?
1. Identification of carriers.
2. Pre-implantation genetic diagnosis (PGD)
3. Prenatal testing.
89
Describe what identification of carriers (3), pre-implantation genetic diagnosis (2) and prenatal testing (2) is.
Identification of carriers:
1. Offered to people with a family history of a genetic disorder.
2. Couples can be tested before having children to determine risk
3. Allows people to make informed decisions about things like having children and prenatal testing.
Pre-implantation genetic diagnosis:
1. Carried out on embryos created from IVF.
2. Involves screening embryos before they are implanted.
Prenatal testing:
1. Screening unborn babies
2. Offered to pregnant ladies with a family history of GD.
90
What are the advantages and disadvantages of identification of carriers (4N), Pre-implantation genetic diagnosis (2P,3N)?
Identification of carriers:
1. Finding out that you are a carrier of a genetic disorder may cause emotional stress.
2. Tests are not always 100% accurate and can have false results so people could be basing important decisions on wrong information.
3. It may uncover other genetic abnormalities which could cause even more stress.
4. There are concerns that in the future, employers and life insurance companies could use the results which would be genetic discrimination.
Pre-implantation genetic diagnosis:
1. It reduces chances of having babies with genetic disorders.
2. Only the embryos that are healthy are implanted to avoids the issue of abortion which prenatal testing doesnt.
1. Can be used to find out other characteristics such as gender and eye colour so there are concerns for future ‘designer babies’.
2. 30% success rate in women under 35.
3. False positives.
91
What are the 3 types of prenatal testing?
1. Amniocentesis
2. Chorionic villus sampling (CVS)
3. Non-invasive prenatal diagnosis.
92
Describe the 3 types of prenatal testing (they’re all 3).
Amniocentesis:
1. Carried out between 15-20 weeks of pregnancy.
2. Sample of amniotic fluid is collected via the abdomen with a very small needle which contains foetal cells.
3. DNA is analysed.
Chorionic Villus sampling:
1. Carried out between 11-14 weeks
2. Sample of cells taken from the chorionic vili/placenta are collected through the abdominal wall or the vagina.
3. DNA is collected and analysed.
Non-invasive prenatal diagnosis:
1. DNA fragments are collected from blood plasma of the mother during pregnancy.
2. 10-20% is foetal cells.
3. Foetal DNA becomes detectable at 4-5 weeks but testable at 7-9.
93
What are the positives and negatives of amniocentesis (1,1) and CVS (1,2)?
Amniocentesis:
1. Risk of miscarriage is only 1%
2. Results aren’t available for 2-3 weeks.
Chorionic Villus sampling:
1. Can be carried out earlier so decision about abortion can be made earlier so less physically traumatic.
1. Risk is miscarriage is higher-1-2%.
2. Initial results available in a few days but more in depth results take 2+ weeks.
