AS Topic 2 Flashcards
(155 cards)
1
Q
Why are cell membranes vital structures?
A
They create an enclosed space separating the internal cell environment from the external cell environment
2
Q
What does a cell membrane consist of?
A
Phospholipid bilayer containing proteins, cholesterol, glycoproteins and glycolipids
3
Q
What are phospholipids made up of?
A
a molecule of glycerol
a polar hydrophilic phosphate group (head)
2 non polar hydrophobic fatty acid tails (lipid tail)
4
Q
How do the phospholipids contribute to the structure of the cell membrane?
A
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.
5
Q
What does the term ‘fluid mosaic’ mean in reference to cell membranes?
A
The bilayer is fluid as particles are always constantly moving
Different types of protein are scattered through the bilayer like a mosaic
6
Q
What are models of membrane structure?
A
Interpretations of data which can change when scientific advances enable new discoveries. Models represent real life structures and processes
7
Q
What is the role of proteins within the cell membrane?
A
Involved with cell transport and communication
8
Q
What is the difference between glycolipids and glycoproteins?
A
Glycolipids - lipids with carbohydrate attached
Glycoproteins - proteins with carbohydrate attached and are longer than glycolipids, makes the membrane more rigid
9
Q
What is the difference between intrinsic and extrinisic proteins?
A
Intrinsic/integral - embedded within the membrane, precise arrangement determined by hydrophillic and hydrophobic regions
Extrinsic/peripheral - attatched to the outer or inner surface of the membrane
10
Q
What is the location and function of glycolipids and glycoproteins in the cell membrane?
A
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
11
Q
What is the role of cholesterol within the cell membrane?
A
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
12
Q
What are the properties of gas exchange surfaces?
A
-surface area to volume ratio
-diffusion pathway
-concentration gradient
13
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)
14
Q
What is Fick’s Law?
A
15
Q
What does Fick’s law predict the rate of diffusion to be
A
This means that diffusion rate will double if surface area or concentration gradient increases/diffusion pathway halves
Or if the thickness halves
16
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 steep concentration gradient)
- 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
17
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
18
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
19
Q
What is diffusion?
A
The net movement of particles from an area of high concentration to an area of low concentration going down the concentration gradient
20
Q
When does diffusion occur, and when does it stop?
A
Wherever there is a concentration gradient, and Diffusion will continue until equilibrium is reached
21
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)
22
Q
What molecules require facilitated diffusion, and why?
A
Large, polar molecules (cannot fit through phospholipid bilayer and cannot pass through hydrophobic tails)
Ions
23
Q
What is facilitated diffusion?
A
Facilitated diffusion is the passive movement of larger/polar molecules across a membrane, from a region of high concentration to a region of low concentration via protein channels
24
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, as a result of change in shape, the ion or molecules crosses the membrane (direction dependent on concentration gradient)
25
What is a channel protein?
Pores that extend from one side of the membrane to the other, allowing charged substances to diffuse through. Have a FIXED SHAPE
26
What is passive transport?
No metabolic energy required for the transport, driven by concentration gradient.
27
what are the steps of facilitated diffusion through a carrier protein
1. First a large molecule attaches to a carrier protein in the membrane
2. The protein changes shape
3. This releases the molecule on the opposite side of the membrane
28
What is osmosis?
the net movement of water particles from an area of high water potential to an area of low water potential through a partially permeable membrane
29
How does the partial permeability of the surface membrane of the cells allow osmosis to take place?
Is a barrier to some solutes, but not water. Enables a concentration gradient of solutes/water
30
What happens when water moves into a cell via osmosis? (animal vs plant)
Animal cell - can burst
Plant cell - cell wall prevents bursting
31
What happens when water moves out of a cell via osmosis? (animal vs plant)
Animal cell - shrivels
Plant cell - vacuole and cytoplasm shrink away from the cell wall
32
What is active transport?
The movement of a substance against a concentration gradient, requiring ATP and a CARRIER protein
33
What are some examples of active transport?
Absorption of some products of digestion from the digestive tract into the blood
Loading inorganic ions from the soil into root hair cells
34
When does active transport occur
Occurs when diffusion cannot meet needs of cell quick enough or if against concentration gradient
35
Process of active transport broken down
→ Shape of carrier protein is complementary to molecule they carry
→ binding
→ ATP hydrolysed - ADP + P (energy released)
→ carrier protein changes shape
→ molecule transported across membrane
→ 1 way flow molecule can only fit into carrier protein on 1 side of the membrane (ensures low to high concentration)
36
What is exocytosis?
Exocytosis is the release of substances, usually proteins or polysaccharides, from the cell
37
How does exocytosis occur, and what is an example of this?
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
38
What is endocytosis?
Endocytosis is taking in substances from outside the cell
39
How does endocytosis occur, and what is an example of this?
A cell can surround a substance with a section of its cell membrane where it then pinches off to form a vesicle inside the cell containing the ingested substance ACTIVE PROCESS
Example - white blood cells ingesting bacteria (phagocytosis)
40
What are proteins
long chains of peptide molecules e.g. amino acids
41
What are amino acids?
Monomers of polypeptides
42
How do amino acids form polypeptides?
Peptide bonds form between amino acids, these are covalent bonds formed via condensation reactions (loss of water molecule)
43
What is the chemical structure of an amino acid
Amino acids contain an amino group (-NH2), a carboxyl group (-COOH) and a carbon containing R group (also known as the variable side group)
They all have the same general structure: a central carbon atom bonded to an amine group, a carboxyl group, a hydrogen and a residual group
44
What is primary structure?
The sequence of amino acids in the polypeptide chain, bonded by covalent peptide bonds. This is specific for each protein
45
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
46
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)
47
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
48
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
49
What is quaternary structure?
Occurs in proteins that have more than one polypeptide chain working together, same bonds responsible for tertiary structure
50
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 hydrophilic groups orientate themselves on outside of protein
3D shape critical in role of binding to other substances
Tertiary and potentially quaternary structure
51
Why are globular proteins soluble
Proteins soluble - water molecules surround polar hydrophilic R groups + easily transported in fluids due to hydrophilic side chains that interact with water molecules hydrophobic amino acids hide deep within the protein well away from water
52
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
53
What is the structure of fibrous proteins?
Long strands of polypeptide chains with cross linkages due to hydrogen bonds. Little/no tertiary structure.
54
What are the properties of fibrous proteins?
Insoluble due to hydrophobic R groups on the outside.
Mainly involved in structural and support roles
55
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)
56
What are some examples of globular and fibrous proteins?
Globular - haemoglobin
Fibrous - collagen and keratin
57
Structure of haemogloblin
globular protein made up of 4 polypeptide chains
Has iron-containing prosthetic haem (Fe2+) groups that bind to oxygen which releases when required forming oxyhaemoglobin
4 sub units and a haem group, four oxygen molecules = 8 oxygen atoms
58
Functions of a haemogloblin
carries oxygen around the body in blood due to its solubility
59
Structural and functional differences of globular and fibrous proteins
Fibrous proteins straight chains globular compact and spherical
Globular soluble fibrous not
Fibrous involved in structural functions globular isn't
Globular involved in catalysis as enzyme fibrous not
60
Differences between collagen and Haemogloblin
61
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
62
What is an enzyme?
A biological catalyst that speeds up the rate of reaction by reducing the activation energy of reactions
63
What is the structure of an enzyme?
Globular protein with an active site and charged R groups on the outside of molecules (hydrophilic)
64
Why are enzymes described as biological catalysts?
They are proteins which reduce the activation energy of biological reactions
65
What is an active site
The active site is the region of catalytic function and it is complementary to the substrate
Highly specific due to their tertiary structure
66
What is the effect of changing enzyme concentration on the initial rate of reaction?
1. Increasing enzyme concentration increases the initial rate of reaction because more active sites are available for substrate molecules to bind to.
2. This leads to more enzyme-substrate complexes forming per unit time.
3. However, if the substrate concentration is limiting, then increasing enzyme concentration will have no further effect — the rate will level off (plateau).
67
What type of protein is an enzyme?
Globular, with complex tertiary structure
68
What is the difference between intercellular and extracellular proteins?
Intercellular - produced and function inside cell
Extracellular - secreted by cells and catalyse reactions outside cells
69
How do enzymes reduce activation energy?
By providing an alternative reaction pathway
70
How can pH and temperature alter enzyme activity?
They can alter protein structure and change the shape of the active site - denaturation
71
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
72
What creates enzyme specificity?
The complementary nature of the active site and substrate
73
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
74
What is the lock and key theory?
The theory that the substrate fits exactly into the active site
The substrate molecules form temporary binds with amino acids of the active site to produce an enzyme substrate complex
When the reaction has taken place the products are released, leaving the enzyme unchanged
75
Why do enzymes only catalyse one specific reaction
Each enzyme will only catalyse one specific reaction because only one shape of substrate will fit into its precisely shaped active site
76
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
77
How does the induced fit theory maximise the ability of the enzyme to catalyse a reaction?
The active site is flexible and changes shape when the substrate binds.
This allows the enzyme to fit more closely around the substrate (1).
The change in shape strains bonds within the substrate (1),
Which lowers the activation energy of the reaction (1).
This increases the chance of a successful enzyme-substrate complex forming (1).
78
what is activation energy
Minimum amount of energy required to start a reaction
Energy needed to break bonds in reactants so that new bonds can form, resulting in production of products
79
What is an active sites shape determined by
The active sites shape is determined by its tertiary structure which is determined by its primary structure
80
What happens if an enzyme is altered to have a different tertiary structure
a different tertiary means a different shaped active site
If the substrate shape doesn't match the active site, an enzyme substrate complex won't be formed and the reaction wont catalyse - the enzyme will no longer be able to carry out its function
81
What can change the active site
changes in pH or temperature
If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced
82
how is the rate of reaction is measured
by determining the quantity of substrate used or the quantity of product formed in a given time
E.g. when the enzyme catalase is used to break down hydrogen peroxide to water and oxygen
The rate of reaction can be found by measuring the volume of oxygen given off in a known time
83
What happens as substrates are used up
there are fewer substrate molecules to collide with and bind to the enzyme so reaction slows down and eventually stops and no further increase in the product occurs
enzyme concentration eventually has no further effect - substrate concentration has become a limited factor
84
What does a steeper slope on an enzyme concentration graph mean
higher initial rate of reaction
85
before substrate concentration becomes a limited factor, what happens in the reaction
The higher the substrate concentration, the faster the reaction - more substrate molecules means a collision between enzyme and substrate is more likely and so more active sites will be used
until a point of ‘saturation’
86
what happens in a graph when all active sites are used
plateau
87
What are nucleotides in DNA and RNA made from?
pentose sugar
nitrogen containing organic base
phosphate group
88
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
89
What are the components of an RNA nucleotide?
Ribose sugar with a hydroxyl (OH) group at the 2’ position
Phosphate group
Organic base A U C or G
90
Which bases are purines, and what does this mean?
Purine = double ringed structure
A and G
91
Which bases are pyrimidines, and what does this mean?
Pyrimidine = single ring structure
C, U and T
92
What type of bonds join nucleotides in DNA and RNA?
Phosphodiester bonds
93
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
94
what are genes
a sequence of bases that codes for a sequence of amino acids
95
structure of DNA
long chain polymer, it is a large molecule made up of many smaller units joined together
Each of these smaller units are nucleotides/mononucleotides
Every molecule of DNA is made of two strands
Each of the two strands is made from thousands of nucleotides
DNA molecules form a spiralling shape called a double helix
96
whats a pentose sugar
a sugar with 5 carbons
97
what are the names of the 4 possible DNA bases
1. Adenine
2. Thymine
3. Cytosine
4. Guanine
98
Why is DNA antiparallel?
It is made up of 2 polynucleotides running in opposite directions
99
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
100
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
101
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
102
What happens in transcription?
Enzyme RNA polymerase 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/template 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
103
What is the difference between the antisense/template strand and the sense/coding strand?
The antisense/template strand is the strand used to make an mRNA copy
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)
104
What direction does RNA polymerase move down the template strand, and why?
Moves in 3’ to 5’ direction as mRNA moves in 5’ to 3’ direction
105
What happens 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 between amino acids. 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.
106
What is translation
Turning the sequence of bases in the genetic code into a sequence of amino acids
107
What is the role of tRNA in translation?
transport amino acids from cytoplasm to the ribosome
tRNA has an anticodon which binds to/recognises codon on mRNA
each tRNA carries a particular amino acid
108
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
109
What type of replication does DNA undergo, and what does this mean?
Semi-conservative, meaning that half of the strands in the new DNA molecule are from the original DNA molecule
This means there is genetic continuity between generations of cells
110
How does the process of DNA replication occur?
Enzyme DNA 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. This process is described as semi conservative because each new DNA molecule consists of one original (parental) DNA strand and one newly synthesised strand
111
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 after many generations bacteria was transferred to a medium with a lighter isotope of nitrogen (N14). DNA was extracted from bacteria after 1, 2 and several rounds of replication and centrifuged after each replication.
1st replication - single band of ‘medium’ density produced ruling out conservative replication (could be dispersive or semi conservative)
2nd replication - formed 2 bands, one half heavier than other (one uses N15 as template and other N14)
112
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
113
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
114
Which direction can DNA polymerase build the new strand in?
ONLY in the 5’ to 3’ direction
115
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
116
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
117
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
118
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
119
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
120
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
121
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
122
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
123
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
124
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.
125
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
126
Why do people with CF have breathing difficulties?v
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 concentration gradient for gas exchange, loss of surface area and elasticity = reduced gaseous exchange
127
What types of genetic mutation are there?
deletion
insertion
substitution
duplication
nonsense
frameshift
128
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.
129
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
130
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
131
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
132
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
133
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
134
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
135
What is a gene?
sequence of bases/nucleotides in DNA
that codes for the primary structure/amino acid sequence/polypeptide
136
What are alleles?
Alternative forms of a gene occupying the same locus on a chromosome
137
What is genotype?
All of the alleles an organism carries on it’s chromosomes
138
What is phenotype?
The observable characteristics of an organism
139
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
140
What is the difference between a dominant and recessive allele?
Dominant - always expressed
Recessive - only expressed if no dominant allele is present
141
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
142
What is incomplete dominance?
Where a trait from a dominant allele is not completely expressed over the recessive allele trait (it ‘dilutes’ it)
143
What is monohybrid inheritance?
The inheritance of a characteristic controlled by a single gene
144
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
145
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
146
What are the types of genetic screening?
identification of carriers
preimplantation genetic diagnosis
pre natal testing
147
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
148
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
149
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
150
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
151
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
152
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.
153
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
154
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.
155
What is an inherited recessive disorder?
Caused by a faulty allele
Only expressed in homozygous condition
