Bio topic 2 - Genes and Health

Q1. c) Name the place in a eukaryotic cell where messenger RNA will be synthesised (1)

Nucleus

(d) Describe one advantage and one disadvantage to these parents of genetic screening of their fetus (2)

Advantage - Less stress / Can prepare for child w achondroplasia / can make an informed choice
Disadvantage - Stress to parents / false positive / risk of miscarriage

Q2. c) Explain why people with this gene mutation can’t convert phenylalanine to tyrosine (4)

Change in base sequence of gene
Change in amino acid / primary structure
Changes in R groups leading to different types of bonding
Changes to active site so enzyme-substrate complex can’t be made

(d) Explain why a gene mutation involving the replacement of one base with another has less effect than the loss of a base (2)

Loss causes whole amino acid sequence to change / frame shift
Replacement only changes one amino acid
No. of aas remains the same w replacement

Q3. State what is meant by the term template for the synthesis of messenger RNA (1)

RNA nucleotides attach to this strand / complementary to RNA nucleotides

Q4. Describe how transcription is involved in the synthesis of an enzyme (4)

DNA unzips hydrogen bonds
Template strand used for mRNA synthesis
RNA polymerase used to join RNA nucleotides
Complementary base pairing of A with U, not T

(b) Explain the meaning of Triplet code (2)

Each amino acid is coded for by 3 nucleotides / bases e.g 12 bases code for 4 aas

(ii) Non-overlapping (2)

Each base is only used once in a triplet
AAT + AAC + CAG + TTT gives 4 codes

(iii) Degenerate (2)

More than one code can be used for a particular aa
AAT and AAC code for leucine

(d)* Describe how translation of this mRNA synthesises part of a polypeptide molecule (5)

mRNA with sequence UUA UUG GUC AAA
Ribosome is involved
Each tRNA molecule is attached to one specific aa e.g UUU = lysine
Anticodons on tRNA bind to codons on mRNA e.g UUA codon and AAU anticodon
Hydrogen bonds between bases of tRNA and mRNA
Peptide bonds formed between adjacent aas

Q7. (a) Explain the nature of the genetic code (2)

Non-overlapping
Degenerate
Universal

*(b) Describe the process of DNA replication (5)

Semi-conservative replication
DNA unwinds / unzips
Mononucleotides line up along both strands
Complementary base pairing
Hydrogen bonds formed between bases
Formation of phosphodiester bonds between adjacent mononucleotides in condensation reaction
DNA polymerase / helicase / ligase involved

Q8. (iii) An embryo, created by IVF, can be screened before placed in mother’s uterus (1)
Name this type of genetic screening

PGD - Pre-implantation genetic diagnosis / screening

(iv) Explain one ethical issue relating to the use of prenatal genetic screening (2)

May result in choice of abortion
Unethical to cause death of foetus / risk false positive
Healthy foetus could be aborted
Parents not prepared for child with genetic disease

Q1. (iv) Describe the role of tRNA in production of protein part of a glycoprotein (2)

tRNA anticodons are complementary to mRNA codons
tRNA binds to ribosome

Q4. Compare and contrast the process of transcription w process of DNA replication (4)

Both involve formation of phosphodiester bonds
Both involve DNA helicase (unzipping the DNA)
Transcription involves DNA polymerase, DNA replication involves RNA polymerase
Transcription uses RNA nucleotides, DNA replication uses DNA nucleotides
Transcription produces single stranded mRNA, replication produces double stranded DNA

Q6. State what is meant by the term gene (1)

Section of DNA that codes for a specific protein

(iii) Explain how a change of one amino acid could lead to a change in the structure and properties of the haemoglobin protein (4)

Different sequence of aas / primary structure
Different aa = different R group therefore changes 3D shape due to change in hydrogen / disulfide / ionic bonds
Haemoglobin may not bond to oxygen

Q7. (ii) Describe the role of tRNA in the production of leptin (3)

tRNA molecules transport amino acids to ribosome
tRNA molecule has an anticodon that binds to mRNA codon
each tRNA carries a particular aa

(iii) Describe how the primary structure of leptin enables it to be soluble in water (3)

Primary structure determines folding of polypeptide forming a globular structure
Hydrophobic R groups located in centre / hydrophilic R groups located on outside of protein
Water forms hydrogen bonds w hydrophilic / protein groups

Q8. Describe how a frameshift mutation could result in the production of leptin with a variety of shorter primary structures (2)

Different codons produced / adding or removing 1 or 2 nucleotides changes triplet code
Introducing a new start / stop codon
coding for a shorter sequence of aas

Q9. Describe how mRNA is synthesised at a template strand of DNA (2)

RNA nucleotides align with complementary bases on DNA
RNA nucleotides joined together by RNA polymerase / phosphodiester bonds

(ii) Describe the differences between the structure of DNA and the structure of RNA (3)

DNA is double stranded, RNA is single stranded
DNA contains adenine and thymine base pairs, RNA contains adenine and uracil base pairs
DNA contains deoxyribose, RNA contains ribose

Q10. Give 3 differences between replication of DNA and transcription of DNA (3)

Replication involves DNA nucleotides, transcription involves RNA nucleotides
Replication produces double stranded DNA, transcription produces single stranded RNA
Replication uses DNA polymerase, transcription uses RNA polymerase
Replication produces identical copies, transcription produces a complementary copy

Q12. Assess the effect these mutations have on the human respiratory system (6)

Cilia struggle to move mucus out of lungs leading to increased risk of lung infections
All 3 mutations reduce chloride transport
F508del mutation results in less CFTR protein channels being produced
F508del results in lower chloride transport than other mutations
G551D and G551S have higher chloride transport because correct no. of protein channels produced
Fewer CFTR protein channels results in less transport of chloride ions
G551S mutation is less severe than G551D
Thicker mucus increases diffusion distance, reduces surface area and reduces conc. gradient
G551D and G551S mutations = incorrect shape of CFTR protein channels
Incorrect shape = reduced function of transporting chloride ions
Mutation may affect tertiary structure of CFTR protein (positioning of hydrophilic parts of protein channel)

Q13. Removing one base from DNA sequence will affect primary structure
Changing one base may not
Explain why (4)

Deletion could affect every codon on mRNA, substitution will only affect one
Deletion more likely to affect position of stop / start codon
Deletion results in different sequence of aas, substitution may not affect
Substitution may code for the same aa
Same aa due to degenerate nature of genetic code

Q15. Describe how nucleotides join together to form DNA (2)

Condensation reaction by phosphodiester bonds

Q17. Explain why this mutation affects function of haemoglobin (3)

1 triplet affected / different triplet code produced
Mutation could change 1 aa, changing the bonds formed between R groups
Haemoglobin would no longer be able to bind to oxygen

(iii)* Devise a lab procedure to compare the effectiveness of penicillin with one of the new antibiotics (6)

Prepare agar plates with bacterial cultures
Prepare solutions of new antibiotic and penicillin (same concentration)
Place onto paper discs
Control time and temp of incubation
Measure zone of inhibition
Repeat for effective antibiotics
Use a stats test to determine which is most effective

Q20. (i) Describe the role of the CFTR protein in ensuring mucus produced in lungs has right consistency (3)

Chloride ions move into mucus
Sodium ions leave cells increasing solute concentration in mucus
Water moves out of cells by osmosis (into the mucus)

Q21. Describe the roles of transcription and translation in synthesis of a globular protein by a muscle cell (5)

Gene for globular protein is transcribed
Complementary base pairing between RNA nucleotides and DNA to produce mRNA
mRNA leaves nucleus and attaches to ribosome
mRNA codons bind to tRNA anticodons
tRNA provides specific aas
Sequence of bases determines sequence of aas / primary structure of protein

Q23. Compare and contrast the structure of ATP and DNA (3)

Both contain a sugar, phosphate and base
ATP contains ribose, DNA contains deoxyribose
ATP contains only adenine, DNA could contain other bases
ATP contains 3 phosphates, DNA contains 1

Q1. Compare and contrast molecular structures of globular and fibrous proteins (4)

Both are chains of aas joined by peptide bonds
Both contain hydrogen bonds / disulfide bridges / ionic bonds
Globular is spherical, Fibrous is long strands
Globular contains hydrophilic groups on the outside, Fibrous contains hydrophobic groups on the outside
Globular have 3D shapes, fibrous have little or no tertiary structure

Q2. State why enzymes are described as biological catalysts (1)

Lower activation energy and speed up the rate of reaction without being chemically used up

Q3. (ii) Describe an experiment that could be carried out to investigate effect of enzyme concentration on initial rate of reaction (4)

Use 5 concentrations of enzyme
Substrate concentration not limiting
Measure oxygen produced in gas syringe every 10 seconds (for 30 seconds) using a stopwatch
Control temperature
Repeat for other concentrations
Control with no enzyme / distilled water used
Plot a graph to show effect of increasing enzyme concentration on volume of oxygen produced

Q8. Describe how a peptide bond is formed (2)

Through a condensation reaction with the amine group and carboxyl group of adjacent aas

Q18. Describe how the structure of phospholipase allows it to hydrolyse phospholipids (4)

Enzyme structure determined by sequence of aas
Tertiary structure provides an active site complementary to part of phospholipid / ester bond to break ester bonds between glycerol and fas

Q1. Use Fick’s law of diffusion to explain the adaptations of gas exchange surfaces (5)

Rate of diffusion is proportional to SA = Large SA:V ratio in alveoli
Rate of diffusion is proportional to difference in concentration = breathing / blood flow maintains difference in gas concentrations
Rate of diffusion is inversely proportional to diffusion distance = walls of alveoli / capillaries are one cell thick
Shorter diffusion distance due to flattened cells forming alveoli and capillary walls

Q2. (a) Explain how the structure of a flatworm is adapted to obtain oxygen from the water (2)

Large SA:V ratio so shorter diffusion distance

Q3. Describe what is meant by the term fluid mosaic with reference to cell membranes (2)

Fluid refers to movement of phospholipids in cell membrane
Mosaic refers to random assortment of proteins within membrane

Describe and explain how the lungs of a mammal are adapted for rapid gas exchange (5)

Alveoli are one cell thick and covered with capillaries which reduces diffusion distance
Ventilation in alveoli maintains concentration gradient
Large no. of RBCs maintains concentration gradient
Fick’s law = Diffusion rate is proportional to surface area

Q4. (ii) In mammals, blood passes through the heart twice for each circulation of the body. Suggest how this type of circulation enables mammals to carry out effective gas exchange (3)

One side of the heart transports blood to the lungs, other to body
Oxygenated and deoxygenated blood are separated and maintains conc. gradient
BP is lower to lungs, higher to body
Supply of o2 to body cells maximised as mammals need a good supply of oxygen to meet high metabolic needs

(a) Describe the structure of a cell membrane (5)

Phospholipid bilayer with tails facing each other
Phospholipid heads are hydrophilic, tails hydrophobic
Random assortment of proteins in the membrane
2 diff locations of proteins (extrinsic / intrinsic)
contains glycoproteins / glycolipids
Cholesterol within the membrane gives membrane flexibility and fluidity

(b) Suggest two properties of molecules that enable them to enter a cell by diffusion (2)

Small
Non-Polar
Lipid soluble

Describe one similarity and one difference between facilitated diffusion and active transport (2)
(i) similarity (1)
(ii) difference (1)

Similarity = both require carrier proteins
Difference = Facilitated diffusion doesn’t require energy / moves molecules down conc. gradient instead of against

Q6. Explain how the partial permeability of the surface membrane of the cells lining the bronchi allows osmosis to take place (2)

Partially permeable membrane is a barrier to some solutes but not water
Enables conc. gradient of solutes / water

Q7. Describe how the structure labelled B is involved in passive transport (3)

Channel protein allowing movement of large / polar molecules by diffusion from high conc to low conc down conc. gradient

Q1. Explain why betalain molecules can’t move through intact cell membranes (3)

They are too large to move through the cell membrane
There are no carrier proteins for betalain molecules to move through
Betalain molecules are polar and repelled by hydrophobic fatty acid tails

Q5. Diffusion and active transport are mechanisms by which molecules can enter cells. Compare and contrast these two mechanisms. (3)

Both move molecules through the cell membrane
In both, molecules can move through proteins
Diffusion is a passive process, active transport requires energy
Diffusion occurs down a concentration gradient whereas active transport occurs against a concentration gradient

Q6. Compare and contrast the processes of endocytosis and exocytosis. (3)

Both involve vesicles
Both involve energy from ATP
Endocyosis involves molecules entering cell, exocytosis involves molecules leaving
Endocytosis involves formation of vesicles, exocytosis involves vesicles fusing w cell membrane

(i) Explain why ATP is required for the movement of sodium ions into the cell (2)

Sodium ions are being moved against the conc. gradient through proteins using active transport

(ii) Describe how glucose molecules move into the cell (2)

Glucose molecules bind to a carrier protein and move from an area of high to low concentration (by facilitated diffusion)

Q9. Give one function of the glycoproteins found in the cell surface membrane (1)

Cell-to-cell recognition

(ii) Explain how the structure of a phospholipid molecule contributes to the partial permeability of a cell surface membrane (3)

Phospholipid molecule contains a hydrophilic phosphate head and hydrophobic fatty acid chains allows non-polar molecules to pass through the membrane
Polar molecules cannot pass through phospholipid bilayer

Q10, A baby was born with an abnormal heart (hole in septum between the 2 ventricles)
Oxygen diffuses between alveoli of lungs and blood
Fick’s law → Rate of diffusion = Surface area x conc. diff/diffusion distance
*Assess the effect of this heart defect on the rate of oxygen diffusion between the alveoli and blood (6)

Rate of diffusion would be lower
Blood entering lungs from abnormal heart = more oxygen (8kPa) than normal (5kPa)
Oxygen in blood increased by 2kPa instead of 8 with abnormal heart resulting in a smaller difference in concentration between alveoli and RBCs (6 and 9kPa)
SA of alveoli and diffusion distance aren’t affected
Fick’s law = conc. gradient is proportional to rate of gas exchange
Lower conc. gradient for oxygen between alveoli and blood = lower rate of o2 diffusion

(iii) Give reasons for the variation in the lung volumes of healthy individuals (2)

Different weight / height
Different gender
Different age

(iv) Give a reason for calculating the surface area for gas exchange to volume ratio in this investigation (1)

To allow valid comparison / show differences

Q12. Give two differences between endocytosis and exocytosis (2)

Endocytosis involves molecules moving into a cell, exocytosis involves them leaving
Endocytosis involves the formation of vesicles, exocytosis involves the cell membrane fusing with vesicles

Q13. Explain how phospholipids form a cell surface membane (3)

Hydrophilic parts associate with water
Hydrophobic parts repel water
Phospholipids form a bilayer with hydrophobic regions pointing towards each other

Q14. Explain why individuals with severe emphysema will tire more easily than healthy individuals (3)
→ Higher total lung volume / lower SA:V ratio / lower SA

They have a lower SA:V ratio so longer diffusion distance
therefore reduction in o2 uptake so less o2 for aerobic respiration leading to more anaerobic respiration (causing fatigue)

Q15. Explain why the phospholipids are arranged in two layers in a cell surface membrane (3)

Hydrophilic regions associated with water
Hydrophobic regions repel water
but need 2 layers as water-based solution on either side of cell membrane (separating tissue fluid from cytoplasm)

Q17. Describe the function of carrier proteins in a cell surface membrane (4)

Involved in facilitated diffusion
To carry large molecules from high to low conc
Involved in active transport and needs ATP to move molecules against conc. gradient / low to high conc

Assess the factors that would cause maltose to be detected in tube A before tube B (4)

Tube A = Surface area greater than B (shorter diffusion distance)
Fick’s law = Rate of diffusion is proportional to surface area therefore increased rate of diffusion of maltose
Tube A = could’ve had a higher temp
Higher temp = Higher rate of diffusion

Q28 Describe the structure of the cell surface membrane (3)

Cell membrane is mainly phospholipids and protein
Phospholipids form a bilayer
Intrinsic / extrinsic proteins

Q29. Give the name of the bond that joins a fatty acid molecule to a glycerol molecule in a phospholipid (1)

Ester bond

Q1. (a) (i) Describe the difference between somatic gene therapy and germ line gene therapy (2)

Somatic = body cells while Germ = gametes
Somatic can’t be inherited, Germ can
Somatic = legal, Germ = illegal
Somatic = temporary, Germ = potential cure

*(ii) Suggest how somatic gene therapy could enable cells lining the lungs to function normally in people with CF (4)

Using a vector (virus / liposome), a functional copy of the gene that codes for CFTR protein is introduced into patient’s cells into the lungs through inhalation / aerosol
CFTR protein made by transcription allows chloride ions to leave cells
Water leaves cells by osmosis
Mucus is less sticky

(b) Rhythmical tapping of the chest wall during physiotherapy can relieve the symptoms of CF in the lungs. Suggest an explanation for this. (2)

Loosens mucus to expel from lungs more easily
Better breathing

Q2. Explain why people with CF can have breathing difficulties (4)

Produces thicker mucus blocking trachea / alveoli
Cilia unable to move mucus out of lungs
Reduced flow of air / o2 to alveoli
Reduced conc. gradient for o2 in alveoli
Loss of surface area
Reduced gas exchange
Trapped bacteria may result in more respiratory infections

Q3. Explain the meaning of the term recessive allele (3)

Both alleles need to be present in order for recessive phenotype to be expressed
Different form of a gene on the same locus / position
Different base sequence

Q6. People with CF require a higher energy diet than people w/o. They are also more likely to develop problems in the pancreas. Men with CF are less likely to be able to release sperm. Discuss why a person with CF could have these symptoms (6)

Pancreas
Thicker mucus than normal means pancreatic enzymes can’t enter intestine because pancreatic duct blocked with mucus
High energy diet required because digestion is less efficient
Pancreatic enzymes trapped behind mucus damage pancreatic cells such as those that produce insulin
Cysts form (in pancreas)

Sperm
Sperm can’t leave the testes because sperm duct blocked with mucus

Gene mutation causes non-functioning CFTR protein channel
thus chloride ions can’t move out of epithelial cells
Accumulation of sodium + chloride ions in cells (causes water to move out of mucus by osmosis / prevents water from moving into mucus)

Q7. CF is a condition that affects breathing. Explain why CF affects the rate of oxygen uptake in the lungs (3)

Thicker mucus
Accumulation of mucus which can’t be moved by cilia
Restricts air flow through bronchi / increases diffusion distance in alveoli

Q8. Explain why thicker mucus is produced if the functioning of the CFTR channel protein is impaired (2)

Chloride ions can’t leave the cell through the CFTR protein channel
Sodium ions don’t move out of cells / into mucus
Therefore water moves into cells / out of mucus by osmosis

Q10. (ii) Explain why different mutations in the CFTR gene can lead to differences in the severity of the symptoms of cystic fibrosis (2)

Different mutations will have different effects on protein produced
Chloride ion transport affected by extent of changes to CFTR protein
Varying thickness of mucus

Q11. (ii) Doctors give dietary supplements and digestive enzymes to children with CF. Dietary supplements include carbs, proteins and lipids + vitamin and mineral supplements. Explain why (5)

CF causes production of thicker mucus
Thicker mucus blocks pancreatic duct
This prevents enzymes digesting carbs / lipids / proteins in intestines
resulting in reduced absorption of products of digestion into the blood
Reduced aas slows growth rate
Dietary supplements would increase growth rate

Q12. (i) Describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency. (3)

Chloride ions leave cells through CFTR channel protein
Sodium ions leave cells (following chloride ions)
increasing solute conc. in mucus
Water moves out of cells by osmosis (into mucus)

Q14. Assess the advantages and disadvantages of these types of screening for genetic disorders (6)

Q15. Name the prenatal test that could be used to detect Tay-Sachs disease at 11 weeks of pregnancy (1)

Chorionic villus sampling (CVS)

(c) Explain why this couple may choose not to have this test. (3)

Test result may be inaccurate (false positive)
False positive could lead to termination of healthy fetus
Increased risk of miscarriage due to procedure
Abortion might be against values / beliefs of parents

Q16. What is meant by the term gene (1)

A section of DNA that codes for a specific protein

Q18. Explain what is meant by an inherited recessive disorder (2)

Caused by a faulty allele that is only expressed in homozygous condition / if 2 recessive alleles are inherited

Q20. (ii) State and justify a suitable method of collecting cells for prenatal testing (3)

CVS or amniocentesis
CVS = cells / tissue taken from placenta / chorionic villus between 10-14 weeks of pregnancy
Benefit of earlier diagnosis

Amniocentesis = Amniotic fluid containing cells collected between 14-20 weeks of pregnancy
Lower risk of miscarriage

Q22. (i) State what is meant by the term allele (2)

Different version of a gene found at same locus / place (on a chromosome)