Topic 2 Genes and health

Question 1

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

Answer 1

-Each tRNA brings a specific amino acid to the ribosome.
-The tRNA with the complementary anticodon binds to the mRNA codon.
-tRNA binds to the ribosome.

Question 2

Compare and contrast the processes of transcription and DNA replication . (4)

Answer 2

-Both involve the formation of phosphodiester bonds.
-Both involve DNA helicase unzipping the DNA.

-Transcription uses RNA nucleotides whereas DNA replication uses DNA nucleotides.
-Transcription uses RNA polymerase whereas DNA replication uses DNA polymerase.
-Transcription produces a single strand of mRNA whereas DNA replication produces double stranded DNA.

Question 3

What is a gene? (2)

Answer 3

-A sequence of bases in DNA.
-That codes for a polypeptide.

Question 4

Explain how a change of one amino acid may lead to a change in structure and properties of the haemoglobin protein. (3)

Answer 4

-Different sequence of amino acids.
-A different amino acid will have a different R group.
-Therefore tertiary structure will change.
-Meaning haemoglobin may not bond to oxygen.

Question 5

Leptin is a protein. Describe the role of tRNA in the production of leptin. (3)

Answer 5

-tRNA molecules transport amino acids to the ribosomes.
-tRNA molecules has an anticodon that binds to a codon on the mRNA.
-Each tRNA carries a particular amino acid.

Question 6

Describe how an insertion or removal of 1 or 2 nucleotides from a gene result in the production of leptin with a variety of shorter primary structures. (2)

Answer 6

-Adding or removing 1 or 2 nucleotides changes the triplet code.
-Introducing a new stop codon.
-Coding for a shorter sequence of amino acids.

Question 7

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

Answer 7

-RNA aligns with complementary bases on DNA.
-RNA polymerase joins together free RNA nucleotides.

Question 8

Describe the differences between the structure of DNA with the structure of RNA. (3)

Answer 8

-DNA is double stranded whereas RNA is single stranded.
-DNA contains deoxyribose whereas RNA contains ribose.
-DNA contains Thymine whereas RNA contains uracil.

Question 9

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

Answer 9

-Condensation reaction.
-Phosphodiester bonds form.
-DNA polymerase.

Question 10

Explain why substitution of a base affects the function of a haemoglobin molecule. (3)

Answer 10

-One triplet code is affected.
-Meaning there could be a change in an amino acid.
-Causing tertiary structure to change.
-Haemoglobin would no longer be able to bind to oxygen.

Question 11

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

Answer 11

-Chloride ions leave cells through CFTR channel protein.
-Sodium ions then leave following chloride ions.
-Increasing solute concentration in mucus.
-Water moves out of cells into mucus via osmosis.

Question 12

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

Answer 12

-The sequence of DNA for globular protein is transcribed.
-Complementary base pairing between RNA nucleotides and DNA to produce mRNA.
-mRNA leaves nucleus and attaches to ribosome.
-Pairing between codons on mRNA and anticodons on tRNA.
-tRNA provides specific amino acids.
-Sequence of bases determines sequence of amino acids.

Question 13

State where transcription occurs in animal cells. (1)

Answer 13

-Nucleus.

Question 14

Betalains are large polar molecules. Explain why they can’t move through intact cell membrane. (3)

Answer 14

-Betalain molecules are too large to move through the cell membrane.
-No carrier/channel proteins for betalain molecules to move through.
- Betalain molecules are polar and are repelled by hydrophobic fatty acid tails.

Question 15

Compare and contrast diffusion and active transport as methods for molecules entering the cell. (3)

Answer 15

-Both move molecules through phospholipid bilayers.
-In both, molecules can move through proteins.

-Diffusion occurs down a concentration gradient, whereas active transport occurs against a concentration gradient.
-Diffusion doesn’t require ATP whereas active transport does.

Question 16

Compare and contrast exocytosis and endocytosis . (3)

Answer 16

-Both processes involve vesicles.
-Both processes involve energy from ATP.

-Exocytosis moves molecules out of cell whereas endocytosis moves molecules into cell.
-Exocytosis involves vesicles fusing with cell surface membrane whereas endocytosis involves the formation of vesicles.

Question 17

Describe how glucose molecules moves into the cell. (2)

Answer 17

-Facilitated diffusion.
-Through carrier proteins.

Question 18

One function of glycoproteins found in cell surface membrane. (1)

Answer 18

-Act as receptors on cell surface membrane.

Question 19

Explain how phospholipids form a cell surface membrane. (3)

Answer 19

-Hydrophilic head associates with water.
-Hydrophobic tail repels water.
-Bilayer forms with hydrophobic tail pointing towards centre of bilayer.

Question 20

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

Answer 20

-Involved in facilitated diffusion.
-Movement of large molecules.
-From high concentration to low concentration.
-Involved in active transport.
-Needs ATP to move molecules against concertation gradient.

Question 21

Describe why single celled organisms don’t need a specialised gas exchange surface. (2)

Answer 21

-Can rely on diffusion to uptake oxygen.
-Large SA:V ratio.
-Short diffusion distance.

Question 22

Describe structure of cell surface membrane. (3)

Answer 22

-Cell membrane made up of phospholipids and proteins.
-Phospholipids form a bilayer.
-Proteins float in phospholipid bilayer.
-Proteins may span bilayer or be located in only one layer.

Question 23

Explain how the structure of human lungs enables rapid gas exchange. (4)

Answer 23

-Many alveoli provide a large SA:V ratio.
-Alveoli and capillaries have one cell thick walls meaning they have a short diffusion distance.
-High concentration gradient maintained by circulation/ventilation.
-Capillary network around alveoli provide large SA for gas exchange.

Question 24

Men with cystic fibrosis release less sperm, and they may also require a higher energy diet than normal.
Discuss why a person with cystic fibrosis can have these symptoms. (6)

Answer 24

-Cystic fibrosis creates thick stickier mucus than normal.
-This causes the pancreatic duct to be blocked with mucus so digestive enzymes cant enter the intestines.
-High energy diet required as digestion is less efficient.
-Digestive enzymes trapped behind mucus damage pancreatic cells such as those that produce insulin.
-Cysts can form in pancreas.
-Sperm cant leave testes as sperm duct blocked with mucus.
-Gene mutation.
-Causing non functioning CFTR protein channel.
-Chloride ions cant move out of epithelial cells.
-Accumulation of sodium and chloride ions in cells causes water to move out of mucus via osmosis.

Question 25

Explain why cystic fibrosis affects rate of oxygen uptake in lungs. (3)

Answer 25

-Mucus cannot be moved by cilia.
-Restricts air flow through bronchi.
-Increasing diffusion distance in alveoli.

Question 26

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

Answer 26

-Chloride ions cant leave through CFTR protein channel.
-Sodium ions don’t move out of cells.
-Causing water to move into cells via osmosis.

Question 27

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

Answer 27

-Chronic villus sampling.

Question 28

Explain why a couple may choose not to have a chronic villus sampling test. (3)

Answer 28

-Test result may be inaccurate.
-Increase risk of miscarriage due to procedure.
-False positive may lead to termination of fetus.
-Abortion against values or beliefs of parents.

Question 29

What is an inherited recessive disorder. (2)

Answer 29

-A recessive disorder is one caused by a faulty allele.
-Only expressed in homozygous condition.

Question 30

What is an allele. (2)

Answer 30

-Allele is a different version of a gene.
-Found at the same locus.

Question 31

Describe what happens to proteins following translation until they’re released from the cell. (3)

Answer 31

-Proteins are folded on the RER.
-Proteins are packaged into transport vesicles.
-Protein modified in Golgi apparatus.
-Exocytosis of protein.

Question 32

Explain why enzymes that are incorrectly folded can’t carry out their function. (3)

Answer 32

-Tertiary structure would be different.
-Meaning active site of enzyme would not be able to bind with substrate.
-Meaning it wouldn’t be able to catalyse reaction.

Question 33

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

Answer 33

-Both are chains of amino acids joined by peptide bonds.
-Both contain hydrogen bonds.
-Globular proteins have hydrophilic groups on outside whereas fibrous proteins have hydrophobic groups on outside.
-Globular have tertiary structure whereas fibrous have little to none tertiary structure.
-Globular are folded into compact shapes whereas fibrous have long chains.

Question 34

How is a peptide bond formed? (2)

Answer 34

-Condensation reaction.
-Between amino acid and carboxyl group of adjacent amino acid.

Question 35

Name an element in an R group that is not found in carbohydrates. (1)

Answer 35

-Nitrogen/Sulfur.

Question 36

Name the products formed when several amino acids are joined together. (1)

Answer 36

-Polypeptide and water.

Question 37

RNA produced during transcription is known as pre-mRNA.
Pre-mRNA can be modified before being translated on the ribosome.

Describe how pre-mRNA may be modified before being translated on the ribosome. (2)

Answer 37

-Pre-mRNA contains exons and introns.
-Introns removed and exons spliced together to produce strand of mRNA.

Question 38

RNA produced during transcription is known as pre-mRNA.
Pre-mRNA can be modified before being translated on the ribosome.

Explain why modification of pre-mRNA enables one gene to give rise to more than one protein. (2)

Answer 38

-Exons can be spliced together in a different order.
-Therefore producing different sequence of amino acids.