Topic 2 - Genes and Health Flashcards
1
Q
What are the properties of gas exchange surfaces?
A
- surface area to volume ratio
- diffusion pathway
- concentration gradient
2
Q
How does surface area to volume ratio affect different organism exchange systems?
A
As organisms increase in size, their SA:Vol ratio decreases. This means there is a longer distance for diffusion, so larger multicellular organisms have evolved adaptation to facilitate the exchange of substances (e.g. alveoli in mammals, gills in fish)
3
Q
What is Fick’s Law?
A
rate of diffusion ∝ (surface area x difference in concentration) / thickness of exchange surface
4
Q
What is the equation for Fick’s Law?
A
Rate = P x A x (C1 - C2)/T Where P = permeability constant A = surface area C1-C2 = difference in concenrration T = thickness of exchange surface
5
Q
How does Fick’s law explain the adaptation of mammalian gas exchange surfaces?
A
- rate of diffusion proportional to surface area (alveoli have large surface area)
- rate of diffusion proportional to difference in conc (breathing and constant blood flow maintains difference in gas conc)
- rate of diffusion inversely proportional to thickness of exchange surface (walls of alveoli/capillaries one cell thick)
- diffusion distance shortened due to flattened cells forming alveoli and capillary walls
6
Q
What are the adaptations of the mammalian lung?
A
- cilia hair in trachea wafts mucus, which traps dust and pathogens
- bronchioles have smooth muscles and elastic fibres to allow adjustment of size of airway
- ALVEOLI
7
Q
How are the alveoli adapted for efficient gas exchange?
A
Good blood supply creates a steep concentration gradient, alveolar wall and capillary wall are only 1 cell thick, layer of moisture lines alveoli so O2 and CO2 dissolve and exchange occurs in solution
8
Q
What is diffusion?
A
The net movement of a substance from a region of its higher concentration to a region of its lower concentration (down a concentration gradient)
9
Q
When does diffusion occur, and when does it stop?
A
Wherever there is a concentration gradient, and it stops when the particles of the substance are evenly spread throughout the whole volume
10
Q
What are the properties of molecules that move by simple diffusion?
A
Small (can fit between phospholipids)
Non-polar (can interact with hydrophobic non polar tails)
11
Q
What molecules require facilitated diffusion, and why?
A
Large, polar molecules (cannot fit through phospholipid bilayer and cannot pass through hydrophobic tails)
Ions
12
Q
What is facilitated diffusion?
A
Facilitated diffusion is the process of molecules or ions diffusing across a biological membrane via specific transmembrane integral proteins.
13
Q
What is a carrier protein?
A
A transmembrane protein that switches shapes when the ion or molecule binds onto a specific site on the protein, which then changes shape and as a result the ion or molecules crosses the membrane (direction dependent on concentration gradient)
requires atp
14
Q
What is a channel protein?
A
Pores that extend from one side of the membrane to the other, allowing charged substances to diffuse through. Have a FIXED SHAPE
15
Q
What is passive transport?
A
No metabolic energy required for the transport, driven by concentration gradient.
16
Q
What is osmosis?
A
The net movement of water molecules from a solution with a lower concentration of solute to a solution with a high concentration of solute through a partially permeable membrane
17
Q
How does the partial permeability of the surface membrane of the cells allow osmosis to take place?
A
Is a barrier to some solutes, but not water. Enables a concentration gradient of solutes/water
18
Q
What happens when water moves into a cell via osmosis? (animal vs plant)
A
Animal cell - can burst
Plant cell - cell wall prevents bursting
19
Q
What happens when water moves out of a cell via osmosis? (animal vs plant)
A
Animal cell - shrivels
Plant cell - vacuole and cytoplasm shrink away from the cell wall
20
Q
What is active transport?
A
The movement of a substance against a concentration gradient, requiring ATP and a CARRIER protein
21
Q
What are some examples of active transport?
A
- Reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
- Loading inorganic ions from the soil into root hair cells
22
Q
What is exocytosis?
A
Exocytosis is the release of substances, usually proteins or polysaccharides, from the cell
23
Q
How does exocytosis occur, and what is an example of this?
A
Vesicles containing substance pinch off from sacs of Golgi apparatus, move towards and fuse with the cell surface membrane to be released outside of the cell. ACTIVE PROCESS
Example - insulin released into blood by exocytosis
24
Q
What is endocytosis?
A
Endocytosis is taking in substances from outside the cell
25
How does endocytosis occur, and what is an example of this?
Cell surrounds a substance with a section of cell surface membrane, the membrane engulfs the substance and pinches off inside the cell to form a temporary vacuole. ACTIVE PROCESS
Example - white blood cells ingesting bacteria (phagocytosis)
26
Why are cell membranes vital structures?
They create an enclosed space separating the internal cell enviornment from the external cell environment
27
What is the structure of a cell membrane?
Phospholipid bilayer containing proteins, cholesterol, glycoproteins and glycolipids
28
What are phospholipids made up of?
- a molecule of glycerol
- a phosphate group (head)
- 2 fatty acid tails (lipid tail)
29
How do the phospholipids contribute to the structure of the cell membrane?
Due to the hydrophilic phosphate head of the molecule, it attracts other polar molecules like water. The fatty acid tails are non polar and are therefore hydrophobic, this means the phospholipids become arranged so the tails have no contact with the water.
30
What does the term 'fluid mosaic' mean in reference to cell membranes?
Fluid refers to the movement of the phospholipids in the plane of the membrane
Mosaic refers to the random association of proteins within the membrane
31
What are models of membrane structure?
Interpretations of data which can change when scientific advances enable new discoveries. Models represent real life structures and processes
32
What is the role of proteins within the cell membrane?
Involved with cell transport and communication
33
What is the difference between intrinsic and extrinisic proteins?
Intrinsic - embedded within the membrane, precise arrangement determined by hydrophillic and hydrophobic regions
Extrinsic - attatched to the outer or inner surface of the membrane
34
What is the difference between glycolipids and glycoproteins?
Glycolipids - lipids with carbohydrate attached
| Glycoproteins - proteins with carbohydrate attached
35
What is the location and function of glycolipids and glycoproteins in the cell membrane?
Location: present on surface of cell membrane
Function: aid cell to cell communication by attaching as cell markers or binding with substances at the cell surface
36
What is the role of cholesterol within the cell membrane?
Found between the phospholipids where it regulates membrane fluidity by stopping the phospholipid tails from packing too closely together,
It increases the mechanical strength and stability of membranes (at higher temps too) and without it membranes would break down and cells would burst
37
What are nucleotides in DNA and RNA made from?
- pentose sugar
- nitrogen containing organic base
- phosphate group
38
What are the components of a DNA nucleotide?
Deoxyribose sugar with hydrogen at the 2' position
Phosphate group
Organic bases A T C or G
39
What are the components of an RNA nucleotide?
Ribose sugar with a hydroxyl (OH) group at the 2' position
Phosphate group
Organic base from A U C or G
40
Which bases are purines, and what does this mean?
Purine = double ringed structure
| A and G
41
Which bases are pyrimidines, and what does this mean?
Pyrimidine = single ring structure
| C, U and T
42
What type of bonds join nucleotides in DNA and RNA?
Phosphodiester bonds
43
How are phosphodiester bonds formed?
When separate nucleotides are joined by condensation reactions occurring between the phosphate group of one nucleotide and the pentose sugar of another. This creates a sugar-pentose backbone in DNA and RNA
44
What is the structure of DNA?
Double helix structure
45
Why is DNA antiparallel?
It is made up of 2 polynucleotides running in opposite directions
46
How do the bases pair in DNA?
Purine A with pyrimidine T (2 H bonds)
Purine G with pyrimidine C (3 H bonds)
Hydrogen bonds form between complementary bases
47
What is the difference between RNA and DNA?
RNA is only made up of 1 polynucleotide strand, whereas DNA is made up of 2
RNA = ribose sugar, DNA = deoxyribose sugar
RNA is relatively short compared to DNA
48
What is the difference between transcription and translation?
Transcription occurs in the nucleus and is when DNA is transcribed and mRNA is produced
Translation occurs in the cytoplasm and is when mRNA is translated and a polypeptide is formed
49
What happens in transcription?
Enzyme unwinds DNA molecule, breaking H bonds, and exposing the gene to be transcribed.
RNA nucleotides line up and pair with complementary bases on the antisense strand. RNA polymerase bonds the RNA nucelotides together to form the backbone of the mRNA molecule which then leaves via a nuclear pore and DNA reforms
50
What is the difference between the antisense/template strand and the sense/coding strand?
The antisense strand is the strand of DNA that RNA nucleotides pair with
The other strand is known as the sense or coding strand as mRNA will have the same base sequence as this strand (T replaced by U)
51
What direction does RNA polymerase move down the template strand, and why?
Moves in 3' to 5' direction as mRNA grows in 5' to 3' direction
52
What happpens in translation?
Once in cytoplasm, mRNA attaches to a ribosome. Each tRNA molecule has the complementary anticodon to the codon on the mRNA. tRNA molecules then form H bonds with the codons on the mRNA to bring amino acids, which form peptide bonds. 2 tRNA molecules are on the ribosome at a time, the process continues until a stop codon, when the polypeptide chain moves away and translation is complete.
53
What is the role of tRNA in translation?
- transport amino acids to the ribosome
- tRNA has an anticodon which binds to/recognises codon on mRNA
- each tRNA carries a particular amino acid
54
What is the structure of globular proteins?
Polypeptide chain folded into compact spherical shape. Non polar hydrophobic regions orientated towards the centre of the protein (away from aqueous surroundings), polar hydrophillic groups orientate themselves on outside of protein
Tertiary and potentially quaternary structure
55
What are the properties of globular proteins?
They are water soluble due to the hydrophillic side chains that project from outside the molecule.
Mostly involved in physiological roles
56
What is the structure of fibrous proteins?
Long strands of polypeptide chains with cross linkages due to hydrogen bonds. Little/no tertiary structure.
57
What are the properties of fibrous proteins?
Insoluble due to hydrophobic R groups on the outside.
| Mainly involved in structural roles
58
What are the similarities between globular and fibrous proteins?
They both are chains of amino acids joined by peptide bonds
| They both are joined by named bonds (e.g. hydrogen, ionic, disulphide)
59
What are some examples of globular and fibrous proteins?
Globular - haemoglobin
| Fibrous - collagen and keratin
60
What are amino acids?
Monomers of polypeptides
61
How do amino acids form polypeptides?
Peptide bonds form between amino acids, these are covalent bonds formed via condensation reactions (loss of water molecule)
62
What is primary structure?
The sequence of amino acids in the polypeptide chain, bonded by covalent peptide bonds. This is specific for each protein
63
What is secondary structure?
Hydrogen bonds forming between weak, negatively charged nitrogen and positively charged hydrogen atoms creating either an a helix or B pleated sheet
64
What is an α helix and how does it form?
The α-helix shape occurs when the hydrogen bonds form between every fourth peptide bond (between the negative oxygen of the carboxyl group and the positive hydrogen of the amine group)
65
What is a β-pleated sheet and how does it form?
The β-pleated sheet shape forms when the protein folds so that two parts of the polypeptide chain are parallel to each other enabling hydrogen bonds to form between parallel peptide bonds
66
What is tertiary structure?
The three dimensional arrangement of the polypeptide chain in space, brought about by additional bonds (hydrogen, ionic, disulphide, weak hydrophobic interactions) between R groups
67
What is quaternary structure?
Occurs in proteins that have more than one polypeptide chain working together, same bonds responsible for tertiary structure
68
What is the nature of the genetic code?
Non overlapping - each base only read once, and adjacent codons do not overlap
Degenerate - multiple codons can code for same amino acids to limit the effect of mutations
Universal - almost every organism uses same code and same triplet codes code for same amino acids
69
How is transcription involved in the synthesis of an enzyme?
DNA strand unwinds in nucleus and hydrogen bonds between bases are broken. Antisense strand is used for mRNA synthesis, RNA polymerase links RNA nucleotides. Complementary base pairing of A with U on RNA rather than T
70
What is an enzyme?
A biological catalyst that speeds up the rate of reaction by reducing the activation energy of reactions
71
What is the structure of an enzyme?
Globular protein with an active site and charged R groups on the outside of molecules (hydrophilic)
72
Why are enzymes described as biological catalysts?
They are proteins which reduce the activation energy of biological reactions
73
What is the effect of changing enzyme concentration on the initial rate of reaction?
Enzymes reduce activation energy. Active sites of enzymes become occupied but as substrate concentration decreases it becomes the limiting factor as not all active sites are occupied.
74
What type of protein is an enzyme?
Globular, with complex tertiary structure
75
What is the difference between intercellular and extracellular proteins?
Intercellular - produced and function inside cell
| Extracellular - secreted by cells and catalyse reactions outside cells
76
How do enzymes reduce activation energy?
By providing an alternative reaction pathway
77
How can pH and temperature alter enzyme activity?
They can alter protein structure and change the shape of the active site - denaturation
78
What must happen for a reaction to occur between the substrate and active site of an enzyme?
Substrates must collide with the active site at the correct orientation and speed in order for a reaction to occur
79
What creates enzyme specificity?
The complementary nature of the active site and substrate
80
What determines the shape of the active site of an enzyme, and what can alter this (apart from temp and pH)?
Determined by the complex tertiary structure of the protein
If the tertiary structure is altered in any way (different polypeptide chain sequence), the active site will change and the substrate will not fit
81
What is the lock and key theory?
The theory that the substrate fits exactly into the active site
82
What is the induced fit theory?
The enzyme and its active site (and sometimes substrate) can change shape slightly as the substrate molecule enters the enzyme
Conformational change
83
How does the induced fit theory maximise the ability of the enzyme to catalyse a reaction?
Conformational change
| Ensures an ideal binding arrangement between the enzyme and substrate
84
Why is a change in the sequence of bases of DNA an issue?
Could change a triplet that makes up a gene, which could then change the amino acid sequence of the primary structure which may substantially alter the proteins 3d shape and therefore properties
85
What type of replication does DNA undergo, and what does this mean?
Semi-conservative, meaning that the strands are separated and both are used as a template
86
How does the process of DNA replication occur?
Enzyme helicase breaks hydrogen bonds between complementary bases. DNA strands unwind, and free floating nucleotides then align themselves with the correct base pairings. The enzyme DNA polymerase links the adjacent nucleotides with phosphodiester bonds in condensation reactions to form new complementary strands. DNA ligase used on lagging strand.
87
How do free nucleotides in the nucleus create a new strand of DNA?
They are nucleoside triphosphates, so when DNA polymerase comes to join them up, it cleaves off the 2 extra phosphates and uses the energy released to create phosphodiester bonds of the new sugar-phosphate backbone
88
How did Meselsohn and Stahl's experiment prove DNA replication was semi conservative?
Grew bacteria in cultures of a 'heavy' isotope of nitrogen (N15), and then transferred them to a medium with a lighter isotope of nitrogen (N14). DNA was centrifuged after each replication.
1st replication - single band of 'medium' density produced (could be dispersive or semi conservative)
2nd replication - formed 2 bands, one half heavier than other (one uses N15 as template and other N14)
89
How do we know that DNA replication is semi-conservative?
Meselsohn and Stahl experiment
| Used heavy and light strands of DNA to distinguish method of DNA replication
90
What were the different modes of DNA replication suggested before Meselsohn and Stahl's experiment?
Conservative - strands separate but new strands join together to form entirely new molecule and 'old' strands stay together
Semi-conservative - strands separate and are joined by a new strand
Dispersive - new DNA mixture of both old and new DNA
91
Which direction can DNA polymerase build the new strand in?
ONLY in the 5' to 3' direction
92
What strand is the leading strand, and what does this mean?
The original DNA strand starting at 3', meaning it can be synthesised by DNA polymerase continuously, moving towards the replication fork
93
What strand is the lagging strand, and what does this mean?
The other DNA strand where DNA polymerase moves AWAY from the replication fork from the 5' end. This means DNA polymerase can only synthesise the strand in short segments called Okazaki fragments, and DNA ligase is required to join the lagging strand segments
94
What is the role of DNA ligase and how does it work?
To connect lagging strand segments
| It catalyses the formation of phosphodiester bonds to form a continuous strand
95
What is cystic fibrosis?
A recessive genetic disorder of the cell membrane, where abnormally thick and stick muscus is produced in the body's passageways
96
What causes cystic fibrosis?
A mutation in the CFTR gene which leads to production of non functional chloride ion channel proteins, reducing the movement of water via osmosis into the mucus
97
What impacts does cystic fibrosis have on the respiratory system?
- cilia unable to move thick and sticky mucus so microorganisms are not removed from the lungs and lung infections occur more frequently
- mucus builds up in the lungs and can block airways, limiting gas exchange
- SA for gas exchange reduced, causing respiratory issues
98
What impacts does cystic fibrosis have on the digestive system?
- can block pancreatic duct, preventing digestive enzymes from entering the small intestine, meaning key nutrients may not be available for absorption
99
What impacts does cystic fibrosis have on the reproductive system?
- mucus can cause fertility issues
- in men: tubes of testes blocked, preventing sperm reaching penis
- in women: thickened cervical mucus can prevent sperm reaching the oviduct to fertilise an egg
100
What are the differences between somatic gene therapy and germ line gene therapy?
Somatic = body cells, germ line = all cells, including gametes
Somatic is legal, germ line illegal
Somatic therapy is temporary treatment, germ line can be inherited
101
How can somatic gene therapy enable cells lining the lungs to function normally in people with CF?
Functional gene that codes for CFTR inserted into a plasmid, which is then put into the lungs via a nebuliser. The CFTR protein is made (transcription/translation) allowing chloride ions to leave the cells, and water follows via osmosis. This reduces the stickiness of the mucus.
102
How can rhythmical tapping of the chest wall during physiotherapy relieve the symptoms of CF in the lungs?
Loosens mucus, expelled from lungs more easily, clearer airways and better breathing
103
Why do people with CF have breathing difficulties?
Mucus is more viscous and sticky - this means it builds up and blocks trachea/bronchioles and the cilia are unable to remove it. Reduced air flow to alveoli, reduced conc gradient for gas exchange, loss of surface area and elasticity = reduced gaseous exchange
104
What types of genetic mutation are there?
- deletion
- insertion
- substitution
- inversion
- duplication
105
How can a gene mutation affect protein structure?
A change in base sequence causes a change in amino acid/primary structure of a protein. This causes different R groups to be formed, leading to different types of bonding, which can alter the shape of the protein.
106
What is an insertion mutation and how does it affect transcription and translation?
When a nucleotide is randomly inserted into the genetic code
Can cause a frame shift by altering triplets downstream, potentially dramatically changing the amino acid sequence and therefore polypeptide function
107
What is a deletion mutation and how does it affect transcription and translation?
Where a nucleotide is randomly deleted
| Causes a frame shift and changes every subsequent triplet, can affect amino acids sequence and also polypeptide function
108
What is a substitution mutation and how does it affect transcription and translation? (different types?)
Where a base in DNA is randomly swapped for another - this will not have knock on impacts
Silent - no change due to degenerate nature of genetic code
Missense - single amino acid changed
Nonsense - premature stop codon
109
What is a duplication mutation and how does it affect transcription and translation?
Production of one or more copies of a gene/region of a chromosome. 2 copies of the gene appear on the same chromosome.
Mutation not harmful
110
What is an inversion mutation and how does it affect transcription and translation?
During the crossing over of meiosis, DNA of a single gene is cut but inverted 180 degrees before being rejoined to the same region.
This frequently results in a non functional protein as the original gene can no longer be expressed
111
Why does a substitution mutation have less effect than a deletion mutation?
Deletion mutation causes frame shift and whole amino acid sequence to change.
Substitution mutation only changes one codon/amino acid, number of amino acids remains the same
112
What is a gene?
- sequence of bases/nucleotides in DNA
- that codes for the primary structure/amino acid sequence/polypeptide
113
What are alleles?
Alternative forms of a gene occupying the same locus on a chromosome
114
What is genotype?
All of the alleles an organism carries on it's chromosomes
115
What is phenotype?
The observable characteristics of an organism
116
What do homozygous and hetereozygous mean?
Homozygous - Pair of alleles that produce a characteristic that are the same, e.g. HH or hh
Hetereozygous - Pair of alleles that will produce a characteristic that will be different e.g. Hh
117
What is the difference between a dominant and recessive allele?
Dominant - always expressed
| Recessive - only expressed if no dominant allele is present
118
What is the meaning of the term recessive allele?
Both alleles must be present in order for recessive phenotype to be expressed.
AND different form of a gene/same locus/different base sequence
119
What is incomplete dominance?
Where a trait from a dominant allele is not completely expressed over the recessive allele trait (it 'dilutes' it)
120
What is monohybrid inheritance?
The inheritance of a characteristic controlled by a single gene
121
Who is Mendel and what did he do for genetics?
He was a monk and carried out a huge number of breeding experiments between garden pea plants. He established 'heredity units', which are now called genes
122
What is the use of pedigree diagrams?
Family pedigree diagrams can be used to trace the pattern of inheritance of a specific trait, e.g. a genetic disorder, through generations of a family
123
What is the use of the chi squared test?
Can determine if there is a significant difference between observed and expected results in an experiment
124
What is the chi squared equation?
Chi squared = Σ(O-E)^2 / E
Where O = observed results
and E = expected results
125
How do you work out degrees of freedom?
Number of classes - 1
126
How can you analyse the results of a chi-squared test?
- if chi squared represents a greater probability than the critical probability, you reject the null hypothesis (results are not due to chance)
- if chi squared represents a smaller probability than critical probability, then you accept the null hypothesis (results are due to chance)
127
What are the types of genetic screening?
- identification of carriers
- preimplantation genetic diagnosis
- pre natal testing
128
How does PIGD work and what are the benefits and issues?
PIGD = pre implantation genetic diagnosis
Analysis of genes in embryos created through IVF to check for genetic conditions
BENEFITS: reduces chance of having baby with genetic disorder, avoids abortion
ISSUES: 'designer babies', false results lead to poor decisions
129
What is amniocentesis?
A diagnostic test carried out during pregnancy, performed at 14-20 weeks and involves inserting a needle into amniotic fluid to collect cells that have fallen off the placenta and foetus
130
What is CVS and how does it work?
CVS = chronic villus sampling
A test carried out during pregnancy where a sample of cells are removed and tested from the placenta. Checks baby for inherited disorders such as Down's syndrome and rarer diseases
131
What are the benefits and issues with pre natal testing?
BENEFITS: allows parents to make informed decisions, can help parents prepare for future of the child
ISSUES: each procedure brings risk of miscarriage, ethical implications if choice made for abortion
132
What is the identification of carriers and what are the benefits and issues with it?
Genetic testing carried out on adults to show whether people with no symptoms carry the allele for particular disorders
BENEFITS: families can make informed decisions before choosing to become pregnant, women can decide to have prenatal testing
ISSUES: finding out you're a carrier can cause emotional stress, hard to find a partner, employers and insurance may use information against you
133
What are some of the ethical and social issues related to genetic screening?
Embryo has a right to life (abortion is murder)
False positives or negatives
Who has right to decide if tests should be performed
Risk of miscarriage of healthy child
More stress for parents.
134
Advantage and disadvantage to parents genetic screening their fetus?
Adv - allows them to make an informed choice, prevents baby dying in pregnancy
Disadv - cause parents emotional stress, risk of false positives/negatives, can cause miscarriage of healthy child
135
Why do cigarette smokers have a higher risk of developing lung cancer than non smokers?
Cigarettes contain carcinogens/are an environmental risk factor
This increases the number of mutations in cells, increasing the risk of uncontrolled cell division.
136
What are the stop codons in the genetic code?
UAG, UAA, and UGA
(TAG, TAA, TGA)
137
What is an inherited recessive disorder?
Caused by a faulty allele
Only expressed in homozygous condition
