1
Q
in genetic screening, why do carriers sometimes show a false positive
A
the recessive allele may be detected
2
Q
what does implantation diagnosis consist of
A
embryos are created through IVF are tested to see if they carry faulty allele. Only the healthy embryos will be implanted
however the process is expensive and unreliable
3
Q
define allele
A
a version of a gene
4
Q
define a recessive allele
A
an allee which isn’t expressed when a dominant allele is present
5
Q
define dominant allele
A
an allele is always expressed
6
Q
define incomplete dominance
A
neither allele is dominant over the other and the resultant phenotype is a mix
7
Q
what symptoms can cystic fibrosis present in gas exchange
A
mucus can block bronchioles which leads to less O2 to the alveoli so smaller concentration gradients
thin layer of mucus can make it difficult for O2 and CO2 to diffuse
8
Q
what symptoms can cystic fibrosis present in reproduction
A
in men - sperm duct blocked with mucus so sperm can’t leave the testes
in women - mucus blocks the cervix so sperm cannot reach the egg
9
Q
what symptoms can CF present in digestion
A
blocks the pancreatic duct so digestive enzymes cannot reach the digestive system so food isn’t properly digestive and nutrients aren’t absorbed so there is difficulty gaining weight
enzymes trapped in the pancreas cause fibrosed cysts and damage insulin producing cells which can also lead to diabetes
10
Q
what does amniocentesis consist of
A
a syringe with a needle is inserted into the amniotic sac and fluid is extracted and foetal cells are then separated. This is cultured for 2-3 weeks
DNA is karyotyped, biochemical tests are also carried out on both the fluid and cells
this is when the foetus is 14-16 weeks
11
Q
what does chorionic villus sampling consist of
A
a syringe is inserted in the vagina to take a sample of embryonic tissue from the placenta (the chorionic villus).
DNA is karyotyped when the fetus is 8-10 weeks old
11
Q
why do people with CF have sticky mucus
A
the CFTR channel protein is non-functional therefore the Na+ channel (ENac) is always open so Na+ ions move into the cell and to the tissue fluid on the basal membrane
this causes the Cl- to move down the concentration gradient, water goes out from the mucus and into the cell and tissue fluid
11
Q
what are the factors that one must consider in relation to prenatal screening
A
risk of miscarriage, potential abortion, religious beliefs of right to life, cost of healthcare, risks/consequences of false positives/negatives
12
Q
what is meant by monohybrid inheritance
A
inheritance of 1 characteristic
13
Q
when can mutations occur
A
DNA replication, transcription and translation
14
Q
how do bodies decrease the viscosity of mucus on the apical membrane
A
Cl- is pumped into the cell across basal membrane
Cl- diffuses through open CFTR channels to outside apical membrane
Na+ diffuses down electrical gradient in mucus
Elevated salt concentration in the mucus draws water out of the cell and into the mucus via osmosis
15
Q
what did Meselon and Stahl’s experiment consist of
A
- E coli bacteria cultured in 15-N containing medium
- transferred into a 14-N containing medium
- DNA extracted after each generation and centrifuged into BaCl solution
the heavier the DNA was, the deeper it sank in the test tube
16
Q
how did Meselon and Stahl’s experiment disproved the other theories
A
- In a conservative model, super heavy DNA would be expected with a newly lighter DNA as generations passed - 1 of each
- In dispersive, only 1 layer of equally dense DNA would be seen getting lighter and lighter - a mix of heavy and light
- Results showed intermediate strands of 1/2 heavy and 1/2 light after 1 generation which disproved conservative
After 2 generations, 2 layers were shown, 1 intermediate and 1 light which disproved fragmentary
semi conservative was 1 strand of intermediate and 1 strand of light in a double helix
17
Q
why isn’t heat used to accelerate reactions in organisms rather than enzymes
A
heat would damage cell tissues
18
Q
how do enzyme concentration affect the reaction rates
A
as the enzyme concentration increases, the rate increases as there is a higher chance of successful collisions therefore more enzyme-substrate complexes formed per unit of time so more products are released
19
Q
in experiments how could
temperature be controlled
pH be controlled
A
using a water bath with the temperature as close to optimum as possible
using a buffer solution as close to optimum
20
Q
what happens during semi-conservative replication of DNA
A
- DNA helicase breaks the hydrogen bonds between bases to unzip DNA
- DNA nucleotides align with their complementary bases and DNA polymerase creates phosphodiester bonds that join nucleotides together
- DNA ligase joins the partly formed strands together
- 2 identical daughter strands are created - 1 old and 1 new
21
Q
what did the conservative DNA replication model mean
A
1 whole completely new double helix is synthesised
22
Q
what did the dispersive/fragmentary DNA replication model mean
A
the new DNA molecule was created as a mix of old and new parts
23
what does the induced fit hypothesis state
enzyme changes shape to fit substrate when substrate is near while lock and key model theorizes that the enzyme and substrate are always complementary in shape and the enzyme doesn't change shape
24
what are enzymes
biological catalysts
25
how do enzymes accelerate rates of reaction
Lower activation energy by providing a lower energy pathway, a more favourable pH in the active site
using charge to put strain in bonds to break them
bring reactants together by using charge so that bonds form more easily
26
what types of proteins are enzymes
globular
27
what are intracellular enzymes
enzymes that work inside the cell
e.g. DNA polymerase
28
what are extracellular enzymes
enzymes that work outside the cell
e.g. digestive enzymes
29
Explain Lock and Key Theory
1. Random movement causes enzyme and substrate to collide and the substrate enters the active site.
2. Enzyme-substrate complex forms = shared groups attract, distort the substrate and aid in bond breaking/formation
3. Products are released from active site, leaving it undamaged and ready to accept a new substrate
30
what does structure of a protein determine
its function
30
what type of protein is haemoglobin
globular
30
what type of protein is collagen
fibrous
31
describe structure of haemoglobin
globular with 4 polypeptide chains -2 alpha and 2 beta - each containing a haem prosthetic group
31
what 2 types of secondary structure are there
alpha helix or beta pleated sheet
31
describe the structure of collagen
primary structure = repeating amino acid sequence
3 polypeptide chains coiled around each other
cross linking between chains
32
how is a tertiary structure of a protein created
alpha helix / beta pleated sheet fold further and create a new structure held together by disulphide bridges and ionic bonds between R groups
32
how is the quaternary structure of a protein created
folded polypeptides joined by hydrogen bonds - disulphide bridges and ionic binds between R groups
32
what is the general formula for an amino acid
a central carbon, a hydrogen, an amine group (NH2) and a carboxylic acid (COOH)
33
how are peptide bonds created
the OH in the carboxyl joins the H in another amino acid in a condensation reaction to remove water and form peptide bonds
34
what is the primary structure of a protein
sequence of amino acids
35
how does secondary structure of a protein formed
amino and carboxyl groups carry small amounts of charge
charge is negative on the CO and positive on the NH
result in H bonds forming between parts of the chain to stabilize the structure - alpha helix and beta pleated sheet
36
describe the role of tRNA in the production of protein part of a glycoprotein
each tRNA brings a specific amino acid to the ribosome
the tRNA with the complementary anticodon binds to mRNA codon
tRNA bonds to ribosome
37
compare and contrast the process of transcription with the process of DNA replication
Similarities:
involve formation of a polynucleotide
involve DNA helicase
Differences:
transcription uses RNA nucleotides whereas replication uses DNA nucelotides
transcription uses RNA polymerase whereas replication uses DNA polymerase
transcription produces a single strand of mRNA/only copies template strand of DNA whereas replication produces double stranded DNA/ copies both strands of DNA
38
explain how change of 1 amino acid could lead to a change in the structure and properties of haemoglobin protein
different sequence of amino acids/primary structure
a different amino acid will have a different R group therefore secondary/tertiary/quaternary structure will change due to a change in a hydrogen bond holding the molecule in its 3D shape
haemoglobin may not bond to oxygen
39
describe the role of tRNA in the production of leptin
tRNA molecules transport amino acids to the ribosome
tRNA molecules has an anticodon that bonds to/recognises a codon on each mRNA
each tRNA carries a particular amino acid
40
describe how the primary structure of a protein allows it to be soluble
primary structure/ sequence of amino acids determines the folding of polypeptides
forming globular structure
hydrophobic R groups located in the centre of the protein/ hydrophilic r groups on the outside
water forms hydrogen bonds with protein/ hydrophilic groups
41
describe how a frameshift mutation could result in the production of leptin with a variety of shorter primary structures
adding/removing one or 2 nucleotides changes the triplet code
introducing a new stop/start codon
coding for a shorter sequence of amino acids
42
describe how mRNA is synthesised at a template strand of DNA
RNA nucleotides align with complementary bases on DNA
RNA nucleotides joined together by RNA polymerase
43
describe the differences between DNA and RNA
DNA:
double stranded
contains deoxyribose sugar
contains thymine as a group
RNA:
single stranded
ribose sugar
contains uracil as a group
44
explain why deletion and substitution have different effects on protein structure
deletion could affect every codon on the mRNA/ substitution will only affect 1 codon
deletion is more likely to affect the position of a stop/start codon
deletion results in a different sequence of amino acids/ substitution may not affect sequence of amino acids
substitution may code for same amino acid
due to degenerate nature of genetic code
45
explain why antibiotics that bind to ribosomes could affect the production of proteins in bacteria
ribosome shape is altered
mRNA is prevented from binding to the ribosome/causing change in the tRNA binding
therefore translation cannot occur
protein/polypeptide isn't synthesised
46
why might ribosome-binding antibiotics be used to treat bacteria that are resistant to other antibiotics
bacteria have not been exposed to new antibiotics before/ bacteria don't have mechanisms to make them resistant to other new antibiotics
bacteria have developed resistance to other antibiotics by evolving
therefore there has been no advantage to possessing a mutation to bypass the new antibiotic
47
describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency
Cl- ions leave the cells
Na+ ions leave the cells
increasing the solute concentration
water moves out of the cell and into mucus by osmosis
48
describe the roles of transcription and translation in the synthesis of a globular protein by a muscle cell
the gene/ sequence of DNA for the globular proteins is transcribed
complementary base pairing between RNA nucleotides and DNA
mRNA leaves the nucleus and attaches to a ribosome
pairing between codons on mRNA and anticodons on tRNA
tRNA provides specific amino acids
the sequence of bases/codons determines the sequence of amino acid/ primary structure of the protein
49
compare and contrast the structure of ATP and a DNA nucleotide
Both:
contain phosphate, pentose sugar and a base
Differences:
a DNA nucleotide contains deoxyribose whereas ATP contains ribose
a DNA nucleotide could contain other bases whereas ATP only contains ATP
a DNA nucleotide contains 1 phosphate whereas ATP contains 3 phosphates/ is a triphosphate
50
explain the importance of primary structure functioning of ATPase
primary structure determines interaction between amino acids/ R groups
primary structure determines folding/ tertiary structure
therefore affecting shape of active site which would be complementary to ATP
51
Factor VIII is involved in blood clotting
Explain how a change in the primary structure of VIII could cause difficulties with blood clotting
a different primary structure results in a different sequence of amino acids
change in R group changes folding/ bonding/ secondary structure/ tertiary structure
changing shape/charge of the active site prevents a substrate from being able to bind
stopping/reducing production of fibrin
52
why are enzymes described as biological catalysts
they lower the activation energy and speed up the rate of biological reactions
53
describe what happens to proteins following translation until release form cell
proteins folded in the rough endoplasmic reticulum
proteins packaged and transported in vesicles
proteins then modified in the Golgi apparatus
leave via exocytosis
54
explain why enzymes that are incorrectly folded cannot carry out their function
the tertiary structure/ 3D shape would be different
therefore the active site of the enzyme would not fit/bind with the substrate/ would not be able to form an enzyme-substrate complex
therefore unable to catalyse reactions
55
describe how an enzyme could break down the polysaccharide components
hydrolysis of glycosidic bonds
56
compare and contrast molecular structure of globular and fibrous proteins
Both:
chains of amino acids
contain H bonds holding their 3D structures
Differences:
Globular have hydrophilic groups on the outside whereas Fibrous have hydrophobic groups on the outside
Globular have lots of tertiary structure and fibrous have little/no tertiary structure
57
describe how the structure of phospholipase allows it to hydrolyse phospholipids
Primary structure made up of different amino acids joined by enzyme catalysed peptide formation
R groups fold (e.g disulfide)
TERTIARY structure determines active site
Active site is specific to the ester bond in phospholipids
Lysis occurs and specific bonds form to allow this
58
give 2 differences between endocytosis and exocytosis
exocytosis - involves molecules/substances leaving the cells, involves vesicles fusing with cell surface membrane
endocytosis - involves molecules/substances entering the cells, involves formation of vesicles
59
explain why betalain molecules cannot move through intact cell membrane
too large to move through the cell membrane
there are no carrier/channel proteins for betalains to move through
they're also polar and are repelled by the hydrophobic fatty acid tails/ cannot move through fatty acid tails
60
hydrolysis
breaking a chemical bond between 2 molecules involving a water molecule
61
fibrous proteins
long chain proteins that are insoluble and usually have structural roles
have hydrophobic r groups on the outside have little tertiary structure
62
condensation reaction
a type of reaction that bonds 2 molecules together with the removal of water and the formation of a chemical bond
63
dipeptide
a molecule formed by the condensation of 2 amino acids
64
primary structure
sequence of amino acids
65
secondary structure
formation of alpha helixes or beta pleated sheets
66
tertiary structure
the way a protein folds into a 3D structure
67
hydrogen bond
a weak bond formed between a slightly positive hydrogen and a slightly negative oxygen/other atom
68
what is haemoglobin
an example of a globular protein
used to transport oxygen
made up of 4 polypeptide chains each containing a haem group
69
collagen
example of a fibrous protein, provides strength to many different cell types and make up connective tissues
70
what is an intracellular enzyme
enzyme that works within the cell
71
what is an extracellular enzyme
an enzyme that works outside of the cell
72
what is ribosomal RNA
RNA that makes up ribosome
73
what is a ribosome
an organelle found in the cytoplasm that carries out protein synthesis
74
what is the function of an R group
a side chain that is attached to a molecule that determines chemical properties
75
what is the importance of hydrogen bonds
affects how many bonds form and where, will affect secondary and tertiary structure
76
what is the importance of hydrophobic and hydrophilic amino acid side group chains
hydrophilic = soluble in water, can affect water potential when dissolved in blood plasma
hydrophobic = insoluble in water, has no water effect
77
how do ionic bonds form
between oppositely charged side chains on different amino acids
78
what are peptide bonds
the bonds that are formed between amino acids
79
what is the structure of a phospholipid
1x glycerol
2x fatty acids
1x phosphate group
80
which part of a phospholipid is hydrohpilic and which is hydrophobic
head = hydrophilic - interacts with water
tail = hydrophobic - made up of hydrocarbons
81
what happens when many phospholipids interact with water
create spherical clusters with tails facing inwards to shield themselves from the water with their glycerol heads
forms a bilayer/micelle
82
what does the phospholipid bilayer make up
cell surface membrane
83
what are some features of the phospholipid bilayer
selectively permeable - allows small, non-polar molecules to cross
has a hydrophobic barrier won't allow large non-polar/polar to cross
84
why is the fluid mosaic model named this way
membrane is fluid and has a mosaic like arrangement of proteins
85
how much mass of a membrane is made up of proteins
between 25% and 75%
86
what kind of proteins are in the membrane
integral and peripheral proteins
87
what are integral proteins and what do they do
they span the width of the membrane and help to transport substances that cannot diffuse across the membrane but are still vital to the cells functioning
eg glucose through carrier protein through facilitated diffusion
88
what a peripheral proteins and what do they do
confined to inner and outer surface of the membrane
may be free or bound to an integral protein
proteins on the extracellular side of membrane act as transmitters/involved in cell recognition
89
what are glycoproteins
protein molecules with polysaccharides attached
90
what factors affect membrane fluidity
cholesterol and temperature
91
how does cholesterol affect membrane fluidity
vital in controlling membrane fluidity
the more cholesterol, the less fluid - more rigid and less permeable
has a hydrophobic region so its able to create a further barrier to polar substances moving through its membrane
binds to hydrophobic tail of a phospholipid, causing them to pack more closely together which restricts their movements
helps maintain shape of animal cells - RBCs
92
how does temperature affect membrane fluidity
temp below 0 degrees - increases permeability, phospholipids are packed closely together and the membrane is rigid, channel and carrier proteins denature and ice crystals form which could pierce the membrane
temp between 0-45 degrees - phospholipids can move and aren't as tightly packed, membrane is partially permeable, as temp increases phospholipids can move more because they have more energy
temps above 45 - phospholipid bilayer starts to melt, water inside cells expands which putting more pressure on membrane, the channel and carrier proteins denature
93
define facilitated diffusion
the overall net movement of molecules and ions from a region of high concentration to a region of low concentration down a concentration gradient
94
what is the type of some proteins that are involved in facilitated diffusion
carrier proteins
95
what happens when an ion/molecule binds to a carrier protein
it changes shape and therefore the molecule is able to cross the molecule
96
what is another name for diffusion
passive transport as it uses no energy
97
define active transport
movement of molecules/ions from an area of low concentration to an area of high concentration against a concentration gradient, using energy from ATP
98
where is the energy for active transport sourced from
adenosine triphosphate
99
how is ATP formed and how is it used
1. it is formed during respiration, the breakdown of energy store molecules
2. the substances to be transported across the membrane binds to the carrier protein
3. one phosphate group is removed from ATP by hydrolysis and ADP forms
4. a small amount of energy is required to break the bond holding the end phosphate in ATP
5. once removed, phosphate group becomes hydrated
lots of energy is released as bonds form between water and phosphate
100
how is a phosphate group removed from ATP
hydrolysis
101
what is ADP
adenosine diphosphate
102
how is active transport sometimes referred to as
pumping
the pumping of substances across membranes that occurs in every cell
103
what is a glycolipid
a lipid with polysaccharides attached via glycosidic bonds
104
what processes are used when large molecules/quantities of molecules need to be transported across a membrane
endocytosis
exocytosis
105
what is a vesicle
small membrane bound sacs containing substance
106
what is the process of exocytosis
vesicles fuse with the cell membrane and the contents are released
107
what is an example of exocytosis
insulin is released to the blood via exocytosis
108
what is the process of endocytosis
1. substances are taken into the cell by the creation of a vesicle from the cell surface membrane
2. part of the membrane engulfs the solid/liquid material to be transported
3. in some cases, the substances which is to be absorbed, attaches itself to a receptor in the membrane and is then absorbed by endocytosis
109
what is an example of endocytosis
cholesterol being taken in by cells
white blood cells ingesting bacteria
110
Describe how the primary structure of leptin enables it to be soluble in water.
primary structure determines the folding of polypeptide
forming globular structure
hydrophilic r groups located on the outside of the protein
water forms hydrogen bonds with the protein
111
Gene drives can be used to 'force almost any genetic trait through a population'
Multiple genetic crosses were carried out between individuals homozygous for a recessive allele and individuals heterozygous for the same gene.
Describe how the outcome of these crosses would be affected if a gene drive was used with the recessive allele.
without the gene drive, expected outcome would be 50% heterozygous and 50% homozygous recessive offspring
with a gene drive, the proportion of individuals with homozygous recessive alleles would increase
the stronger the gene drive, the greater the proportion of homozygous recessive
112
People with cystic fibrosis require a higher energy diet than people without cystic fibrosis.
They are also more likely to develop problems in the pancreas.
Men with cystic fibrosis are less likely to be able to release sperm.
Discuss why a person with cystic fibrosis could have these symptoms
mucus stickier than normal
digestive enzymes cannot enter intestine as pancreatic duct is blocked with mucus
high energy diet is required as digestion is less efficient
pancreatic enzymes trapped behind mucus damage pancreatic cells - some insulin producing
pancreatic cysts can form
sperm can't leave as sperm duct blocked with mucus
gene mutation - non-functioning CFTR channel protein so chloride ions cannot move out of epithelial cell
accumulation of sodium and chloride ions in cells causing water to move out of mucus via osmosis
113
Explain why cystic fibrosis affects the rate of oxygen uptake in the lungs.
people with CF have thick, sticky mucus. accumulation of mucus cannot be moves by the cilia restricts air flow through the bronchi. it also increases diffusion distance, so rate of oxygen diffusion is longer
114
Describe how nucleotides join together to form DNA.
condensation reactions which form phosphodiester bonds using DNA polymerase
115
explain why Meselson and Stahl accepted one of the models for DNA replication and rejected the other
conservative model was rejected/ semi-conservative was accepted
due to generation 1 having a single band halfway between N14 and N15
because DNA has one strand containing N14 and one strand N15
further generations would also have no band at N15
116
These new antibiotics attach to a site on the ribosome not affected by any known
antibiotics.
Deduce why these new antibiotics might be used to treat bacteria that are resistant to other antibiotics.
bacteria haven't been exposed to new antibiotics before
bacteria have developed resistance to other antibiotics due to natural selection
therefore no mutation present to give resistance
117
Scientists have isolated these new antibiotics and tested their effectiveness against bacteria that are resistant to other types of antibiotic.
Devise a laboratory procedure to compare the effectiveness of penicillin with one of the new antibiotics.
prepare agar plates with bacterial cultures
prepare solutions of new antibiotic and penicillin
place onto paper discs
control time + temp of incubation
same concentration and volume of both antibiotics
measure area of inhibition
repeat for effective antibiotics
118
Describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency.
chloride ions leave cells
sodium ions leave cell
increasing solute concentration in mucus
water moves out of cells via osmosis
119
Describe the roles of transcription and translation in the synthesis of a globular protein by a muscle cell.
the gene for the protein in transcribed
complementary base pairing betwee RNA nucleotides and DNA
mRNA leaves the nucleus and attaches to a ribosome
pairing between codons on mRNA and anticodons on tRNA
tRNA provides specific amino acids
the sequence of bases determines the sequence of amino acids
120
Explain why different mutations in the CFTR gene can lead to differences in the
severity of the symptoms of cystic fibrosis.
different mutations will have different effects on the protein
chloride ion transport affected by the extent of changes to the CFTR protein
varying stickiness of mucus
121
Doctors give dietary supplements and digestive enzymes to children with cystic fibrosis.
Dietary supplements include carbohydrates, proteins and lipids, as well as vitamin and mineral supplements.
Explain why these children would be given dietary supplements and digestive enzymes.
cystic fibrosis causes production of stickier mucus
which blocks pancreatic duct
prevents enzymes digesting carbohydrates in intestines
reduced absorption of products of digestion into the blood
reduced vitamins = slower growth rate
dietary supplements would increase growth rate
122
Explain what is meant by an inherited recessive disorder.
caused by a faulty allele
that is only expressed in the absence of a normal allele
123
Individual 12 is pregnant and wants to know if her baby has alkaptonuria.
State and justify a suitable method of collecting cells for prenatal testing
CVS - cells taken from the placenta between 10-14 weeks of pregnancy
earlier diagnosis is beneficial
124
Explain why ATP is required for the movement of sodium ions into the cell.
sodium ions are being moved against concentration gradient
using active transport
125
Describe how glucose moves into cells by facilitated diffusion
carrier protein
moves from a high conc to a low conc
glucose binds to a carrier protein
126
Explain how the structure of glycogen allows it to be an energy store.
polymer of glucose
to provide glucose for respiration
branched for rapid hydrolysis
127
The phospholipid bilayer is important in controlling the movement of molecules through the membrane.
Explain how the structure of a phospholipid molecule contributes to the partial permeability of a cell surface membrane.
contains polar phosphate heads and non-polar fatty acid chains
allows non-polar molecules to pass through the membrane
polar molecules can't move through
128
Explain how phospholipids form a cell surface membrane.
hydrophilic parts associate with water
hydrophobic part repel water
bilayer forms with hydrophobic parts pointing towards each other
129
Explain why the phospholipids are arranged in two layers in a cell surface membrane.
hydrophilic region orientated towards water
hydrophobic regions away from water
two layers as aqueous solution is on both sides of cell membrane
130
Describe the function of carrier proteins in a cell surface membrane.
involved in facilitated diffusion
movement of polar molecules
from a high conc to a low conc
involved in active transport
needs atp to move molecules against conc grad
131
Explain one way in which an investigation on effects of changing the concentration of sodium chloride solution on the mass of onion tissue could be improved
same age/type of onion increases repeatability and validity
132
How many times does an oxygen molecule cross a cell surface membrane to move from the centre of an alveolus to the centre of a red blood cell?
5
133
Describe why single-celled organisms, such as Valonia ventricosa, do not need a specialised gas exchange surface.
can rely on diffusion to take in oxygen
large SA:V ratio
short diffusion distance
134
Describe the structure of the cell surface membrane.
mainly phospholipids + proteins
phospholipids form a bilayer
fluid-mosaic model
proteins may span the bilayer
135
Describe the structure of a DNA mononucleotide.
deoxyribose/pentose sugar, a nitrogenous base
and a phosphate group
deoxyribose and any of the bases
136
Describe how DNA is replicated
hydrogen bonds between the bases break by DNA Helicase
DNA nucleotides line up by complementary base pairing
adjacent nucleotides joined by DNA polymerase
137
Explain why a change in the base sequence of the gene coding for myoglobin could change its tertiary structure
change in base sequence causes a change to the triplet code
therefore a change in the amino acids
changing the bonding and therefore tertiary structure
138
explain why thicker mucus is produced if the functioning of the CFTR channel protein is impaired
chloride ions can't leave the cell
sodium ions do not move into the mucus
water moves into cell via osmosis
139
Devise a valid investigation to compare the effects of ethanol and propanol on the permeability of beetroot membranes.
use the same concentrations of propanol and ethanol
control temperature using a water bath
use a colourimeter to measure absorbance
repeat to calculate a mean
140
Evaluate the effects of smoking on the respiratory system, heart and pulmonary circulation.
smoking decreases FEV and reduces surface area of alveoli and volume of air in lungs and reduces gas exchange
non-smokers do not develop emphysema
heart: smoker has a larger RV and therefore reduced volume of blood to lungs
smoker has narrow pulmonary artery therefore reduced blood flow to the lungs
reduced oxygenation of blood, heart attack due to lack of oxygen, reduced pulmonary artery = increase in RV size
reduced artery size = increase in blood pressure
141
Explain why emphysema affects the rate of gas exchange between the alveolus and the blood.
reduced rate of gas exchange
reduced rate of diffusion
smaller surface area and greater diffusion distance
SA is directly proportional to the rate of diffusion
142
Describe the role of RNA in the formation of this polypeptide chain.
mRNA leaves the nucleus
mRNA binds to a ribosome
anticodons of tRNA bind to complementary codons on mRNA
tRNA molecules carry specific amino
acids
the sequence of bases on mRNA determines the sequence of amino acids
143
Give three differences between the structures of collagen and haemoglobin
collagen is a fibrous protein whereas haemoglobin is a globular protein
collagen is composed of three polypeptide (chains) whereas haemoglobin is composed of four polypeptide
collagen has (little to no) tertiary structure whereas
haemoglobin has a quaternary structure whereas collagen does not
hydrophilic (R) groups on (surface of) haemoglobin and hydrophobic (R) groups on (surface of) collagen
144
A new technique known as gene silencing has been developed to treat this disease. Molecules known as small interfering RNA (siRNA) combine with mRNA to prevent translation.
Deduce how siRNA may be used to prevent the development of porphyria.
siRNA binds to the mRNA (from the mutated allele)
(1)
* mRNA cannot bind to ribosome (1)
* tRNA is prevented from binding with mRNA(1)
* {polypeptide / protein} not synthesised (1)
* (no development of porphyria) as the faulty
enzyme is not produced (1
145
Describe the structure of a DNA mononucleotide
deoxyribose sugar, a nitrogenous base and a phosphate group
deoxyribose and adenine, guanine, cytosine and thymine
146
Describe how DNA is replicated
hydrogen bonds between the bases are broken
via DNA helicase
DNA nucleotides line up against each DNA strand via complementary base pairing
adjacent nucleotides joined by DNA polymerase
147
Describe how a mutation can change the primary structure of a protein
there is a change in the base sequence of the DNA
this changes the sequence of bases in mRNA
causing a change in the amino acid sequence at translation
148
The CFTR protein is produced in cells of the lung and is involved in the
transport of chloride ions.
Describe the location of the CFTR protein in the cell membrane of one of these cells.
CFTR is in the phospholipid bilayer
it extends though both layers of the bilayer
149
he most common mutation in the CFTR gene produces a protein that has the incorrect shape.
Explain why a change in the primary structure of a protein changes the three-dimensional (3D) structure of this protein..
the amino acids in the protein are changed
therefore there will be different R groups
this will change the bonds formed between amino acids and R group
polypeptide fold differently and a different tertiary structure of protein
150
Explain why alcohol affects the concentration of betalain in these cells.
decreases betalain concentration (in the cells)
* due to betalain {diffusing out / moving down a
concentration gradient} (1)
* (because) the alcohol increases membrane
permeability (1)
* membrane {lipids/ phospholipids} dissolve in
alcohol
151
Compare and contrast the use of pre-implantation genetic diagnosis (PGD) and amniocentesis
(both) look for any genetic condition (so
parents can make informed decisions
PGD before implantation / amniocentesis
after implantation (1)
* (increased) risk of miscarriage with
amniocentesis (1)
* embryo tested in PGD / amniotic fluid
tested in amniocentesis
152
Describe two different social issues related to the use of PGD
selecting one embryo over another / loss of a
potential life (1)
* risk of identifying other conditions / selecting
for other characteristics (1)
* {costly / emotional strain } as not always
accurate
153
Explain why cystic fibrosis affects digestion.
produces) sticky mucus (1)
* (which) { blocks / reduces } flow of {pancreatic
juice / enzyme from pancreas } (1)
* (so) reducing digestion (1)
* {blocks / reduces } flow of bile
154
Give a reason why some pregnant women may choose chorionic villus sampling rather than amniocentesis.
earlier in pregnancy when test can be carried out
* results available sooner (due to being carried out
earlier in pregnancy
155
Determine why the sequence of bases in these anticodons is 83% the same as the sequence of bases on the DNA template strand.
(only) U replaced by T (1)
* (so the other) 10 bases out of 12 are the same
156
state 2 features of DNA and explain how each is inportant for semi conservative replication
double stranded - both strands can act as templates
weak hydrogen bonds so easily broken but collectively strong to prevent DNA from falling apart
complementary base pairing - little chance of mutation
157
use knowledge of enzymes and DNA structure to explain why the arrows of the direction of DNA polymerase point in opposite directions
both enzymes are running in the 5-3 direction / DNA strands run in opposite directions
Therefore shape of nucleotides are different
DNA polymerase active site has a specific shape
site can only bind with the 3 end of DNA / end with nucleotides
158
Describe the structure of a globular protein
polypetides folded
held together by hydrogen bonds
bonds between R groups
hydrophilic R groups arranged on the outside
159
Describe the fluid mosaic structure of a cell membrane
phospholipid bilayer
proteins span the membrane
glycolipids/ glycoproteins present
160
Explain how mRNA can be used to produce a specific protein to act as an antigen
strand of mRNA has sequence of bases for the protein
mRNA attaches to ribosome
mRNA is translated therefore tRNA with anticodon binding to codon on mRNA bring specific amino acids
peptide bonds form between amino acids to form protein
161
state what is meant by sex linkage
allele responsible for a trait is located on a sex chromosome so the expression of the trait is related to gender
SNAB Biology Edexcel
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